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The use of Micro-organisms to extract metals from their ores.

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Introduction

The use of Micro-organisms to extract metals from their ores In 1752, a stream of blue-green liquid running from excavated rock at the Rio Tinto mine, was noticed, which when passing over old iron implements, left a brown film. On scraping this film off, it was pure copper. Initially, they thought, the copper ions were being leached from the ore-crushing waste by inorganic chemical reactions, such as those used to extract metals from their ores. In 1947, microbiologists discovered that this transformation was due to micro-organisms. Thiobacillus thio-oxidans obtain their energy through oxidising S2- ions. They are present in insoluble minerals of copper, zinc and lead. Their oxidation by bacteria releases metal ions into solution. Humans require an expensive, high temperature smelting process to achieve similar results. In the 1980s, the exhaustion of high-grade ores and the decreasing copper prices caused the failing of the copper industry. They turned to cost effective and less polluting technologies. ...read more.

Middle

An acidic leaching solution, containing bacteria is pumped down the central hole. Pumped from the other holes is the resulting solution, rich in copper ions. The miners are reluctant to use biological processes due to their slowness. They have finally been applied to low-grade ores where traditional methods aren't cost-effective. If metals could be extracted from lower grade ores, tailings sites could be transformed into sources of raw materials instead of pollution. Research on biological techniques of metal extraction is rare, but experts see environmental regulations as key to encouraging research. This is rejected by the mining industry, arguing that it has always been advancing research barriers, searching for new techniques e.g. they funded the biohydrometallurgy research. If society wants the mining industry to protect the environment, they must accept higher prices. Gold mining is risky, after finding deposits, the gold's extraction is also difficult. Roughly 30% of the world's gold reserves occur as microscopic particles of gold encapsulated in a mineral matrix. ...read more.

Conclusion

Equation 3 2nd stage: separate oxidation reactions: Fe(II) Fe(III) Equation 4 As(III) As(V) Equation 5 Wastewater is treated with limestone, neutralising the sulphuric(VI) acid, causing the precipitation of iron(III) arsenates, FeO(OH) and CaSO4.2H2O. Possibly, the precipitated material and dissolve arsenic(V) into water, but the highest concentration in such rivers doesn't reach the US limit. They couldn't progress beyond the 1dm3 reaction vessel before the technology was sold to BacTech, who progressed to a 450 dm3 laboratory plant, then to a 32 m3 transportable plant which was used for test runs around the world, giving excellent results under varied conditions. 11 years later, the first full-scale plant using this process was commissioned. The mine operated as an open-cut until 1992, when accessible oxide layers became uneconomic. In 1993, underground mining allowed access to the deeper layers. The mining process can be seen in diagram 4. The cost of running this plant is low because they use locally Quarried calcrete to neutralise effluent and the oxidised concentrate. Other reagents are bacterial nutrients, mainly in the form of ammonium phosphate. Recent work shows that bacterial recovery of base metals is feasible and economically competitive. Diagram 2 ...read more.

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