Incoming Exchange Student - Final Degree Project

Incoming Exchange Student - Final Degree Project

Erasmus x Techno □ Other (specify):

Degree course: Grau en Enginyeria Química Pla 2009

Title: Metal separation from multi metallic solutions by sorption on and

desorption from grape stalks

Document: Final Degree Project

Student : Pieter Busschaert

EPS Advisor: Nuria Fiol

Department: Eng. Química, Agrària I Tecn. Agroalimentària

Delivered on: 06/2016

Metal separation from multi metallic solutions by sorption

on and desorption from grape stalks

Pieter Busschaert

DETAILS PLACEMENT

Period: 08/02/2016 – 13/06/2016

Institute: Universitat de Girona

Lab: Escola Politècnica Superior, MMa

Address: UdG, Escola Politècnica Superior

Ava. Lluis Santalo s/n

17071 Girona, Spain

City: Girona

Country: Spain

Supervisor from host institute: prof. dr. Núria Fiol

Supervisor from Odisee: prof. dr. Patrick Demeyere

Abstract

During the last years, problems related to soil and freshwater contaminations have often stood in the

center of interest. Accumulated pollutants in the soil can end up in the water by dissolving in it. Heavy

metals are part of the group of chemical elements that have strongly increased in the environment by

human activities such as the mine and metallurgy industries. One of the highest concentrations of heavy

metals in wastewaters can be found in Acid Mine Drainage (AMD). This are the outflows of abandoned

metal mines which are flooded when they are taken out of service.

In order to prevent health problems and environment disasters, those metals must be removed from

the water. Different techniques to eliminate those metals are used such as complexation, ion exchange

and sorption, but it is still a very difficult and expensive process. Previous studies have shown that

sorption processes with grape stalks can be a cheap alternative for sorption processes with activated

carbon. During the sorption process, metals react differently. This difference in metal sorption can be

used for selective separation of metals in binary mixtures.

The objective of this work will be working on a method to separate those metals using grape stalks and

bring them in a useable solution. The separation of binary metal mixtures of lead and cadmium and

copper and nickel will be studied by using flow up columns filled with grape stalks for the sorption and

desorption processes. Desorption will be studied by using different reagents at different concentrations

in order to obtain a solution with only one metal.

Acknowledgements

I have chosen to do my internship and thesis at the University of Girona (UdG) in the north of Spain. The

reason I did this was to get experience abroad and get to know new people and customs. I had a great

time here with a lot of amazing people who made this stay immensely enjoyable for me.

In the first place I want to thank prof Dr. Núria Fiol, prof Dr. Florencio de la Torre and Jordi Poch who

give me all the help I needed during this internship. They were always there when I had questions or

problems and guided me through the project. I also want to thank Odisee for giving me the chance to

take part in this unforgettable adventure and in particular prof Dr. Patrick Demeyere for his help and

feedback before, during and after the internship. Also thanks to my lab partners to create pleasant

working hours.

Special thanks to my parents and girlfriend who encouraged me to jump into this special adventure and

to always support me during my stay.

Thank you all for giving me a great stay here and fantastic memories I will always cherish.

Pieter Busschaert

Table of contents 1 INTRODUCTION ................................................................................................................................... 12

1.1 METALS IN FRESHWATER ............................................................................................................ 12

1.1.1 What are heavy metals ....................................................................................................... 12

1.1.2 Occurrence .......................................................................................................................... 12

1.1.3 Mine drainage ..................................................................................................................... 13

1.1.4 Rivers Odel and Tinto .......................................................................................................... 14

1.1.5 Problems and (health)risks ................................................................................................. 15

1.1.6 Treatments of removal ....................................................................................................... 15

1.1.6.1 Complexation .................................................................................................................. 15

1.1.6.2 Reverse osmoses ............................................................................................................. 15

1.1.6.3 Ion exchange ................................................................................................................... 16

1.1.6.4 Sorption ........................................................................................................................... 16

1.1.7 Metal sorption .................................................................................................................... 17

1.2 GRAPE STALKS ............................................................................................................................. 18

1.2.1 Occurrence .......................................................................................................................... 18

1.2.2 Chemical compounds .......................................................................................................... 18

1.2.2.1 Lignin ............................................................................................................................... 18

1.2.2.2 Cellulose .......................................................................................................................... 19

1.2.2.3 Hemicellulose .................................................................................................................. 19

1.2.2.4 Polyphenols ..................................................................................................................... 20

1.2.3 Advantages of grape stalks ................................................................................................. 20

1.2.4 Metal affinity to grape stalks in fixed bed columns ............................................................ 20

1.3 METAL SEPARATION BY USING COLUMNS ................................................................................. 21

1.3.1 Breakthrough curves ........................................................................................................... 21

1.3.2 Mathematical models ......................................................................................................... 22

1.3.2.1 Yoon and Nelson model .................................................................................................. 22

1.3.2.2 Thomas Model ................................................................................................................ 23

1.3.2.3 Adams-Bohart model ...................................................................................................... 23

1.3.3 Desorption of loaded columns ............................................................................................ 23

1.3.4 Calculations of the absorbed and desorbed amount of metal ........................................... 24

1.4 FAAS ............................................................................................................................................ 25

1.4.1 Method................................................................................................................................ 25

1.4.2 Components ........................................................................................................................ 25

1.4.2.1 Hollow cathode lamp ...................................................................................................... 25

1.4.2.2 Flame and burner ............................................................................................................ 26

1.4.2.3 Monochromator .............................................................................................................. 27

1.4.2.4 Detector .......................................................................................................................... 28

2 OBJECTIVES ......................................................................................................................................... 29

3 EXPERIMENT ....................................................................................................................................... 30

3.1 COLUMN PREPARATION ............................................................................................................. 30

3.1.1 Grape stalks ......................................................................................................................... 30

3.1.2 Column ................................................................................................................................ 30

3.2 EXPERIMENTAL SET-UP ............................................................................................................... 30

3.2.1 Equipment ........................................................................................................................... 30

3.2.2 Flow rate ............................................................................................................................. 30

3.2.3 Sorption process ................................................................................................................. 31

3.2.4 Desorption process ............................................................................................................. 31

3.3 ANALYSIS OF THE METALS .......................................................................................................... 31

3.3.1 FAAS .................................................................................................................................... 31

3.3.2 Stock solutions .................................................................................................................... 31

3.3.2.1 Copper ............................................................................................................................. 31

3.3.2.2 Nickel ............................................................................................................................... 32

3.3.2.3 Lead ................................................................................................................................. 32

3.3.2.4 Cadmium ......................................................................................................................... 32

3.4 Metal mixtures and desorption reagents ................................................................................... 32

3.4.1 Calculations of metal mixtures ........................................................................................... 32

3.4.2 Calculations of desorption reagents ................................................................................... 33

3.4.2.1 HCl solutions ................................................................................................................... 33

3.4.2.2 NaCl and CaCl2 solutions ................................................................................................. 33

3.4.3 Experiments that will be conducted for the Pb/Cd experiments ....................................... 34

3.4.4 Experiments that will be conducted ................................................................................... 34

4 RESULTS............................................................................................................................................... 35

4.1 Binary mixtures of lead and cadmium ........................................................................................ 35

4.1.1 Effect of HCl concentration ................................................................................................. 36

4.1.1.1 Desorption with HCl at a pH of 1.00 ............................................................................... 36





4.1.1.6 Discussion of desorption with HCl .................................................................................. 41

4.1.2 Effect of reagents ................................................................................................................ 42

4.1.2.1 Desorption with NaCl (7.8 mM) ...................................................................................... 42

4.1.2.2 Desorption with CaCl2 ( 3.9 mM) .................................................................................... 43

4.1.2.3 Discussion of desorption with NaCl and CaCl2 ................................................................ 44

4.2 Binary mixtures of Copper and Nickel ........................................................................................ 45

4.2.1 Effect of HCl concentration ................................................................................................. 46






4.2.1.6 discussion of desorption with HCl ................................................................................... 51

4.2.2 Effect of reagents ................................................................................................................ 52

4.2.2.1 Desorption with NaCl (7.2 mM) ...................................................................................... 53

4.2.2.2 Desorption with CaCl2 (3.6 mM) ..................................................................................... 54

4.2.2.3 discussion of the desorption with NaCl and CaCl2 .......................................................... 55

4.2.3 Mathematical models ......................................................................................................... 56

4.2.3.1 Yoon and Nelson model .................................................................................................. 56

4.2.3.2 Thomas model ................................................................................................................. 57

4.2.3.3 Adams-Bohart model ...................................................................................................... 59

5 CONCLUSION ....................................................................................................................................... 61

6 BIBLIOGRAPHY .................................................................................................................................... 62

List of figures

Figure 1 : Human activities that cause contamination with metals

(http://www.texasintegrative.com/wp-content/uploads/2015/05/Toxic-Heavy-Metals.jpg)......12

Figure 2: steps in the process of AMD

(http://old.post-gazette.com/regionstate/19981208minegraphic3.asp).....................................13

Figure 3: The Iberian pyrite belt

(http://www.sec.gov/Archives/edgar/data/1377085/000120445907001642/

lundintechrep.htm)…….…………………………………………………………………………………………………………….14

Figure 4: Rio Tinto and Rio Odiel

(http://amazingworldfactsnpics.com/amazing-2/surprising-landscapes-around-world/6/)

(https://en.wikipedia.org/wiki/Odiel)...........................................................................................15

Figure 5 : principle of reverse osmosis

(http://puretecwater.com/what-is-reverse-osmosis.html)...........................................................16

Figure 6: Ion exchange

(http://www.popularmechanics.com/home/interior-projects/how-to/a150/1275126/)............16

Figure 7: absorption and adsorption

(http://chemistrytwig.com/wp-content/uploads/2013/09/absorptionadsorption.jpg)...............17

Figure 8: grape stalks …………………………………………………………………………………………………………………………...18

Figure 9: small segment of lignin polymer

(https://en.wikipedia.org/wiki/Lignin#/media/File:LigninStructure.png).....................................19

Figure 10: two unlinked B-D-glucose molecules

(http://antoine.frostburg.edu/chem/senese/101/consumer/faq/what-is-cellulose.shtml).........19

Figure 11: Corilagin

(https://nl.wikipedia.org/wiki/Tannine)........................................................................................20

Figure 12: progress of the mass transfer zone

(http://chem-tips.blogspot.com.es/2012/08/molecular-sieve.html)............................................21

Figure 13: typical breakthrough curve

(http://facstaff.cbu.edu/rprice/lectures/adsorb.html).................................................................22

Figure 14 : typical desorption curve

(http://www.fbp.ichemejournals.com/cms/attachment/2024162035/2044029851/gr6_lrg.gif)24

Figure 15: sketch of the components of the FAAS

(http://chemicalinstrumentation.weebly.com/flame-aas.html)...................................................25

