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Mining with Microbes.

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Introduction

Mining with Microbes A new method of extracting metals from their ores is being developed that is more, than others before. This alternative technique uses Thiobacillus ferro-oxidan and Thiobacillus thio-oxidan bacteria to leach metal elements from their ores. These bacteria live by oxidising ions found in insoluble minerals of copper. When the bacteria oxidise the S2- ions in the copper mineral, the valuable metal ions are left in solution, from which they can be removed. The microbes work best in acidic conditions (pH 2-3) and in a warm temperature (20-55oC). Firstly, the tailings of ore from previous copper mining are laid on an impermeable. The bacteria are then sprayed onto the piles of ore, in an acidic solution, and left to work. The Thiobacillus ferro-oxidan and Thiobacillus thio-oxidan (T. ferro- and T.thio-oxidan) microbes oxidise S2- and Fe2+ ions thus releasing the copper into solution. The equations for the reactions the bacteria use to live are summarised below: Fe2+ � Fe3+ + e- and S2- + 4H2O � SO42- + 8H+ + 8e- This results in the release of Cu2+ ions into solution: ...read more.

Middle

arsenates, iron oxohydroxdide and gypsum to form a gelatinous precipitate. 397 The gold is then extracted from this mixture using a process called cyanidation. In cyanidation, metallic gold is oxidized and dissolved. The oxidant employed is atmospheric oxygen, which causes the dissolution of gold and the formation of sodium cyanoaurite and sodium hydroxide. The reaction involved with this process is as follows: 4Au + 8NaCN + 2H2O + O2 � 4NaAu(CN)2 + 4NaOH When gold dissolution is complete, the gold-bearing solution is separated from the solids and the gold can be removed by electrolysis. The main advantage of using bacteria to oxidise insoluble ions and release metal ions into solution is the benefit to the environment. During traditional copper extraction, the ore is smelted at very high temperatures, the sulphur in it is converted into sulphur dioxide. This waste gas is the main contributor to acid rain, which in the past before sulphur dioxide emissions were strictly regulated caused major damage to lakes, forests and buildings. ...read more.

Conclusion

It is possible that that acidic rain or river water may slowly dissolve arsenic(V) and release into the water. However, it is unlikely that the concentrations will reach hazardous levels. One reason why microbes are used as a primary extraction process for gold and not copper is the speed at which the microbes work. Companies are hesitant adopt the technology as they will not see the benefits for a long time. Gold however, is much more valuable, so profit can be made although the process takes more time. A new mining process like bacterial leaching must go through several stages before it can operate commercially. Firstly the technology has to be developed on a laboratory scale. Then plans to apply it to field locations have to be produced as well as larger scale prototypes. When the process is well refined (i.e. what works best at what temperatures, pH, pressure e.t.c) the technology has to be applied full scale. Then the necessary adjustments made to previous plants, or new plants constructed. Only when the new process is working effectively and making a profit will the adapted 999 or new plants be operating commercially. 1 Gareth Johns ...read more.

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