Enhanced adsorption of Cu~(2+), Ni~(2+), Cd~(2+) and Zn~(2+) ions onto physico-chemically modified agricultural waste: kinetic, isotherm and thermodynamic studies

摘要

Removal of Cu2+, Ni2+, Cd2+ and Zn2+ ions from single-and multi-component aqueous solution using porous activated carbon (PAC) has been studied. The PAC was prepared by controlling the carbonation temperature of agricultural waste at 500 degrees C and followed by the acid treatment (10 N H2SO4). The structural morphology and elemental composition of PAC have been determined by SEM and EDX, respectively. Batch adsorption studies have been carried out to optimize the adsorption parameters such as solution pH, adsorption dosage, initial metal ion concentration and contact time. Metal ions concentrations have been determined by atomic absorption spectrophotometer. Adsorption kinetic equations (pseudo-first order, pseudo-second order, Elovich and intraparticle kinetic models) have been examined to identify the adsorption process and mechanism using adsorption data of contact time. The adsorption kinetic studies show that the adsorption of metal ions onto the PAC follows the second-order kinetic model, and the maximum adsorption capacities of the Cu2+, Ni2+, Cd2+ and Zn2+ ions were calculated as 57.2, 68.1, 44.2 and 49.3 mg/g, respectively. The adsorption isotherm results suggest that the Freundlich isotherm has been fitted well with experimental data of mono-and multi-layer adsorption. The effect of temperature on the adsorption of (Cu2+, Ni2+, Cd2+ and Zn2+) on PAC has been studied at 298, 303, 308, 313 and 318 K, and thermodynamic parameters such as Gibbs free energy change (Delta G degrees), enthalpy change (Delta H degrees) and entropy change (Delta S degrees) have been evaluated. This study shows that the adsorption process of metal ions onto PACs is endothermic, feasible and spontaneous in nature.