Figure 16: hollow cathode lamp

(https://en.wikipedia.org/wiki/Hollow-cathode_lamp#/media/

File:Hollow_Cathode_Lamp.svg)……………………………………………………………………………..………………..26

Figure 17: emission of a hollow cathode lamp

(http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/

AASTheory.htm)………………………………………………………………………………………………………..……………..26

Figure 18: premix burner

(http://encyclopedia2.thefreedictionary.com/Propane+burner)..................................................27

Figure 19: Nebulizer

(http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/

AASTheory.htm)………………………………………………………………………………………………………………………..27

http://www.texasintegrative.com/wp-content/uploads/2015/05/Toxic-Heavy-Metals.jpg

http://www.sec.gov/Archives/edgar/data/1377085/000120445907001642/%20lundintechrep.htm

http://www.sec.gov/Archives/edgar/data/1377085/000120445907001642/%20lundintechrep.htm

http://amazingworldfactsnpics.com/amazing-2/surprising-landscapes-around-world/6/

https://en.wikipedia.org/wiki/Odiel

http://puretecwater.com/what-is-reverse-osmosis.html

http://www.popularmechanics.com/home/interior-projects/how-to/a150/1275126/

http://chemistrytwig.com/wp-content/uploads/2013/09/absorptionadsorption.jpg

https://en.wikipedia.org/wiki/Lignin#/media/File:LigninStructure.png

http://antoine.frostburg.edu/chem/senese/101/consumer/faq/what-is-cellulose.shtml

https://nl.wikipedia.org/wiki/Tannine

http://chem-tips.blogspot.com.es/2012/08/molecular-sieve.html

http://facstaff.cbu.edu/rprice/lectures/adsorb.html

http://www.fbp.ichemejournals.com/cms/attachment/2024162035/2044029851/gr6_lrg.gif

http://chemicalinstrumentation.weebly.com/flame-aas.html

https://en.wikipedia.org/wiki/Hollow-cathode_lamp#/media/ File:Hollow_Cathode_Lamp.svg

https://en.wikipedia.org/wiki/Hollow-cathode_lamp#/media/ File:Hollow_Cathode_Lamp.svg

http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/%20AASTheory.htm


http://encyclopedia2.thefreedictionary.com/Propane+burner



Figure 20: principle of a photomultiplier tube

(https://nl.wikipedia.org/wiki/Fotomultiplicator).........................................................................28

Figure 21: breakthrough curves of lead and cadmium (conditions: Ci,Pb = 0.4 mM ; Ci,Cd = 0.4 mM ;

column length = 7 cm ; flow rate = 30ml/hour ; Ct/Ci = concentration of the metal devided by the

initial concentration) ………………………………………………………………………………………………………………..35

Figure 22: desorption curves of Pb and Cd while using 100 mM HCl solution( pH of 1.00)

(conditions: Pb sorbed = 60.50 mg ; Cd sorbed = 11.34 mg ; flow = 30 ml/hour)……..………………..36

Figure 23: desorption curves of Pb and Cd while using 31 mM HCl solution ( pH of 1.51)


Figure 24: desorption curves of Pb and Cd while using 7.8 mM HCl solution ( pH of 2.11)

(conditions: Pb sorbed = 60.50 mg ; Cd sorbed = 11.34 mg ; flow = 30 ml/hour)……………………….38





Figure 27: concentration of separated Pb in function of the pH when using HCl as desorption reagent…41 Figure 28: desorption curves of Pb and Cd while using NaCl with a concentration of 7.8 mM


Figure 29: desorption curves of Pb and Cd while using CaCl2 with a concentration of 3.9 mM


Figure 30: breakthrough curves of nickel and copper (conditions: Ci,Ni = 0.4 mM ; Ci,Cu = 0.4 mM ; column length = 7 cm ; flow rate = 30ml/hour ; Ct/Ci = concentration of the metal at time t devided by the initial concentration) ………………………………………………………………………………………..45

Figure 31: desorption curves of Ni and Cu while using 26.9 mM HCl solution( pH of 1.57)

(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)………………………….46


(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)………………………….47


(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)..……………………….48


(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)…………………………49


(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)…………………………50

Figure 36: concentration of separated Cu in function of the pH when using HCl as desorption reagent ………………………………………………………………………………………………………………52

Figure 37: desorption curves of Ni and Cu while using 7.2 mM NaCl solution

(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)………..………………..53

Figure 38: desorption curves of Ni and Cu while using 3.6 mM CaCl2 solution

(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour) ………..……………….54

Figure 39: breakthrough curves of Pb and Cd with theoretical curves calculated with Yoon and Nelson

Model ………………………………………………………………………………………………………………………………………56

Figure 40: breakthrough curves of Cu and Nu with theoretical curves calculated with Yoon and Nelson

Model ………………………………………………………………………………………………………………………………………57

Figure 41: breakthrough curves of Pb and Cd with theoretical curves calculated with Thomas Model…..58

Figure 42: breakthrough curves of Cu and Ni with theoretical curves calculated with Thomas Model……58

Figure 43: breakthrough curves of Pb and Cd with theoretical curves calculated with Adams-Bohart

Model ………………………………………………………………………………………………………………………………………59

Figure 44: breakthrough curves of Cu and Ni with theoretical curves calculated with Adams-Bohart

Model ………………………………………………………………………………………………………………………………………60

List of tables

Table 1: experiments that will be conducted for the desorption of lead and cadmium from grape stalks ……………………………………………………………………………………………………………………………..34

Table 2: experiments that will be conducted for the desorption of nickel and copper from grape stalks ……………………………………………………………………………………………………………………34 Table 3: sorbed and separated amounts of lead and cadmium after sorption process……………………….….36 Table 4 : amounts of sorbed and separated lead and cadmium when using 100 mM HCl..…………………….37

Table 5: amounts of sorbed and separated lead and cadmium when using 31 mM HCl….……………………..38

Table 6: amounts of sorbed and separated lead and cadmium when using 7.8 mM HCl………………………..39



Table 9: amounts of sorbed and separated lead from the grape stalks when using HCl ………………………..41

Table 10: amounts of sorbed and separated Cadmium from the grape stalks when using HCl ……………..41

Table 11: amounts of sorbed and separated lead and cadmium when using 7.8 mM NaCl …………………..43

Table 12: amounts of sorbed and separated lead and cadmium when using 3.9 mM CaCl2……………………44

Table 13: amounts of sorbed and separated lead from the grape stalks when using

NaCl and CaCl2 ……………………………………………………………………………………………………………………….44

Table 14: amounts of sorbed and separated cadmium from the grape stalks

when using NaCl and CaCl2 …………………………………………………………………………………………………….44

Table 15: sorbed and separated amounts of nickel and copper after sorption process …………………………46 Table 16: amounts of sorbed and separated nickel and copper when using 26.9 mM HCl ….…………………47

Table 17: amounts of sorbed and separated nickel and copper when using 11.7 mM HCl .……………………48

Table 18: amounts of sorbed and separated nickel and copper when using 7.2 mM HCl ………………………49



Table 21: amounts of sorbed and separated nickel from the grape stalks when using HCl ……………………51

Table 22: amounts of sorbed and separated copper from the grape stalks when using HCl ………………….51

Table 23: amounts of sorbed and separated nickel and copper when using 7.2 mM NaCl……………………..53

Table 24: amounts of sorbed and separated nickel and copper when using 3.6 mM CaCl2 ……………………54

Table 25: amounts of sorbed and separated nickel from the grape stalks when

using NaCl and CaCl2 ………………………………………………………………………………………………………………55

Table 26: amounts of sorbed and separated copper from the grape stalks when

using NaCl and CaCl2 ………………………………………………………………………………………………………………55

Table 27 : Yoon and Nelson model, calculated constants ………………………………………………………………………56

Table 28 : Thomas model, calculated constants ……………………………………………………………………………………57

Table 29 : Adams-Bohart model, calculated constants ………………………………………………………………………….59

12

1 INTRODUCTION

1.1 METALS IN FRESHWATER

1.1.1 What are heavy metals

Heavy metals are all metals with a high density, but there is no definition that is generally accepted.

Sometimes other criteria are used such as atomic weight, atomic number or periodic table position.

Heavy metals occur naturally in the Earth’s crust and can not be destroyed or degraded. Examples of

heavy metals are: lead, cadmium, mercury, etc. Some of those metals are essential for life if they appear

in small amounts. However, higher concentrations due to bioaccumulation can lead to health risks.

1.1.2 Occurrence

Heavy metal can get into the water in many different ways. They are already naturally presented in the

environment in which they are especially presented in rocks. These metals can be released from those

rocks in the form of ions by coming into contact with water, mostly acid. In nature, there is a quasi-

equilibrium between the release into the water and again participate as sediment. However, human

activities have disturbed this balance with the rapid development of various industries such as mine and

metallurgy. The figure below shows different ways in which metals get into the water. (Taylor, 2015)

Figure 1 : Human activities that cause contamination with metals

(http://www.texasintegrative.com/wp-content/uploads/2015/05/Toxic-Heavy-Metals.jpg)

http://www.texasintegrative.com/wp-content/uploads/2015/05/Toxic-Heavy-

13

1.1.3 Mine drainage

One of the most polluting processes is Acid Mine Drainage (AMD). Acid mine drainage, or also known as

acid rock drainage, is a water polluting problem when water reacts with rocks containing sulphur-

bearing metals in an abandoned mine. Mining often happens in underground areas, so water must be

pumped out during the process. When the mining activities in the mine stops, the pumping is also ended

and the water floods the mine. The surrounding rocks are now exposed to air and water, so the metals

in the rocks start oxidizing, which results in acid production in the water. The most know pollutions are

the ones with iron, giving the water a yellow to red colour. But also other metals can dissolve in the

water, with or without a colour change of the water as result. (deadreign, 2015) (earthworks, sd)

Figure 2: steps in the process of AMD

(http://old.post-gazette.com/regionstate/19981208minegraphic3.asp)

The region in Spain that suffers most under acid main drainage is the Iberian pyrite belt with the rivers

Odel and Tinto.

http://old.post-gazette.com/regionstate/19981208minegraphic3.asp

14

1.1.4 Rivers Odel and Tinto

The Iberian pyrite belt is a geographic region situated in the south of the Iberian Peninsula between

Alcácer does Sal in Portugal and Seville in Spain. It was formed by volcanic activity, which has led to

massive deposition of sulphide ores, making it an ideal environment for mining. Ever since the Roman

times, but especially during the industrial revolution a lot of mining sites were opened, which has led to

many abandoned mines now. These abandoned and flooded mines are the cause of one of the World's

largest accumulations of mine wastes and acid mine drainage, particularly in the Rio Tinto mining district.

(Leiste, 1996) (Sanchez, 2008)

Figure 3: The Iberian pyrite belt

(http://www.sec.gov/Archives/edgar/data/1377085/000120445907001642/lundintechrep.htm)

Two important rivers in that area are the rivers Odiel and Tinto, both reported for serious acid mine

drainage. The odiel river has its source in the Sierra de Aracena and the Tinto river in the Sierra Morena.

