MILLET HUSK AS EFFICIENT ADSORBENT FOR REMOVAL OF … 337... · The SEM experiment was carried out...

Dutse Journal of Pure and Applied Sciences (DUJOPAS) Vol. 3 No. 1 June 2017

337

MILLET HUSK AS EFFICIENT ADSORBENT FOR

REMOVAL OF LEAD, CADMIUM, AND NICKEL IONS

FROM AQUEOUS SOLUTION

Samaila Muazu Batagarawa Department of Pure and Industrial Chemistry,

Umaru Musa Yar’adua University, Katsina.

Lateefat Yusuf Dayo Department of Pure and Industrial Chemistry,

Umaru Musa Yar’adua University, Katsina.

Abstract

apid industrialisation has led to the discharge of heavy metals into the environment and this has

been of great concern because of its health effect on human being. The purpose of this study is to

investigate the utilization of millet husk as a low cost adsorbent for removal of Lead (II), Cadmium

(II) and Nickel(II) ions from aqueous solution. Carbonised millet husk, acid treated carbonised millet husk, and

powdered particles size 300µm and 500µm were used for this experiment. FT IR and SEM characterisations

were carried out on the samples. Batch experiments were carried out to determine the effect of various

parameters. The sorption process was relatively fast and equilibrium was reached after about 40 min of contact

at 100 rpm. Maximum removal efficiency for the three metal ions was observed at pH 5.5. The optimum

conditions were applied on environmental samples collected from typical urban waste water which is used for

irrigation purpose. It was discovered that millet husk can be used as a cost effective adsorbent for the removal

of heavy metal ions from industrial effluents.

Key words: Millet husk, effluent, waste water carbonised millet husk, acid treated carbonised millet

husk, micrometer, adsorbents, Lead ion ,Cadmium ion and Nickel ion.

Introduction

Rapid industrialization has led to increased disposal of heavy metals to the environment (Asari et al,

2010). Effluents from industrial processes such as electroplating, mining, nuclear power operations,

manufacturing batteries, refining ores, fertilizer industries, tanneries, dyes, pigments, paper

industries and pesticides have been identified to contain high level of heavy metals (Rudre et al, 2012).

Additional heavy metals may be introduced into underground water resources from the dissolution

of underlying rock formation (Staudt, 2004; Freeman, 1998). According to World Health Organization

(WHO), the metals of most immediate concern are Cr (III), Cr (VI), Zn, Cd, Cu, Ni, Hg, Pb, Al, Mn

(Quek et. al., 1998). These metals cause direct toxicity to bio-ecosystem. Various techniques have been

R


338

developed for the removal of heavy metals from contaminated water. Conventional methods for

heavy metal removal from industrial waste water include membrane filtration, ion exchange

(Paknikar, et al., 2003), chemical precipitation, electrochemical reduction, reverse osmosis (Ake et al.,

2001), and co-precipitation (Kim, et a.l, 2002). Most of these methods suffer from draw backs such as

disposal of huge volumes of metal sludge, high capital and operational cost which are not suitable

for small scale industries (Annadurai et al, 2002, Ingwe, 2007). Another powerful technology is

adsorption of heavy metals by activated carbon for treating domestic and industrial waste water

(Horikoshi et al., 1981). The major disadvantage of using this adsorbent is its high price and its high

regeneration cost (Azku et al., 2009). This has led researchers to look for more adsorbents which is

effective and economical. In recent years considerable attention has been devoted to the study of

different types of low cost agricultural by products as adsorbents for the removal of heavy metals

from contaminated water by method of adsorption (Opeoluwa et al., 2009). Agricultural by-products

such as rice bran, rice husk, wheat bran, wheat husk, saw dust of various plants, bark of trees,

groundnut shells, coconut shells, back gram husk, hazel nut shells, walnut shells, cotton seed hulls,

millet husk., waste tree leaves, maize corn cob, sugarcane bagasse, banana, orange peels, soya bean

hulls, grapes stalks, water hyacinth, sugar beet pulp, sunflower stalks, coffee bean, cotton stalk etc

have all been tried (Anadurai et al, 2007; Cimino et al, 2000; Hashemain et al, 2008; Mohanty et al

2005). The advantages of adsorption over conventional treatment method includes simple design,

low cost, high efficiency, minimization of chemical or biological sludge, no additional nutrient

requires and regeneration of adsorbents and possibility of metal recovery (Dhiraj et al, 2008).

