Preparation of Carbonaceous Heavy Metal Adsorbent from Shorea Robusta Leaf Litter Using Phosphoric Acid Impregnation

Preparation of Carbonaceous Heavy Metal Adsorbent from Shorea Robusta Leaf Litter Using Phosphoric Acid Impregnation Surya Narayan Dash 1, Ramachandra Murthy.Ch.V 2 1-Sr. Asst. Professor of Chemical Engineering, GMR Institute of Technology, Rajam, Srikakulam Dist., Andhra Pradesh, India 2-Professor & HOD of Chemical Engineering, Andhra University, Visakhapatnam, Andhra Pradesh, India doi:1.688/ijessi.1313 ABSTRACT In the present study, Shorea Robusta leaf litter, a non-convectional material, is proposed as a novel material for preparation of carbonaceous adsorbent impregnated with phosphoric acid, used for the reduction of Zinc and Copper metal ions from aueous phase. For batch process, operating variables studied were adsorbent dose, contact time, initial metal ion concentration, ph and temperature. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly ph-dependent. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modeled using the pseudo-first-order and pseudo-second-order kinetic uations, and intra-particle diffusion model. Among the kinetic models studied, the pseudo-second-order uation was the best applicable model to describe the sorption process. Euilibrium isotherm data were analyzed using the Langmuir, Freundlich and Temkin isotherms. The Langmuir model yields a much better fit than the Freundlich and Temkin models. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The value of H is negative, indicating that the Zinc and Copper adsorption by the simulated activated carbon are exothermic in nature. Key Words: Adsorption, Heavy metals, Isotherms, Kinetics, Shorea Robusta, Thermodynamics 1. Introduction In recent years, the excessive release of heavy metals into the environment is a major concern worldwide. The Zinc and Copper are the prime metals, which are used in manufacturing processes of galvanizing, sheets for roofing and guttering, metal plating, radiator, dye casting, alloys, chemicals, pigments and finally exits from the industry and mining areas as pollutants in the effluent (Altin, e.t. 1983). There are several methods to remove Zinc and Copper from aueous solutions, such as chemical precipitation, ion exchange, electrolysis and carbon adsorption (Amuda, 27 and Ascheh, e.t. 1995) Most of these methods ruire high capital cost, skilled supervision, ruires post treatment, produces toxic byproducts etc. that developing countries may not afford such technologies. Much has been exhibited lately in the use of adsorption techniue for removal of 296

Zinc and Copper from wastewater. A number of sorbents used so far promegranate peel (Ashtoukhy, 28) degreased coffee beans (Baba, 27), dried animal bones (Banat, 2) peanut hull pellets (Brown, 2), fly ash (Demirbas, 28), agricultural products (Carroti, 1997, Cetin, e.t. 27 and Chen, e.t. 23) etc. The intensity of adsorption is very less in most of these above studies. The so far used commercial sorbents uses precursors like wood, bamboo, low rank Turkish coal, coconut shell, saw dust & rice husk etc. (Dash, e.t 28) most of these ruire high operating cost, are limited in supply and costly. Hence withered leaf litter, waste material, which limited use as fodder is used as a precursor in the present paper for the preparation of activated carbon impregnated with phosphoric acid. The leaf litter was already used as adsorbent for the removal of phenol (Mishra, 22) and zinc (Dash, e.t 28) and copper. The prepared activated carbon is used as adsorbent for removal of Zinc and Copper from different concentration aueous metal solutions. 2. Materials and Methods 2.1. Preparation of Activated carbon The withered leaf litter was collected and dried at 5 C in an oven after sorting the twigs; foreign material etc. the sample was then grinded in a ball mill. The resulting powder was sieved to sizes 8 9 mesh. Then the sample were washed with diluted acids, followed by distilled water to remove the foreign materials adhering to these particles and dried at 1 C for 4 hours. The resulting material was washed with dilute HCl and dried again at 1 C for 6 hours. These materials were impregnated (Gupta, e.t. 2) with H 3 PO 4 solution (2N) after soaking of 6 hours. It was dried before carbonization at 5 C for 1 hour in an inert atmosphere. The resulting material was again washed with distilled water and dried for 6 hours. Characterization of the prepared activated carbon was carried out by appropriate procedure. The analysis (Saravanane, 22 and Singh, e.t. 1993) of the modified activated carbon is presented in Table -1. 2.2. Chemicals The aueous solutions of Zn 2+ and Cu 2+ were prepared for this study by dissolving weight uantities of ZnSO 4 and Cu(NO 3 ) 2 in 1 lit of double distilled water to make their synthetic solutions. Solutions of.1m NaOH and.1m HNO 3 were used for ph adjustment. Constant ionic strength.1 N NaNO 3 was used in all experiments. All chemicals used were of analytical grade and were obtained from Merck, Germany. 2.3. Adsorption procedure Batch sorption (Taha, 21) experiments were carried out by adding the adsorbent at room temperature using prepared Zinc solution and Copper solution. A shaker was used to agitate the mixture at 12 rpm and their content was filtered through.45 mm membrane filter (Whatman). Samples were taken at certain intervals for the purpose of studying the dynamics of the sorption process. Otherwise uilibrium was allowed to occur and then the bottles were removed from the 297