Both rivers come together in an estuary at of the city of Huelva, where they flow into the sea. Because

they both flow through the Iberian pyrite belt, they have a lot of dissolved metals in the water which

give them a typically red-wine colour. Previous work has used the concentrations found in these rivers

as a basis for metal mixtures. The best results were found with metal concentrations of 0.4 mM which

will be used during this study.

http://www.sec.gov/Archives/edgar/data/1377085/000120445907001642/lundintechrep.htm

15

Figure 4: Rio Tinto Rio Odiel

(http://amazingworldfactsnpics.com/amazing-2/surprising-landscapes-around-world/6/)

(https://en.wikipedia.org/wiki/Odiel)

1.1.5 Problems and (health)risks

Acid mine drainage may have serious consequences for the environment and living beings, in the first

place for fish and plants, but ultimately for all living organisms. Acid mine drainage is responsible for the

pollution of ground waters and streams and provides a degradation of the quality of water. Heavy

metals can not be degraded and will therefore accumulate in water organisms. This process is called

bioaccumulation. By eating those organisms the metals will also accumulate in the human body and can

cause many health risks such a cancer, organ damage and even death. (Water health , sd) In order to

prevent those risks, metals should be removed from the water. Several treatments for removal are

presented in section 1.1.6.

1.1.6 Treatments of removal

1.1.6.1 Complexation

A first step in the removal of metals in wastewater is complexion. This type of removal only works for

high concentrations of metals and is not 100% efficient. Complexation is a process in which two or more

particles form together a new and bigger particle. When one of those starting particles was a metal, the

complex formed is known as a metal complex. This complex, with a higher mass as the metal from which

it is formed, will be more likely to precipitate then dissolved metals.

1.1.6.2 Reverse osmoses

A reversed osmosis is a technique used for the purification of water using a semipermeable membrane

which works as a filter. A pump pushes the water through a membrane in a flow that is reversed to that

in osmosis. If the pressure is high enough, the pure water will be pressed through the membrane,

without taking the dissolved substances. By constantly removing the pure water a continuous

purification process will occur. (PuretecIndustrialWater, 2012)

http://amazingworldfactsnpics.com/amazing-2/surprising-landscapes-around-world/6/

https://en.wikipedia.org/wiki/Odiel

16

Figure 5 : principle of reverse osmosis

(http://puretecwater.com/what-is-reverse-osmosis.html)

1.1.6.3 Ion exchange

Ion exchange is the replacement of undesirable ions with a certain charge by desirable ions of the same

charge in a solution, by using an ion-permeable absorbent. There are two types of ion exchangers, the

first ones are the cation exchangers. This type of exchangers ensures the exchange of positively charged

ions. The second ones are the anion exchangers for the negatively charged ions. (Lenntech, 2008)

Figure 6: Ion exchange

(http://www.popularmechanics.com/home/interior-projects/how-to/a150/1275126/)

1.1.6.4 Sorption

Sorption is a process in which a substance will be attached to another one. A component can be

selectively separated from a mixture when using a sorbent that is selectively for that particular

component. Adsorbents are mostly porous solid faces and the adsorption takes place on the pore walls

inside the particles. An adsorption process can be divided in four steps. First the solute diffuses through

the solutions to an area close to the adsorbents. Then the solute diffuses into the pores of the

adsorbents. The third step is to diffuse to the pore walls. At least, the final step is the real adsorption to

the pore wall surface. (Volesky, 2003) (Liu, 2014)


http://www.popularmechanics.com/home/interior-projects/how-to/a150/1275126/

17

There are different types of sorption, the first one, ion exchange has already been described above. The

other types are absorption and adsorption. When using an absorption process the molecules will enter

in some kind of bulk material. By adsorption on the other hand, the molecule will only be taken up by

the surface. The attraction may often be based on electrostatic charges, oxidation/reduction reactions,

physical phenomena or a variety of chemical bindings. Mostly it is possible that several of these

processes take place together, and then it is simply referred to as sorption. (chemistrytwig, 2013)

Figure 7: absorption and adsorption

(http://chemistrytwig.com/wp-content/uploads/2013/09/absorptionadsorption.jpg)

The most widely used adsorbent is activated carbon. Activated carbon is a quite expensive sorbent,

that’s why new low cost alternatives are developed. One of the alternatives that already has been found

is sorption onto low cost biosorbents. Those biosorbents can be microbial organisms or even some

plants like coffee plants or grape stalks, as used in this work.

1.1.7 Metal sorption

Earlier studies have already shown that the removal of metals from binary metal mixtures of Cu(II) and

Ni(II) and Cd(II) and Pb(II) can be obtained when using grape starks (Villaescusa et al. 2004). These heavy

metals can be removed from wastewaters by sorption processes. The most widely used adsorbent is

activated carbon, but it is too expensive that’s why new low-cost alternatives are developed such as the

grape stalks. The sorption of metals by this kind of material might be due to the presence of carboxyl,

hydroxyl, sulphate, phosphate and amino groups that can bind metal ions. (Pujol, 2013)

http://chemistrytwig.com/wp-content/uploads/2013/09/absorptionadsorption.jpg

18

1.2 GRAPE STALKS

1.2.1 Occurrence

Grape stalk waste, which is generated in large amounts (at about 10,000 t/year) in the Mediterranean

areas because of the wine industry, can be used as a low cost sorbent (Pujol, et al., 2013). The grape

stalks represents between 2.5% and 7.5% of the weight of grapes.

Figure 8: grape stalks

1.2.2 Chemical compounds

The most important components of grape stalks are:

1.2.2.1 Lignin

Lignin is an important organic structure in plants for the bindings of cells which constitute wood. Its

chemical structure is a dendritic network of cross-linked phenyl polymers which is different for every

species. In the figure below, a small segment of a lignin polymer is presented. (ILI, 1992)

19

Figure 9: small segment of lignin polymer

(https://en.wikipedia.org/wiki/Lignin#/media/File:LigninStructure.png)

1.2.2.2 Cellulose

Cellulose is a chain of B-D-glucose molecules bound in exactly the same way. It is the main component in

the cell walls of plants and gives them their strength. The sugar units are linked when water is being

formed by combining the OH-group of one sugar with the H of the other one. In the figure below can be

seen how those two glucose molecules bind. (Frostburg, 1997)

Figure 10: two unlinked B-D-glucose molecules

(http://antoine.frostburg.edu/chem/senese/101/consumer/faq/what-is-cellulose.shtml)

1.2.2.3 Hemicellulose

Polyose or hemicellulose is a collective name for a series of closely related carbohydrates that are made

in plants. It is similar to cellulose, but with other sugars in the chain such as xylan and mannose.

https://en.wikipedia.org/wiki/Lignin#/media/File:LigninStructure.png


20

1.2.2.4 Polyphenols

Polyphenols are a group of chemical compounds, which occur in plants. A polyphenol molecule consists

of more than one phenolic group. They are classified in tannins, phenylpropanoids and flavonoids.

Tannins are a group of polyphenols that have an influence on the taste, color and texture of wine. It is a

biomolecule that binds to and precipitates proteins and various other organic compounds. As an

example of a typical tannin, in figure 11 is shown the structure of corilagin

Figure 11: Corilagin

(https://nl.wikipedia.org/wiki/Tannine)

1.2.3 Advantages of grape stalks

The use of grape stalks has two major advantages. The first one is the fact that it is a low cost material

which reduces the industrial waste of process by-products by giving them an added value. This large

amount of waste creates otherwise economic and environmental problems. The second advantage is

that it is a natural product that can be used both in his raw form as well as after pre-treatment.

1.2.4 Metal affinity to grape stalks in fixed bed columns

Some metals can have a higher or a lower affinity for a sorbent than others. At the beginning of a

sorption process in fixed bed columns all metals will totally adsorb because there are plenty of free

active sites where they can react. During the process the availability of those active sites will decrease

and the metals with a lower affinity for the sorbent will be pushed off by others with a higher affinity,

resulting in an overconcentration of the metal released in the outlet solution.

https://nl.wikipedia.org/wiki/Tannine

21

The affinity of metals for grape stalks has already been studied in previous works. The four metallic ions

studied (Cu, Ni, Pb, Cd) were all sorbed onto the grape stalks in the fixed bed, but the sorbent has

different affinity for each metal. During this work it was observed that, when using binary metal

mixtures of Cd,Pb, Cu and Ni only lead didn’t suffer overconcentration. This means that the affinity of

the grape stalks for leads is the highest of those four metals. Copper was only overshoot by lead, which

means that grape stalks has a lower affinity for copper than lead, but a higher affinity for copper and

nickel. The last experiment to determine the order of affinity was with a binary mixture of Nickel and

Cadmium. This experiment showed that cadmium has a higher affinity, therefore, the sequence of

affinity is Pb>Cu>Cd>Ni (Oñate, 2009). These differences in affinity can allow us to separate those metals

in binary metal mixtures.

1.3 METAL SEPARATION BY USING COLUMNS

1.3.1 Breakthrough curves

Breakthrough curves are plots of the concentration of sorbate measured at the end of the column in a

relationship to the time (or volume) during the sorption process. When a fluid enters a column with a

fixed bed, it first will come in contact with the first few layers of the sorbent. In these layers the

components in the fluid will react with the free active sites on the sorbents so they can’t pass through

the column. The next amount of fluid will run a bit further to find new free active sites on the sorbent.

This is called the mass transfer zone (MTZ). So the amount of material (in this case metals) sorbed within

the bed will depends on the position in the column and the time. The progress of a mass transfer zone

can be seen in the figure below.

Figure 12: progress of the mass transfer zone

(http://chem-tips.blogspot.com.es/2012/08/molecular-sieve.html)

Because the first drops of liquid have a lot of free spaces to sorb on the sorbent, the first drops on the

outlet will have few or no solute remaining until the bed becomes saturated. The breakthrough point is

the moment when the amount of not adsorbed solute begins to emerge. From this point on, more and

more solute will reach the end of the column until all of it runs through the column without any sorption.

At this moment the fixed bed is totally saturated and becomes ineffective. A typical breakthrough curve

presents an S-shape as can be seen in the figure below.

http://chem-tips.blogspot.com.es/2012/08/molecular-sieve.html

22

Figure 13: typical breakthrough curve

(http://facstaff.cbu.edu/rprice/lectures/adsorb.html)

1.3.2 Mathematical models

Mathematical models describes theoretical concentration-time profiles. They are used to predict the

concentration of the metals at any time during the sorption. Since the metal concertation in the liquid

that moves through the bed constantly changes it is difficult to describe such a model. The fundamental

equations for a fixed-bed column depends on the mechanisms responsible for the process and include

mass balances between solid and fluid face, rate of process, etc. Various simple mathematical models

such as Yoon and Nelson model, Thomas model and Adams-Bohart model have been developed.

1.3.2.1 Yoon and Nelson model

The Yoon and Nelson model (1984) is a simple model to predict the breakthrough curves for adsorption.

