Lime is used in the metallurgical processing of different copper ore types, ranging from flotation of copper sulphide minerals to leaching of copper oxides by acid lixiviants. The main products from such operations are copper concentrates (containing 25 – 30% Cu) and copper cathodes (>99% Cu). Lime, also known as quicklime, is also used to manage, limit, or treat potential impacts from acid mine drainage.
Copper sulphide minerals are recovered from ore as a mineral concentrate in multiple steps. The first step is to separate non-sulphide minerals that are of no value (called gangue minerals), from sulphide minerals. Copper sulphide minerals are then separated from iron sulphide minerals (e.g., pyrite).
Lime is used to control the mineral slurry pH and to render mineral surface properties suitable for copper mineral flotation and pyrite depression. Additionally, lime can be used to limit corrosion of steel balls used in the milling steps preceding flotation.
Some copper ore types are not amenable to physical mineral separation by flotation. Such ore types are subjected to leaching in heaps or tanks, typically using sulphuric acid, resulting in the dissolution of copper and other impurities.
Copper is recovered from solution by solvent extraction and electrowinning, while dissolved impurities remain in the solution. In higher rainfall geographies, such soluble impurities risk being leached from the residue during rainfall events causing environmental contamination. Lime is used to precipitate such soluble impurities to prevent environmental discharge.