Pertanika 8(2), 223 - 230 (1985)

Copper(II) Adsorption by Waste Tea Leavesand Coffee Powder

W.T. TANChemistry Department,

Faculty of Science and Environmental Studies,Universiti Pertanian Malaysia,Serdang, Selangor, Malaysia.

Key words: Uptake; pH; concentrations; competitive reaction; adsorption; chelation.

ABSTRAK

Bahan- bahan minuman yang telah digunakan seperti serbuk kopi dan daun teh darzpada hasiltempatan didapati berkebolehan mengasingkan ion-ion kuprum(II) darzpada larutan akuas. Ciri-ciripengambilan Cu(II) oleh hampas bahan-bahan minuman tersebut dikaji secara szstematik. Didapatipengambilan Cu(II) ini bergantung pada pH, kepekatan logam, sifat-sifat fizikal substrat dankekuatan ion. Ion-ion/molekul-molekul yang bersaing seperti Pb(II) dan bahan aktif permukaanseperti Triton X-lOa menganggu proses pengambilan kuprum. Kadar pengambilan ini bertambahmengikut pH dan untuk kedua-dua bahan terse but julat pH bagi pengambilan maksimum ialahantara 5 - 7. Pergantungan kepekatan logam Cu(II) mengikut "Isotherm Langmuir. " Keputusan­keputusan didapati selaras dengan mekanzsma-mekanzsma yang mana pengambzlan Cu(II) ini adalahdzsebabkan oleh serapan ion spesifik melalui pengkelatan dan tindakbalas pertukaran ion.

ABSTRACT

The consumed coffee powder and tea leaves of local produce were found to be able to removesubstantial amounts of Cu(II) ions from aqueous solution. The characterzstics of Cu(II) uptake onthese beverage waste were systematically investigated. It was found that the Cu(II) uptake wasdependent on pH, metal concentration, physical nature of substrate and ionic strength. Competingions/molecules such as Pb(II) and surfactant such as Triton X-lOa interfere in the uptake of Cu(II).The degree of uptake increases with pH and the pH range for maximum uptake was found to be 5 - 7

for both wastes. Metal concentration dependent assumed a Langmuir Isotherm. The results obtainedwere found to be conszstent with the mechanzsms that Cu(II) uptake was due to specific ion adsorptionvia chelation and some degree of ion-exchange reaction.

INTRODUCTION

Man's awareness of the importance of wasteutilization and the detrimental effects of heavymetal pollution has led to considerable researchefforts aimed at understanding the interaction ofmetal with wastes and hence the ultimate use ofwastes for the removal of heavy metal fromwastewater. Several natural and waste polymericmaterials have been demonstrated to removeheavy metals from wastewater. They includebark waste (Randall 1974), waste tire rubber(Netzer et al., 1974; Knocke and Hemphill,1981), 'activated carbon' (Netzer and Norman,

1973) and peat moss (Chaney and Hundemann,1979). Other naturally occuring media possess­ing metal removing capability are clay (Huang etai., 1977; Farrah and Pickering, 1976, 1977),hydrous iron and manganese oxides (Guy et al.,1975; Posselt et al., 1968).

From the literature, several possible interac­tions responsible for the uptake of metal can bereadily discerned:

a. metal chelation by organic matter such as inpeat moss (Chaney and Hundemann, 1979),

b. metal-clay colloid ion exchange reactionsuch as in clay (Guy et al., 1975),

W.T. TAN

c. metal-disulfide bonding such as in wasterubber (Netzer et at., 1974; Knocke andHemphill,1981).

TABLElbChemical composition of the insoluble portion of

roast coffee (dry weight basis) (Sivetz 1963)

MATERIALS AND METHODS

their contribution as solid wastes to the environ­ment is not significant (Moore and Moore 1976),its potential re-use for other purposes like metalremoval should not be overlooked. However,before this can be fully realized, the charac·teristics of the metal uptake by these wastesshould be studied in some detail.

The present studies were designed to investi­gate systematically the uptake characteristics ofcopper (II) by tea leaves and coffee powderwastes. Each waste beverage was studiedseparetely to determine its metal uptake charac­teristics as a function of pH, metal, ionicstrength, physical nature of the substrate and inthe presence of surfactant and competing metalIons.

The extent of the metal substrate (waste)interaction are in general dependent on pH,metal concentration, presence of competingmetal ions, ionic strength and nature ofsubstrate.