This model assumes that the rate of decrease in the probability of adsorption for each adsorbate

molecule is proportional to the probability of sorbate sorption and the probability of sorbate

breakthrough on sorbent. (M. Calero, 2009) By plotting ln[C/(CF-C)] in function of the time, the two

important constants for this curve can be calculated. This model don’t requires the characteristics of the

adsorbate or the parameters of the bed, what makes it an easy model to work with, but less valuable to

predict under variable conditions.

ln𝐶

𝐶𝐹 − 𝐶= 𝐾𝑌𝑁𝑡 − 𝑡1

2⁄ 𝐾𝑌𝑁

With C = concentration at set time

CF = final concentration ( = start concentration)

KYN = Yoon and Nelson’s proportionality constant (to be calculated)

T1/2 = time for retraining 50% of initial adsorbate (to be calculated)

http://facstaff.cbu.edu/rprice/lectures/adsorb.html

23

1.3.2.2 Thomas Model

Another model to predict breakthrough curves is the Thomas model. This model is one of the most

general models to describe breakthrough curves in fixed bed columns for biosorption. The model is

based on second order kinetics and the Langmuir isotherm. To calculate the constants of this model,

ln[(CF/C)-1] has to be plotted in function of the time. (M. Calero, 2009) (Zhe XU, 2013)

ln (𝐶𝐹

𝐶− 1) =

𝑘𝑇𝐻𝑞𝐹𝑚

𝑄− 𝑘𝑇𝐻𝐶𝐹𝑡



KTH = Thomas rate constant (to be calculated)

m = mass of adsorbate

qF = maximum concentration of solute in the solid phase (to be calculated)

Q = mg sorbed / G sorbate (experimental)

1.3.2.3 Adams-Bohart model

A model to describe the initial part of the breakthrough curves is the Adams-Bohart model (1920). This

model describes the breakthrough curve for C values lower than 0.15 times the initial concentration. The

Adams-Bohart model describes the relationship between C/Ci and t in a continuous system. To calculate

the constants of this model, ln[(CF/C)-1] has to be plotted in function of the time. (M. Calero, 2009)

ln (𝐶𝐹

𝐶− 1) = ln [𝑒𝑥𝑝 (𝑘𝐴𝐵𝑄

𝐻

𝑢) − 1] − 𝑘𝐵𝐶𝐹𝑡



KAB = kinetics constant (to be calculated)

H = height of the column

u = maximum concentration of solute in the solid phase (to be calculated)

Q = mg sorbed / G sorbate (experimental)

1.3.3 Desorption of loaded columns

As explained in section 1.2.3 metals can be separated from binary metal mixtures by using sorption

processes on grape stalks. One of the metals is partially separated, while the other one is sorbed onto

the grape stalks together with the remaining of the separated metal. A possible solution to separate the

other metal from the grape stalks is a desorption process. Desorption is the process whereby a

substance, in this case the metal, is released from or through a surface. A typical desorption curve is a

showed in the picture below. This desorption will be tested during this work.

24

Figure 14 : typical desorption curve

(http://www.fbp.ichemejournals.com/cms/attachment/2024162035/2044029851/gr6_lrg.gif)

1.3.4 Calculations of the absorbed and desorbed amount of metal

To calculate the absorbed amount of metal ions on the grape stalks, it is needed to measure the amount

of metals that went through the column without sorption. This amount can be calculated using the

breakthrough curves when plotting the concentration as a function of the volume of solution that went

through the column. The surface beneath the curve is the amount of molls or grams that didn’t get

sorbed. Another concentration that is needed to calculate this amount is the total amount of molls or

grams that went in the column. This amount is the total volume multiplied with the initial concentration.

Amount without sorption : ∑𝐶𝑡+𝐶𝑡+1

2∗ (𝑉𝑡+1 − 𝑉𝑡) (1)

Ct = concentration at the end of the column at time t

Vt = volume that passed through the column at time t

To know the amount of sorbed metals it is needed to take the difference between those 2 values. To

calculate the Q-value (the amount of metals (in mg) / gram of grape stalks) this experimental value has

to be divided by the amount of sorbate used.

Another important number is the percentage that comes back into solution after desorption. This value

can be calculated by dividing the total amount of desorbed material with the total amount of absorbed

material and multiply with 100%. To know the amount of desorbed material you need to measure the

area underneath the desorption curve, which is typically a gauss curve. This can also be calculated with

formula 1.

The concentrations at the outflow of the column can be measured with flame atomic absorption

spectrometry (FAAS).

http://www.fbp.ichemejournals.com/cms/attachment/2024162035/2044029851/gr6_lrg.gif

25

1.4 FAAS

1.4.1 Method

Flame Atomic Absorption Spectrometry is a good technique for a quantitative analysis of metals. It is an

analysis technique based on the selective absorption of optical radiation by atoms. The first step is

atomizing a sample in a flame. Secondly a special type of lamp (hollow cathode lamp) will emit light of a

specific wavelength in the flame. This emitted light is partially absorbed by the atoms in the flame. The

amount of absorption is proportional to the concentration of atoms in the flame and thus also in the

sample. The figure below shows the structure of an FAAS. (Flame Atomic Absorption Spectrometry, sd)

(Principle of Atomic Absorption, sd)

Figure 15: sketch of the components of the FAAS

(http://chemicalinstrumentation.weebly.com/flame-aas.html)

1.4.2 Components

1.4.2.1 Hollow cathode lamp

The lamp used in FAAS is a hollow cathode lamp. This is a gas discharge tube that consists of a glass tube

with the quartz window filled with neon or argon gas under pressure. The anode is made of tungsten

and the hollow cathode contains the element that has to be determine. After applying a constant

current through this lamp, the noble gas will be ionized. This stream of noble gas ions has enough kinetic

energy to release metal ions from the cathode. This causes the creation of an atom cloud of the metal to

be measured around the cathode. Those sputtered atoms will become excited by collisions with the

noble gases. When returning to the ground state those atoms send a characteristic radiation which has

exactly the right energy to measure the sample. The amount of absorption of this radiation is

proportional to the concentration.

http://chemicalinstrumentation.weebly.com/flame-aas.html

26

Figure 16: hollow cathode lamp

(https://en.wikipedia.org/wiki/Hollow-cathode_lamp#/media/File:Hollow_Cathode_Lamp.svg)

Figure 17: emission of a hollow cathode lamp

(http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/AASTheory.htm)

As can be seen in the figure above, the hollow cathode lamp must contain the element being

determined. There are two types of hollow cathode lamps. The first ones contain only one metal and

can only be used for the determination of that specific metal. The second ones are called multi element

lamp and have an alloy of different metals as cathode. Those lamps can be used for the determination of

all metals that are presented in this alloy.

1.4.2.2 Flame and burner

In order to have a flame there must be both fuel and an oxidant. The flame required for spectrometry

needs a high temperature in order to vaporize, atomize and ionize the metals. To require those high

temperatures of 2300K acetylene is used as fuel with air as oxidant. To reach higher temperatures pure

oxygen can be used instead of air, but this lowers the sensitivity due to high burning velocity.

The fuel and oxidant are forced into the flame, but these results in a turbulent flame which is negative

for the sensitivity. To solve this problem, premix burners are used. A premix burner is a burner which

already mixes the fuel and air before it has reached the actual burner mouth.

https://en.wikipedia.org/wiki/Hollow-cathode_lamp#/media/File:Hollow_Cathode_Lamp.svg

http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/AASTheory.htm

27

Figure 18: premix burner

(http://encyclopedia2.thefreedictionary.com/Propane+burner)

Figure 19: Nebulizer

(http://faculty.sdmiramar.edu/fgarces/labmatters/instruments/aa/AAS_Theory/AASTheory.htm)

1.4.2.3 Monochromator

A monochromator is used to select a specific wavelength of light, which is absorbed by the sample. The

light selected by the monochromator is directed onto a detector. There are different types of

monochromators such as prisms.

http://encyclopedia2.thefreedictionary.com/Propane+burner


28

1.4.2.4 Detector

Nowadays the most used detectors are photomultipliers tubes (PMT) instead of light measurements.

Those PMT have a high sensitivity for light in the range between UV and Near-IR. A photomultiplier tube

is composed of several diodes. If the light hits the cathode, which is photosensitive, it will produce ions

which will flow to the first diode. Due to the potential, those ions will pass each diode and the number

of ions will increase exponential. This causes a high amount of ions that will hit the anode and causes

the high sensitivity. The principle a photomultiplier tube is showed in the figure below.

Figure 20: principle of a photomultiplier tube

(https://nl.wikipedia.org/wiki/Fotomultiplicator)

https://nl.wikipedia.org/wiki/Fotomultiplicator

29

2 OBJECTIVES

The general purpose of this work is to separate metals from binary metal mixtures of copper and nickel

and lead and cadmium by using grape stalks. To achieve this objective, sorption and desorption process

will be studied using flow up columns filled with grape stalks. The main purpose during this work is to

optimize the desorption process. The effect of two parameters will be studied

1) The effect of the concentration of the desorption reagent on the separation of two binary metal

mixtures. To do this, HCl with different pH (and thus also different concentration) will be used

during the desorption of the metal mixtures of lead and cadmium and copper and nickel.

2) Secondly, when the optimal concentration of HCl for the desorption of those metal mixtures is

found, this optimal concentration will be used to test the desorption with NaCl and CaCl2 to

check the influence of ions (Na+ / Ca2+) used.

30

3 EXPERIMENT

3.1 COLUMN PREPARATION

3.1.1 Grape stalks

During the production of wine a lot of grape stalks remain as waste product. Parts of those grape stalks

can be used for metal separation. The grapes stalks used in this set of experiments were supplied by a

wine manufacturer of the Costa Brava region in Spain.

Only small parts of the grape stalks can be used to fill the fixed beds. Usable parts of the grape stalks

were cut into small pieces, washed with water and dried in the oven by 55-60 oC during one night. The

dried pieces were grinded and afterwards sieved with an automatic sieve to select a particle size

between 0.25 and 0.50 mm.

From this fraction, 2.00 grams was weighed and placed in the column. This amount of grapes stalks is

chosen because previous works gave the best results with this amount of grape stalks. The column with

fixed grape stalks was washed for several hours with milli-Q water to remove all impurities that could

give unwanted side reactions. The washing step was also needed in order to give the grape stalks a

chance to swell to maximum humidity. If dry grape stalks were used during the experiment, there would

be no outflow during the first minutes.

3.1.2 Column

The fixed bed columns used during this set of experiments have a length of 10 cm, an inner diameter of

1.0 cm and are made out of glass. Glass wool was used as a filter in order to ensure that the small

particles of the grape stalks would not leave the column.

3.2 EXPERIMENTAL SET-UP

3.2.1 Equipment

The experimental set-up consists of a peristaltic pump, which ensures a constant current of metal

solution through the column, a fixed column with grape stalks, a fraction collector and a laptop with

program to automate the process. The connection between those parts was made by tubes with a

colour code. This colour code represents the inner diameter of the tube. During this set of experiment

the tubes with colour code gray-gray were used (inner diameter of 1.30mm).

3.2.2 Flow rate

Earlier research about the flow rate has shown that a rate of 30 ml/hour give good results when using

grape stalks of this size for the separation of binary metal mixtures of Cu/Ni and Cd/Pb. This flow rate

was programmed with the peristaltic pump and used for all experiments.