shaker for analysis. The sorbent was separated from the samples by centrifugation and the upper layer was analyzed for the metal under consideration using Atomic Adsorption Spectrophotometer following standard procedures. Each experiment was carried out in duplicate and the average results are presented in this work. The adsorption of Zinc and Copper on the developed activated carbon was conducted in 25 ml conical flasks. A known amount of adsorbent was contacted with a known concentration of metal bearing solution in a flask and with working volume of 3 ml at desired temperature and ph. The flasks were shaken at constant speed on a rotary shaker for 1 min, allowing ample time for adsorption uilibrium (pre determined). Samples were taken and adsorbent was separated from medium using Whatman filter paper and the concentration of both ions in the supernatant measured using an Atomic Absorption Spectrophotometer (GBC Avanta Ver 1.32, Australia) at wave lengths of 213.9 nm (for Zn) and 327.4 nm (for Cu), slit width.7 nm and lamp current 3 ma. The amount of adsorption at uilibrium, computed as follows [19] : Co C V (1) X Co C Percent adsorption (%) = 1 C o (mg/g) and the percent adsorption (%) was (2) where C o and C are the initial and uilibrium concentrations (mg/l), V volume of solution, X the weight of activated carbon (g) and C the solution concentration at the end of adsorption. 3. Results and Discussion 3.1 Effect of adsorbent Dose The effect of adsorbent concentration on the removal of Zn 2+ and Cu 2+ were studied by varying the dose of adsorbent from 7 g/l at fixed amount of ph, temperature and sorbate concentration. The adsorption of Zn increases from % 72.25% as the adsorbent dose increases from 7g/L. Similarly the adsorption of copper increases from % 7.96 % as the adsorbent dose increases from 7 g/l. This is due to the increased availability of active adsorption sites arising due to the increase in effective surface area resulting from the increases in dose of adsorbent or due to conglomeration of the adsorbent (Meikap, 25 and Mehmet, 27). So by optimizing the adsorbent dose it was found that the optimum uptake of Zn and Cu would occur at 3.8 g/l and 3.2 g/l respectively. It indicates that the optimum adsorbent dose for adsorption of Zinc and Copper are 3.8 g/l and 3.2 g/l respectively. 3.2 Effect of Contact Time 298

