The Isa Process was originally developed for the CRL copper electrorefinery in Townsville. It was subsequently licensed to the Copper Range Company for its White Pine copper refinery.
The next licence issued was for an electrowinning application at the Broken Hill Associated Smelters (“BHAS”) lead smelter at Port Pirie, in South Australia. BHAS commissioned in 1985 a solvent extraction and electrowinning (“SX–EW”) to recover copper from copper–lead matte produced as a by-product of the lead smelting operations. The process used involves leaching the copper from the material using an acidic chloride–sulfate solution, followed by solvent extraction to concentrate the leached copper and electrowinning.
Electrowinning copper differs from electrorefining in that electrorefining uses a copper anode that is dissolved and redeposited on the cathode, while in electrowinning the copper is already in solution and is extracted from the solution by passing a current through the solution using an inert lead-alloy anode, and a cathode.
The chloride in the leach solution at Port Pirie proved to be a problem for the stainless steel cathodes of the Isa Process. A small amount of the chloride ions in the leach solution passed through the solvent into the electrolyte, leading to a reported chloride concentration of 80 milligrams per liter (“mg/L”) in the electrolyte. The presence of the chloride in the electrolyte caused pitting corrosion of the stainless steel cathode plates. After trying other types of stainless steel, BHAS switched to using titanium cathode plates.
Other electrowinning operations followed, including Gibraltar Mines’ McLeese Lake operation and Magma Copper’s San Manuel copper mine in 1986, the Mexicana de Cananea operation in Mexico in 1989, and the Gunpowder Copper Limited operation at Gunpowder in north-west Queensland 1990. These operations did not suffer the chloride corrosion problems experienced by BHAS.