Foam fractionation of cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III)

Abstract

An experimental investigation is presented of the batch foam fractionation of the cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III) from 1.0 × 10 −5 M (metal concentration) alkaline aqueous solutions, with the cationic surfactant hexadecyltrimethylammonium chloride. The effects are established of the presence of CN − over the concentration range 2.5 × 10 −5M−1.0 M, of the presence of NO 3 − over the concentration range 0.05–0.75 M, and of interferences to metal foam fractionation provided by 0.50 M concentrations of NO 3 −, Br −, CN −, Cl − or SO 4 2−. Results are discussed in terms of the complex cyanide species of each metal that may have been present and in terms of the extent of hydration of the complex cyanide anions and of the potentially-interfering simple anions. The selectivity sequence, Au(CN) 4 −Hg(CN) 4 2−Cd(CN) 4 2−Zn(CN) 4 2− is established, both from data for single-metal solutions and for solutions containing equimolar concentrations of all four metals. A partial separation of the metals can be achieved in the presence of high concentrations of NO 3 −, which can be improved by taking maximum advantage of flotation rate differences.