It has been suggested that the metal uptakecapacity of peat moss is due to the chelatingproperties of its constituents especially lignin andcellulose. These materials constitute the majorconstituents of the cell walls and possess polarfunctional groups such as alcohols, aldehydes,ketones, carboxylic acids, phenolic hydroxidesand ethers. The polar nature of these complexmaterials can remove large quantities of metalions from aqueous solutions (Chaney andHundemann, 1979). Since the chemical compo­sition of the insoluble cell wall for tea leaf andcoffee wastes are largely made up of celI"ulose,lignin and some structural proteins (Table 1)(Harler, 1963; Sivetz, 1963), its use for metalremoval should be feasible.

In Malaysia, like in many other countries,tea and coffee are the traditional drinks of mostMalaysian adults. Usually, the locally producedtea leaves and roast coffee or its powder are soldin disposable bags. The normal practice afterthe brewing of tea and coffee in hot water is todispose off it as waste. These wastes usuallyconstitute part of the household waste. Although

Constituent

Carbohydrate (43%)

Caramelized sugars

Hemi·cellulose (hydrolyzable)

Fi ber (not hydrolizable)

Oils

Proteins

Percentage

7

14

22

15

11

TABLE laPercentage composition of the ethanol insoluble

material of black tea (dry weight basis)(Harler 1963).

Constituent

Cell wall material

Hot water·soluble polysaccharide andproteins

Hot water insoluble proteins

Lignin and structural proteins

Cellulose

Percentage

46.8

9.6

12.1

14.7

37.2

Apparatus

In International Laboratory double beamatomic absorption spectroscopy (model 651) wasused for the analysis of copper content of thesolutions. The simultaneous analysis of copperand lead contents of the solutions was carried outby a Princeton Applied Research PolarographicAnalyzer, Model 384 equipped with staticMercury Drop Electrode (Model 303) using diffe­rential pulse mode at 2mVIS, and pulseamplitude of 50mV. The orion pH meter (Model601) was used to determine the pH of the solu­tions.

224 PERTANIKA VOL. 8 NO.2. 1985

COPPER(II) ADSORPTION BY WASTE TEA LEAVES AND COFFEE POWDER

Treatment of Tea and Coffee Waste

Both the tea leaves and coffee used in thestudies are processed and distributed by localcompanies.

Tea leaves and roast coffee (coarse grain)were brewed in hot water for 10 minutes. Theused tea leaves were then removed from its bagsand dispersed in dilute acid solution (10 -2MHNO ) for two hours. They were then filtered

3

and washed with deionised distilled water(DDW). (DDW was prepared by running labora­tory distilled water through Millipores purifi­cation system once before use). This process ofcleaning and filtering was repeated when neces­sary to remove any metal ions and acid adheringto the tea wastes. The residue was air dried inthe sun. The used coarse grain coffee was airdried and powdered into smaller grains by usingmortar and pestle. The resulting coffee powderwas then subjected to the same cleaning treat­ment given to tea waste. For most studies, airdried samples were used. However, wastes whichwere activated in the oven at IIO°C for twohours were also used for some studies. The grainsize of tea leaves waste as determined by U.S.Standard sieve was 60 mesh, and that of coarsecoffee and powdered coffee were 20 and 80 meshrespectively.

Procedure

The uptake of copper by the separate wastebeverages was studied by adding a knownquantity of the treated tea leaves and coffeepowder wastes to metal ion solutions havinginitial metal concentration of 0 - 25.0 uglml in50.0 ml sample solutions. A total of 100 mlcopper solution was prepared and divided intotwo equal portions of 50 ml.

One portion is used as control (i.e. onewithout added substrate) while substrate isadded to the other. The containers used werepolyethylene bottles of 100 ml capacity. Themixture was shaken for four hours followed bydecantation or filtration (when necessary) andmetal analysis. The difference between thecontrol reading and sample readings (with

waste) was taken as the amount of metal takenup by the waste. Four hours was found to besufficient for the equilibrium uptake of metal bythe substrate.

The effect of pH on the metal uptakeprocess was studied by introducing 30 mg wastebeverage to 50.0 ml of 2 ppm eu solution atdifferent pHs of between I and 3 (adjusted byHNO 3)' 4 and 6 (adjusted by 10 -3M potassiumacetate) in 1.0 X 10 -2 M KNO. 10 -3 M

. 3

KHfO /K 2HPO 4and 10 -3MNH/NH 2Cl wereused as buffers for pH 7 and pH > 7 respecti­vely. Ionic strength was maintained at a constantlevel by using O.lOM KNO 3' The metal uptakestudies' were carried out at different values ofionic strength set by KNO 3 from O.OOIM to0.50M KNO 3 and different amount of strongsurfactant set by Triton X 100 from 0.0001 to0.002% (V IV). With the exception of repro­ducibility studies, all the other studies werecarried out once experimentally. The reproduci­bility study on the percentage of Cu uptake by 30mg tea waste from 50 ml solution of 2 ppm Cuproduced a mean of 62% with a relative stan­dard deviation of 5% (for four replications) atpH 6.0.