This work deals with the utilization of agricultural waste materials as adsorbent for removal of toxic

heavy metals from aqueous solutions. Millet husk will was used as an adsorbent to remove some

heavy metals from standard aqueous samples.

Materials and Methods

Sample Preparation

The millet husk used for the experiment was collected from a local millet mill in Katsina metropolis.

The samples were collected in a polyethylene bag and transported to the laboratory for further

treatment. The millet husk was first handpicked to remove dirty particles and washed with tap water

several times to remove adhering particles. It was later washed twice with deionized water, drained

and oven dried for 12 hours at 90°C. The dried millet husk was cleaned according to the method used

by Guilbert (2012). The millet husk was soaked in 1M HNO3 for 24 hours at room temperature. This

was done to remove soluble organic compounds in the husk. The acid soaked millet husk was filtered

and washed several times with tap water then with deionised water until a fairly constant pH was

obtained .The acid cleaned husk was oven dried at 90°C for 24 hours. It was grinded using pestle and

mortar and sieved to obtain 300 and 500µm sizes using a sieve mesh and kept in an acid cleaned

plastic container for analysis. These were labelled as MH300 and MH 500

Preparation of stock solutions


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All chemicals used in this work were of analytical purity (AR grade). The stock solution of Pb(II)

metal ion was prepared using 1.60gm of analytical grade PbNO3 dissolved in 1000ml de-ionized

water . The stock solution of Cd(II) metal ion was prepared from 2.28gm of analytical grade

CdSO4.8H2O and was dissolved in 1000ml de-ionized water. The stock solution of Ni(II) metal ion

was also prepared using 4.48gm of NiSO4.6H2O dissolved in 1000ml de-ionized water. The aqueous

solutions of these metal ions were diluted with de-ionized water to obtain the working solution of

desired concentrations.

Characterization of Adsorbents

Scan Electron Microscopy (SEM)

The SEM experiment was carried out on the adsorbent using Philip XL30 at accelerating voltage of

10KV, beam size 3.0 and of different magnifications. The micrographs before and after the adsorption

of metal ions were taken and compared to study the morphology before and after adsorption.

Fourier Transform Infrared (FTIR) Spectroscopy

Functional group elucidation was done using Cary 630 FTIR Spectrophotometer (Agilent

Technologies) with spectra range of 4000 - 650cm-1. Characterization of the adsorbent was done before

and after adsorption of metal ions.

Batch adsorption Experiments

Batch adsorption experiments were performed at different metal ion concentrations, pH, adsorbent

dose, contact time and agitation rate. For each adsorption experiment, 50ml aqueous solution of each

metal ion was equilibrated with varying sorbent dosage (30 – 100mg), contact time (30 – 60min). The

pH was adjusted to 2.5 – 8.5 and agitation rate of (100 – 300rpm).The experiments were carried out

using an orbital shaker (Scigenics Biotech Orbitek). After that, the mixture was filtered through a

Whatman No. 4 filter paper to separate the adsorbent from the solution. The residual metal ion

concentration in solution was determined by Atomic Absorption spectrophotometer (Bulk scientific

model VGP 210). All experiments were replicated thrice and results were averaged. The removal

percentage and adsorbent capacity were calculated from the relationship: % 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 = 𝐶0− 𝐶𝑒

𝐶0𝑥 100

𝑞𝑒 = (𝐶0− 𝐶𝑒)𝑉

𝑤

Where Co and Ce are the concentrations (mg/L) of metal ions initially and at equilibrium time, while

qe is the amount adsorbed (mg/g), w is the weight of the adsorbent (mg), while V is the volume of

the solution in litres. (Bhattachaya et al., 2008; Garg et al, 2008 ; Ibrahim et al., 2006; Wang et al, 2008)

