Lead & Zinc
Due to the low zinc and lead content, run-of-mine lead-zinc ores must be concentrated before downstream processes such as hydrometallurgy or pyrometallurgy.
Processing begins with multi-stage crushing and grinding. Crushing is usually a dry process, with primary crushing at the mine using a jaw crusher, followed by cone crushers. The ore is then wet ground in rod and ball mills to achieve the desired particle size.
Lead-zinc ores can be processed using gravity separation or flotation, depending on the ore characteristics:
Lead-zinc minerals can be effectively treated by gravity separation due to the significant difference between their specific gravities and that of the associated gangue. Depending on the ore characteristics, beneficiation may involve either multi-stage cleaning with advanced gravity separators or a pre-concentration stage using gravity methods (commonly heavy media) followed by flotation.
If mineral veins detach cleanly from the host rock, the ore can be upgraded into coarse particles through gravity separation methods, such as shaking tables or jigs.
When the liberation degree of lead-zinc ore is low, fine grinding becomes necessary. Under such conditions, flotation is the preferred beneficiation method for complex sulfide ores. The finely ground particles are introduced into the flotation circuit. In differential flotation, lead minerals are recovered first by depressing zinc; zinc is then activated and subsequently floated. If the ore also contains lead-zinc oxides or carbonates, their separation follows the recovery of sulfides.
With the depletion of sulfide ores and the increasing demand for oxide resources, the sulfidization–flotation route is employed to process oxide, sulfate, and carbonate Pb-Zn minerals. This method modifies the mineral surfaces by converting the oxidized layer into a sulfide surface, which is more hydrophobic and thus more amenable to flotation.
Since the final concentrates contain significant amounts of water, they are transferred to concentrate thickeners for dewatering before filtration. The end product is a filter cake with a residual moisture content of about 8–9%.