Ion-Exchange of Lead (II) and Cadmium (II) by Brown Coal

Abstract

In this study, the influence of experimental conditions (reaction time, solution pH, initial concentration of metallic ion) on ion-exchange properties of Pb²⁺ and Cd²⁺ by an Australian brown coal was investigated. In order to change the cation-exchange properties, brown coal was heated up to 300°C and the behavior of the cation exchange was also examined. In all samples, the adsorbed amount of metallic ions increased with contact time, and after 60 min the amount of M²⁺ adsorbed reached an equilibrium. Moreover, the amount of M²⁺ adsorbed increased with increasing solution pH and initial concentration of M²⁺. The maximum adsorbed amount of Pb²⁺ and Cd²⁺ from the aqueous solutions at pH 6 was 1.5 and 0.7 mmol/g, respectively. Although the amount of carboxyl groups in the brown coal decreased by heat-treatment, the behavior of cation-exchange for the heat-treated brown coal was similar to that for the untreated brown coal. In the cation-exchange experiment from the solution containing Pb²⁺, Cd²⁺ and so on, the heat-treated brown coal adsorbed Pb²⁺ preferentially.