Reagents

All chemicals were of reagent grade andwere used without further purification except forconcentrated nitric acid which was distilled oncefrom all glass-still. Potassium nitrate was re­crystallized once from the distilled nitric acid of

4M. Analar grade Cu(NO 3) 2' Pb(NO 3) 2 saltswere used to prepare 1000 ppm Cu(lI) and 1000ppm Pb(lI) respectively in deionized distilledwater.

RESULTS

Effect ofpH

Fig. 1 represents the amount of copper (II)taken up by the waste beverage as a function ofpH. The degree of uptake increases as pH in­creases as shown by the decreasing amount of Cuin solution with changes in pH. The optimumpH range for maximum metal uptake appear to

PERTANIKA VOL. 8 NO.2, 1985 225

W.T. TAN

600

500

a.!.-

400:s..>0

'"!:1«

300 ~:>a:""-"-0

200u

100

Fig. 2. Copper intake isotherms at pH 6. Oin 50 mlsolutions containing:.& 20 mg tea waste• 10 mg coffee waste

TABLE 2Physical effect of wastes on the uptake of copper;

pH 6, 30 mg beverage, (eu)initi., =

4.1 ppm in 50 ml solution

Nature of the Substrate

Metal uptake by the increasing concentra­tion of the beverage substrate was approximatelylinear below lO mg substrate for both the tea andcoffee.

A rather small difference in the metaluptake capacity of 3% was seen between theactivated (oven heating at ll2°C for 4 hours)and the non-activated beverage wastes (air dry­ing) as shown in Table 2. Table 2 also indicatesthat the effect of grain size of coffee on the metal

!i:l 200~U

>0

'"~

150

fi: 0

:> (.a:<oJ

'""- lOa0u

50 .;•

5 10 20

£QlULIBlUIJH cu, ,ug/mJ.

Fig.

OL---L__---'L..--__...L-__-L.__--'_......

1 3 5 7 9pH

1. Copper uptake as /I fllflCtwn of pH.30 mg beverage waste: .& tea,

• coffee, [Cul'mt,al = 2ppm in 50 mlsolution

Effect ofMetal Ion Concentration

250

It was observed that the metal uptakedecreased at the more alkaline condition for teabut not for coffee substrates. At pH > 7, the teasample solution which was originally colourlessturned brownish orange. The solution becamemore brownish orange as it became morealkaline indicating denaturalization of some cellwall constituents. This denaturalization mayhave caused the reduction of interacting sitesand hence reduce Cu(II) uptake by the teawaste.

lie between 5 to 7 and 6 to 9 for wastes tea leavesand coffee powder respectively. Hence, in all the 300

other studies, a pH of about 6 was employed.

100

80

~H

~...:I

~ 60

i:ico:'-'I

'" 4081IC.

20

% copper uptake by

tea coffee(fine) (coarse)

74 82

Fig. 2 shows that as the concentration ofcopper ion introduced to the fixed quantity oftea or coHee waste at weakly acidic conditionswas increased, a sharp increase in the uptake ofcopper was seen until a certain concentrationwas reached, above which the slope levelled off.These two concentration dependent curvesassume a Langmuir Isotherm.

Activated

Non activated 72 81 54

226 PERTANlKA VOL. 8 NO.2, 1985

COPPER(II) ADSORPTION BY WASTE TEA LEAVES AND COFFEE POWDER

uptake capacity is more drastic: everything beingequal, the finely ground coffee powder (80 mesh)was able to remove 27% more metal from thesolution than the coarse grained coffee (20mesh). As a result, the finely ground and airdried coffee waste were used in all the otherstudies.

Competitive Effects

Table 3 demonstrates the progressivedecrease in the uptake capacity of both the tea

TABLE 3Effect of ionic strength on the uptake of copper

by the 20 mg beverage wastes at pH 6; (eu 2+) .. I

2.1 ppm in 50 ml solution tn,tla

and coffee wastes on the addition of increasingconcentrations of potassium nitrate and hence itsincreasing ionic strength. This suggests the possi­bility of uptake of K + by wastes and hence thecompetitive effect between this ion and the otherions in solution.