Effect of metal ion concentration

To study the effect of metal ion concentration, 0.05g of CMH was measured into three different

conical flasks containing 50ml of the different varied concentrations of Pb(II) solution (2, 5, and 10

mg/L). The flask was corked and agitated at 300 rpm for 30 min. The mixture was filtered and the

filtrates were analyzed for the residual metal ion concentration using Atomic Absorption

Spectrophotometer. The experiment was repeated using ATCMH for the removal of Pb(II), Cd(II) and

Ni(II) ions from aqueous solutions at different concentrations.


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Effect of adsorbent dosage

The effect of adsorbents on the removal of heavy metal ions from aqueous solutions was studied by

varying the amount of adsorbents from 30, 50, 70 and 100mg.This was done by measuring 50ml of

5mg/L aqueous solution of Pb (II) into four conical flasks followed by the addition of varying amount

of CMH into each flask. The mixtures were corked and agitated at 300rpm for 30min and filtered.

The filtrates were analyzed for the residual metal ions. Similar experiment was repeated using

ATCMH for the removal of Pb(II), Cd(II) and Ni(II) ions.

Effect of pH

The effect of adsorbate pH was studied by measuring 50ml of 5mg/L Pb (II) solution into four

different conical flasks maintaining the pH at 2.5, 3.5, 5.5 and 8.5 using 0.1M HCl or 0.1M NaOH prior

to the experiment. A predetermined amount of CMH was added separately into each conical flask.

The flasks were corked and agitated at 300 rpm for 30min. The mixtures were filtered and the filtrates

analyzed. This experimental procedure was repeated using ATCMH as adsorbent for the removal of

Pb(II), Cd(II) and Ni(II) ions.

Effect of contact time

The effect of contact time on the removal of metal ions was studied by adding a predetermined

amount of CMH into 50ml of 5mg/l, Pb (II) solution in four different 250ml conical flasks and the pH

was adjusted to the optimum value. The flasks were corked and agitated at 300 rpm for different

varied time (20, 30, 40 and 60 min). The mixtures were filtered and the filtrates were analyzed. This

procedure was repeated using ATCMH as adsorbent for the removal of Pb(II), Cd(II) and Ni(II) ions.

Effect of Rate of agitation

The agitation rate was varied from 100 to 300 rpm on each metal ion so as to study the effect of

agitation on the adsorption of heavy metal ions. A predetermined amount of CMH was added into

four different flasks containing 50ml of 5mg/l Pb(II) solution. The pH was adjusted to the optimum

value. These were corked and agitated for a predetermined time and the mixtures were filtered and

the residual metal ions in the filtrate were determined. This batch adsorption was repeated using

ATCMH as an adsorbent to remove Pb(II), Cd (II) and Ni (II) ions.

Reusability of the adsorbent

The used adsorbent was soaked in 50ml 0.1M HCl for 2hrs. It was filtered and rinsed in deionised

water several times to remove the excess acid. It was reused for the second time by treating it with

50ml of the waste water sample for a predetermined time and agitated rate. The filtrates were

analysed using AAS. The reusability experiment was carried out on each of the adsorbents for the

second time and the filtrates were analysed using AAS.

Results and Discussion


340

Effect of metal ion concentration

The effect of metal ions concentration was investigated by varying different concentrations of the

metals solution with 50mg adsorbent while keeping the agitation rate at 300rpm and contact time at

30min. It can be observed in Fig 1 and 2 that equilibrium was attained when 5mg of the adsorbents

was used. Highest percentage adsorption of Pb(II), Cd(II) and Ni(II) ions using CMH were 98%, 94%

and 94% and with ATCMH, 97%, 92% and 94% for Pb(II), Cd(II) and Ni(II) ions respectively.

