Electrowinning of Silver from Non-circulated Silver Nitrate Electrolyte using Spent Graphite Electrodes as Anode

Abstract

The electrowinning of silver from non-circulated aqueous silver nitrate electrolytic bath was investigated using cylindrical graphite rods recovered from spent zinc-carbon batteries as anode and a slab of ultrapure silver metal as cathode. The effects of current density and temperature on product quality, current efficiency, and specific energy consumption were also investigated at voltages ranging from 1.2 to 2.5 V. Visual examination of electrodeposited product at the cathode was combined with analysis of the cathodic product by X-Ray Diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM/EDS), followed by measurement of current efficiency and specific energy consumption. The results indicated that graphite rods recovered from spent zinc-carbon batteries are effective at functioning as anodes for the electrowinning of silver from non-circulated nitrate baths, even at room temperatures. Increasing the current density resulted in an increase in current efficiency, increase in energy consumption and deterioration in electrodeposited product quality, evidenced by the formation of dendrites. Utilisation of voltages above 2.0 V resulted in physical deterioration of the cylindrical graphite at the anode. Analysis by XRD revealed distinct and well defined peaks of silver metal with minor impurities at high current densities. Finally, high concentrations of silver metal (above 99.0 wt%) were revealed by SEM/EDS with minor contamination of aluminium and gold.