The competitive effect was further studiedbetween two metal ions which were taken up bythe same substrate in the same solution at pH 6.This was done by varying the concentration ofPb(II) ions onto the fixed amount of Cu: 5 ppmCu in 50 ml solution. The two metal ions con­centrations at equilibrium were determinedsimultaneously by differential pulse polaro­graphy. Results are summarized in Fig. 4. Itdemonstrates an obvious decrease in the uptakeof copper by wastes from both beverages in theface of increasing competing metal ions. In thepresence of 2 ppm Pb in 50 ml solution, theamount of copper uptake was 49 and 67 % of the5 ppm Cu originally present for 30 mg tea and 30mg coffee substrates respectively. However,. afurther addition of ten fold excess of Pb concen­tration caused a further decrease in the amountof Cu uptake by approximately 10 and 5 fold fortea and coffee respectively. Concentrationdependent curve for Pb was found to be of theLangmuir type.

80

~ 60

~::>

'"'"'" 408

5 10 15 20 25 4 8 12 16 20

WEIGH!' OF BEVERAGE WASTE (eng)

Fig. 3. Copper uptake at pH 6 as a function ofthe dry weight of A tea waste;

• coffee waste, [CU]init,al = 100 /lg.

L£AD ADDED (ppm)

Fig. 4. Effect· of added Pb on copper uptake byA 30 mg tea waste; • 30 mg coffee waste at

pH 5.9, [CU]iniUal = 5 ppm

PERTANIKA VOL. 8 NO.2, 1985 227

W.T. TAN

A qualitative experiment involving TritonX 100, a strong surfactant was carried out todetermine the competitive adsorption effect ithad on the observed Cu uptake. Addition of upto 0.0003% Triton- X 100 produced no changein the Cu uptake by the beverage wastes. Anobvious change was observed at Triton- X 100concentration greater than 0.0005% (V IV). Anaddition of 0.0020% surfactant to both tea andcoffee wastes suppressed copper uptake byalmost an equal magnitude (10 ± 1%).

DISCUSSION

These studies have shown conclusive eVI­dence that the tea leaves and coffee wastes areable to remove metal ions such as Cu(II) fromsolution. The extent of removal is a function ofpH, ionic strength, metal ion concentration,nature of waste substrate used and presence ofother competing ions or molecules.

That such uptake of metal is due basicallyto an adsorption process was qualitatively provenby Triton- X 100 studies. Being a strong surfac­tant, Triton- X 100 has been commonly acceptedas a strong adsorbate. The reduction of metaluptake by the wastes in its presence could only beexplained by blocking of their interacting sitesby the surfactant which is preferentially adsorb­ed onto the substrate. These observations areconsistent with a mechanism in which adsorptionis responsible for the uptake of metal by the

beverages.

The actual mechanism involved in theadsorption process of metal by the wastes cannotbe easily determined. However studies on thefactors governing metal uptake as mentionedearlier revealed results which are consistent withspecific adsorption via chelation and somedegree of ion exchange reaction.

To illustrate chelation, we consider theequilibria between the polyphenol, which makeup almost one-third of the total dry matter in tea(Harler 1963), and other ions present as shown inFig. 5.

When pH is greater than 3, the interactingsites can dissociate to form negatively chargedsurfaces which can interact with metal ions intwo possible ways:

I. formation of a counter ion layer,

II. specific adsorption of ions onto the surfacevia chelation as shown in Fig. (5).

Based. on this model, the various pheno­mena of metal adsorption by the beverage wastescan be readily explained. In the presence ofproton, Cu 2+ has to comp.ete with it for interact­ing or chelation sites of the substrate. Hence themore acidic the medium the lesser the chance forCu 2+ to interact with the adsorbent, whichresults in decreased metal uptake. On the con­trary, as pH increases, Cu 2 + faces lesser degree ofcompetition from H + for the interacting sites.This competitive effect does explain why therewas no detectable copper uptake at pH ,.;; 2 andgreater copper intake as pH increased (Fig. 1).

oH

oH

-2H +

,+2H +

o o

+cu 2 +

<-cu 2 +

•

o ,, ,\ /

Cu

o

228

Fig.. 5. Interaction of Gu(U) and H + ions with polyphenol groups of beverage wastes.

