Immobilization and Adsorption Study Related to the Mechanisms of Lead (II) and Cadmium (II) Retention by Phosphate Rock in Multi-Metal System: Analysis via Differential Pulse Stripping Voltammetry Method

The feasibility of phosphate rock, PR as an adsorbing and immobilizing agent for Cd2+ and Pb2+ in multi-metal solution and the interface reaction of PR and the metals were investigated. The equilibrium concentration of Pb2+ in each solution adsorbed by PR surpassed the detection limit of the analytical method employed (DPASV) such that no peaks of Pb2+ were detectable. This indicates that Pb2+ was highly immobilized during metal retention since very low concentration of Pb2+ remained in the solution compared to Cd. In pH-free and pHcontrolled systems adsorption on PR of Pb was up to 91.96 % while for Cd, adsorption was only about 60-95 % of the initial amount. Three adsorption isotherm models were studied, Freundlich, Langmuir, and Temkin. The equilibrium sorption data were evaluated and found that Langmuir model exhibits the highest correlation coefficient value. In the Langmuir model, the maximum monolayer coverage capacity qm is 81.97 mg/g, Langmuir constant KL is 0.0632, and the separation factor RL is 0.148 which is 0