Lime is a key component in a number of nonferrous metal applications.
Both quicklime and hydrated lime are widely used in the flotation or recovery of many non-ferrous ores -- in particular, copper ore flotation in which lime acts as a depressant (settling aid) and maintains proper alkalinity in the flotation circuit. In the recovery of mercury from cinnabar, lime is used to remove sulfur. Lime is also used in the flotation of zinc, nickel, and lead bearing ores. It is often used as a conserving agent to assist in the recovery of xanthates, another flotation chemical.
Lime is also extensively used in the recovery of gold and silver in the cyanide leaching process to curtail the loss of cyanide, a costly dissolution reagent, and for pH control. To process gold and silver, lime and cyanide are added to gold ore in a cyanide mill’s grinding circuit. The crushed lime, cyanide, and gold are then combined with cyanide and lime solutions. When lime and cyanide solutions are introduced, the gold particles are polished by the grinding action, and the solutions are heated by friction and liberated from the gold ore. Lime has several functions in this process, most notably it maintains proper pH in the cyanide solution, thereby keeping it in the liquid phase, preventing the formation of hydrogen cyanide gas and its loss into the atmosphere.
Alumina & Bauxite
Quicklime is used in varying amounts to remove silica from bauxite ore and for causticization in the manufacture of' alumina. The amount of lime used depends largely on the quality of the bauxite. Purer ores require less lime and more limestone (Sinter process), while ores high in impurities require more lime (Bayer process). In both cases, lime is required for desilification.
Lime is used to produce metallic magnesium. In thermal reduction techniques, magnesium oxide from dolomitic quicklime is reduced with ferrosilicon at high temperatures. This process produces a gaseous magnesium which is ultimately condensed. Lime can also be used in electrolytic processes of magnesium production.
In the smelting and refining of copper, zinc, lead, and other non-ferrous ores, noxious gas fumes of SO2 can be neutralized by passing them through a scrubber with "milk-of-lime" (diluted hydrated lime in an aqueous suspension) to avert the formation of sulfuric acid in the atmosphere as well as the corrosion of plant equipment. After smelting nickel, the nickel is precipitated in a boiling solution with "milk-of-lime." In the electrolytic refining of copper, cathode sheets are dipped in lime water to protect them from sulfur in the "melting down" process. Some plants use lime to reduce zinc chloride from galvanizing skimmings, reclaiming zinc hydroxide in the process. Substantial quantities of quicklime are used as a flux in the manufacture of low-carbon and ferro chromes.
Lime is employed in uranium beneficiation mills operating acid leach systems. Lime neutralizes the acidic waste effluent before discharge.
In the concentration of rock phosphate, lime is used to precipitate the build-up of waste fluorine.