Gold Bio-Oxidation Process Alternative
The Bio-Oxidation process is an alternative to the processes before mentioned, and its applicability has been accepted. The success of the process depends on the activity of some micro-organism (e.g. thiobacillus ferrooxidans) and ability to oxidize sulphur and produce sulphates, and also to oxidize ferrous ion to ferric ion.
Thiobacillus ferrooxidans is an aerobic, acidophilic, rod-shaped, autotrophic, gram-negative bacterium. It is approximately 0.5 µm in width and 2 µm in length. Presents isoelectric point in the range 4.0 – 5.0, and its normal temperature is 28 – 35 oC.
The main source of energy is ferrous ion, but sulphur and other reduced compounds can be utilized. Also, this bacterium takes basic nutrients such as N, P, K, and Mg so that can complete his metabolism.
Sulphide oxidation as bio-hydrometallurgical process involves metabolic, enzymatic, and no-enzymatic reactions. In the process, insoluble material is oxidized and other metals are liberated into the solution. The oxidation can be done by direct attack on the mineral surface or by action of products formed during previous reactions. The mechanism is very complex, and is considered a process influenced by direct and indirect mechanisms.
Once finished the process, the pulp is neutralized and sent to cyanidation.
Conditions are listed below.
Bacterium: thiobacilius ferrooxidants
- Solids: 25%
- Temperature: 25 – 30 oC
- pH: 1.8
- Fe +3: 25 ppm
- Inoculation: 1.1 x !07 bacterium/mL
- Bacterial volume: 5 liters
- Time: 80 – 290 hours
The next tables show results obtained.
Oxidation.
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