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XXII ENTMME I VIl MSHMT- Ouro Preto-MG, novembro 2007.

A PERSPECTIVE OF CHAR USE lN THE TREATMENT OF INDUSTRIAL LIQUID EFFLUENTS CONTAlNING HEAVY METALS

1 2 3 T.S. Gucdes , M.B.Mansur and S.D.F. Rocha 3 contacting author, sdrocha(â1demin.uting.br Universidade Federal de Minas Gerais, 1Chcmical Enginccring undcrgraduatc studcnt, 2Metallurgical and Materiais Engineering Dcpartment and 3 Mining Engincering Dcpartment 3Rua Espírito Santo 35 , 7" andar, Centro, 30160-030 - Belo Horizonte, MG, Brazil.

RESUMO

O carvão de ossos bovinos já é utilizado tradicionalmente na remoção de cor na indústria do açúcar. Esta excelente característica adsorvcnte tem impulsionado sua utilização cm diversas outras áreas, tais como na indústria minero­ metalúrgica, para a remoção de metais presentes cm efluentes líquidos. Esse trabalho apresenta uma comparação entre as características do carvão de ossos produzido no Brasil c aqueles disponíveis no mercado internacional, c também apresenta o desempenho do carvão nacional na remoção de Zn, Cu, Cd, Co, Pb e Ni , metais comumente present~s em efluentes da indústria minero-metalúrgica. Os resultados apontam numa perspectiva de utilização do carvão de osso no tratamento de efluentes líquidos industriais contendo metais já que se observou uma remoção satisfatória dos metais estudados. Foram avaliados os tratamentos de um efluente proveniente da indústria do zinco e efluentes sintéticos. O carvão de ossos bovinos de granulomctria fina apresentou resultados mais satistàtórios do que o de granulometria grosseira; esse é um dado importante, tendo em vista que o carvão fino é um produto de baixo valor agregado. As vantagens e limitações da aplicação do carvão são discutidas, bem como as possibilidades de destinação final do adsorventc carregado com metais. Quando a operação se dá em coluna, observou-se uma competição entre os metais cádmio e o zinco, para o efluente industrial, o que merece estudo adicional.

Palavras chaves: adsorção, remoção de metais, carvão de ossos bovinos

ABSTRACT

Bonc char is traditionally uscd for color and turbidity remova! in sugar processes. Due to its exccllent adsorptive character its utilization has bccn studicd and expandcd to other applications, such as the metais remova! from mining anel metallurgical eftluents containing metais, and also for the remova! of residual color and organic matter from textile cftlucnts. A comparison bctwcen thc charactcristics of imported and national Bonc char is reported in this work. The perfonnance and also thc kinetic of Bonc char for the remova! of Zn, Cu, Cd, Co, Pb and Ni present in acidic solutions are presentcd. Thc results dcpict a good perspective of processes with bone char. The use of bonc char for the remova! of metais form ctllucnts generated by the industry has shown promising rcsults. Best results were obtained using the fine fraction of bonc char in comparison with thc com·sc fraction; this is an important rcsult sincc the fine fraction of bone char h as a low commercial value. Thc advantages and limitations of the application of bone char are discussed, as well as the possible attractivc for the final dcstination of metal loaded charcoal. A competitive separation betwecn metais zinc and has bcen vcrifíed in column operations, so further studies are necessary.

Key-words: adsorption, metais remova!, bone char Thematic arca: effluent treatment 428

Thiago Santos Guedes, Marcelo Borges Mansur and Sônia Denise Ferreira Rocha

1. INTRODUCTION

Due to its high toxicity to human healthy and also to cnvironment, heavy metais must be removed from wastcwatcrs generated by many types of industries such as metal processing, metal rccycling as well as surfacc treatmcnt companies (galvanization) and many others. The wastewaters are mainly contaminatcd with hcavy metais such as Zn, Cu, Cd, Co, Pb and Ni. The effluents are usually trcatcd by a prccipitation processes, using an alkali as prccipitant agcnt for metais hydroxides. Precipitation of metais is largely used duc to the low cost of alkalis usually availablc, and its rclativcly casy operation. However, duc to the strcngthening of cnvironmental standards and also to thc necding of rccycling watcr in the processes, altemative processes have been investigated (Sonumc & Ghate, 2004), mainly in cases when metais are complexed, associated with organic compounds and also for trace conccntrations.

