Bacterial succession in bioheap leaching

Bioheap leaching of secondary copper ores is applied commercially at operat ions in Chile and Australia. Bioheap leaching of sulfidic refractory gold o res has been demonstrated at large scale. There is limited comprehension of what actually occurs microbiologically in full-scale bioheap operations, d espite the commercial achievement of copper ore bioheap leaching and the an ticipated technical and commercial success of gold ore bioheap leaching. Co pper bioheaps are typically inoculated with the bacteria contained in the r affinate, whereas, sulfidic refractory gold ore bioheaps can be inoculated with bacteria developed in a separate reactor. Chemical and physical condit ions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed. Redox, acidity, temperature, oxygen and solution chemistry conditions can vary widely during the oxidat ion period. Such conditions likely select for microorganisms or may, in fac t, effect a succession of organisms in portions of the bioheap. Bioheap sol utions are recycled and constituent build-up over time also affects the mic robiology. Heterotrophic microorganisms may also play some role in bioheap leaching. Understanding the microbiology of bioheaps is key to advancing co mmercial bioheap applications. Such knowledge will increase the ore types a s well as the diversity of mineral deposits that can be processed by biohea p technology. It will also enable better control of conditions to improve l each rates, metal recoveries and costs. This paper briefly explains commerc ial practices, describes chemical, physical and microbiological monitoring of bioheap, considers conditions that control microbial populations in bioh eaps, and examines the types of ore deposits that could be bioleached, if t he microbiology was elucidated.