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In 2012, Y. G. Bermúdeza, 1, and his colleagues studied an experimental design technique factorial design 33 in which they used the brown seaweed Sargassum muticum for biosorption of chromium(VI) from the aqueous solutions. The three factors initial metal concentration, sorbent dosage and temperature were considered at three markedly different levels. The algal biomass is highly pH dependent for the biosorption of chromium(VI) and at low pH favors higher metal-ion removal. At pH 2, the S. muticum exhibited the higher Cr(VI) uptake capacity. By using ANOVA, an empirical model was developed and validated which incorporated interaction effects of all parameters and optimization using response surface methodology. The optimization study indicated 84% as maximum removal (a sorbent dosage of 2 g/L with 20 mg/L of metal concentration) at 50o C. Kinetics and isotherm models were obtained at these optimal conditions. Chemical sorption of pseudo-second order kinetically followed the process of biosorption of Cr(VI) with S. muticum. Two-parameter isotherm models (Freundlich, Langmuir and Temkin) were used to analyze the experimental data. The Langmuir model described most appropriate equation for the isotherm profiles.
2012, B. Kiran and A. Kaushik took an indigenously isolated cyanobacterial strain, Lyngbya putealis HH-15 isolated from metal contaminated site and studied treatment of industrial effluent by considering the competitive biosorption in tertiary and quaternary metal system (cadmium, lead, nickel and chromium). Investigation in terms of equilibrium isotherms showed the effect of presence of other metal ions on chromium biosorption and results indicated that the number and type of metal ions in solution influences the uptake capacity of biosorbent. As inferred from determination's coefficient high value, the Freundlich model is lesser applicable to the experimental data as compared to Langmuir. Experimental results and model parameters deduced that the biosorbent in single metal system with quite high biosorption capacity can still be utilized with a reduced efficiency for the removal of chromium from aqueous solution in the presence of other metals like lead, nickel and cadmium.
E. Pehlivan and his team members, explored the sorption potential of Osage Orange (Maclura Pomifera) for the removal of Cr(VI) ion. At the removal of Cr(VI) ion influence of contact time, solution pH, initial metal concentration, amount of biosorbent and ionic strength was studied. In a batch arrangement biosorption of Cr(VI) with pulp and peel was investigated. In aqueous phase, the initial and equilibrium concentrations of Cr(VI) ions were determined by spectro-photometry. The sorption process was pH and concentration dependent. The sorption of Cr(VI) ions increased with a decreasing pH until pH 2. The increase in sorption resulted due to the increase in initial Cr(VI) ions concentration in aqueous phase. The sorption data satisfied the Langmuir sorption model within the concentration range studied. Maximum biosorption capacity by Langmuir sorption model at pH of 2 for M. Pomifera pulp was 0.92 mmol of Cr(VI)/g and for M. Pomifera peel was 0.55 mmol of Cr(VI)/g.
D. H. K. Reddya, c, and his companions developed a cation exchange by means of chemical modification of the biosorbent Moringa leaves powder by esterifying citric acid with NaOH followed by treatment. The modified biosorbent was used for the removal of Ni(II), Cd(II) and Cu(II) from aqueous solution and characterized by XRD,FTIR and SEM techniques. Different operational parameters were studied as the effect of biomass dose, pH, temperature, equilibrium time and initial metal ion concentrations. Kinetic parameters analyzed the experimental data and noticed that pseudo-second-order was followed biosorption of three metal ions. Freundlich, Langmuir, Dubinin-Radushkevich and Temkin isotherm models were used to analyze equilibrium data. The thermodynamic properties, ΔG°, ΔH° and ΔS° showed that biosorption of Cu(II), Cd(II) and Ni(II) were spontaneous onto CAMOL, with feasible temperature range of 293-313 K. In addition, the CAMOL regenerated and re-used for machining.
In June 2012, Y. Dinga, D. Jinga and other members noticed that safe rice supply is threatened by toxic Cadmium metal. Cd from large-scale effluent was potentially removed by Rice straw as it issued a short biosorption equilibrium of 5 min , at a pH range of 2.0-6.0 it has high removal efficiency and high biosorption capacity (13.9 mg g−1). The main Cd biosorption mechanism is Cd2+ ion exchange with Na+, K+, Ca2+ and Mg2+, plus chelation with functional groups such as, Csingle bondO, Cdouble bond; length as m-dashC, Osingle bondH and carboxylic acids. about 80% of the aquatic Cd absorbes and the Cd content in rice straw reaches 8-10 mg g−1 when 0.5% (w/v) rice straw exposed for 3 h to shake 50 mg mL−1 CdSO4 solution at 150 r min−1, which suggests that the metal-enriched rice straw can become high quality bio-ore.
