Copper(I) selective chemisorption on magnetite (Fe3O4) over gold(I) ions in chloride solution with cyanide

Abstract

The potential sweep method, adsorption kinetics and isotherm studies, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) after adsorption tests of copper(I) and gold(I) ions using magnetite were performed to investigate the mechanism of selective copper(I) adsorption over gold(I) ion from chloride solution with small amount of cyanide. The electrochemical analysis reveals that the reduction potential is −0.81 V for Au and + 0.38 V for copper (vs. Ag/AgCl) which lead to selective adsorption of Cu over Au from chloride solution with cyanide because the adsorption could be achieved when the reduction potential of the metal ion is higher that of Fe2O3/Fe3O4 pair in the magnetite. By the kinetics and isotherm studies, the chemisorption was found to be well fitted to the pseudo-second-order model and monolayer adsorption of Cu ions on the surface of magnetite. The XPS and TEM results indicates that the ratio of Fe(II) in the iron of the magnetite decreased from 74% to 43% due to the oxidation. Consequently, the mechanism of adsorption using magnetite was depends on the reduction potential of metal ions to selectively receive electrons generated during the oxidation of magnetite in the chloride solution with cyanide.