Recovery of copper from Chilean mine waste waters

Two copper-containing waste-water streams from a Chilean mine site were identified as potential sources of revenue: Source 1 is raffinate from a copper solvent-extraction circuit; Source 2 originates from a reservoir receiving acid mine drainage as a result of natural snow melt. The streams are currently treated with lime to increase the pH for process and environmental purposes; any dissolved copper is precipitated, which renders it unrecoverable via the mine's conventional sulphide flotation process. These streams contain 80 to 240 mg/L dissolved copper that can be profitably recovered. An options analysis identified four potential technologies that may be applicable: BioteQ (biological or chemical precipitation of copper as the sulfide, which could then be processed through a nearby concentrator or smelter), EMEW (direct electrowinning of copper to produce high-purity saleable copper metal in the form of cylindrical tubes or metal powder), ELSA (a proprietary technology that produces a 95% copper sludge by cementation with iron), and ion exchange (a well-known technology that is widely applied in a variety of waste-water applications, particularly for the removal or recovery of low concentrations of valuable or toxic metals). This paper describes the ion-exchange concept and provides a preliminary process design, financial estimate, and economic feasibility assessment for the application of ion exchange to the recovery of copper from these two waste-water sources. Advantages of ion exchange compared with the other process options are discussed.