Abstract
Biomining, the biotechnology that uses microorganisms to extract metals from ores and concentrates, is currently used exclusively for processing reduced ores and mine wastes. Metals of economic value also occur extensively in oxidized ores, such as nickel laterites. While these are not amenable to oxidative dissolution, the ferric iron minerals they contain can, in theory, be disrupted by iron reduction, causing associated metals to be released. We have harnessed the ability of the facultatively anaerobic, acidophilic bacterium Acidithiobacillus ferroooxidans to couple the oxidation of elemental sulphur to the reduction of ferric iron in the goethite fraction of a limonitic nickel ore at 30 °C. Nickel and other metals (Co, Cr and Mn) were effectively solubilised and maintained in solution due to the low pH (1.8) of the leach liquor. The results highlight the potential for the bioprocessing of oxidized, iron-rich ores using an approach that is energy-saving and environmentally-benign compared with metallurgical processes currently applied to the extraction of Ni from lateritic ores.
Highlights
Bioprocessing of metal ores and mineral concentrates has, over the past 50 years, developed from a low-key technology (“dump” leaching of waste rocks at copper mines in the USA) to far more controlled and sophisticated operations involving irrigated and aerated heaps and temperature, aeration- and pH-controlled stirred tanks, each typically ~1000 m3 in size [1,2]
We have explored the possibility that iron reduction carried out at low pH by At. ferrooxidans could be used to mediate the dissolution of ferric iron minerals present in nickel laterites, thereby facilitating the solubilisation and recovery of the nickel and other metals of economic interest present in the ore
The novel approach demonstrated in this work has a number of advantages over hydro/pyrometallurgical processes and previously proposed techniques for bioprocessing nickel laterites, including: (i) the use of a relatively low-cost inorganic energy source to fuel the process; (ii) operation at ambient temperatures; (iii) much smaller biomass production compared to using heterotrophic microorganisms, such as fungi, as the sources of organic acids; and (iv) the low pH (
Summary
Bioprocessing of metal ores and mineral concentrates has, over the past 50 years, developed from a low-key technology (“dump” leaching of waste rocks at copper mines in the USA) to far more controlled and sophisticated operations involving irrigated and aerated heaps The metal-hosting minerals in ores and concentrates currently amenable to biomining are all reduced and mostly sulphidic. The intimate association of base metals with ferric iron minerals in limonites means that these ores are not amenable to processing by conventional oxidative mechanisms employed in biomining. Bioprocessing of nickel laterites has previously been explored (using either iron-chelating organic or strong mineral acids produced as by-products of microbial metabolism), slow rates and low yields of nickel extraction have precluded these approaches being developed as commercial operations. Mediate the dissolution of ferric iron minerals present in nickel laterites, thereby facilitating the solubilisation and recovery of the nickel and other metals of economic interest present in the ore Such an approach represents, in essence, a reverse of the processes involved in conventional biomining
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