Experiments were conducted for the effect of contact time on the adsorption of Zinc and Copper. It was found that the rate of removal of Zinc and Copper metal ions increases with increase in contact time to some extent. Further increase in contact time does not increase the uptake due to deposition of metal ions on the available adsorption sites on the adsorbent material. So taking the optimum adsorbent doses and varying the contact time it is found that up to 3 min (for Zn) and 45 min (for Cu), the uptake of metal ions increases and remains constant in further increasing the contact time. The removals are around 82.63 % and 8.65 % for Zinc and Copper respectively. Therefore the optimum contact time for the removal of Zinc metal is 3 min and Copper is 45 min. For further optimization of other parameters, the contact time was considered as the uilibrium time corresponding to the adsorbent and adsorbate. 3.3 Effect of Initial Metal ion Concentration From the experiment the rate of sorption of zinc ions decreased from 82.63 % - 7.12 % as the concentration increases from 1 1 mg/l. Similarly the rate of sorption of copper ions decreased from 8.65 % - 7.62 % as the concentration increases from 1 1 mg/l. Hence it is clear that as the initial Zinc and Copper metal concentrations increases, the adsorption rate decreases. 3.4 Effects of ph The ph of the wastewater or the aueous solution is an important controlling factor (Abollino, 23) in the adsorption process and thus the role of hydrogen ion concentration was examined from the solution at different ph. It was observed in the present investigations that with the increase in ph of the solution, the extent of removal of the Zinc and Copper ions increases. The extent of removal of zinc was investigated at solution ion concentrations of 1 mg/l 1 mg/l from ph 1 9. By changing the ph from 1 9 it was observed that the highest uptake of metal ion for 1 mg/l solution occurs at ph of 1. (Fig. 1). This happens due to that as the ph increases the activated carbon surface changes. Similarly, the uptake of copper ions increases with increases in ph from 1 6 (Fig. 2) and then decreases. Therefore the optimum ph of solution for maximum uptake of copper ion is 6.. This means that at higher H + ion concentration, the adsorbent surface becomes more positively charged, thus reducing the attraction between adsorbent and metal ions. Adjustment of ph was accurately made in adsorbate solutions of various concentrations by using.1m NaOH and.1m HNO 3 solutions. 3.5 Effects of Temperature From the experiments, by varying the temperature of the metal solution from 3 C 6 C we found that the removal capacity of both the metals using the sorbent decreases which were shown in the Fig. 3 and Fig. 4. 299

3.6 Adsorption Isotherm Studies In order to determine the adsorption potential of the biosorbent, the study of sorption isotherm is essential in selecting an adsorbent for the removal of Zinc & Copper. Two important physiochemical aspects for the evaluation of the adsorption process as a unit operation are the uilibria of the adsorption and the kinetics. An uilibrium study gives the capacity of the adsorbent. The uilibrium relationships between adsorbent and adsorbate are described by adsorption isotherms, usually the ratio between the uantity adsorbed and that remaining in solution at a fixed temperature at uilibrium. The most widely used isotherm uation for modeling uilibrium (Yong, 27) is the Langmuir uation, based on the assumption that there is a finite number of binding sites which are homogeneously distributed over the adsorbent surface, these binding sites have the same affinity for adsorption of a single molecular layer and there is no interaction between adsorbed molecules. The Langmuir isotherm expressed as: C 1 1 C (3) K where a max max is the adsorbate loading (mg/g) at uilibrium, C the uilibrium concentration in the fluid (mg/l), max the adsorption capacity (mg/g) and K a sorption uilibrium constant (L/mg). max represents a practical limiting adsorption capacity when the surface is fully covered with heavy metal ions and assists in the comparison of adsorption performance, particularly in cases where the sorbent did not reach its full saturation in experiments. A plot (Fig. 5 and 6) of C versus C should indicate a straight line of slope 1 max and an intercept of1 K a max. The Freundlich isotherm is the earliest known relationship describing the adsorption uation and is often expressed as: e K C (4) f 1/ n e where, e = x / m, the amount adsorbed (mg/g) C e = the uilibrium concentration of the adsorbate (mg/l) K f = the Freundlich constant related to the adsorption capacity 1/n = the Freundlich constant related to the adsorption intensity This above uation is conveniently used in the linear form by taking the logarithmic of both sides as: 1 ln e ln K f ln C (5) e n When ln e was plotted against ln C e, straight lines with slopes 1/n were obtained (Fig. 7 and Fig. 8), which shows that the adsorption of Zinc and Copper follows the Freundlich isotherm. The Freundlich constants K f, 1/n and R 2 values are calculated from Fig. 7 and Fig. 8 and the values at different temperatures are tabulated in Table 2 and 3. 3

