The chemical stability of heavy metal xanthates

The precipitation of lead, copper and iron xanthates was studied as a function of metal and xanthate ion concentration. These precipitates were suspended in aqueous solutions of pH 3.5 to 11.5 and 25° to 60°C. The concentrations of xanthate and metal ions obtained upon dissolution of the metal xanthates were measured to establish their solubilities as functions of pH and temperature. The concurrent hydrolysis and decomposition of these ions led to the formation of insoluble products such as metal sulphides, hydrated oxides and carbonates. These became deposited on the undissolved fraction of the metal xanthate precipitate. The ultraviolet and infrared spectroscopic methods and X-ray diffraction, differential thermal analysis and vapour phase chromatography were used to characterise the products of decomposition. The state of oxidation of copper and iron in the corresponding metal xanthate was investigated with the aid of EPR, ESCA and studies of the Mossbauer effect. Cuprous and ferric ethylxanthates were found to be the stable forms. Ferrous ions did not react with xanthate ions. A hydroxyxanthate of iron was detected at pH 5 to 6 by Mossbauer study. The optimum pH for the formation of dixanthogen in Fe³⁺/(EtX)⁻ system was found to be in the range of 2.5 to 3.7.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat