Approximately 50% of the world’s copper is produced by Solvent Extraction and Electrowinning. During the solvent extraction process, copper is transferred, via an oxime extractant from the leach solution, to the copper electrowinning electrolyte. Small amounts of iron are also transferred with the copper, due to a small degree of chemical loading and physical entrainment of iron-containing leach solution in the loaded organic. This iron accumulates in the electrowinning circulation and must be controlled.
The conventional method of iron control at most sites is to bleed a volume of electrolyte from electrowinning to the leach circulation. This bleeding is effective in controlling the accumulation of iron but had a number of drawbacks. The bleed from electrowinning results in loss of acid, copper and cobalt sulphate. This has to be made up by addition of cobalt sulphate, high purity water and makeup acid as well as cobalt sulphate to electrowinning and re-extraction of copper.
At acid generating production facilities, the bleed volume increases the volume of leach solution and increases the requirement to bleed from the leach solution (due to a positive water balance). The leach solution bleed is neutralized with lime, and sent to tailings. Bleeding from the leach solution increases costs for neutralization and decreases the steady state iron levels in leach.
The FENIX Iron Control system replaces the bleed system of iron control. The FENIX unit loads iron from the electrowinning solution on a sulphonated monophosphonic acid resin followed by stripping using a novel cuprous sulfate elution solution. The FENIX system delivers significant savings in reagent consumption (acid and cobalt sulphate for electrowinning, lime for neutralization of the raffinate bleed) and has the potential to deliver higher current efficiencies in copper electrowinning, leading to increased copper production.