Adsorption is an intcresting alternative to be used whcn it is dcsircd to gel such lowcr residual concentrations of contaminants in water. ln opposition to precipitation, therc is no limit for the residual concentration of metais in the solution. ln the case of precipitation, the residual conccntration of metal is dctcrmincd by thc solubility of thc metal hydroxide, also a function of the system tempcraturc. The residual conccntration of the contaminant in the solution after a treatmcnt using adsorption depends on various factors, mainly thc aftinity bctween adsorbcnt and lhe adsorbate and the operational conditions of the process. Adsorption can be used for immobilization of species "in situ". Many investigations have been carried out with a variety of organics adsorbents such as activated , biomass and also inorganic, zeolites, clays, solids wastes (Kadirvelu et ai, 200 I; Hanzlik ct ai., 2002; Aklil et ai., 2004). The present work depicts the use of bone char in thc remova! of metais Zn, Cu, Cd, Co, Pb and Ni present in acidic solution and also Zn, Cd and Pb from an industrial effluent from zinc mining industry. The bone char used is produccd by a Brazilian company from bonc wastes. Thc kinetic of adsorption and also the adsorptive capacity for ali metais was determined.

The bone charcoal is produced by the pyrolisis of crushed ox at 800°C in atmosphere of limited concentration of oxygen. Bone charcoal contains about I 0% of carbon on the opposite of normal activatcd carbon, which is majoritary carbon. Bones charcoals present mainly hidroxiapatite and minor amounts of calcium carbonatc. Thc presence of carbonates gives to bone char a buffer capacity. Despitc thc bone char is used in sugar proccss for more than a century, its use as adsorbent for diverse compounds has been the objcct ofmany studics (Cheung et a/., 2000; Dahbi et a/., 2002; Wilson et ai., 2003; Cheung et a!., 2004; Ko et ai., 2003; Choy and McKay, 2005; Guedes and Rocha, 2005). Wilson et a/. (2003) invcstigated the adsorption of and zinc by bonc char Brimac 216 20/60 (250-850 11m). The experiments were carried out with 20 mg/L of charcoal in solutions containing O mg/L to 4000 mg/L of Cu and O mg/L to 2000 mg/L of Zn prepared from their nitrates, without adjust of pH. A good agrecmcnt of results with thc Langmuir adsorption model was observed, cquation I, being the maximum adsorption capacity (Omox) dctennined as cqual to 27±1 mg/g and 24±3 mg/g for Cu and Zn, respectivcly .

.c,_ --.C..c.._ = + Qc KL X Qmax Qmax (I)

where: Ce: equilibrium concentration (mgmera1/L); Qe: ratio of amount adsorbed and adsorbcnt mass (mgmctallgadsorbcnt); Omax: maximum adsorptive capacity (mgmctallgadsorbcnt) ; KL: Langmuir constant (LI mgmctaJ).

Guedes & Rocha (2005) obscrved that thc Brazilian bone charcoal prescnts similar adsorptive capacity to thc imported (Brimac) for lhe remova! of zinc and copper. Adsorption cxpcrimcnts with I O mg/L of bone charcoal of two sizes (- 6+ 16) mesh Tyler and ( -20+40) mcsh Tylcr, in contact with solutions containing 50-300 mg/L of Cu and 50-300 mg/L of Zn, preparcd from thcir , initial pl-1 equal to 4,0 wcre carricd out at ambient tcmpcraturc (28"C). The maximum adsorptive capacity was detcrmincd for coppcr and zincas 25.7 mg/g and 25.3 mg/g, rcspcctively.

