Abstract
This review has as its underlying premise the need to become proficient in delivering a suite of element or metal products from polymetallic ores to avoid the predicted exhaustion of key metals in demand in technological societies. Many technologies, proven or still to be developed, will assist in meeting the demands of the next generation for trace and rare metals, potentially including the broader application of biohydrometallurgy for the extraction of multiple metals from low-grade and complex ores. Developed biotechnologies that could be applied are briefly reviewed and some of the difficulties to be overcome highlighted. Examples of the bioleaching of polymetallic mineral resources using different combinations of those technologies are described for polymetallic sulfide concentrates, low-grade sulfide and oxidised ores. Three areas for further research are: (i) the development of sophisticated continuous vat bioreactors with additional controls; (ii) in situ and in stope bioleaching and the need to solve problems associated with microbial activity in that scenario; and (iii) the exploitation of sulfur-oxidising microorganisms that, under specific anaerobic leaching conditions, reduce and solubilise refractory iron(III) or manganese(IV) compounds containing multiple elements. Finally, with the successful applications of stirred tank bioleaching to a polymetallic tailings dump and heap bioleaching to a polymetallic black schist ore, there is no reason why those proven technologies should not be more widely applied.
Highlights
There are strong drivers to become more efficient in metal extraction because, for some metals, discoveries of new high-grade deposits or large low-grade deposits are too few to match the predicted growing demand
Estimates such as these highlight the need for new discoveries, more efficient element extraction from known reserves, the processing of mine waste or tailings and the recycling of industrial and urban metal-rich waste The focus of this review is on the extraction of metals from minerals, polymetallic ores, waste or tailings, using proven biotechnologies and highlighting some innovative potential variants
While ferric ions may be released directly during the dissolution of some gangue minerals, for example chamosite (FeII3MgFeIII)5AlSi3AlO10(OH)8, the iron-rich end-member of the chlorite group of minerals, or nontronite Na0.3FeIII2(Si,Al)4O10(OH)2·nH2O), a swelling clay found in some ores, it is mainly regenerated from ferrous ion oxidation by acidophilic microorganisms (reaction (9))
Summary
There are strong drivers to become more efficient in metal extraction because, for some metals, discoveries of new high-grade deposits or large low-grade deposits are too few to match the predicted growing demand. Estimates of the same order for metals depletion within 50 years (Cu, Pb, Mn, Ag, Sn, Zn) and within 100 years (Fe, Ni, U) were obtained independently [6] and it was suggested that the platinum group metals would be exhausted in 150 years Estimates such as these highlight the need for new discoveries, more efficient element extraction from known reserves, the processing of mine waste or tailings and the recycling of industrial and urban metal-rich waste The focus of this review is on the extraction of metals from minerals, polymetallic ores, waste or tailings, using proven biotechnologies and highlighting some innovative potential variants. There are many applications in which microorganisms mobilise or immobilise elements in the environment using innovative biochemical processes Those processes and applications of bioleaching, biooxidation and bioreduction not targeting metals extraction have been excluded in order to keep the review to manageable size. The review does not include data on metal recovery from manufactured products, sludges, electronic waste, etc.; topics for which there are already substantial bodies of literature, including some informative reviews [13,14,15,16,17,18]
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