The Temkin isotherm is also often used for represent the uilibrium adsorptive behavior between two phases composing the adsorption system. The Temkin isotherm is expressed as: e a bln C e (6) where, x e =, the amount adsorbed (mg/g) m C e = the uilibrium concentration of the adsorbate (mg/l) a, b = Constant related to energy and capacity of adsorption. When e was plotted against ln C e, straight line were obtained (Fig. 9 and Fig. 1), which shows that the adsorption of Zinc and Copper follows the Temkin isotherm. The constants a, b and R 2 values are calculated from Fig. 9 and Fig. 1 and the values at different temperatures are tabulated in table - 3. The linearized Langmuir, Freundlich and Temkin adsorption isotherms of Zinc & Copper ions obtained at the temperatures 3, 4, 5 and 6 ºC at their respective optimum ph values are given in Figs. 8-13 respectively. The K F, 1/ n, max, K a, a and b values evaluated from the isotherms at different temperatures with the correlation coefficients are also presented in Table-2 and 3. 3.7 Sorption Kinetics Kinetics and uilibrium of adsorption are the two major parameters to evaluate adsorption dynamics. It is important that a kinetic model is basically a mass balance which involves different variables describing mass transfer mechanisms within the adsorbent particle. It should not be regarded as a mathematical uation formulating the intra-particle diffusion rate. This is a very important point that is generally overlooked. In fact several kinetic models, currently in use, prove inaduate because of the applied simplifications alter the mass balance within the particle. The different kinetic models are like pseudo first order and pseudo second order. The first order rate uation of Lagergren is one of the most widely used for the sorption of a solute from the liuid solution and is represented as: ln ln K (7) t e t e 1, ad where, e is the mass of metal adsorbed at uilibrium (mg/g), t is the mass of metal adsorbed at time t (mg/g) and K 1, ad is the first order reaction rate constant (L/min). The pseudofirst order considers the rate of occupation of adsorption sites to be proportional to the number of unoccupied sites. A straight line of ln e t verses t indicates the application of the first-order kinetic model (Fig. 11 and Fig. 12). A pseudo-second-order uation based on the adsorption uilibrium capacity may be expressed as: t 2 t K2, ade where, 1 t e (8) K 2, ad is then second order reaction rate uilibrium constant (g/mg.min). A plot 31

(Fig. 13 and Fig. 14) of second order kinetic. t t verses t should give a linear relationship for the applicability of the 3.8 Determination of Thermodynamic Parameters Thermodynamic parameters such as enthalpy change G and entropy change S can be estimated using uilibrium constants changing with temperature. The free energy change of the sorption reaction is given by the following uation: G RT ln (9) K a H, free energy change where G is standard free energy change, J; R the universal gas constant, 8.314 Jmol -1 K -1 and T the absolute temperature, K. The free energy change indicates the degree of spontaneity of the adsorption process and the negative value reflects a more energetically favorable adsorption. The uilibrium constant may be expressed in terms of enthalpy change of adsorption as a function of temperature as follows: d ln K a H (1) 2 dt RT According to E. (1), the effect of temperature on the uilibrium constant K a is determined by the sign of H. Thus when H is positive, i.e., when the adsorption is endothermic, an increase in T results in an increase in K. Conversely, when H is negative, i.e., when the a adsorption is exothermic, an increase in T causes a decrease in K a. This implies a shift of the adsorption uilibrium to the left. The integrated form of E. (1) becomes H ln K a Y (11) RT E (11) can be rearranged to obtain RT ln K a H TRY (12) where S is RY. The change with temperature of the free energy change and the uilibrium constant can be represented as follows: G H TS (13) H S ln K a (14) RT R E (14) shows clearly that the adsorption process (Aguado, 29 and Sikaily, 27) is composed of two contributions, enthalpy and entropic, which characterize whether the reaction is spontaneous. The free energy changes for the zinc and copper adsorption to activated carbon were determined by using the uilibrium constants obtained from Langmuir isotherm model. The G and -TS values at different temperatures (3, 4, 5, 6 ºC) are given in Table.4. As seen from Table.4, the values of G confirm the feasibility of the process with a high 32

