Evaluation of the efficiency of ZnCl2 activated cocoa pod husk charcoal on the removal of Cu2+, Cd2+, and Pb2+ ions from aqueous solution

Abstract

The efficiency of ZnCl2-activated cocoa pod husk charcoal (ACPHC) in removing Pb(II), Cu(II) and Cd(II) ions from aqueous solution was investigated under different conditions of shaking speed, contact time, adsorbent dose, adsorbate concentration, pH, and temperature with a view to widening the applications of the husk. Adsorption equilibrium, kinetics and desorption studies were conducted. Activated carbon produced at 650 °C was found to give the best desired properties. The optimum shaking time and pH value were 45 min and 6. The shaking speed of 700 rpm gave maximum removal efficiency (mean ± sd) 97.02 ± 0.34%, 96.24 ± 0.19%, and 96.85 ± 0.01% for Pb(II), Cu(II), and Cd(II) ions at the optimum pH, 25 °C, and 0.1 g adsorbent/25 ml solution with adsorption capacities of 2.426, 2.406, and 2.421 mg/g, respectively. While the average capacity at the optimum contact time was 2.290 mg/g. Non-linear Temkin and Redlich–Peterson and linear Langmuir isotherm models gave the best description of the adsorption equilibrium of the metal ions onto ACPHC surface, while pseudo-second order kinetics model gave the best description of the adsorption kinetics. The rate of removal of the metal ions was in the order Pb(II) > Cu(II) > Cd(II). The regeneration of the spent adsorbent was efficient with respect to the considered metal ions. The recovery values were 96.72 ± 0.43%, 92.76 ± 0.49%, and 91.66 ± 0.34% for Pb(II), Cu(II), and Cd(II) ions, respectively. Thus ACPHC was found to be an efficient low-cost material for the removal of the studied metal ions from aqueous solution.