31

3.2.3 Sorption process

A binary mixture of 0.4 mM lead and 0.4 mM cadmium or 0.4 mM copper and 0.4mM nickel was send

through the columns for a fixed time with a constant flow of 30 ml/hour. The sorption times for the

mixture of lead and cadmium were 31 hours and 20 minutes and the sorption times for copper and

nickel were 35 hours. These times were used in all the experiments to always have the same separation

volume and the same amount of loaded metals on the grape stalks. During the sorption process a

sample was taken every 30 minutes to analyse the amount of metals. With those results the separation

volume and the amount of separated metals will be calculated. (We established that the concentration

of the other metal should be below 1mg/l in order to have a separation)

3.2.4 Desorption process

Desorption processes were done with the columns which have been loaded using the above sorption

process. The desorption reagents used for the desorption process were HCl at different concentrations,

NaCl and CaCl2. The concentrations of NaCl and CaCl2 used were based on the results that were obtained

with the desorptions using HCl. Samples were taken every 30 minutes to check the separation volume

and the amount of metal that is separated.

3.3 ANALYSIS OF THE METALS

3.3.1 FAAS

Flame atomic absorption spectroscopy (FAAS) is a technique used in analytical chemistry for

determining the concentration of an analyte in a sample. Hollow cathode lamps are the light sources

and they emit the light that is required for the analysis. For the experiments with a binary mixture of

lead and cadmium two hollow cathode lamps were needed. When testing the binary mixture of copper

and nickel a multi element lamp was used. The lamp was placed in position 2 for al measurements.

In order to obtain a flame both fuel and an oxidant are needed. The FAAS during this experiment was

equipped with a flame that used acetylene and oxygen to ensure a high temperature.

3.3.2 Stock solutions

All standards were prepared from a standard solution of 1000 +/- 2 mg/l from Panreac quimica.

3.3.2.1 Copper

Since the calibration curve with the FAAS of copper goes from 0.1 to 10 mg/l the standards of copper

had to be prepared within this range. To make this calibration an automatic diluter was used so only the

highest standard was needed. Another standard of 5 mg/l was also made to check the instrument.

The wavelength used during the analyses was 324.7 nm.

32

3.3.2.2 Nickel

The optimum working range for Nickel is between 0.1 and 20 mg/l. A calibration curve was made by

using a stock solution of 20 mg/l and an automatic diluter which made the other standards

automatically. Again a stock solution of half the concentration was used to check the equipment. In this

case this is 10 mg/l. The wavelength for nickel was 232.0 nm

3.3.2.3 Lead

The lead standards had to be prepared in a range from 0.1 to 30 mg/l. An automatic diluter was used so

only the highest stock solution was necessary. A stock solution of half the concentration was used to

check the equipment. The optimal wavelength for lead is 405.8 nm

3.3.2.4 Cadmium

The calibration curve of cadmium has a range between 0.02 and 3 mg/l. A stock solution of 3 mg/l was

made and other stock solutions were automatically measured with the automatic diluter. Also for these

analyses the equipment was tested with a concentration of 1.5 mg/l. The wavelength used was 326.1

nm.

3.4 Metal mixtures and desorption reagents

3.4.1 Calculations of metal mixtures

The metal mixtures needed for those experiments contain 0.4 mM of each metal. Two different binary

metal mixtures were made. The first one contained lead and cadmium and the second one contained

copper and nickel. The used chemicals were CdCl2 . 2,5 H2O (98%) and PbCl2 (99%) from Panreac quimica

and CuCl2 . 2 H2O (99%) and NiCl2 . 6 H2O (98%) from Scharlab.

M(CdCl2 . 2,5 H2O) = 228.35 g/moll

M(Cd) = 112.41 g/mol

M(PbCl2) = 278.11 g/mol

M(Pb) = 207.2 g/mol

M(CuCl2 . 2 H2O) = 170.48 g/mol

M(Cu) = 63.55 g/mol

M(NiCl2 . 6 H2O) = 237.69 g/mol

M(Ni) = 58.69 g/mol

To make 2 litres of the Cd/Pb mixture, 0.183 gram of CdCl2 . 2,5H2O and 0.222 gram of PbCl2 were

weighed on the balance. The weighed products were then dissolved in a volumetric flask of 2L with milli

Q water.

To make 2 litres of the Cu/Ni mixture, 0.136 gram of CuCl2 . 2 H2O and 0.190 gram of NiCl2 . 6 H2O were

weighed on the balance. The weighed products were then dissolved in a volumetric flask of 2L with milli

Q water.

33

3.4.2 Calculations of desorption reagents

3.4.2.1 HCl solutions

For the desorption process with HCl, different concentrations were tested while using the pH to

determine the concentration.

pH = -log(concentration)

3.4.2.2 NaCl and CaCl2 solutions

Experiment with Pb/Cd mixture

The ideal pH of HCl found was a pH of 2.11. Solutions of NaCl and CaCl2 with a concentration

that corresponds with this pH are prepared. A HCl-solutions with a pH of 2.11 contains 7.8 mM

H+.

o NaCl solution

To work under the same conditions used with HCl a solution with a concentration of

7.8 mM Na+ was prepared.

M(NaCl) = 58.44 g/moll

To make 1 litre of the NaCl solution, 0.454 gram of NaCl was weighed on the balance.

and dissolved in a volumetric flask of 1L with milli Q water

o CaCl2 solution

To work under the same conditions used with HCl a solution with a concentration of 3.9

mM Ca2+ was prepared. Only half of the concentration was needed because Ca has a

double charge.

M(CaCl2) = 110.98 g/moll

To make 1 litre of the CaCl2 solution, 0.431 gram of CaCl2 was weighed on the balance

and dissolved in a volumetric flask of 1L with milli Q water

Experiment with Pb/Cd mixture

The ideal pH found with HCl is a pH of 2.14. Solutions are prepared the same as described above.

34

3.4.3 Experiments that will be conducted for the Pb/Cd experiments

Table 1: experiments that will be conducted for the desorption of lead and cadmium from grape stalks

Reagent/Concentration 100 mM

31 mM

7.8 mM

1.1 mM

0.2 mM

HCl X pH 1.00

X pH 1.51

X pH 2.11

X pH 2.95

X pH 3.69

First the optimum concentration of the desorption reagent will be tested while using different concentrations HCl corresponding to different pH’s. After determining the optimum concentration, the effect of other ions will be tested to find the best ion for the exchange. To test this a desorption with NaCl and a desorption with CaCl2 solutions will be conducted. Considering that the main mechanism for the sorption and desorption is an ionic exchange, the concentration multiplied with the charge should be the same in order to work under the same conditions.

3.4.4 Experiments that will be conducted

Table 2: experiments that will be conducted for the desorption of nickel and copper from grape stalks

Reagent/Concentration

26.9 mM

11.7 mM

7.2 mM

4.8 mM

2.2 mM

HCl X pH 1.57

X pH 1.93

X pH 2.14

X pH 2.32

X pH 2.65

35

4 RESULTS

4.1 Binary mixtures of lead and cadmium

In figure 21 the breakthrough curves of lead and cadmium are presented while working with a full

column and a metal mixture of 0.4 mM lead and 0.4 mM cadmium. The y-axes presents the ratio

between the concentration at a set time and the initial concentration of each metal. The x-axis presents

the time.

Figure 21: breakthrough curves of lead and cadmium (conditions: Ci,Pb = 0.4 mM ; Ci,Cd = 0.4 mM ; column length = 7 cm ; flow rate = 30ml/hour ; Ct/Ci = concentration of the metal at time t divided by the initial

concentration) During the first seven hours there are no metals detected at the outflow of the column, so all metals are sorbed by the grape stalks. After seven hours the solution starts to contain some cadmium. Between the 7th hour and the 25th hour only cadmium is detected. This means that all the lead is still sorbed by the grape stalks and cadmium is not. During these eighteen hours a separation of cadmium is achieved. The amount of separated cadmium is 20.23 mg in 540 ml which gives a concentration of 37.46 mg/l. Those values are calculated with formula (1). The breakthrough curve of cadmium shows an overshoot after eleven hours. This means that the concentration of cadmium by the outflow of the column is higher than the initial concentration. During this overshoot some of the sorbed cadmium is desorbed and replaced by lead. After several hours the overshoot starts to decrease and the breakthrough curve goes to a stable value of one. The breakthrough curve of lead starts to increase after twenty-five hours, this means that not all the lead is sorbed anymore. This curve will go to a ratio of one quite fast, without an overshoot. When both curves reach the stable value of one, the initial metal mixture pass through the column without being sorbed and the column is saturated with both lead and cadmium.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 5 10 15 20 25 30 35

Ct/

Ci

Time (hours)

Breakthrough curves of Pb and Cd

Pb

Cd

36

After 31 hours and 20 minutes, the sorption process is stopped because the concentration of lead starts to increase. To always have the same amount of metals sorbed onto the grape stalks, this experimental time will be used in further experiments. In order to be able to calculate the metal desorbed afterwards, the Q-values have to be calculated. This Q-value is the amount of metal (in mg) that is sorbed on 1.00 g of grape stalks. The total amount of sorbed lead is 60.50 mg, so that gives a Q-value of 30.25 mg/g. From cadmium only 11.34 g is sorbed, so the Q-value is 5.67 mg/g.

Table 3: sorbed and separated amounts of lead and cadmium after sorption process

Lead Cadmium

Sorbed (mg) 60.50 11.34

Q-value (mg/g) 30.25 5.67

Separated (mg) 0 20.23

Separation volume (ml) 0 540

Separated (mg/l) 0 37.46

4.1.1 Effect of HCl concentration 4.1.1.1 Desorption with HCl at a pH of 1.00

Figure 22: desorption curves of Pb and Cd while using 100 mM M HCl solution (pH of 1.00)

(conditions: Pb sorbed = 60.50 mg ; Cd sorbed = 11.34 mg ; flow = 30 ml/hour)

In figure 22 can be seen that the desorption of both lead and cadmium started immediately and that the

decrease of concentration starts at the same time. To have separation only one metal should be

desorbed while the concentration of the second one is less than 1 mg/l. For this concentration of HCl

there is a separation after 2 hours of desorbing and this separation lasts for 8 hours. During the total

experiment 32.49 mg or 53.4 % of the sorbed lead and 0.08 mg or 0.5 % of the sorbed cadmium is

desorbed. More important is the amount of separated lead (the amount of desorbed lead between the

2nd and the 10th hour of the desorption process) and this is only 2.30 mg or 3.8 % of the sorbed lead.

During the separation, 240 ml pass through the column, so this gives a concentration of 9.58 mg/l lead

in the separated volume.

