Gold Bioprocessing

The use of microorganisms in gold processing is an established technique (Brierley, 2008). Specifically, the pre-processing of gold-containing sulfide ores, in stirred tank biooxidation reactors (BIOX®) has been an international commercial success (Rawlings et al., 2003). The biooxidation process enables the liberation of gold encapsulated in sulfide minerals, making the gold available for processing via traditional inorganic routes, such as cyanide leaching followed by electrochemistry (Olson et al., 2003; Brierley, 2010). Although bioleaching is an established technique many opportunities exist for further optimisation of the method, undoubtedly this will be aided by the advancements in molecular techniques (e.g., Demergasso et al., 2003). An exciting opportunity, revealed by the study of gold geomicrobiology, is to use gold-targeting microorganisms to generate cyanide directly onto the surface of the gold-containing minerals, limiting the necessity for transport and reducing the total quantity of cyanide required. Using scanning electron and scanning tunnelling microscopy the microorganism Chromobacterium violaceum was shown to directly attach to the surface of gold, form biofilms and produce cyanide, which in-turn solubilises gold (Fairbrother et al. 2009). This study could lead the way for the development of in situ gold leaching methods, where gold could be targeted and extracted directly from deep sub-surface deposits
In many gold mines large quantities of gold (in some case >20 %) are lost because the gold contained in the rock is low grade or based on its mineralogy and current processing techniques not recoverable. This costs companies money and shortens the life of mines. The advances in our understanding of biogeochemical gold cycling suggest that this can avoided using low-cost biogeochemical approaches. Recent research has shown that microbiota mediate the formation of secondary gold grains, at sites such as the Prophet Gold Mine in Queensland. Laboratory test have shown that recoverable gold grains are former within months. To test this we are have established a collaboration John Parsons (Prophet Gold Mine, Qld.). This research aims to provide a low cost, low tech, environmentally sustainable solution for problem ores, in particular carbonaceous ores that are pre-robbing during cyanidation.