G.D. FERRONI, Laurentian University L.G. LEDUC, Laurentian University
Title
Chemical and biological leaching of sterile and nonsterile low-grade ore
Abstract Text
The chemolithotrophic bacterium Acidithiobacillus ferrooxidans can be used to leach copper (Cu) and nickel (Ni) from low-grade sulfide-based ores in a process called bioleaching. Lab studies often employ pulverized ore slurries as the substrate, and the pulverized ore is not sterilized. Thus the reactivity of the ore is not changed, but it can be a source of A. ferrooxidans and other microbes. The purpose of this investigation was to compare sterile and nonsterile pulverized ores with regard to the extent of chemical and biological leaching and to maximize the leaching by A. ferrooxidans. Uninoculated (chemical leaching) and inoculated (bioleaching) flasks contained pulverized ore (sterile or nonsterile) and basal salts solution. Replicate flasks were sampled weekly during an approximately two-month incubation period, and Cu and Ni were measured by atomic absorption spectrophotometry. Sterile and nonsterile ores yielded very similar pHs; the pH stabilized at around 3.7 within 10 days and was maintained for the length of the observation period (42 days). For both Cu and Ni, the amount leached chemically was not significantly different for sterile and nonsterile ores. Similarly, the amount leached biologically was not significantly different. Thus, subsequent studies employed sterile ores, which eliminated a possible source of contamination. The pH of the ore slurry was shown to be important as slurries set to pH 1.5 leached significantly more Cu and Ni than slurries set to pH 3.0 and 4.5. Additional experiments examining the optimum pH for bioleaching are underway.
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