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Gold Heap Leach Components
Mine/Ore Source.
The material to be leached at any particular site can be obtained from several sources, such as newly mined ore, previously stockpiled low grade ore, mine ralized waste rock, and/ or milled waste/tailings. Although each of these sources is amenable to heap leach, the majority of currently operations heap leach projects involve newly mined ore derived from open pit mining, this being the most economic technique for development of large volume, low-grade deposits.
Ore preparation.
The metallurgy of the ore dictates the method by which the ore should be pretreated prior to leaching. As a corollary, the pretreatment may also dictate the method and configuration of heap operation and construction. Generally, ores amenable to leaching are of an oxide nature. Depending upon the complex in which the metal is held, the ore is required to be of a particle size to allow solution contact and dissolution. Ore pretreatment can be range from none (for run of mine) to crushing, crushing and agglomeration, or agglomeration only (for fine grained ore or tailings). In addition to these fairly standard pretreatments, chemical pretreatment of sulfidic ores to enhance subsequent leaching has been shown to be technologically feasible, although the associated cost has generally proven uneconomic.
The major purposes of ore preparation for heap leaching are to produce an ore fine enough to allow solution contact with the metals and to have an ore permeable and stable enough to allow an adequate leaching rate through the heap. These requirements may be contradictory in some cases where the optimum leach size results in low permeability. The amount of effort and expense incurred in ore preparation is directly related to the economics of the metal recovery. For example, if the incremental cost of crushing from a coarse to a finer size is not outweighed by the incremental value of increased recovery, finer crushing is not warranted.
