Assessing a Two-Stage Heap Leaching Process for Platreef Flotation Concentrate

Abstract

The Platreef is a relatively rich ore body in terms of the presence of platinum group metals (PGMs) and base metals (BMs). It differs from the Merensky and UG2 ore bodies in that a significant portion of the PGMs are associated with the silicates or on base metal sulphide-silicate grain boundaries, it has an unfavourable Pt to Pd ratio and although there is significant Au, there is much less Rh and Ru than in the Merensky or UG2 ores. Additionally, a large portion of PGMs occur as bismuth-tellurides and arsenides, which have been observed to be slow floating, requiring high mass pulls to obtain high concentrator recoveries. The high mass pulls invariably leads to grade dilution. Due to this unique mineralogy the conventional process of milling, flotation, smelting and matte pressure leaching leads to marginal process economics, with high energy and water costs, high skilled labour requirements and large capital and operating costs. Moreover, the Platreef resource lies in an arid area of South Africa, with a low skilled labour pool and poor electrical infrastructure. Additionally, a considerable amount of the PGMs will report to the tailings and will not be recoverable by flotation. A novel flowsheet to process this ore is proposed here, which represents a parallel low-cost route, along the standard method.This revolves around a two-stage heap leaching process consisting of a high temperature bioleach to extract base metals followed by a precious metals heap leach. This is currently being evaluated through preliminary bench scale test work. The results so far, which will be presented, have been promising.