The increase in adsorption at the initial stage was due to the availability of vacant sites on the surface

of the adsorbent. It is generally expected that as the concentration of the adsorbate increases the metal

ions removed should increase according to Ibrahim (2011).This result is in agreement with the

expected trend. It is believed that increase in concentration of the adsorbate brings about increase in

competition of adsorbate molecules for few available binding sites on the surface of the adsorbent,

hence increasing the amount of metal ions removed (Ibrahim et al., 2009). However, the decrease in

the percentage removal in the case of Cd(II) using MH300 and Ni(II) ions using MH500 as the

adsorbate concentration increased to 10mg/l according to Ibrahim (2011) can be associated with

limited number of exchangeable sites on the adsorbent which became saturated above certain

concentration.

Effect of Adsorbent Dosage

The dependence of adsorption of Pb(II), Cd(II) and Ni(II) ions on adsorbents dose was investigated

by varying the quantity of MH300 and MH500 from 30mg to 100mg while keeping the agitation rate

at 300rpm and contact time of 30min. Fig 3 and 4 showed that as the adsorbent dose increased from

30mg to 100mg, the percentage of Pb(II), Cd(II) and Ni(II) ions removed from the aqueous solution

Pb(II) Cd(II) Ni(II)

0

20

40

60

80

100

% A

dsorb

ed

Fig 2: Effect of metal ion concentration on heavy metals

removal using MH500 as an adsorbent

2mg/l

5mg/l

10mg/l


0

20

40

60

80

100

Fig 1: Effect of metal ion concentration on heavy metals

removal using MH300 as an adsorbent

% A

dsorb

ed

2mg/l

5mg/l

10mg/l


341

decreased. Optimum removal was achieved using 30mg adsorbent dose with a maximum percentage

removal of 98% Pb(II), 96% Cd(II) and 97% of Ni(II) ions using MH300 and 98% Pb(II), 92% Cd(II)

and 95% Ni(II) ions using MH500.

Adsorbent dosage study is an important parameter in adsorption studies, because it determines the

capacity of adsorbent for a given initial concentration of metal solution (Mousavi et al, 2010). When

the adsorbent dose was increased, the adsorption capacity (the amount adsorbed per unit mass of

adsorbent) decreased using the two adsorbents for the three metal ions. The decrease in adsorption

capacity with increase in the adsorbent dose was largely due to the increase of free adsorption sites

(Mousavi et al, 2010). The decrease in the percentage adsorption of the three metal ions with increased

adsorbent dose, could be due to crowdedness of the adsorbent particles at higher dosage (Bernard,

2013). This lead to decrease in the total surface area of the adsorbent particles available for the metal

ions, thereby leading to decrease in amount of metal ions removed from the aqueous solution.

Effect of pH

The effect of pH on the adsorption of Pb(II), Cd(II) and Ni(II) ions were carried out using different

pH values ranging from 2.5 to 8.5 while keeping other parameters constant. From Fig 5 and 6, it could

be observed that the percentage adsorption of Pb(II), Cd(II) and Ni(II) ions by MH300 and MH500

increased as the pH increased from 2.5 to 5.5. Beyond pH 5.5, there was a decrease in the percentage

adsorption of the heavy metals adsorbed.The highest percentage adsorption of Pb(II), Cd(II) and


0

20

40

60

80

100

% A

dsorb

ed

Fig 4:Effect of MH500 dosage on the removal

of heavy metals

30mg

50mg

70mg

100mg


0

20

40

60

80

100

% A

dsorb

ed

Fig 3:Effect of MH300 dosage on the removal

of heavy metals

30mg

50mg

70mg

100mg


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Ni(II) ions using MH300 are 99%,96% and 97%. With MH500, the percentages adsorbed are 97%

Pb(II), 94% Cd(II) and 94% Ni(II) ions respectively.

pH plays significant role in controlling the adsorption of heavy metals (Mandy et al, 2011). pH affect

the activity of the functional groups on the adsorbent and the degree of ionisation (Park et al, 2010;)

At lower pH, the overall surface charge of the adsorbent will be positive and the adsorbent surface is

surrounded by hydrogen ion (H+), this block the metal ions from binding sites of the adsorbents. As

the solution pH increases, the adsorbent surface becomes deprotonated and more negatively charged

surface becomes available hence an attraction between the positive metal cations occur (Bernard et al

2013). The increase in metal ion adsorption with increase in pH was due to decrease in competition

between hydrogen ion and metal ion for the surface site as a result of decrease in positive surface

charge (Ali et al, 2012). At higher pH, precipitation of metal ions occurred, thus leading to decrease

in adsorption of metal ions. Similar trend was observed by Chigondo et al, (2013) where Pb(II) ion

was removed from aqueous solution using Baobab fruit shells.