In 2011, W. N.L. dos Santosa, b, , D. D. Cavalcantea, b, c and other members used the natural adsorbent Agave sisalana (sisal fiber) for Cd(II) and Pb(II) ions biosorption. Study of the ions adsorption on the solid phase and quantitative determination was done by flame atomic absorption spectrometry. Specific BET surface area and the sisal structure was investigated by the Fourier Transform Infrared spectroscopy (FTIR). Followings parameters: contact time, pH and biomass amount were considered to investigate the biosorption potential of sisal for the removal of the ions from aqueous solution. To see the adsorption behavior of the ions they used Freundlich and Langmuir isotherms. Sisal showed surface area to adsorption about 0.0233 m2 g− 1, and the functional groups CO, OH as the main contents. Freundlich isotherm proposed solid understanding that interactions between adsorbed molecules accompanies a monolayer sorption with a heterogeneous energetic distribution of active sites. At 296 K and pH 7, the maximum monolayer biosorption capacity was 1.34 mg g− 1 for Pb (II) and 1.85 mg g− 1 for Cd (II). For phase solid, biosorption of cadmium and lead in polluted natural waters be used.
In 2011, I. L. R. Ricoa and his colleagues collected Sargassum muticum, S.m. and Gracilaria caudata, G.c. from coasts of Cuba and tested for biosorption of nickel. At pH 5 for G.c and pH 3 for S.m metal efficiently bounds to it. Adsorption isotherms showed that G.c. was less efficient than S.m. at optimal pH: 45 mg Ni g−1 for G.c and 70 mg Ni g−1 for S.m. adsorption capacity reached to its maximum. In isotherms model, Langmuir equation gave better experimental results than Temkin and Freundlich equations. By varying sorbent dosage, metal concentration, temperature and particle size sorption kinetics were noted and used to develop pseudo-second order rate equation and the intra-particle diffusion equation.
In January,2011 A. Yipmantina, b and his companions used an efficient biosorbent Chondracanthus chamissoi for Pb(II) and Cd(II). With pH increase efficiency of adsorption increases and becomes optimal at pH 4. 1.37 mmol Pb g−1 and 0.76 mmol Cd g−1 were noted to be highest adsorption capability. Cd(II) was preferred over Pb(II) by biosorbent, however these metals were not enough to separate by a simple adsorption step. The uptake kinetics of metal concentration, particle size and sorbent dosage was managed by the resistance to intra-particle diffusion with restricted impact. At that moment they noticed that kinetic uptake and capacity of adsorption will not be improved by grinding the biomass. The Adsorption of metal ions most likely occurs as it interact with carrageenan (as one of biosorbent main part).As stated by HSAB rules, sulfonic groups have less affinity for Cd(II) than for Pb(II).
In 2011, O. L. Kanga and team members experimented the adsorption of Cr(III) at dissimilar pH values (2-6) on Kappaphycus alvarezii waste biomass with the chemical compositions of Cr-Cd and Cr-Cu and 10-50 mg L-1 as initial metal concentration. As adsorption capacities of Cr(III) were somewhat pH dependent, and at pH 3, the adsorption capacity was maximum (0.86 mg g-1). The adsorption capacity was concealed due to the existence of Cd(III) and Cu(II) in the solution and increased as initial metal concentration increases. Freundlich, BET and Langmuir isotherms evaluated the adsorption equilibrium of Cr(III). SEM and FTIR characterized the adsorption mechanisms. Complexation mechanism coupled with ion exchange as the main one.
In 2011, M. López-Mesasa, and the group studied the adsorption ability of cork wastes to remove Pb(II) and Cd(II) from aqueous solutions. They investigated the aqueous pH influence, initial metal concentration and biosorption kinetics, as a pH reliant profile. If the metals were mixed or in individual solutions separately, the adsorption was found maximum for both metals at pH 5. When they studied the mixed metals solution they found that the P-factor approach corroborated competition between the metals and reduction in the Cd(II) uptake, behavior possibly happened as the metal was less attracted towards equivalent active sites of the cork. At the end, the cork's biosorption process modification in morphology and chemical structure was confirmed by SEM and FTIR correspondingly. As not being changed by the process, cork proves to be a competent biomaterial.
