Describe the processes used to extract copper and gold from their ores using bacterial leaching - In each case, explain how the micro-organisms liberate the metal from its ores and describe how the metal is then extracted from the mixture.

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Q1:-   Describe the processes used to extract copper and gold from their ores using bacterial leaching. In each case, explain how the micro-organisms liberate the metal from its ores and describe how the metal is then extracted from the mixture.

Bacterial Leaching of ores and other Materials

Bacterial leaching is a process in which bacteria is used to extract heavy metals from low grade ores and tailings (left from an earlier traditional mining).

In mining industry, bioleaching is a new technique used to extract minerals such copper and Gold from their low grade ores. The main agents used in bioleaching process are micro organisms such as Chemolithoautotrophs; they capture carbon for the synthesis of cellular components not from organic nutrients but from carbon dioxide (CO2) in the atmosphere. These bacteria are Thiobacillus Ferrooxidans and

Thiobacillus Thiooxidans. Thiobacilli grow in acidic environment because they are acidophilic (acid loving). They drive energy by the oxidation of the Ferrous iron and Sulphur part of the mineral for their survival. They grow at PH value from 1 to 4 and strictly under aerobic conditions.

Bacterial Leaching has been divided into two mechanisms:-

  • Direct Mechanism: - Direct mechanism is that in which bacteria is physically attached to the mineral surface. In this reaction, the electron passes into the bacterial cell which produces ATP (Adenotriphosphate), is the energy currency of the cell which reduces oxygen molecules to water.


             
Thiobacillus attached directly to the mineral surface

  • Indirect Mechanism: - In indirect mechanism, bacteria do not need to be in contact with mineral surface.

(200 words)

Extraction of metal (Copper & Gold) from its ores:-

Crushing & Grinding:-

The ore is put into mills with liquid (mostly water). The mill rotates causes ores and liquid to crush against one another, which breaks the ores into smaller pieces. The solution after crushed and grinding is called slurry.

Flotation &Thickener:-

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Liquids called reagents in which one attracts metal and other makes bubbles are added to the slurry in a large container in the presence of air. As agitators mix the slurry, metal and reagents are attracted to each other. After this the heavy metals (copper & Gold) are settled down in the container and the lighter liquid which contains other impurities, reagents and water rests at the top of the container which is then drained away.

Extraction of Gold

Bacterial Leaching of mineral Arsenopyrite (FeAsS):-

The Gold metal can be extracted from minerals like Arsenopyrite, Pyrite,

Chalcopyrite. The bacterial ...

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