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The extraction of metals from their ores using micro-organisms.

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Introduction

The extraction of metals from their ores using micro-organisms. New processes for mining. The extraction of Copper. Copper mining has been a main source of copper for many thousands of years. The most common form that copper is found in is in its ores, copper oxides and copper sulphides. Copper can be extracted from its ores by using bacteria this process is called biohydro-metallurgy. The bacteria that are used to extract pure copper are 'Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans these bacteria live by oxidising Fe2+ and S2- ions, these ions are present in insoluble minerals of copper, zinc and lead and the oxidation releases the ions into solution where they can be extracted as metals.'1 Bacteria at work. The waste left over from previous ore crushing, (tailings), are heaped up on ground that is impermeable and the ground is sprayed with a leaching solution which contains Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans, 'this leaching solution is ideal as bacteria thrive in acidic conditions. ...read more.

Middle

The problems that result from roasting and cyanidation mean that only a fraction of the gold is extracted from the sample. 3 Bacteria at work. If the refractory sulphide concentrate is treated with a thermophilic bacterium, Sulpholobus acidocalderius, it helps catalyse the oxidation of sulphide ions and then this resulting mixture, when treated with sodium cyanide, produces a total extraction of the gold. More research lead to the discovery of a mixture of different thermophilic bacterium that worked over a range of temperatures, PHs, and arsenic conditions making it ideal for gold extraction in other countries and increasing the extraction process even more. The bio-oxidation process works in two stages, taking arsenopyrite as an example, the bacteria catalyses the formation of iron(II), arsenic(III) and sulphur(VI): FeAsS Fe(II) + As(III) + S(VI) During the second stage two of the products are oxidised: Fe(II) Fe(III) As(III) As(V) All the products from the oxidation of arsenopyrite are soluble in water, so after the process has taken place the water is treated with hydrated calcium hydroxide, this neutralises sulphuric acid and helps form a layer of iron(III) ...read more.

Conclusion

Bio-oxidation is cost effective, efficient, safe, and environmentally friendly. Compared to roasting, bio-oxidation reduces capital costs by 12-20%, operating costs by 10% and construction time by 25%. The yield of gold is also increased, the process doesn't take months and the process is extremely profitable. By using the bacterial process primarily it eliminates the emissions produced by roasting, large amounts of SO2, As2 and O3, and also the costs of disposing of arsenic. The operation is simple and a skilled workforce isn't required, the plants are also healthier and safer. Only 20% of all the refractory gold treatment plants use bio-oxidation, for this to increase the governments would need to provide funding. Political powers would also need to approve and regulate new processes, checking it is safe and not very environmentally damaging. 5 Sources: 1 Article one - by John Merson, Mining with microbes 2 Article two - extracting copper ions from leaching solutions 3 Article three - by Jack Barrett and Martin Hughes, A Golden Opportunity 4 http://e-mj.com/ar/mining_copper_extraction.htm, 5 http://e-mj.com/ar/mining_bacterial_oxidation.htm, articles from the engineering and mining journal from 1999. 1 Rachel Jeffreys. ...read more.

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