0 2 4 6 8 10 12 14 16

0

1

2

3

4

5

0

1

10

100

1000

10000

Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with HCl pH 1.00

Pb

Cd

37

Table 4 : amounts of sorbed and separated lead and cadmium when using 100 mM HCl

Lead Cadmium

Desorbed amount (mg) 32.49 0.08

Desorbed amount ( % of sorbed) 53.7 0.5

Separated amount (mg) 2.30 0

Separated amount ( % of sorbed) 3.8 0


Concentration separation (mg/l) 9.58 0

4.1.1.2 Desorption with HCl at a pH of 1.51

Figure 23: desorption curves of Pb and Cd while using 31 mM HCl solution (pH of 1.51)


Figure 23 shows the desorption curves of lead and cadmium while using HCl at a pH of 1.51. Using these

conditions, the decrease in cadmium concentration still starts immediately while the concentration of

lead is increasing in the beginning. The separation starts this time after 2 hour and last for 22 hours.

During this experiment 31.53 mg or 52.1 % of the sorbed lead and 1.13 mg or 6.5 % of the sorbed

cadmium is desorbed. This is more or less the same quantity as in the previous experiment when using

100 mM HCl as desorbent agent, but there is a difference in the amount of separated lead. When

looking to the separation, a total amount of 8.74 mg or 14.4 % of the sorbed lead is found. This is almost

4 times more than in the previous experiment. The separation volume is this time 690 ml with a

concentration of 12.7 mg/l.

0

20

40

60

80

1

10

100

1000

0 5 10 15 20 25 30 Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with Hcl of pH 1,51

Pb

Cd

38

Table 5: amounts of sorbed and separated lead and cadmium when using 31 mM HCl

Lead Cadmium


Desorbed amount (% of sorbed) 52.1 6.5


Separated amount (% of sorbed) 14.4 0




Figure 24: desorption curves of Pb and Cd while using 7.8 mM HCl solution (pH of 2.11)


When using a HCl solution at a pH of 2.11, the concentration of lead at the outflow keeps increasing for

the first 5 hours until reaching the maximum, as can be seen in figure 24. On the contrary, the decrease

in cadmium concentration still starts immediately. Due to the fast decrease of the concentration of

cadmium and the 4 hours increase of the concentration of lead, a good separation can be obtained. To

have a separation, the amount of cadmium should be below 1 mg/l and this is the case after 3 hours.

The separation time starts after 3 hours and lasts for 21 hours. The total amount of desorbed lead is

49.53 mg or 81.9 % of the sorbed lead and the amount of desorbed cadmium is 1.62 mg or 9.2 % of the

sorbed cadmium. Also the amount of separated lead is much higher than with the previous experiments

when using a lower pH. During the 21 hours of separation, 37.00 mg or 61.2 % of the sorbed lead is

separated in a total volume of 630 ml. This gives a concentration of 58.7 mg/l lead for the separated

volume.

0

20

40

60

80

0

50

100

150

200

250

0 5 10 15 20 25 30 con

cen

trat

ion

Cd

(m

g/l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with pH 2.11

Pb

Cd

39

Table 6: amounts of sorbed and separated lead and cadmium when using 7.8 mM HCl

Lead Cadmium










Figure 25 presents the desorption curves of lead and cadmium when using HCl at a pH of 2.95. The first

thing that can be seen is that this time there is an increase of cadmium concentration in the first hour.

Also, the decrease of cadmium concentration is much slower which results in a long tailing. Since there

is only separation when the amount of desorbed cadmium is below 1 mg/l this tailing results in a shorter

separation time. The desorption curve of lead, on the other hand, looks the same as in the previous

experiments performed at low pH, but has a longer increasing and the maximum concentration is much

lower. The separation starts after 19 hours of desorption and last for 30 hours. The total amount of lead

desorbed during the experiment is 42.36 mg or 70.03 % of the sorbed lead and the amount of desorbed

cadmium is 4.97 mg or 28.2 % of the sorbed cadmium. The amount of separated lead on the other hand

is only 9.04 mg or 14.94 % of the sorbed lead due to the long tailing of cadmium. The separation volume

is 900 ml (more separation volume due to longer time of experiment). The concentration of the

separated volume is 10.05 mg/l lead.

0

10

20

30

40

0

20

40

60

80

100

0 10 20 30 40 50 60

Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)


Pb

Cd

40


Lead Cadmium










In figure 26, the desorption curves of lead and cadmium are presented when using a HCl solution at a pH

of 3.69 as desorption reagent. The shape of those curves is totally different as in the experiments using

more concentrated HCl what means that something happens when the pH becomes too high. As can be

seen in the figure, this time the desorption curve of lead has always a lower concentration value than

the desorption curve of cadmium at the same time. Both curves don’t go below the separation value of

1 mg/l which means that there is no separation possible. The total amount of desorbed lead is 2.15 mg

or 3.6 % of the sorbed amount and the amount of desorbed cadmium is 2.29 mg or 13.0 % of the sorbed

amount.


Lead Cadmium



Separated amount (mg) 0 0

Separated amount (% of sorbed) 0 0


Concentration separation (mg/l) 0 0

0

1

2

3

4

5

0

5

10

15

20

0 5 10 15 20 25 30

Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with pH 3,69

Pb

Cd

41

4.1.1.6 Discussion of desorption with HCl

Table 9: amounts of sorbed and separated lead from the grape stalks when using HCl

HCl (pH) Desorbed amount of Pb (mg)

Desorbed amount of Pb (%)

Separated amount of Pb (mg)

Separated amount of Pb (%)

Separation volume (ml)

Concentration separation (mg/l)

1.00 32.49 53.7 2.30 3.8 240 9.58

1.51 31.53 52.1 8.74 14.4 690 12.67

2.11 49.53 81.9 37.00 61.2 630 58.73

2.95 42.36 70.0 9.04 14.9 900 10.05

3.69 2.15 3.6 0.00 0.0 0 0.00

Table 10: amounts of sorbed and separated Cadmium from the grape stalks when using HCl

HCl (pH) Desorbed amount of Cd (mg)

Desorbed amount of Cd (%)

Separated amount of Cd (mg)

Separated amount of Cd (%)



1.00 0.08 0.5 0.00 0.0 0 0.00

1.51 1.13 6.5 0.00 0.0 0 0.00

2.11 1.62 9.2 0.00 0.0 0 0.00

2.95 4.97 28.2 0.00 0.0 0 0.00

3.69 2.29 13.0 0.00 0.0 0 0.00

Figure 27: concentration of separated Pb in function of the pH when using HCl as desorption reagent When looking at the separated amount of lead and the concentration of the separated solution in table 9, there can be seen that an optimum for the separation can be found at a pH of 2.11. Another thing that can be seen with those results is that a metal separation can be obtained between pH 1.00 and pH 2.95. This means that the amount of protons is crucial to achieve separation. In figure 27 the concentration of the separated lead solution is plotted in function of the pH when using HCl as desorption reagent.

0

10

20

30

40

50

60

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

Co

nce

ntr

atio

nP

b (

mg/

l)

pH

Concentration of separated Pb (mg/l) in functionof pH

42

This figure also shows that the optimum concentration of the separated lead is found at a pH of 2.11. A separation of cadmium on the other hand can’t be achieved during the desorption process as can be seen in table 10. To find a desorbent reagent with a better separation efficiency, other desorption reagents will be tested when using the best found condition. The optimum concentration for HCl was found at a pH of 2.11 which corresponds with a H+ concentration of 7.8 mM.

4.1.2 Effect of reagents

As seen in table 8, the optimum pH for a desorption with HCl is a pH of 2.11, which corresponds with a

H+ concentration of 7.8 mM. The two other reagents that will be tested are NaCl and CaCl2. Considering

the ionic exchange, not only the concentration is important, but also the charge of the used ions. When

using HCl, the ions that are responsible for the desorption are the protons, which have a charge of +1.

When using NaCl, the responsible ions for the desorption are the sodium ions, which also have a charge

of +1, so the same concentration of 7.8 mM should be used to work under the same conditions. In the

case of CaCl2 the responsible ions for the desorption are the calcium ions which have a charge of +2, so

only half of the concentration, 3.9 mM, should be used.

4.1.2.1 Desorption with NaCl (7.8 mM)

Figure 28: desorption curves of Pb and Cd while using 7.8 mM NaCl solution


As can be seen in figure 28, cadmium and lead can be desorbed by using Na+ ions. The concentration of

lead and cadmium decrease at more or less the same time when using NaCl as desorption reagent.

During the process there is no time when there is separation, because both metals have approximately

the same concentration at every time. The total amount of desorbed lead is 2.33 mg or 3.85 % of the

sorbed lead and the total amount of desorbed cadmium is 2.55 mg or 22.5 % of the sorbed cadmium. On

other thing is that the amount of desorbed lead is quite low comparing with the results obtained when

using HCl (49.3 mg) . This means that Na+ isn’t strong enough to replace all the lead and cadmium from

the grape stalks

0

10

20

30

40

0

10

20

30

40

0 5 10 15 20 25 30 Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with NaCl

Cd

Pb

43

Table 11: amounts of sorbed and separated lead and cadmium when using 7.8 mM NaCl

Lead Cadmium







4.1.2.2 Desorption with CaCl2 ( 3.9 mM)

Figure 29: desorption curves of Pb and Cd while using 3.9 mM CaCl2 solution


Cadmium and lead can be desorbed by using Ca2+ ions. When using CaCl2 as desorption reagent, the

concentration of lead is higher than the concentration of cadmium but they decrease at the same time.

Since the concentration of cadmium is below 1mg/l after 7 hours, there is a separation, but only for a

low amount of lead. The total amount of desorbed lead is 11.7 mg or 19.3 % of the total sorbed amount

and the total amount of desorbed cadmium is 3.8 mg or 21.8 % of the total sorbed amount. From this

amount, only 4.51 mg or 3.80 % is separated lead in a separation volume of 540 ml. This gives a

concentration of 8.3 mg/l lead in the separated volume. Ca-ions are thus also not strong enough to

replace all the lead and cadmium.

0

10

20

30

40

50

60

70

0

20

40

60

80

100

120

0 5 10 15 20 25 30 Co

nce

ntr

atio

n C

d (

mg/

l)

Co

nce

ntr

atio

n P

b (

mg/

l)

Time (hours)

Desorption with CaCl2

Cd

Pb

44

Table 12: amounts of sorbed and separated lead and cadmium when using 3.9 mM CaCl2

Lead Cadmium







4.1.2.3 Discussion of desorption with NaCl and CaCl2

Table 13: amounts of sorbed and separated lead from the grape stalks when using NaCl and CaCl2

Desorbed amount of Pb (mg)

Desorbed amount of Pb (%)

Separated amount of Pb (mg)

Separated amount of Pb (%)



HCl (pH = 2.11)

49.53 81.9 37.0 61.2 630 58.73

NaCl 2.33 3.9 0 0 0 0

CaCl2 11.7 19.3 4.5 3.80 540 8.33

Table 14: amounts of sorbed and separated cadmium from the grape stalks when using NaCl and CaCl2

Desorbed amount of Cd (mg)

Desorbed amount of Cd (%)

Separated amount of Cd (mg)

Separated amount of Cd (%)



HCl (pH = 2.11)

1.62 9.2 0 0 0 0

NaCl 2.55 22.5 0 0 0 0

CaCl2 3.8 21.8 0 0 0 0

When comparing the different desorbent reagents, in table 13, there can be seen that there is a big difference in amount of desorbed lead. This means that NaCl is the worst desorption reagent for lead and HCl at a pH of 2.11 is the best desorption reagent for lead. In table 14 can be seen that for the desorbed amounts of cadmium this difference is smaller and that HCl is in this case is the worst desorption reagent. Another and more import thing that can be seen is the amount of separated lead and cadmium. In table 14 can be seen that there is never a separation for cadmium, but table 13 shows that both HCl at pH 2.11 and CaCl2 have a separation for lead. Because HCl is the best desorption reagent for lead and the worst for Cd, this gives a good separation.