preference of zinc and copper on the activated carbon at lower temperatures. However, the entropic contribution is even larger than the free energy of adsorption G H TS. Therefore, it can be said that the adsorption of zinc and copper ions is entropically governed. From the ln K versus 1 T plot (Fig.15 and 16), the standard enthalpy change was obtained for a zinc as -39.69 kjmol -1 and for copper as -29.13 kjmol -1. The value of indicating that the sorption reaction is exothermic. H is negative, Table 1. Analysis of Activated carbon Moisture Content 8.24 % Ash Content 16.85 % Average Particle size.296 mm Matter Soluble in.241 mg/l water Matter soluble in Acid.286 mg/l ph with water 5.92 Iron Content.25 mg Decolorizing Power 5.81 Porosity 68 % Bulk Density 382.5 kg/m 3 Table 2: Estimated isotherm models and their constant values for Zinc Temp ( C) C Langmuir Isotherm 1 1 C K a max max Freundlich Euation 1 ln e ln K f ln C n e Temkin Euation a bln e C e R 2 K a max R 2 K f R 2 a b 33

3.9876.31 26.6.976 6.394.4896.9792 7.6112 5.48 4.9934.118 3.3.9871 3.72.6162.969 2.523 5.9797 5.9912.65 35.21.9736 2.495.7168.982 -.9812 6.7293 6.9986.42 36.23.9888 1.828.7386.9653-2.9592 6.4285 Temp ( C) Table 3: Estimated isotherm models and their constant values for Copper C Langmuir Isotherm 1 1 C K a max max Freundlich Euation 1 ln e ln K f ln C n e Temkin Euation a bln e C e R 2 K a max R 2 K f R 2 a b 3.9941.13 38.17.9857 4.985.6123.974 3.8881 7.5354 4.9984.6 45.66.9851 3.45.7224.9694-1.3794 8.4162 5.9944.37 49.2.9875 2.15.7669.9661-4.539 8.3166 6.999.27 49.26.9883 1.622.7863.9658-6.1778 7.968 Table 4: Estimated the Kinetic parameters in adsorption of Zn and Cu Metal Pseudo First Order Kinetic Model Pseudo Second Order Kinetic Model Ion e (Exp) K 1 e (Cal) R 2 K 2 e (Cal) R 2 Zinc 2.17.1167 2.83.982.148 3.6.9951 Copper 2.52.826 2.77.9842.221 3.28.9992 Table 5: Estimated the thermodynamic parameters in adsorption of Zn and Cu Temp. ( C) Metals 3 4 5 6 Thermodynamic parameters ΔG (kjmol -1 ) -TΔS (kjmol -1 ) Zn 2.95 58.78 Cu 5.14 49.9 Zn 5.56 6.72 Cu 7.32 5.71 Zn 7.34 62.66 Cu 8.85 52.33 Zn 8.78 64.6 Cu 1. 53.95 34

Metal Uptake, e e e INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 25 2 15 1 5 1 2 3 4 5 Ce ph=1 ph=2 ph=3 ph=4 ph=5 ph=6 ph=7 ph=8 ph=9 Figure 1 Effect of ph for Zinc adsorption 25 Ce Vs e 2 15 1 5 1 2 3 4 5 Ce ph=1 ph=2 ph=3 ph=4 ph=5 ph=6 ph=7 ph=8 ph=9 Figure 2 Effect of ph for Copper adsorption 25 2 15 1 5 1 2 3 4 Euilibrium Concentration, Ce For 3 C For 4 C For 5 C For 6 C 35

