What is Bioleaching?

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Bioleaching is a method used for extraction of precious and base metals from hard to treat ore with the aid of bacterial microorganism. Bioleaching is used to recover copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver and cobalt. Bioleaching is considered to be an efficient and an ecological friendly process commonly used by the miners as an alternative method to roasting or smelting, especially when there are lower concentrations of metal in the ore. Bioleaching produces no offensive gases as it is a hydro metallurgical form of treatment. The process involves the bacteria feeding on the nutrients in the ore there by separating the metal. The metal can then be collected from the bottom of the solution. Bioleaching is possible because of the unique microorganism’s ability to react and breakdown the mineral deposits in the ore. Bioleaching technology was first developed by Bactech Mining Corporation (REB gold Corporation) effective December 2010. The registered trademark for REB gold’s bioleaching technology is BACOX.  

What is mechanism involved in Bioleaching?

Bioleaching refers to the use of bacteria, primarily Thiobacillus ferrooxidans, Leptospirillum ferrooxidans and Thermophilic species of Sulfobacillus, Acidianus and Sulfolobus to leach metals of value such as Copper, Zinc, Uranium, Nickel and Cobalt from sulphide mineral ore.These bacteria tolerate acids and metabolize sulphur. The bacteria act as a catalyst to accelerate the natural processes inside the ore. The particular bacteria use a chemical reaction known as “Oxidation reaction” to convert metal sulphide crystals into sulphates and sheer metals.

Oxidation reaction is the reaction where a substance loses its electrons. The element parts of ore are separated into precious metals and the unused sulphur and other acidic chemicals. At the end of the process, adequate materials build up at the bottom of waste solution, which is then filtered to get to the pure metal. Only those ores that contain sulphur can only be bioleached, since the bacteria feed on sulphur. For certain types of metals, like Copper, bioleaching process is the primary choice as it is very low in terms of costs, even though it is a relatively slow process (compared to smelting). For certain developing parts of the world or with respect to some metals, this environment-friendly, effective and economical procedure offers an elegant alternative.

What are the projects that are carried out in Bioleaching?

Several bioleaching projects are being carried out for bioleaching copper. About 20% of extracted copper comes from bioleaching. The most significant research is carried by the Chilean National Copper Corporation (CODELCO) and BHP Billiton. The proposal aims for the large scale build out of a plant for the bioleaching of copper concentrates. Similar large scale project using bioleaching is being carried on in Mexico and also in Chile.

What are the advantages of Bioleaching?

• Bioleaching is much better and cleaner than the heap leaching using Cyanide
• Significant advantage of bioleaching method is found in the pretreatment of refractory gold in ores and concentrates with high arsenic content. This is because, the bacteria tends to attract the arsenic minerals and oxidizes it
•  It does not also contaminate the environment and so it is a eco- friendly process
• Operating the bioleaching plant is very simple, as bacteria do most of the work
• Bioleaching is a relatively low cost procedure, compared to other options such as roasting or smelting

Many countries can benefit from the bioleaching technology by increasing their efforts in this methodology. Most of the developing countries do not have the infrastructure or principal investment required for smelting. Especially those developing countries where the land has sufficient ore, can experience a dramatic transformation in their nation's economy with the adoption of bioleaching to extract essential metals.

For more information on related topics. click on the links below:

Anerobic bacteria and how they help

Other metabolic processes that have Industrial applications