Equilibrium Biosorption Kinetics of Lead (II) and Nickel(II) Ions from Aqueous Solution on Snail Shell Derived Chitosan

Abstract

The present research focuses on the use of snail shell derived chitosan as potential adsorbent for removal of Pb(II) and Ni(II) from aqueous solution. The metal binding capacity, pH dependence of metal uptake, contact time, ionic concentration, adsorbent dose, temperature, ionic strength, adsorption capacity and adsorbed metal recovery were investigated. For metal specie Pb(II), the greatest adsorption was obtained when the pH of the solution was 4. When Ni (II) was evaluated, pH 7 was the optimal for its adsorption. About 0.3g of chitosan was found to be enough to remove 97.095% of lead and 68.267% of nickel at the initial concentration of 50mg/L from 30ml aqueous solution in 120mins. The pseudo first order kinetic, pseudo second order kinetic, intra-particle diffusion, Elovich and mass transfer models were used to correlate the kinetic data. The kinetic data were fitted with the pseudo second order kinetic model for both metals. The experimental equilibrium parameters were tested by the biosorption isotherms like Langmuir, Freundlich, and Temkin. Adsorption result fitted with these adsorption isotherms showed that the Tempkin adsorption isotherm fits the data well with correlation coefficient (R2) = 0.991 for lead and 0.972 for nickel while Freundlich isotherm explained the biosorption process with (R2) = 0.892 for nickel and 0.991 for lead. Thermodynamics parameters: Gibbs free energy ΔGo, enthalpy change ΔHo, and entropy change ΔSo were calculated. The result obtained indicated that lead (II) ion adsorption process has a high negative value for ΔGo and nickel (II) ion has a high positive value for ΔGo, a high negative value for ΔHo in both metal biosorption analysis and a negative and positive value for ΔSo in nickel and lead respectively. This shows that the entire process is exothermic (-ΔH), while the lead adsorption process is rapid (-ΔG). From the experimental result snail shell derived chitosan could be used as a biosorbent for treatment of water contaminated with nickel and lead ions.