Lime addition in mining refers to the controlled addition of lime (typically calcium oxide, CaO, also known as quicklime, or calcium hydroxide, Ca(OH)₂, also known as hydrated lime or slaked lime) to ore slurries, process solutions, or waste streams during mineral processing operations. Lime is one of the most widely used chemical reagents in the mining industry due to its versatility, relative low cost, and effectiveness in pH control, reagent recovery, detoxification, and mineral separation across bauxite, gold, iron ore, and diamond mining operations.
In gold mining, lime is used primarily in cyanide leaching circuits to maintain a sufficiently high pH (typically between 10.5 and 11.5) to prevent the formation of toxic hydrogen cyanide gas and to optimize gold dissolution kinetics. Lime is also used in cyanide detoxification processes (such as the INCO SO₂/air process) where pH control is essential for effective cyanide destruction before discharge of tailings solution. In flotation circuits used to process complex gold-copper or gold-sulfide ores, lime is used to depress pyrite and regulate the pulp chemistry to enhance selective flotation of target minerals.
In bauxite processing, lime (as calcium oxide) may be added to the Bayer Process digestion circuit to improve the removal of reactive silica, which would otherwise form sodium aluminum silicate (desilication products) and consume valuable caustic soda. Lime is also added to red mud (bauxite residue) to improve its geotechnical properties and facilitate dry stacking.
In iron ore processing, lime is added in pelletizing plants as a flux to control basicity and improve pellet quality. In diamond processing operations, lime may be used for pH adjustment in dense media separation circuits. Lime is also used widely in tailings dam neutralization and acid mine drainage treatment across all mining commodities.