Adsorption of Pb(II) ions from aqueous solutions using chemically treated and untreated cow dung ash

Abstract

Batch experiments were conducted to evaluate the removal of Pb(II) ions from aqueous solutions using chemically and thermally activated cow dung (CTAC) ash and non-chemically but thermally activated cow dung (NTAC) ash under various experimental conditions. The optimum pH for the adsorption process using CTAC and NTAC was 5, while the optimum times using CTAC and NTAC were 240 and 180 min, respectively. Freundlich, Temkin, and Langmuir isotherm models were used to analyze the generated adsorption data. The Freundlich model had the highest coefficient of determination (R2) values that ranged from 0.989 to 0.999. The values of separation factor (RL) deduced from Langmuir isotherm were between 0 and 1 for both CTAC and NTAC ashes for the whole temperature range, which indicated favourable adsorption. Adsorption of the Pb(II) ions followed the pseudo-second-order kinetic model based on the R2 values that approached unity. Thermodynamic analyses revealed that the ΔH° values for CTAC and NTAC ashes were -8.69 and -11.39 kJ/mol, respectively, which indicated that ion adsorption was exothermic. Negative ∆S° values for the two adsorbents showed that the level of entropy was low at the solid/solvent interface during the adsorption process.