Zinc concentrate leach

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

The example being considered under zinc ore pertains to acid pressure leaching of zinc concentrates developed by Sherritt Gordon Mines Ltd. in Canada. The basic reaction involved is... 

If the low rade ore is a zinc mineral, then zinc concentrate obtained from the flotation process is calcined and leached with water to remove zinc. Silver and lead are left in leach residues. Residues are treated like lead concentrates and fed into lead smelters. Silver is recovered from this lead concentrate by various processes described above. 

Parker, E.G., "Oxidative Pressure Leaching of Zinc Concentrates", Fifth Annual District Six Meeting of CIMM, Kimberley, B.C.,... 

All the ores are concentrated in complex mills by selective froth flotation lu produce individual copper, zinc, lead, and, infrequently, silver concentrates. The copper and lead concentrates are smelted to produce lead and copper bullions from which silver is recovered by electrolytic or fine refining. The silver bearing zinc concentrates are commonly processed by leaching and electrolytic methods. Silver is ultimately recovered as a byproduct from zinc plant residues. Canada is a leading silver mining country. Other important sources of silver are Mexico, die United States, Peru, the former U.S.S.R., and Australia. See also Mineralogy. 

Electrolytic Process—in which oxidized zinc concentrates are leached in sulfuric acid and then electrolyzed to plate SHG (special high-grade zinc metal) on the cathode and to regenerate the add on the anode. 

A. F. Chinn, R. T. McAndrew, R. L. Hummel and J. E. Mouland, Application of Short Bed Reciprocating Flow Ion Exchange to Copper/zinc Separation from Concentrated Leach Solutions, Hydrometallurgy, 30, 431-444 (1992). 

A comparison of heavy metal levels in tap water, borehole water and treated water (Table 3) showed that borehole water had hi concentration of zinc ions (10-17 ppm). Tap water mostly showed non-detectable levels of the ion. This shows that the surface pollution ends up with zinc being leached into underground water. This type of pollution is disturbing and deserves attention. Treated effluent had reduced zinc levels from non-detectable levels to 98ppm (Table 2). The higher levels of zinc could be explained by incomplete precipitation that could have taken place. Further and repeated precipitation procedures can reduce the zinc levels further. 

Commercial installations based on spray-drying technology are currently in use in the mining industries around the world. Examples of products that are spray dried include chromium concentrate, copper concentrate, lead-manganese-molybdenum-tin-zinc concentrate, yellow cake, precious metal slime, zinc leach residue, and rock phosphate. 

The ZPL process consists of an autoclave, in which zinc concentrate reacts with pure oxygen under pressure, and a sulphur separation area. This plant produces a zinc sulphate/jarosite residue sliury which is piunped to the sulphide leaching plant for further processing, and the production of elemental sulphur. 

The complex system of recycle streams betwe i and within each of ftie operating units ensures a higih overall recovery of the major products. For example, lead, bismuth and precious metals are recovered firom both the lead concentrates and the zinc concentrates treated. Recovery of lead is also significantly enhanced by operation of ftie slag fuming and oxide leaching circuits. Lead not recovered directly to bullion in the KIVCET furnace is recycled... 

The capacity was 170,000 tonnes of zinc per year after the 1988 modernisation of the plant. Today the current roasting capacity has been increased to about 190,000 tonnes, see Figure 1. After the 1998 expansion, based on the direct leaching of zinc concentrates, the new total capacity of the Kokkola plant is about 225,000 tonnes of SHG zinc (99.995 %) per year. The latest on-going expansion will further increase both the leaching and roasting capacity to... 

The object of this ptq>er is to describe a process developed to treat a Canadian zinc concentrate. The first part of the paper examines the ferric sulphate leaching of the concentrate. The second part examines the effects of ferrous oxidation by SO2/O2 this reoxidation can be effected in-situ, i.e., during the leach, or ex-situ in a separate vessel. The third part briefly discusses options to treat the resultant leach solution and recover the zinc from it. 

R.W. Adams, P. Mangano, E.G. Roche and S.J. Carpenter, Direct Leaching of Zinc Concentrates at Atmospheric Pressure , Lead-Zinc 90. T.S. Mackey and R.D. Prengaman, Eds., The Minerals, Metals and Materials Society, Wartendale, PA, U.S.A., 1990, 351-372. 

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