Electrophoretic studies of the adsorption of gold and silver from aqueous cyanide solutions onto activated carbon

This study investigates the effects of Au(CN)2−, Ag(CN)2−, and Ca2+ ions in suspension solutions after adsorption onto activated carbon by measuring the zeta potential across various pH levels. It was found that polyvalent cations like Ca2+ significantly reduce the negative zeta potential by interacting with the negatively charged groups on the carbon's surface. In contrast, monovalent cations such as K+ from Au(CN)2− and Ag(CN)2− do not influence the zeta potential in alkaline and weakly acidic conditions. These precious metal cations are believed to adhere to uncharged active sites on activated carbon through chemisorptive interactions. The presence of co-adsorbed cations and anions suggests close spatial positioning on the activated carbon surface. Additionally, in strongly acidic conditions, protons may create new positive sites on the carbon, allowing for the electrostatic adsorption of Au(CN)2− and Ag(CN)2− ions. Notably, in the presence of Ca2+ and Au(CN)2− ions, a complex cation [Ca+ Au(CN)2−]+ may additionally form, enhancing adsorption dynamics.