| Description |
Gold is an important metal for a variety of uses and applications. A primary method of refining gold is electrowinning; it is used throughout the world and is becoming more and more common not only for gold processing but for other metals as well. To better understand and mitigate the negative effects of gold electrowinning, specifically anode corrosion and emissions, the effects of electrolyte composition (cyanide, chloride, hydroxide, sulfate and silicate), current density, and temperature in electrowinning cells were examined. Stainless steel electrodes were used. The emissions for gold electrowinning were also studied; specifically, ammonia and hydrogen cyanide gas evolution were examined while varying temperature, current density, and concentration of cyanide and hydroxide. The data indicate that the greatest cause of increased anode corrosion rate is temperature. Lower temperatures examined did not cause significant corrosion except in one anode which had high cyanide and high silica. Silica is often used as a corrosion inhibitor and at low concentrations large corrosion rates were not observed, however, very high corrosion rates were observed with high concentrations of silica. At high temperature the greatest contributor to increased corrosion rate was large amounts of silica in the electrolyte. Low ion concentrations in the electrolyte showed sulfate as the greatest contributor to corrosion rate. Cyanide concentration had a small effect on corrosion rate. Corrosion was observed at varied current density, chloride, and hydroxide, however, there was not a significant linear relationship. Significant pitting was observed in the anodes exposed to high levels of chloride. The amount of ammonia evolved from the electrowinning cell was found to be directly proportional to the amount of cyanide loss in any given test. The largest contributor to cyanide destruction was temperature and cyanide concentration. The effects of hydroxide and current density were small and not statistically significant. The evolution of hydrogen cyanide was found to be negligible. |