45

4.2 Binary mixtures of Copper and Nickel

Figure 30: breakthrough curves of nickel and copper (conditions: Ci,Ni = 0.4 mM ; Ci,Cu = 0.4 mM ; column length = 7 cm ; flow rate = 30ml/hour ; Ct/Ci = concentration of the metal at time t divided by the initial

concentration) The figure above shows the breakthrough curves of copper and nickel. The y-axes present the ratio between the concentration at a set time and the initial concentration of each metal and the x-as presents the sorption time. During the first three hours there are no metals detected at the outflow of the column, so all metals are sorbed by the grape stalks. After three hours the solution starts to contain some nickel. Between the third 3rd hour and the 12th hour only nickel is detected. This means that all the copper is still sorbed by the grape stalks and nickel is not. During these nine hours a separation of nickel is achieved. The amount of separated nickel is 2.22 mg in 270 ml which gives a concentration of 8.22 mg/l. The breakthrough curve of nickel shows an overshoot after ten hours. This means that the concentration of nickel by the outflow of the column is higher than the initial concentration. During this overshoot some of the sorbed nickel is desorbed and replaced by copper. After several hours the overshoot starts to decrease and the breakthrough curve goes to a stable value of one. The breakthrough curve of copper starts to increase after twelve hours, this means that not all the copper is sorbed anymore. This curve will go to a ratio of one quite fast without an overshoot. When both curves reach the stable value of one, the initial metal mixture pass through the column without being sorbed and the column is saturated with both nickel and copper. When the sorption process is complete, the grape stalks are saturated with both nickel and copper. In order to be able to calculate the metal desorbed afterwards, the Q-values has to be calculated. This Q-value is the amount of metal (in mg) that is sorbed on 1.00 grams of grape stalks. The total amount of sorbed nickel is 3.56 mg, so that gives a Q-value of 1.78 mg/g. From copper 20.79 mg is sorbed, so the Q-value is 10.40 mg/g.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 10 20 30 40 50 60

Ct/

Ci

Time (hours)

Breakthrough curves of Ni and Cu

Ni

Cu

46

Table 15: sorbed and separated amounts of nickel and copper after sorption process

Nickel Copper

Sorbed (mg) 3.56 20.79

Q-value (mg/g) 1.78 10.40

Separated (mg) 2.22 0


Separated (mg/l) 8.22 0

4.2.1 Effect of HCl concentration 4.2.1.1 Desorption with HCl at a pH of 1.57

Figure 31: desorption curves of Ni and Cu while using 26.9 mM HCl solution (pH of 1.57)

(conditions: Ni sorbed = 3.56 mg ; Cu sorbed = 20.79 mg ; flow = 30 ml/hour)

Figure 31 shows the desorption curves of nickel and copper while using HCl at a pH of 1.57. Using these

conditions, the desorption of nickel and copper starts immediately, but the decrease of concentration is

faster with nickel. This gives the chance to have some time when a separation of copper is possible. The

separation starts after 1 hour and last for only 2 hours. During this experiment 0.09 mg or 2.5 % of the

sorbed nickel and 0.27 mg or 1.3 % of the sorbed copper is desorbed. When looking to the separation, a

total amount of 0.18 mg or 0.9 % of the sorbed copper is found. During these 2 hours of separation, 60

ml of solution went through the column, what gives a concentration of 3.00 mg/l of desorbed copper in

solution.

0

1

10

100

1000

0

1

10

100

1000

0 1 2 3 4 5 6

Co

nce

ntr

atio

n C

u (

mg/

l)

Co

nce

ntr

atio

n N

i (m

g/l)

Time (hours)

Desorption with HCl pH 1,57

Ni

Cu

47

Table 16: amounts of sorbed and separated nickel and copper when using 26.9 mM HCl

Nickel Copper



Separated amount (mg) 0 0.18

Separated amount (% of sorbed) 0 0.9


Concentration separation (mg/l) 0 3.00




In figure 32 can be seen that the desorption of both nickel and copper starts immediately. The decrease

of concentration for both metals starts at the same time, but the concentration of copper is higher. To

have separation only one metal should be desorbed while the concentration of the second one is less

than 1 mg/l. For this concentration of HCl, there is separation after 2 hours of desorbing which last for 5

hours. During the total experiment 0.07 mg or 1.9 % of the sorbed nickel and 4.34 mg or 20.9 % of the

sorbed copper is desorbed. More important is the amount of separated copper (the amount of

desorbed copper between the 2nd and the 7th hour of desorption process) and this is 2.77 mg or 13.3 %

of the sorbed copper. During the separation 150 ml pass through the column, so this gives a

concentration of 18.47 mg/l copper in the separated volume.

0

100

200

300

400

500

0

50

100

150

200

0 2 4 6 8 10 12

Co

nce

ntr

atio

n C

u (

mg/

l)

Co

nce

ntr

atio

n N

i (m

g/l)

time (hours)


Ni

Cu

48


Nickel Copper










When using a HCl solution at a pH of 2.14 the desorption maximum of copper is found later than the one

of nickel. The concentration of copper at the outflow keeps increasing for the first 3 hours until reaching

the maximum, as can be seen in figure 33. On the contrary, the decrease of nickel concentration still

starts immediately. Due to the fast decrease of nickel concentration and the 3 hours of increasing

copper concentration a good separation can be obtained. To have a separation, the amount of cadmium

should be below 1 mg/l and this is the case after 3 hours. The separation time starts after 3 hours and

lasts for 21 hours. The total amount of desorbed nickel is 0.18 mg or 5.0 % of the sorbed nickel and the

amount of desorbed copper is 17.84 mg or 85.8 % of the sorbed copper. Also the amount of separated

copper is much higher than with the previous experiments with a lower pH. During the 21 hours of

separation, 15.04 mg or 72.3 % of the sorbed copper is separated in a total volume of 630 ml. This gives

a concentration of 23.87 mg/l lead for the separated volume.

0

50

100

150

200

0

20

40

60

80

0 5 10 15 20 25 30 Co

nce

ntr

atio

n C

u (

mg/

l)

Co

nce

ntr

atio

n N

i (m

g/l)

time (hours)


Ni

Cu

49


Nickel Copper










Figure 34 presents the desorption curves of nickel and copper when using HCl at a pH of 2.32. The first

thing that can be seen is that the decrease of desorbed copper after reaching the maximum is much

faster than in the previous experiment. This results in a lower amount of desorption and thus also a

lower separation. The desorption curve of nickel on the other hand has the same shape as in the

previous experiment. The separation starts after 2 hours of desorption and last for 13 hours. The total

amount of nickel desorbed during the experiment is 0.07 mg or 1.9 % of the sorbed nickel and the

amount of desorbed copper is 9.00 mg or 43.3 % of the sorbed copper. The amount of separation

copper on the other hand is only 4.86 mg or 23.4 % of the sorbed copper. The separation volume is 390

ml what gives a concentration of 12.46 mg/l.

0

50

100

150

200

250

300

0

20

40

60

80

100

120

0 5 10 15 20 25 30

Co

nce

ntr

atio

n C

u (

mg/

l)

Co

nce

ntr

atio

n N

i (m

g/l)

Time (hours)


Ni

Cu

50


Nickel Copper










The desorption curves of nickel and copper while using a HCl solution at a pH of 2.65 can be seen in

figure 35. An important thing that can be seen is that desorption curve of nickel has a long tailing. Since

there is only separation when the amount of desorbed nickel is below 1 mg/l this tailing results in a

shorter separation time than in the previous experiments. The separation starts after 8 hours of

desorption and last for 17 hours. The total amount of nickel desorbed during the experiment is 1.49 mg

or 41.9 % of the sorbed nickel and the amount of desorbed copper is 12.54 mg or 60.3 % of the sorbed

copper. The amount of separation copper on the other hand is only 2.19 mg or 10.5 % of the sorbed

copper. The separation volume is 510 ml what gives a concentration of 4.29 mg/l.

0

20

40

60

80

100

120

0

10

20

30

40

50

0 5 10 15 20 25 30

Co

nce

ntr

atio

n C

u (

mg/

l)

Co

nce

ntr

atio

n N

i (m

g/l)

time (hours)


Ni

Cu

51


Nickel Copper







4.2.1.6 Discussion of desorption with HCl

Table 21: amounts of sorbed and separated nickel from the grape stalks when using HCl

HCl (pH) Desorbed amount of Ni (mg)

Desorbed amount of Ni (%)

Separated amount of Ni (mg)




1.57 0.09 2.5 0.00 0.0 0 0.00

1.93 0.07 1.6 0.00 0.0 0 0.00

2.14 0.18 5.0 0.00 0.0 0 0.00

2.32 0.07 1.9 0.00 0.0 0 0.00

2.65 1.49 41.9 0.00 0.0 0 0.00

Table 22: amounts of sorbed and separated copper from the grape stalks when using HCl

HCl (pH) Desorbed amount of Cu (mg)

Desorbed amount of Cu (%)

Separated amount of Cu (mg)

Separated amount of Cu (%)



1.57 0.27 1.3 0.18 0.9 60 3.00

1.93 4.34 20.9 2.77 13.3 150 18.47

2.14 17.84 85.8 15.04 73.3 630 23.87

2.32 9.00 43.3 4.86 23.4 390 12.46

2.65 12.54 60.3 2.19 10.5 510 4.29

52

Figure 36: concentration of separated Cu in function of the pH when using HCl as desorption reagent When looking at the separated amount of copper and the concentration of the separated solution in table 21, there can be seen that the optimum for the separation can be found at a pH of 2.14. Another thing that can be seen with those results is that there is a separation between pH 1.57 and pH 2.65. This means that the amount of protons is crucial to achieve separation. In figure 35 the concentration of the separated copper is plotted in function of the pH when using HCl as desorption reagent. Figure 36 also shows that the optimum concentration of the separated lead is found at a pH of 2.14. A separation of nickel on the other hand can’t be achieved during the desorption process as can be seen in table 22. To find a desorbent reagent with a better separation efficiency, other desorption reagents will be tested when using the best found condition. The optimum concentration for HCl was found at a pH of 2.14 which corresponds with a H+ concentration of 7.2 mM.