2.MATERIALS AND METHODS

2.1 Batch adsorption experiments

Samples of Brazilian bone charcoal were supplied by Boncchar Carvão Ativado do Brasil located at Maringá-PR, in two distinct size ranges: coarse ( -6+ 16) mesh Tyler and fine ( -20+40) mcsh Tyler. Charcoal was charactcrized with respect to its real density (picnometry with Hc, Stcrcopycnomctcr Quantachrome SPY -3), morphology (Scanning electron microscopy, JEOL, modcl 6360L V), presence of crystalline phases by X-ray diffraction (X-ray Philips­ PAnalytical PW 171 O Diffratometer) and specific surface arca (multiple point BET- Quantachrome- Nova 1200). 429

XXII ENTMME I VIl MSHMT - Ouro Prcto-MG, novembro 2007.

Initially lhe bone charcoal was dried ai 120"C, for a period of time of 2 hours and slored in a dissecalor. Samples withoul pre-lrealmenl of 1.0 g were weighted and placed inlo an erlenmeyer containing lhe synlhelic metal solution with 50, I 00, 150, 200, 250 e 300 mg/L of metal, prepared using ZnS04 . 7H20, CdS04 .8/3H20, CoS04 . 7H20 CuS04.5H 20, NiS04.6H 20 and Pb(N03) 2 salts. The pH was adjusted to the desired value (4,0) with sulphuric acid solution and in the case of , nitric acid was used. The initial solid-liquid ratio was equal to lO mg/L. Erlenmeyers containing lhe solulion and bone char were stirred ai 200 rpm in a shaker Dubnoff under conlrolled temperature of 28"C. i\fter 140 minutes, time enough to gel the equilibrium as verified in a preliminary study, experimenls ended and lhe pulp was vacuum filtercd. Metais concentralions in solution were determined by atomic absorption speclrometry (GBC 932 plus).

2.2 Column adsorption experiments

Semi-conlinuous adsorption experiments were carried out in an acrylic column 53 cm high and 2,2 cm diameter. Bone charcoal of (-20+40) mesh Tyler was previously washed wilh distilled water for a period of time of 2 minutes in a becker, al a solid-liquid ratio of 0.15 g/ml. Further, pulp was fillered and solids were dried at 60°C for 12 hours. The column was filled with 30g of lhe adsorbent. The industrial effluent containing mainly Zn, Cd, Pb and ions was continuously fed lo the column ai a flow rate of 0,014 L/min by a peristaltic pump (Cole-Parmer, Masterflex). Samples were collecled in the column outlet and metais concentrations were detennined by atomic absorption spectrometry (GBC 932 plus).

2.3 Desorption experiments

Desorption experiments were carricd out for two distinct sizes of charcoal: coarse ( -6 + 16 mesh Tyler) and fine ( -20 +40 mesh Tyler). i\ 506.8 mg/1 zinc solution of pH 4.0 (adjusted with sulphuric acid) was prepared in order to load the fresh bone charcoal. F our samples of 5 g of bone eh ar of each size were weight and each one was contacted with 100 ml of the zinc solution previously prepared for 180 min at 28°C and under stirring rate of 240 rpm. The initial and final pH and lhe initial and final zinc concentrations were obtained. After lhe loading step lhe pulp was vacuum filtered and further dried ai 60"C for 12 hours. The solids were homogenized and smaller samples of about 2.4 g were taken. The adsorbed mass on charcoal was determined by a mass balance. The first desorption test was carried out with 10 g/L of bone eh ar in distilled water of pH 5.4 for both sizes of bone char, coarse and fine. The pulp was stirred for 200 minutes at 28°C. i\t lhe end of the experiment, the pH was measured and the pulp was vacuum filtered. The second desorption experiment was carried out with sulphuric acid solution of pH 2.0 ai the same conditions as the Desorption carried out with distilled water. The Desorplion time was extended for 240 minutes.