In 2010, A. Bhatnagara, b, A.K. Minochaa studied the removal of nickel from water by peel waste of Punica granatum (pomegranate). The biosorption of nickel on pomegranate was studied in batches. Pseudo-second-order kinetic model well explained the adsorption process. 52 mg/g was noted to be the maximum adsorption capacity. The adsorption process was endothermic and the Langmuir model verified the data which showed that the Gibbs free energy is negative, representing the adsorption process is of spontaneous nature. The results show that for nickel removal from aqueous solution pomegranate peel waste can effectively be used.
In 2010, A. Thevannan and team members investigated the biosorption of nickel from nickel sulphate solution by barley straw. Solution pH significantly affect the Nickel uptake at (23 ± 0.5 °C), and among the tested values, pH of 4.85 ± 0.10 shows an enhanced uptake value. The Langmuir equation satisfied the nickel adsorption isotherm. At less than 0.02-0.6 M increase in the solution's ionic strength (IS),reduces the nickel uptake to 12%. Crab shells washed with acid (0.04 mmolg-1) showed lesser nickel uptake than Barley straw (0.61 mmolg-1) demonstrating its higher potential for removal of nickel as an adsorbent.
P. Chakravartya and his colleagues investigated at room temperature the Areca catechu as an adsorbent for cadmium(II) ions from aqueous solution during batches. They studied initial metal concentration, contact time, amount of the biomass, pH of solution. In acidic conditions, removal of metal ions quantitatively by adsorbent was effective and achieved equilibrium at pH 6.0 in 30 min. Dubinin-Radushkevich, Freundlich and Langmuir isotherm models best matched to the equilibrium adsorption data. Biosorption process was of the pseudo-second-order as showed by the kinetic. The FT-IR study exposed that carboxyl, hydroxyl, amine and amide groups were key binding groups for cadmium(II).
N. Barkaa and his companions used low-cost, plentiful and natural adsorbent Scolymus hispanicus L. for removal of Cadmium (II) from aqueous solution using batch process technique. Temperature, biosorbent dosage, pH, initial metal concentration, contact time, and adsorbent particle size were used as average function in adsorption study. With decrease in size of particle and increase in dosage of biosorbent, biosorption percentage increases. With an increase in the initial concentration, the equilibrium metal uptake increases. At pH 6.5, adsorption was maximum and adsorption kinetics data were of pseudo-second-order. Langmuir model described the equilibrium data with maximum adsorption capacity of 54.05 mg/g and adsorption was not depending on temperature. The FT-IR results showed that the functional groups were present in adsorption of Cadmium(II)-loaded and unloaded Scolymus hispanicus L. adsorbent.
J. M. LUOa and group members used an effective adsorbent for removing cadmium known as Rhizopus cohnii (R. cohnii) from wastewater. They examined initial metal concentration, the biomass dose and pH as different adsorption conditions. They simulated the adsorption data by two adsorption models . The cadmium uptake was lower in strong acid than in weak acid. At pH value less than 2.0 approximately no cadmium adsorption took place. Freundlich and Langmuir models best described the adsorption data. Cadmium maximum uptake was 40.5 mgg-1 (0.36 mmolg-1) showed by Langmuir in the optimal conditions, higher than most of the adsorbents even activated carbon and biosorbents. They experienced that after five times of adsorption and desorption process, R. cohnii adsorption capacity was still maintaining about 80%.I. FT-IR results showed that for cadmium adsorption hydroxyl, amino and carboxyl groups were responsible on R. cohnii surface.
In 2009, M. Amini and other members used a biomass Aspergillus niger pretreated by NaOH to study initial Ni(II) concentration, initial solution pH and dosage effects on Ni(II) uptake. For modeling and optimization of adsorption process, experimentation was done in batches. Langmuir, Freundlich and (RSM) Response Surface Methodology were used to check the control of three parameters on the Ni(II) uptake. At initial metal concentration of 30 mg/L Ni(II), biomass dosage of 2.98 g/L and pH 6.25, biomass uptake 4.82 mg/Ni(II) g (70.30%) was achieved. Freundlich and Langmuir fairly described the adsorption isotherm. But RSM approach was comparatively good than Freundlich and Langmuir in Ni(II) adsorption prediction. They also used Ni(II) loaded, NaOH pretreated and untreated Aspergillus niger to study the adsorption mechanism using FT-IR analysis.
