Bacterial succession in bioheap leaching

Bioheap leaching of secondary copper ores is applied commercially at operat ions in Chile, Australia, and Myanmar. Bioheap leaching of sulfidic refract ory gold ores has been demonstrated at large scale. There is Limited compre hension of what actually occurs microbiologically in full-scale bioheap ope rations, despite the commercial achievement of copper ore bioheap leaching and the anticipated technical and commercial success of gold ore bioheap le aching. Copper bioheaps are typically inoculated with the bacteria containe d in the raffinate or intermediate leach solution, whereas, sulfidic refrac tory gold ore bioheaps can be inoculated with bacteria developed in a separ ate reactor. Chemical and physical conditions within bioheaps change radica lly from the time the bioheap is stacked and inoculated until bioleaching i s completed. Redox, acidity, temperature, oxygen and solution chemistry con ditions vary widely during the oxidation period. Such conditions likely sel ect for microoganisms or may, in fact, effect a succession of organisms in portions of the bioheap. Bioheap solutions are recycled and constituent bui ld-up over time also affects the microbiology. Organic entrapment in the ra ffinate from the solvent extraction circuit may influence microbial activit y. Heterotrophic microorganisms may also play some role in bioheap leaching . Understanding the microbiology of bioheaps is key to advancing commercial bioheap applications. Such knowledge will increase the ore types as well a s the diversity of mineral deposits that can be processed by bioheap techno logy. It will also enable better control of conditions to improve leach rat es, metal recoveries and costs. This paper briefly explains commercial prac tices, describes chemical, physical and microbiological monitoring of biohe aps, considers conditions that control microbial populations in bioheaps, a nd examines the types of ore deposits that could be bioleached, if the micr obiology was elucidated. (C) 2001 Elsevier Science B.V. All rights reserved .