David M. Collinson

Saline-water bioleaching of chalcopyrite with thermophilic, iron(II)- and sulfur-oxidizing microorganisms

The application of thermoacidophiles for chalcopyrite (CuFeS2) bioleaching in hot, acidic, saline solution was investigated as a possible process route for rapid Cu extraction. The study comprised a discussion of protective mechanisms employed for the survival and/or adaptation of thermoacidophiles to osmotic stress, a compilation of chloride tolerances for three genera of thermoacidophiles applied in bioleaching and an experimental study of the activities of three species in a saline bioleaching system. The data showed that the oxidation rates of iron(II) and reduced inorganic sulfur compounds (tetrathionate) were reduced in the presence of chloride levels well below chloride concentrations in seawater, limiting the applicability of these microorganisms in the bioleaching of CuFeS2 in saline water.

Life in heaps: a review of microbial responses to variable acidity in sulfide mineral bioleaching heaps for metal extraction.

Industrial heap leaching of low grade mineral sulfide ores is catalysed by the use of acidophilic microorganisms. These microorganisms obtain energy for growth from the oxidation of reduced inorganic or organic compounds, including soluble ferrous ion, reduced inorganic sulfur compounds (RISC) and acid-stable organic compounds. By-products of these oxidative processes, such as soluble ferric ion and sulfuric acid create favourable chemical conditions for leaching. This review is focused on the behaviour of common bioleaching microorganisms, their responses to changing pH in an industrial setting, and how both changes and microbial responses can impact the micro and macro environment.

Extremophiles in Mineral Sulphide Heaps: Some Bacterial Responses to Variable Temperature, Acidity and Solution Composition

In heap bioleaching, acidophilic extremophiles contribute to enhanced metal extraction from mineral sulphides through the oxidation of Fe(II) and/or reduced inorganic sulphur compounds (RISC), such as elemental sulphur or mineral sulphides, or the degradation of organic compounds derived from the ore, biota or reagents used during mineral processing. The impacts of variable solution acidity and composition, as well as temperature on the three microbiological functions have been examined for up to four bacterial species found in mineral sulphide heaps. The results indicate that bacteria adapt to sufficiently high metal concentrations (Cu, Ni, Co, Zn, As) to allow them to function in mineral sulphide heaps and, by engaging alternative metabolic pathways, to extend the solution pH range over which growth is sustained. Fluctuating temperatures during start up in sulphide heaps pose the greatest threat to efficient bacterial colonisation. The large masses of ores in bioleaching heaps mean that high temperatures arising from sulphide oxidation are hard to control initially, when the sulphide content of the ore is greatest. During that period, mesophilic and moderately thermophilic bacteria are markedly reduced in both numbers and activity.

The Impact of Heap Self-Heating on Microbial Activity during the Bioleaching of Low-Grade Copper Sulfide Ores

In this study, a dynamically-controlled column was used to evaluate two ores known to cause heap overheating. This enabled the simulation of heap self-heating under controlled conditions. The lixiviant was inoculated with a consortia of mesophilic and moderately thermophilic microorgaisms, and the impact of rapid temperature increases on biological activity and cell numbers was evaluated. During the leaching of ore sample A, the temperature lagged for 29 days before increasing rapidly from 26 to 88 °C. Cell numbers and solution potential increased concomitantly, before both were reduced as the temperature increased past maximum microbial tolerances. Cell numbers began increasing again within 10 days of reaching temperatures that would facilitate mesophilic growth being restored. During the leaching of ore B, the temperature lagged for 4 days before exhibiting a rapid increase in temperature, increasing from 30 to 76 °C over a six-day period. Cell numbers were reduced with the sudden temperature increase, and did not recover over the remainder of the experiment.