D. Gialamouidis and other research members used contact times, biomass concentrations and pH values as conditions to investigate the adsorption of Ni(II) from aqueous solution by Staphylococcus xylosus cells and Pseudomonas sp.. The best determined pH value for S. xylosus was 6.0 and 5.0 for Pseudomonas sp. with biomass concentration of 1.0 g/L for both micro-organisms. Freundlich model best described the adsorption of Ni(II) with highest expected uptake capacity of 89 mg/g for S. xylosus and 508 mg/g for Pseudomonas sp.. About 98% from S. xylosus and 87% from Pseudomonas sp. nickel ions were recovered when biomass was treated with 0.1M HNO3 solution during desorption process which indicates recovery of nickel from biomass is a lot easier.
K. Srividya and K. Mohanty used Catla catla scales In this work the potential of Catla catla scales to remove Cr(VI) ions from aqueous solutions was investigated as a function of agitation speed, initial Cr(VI) concentration, time, biomass dose and initial pH. At 3 hours equilibrium time, 200 rpm agitation, biomass dosage of 0.05 g/L and 1.0 pH they received best adsorption conditions. Freundlich, Dubinin-Radushkevich, Langmuir and Freundlich isotherm models were used to test the equilibrium adsorption data and they also noted that the best suitable for Cr(VI) adsorption is Freundlich model. The adsorption data was analyzed by the Lagergren first-order, intra-particle diffusion and pseudo-second-order and pseudo-second order gave the best association.. FTIR analysis showed that C-O, N-H and O-H groups were main groups to bind Cr(VI).
L. Denga, b and colleagues used non-living green algal Cladophora albida in batch experiments for Cr(VI) adsorption from aqueous solutions. They studied the impact of algal dosage, pH, initial metal concentration, co-existing anions and temperature on C. albida removal efficiency. The change of pH significantly influenced Cr(VI) removal process with considering pH range 1.0-3.0 as optimum. The 2 g L-1 algal dosage was used in experiment as optimum. In first 60 min, the Cr(VI) removal rate of was comparatively fast, after that the rate decreased slowly. They analyzed Cr(VI) and total Cr in solution to study removal process. For Cr(VI) removal, they used both bio-reduction and biosorption. Cr(VI) biosorption was the initial step, moved forward by bio-reduction of Cr(VI) and biosorption of Cr(III). To calculate the practical use of C. albida biomass, they used actual industrial wastewater.
V. Prigionea and research companions studied that biosorption for large amount of metal removal effluents is good rather than using conventional techniques to recover Chromium. They noticed that adsorption of chromium To date most studies about chromium biosorption was done on simulated effluents as organic and inorganic ligands were the problems due to their presence in industrial wastewaters. They studied the characterization of tanning effluent from mycological viewpoint and to remove Cr(III) by different fungal biomasses used same effluent, after the usual treatments, Cr(III) amount was found very low but not enough to be good. The experimentation resulted in Cr(III) removal up to 40%. Different Cr(III) concentrations from synthetic aqueous solutions were tested to remove Cr(III) by the same biomasses to clarify adsorption process mechanism.
In 2008, A. Åžekera and other research members used Spirulina platensis and studied ionic competition, concentration, time, repetitive reactivity and temperature as a function for adsorption of nickel(II), cadmium(II) and lead(II)ions from aqueous solution. The results showed that kinetics were of pseudo second-order. equilibrium of the ions was described by Temkin, Dubinin Radushkevich and Freundlich isotherm models. Single-stage batch adsorption was described by Freundlich isotherm. By ΔS°, ΔH° and ΔG° calculation it was noted that the adsorption process is endothermic. Comparative selectivity of the adsorbent towards Pb2+ was studied in adorption activities for three metal ion system. By repetitive use of S. platensis, large capacity against three metal ions was noted.
