The fungal and chemolithotrophic leaching of nickel laterites Challenges and opportunities
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Nickel is an important metal in human life and in the industry. In recent years, the world nickel demand has been driven by soaring steel production, particularly in China. With the rapid growing demand for nickel coupled with the depletion of high grade sulphide reserves, low-grade nickel ores, which cannot be economically processed by conventional metallurgical processes, become increasingly important sources of nickel. Laterite ore, which is often considered as a low-grade nickel ore, contains several kinds of metal elements including nickel, cobalt, iron, silicon, aluminium, and chromium; and thus, constitutes an alternative source of nickel. The nickel present in nickel laterites is not usually present as discrete minerals, but as cations substituted within manganese oxides, goethite, and/or clays. Because of this, it is difficult to upgrade the ore by beneficiation. As a result, nickel laterites are traditionally processed using pyrometallurgical and hydrometallurgical methods. In recent years, microbiological leaching has been found to be a promising novel technology for recovering valuable minerals from traditionally difficult-to-process ores. Microbial leaching of low-grade ores offers many advantages over other conventional methods due to its relative simplicity, requiring mild operating conditions, low capital costs, low energy input, relatively unskilled labour requirements, and being environmentally friendly. Because of the importance of microbial leaching, recent advances in microbial assisted leaching of nickel laterites are discussed in this paper with emphasis on fungal (chemoorganotrophic) and chemolithotrophic microorganisms. 2010 Elsevier B.V. All rights reserved.
