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Bioheap is a pretreatment process of refractory gold ores and concentrates. Gold recovery by cyanidation can be by pretreamt processes. The main advantages of biooxidation compared to other pretreatment methods are lower costs and more environmentall desirable. Heap leaching of fine grain concentrates is not directly possible. In a recent process named "Geocoat", concentrate is coated on a support rock. In the present paper Mouteh gold concentrate was pretreated by Geocoat technique. The results obtained was statistically studied and interpretated. In this investigation three
effective parameters on concentrate coating were studied. The results indicated that loading capacity of mill was the most important factor. Increasing residence time had no significant effect on the coating process. An economic faculy evaluation was required to determine the optimize residence time. Finally, the increasing number of spraying, . cycles, increased coating percentage. Therefore, spraying of concentrate in a continuous manner would be the best choise.