Adding the 'bio' to metal extraction
Extracting metal from raw materials traditionally involves pyrometallurgy (smelting) or hydrometallurgy. Of the two, hydrometallurgy is the most environmentally friendly as any waste is soluble and can be more easily contained. However, contaminated waste water still presents pollution problems in some cases. An extension to hydrometallurgy, biohydrometallurgy uses an extra microbial phase to further extract metals from mining wastes, metallurgical slags, metal-bearing scrap and power plant ashes. Recognising the potentially important role of this bioprocess in today's economic and green-orientated climate, the EU-funded 'Biotechnology for Metal bearing materials in Europe' (Biomine) project aimed to integrate biotech processes into metal recovery. Biomine researched introduction of the 'bio' element into all the phases of conventional hydrometallurgy. Processes investigated included bioleaching, bio-oxidation, biosorption, bioreduction, bio-accumulation, bioprecipitation, bioflotation, bioflocculation and biosensors. A classic example is during the bioleaching process of pyrites, an iron mineral. Bioleaching involves numerous sulphur and ferrous oxidising bacteria including Acidithiobacillus ferrooxidans. Traditionally, cyanide, a pollutant, was used for extraction of iron during a process known as heap leaching. Project researchers have commercially evaluated the integration of biotech processes into more traditional metal extraction processes on a small scale. This will provide industry with a fair basis on which to make a decision as to whether incorporation of the biological element will bring about increased recovery. Moreover, it may mean a reduction in costs due to energy savings, access to new resources and compliance with environmental regulations. Biomine has opened up a new perception of biohydrometallurgy from two angles, the geological aspect and processing technologies. Overall, the results show that biotechnology is applicable to extend the potential of metal production within Europe with the added bonus that the processes will not incur a serious threat to the environment.