Effect of Contact Time

The effect of contact time on the removal of Pb(II), Cd(II) and Ni(II) ions from aqueous solutions was

investigated at a contact time of 20, 30, 40 and 60 minutes and 300rpm, using predetermined

adsorbent dose. It can be observed in Fig 7 and 8 that, increase in the contact time from 20min to

60min decreased the percentage removal for Pb(II) ions using MH300. 98% removal of Pb(II) ions was

achieved at 20min and this was chosen as the optimum time. The percentage removal of Pb(II)ions

from aqueous solution using MH500 was constant from 20min to 60min. Increase in contact time had

no effect on the percentage removal. The percentage removal of Cd(II) ions for both MH300 and


0

20

40

60

80

100

% A

dso

rbe

d

Fig 5: Effect of pH on the removal of

heavy metals using MH300

pH2.5

pH3.5

pH5.5

pH8.5


0

20

40

60

80

100

% A

dsorb

ed

Fig 6: Effect of pH on the removal

of heavy metals using MH500

pH2.5

pH3.5

pH5.5

pH8.5


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MH500 decreased as the contact time increased, with maximum of 96% and 94% for MH300 and

MH500 respectively. The percentage of Ni(II) ions removed using MH300 increased as the contact

time increased with highest percentage removal of 97% at 60min, whereas the percentage removal

for Ni(II) ions using MH500 increased from 20min to 30min. Further increase in contact time up to

60min had no effect on the amount removed. A highest percentage removal of 95% was achieved at

30min.

Contact time is an important parameter that affects all transfer phenomena including adsorption

process. With increased contact time, the rate of diffusion of metal ions from the solution to the liquid

boundary layer surrounding the adsorbent particles becomes high due to enhanced turbulence and

decreased thickness of the liquid boundary layer (Sadiq, 2014). Rapid adsorption of metal ions during

the initial stage could be due to high concentration gradient between the adsorbate and the number

of available vacant sites on the adsorbent surface (Gupta et al, 2004). Similar results were obtained by

Bernard et al, (2013), where activated carbon prepared from coconut shell was used to remove Pb2+,

Cu2+, Zn2+ and Fe2+ from industrial waste water.

Effect of Rate of Agitation

The effect of agitation rate on the removal of Pb(II), Cd(II) and Ni(II) using MH300 and MH500 was

varied from 100rpm to 300rpm while keeping all other factors constant. It was observed, as shown

in Fig 9 and 10 that as the agitation rate increased from 100rpm to 300rpm, the percentage removal of

Pb(II), Cd(II) and Ni(II) ions decreased for both MH300 and MH500. The highest percentage

adsorption was obtained at 100rpm ( 98%, 96% and 95%) for Pb(II), Cd(II) and Ni(II) ions using

MH300 and 98%, 92% and 95% for Pb(II), Cd(II) and Ni(II) ions using MH500 respectively.


0

20

40

60

80

100

% A

dso

rbe

d

Fig 7: Effect of contact time on heavy metals removal

using MH300

20 min

30 min

40 min

60 min


0

20

40

60

80

100

% A

dso

rbe

d

Fig 8: Effect of contact time on heavy metals

removal using MH500

20 min

30min

40 min

60 min


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Increase in the agitation rate enhances the metal ion diffusion to the surface of the adsorbents and

also causes reduction in the film boundary layer around the adsorbents thereby leading to an increase

in adsorption. The decrease in the percentage of metal ions adsorbed as the rate of agitation increased,

could be due to desorption of some metal ions from the surface of the adsorbents.

