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Originally posted by Geeenius
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From WikipediaHPAL process High pressure acid leach processing is employed for two types of nickel laterite ores. 1) Ores with a limonitic character such as the deposits of the Moa district in Cuba and southeast New Caledonia at Goro where nickel is bound in goethite and asbolite. The advantages of HPAL plants are that they are not as selective toward the type of ore minerals, grades and nature of mineralisation. The disadvantage is the energy required to heat the ore material and acid, and the wear and tear hot acid causes upon plant and equipment. Higher energy costs demand higher ore grades. Heap (Atmospheric) Leach Heap leach treatment of nickel laterites is primarily applicable to clay-poor oxide-rich ore types where clay contents are low enough to allow percolation of acid through the heap. Generally, this route of production is much cheaper - up to half the cost of production - due to the lack of need to heat and pressurise the ore and acid. Ore is ground, agglomerated, and perhaps mixed with clay-poor rock, to prevent compaction of the clay-like materials and so maintain permeability. The ore is stacked on impermeable plastic membranes and acid is percolated over the heap, generally for 3 to 4 months, at which stage 60% to 70% of the nickel-cobalt content is liberated into acid solution, which is then neutralised with limestone and a nickel-cobalt hydroxide intermediate product is generated, generally then sent to a smelter for refining.
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One thing tbat is not mentioned is the recoveries are very different HPAL arounf 90% heap leack really 50 to 65%. Also the acid consumption is significantly higher in heap leach at +500kg/t ore while HPAL is 300 to 400kg/t. Acid can make up 40 to 75% of operating cost. Note 3-4 months leach is quick with most taking significantly longer.