ce/e ce/e Metal Uptake, e INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 Figure 3 Effect of Temperature for uptake of Zinc 3 25 2 15 1 5 1 2 3 4 Euilibrium Concentration, Ce For 3 C For 4 C For 5 C For 6 C Figure 4 Effect of Temperature for uptake of Copper 2.5 2 1.5 1.5 1 2 3 4 ce 3 C 4 C 5 C 6 C Figure 5 Langmuir Isotherm for Zinc adsorption 1.8 1.6 1.4 1.2 1.8.6.4.2 5 1 15 2 25 3 35 ce 3 C 4 C 5 C 6 C 36

ln e ln e INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 Figure 6 Langmuir Isotherm for Copper adsorption 3.5 3 2.5 2 1.5 1.5-1 1 2 3 4 ln Ce 3 C 4 C 5 C 6 C Figure 7 Freundlich Isotherm for Zinc adsorption 3.5 3 2.5 2 1.5 1.5 1 2 3 4 ln Ce 3 C 4 C 5 C 6 C Figure 8 Freundlich Isotherm for Copper adsorption 37

ln (e-t) e e INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 25 2 15 1 5-1 1 2 3 4 ln Ce 3 C 4 C 5 C 6 C Figure 9 Temkin Isotherm for Zinc adsorption 3 25 2 15 1 5-5 1 2 3 4 ln Ce 3 C 4 C 5 C 6 C Figure 1 Temkin Isotherm for Copper adsorption 1st order kinetic plot 1..5. -.5-1. Zn -1.5-2. -2.5 5 1 15 2 25 3 Time t, min 38

ln (e-t) INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 Figure 11 First-order kinetic plot for Zinc adsorption 1st order kinetic plot 1..5. -.5-1. -1.5 Cu -2. -2.5-3. 1 2 3 4 5 Time t, min Figure 12 First-order kinetic plot for Copper adsorption Figure 13 Second-order kinetic plot for Zinc adsorption 39

ln Ka INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21 Figure 14 Second-order kinetic plot for Copper adsorption..29 -.5.3.31.32.33.34-1. -1.5-2. -2.5-3. -3.5-4. -4.5 1/T Zn Figure 15 ln K a vs. 1/T plot for Zinc adsorption 31

ln Ka INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 3,21..29 -.5.3.31.32.33.34-1. -1.5-2. -2.5-3. -3.5-4. -4.5 1/T Cu Figure 16 ln K a vs. 1/T plot for Copper adsorption 4. Conclusions Results on the adsorption of zinc and copper metals from prepared metal solutions by using carbonaceous adsorbent prepared from Shorea Robusta leaf litter impregnated with phosphoric acid as adsorbent showed that this material is an effective adsorbent for the removal of zinc and copper from aueous solutions. The adsorption of zinc and copper by the activated carbon increases by increases the amount of carbon dose and uilibrium occurs at 3.8 g/l for Zinc and 3.2 g/l for Copper respectively. The adsorption of zinc and copper are also increases with in increase of contact time. The maximum sorption reaches after 3min for zinc and 45 min for copper of operations. The sorption capacity decreases with increase in the initial zinc and copper metal ion concentration in the aueous solutions. The adsorption of zinc and copper varies with ph of the aueous solution and maximum reaches at the ph of 1. for zinc and 6. for copper in these experiments. The adsorption of both metals decreases with increase in temperature of metal solutions from 3 C to 6 C. Adsorption of both the metal ions on to the activated carbon surface more satisfied the Langmuir isotherm as compared to Freundlich and Temkin isotherms. Modeling of sorption kinetics showed good agreement of the experimental data with pseudo-second-order kinetic uation for both the metals. The value of H is negative, indicating that the zinc and copper adsorption by the simulated activated carbon are exothermic in nature. 5. References A. Demirbas. (28). Heavy metal adsorption onto agro-based waste materials: A review. Journal of Hazardous Materials. 157: pp. 22-229. A. E. Sikaily. (27). Removal of toxic chromium from waste water using green alga Ulva lactuca and its activated carbon. Journal of Hazardous Materials. 148: pp. 216 228. 311

