Recovery of Silver from Cyanide Solutions Using Electrochemical Process Like Alternative for Merrill-Crowe Process

Abstract

The conventional processes for recovery of silver from cyanide leach solutions are the carbon adsorption, the Merrill-Crowe zinc dust cementation, the Ion Exchange, and Solvent Extraction processes; among other available options for recovery of precious metals from cyanide solutions, Electrocoagulation (EC) is a very promising electrochemical process that does not require high concentrations of silver in cyanide solutions to yield excellent results and neither pretreatment of cyanide solutions like Merrill-Crowe process (deoxygenating and clarification). The present study has been done for the recovery of silver contained in pregnant solution from the cyanidation process using the electrocoagulation technology with iron electrodes, and therefore develops an alternative technology for Merril-Crowe process. The average silver content in pregnant solution was of 52 ppm, recovery was obtained of 99% of silver, with this optimum operating parameters, pH = 8, residence time = 20 minutes and conductivity by addition of sodium chloride = 4 grs/L. Finally the characterization of the solid products formed during the EC process with X-ray Diffraction and Scanning Electronic Microscope was performed, results suggest that magnetite particles and amorphous iron oxyhydroxides are present (Lepidocrocite).