3. RESULTS AND DISCUSSION

3.1 Bone Charcoal Characterization

The Brazilian bone charcoal of coarse and fine sizes presented low humidity content, 2,9% e I ,3%, respectively. These values are in a good agrecmcnt with lhe specification given by lhe producer (<5%). The main physical and chemical properties of both charcoals are depicted in Table I.

T a bl e 1 - M am properl!es o fB raztT tan an tmporte dbone c har Brazilian Bone Property Imported eh ar Carbon content 9-11% 9-11% Soluble ash in acid <3% <3% Tricalcium phosphate 70 - 76% 70-76 Calcium carbonate 7-9% 7-9% Calcium sulphate 0,1-0,2% 0.1-0.2 3 Real density (g/cm ) 2,86 2,81 Total specific surface área (B ET) 129,4 m-!g 123,2 Iron < 0,3% <0.3 Medium Porous diameter 98,6 94,8 Porous volume (cmj/g) 0,3189{d<974,9Â) 0,2919(d<978,5 À) Humidity <5% <5%

The values presented are in accordance with those reported by Wilson et al. (2002), except for the surface area. Figures I and 2 illustrate the high porosily and irregularities on the charcoal surface. Fine particles of carbon, attached to the 430

Thiago Santos Guedes, Marcelo Borges Mansur and Sônia Denise Ferreira Rocha

surface can be observed, since the material was not washed previously. The identification of chemical specics on the surface by SEM, according to Figure 3, cvideoced high contents of calcium and phosphorous, as expected. This is coherent with the raw material ofthe bonc char, and also with the literature (Wilson et a/., 2003). The bearing phasc of phosphorus identified by the X-ray diffraction analysis is the hydroxiapatite. Minor amOtmts of calcite were also identified.

(a) (b) Figure I - Micrographs ofbone char coarse. Secondary electron image. (a) 30x (b) IOOOx

~'"' ...... (a) (b) Figure 2 - Micrographs ofbone ehar fine. Secondary electrons i moges. (a} 30x (b)

!OOOx .. • .. p " " "~ca

Figure 3 - Scanning electron microscopy of fine bone char at region C.

3.2 Batch Adsorption Experiments

The adsorption isotherms (28°C) for the whole metais studied are preseoted in Figure 4 with the points adjusted for lhe Langmuir equation. The relationship between the amount of metal adsorbed per mass of adsorbent (Qe) and the metal equilibrium concentration (Ce) is useful to predict the character of adsorption. Two adsorption models werc tested in order to verify their applicability to the system. The Frcundlich equation derives from an empirical model of adsorption tbat considers that Qc increases linearly witb Ce (equatioo 2) 431

XXII ENTMME I VIl MSHMT- Ouro Preto-MG, novembro 2007.

log Oc = log Kr- + 1/n log Cc (2)

where: Qe: ratio of amount adsorbed and adsorbent mass (mgmctallgadso Ce: equilibrium concentration (mg/L);,bcnt); KF and n: Constants.

jofinecharcoal l O fine charco ai I iOcoar se charc_oaj ()coarse chan.: oal

I·---- o 100 200 300 o 100 200 300 I Ce (mg/L) I Ce (mg/L} _j Co Cd

------1 ~-- 25 30 1 I êi 20 õi jD ,,;;-;;charco ai I O finc-ch-a~c ~~ ~-- ~ Õl 15 l Õl 20 .§. '<>co a rs c charconl_ I E i 10 I - " <)c o a rs c c h arco a j Q) Q) 10 CJ I 1 CJ 5 I I o 0 - I ! o 100 200 300 o 50 100 150 200 Ce (mg/L) Ce (mg/L) I I _ _ _ j L ______J Zn Cu ------10

O fn1e c ha rcoal :k;:=:= Ocoarse charco a! o 100 200 300 Ce (mg/L)

Ni Figure 4 - Adsorption isotherms for metais studied at 28°C.

On the other hand, the Langmuir equation (equation I) derives from a model were the main considerations are adsorption occurring in monolayers, without interactions between solutes. The parameters obtained adjusting both equations to the results are presented in Table 2 anda good agreement with those reported by Wilson et a/., (2003) has been obtained. 8oth models showed a good adjust to experimental results, being the Freundlich model slight superior in some cases. H can be clearly noticed that the bone char of small size presents higher remova! of metais such result is probably related to lhe higher surface area for metais adsorption. The results of isotherm for lead are not presented, since lhe remova! was complete for this metal in a short period of time. So, lhe bone char has a high affinity for lead. 432

Thiago Santos Guedes, Marcelo Borges Mansur and Sônia Denise Ferreira Rocha

Table II- Freundlich and Langmuir equations parameters obtained by di verse metais adsorption in bone char

Bone char size Freundlich equation parametcrs Langmuir cquation paramctcrs Metal KF 1/n R- Kt Q rnax R- Fine 0.755 1.31 0.9799 0,839 25,7 0,9567 Copper Coarse 16.47 2.83 0.9871 0,601 10,9 0,9830 Fine 1.455 3.04 0.9632 0,287 9,3 0,9861 Nickel Coarse 1.047 3.60 0.9359 0,148 5,4 0,9851 Fine 1.569 1.92 0.9225 0,552 25,3 0,9837 Zinc Coarse 0.668 1.72 0.9778 0,102 22,8 0,8989 Fine 6.637 3.31 0.9807 2.567 27.0 0,9962 Cadmium Coarse 2.114 2.65 0.9974 0,498 16,9 0,9878 Fine 32.24 3.78 0.9735 0,904 12,9 0,9963 Cobalt Coarse 0.922 2.59 0.9950 0,177 9,2 0.9785 lt was verificd a mass reduction of the adsorbent during lhe experiments of about 4%. This occurred due to thc dissolution of calcite present in the bone char. The other phases present, calei um phosphate (apatite) and calcium sulfate (anhydrite) are rather insoluble. This was also responsible for the increase in the pH of lhe solution obscrved (Figure 5). The pH was higher for lower initial metal concentration and close lo valucs of about 8.5. For higher metal concentrations, pH values between 7 and 8 were reached, dcpending on lhe metal ion. Exception is for coppcr (adsorplion on fine charcoal) and for copper and lead (adsorplion for coarsc charcoal) when lowcr values for hi gher concentrations were reached. Taking into consideration a 4% of calcium carbonale dissolution, a total carbonale concenlralion in solution was 4x 10·4 Molar (solid-liquid concenlration was I Omg/L). According to Stumm and Morgan

(1981 ), in the Me-H20-C02 system, in lhe presence of earth atmosphere, carbonales are frcqucntly more stable than oxides or hydroxides as solid phases. Thus, in naturally syslems, the concenlralion of some metal ions is conlrolled by lhe solubility of metal carbonates.

For a divalenl cation, the following reactions represenl lhe system:

2 MeC03

9 9 8.5 § l!. 8.5 ~ l!. 8 ~ é o o o 8 ~ é o o o D :.: tl D :.: tl 7.5 ~ liC I ~Ni i 7.5 ~ liC i <> Ni i :I: D o. I . :I: D o. c.. 7 ! o Cu : c.. 7 . o Cu I 6.5 D !!. Pb D : !!. Pb 6 D 1 D D xCo D i xCo · 5.5 D ·~5.5 1- D 5 I ----, -- .. ,- - -- -, :.:Zn i 5 i :.:Zn i o 100 200 300 400 o Cd i o 100 200 300 400 i o Cd - - - - metal concentration (mg/L) metal concentration (mg/L)

(a) (b) Figure 5 - Variation ofpH during the adsorption expcriments (a) fine bone char and (b) com·se bonc char