PERTANIKA VOL. 8 NO.2. 1985

COPPER(II) ADSORPTION BY WASTE TEA LEAVES AND COFFEE POWDER

TABLE 4Affinity of Cu - Pb couple in 50 ml solution containing 30 mg beverage wastes at pH 5.6

I(a) 5.0 ppm Cu + tea waste(a) + 5.0 ppm Pb spike

II (b) 5.0 ppm Cu + coffee waste(b) + 5.0 ppm Pb spike

III (5.8 ppm Cu + 3.5 ppm Pb)+ tea waste

(M 2 +) uptake/ppm

(Cu) : 1.9(Cu) : 1.2(Pb) : 3.8

(Cu) : 3.4(Cu) : 3.1(Pb) : 4.0

(Cu) : 1.4(Pb) : 2.6

% M 2+ uptake

382476

686280

2474

Competitive effect is not only exerted by H +

but also other ions like Pb 2+ as shown in Fig. 4and Table 4. Lead ion appears to have a greateraffinity for the surface of the waste than Cu 2+. Itcan be demonstrated by the results in Table 4,which show greater adsorption of Pb 2+ over thatof Cu 2+ irrespective of the fact that the waste wasadded to the solution already containing bothmetal ions or only one metal ion. There wassome indication that the interactions of Cu - Pbcouple with the wastes involved small but signi­ficant degree of ion-exchange reaction. This isbecause about 6 to 14% Cu adsorbed was releas­ed into the solution after the addition of Pb tothe mixture (Table 4 (I), (II».

The increasing suppression of metal uptakeby beverage waste due to increasing ionicstrength of the sample solutions at pH 6.0 can beattributed to the formation of a counter ion layerby K + ions. These K + layers would invariably actas a deterrent for the specific adsorption ofcopper. In general, K + appears to have a smalleraffinity for the beverage substrate as comparedto that of Cu 2+ and Pb 2+. An addition of asmuch as 0.5M KNO 3 does not cause any drasticdecrease in the copper adsorption by the waste.This occurs because the potassium ion is mono­valent while copper and lead ions are divalent.

The studies carried out so far'concern main­ly the copper uptake by tea and coffee wastesusing a batch technique. Research is now inprogress to investigate the adsorption behaviourof other metals such as zinc, cadmium and lead.

Similar studies shall also be extended to columntechnique and optimum parameters such as pH,flow rate, etc. shall be determined for theremoval of metals from some wastewaters.

ACKNOWLEDGEMENTS

This work was supported by a UniversitiPertanian Malaysia Research Grant and hasbeen presented at the 1984 InternationalChemical Congress of Pasific Basin Societies,Honolulu, Hawaii. The author also wishes tothank Dr. M. Shamin for reviewing the draftcopy and laboratory staff, Talib Ali and C.S.Choo, for their technical assistances and Norainibt Abu Bakar for the typing of the manuscript.

REFERENCES

CHANEY. R.L. and HUNDEMANN. P.]. (1979):]. WaterPollution Control Federation. 51: 17.

FARRAH. H. and PICKERING. W.F. (1976): Aust. ].Chern. 29: 1167.

FARRAH, H. and PICKERING. W.F. (1976): Aust. ].Chern. 30: 1417.

GUY. R.D., CHAKRABARTI, C.L. and SCHRAMM, L.L.(1975): Can.]. Chern. 53: 661.

HARLER. C.R. (1963): 'Tea Manufacture' p. 108. NewYork. Oxford Univ. Press.

HUANG. C.P., ELLIOTT, H.A. and ASHMEAD, R.M.(1977):]. Water Pollution Control Federati·on.49: 745.

KNOCKE, W.R. and HEMPHILL. L.H. (1981): WaterResearch. 15: 275.

PERTANIKA VOL. 8 NO.2. 1985 229

W.T, TAN

MOORE, j.j. and MOORE, E,A, (1976): Environmen­tal Chemistry. p, 318, New York, AcademicPress, Inc.

NETZER, A" WILKINSON, P. and BESZEDITS, S. (1974):Water Research, 8: 813.

POSSELT. H.S., ANDERSON, F.j. and WEBER, W.j. Jr.(1968): Environ. Sci. Technol. 2: 1087.

RANDALL,j.M, (1974): Forest ProductJour, 24: 81.

SIVETZ, M.S, (1963): 'Coffee Processing Technology'Vol. 2, p, 167. Connecticut. The Avi PublishingCompany, Inc,

(Received 7january, 1985)

230 PERTANIKA VOL. 8 NO.2, 1985