4.2.2 Effect of reagents

As seen in table 21, the optimum concentration for HCl is 7.2 mM. The two other reagents that will be

tested are again NaCl and CaCl2. Considering the ionic exchange, not only the concentration is important,

but also the charge of the used ions. When using HCl the ions that are responsible for the desorption

process are the protons which have a charge of +1. When using NaCl, the responsible ions for the

desorption are the sodium ions which also have a charge of +1, so the same concentration of 7.2 mM

should be used to work under the same conditions. In the case of CaCl2 the responsible ions for the

desorption are the calcium ions which have a charge of +2, so only half of the concentration, 3.6 mM,

should be used.

0

5

10

15

20

25

30

1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8Co

nce

ntr

atio

n C

u (

mg/

l)

pH

Concentration of separated Cu (mg/l) in function of pH

53

4.2.2.1 Desorption with NaCl (7.2 mM)

Figure 37: desorption curves of Ni and Cu while using 7.2 mM NaCl solution


As can be seen in figure 37, NaCl desorb both metals. The concentrations of nickel and copper decrease

at more or less the same time when using NaCl as desorption reagent. During the process there is no

time when there is separation, because both metals are desorbed at the same time. The total amount of

desorbed nickel is 2.14 mg or 60.2 % of the sorbed nickel and the total amount of desorbed copper is

1.32 mg or 6.4 % of the sorbed copper.

Table 23: amounts of sorbed and separated nickel and copper when using 7.2 mM NaCl

Nickel Copper







0

2

4

6

8

10

12

14

16

0

10

20

30

40

50

60

0 5 10 15 20 25 30

con

cen

trat

ion

cu

(m

g/l)

con

cen

trat

ion

Ni (

mg/

l)

Time (hours)

Desorption with NaCl

Ni

Cu

54

4.2.2.2 Desorption with CaCl2 (3.6 mM)

Figure 38: desorption curves of Ni and Cu while using 3.6 mM CaCl2 solution


When using CaCl2 as desorption reagent, both metals are desorbed. The concentrations of nickel and

copper starts decreasing at the same time, but the decrease of concentration for nickel is higher than

for copper. This means that there is a separation of copper after 4 hours when the amount of desorbed

nickel is below 1 mg/l. The separation lasts for the next 20 hours. During the experiment a total

desorption of 2.01 mg or 56.4 % of the sorbed nickel and 6.44 mg or 31.0 % of sorbed copper is obtained.

From this 6.44 mg, 3.92 mg or 18.8 % of the sorbed copper is separated. During the separation 600 ml of

solution pass through the column, which give a concentration of 6.53 mg/l.

Table 24: amounts of sorbed and separated nickel and copper when using 3.6 mM CaCl2

Nickel Copper







0

10

20

30

40

50

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Co

nce

ntr

atio

n C

u (

mg/

l)

con

cen

trat

ion

Ni (

mg/

l)

Astitel

Desorption with CaCl2

Ni

Cu

55

4.2.2.3 Discussion of the desorption with NaCl and CaCl2

Table 25: amounts of sorbed and separated nickel from the grape stalks when using NaCl and CaCl2

Desorbed amount of Ni (mg)

Desorbed amount of Ni (%)


Separated amount of Ni (%)



HCl (pH = 2.14) 0.18 5.0 0.00 0.0 0 0.00

NaCl 2.14 60.2 0.00 0.0 0 0.00

CaCl2 2.01 56.4 0.00 0.0 0 0.00

Table 26: amounts of sorbed and separated copper from the grape stalks when using NaCl and CaCl2

Desorbed amount of Cu (mg)

Desorbed amount of Cu (%)

Separated amount of Cu (mg)

Separated amount of Cu (%)



HCl (pH = 2.14) 17.84 85.8 15.04 73.3 630 23.87

NaCl 1.32 6.4 0.00 0.0 0 0.00

CaCl2 6.44 31.0 3.92 18.8 600 6.53

Looking at tables 25 and 26, there can be said that for the desorption process of nickel and copper NaCl isn’t able to do a selective desorption. The highest amount of separation and desorption are obtained when using HCl at a pH of 2.14 as desorption reagent. Besides HCl also CaCl2 obtains a separation for copper, but the amount of mg separated is only a quarter in comparison with a HCl concentration with the same charge of ions.

Another thing that can be seen is that when working with NaCl and CaCl2 the amount of nickel desorbed

is much higher and the copper desorbed of is much lower than when working with HCl. This means that

NaCl and CaCl2 are more selective for replacing nickel than for replacing copper, but due to the low

amount of sorbed nickel on the grape stalks this does not result in a separation.

56

4.2.3 Mathematical models

4.2.3.1 Yoon and Nelson model

The experimental data of the breakthrough curves were calculated by using the Yoon Nelson equation

ln𝐶

𝐶𝐹−𝐶= 𝐾𝑌𝑁𝑡 − 𝑡1

2⁄ 𝐾𝑌𝑁. The calculated parameters are presented in table 27.

Table 27 : Yoon and Nelson model, calculated constants

metal R² KYN T1/2 (hours) Experimental T1/2 (hours)

Pb 0.99 0.57 31.68 not reached

Cd 0.99 1.00 10.57 9,25

Ni 0.98 1.00 7.20 7,50

Cu 0.98 0.26 23.63 22,00

The theoretical breakthrough curves were potted together with the experimental data in figures 39 and

40

Figure 39: breakthrough curves of Pb and Cd with theoretical curves calculated with Yoon and Nelson

Model

0

0,5

1

1,5

2

0 10 20 30 40 50 60 70

Ct/

Ci

Time (hours)


Pb

Cd

Pb theory

Cd theory

57

Figure 40: breakthrough curves of Cu and Nu with theoretical curves calculated with Yoon and Nelson

Model

As can be seen in figure 39 and 40, the experimental curves have a good correlation with the

mathematical curves calculated with the Yoon and Nelson model. The breakthrough curves starts at

more or less the same time and also the t1/2, the time required for retaining 50% of the initial

concentration is close to the theoretical time (table 27). As a conclusion, it can be said that this model

fits the experimental data when using this metals with grape stalks as sorbent. The only part of the

breakthrough curves that can’t be modelled is the overshoot that is found with cadmium and nickel.

4.2.3.2 Thomas model

To plot the experimental breakthrough curves by using the Thomas model, following equation was used

ln (𝐶𝐹

𝐶− 1) =

𝑘𝑇𝐻𝑞𝐹𝑚

𝑄− 𝑘𝑇𝐻𝐶𝐹𝑡. Form this equation, parameters were calculated and presented in

table 28.

Table 28 : Thomas model, calculated constants

metal R² KTH Q q m CF

Pb 0.99 0.014 0.179 35.9 2.00 41.35

Cd 0.99 0.015 0.018 4.5 2.00 68.11

Ni 0.98 0.037 0.032 1.8 2.00 25.59

Cu 0.98 0.011 0.047 10.4 2.00 22.67


42

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 10 20 30 40 50 60 70 80 90

Ct/

Ci

Time (hours)


Ni theory

Cu theory

Ni

Cu

58

Figure 41: breakthrough curves of Pb and Cd with theoretical curves calculated with Thomas Model

Figure 42: breakthrough curves of Cu and Ni with theoretical curves calculated with Thomas Model

In figures 41 and 42 the theoretical breakthrough curves, calculated with the numbers of table 28, are

presented together with the experimental data. The correlation of the experimental data and the

theoretical curves isn’t that good as with the previous model, despite the same R² value. This difference

can be due to the limitation of this model.

This limitation is that its derivation is based on second order kinetics and considers that the sorption is

not limited by the chemical reaction but controlled by mass transfer at the interface (M. Calero, 2009)

Do you know the meaning). This makes this model less suitable for modeling the process with grapes

stalks than the previous model of Yoon and Nelson.

0

0,5

1

1,5

2

0 20 40 60 80 100 120 140 160

Ct/

Ci

Time (hours)


Pb

Cd

Pb thomas

Cd thomas

0

0,5

1

1,5

0 20 40 60 80 100 120

Ct/

Ci

Time (hours)


Ni

Cu

Ni thomas

Cu thomas

59

4.2.3.3 Adams-Bohart model

The experimental data of the breakthrough curves were calculated by using the Adam-Bohart equation

ln (𝐶𝐹

𝐶− 1) = ln [𝑒𝑥𝑝 (𝑘𝐴𝐵𝑄

𝐻

𝑢) − 1] − 𝑘𝐵𝐶𝐹𝑡 . The calculated parameters are presented in table 29.

Table 29 : Adams-Bohart model, calculated constants

metal R² KB u q h CF

Pb 0.88 0.028 0.34 35.94 10.0 41.35

Cd 0.99 0.010 0.11 4.53 10.0 68.11

Ni 0.55 0.011 0.12 1.78 10.0 25.59

Cu 0.72 0.005 0.86 10.4 10.0 22.67


44

Figure 43: breakthrough curves of Pb and Cd with theoretical curves calculated with Adams-Bohart

Model

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 5 10 15 20 25 30 35

Ct/

Ci

Time (hours)


Pb

Cd

Pb Adams-Bohart

Cd Adams-Bohart

60

Figure 44: breakthrough curves of Cu and Ni with theoretical curves calculated with Adams-Bohart

Model

The Adams-Bohart model is only to describe the initial part of the breakthrough curves, for C values

lower than 0.15 times the initial concentration. All experimental breakthrough curves start at another

time than calculated with the Adams-Bohart model, so this model doesn’t fit for this set of experiments.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 10 20 30 40 50 60 70 80 90

Ct/

Ci

Time (hours)


Ni

Cu

Ni Adams-Bohart

Cu Adams-Bohart

61

5 CONCLUSION

After studying the separation of two metals in binary metal mixtures by grape stalks, the following

conclusions were drawn:

A separation of metals from binary metal mixtures of copper and nickel and lead and cadmium

can be achieved by sorption process on and desorption processes from grape stalks. One metal

is separated during the sorption process and the other one during the desorption process.

The concentration of the desorption reagent is important to have a good separation. When

using HCl as desorption reagent, there can be seen that when reaching the optimum

concentration the amount of desorbed metal increases.

When using HCl as desorption reagent, the optimal pH for metal desorption is a pH of 2.1 for

both metal mixtures. Until this pH the amount of separated metal is increasing and after this

optimum a decrease of metal separation can be noticed.

For the binary mixture of lead and cadmium, the use of NaCl and CaCl2 as desorption reagent

results in a partial metal desorption (less than 25 %), but not a metal separation. This means

that Na+ and Ca2+ aren’t strong enough to remove all the lead and cadmium from the grape

stalks and that the metal desorption is not selective.

For the binary mixture of copper and nickel, both salts, NaCl and CaCl2 shows a good metal

desorption for nickel. Since the amount of sorbed nickel on the grape stalks was low compared

to the sorbed copper, this doesn’t lead to a separation. When only looking to CaCl2, a small

amount of separated copper can be achieved. This means that CaCl2 is a bit more selective than

NaCl for the metal desorption of Ni(II) and Cu(II).

The best model to predict the breakthrough curves of Pb(II) , Cd(II), Ni(II) and Cu(II) when using

grape stalks as sorbent is the model of Yoon and Nelson.

62

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