This reactions show that, depending on the total carbonate concenlralion and also ofpH, solid carbonales can be formed in solution. As the bone char contains calcite that dissolves and release in solution carbonate ions, ii is expected that the metal remova! mechanism from solution by bone char may bc thc association between adsorption and also precipitation. The carbonate concentration present in the solution was not enough to respond by the remova( of the metal only by precipitation. Precipitation and adsorplion are complementary processes (Madeira et ai. , 2005). However the extension of each phenomena is not known which thus suggest that the remova( mechanism still deserves additional investigation. 433

XXII ENTMME I VII MSHMT- Ouro Preto-MG, novembro 2007.

3.3 Column Experiments

The industrial effluent under investigation, pH 6,8, eontains 347 mg/L of Zn, 12,3 mg/L of eadmium and 0,7 mg!L of lcad. The sulphate eonccntration is 7,9 g/L. Thc cnvironmental standard for dischargc of cftluents in watcr is 5 mg/L for Zn, 0,1 mg/L for both Cd and Pb (DN I 0/86 COPAM-MG). Figure 7 prcscnts the mpturc curve for cadmium and zinc. Alllcad was removcd (Final concentration was lower than the detection Iimit ofthc spectrometer, equal to 0,001 mg/L). lt is obscrvcd that zinc is prcfcrcntially rcrnovcd, sincc thc rupturc for cadmium occutTed first, despitc zinc continued to be rcmoved.

0.8 • • • • •o o o o o 0.6 IIJ •o o o u o o • l u 0.4 o ~ 0.2 o. • ------, o------T 10 20 30 40 Residence time (min)

Figure 6 - Rupture curve for cadmium and zinc in column experiments.

3.4 Desorption

Fine and coarsc bonc char werc loaded with zinc in ordcr to verify thc desorption step, needed to regenerate the carbon in an industrial process. lt was obtained a fine charcoal with 9,9 mg Zn!g charcoal and a coarse eharcoal loaded with 8. 9 rng/g charcoal. Figure 7 prcscnts thc desoqJtion curves obtained with distilled water of pH 5.4 and sulphuric acid solution of pH 2.0. Thc final pH with distilled watcr was 7.5 for both charcoal and for sulphuric acid solution, pH was cqual to 5.5 for fine charcoal and 3.5 for coarsc charcoal. lt is obscrved that dcscrtion with distilled water was not effcctive and a solution containing l mg/L of zinc was obtained for both charcoal, representing only 1% of desorption.

1.2 1.2

- 1 - 1 ...J ...J • • • • ê> • • • ê> .§. 0.8 • .§. 0.8 • 0:: 0:: • o ,g o 6 0.6 ~ . f • 'E ~ 0.4 •• • 1! 0.4 • 0:: • o 0:: u 02 8 0.2 ••

o.-·-·------~------,------~----~----~ o+----~-­ ---~~--~ o 50 100 150 200 250 o 50 100 150 200 250 Time (min) Time (min)

(a) fine charcoal, distillcd watcr ofpH=5.4 (b) eom·sc charcoaL distillcd water ofpH=5.4

35.0 50.0 45.0 30.0 40.0 ::;- • ~ 25.0 Ch 35.0 .s .s 30.0 ~ 200 ~ ...,]!: 25 .o "E 15.0 :ii 20.0 ~ ~ 100 8 150 u u 10.0 5.0 5.0

00 0.0 +---~---~------~- 50 100 150 200 250 300 50 100 150 200 250 300 Time (mln) Time (min) L______

(c) fine charcoal, sulphuric acid solution of pH = 2,0 (d) coarsc charcoal, sulphuric acid solution ofpH = 2,0

Figure 7- Dcsorption curves for bone char loaded with zmc as a function oftirne 434

