THE CSIRO is currently undergoing pilot-scale testing of bioleaching, which is an alternative to smelting, with an industry partner to evaluate its suitability for incorporation into a commercial bioleaching process.
CSIRO scientist Dr Jason Plumb has isolated a microbe which could lead to a considerable increase in the effectiveness of bioleaching copper from ore.
The minerals industry is constantly searching for better ways to extract metal from ores such as the copper-containing ores chalcocite and chalcopyrite. In recent decades global reserves of chalcocite have been rapidly depleted. Chalcopyrite currently comprises about 80% of the remaining global copper mineral reserve. However it is difficult to extract copper from chalcopyrite using conventional bioleaching technology.
The formation of a ferric hydroxy sulfate precipitate called jarosite on the mineral surface slows the leaching process. As a result, the rate of chalcopyrite bioleaching is very slow at ambient temperatures but increases at temperatures of 60 °C or higher.Dr Plumb obtained samples from a geothermally-heated environment and isolated a novel microbe, which he called JP7.
Dr Plumb then demonstrated that JP7 - a novel species of the genus Acidianus - grew optimally on chalcopyrite at pH 0.8, and at a temperature of 74 °C. The ability of JP7 to grow at such extremes of temperature and pH makes it one of the most extremophilic microbes known to science.
Further experiments were conducted to test the ability of JP7 to bioleach chalcopyrite.Batch bioleaching experiments showed that JP7 leached copper from chalcopyrite even faster than previously described thermophilic organisms.
Bioleaching tests performed at pH 0.8 confirmed the absence of jarosite precipitation on the particles of chalcopyrite. Due to the highly effective bioleaching and the absence of jarosite, the amount of post-leaching residues that remained after bioleaching using JP7 were significantly less when compared with conventional bioleaching. This is of potential value when either disposing of residues or performing further extraction of metals such as gold that may remain in the residues.
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