Z. Chen, W. Ma and M. Han used treated alga Undaria pinnatifidahas biomass for adsorption of copper and nickel ions from aqueous solution and determined the Temkin, Freundlich and Langmuir equilibrium isotherms, intra-particle, pseudo-first-order and second-order diffusion kinetic model. The pH 3-7, adsorption doze 0.1-0.5 g, initial concentration 5-50 mgL-1 was noted and capacity of specific metal uptake increases with increase in initial metal concentration and decrease with decrease on adsorbent doze. The pH value for copper was 4.0 and 4.7 for nickel at best conditions and nearly 1hour 40 minutes was contact time. 38.82 mgg-1 for copper and 24.71 mgg-1 for nickel was maximum uptake by U. pinnatifida at equilibrium. The results of copper and nickel matched to the Temkin and Langmuir isotherm. Adsorption kinetic of copper and nickel ions was best described by pseudo-second-order model as compared to other models.
A. SarÄ±, M. Tuzen, used the red alga (Ceramium virgatum) to investigate the adsorption of Cd(II) ions. They also studied contact time, pH, temperature and biomass dosage as adsorption process affecting parameters. The adsorption isotherms were described by Dubinin-Radushkevich, Freundlich and Langmuir models. 39.7 mgg-1 was the Cd(II) adsorption capacity of C. virgatum biomass. The D-R isotherm model noted that 12.7 kJmol-1 is mean free energy, which indicates that adsorption process was chemisorption based. At 293-323 K, Cd(II) biosorption was exothermic, spontaneous and feasible as calculated by thermodynamic parameters (ΔS°, ΔH° and ΔG°). Cd(II) biosorption on C. virgatum was of pseudo-second-order kinetics.
T. Fan and other research members used Penicillium simplicissimum for adsorption of Pb(II), Zn(II) and Cd(II) and also studied their thermodynamics, kinetics and isotherms in a batch system. They studied initial metal ions concentration, pH, contact time, biomass dose, co-ions and temperature effects on the adsorption. Langmuir and Redlich-Peterson model best described the adsorption data. Dubini-Radushkevich isotherm, chemical ion-exchange was mainly dependent on free energy value for all metal ions. It was noticed that the rate of adsorption of all metal ions was of pseudo second-order kinetics at different temperature ranges. Pb(II), Zn(II) and Cd(II) ions adsorption on Penicillium simplicissimum were spontaneous and endothermic as showed by ΔS°, ΔH° and ΔG° the thermodynamics constants of adsorption process.
O. M. M. Freitas and other team members used Specifically macro algae marine species (Bifurcaria bifurcata, Laminaria hyperborea , Fucus spiralis and Sargassum muticum) abundantly available at the Portuguese coast for effectively removal of toxic metals such as Pb(II), Zn(II) and Cd(II) from aqueous solutions. In solution 75-100 mg/L was the initial metal ion concentrations. Adsorption capacities of 32.3-50.4 mg/g for lead, 18.6-32.0 mg/g for zinc and 23.9-39.5 mg/g for cadmium was observed respectively. From kinetic studies it was noted that in the first 10 min with 75% of the amount of all algal species uptake of metal was relatively fast. Experimentation was of pseudo-second order kinetics. Initial adsorption stage was significantly contributed by internal diffusion mechanism. They studied from results that macro algae species proves to be a cost-effective and efficient method for removal of heavy metals.
Y.N. Mata and research members used the brown alga Fucus vesiculosus for the removal of copper, lead and cadmium and adsorption data satisfied the Langmuir isotherm model and pseudo-second order kinetics. The Pb ≈Cd< Cu metal uptake order was given by the Langmuir isotherm model and the pseudo-second order kinetic model collectively. Maximum metal uptake given by the Langmuir model was: 1.66 mmol/g for Cu, 1.02 mmol/g for Pb and 0.9626 mmol/g for Cd. According to the Langmuir isotherm model equilibrium constants, the biomass affinity of metals was of the order: Cd<Cu<Pb. Biosorption was completed by complexation with algal carboxyl groups of the adsorbed metals and by calcium, algal protons, metals in solution and other light metals ion exchange. Band shift of sulfonate, hydroxyl and carboxyl groups was shown by FTIR spectra.
In 2007, A. E. Ofomajaa and other member used coconut copra meal for adsorption of cadmium and investigated the process against initial metal concentration and pH of the solution. Initial adsorption rate, the equilibrium capacity, and the adsorption rate constant was determined by the pseudo-second-order kinetic analysis. initial metal concentration and solution were the main factors for adsorption of cadmium by copra meal. Initial adsorption occurred due to the ion exchange. To relate the hydrogen ion concentration change of solution with initial metal concentration and equilibrium adsorption capacity mathematical relationships were developed.