Thiago Santos Guedes, Marcelo Borges Mansur and Sônia Denise FctTcira Rocha

Probably, thc zinc rcleased to water was not adsorbcd but only adhcrcd to thc surface ofthc bone char. Whcn desorption was catTicd out with the sulphuric acid solution, the metal conccntration initially incrcascs, thus reaching high valucs, and then decreases, being this phenomena most pronounced for thc fine bone char. This can be attributcd to the precipitation of part of the metal dcsorbcd, dueto thc dissolution of residual carbonate prcscnt in thc bonc char. This is coherent with the final pH values measured in solution, cqual to 5.5 for fine bonc char and 3.5 for coarsc charcoal. Thc levei of dcsorption was 30% for fine charcoal and 40% for coarse charcoal.

4. CONCLUSIONS

lt was observcd that the Brazilian bonc char is similar to the importcd bonc char with similar bchavior in thc remova! of metais from solutions. The adsorption of zinc, cadmium, nickel, cobalt and coppcr was studicd and the Langmuir and Frcundlich models were similar in rcpresenting the systcms. Fine bone char prescntcd highcr loading capacity, but desorption from coarse bone char was better. The mechanism of metal remova! seems to involve an association of carbonatcs precipitation and adsorption, but still descrves investigation. An industrial application requires additional studies in order to determine the cost of the process. It was observed a competition between metais whcn the process was catTied out in column.

5. REFERENCES

Aklil, A.; Mouflih, M.; Sebti, S. Remova! of metal ions from watcr by using calcincd as a new adsorbent. Journa/ of Hazardous Materiais, 2004.

Cheung, C. W.; Choy, K.K.H.; Ko, D.C.K.; McKay, G.; P011er, J. F. S01vtion equilibria of metal ions on bone char. Chemosphere 54, p.2 73-281, 2004.

Cheung, C. \V.; McKay, G.; Porter, J. F. Sorption kinetics for the remova! of copper and zinc from cftluents using bone char. Separation and Puri(ication and Teclmology 19, p.SS-64, 2000.

Choy, K. K. H.; McKay, G. Sorption of cadmium, cooper, and zinc ions onto bone char using Crank diffusion model. Chemosphere, 2005.

Dahbi, S.; Azzi, M.; de la Guardia, M.; Faure, R.; Durand, R. Remova! of trivalent chromium from tannery waste waters using bone charcoal. Analytical and Bioanalytical Chemistry, 2002.

Deliberação Normativa 10/86 do COP AM-MG, 1986.

Guedes, T. S.; Rocha, S. D. F. R. Potencial de adsorção de metais pesados por carvão de ossos bovinos. ln: XXIENTMME, Natal-RN, 2005.

Hanzlík, J.; Jehlicka, J.; Scbek, 0.; Weishauptova, Z.; Machovic, V. Multi-componcnt adsorption of Ag(I), Cd(JI) and Cu(Il) by natural carbonaceous materiais- Water Research 38, p.2178-2184, 2004.

Kadirvelu, K. ; Thamaraiselvi, K.; Namasivayam, C. remova[ ofhcavy metais from industrial wastcwatcrs by adsorption onto preparcd from an agricultura! solid wastc. Bioresource Teclmology 76, p. 63-65, 2001.

Ko, D.C. K., Chun \Vai Cheung., Choy, K.K.H., Por1er, J.F. & McKay, G. Sorption equilibria ofmetal ions on bonc char. Chemosphere, 2003.

Sonume, A., Ghate, R. Devclopments in wastcwater methods. Desalination, 167, 2004.

Wilson, J.A.; Pulford, I.D.; Thomas, S. Sorption of Cu and Zn by bonc charcoal. Enviromnent GenchemisfiJ' and J-Jea!th, v.25, p. 51-56, 2003.

ACKNOWLEDGEMENTS

Authors are grateful to Bonechar- Carvão Ativado do Brasil and also to FAPEMIG- Fundação do Amparo à Pesquisa do Estado de Minas Gerais for the financial suppot1.