Reusability of the adsorbents

The adsorbents used for the waste water adsorption experiment were washed using dilute HCl and

reused for another adsorption experiment. 50% Pb(II) ions was removed using MH300. There was no

adsorption of Pb(II) ions using MH500. 55% Cd(II) ions was adsorbed by the two adsorbents, 43%

Ni(II) ions by MH300 and 28% Ni(II) ions by MH500. Reusing the adsorbents the second time, no

Pb(II) ion was adsorbed by the two adsorbents, 55% and 45% Cd(II) ions was adsorbed by MH300

and MH500. 14% Ni(II) ions was adsorbed byMH300 and no metal ion was adsorbed by MH500.

It could be observed that the percentage of metal ions adsorbed after the first reuse remained

unchanged. This could mean the adsorption sites were still active. However, the reduction in the

adsorption with number reused could be as a result of damage of some active sites, hence low

adsorption. Impurities in the waste water samples could also interfere with the adsorption sites, and

this may contributer to the low adsorption.

Fourier Transform Infrared (FTIR) Spectroscopy


0

20

40

60

80

100

% A

dsorb

ed

Fig 9: Effect of rate of agitation on heavy metal

removal using MH300

100rpm

200rpm

300rpm


0

20

40

60

80

100

% A

dsorb

ed

Fig 10: Effect of rate of agitation on heavy metal

removal using MH500

100rpm

200rpm

300rpm


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The pattern of sorption of metals onto adsorbents is attributed to the active groups and bonds present

on them. The peaks appearing on the FTIR spectrum (Fig.11) was assigned to various functional

groups according to their respective wave number as reported in literature (Farook and Muazu 2013).

The FTIR spectroscopy of the adsorbents displayed the presence of O-H group located in peaks

around 3324cm-1. This indicates the existence of O-H vibrations of Si-OH and H-OH groups of

absorbed water. The peak at 3324cm-1 on the FTIR spectra of MH300 was stretched to 3335cm-1 after

metal ion adsorption indicating the participation of hydroxyl group in the adsorption process. The

up shift of wave number from 1736cm-1 to 1721 cm-1 and 1629cm-1 to 1639 cm-1 is attributed to C=O

stretching and angular vibration of water molecules.

Figure 11a: FTIR spectrum of MH300 before adsorption

Figure 11b: FTIR spectrum of MH300 after adsorption

Scanning Electron Microscopy (SEM)

The scanning electron micrographic examinations of the two adsorbents showed a highly porous

morphology of the millet husk with pores. Figure 12a showed the surface structure of the adsorbent

before adsorption while Figure 12b showed the surface morphologies of the adsorbents after

adsorption of metal ions. Before metal uptake the images revealed that the external surface is full of

cavities characterized by irregular heterogeneous surfaces which suggest that millet husk exhibits a

high surface area and irregular in shape. The seemingly rough surface of the adsorbent is an

indication of high surface area. Some pore openings and cavities which can facilitate the solution flow

into the pores are observed on some of the adsorbents. Absence of some pores and lighter surface of

the adsorbents after metal ion adsorption suggests that metal ions adsorption has taken place. The

formation of white spots on the surface of the adsorbents after metal ion adsorption could be as a

result of precipitation of some of the heavy metals on the surface of the adsorbents.


346

Figure 12 SEM

pictures of MH300 before (a) and after (b) adsorption

Conclusion

This work has demonstrated the possibility of using millet husk as an adsorbent for the removal of

heavy metals from aqueous solutions. The results obtained showed that the adsorbent can be

applicable in the reclamation of waste water. Reducing the size of the adsorbent from 500µm to

300µm had some effect on the efficiency of the adsorbent in the removal of heavy metal ions. Both

FTIR spectra and SEM morphologies indicated significant differences on the adsorbents before and

after the adsorption of metal ions. Millet husk is inexpensive and readily available agricultural waste,

thus this study has provided a cost effective means of reclamation of metal ions from contaminated

water.

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