PROCESS DESCRIPTION

The GEOLEACH ™ process uses iron and sulfur oxidizing microorganisms to facilitate the oxidation and leaching of sulfide minerals in an engineered whole ore heap environment. These include the mesophiles (moderate temperature) bacteria Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans, and thermophilic (high temperature) microorganisms such as the Archaea Sulfolobus and Acidianus.

GEOLEACH ™ utilizes the latest in industry knowledge associated with acid and bioleaching and adds to it the HotHeap™ operating and control philosophy. HotHeap™ is a process that retains the chemical reaction heat so that heaps can operate at high temperatures, high temperatures translate into faster leaching rates and higher metal extractions. In the case of primary copper sulphides, high temperatures are required to achieve any level of economic copper extraction. Aeration to the heap is controlled according to the oxidation rate within the heap and irrigation rate is controlled according to heap temperature, in a ratio to the aeration rate or to maintain a slight net positive advection in the heap. The GEOLEACH ™ process is suitable for high grade waste or underlying hypogene ores emanating from existing operations, as well as in supergene ores. Benefits of GEOLEACH ™ include reduced inventory, faster leaching rates, higher ultimate copper extraction and lower acid consumption. The economic benefits of GEOLEACH ™ are substantial in all applications. GEOLEACH ™ is also suitable for the recovery of zinc, cobalt and nickel from sulfide ores.

Downstream processing operations depend on the type of mineral being bioleached. In the conventional processing of copper and other base metal sulfides, the valuable metal is solubilized and is recovered from the leach solution, while the residue remains on the pad. “On-off” type pads are now being employed more frequently for copper leaching with the acid leach/oxidized material being off-loaded for secondary leaching or impoundment, and the pad reused. A permanent pad may be used, with the pad area being expanded both vertically and horizontally as required.

The GEOLEACH ™ process employs conventional downstream metals recovery methods which are dependant on the metal solubilized. The following figure shows a simplified flowsheet of the GEOLEACH ® process for treating sulfide copper ores.