2. B.C. Meikap. (25). Removal of chromium(vi) from dilute aueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride. Chemical Engg. Sc. 6: pp. 349-359. 3. D. Ascheh and Z. Duvanjak. (1995). Adsorption of copper and chromium by Aspergillus carbonaruius. Biotechnol Prog. 11: pp. 638-642. 4. E. A. Mehmet. (27). Heavy metal adsorption by modified oak sawdust: Thermodynamics and kinetics. Journal of Hazardous Materials. 141: pp. 77-85. 5. E. Ashtoukhy. (28). Removal of Copper (II) and Copper (II) from aueous solution using promegranate peel as a new adsorbent. Desalination. 223: pp. 162-173. 6. F. Banat. (2). Batch zinc removal from aueous solutions using dried animal bones. Separation Purification Technology. 18: pp. 177-184. 7. J. Aguado. (29). Aueous heavy metals removal by adsorption on aminefunctionalized mesoporous silica. Journal of Hazardous Materials. 163: pp. 213-221. 8. J. P. Chen and L. Wang. (23). Characterization of metal adsorption kinetic properties in batch and fixed bed reactors. Chemosphere. 9. L. Monser and N. Adhoum. (22). Modified activated carbon for the removal of copper, zinc, chromium and cyanide from wastewater. Separation and Purification Technology. 26: pp. 137-146. Abollino. (23). Adsorption of heavy metals on Na-montmorillonite, Effect of ph and organic substances. Water Research. 37: pp. 1619-1627. Altin, H.O. Ozbelge and T. Dogu. (1983). Use of general purpose adsorption isotherms for heavy metal-clay mineral interaction, J Colloid Interface Sc. 198: pp. 13-14. S. Amuda. (27). Removal of heavy metal from industrial wastewater using modified activated coconut shell carbon, Biochemical Engg Journal. 36: pp. 174-181. 1. P. Brown. (2). Evaluation of the adsorptive capacity of peanut hull pellets for heavy metals in solution. Advance in Environmental Research. 4: pp. 19-29. 11. P. M. J. Carroti. (1997). Influence of surface ionization on the adsorption of aueous zinc species by activated carbons. Carbon. 35(3): pp. 43-41. 312

12. R. D. Singh and N. S. Rawat. (1993). Adsorption and recovery of Zn (II) ions by fly ash in aueous media. Indian J. Environ Health. 35: pp. 262-267. 13. R. Saravanane. (22). Efficiency of Chemically Modified Low Cost Adsorbents for the Removal of Heavy Metals from Wastewater: A Comparative Study. Indian J. Environmental Health. 44: pp. 78-87. 14. S. Cetin and E. Pehlivan. (27). The use of fly ash as a low cost, environmentally friendly alternative to activated carbon for the removal of heavy metals from aueous solutions. Colloids & Surfaces. 298: pp. 83-87. 15. S. Mishra. (22). Effect of leaf litter (Shorea Robusta) on the Phenol Concentration in the Aueous Media. Indian J. Environmental Protection. 2: pp. 121 127. 16. S. N. Dash and P.S. Sagar. (28). Adsorption of zinc metal from paper mills wastewater by activated carbon prepared from Shorea Robusta leaf litter. Int. Jour. of Nature Environ. & Pollution Techn. 7: pp. 117-122. 17. S. O. Yong. (27). Heavy metal adsorption by a formulated zeolite-portland cement mixture. Journal of Hazardous Materials. 147: pp. 91-96. 18. S. Taha. (21). Heavy metals removal by adsorption onto peanut husks carbon: characterization, kinetic study and modeling, Separation and Purification Technology. 24: pp. 389-41. 19. V. K. Gupta and I. Ali. (2). Utilization of bagasse fly ash (a sugar industry waste) for the removal of copper and zinc from wastewater. Separation Purification Technology. 18: pp. 131-14. 2. Y. Baba. (27). Removal characteristics of metal ions using degreased coffee beans: Adsorption uilibrium of Cadmium (II). Bioresource Tech. 98: pp. 2787-2791. 313