E. Romera and research companions used six different algae (brown, red and green) adsorption capacity to remove of nickel, cadmium, lead, copper and zinc from aqueous solutions. For every single metallic system, the best adsorption conditions were studied. The pH less than 5 for the recovery of Pb and Cu and 6 for Zn, Ni and Cd was optimum. With 0.5 g.L-1 biomass concentration, they obtained the best results. Experimental data satisfied the Langmuir model with the order Ni< Zn< Cu≤ Cd< Pb of adsorption values. With Fucus spiralis, they achieved the best results and lowest level of metal concentration by brown algae in solution. Minimum differences between both theoretical and experimental data was simulated by computer software program.
T. G. P. Vásquez and fellow workers used Rhodococcus opacus to study its adsorption abilities for removal of zinc and cadmium from liquid aqueous streams. On a batch scale, biosorption studies were evaluated on the basis of removal time, initial metal concentration and pH influence. They compared the uptake capacity of Zn2+ and Cd2+ ions adsorbed by R. opacus using Freundlich and Langmuir models. At 26oC and pH 7.0, Cd2+ removal increased up to 60% from 15 ppm initial concentration and Zn removal increased up to 88% from 5 ppm initial concentration. The kinetic constant was 3.37 for Zn2+ and 3.90 g/mg.min for Cd2+ for same initial concentrations and noted that adsorption process was of pseudo-second order.
M. Ziagovaa and other research colleagues used single solutions for adsorption of Cr(VI) and Cd(II) ions by Pseudomonas sp. and Staphylococcus xylosus, and investigated their binary mixture selectivity. They determined Contact time, biomass concentration, pH influence and adsorption of metal was described by Freundlich and Langmuir models. Maximum cadmium uptake capacity was about 278 and 250 mg.g-1 and for chromium 95 and 143 mg.g−1 for both Pseudomonas sp. and S. xylosus. At 5 mg.L-1 Cr(VI) and 10 mg.L-1 Cd(II), Cd(II) ions as the dominant species in binary mixtures reached adsorption selectivity up to 89% for S. xylosus and 96% for Pseudomonas sp. With S. xylosus only, chromium selectivity was about 92%, when chromium (VI) ions were dominant species.
In 2006, X. J. WANGa, b, c and other research companions used dried activated sludge for heavy metal ions removal from aqueous solutions through batches. They determined temperature, initial metal concentration, and solution pH effects. From kinetic studies it was resulted that Pb(II) and Cd(II) uptake process was of pseudo-second-order. The equilibrium matched to both the Freundlich and Langmuir isotherm models. They noticed from the FT-IR results that the binding of amide I group with Pb(II) and Cd(II) ions onto dried activated sludge was the main mechanism of adsorption.
M. Y. Cana and fellow members used cones of Pinus sylvestrisovulate to remove Ni(II) and applied Response Surface Methodology to optimize Ni(II) removal efficiency. For analysis and experimental design, they used a central composite design of 23 full-factorial. The biomass concentration (5-25 g.L-1), pH (2.5-6.5) and initial Ni(II) concentration (10-30 mg.L-1)were considered to be the critical components for removal. They noticed the optimum initial Ni(II) concentration, C0 was 11.175 mg.L-1, biomass concentration, m 18.8 g.L-1 and pH 6.17. Under these circumstances, 99.91% Ni(II) removal efficiency was noted.
Y. LIUa and other research members used living Aspergillus niger for zinc and cadmium removal from aqueous solution. They studied effects of, contact time, initial concentration, agitation rate, temperature and pH on Zn(II) and Cd(II) ions adsorption. The pH value was 6.0 for Zn(II) and 4.0 for Cd(II) at the time of adsorption with 120 r.min-1 agitation rate and 25-30oC temperature for both metals. Under the optimal conditions, at initial concentrations of 150 mg.L-1 for Zn(II) and 75 mg.L-1 for Cd(II), the maximum metal uptake capacities were of 23.70 mg.g-1 and 15.50 mg.g-1 respectively. Adsorption equilibrium took 24 h for zinc and cadmium ions to establish. Adsorption data fitted well to Langmuir model and adsorption was of pseudo-second order kinetics.