Copper beneficiation may consists of: crushing and grinding, washing, filtration, sorting and sizing, gravity concentration, flotation, roasting, autoclaving, chlorination, dump and in situ leaching, ion exchange, solvent extraction, electrowinning, and precipitation. Crushing and grinding is the most energy intensive.
Hydrometallurgical copper recovery is the extraction and recovery of copper from ores using aqueous solutions. Hydrometallurgical operations include the following:
(1) acid extraction of copper from oxide ores;
(2) oxidation and dissolution of sulfides in waste rock from mining or in situ ore bodies (e.g., low grade oxide and sulfide mine wastes);
(3) dissolution of copper from concentrates to avoid conventional smelting. In summary, the copper-bearing ore (and in some cases, the overburden) is leached, then the copper is recovered from the pregnant leachate through precipitation, SX/EW.
Dump leaching is the simplest form of hydrometallurgical beneficiation of low-grade ores, waste rock, and overburden practiced at large, open-pit copper mines. Dump leaching is a method of treating copper ore that has been extracted from a deposit. This method refers to the leaching of oxide and low-grade sulfide ore on typically unlined surfaces. These operations involve the application of leaching solution, which is usually a dilute sulfuric acid solution, collection of pregnant leach solution (PLS), and extraction of copper by SX/EW or cementation. Natural precipitation or mine water is generally used to leach low-grade sulfide ore, while dilute sulfuric acid is commonly used to leach oxide ores. Copper dump leaches are massive, ranging in height from 20 to hundreds of feet, covering hundreds of acres and containing millions of tons of ore. Dump leaching operations may take place over several years.
There are several other types of leaching operations: in situ, heap or pile, vat, and heat or agitated leaching. In some cases, roasting is employed prior to leaching in order to enhance the leachability of the material. In roasting, heat is applied to the ore which enhances its amenability to leaching without destroying the physical structure of the ore particles. The roasted material is then subjected to leaching as described above. The copper-rich leachate, referred to as “pregnant solution,” is subjected to further beneficiation while the waste material is either left in place (in the case of dump, in situ, heap, or pile leaching) or managed in tailing ponds (as in vat, heat, or agitated leaching). The major potential environmental impact of hydrometallurgical beneficiation involves acid seepage into the ground. In addition, hydrometallurgical sludges may contain undissolved metals, acids, and large quantities of water.
Copper is removed from the pregnant leachate through either iron precipitation (or cementation) or solvent extraction and electrowinning. In cementation, once the most popular method for recovering copper from the pregnant leachate, the leachate is combined with detinned iron in a scrap iron cone or vibrating cementation mill where the iron replaces the copper in the solution. The copper precipitates are removed for subsequent pyrometallurgical processing.
In solvent extraction, now the most popular process, an organic chemical (chelator) that binds copper but not impurity metals is dissolved in an organic solvent (often kerosene). The chemical is then mixed with the pregnant leach solution. The copper-laden organic solution is separated from the leachate in a settling tank. Sulfuric acid is then added to the pregnant organic mixture, which strips the copper into an electrolytic solution ready for electrowinning. The barren leachate (or raffinate) is sent back to the leaching system. Electrowinning is the recovery of copper from the loaded electrolyte solution produced by solvent extraction, yielding refined copper metal. The copper-poor (or lean) electrolyte from electrowinning is returned to the SX plant. Excess lean electrolyte from the SX unit is returned to the raffinate pond to be recycled into the leaching circuit. Filter clay is used to filter the electrolyte. Impurities left on the bottom of the electrowinning cells are referred to as “muds” or “slimes.” Both this anode sludge and lead anodes that are no longer usable are periodically removed from the cells and sent to lead smelting facilities for resource recovery. Electrowinning is functionally equivalent to electrolytic refining, but differs in that electrowinning uses a permanent, insoluble anode.
Last update: February 20, 2012
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