Microbial leaching

 

Microbial ore leaching (bioleaching) is the process of extracting metals from ores using microorganisms. This method is used to recover many different precious metals like copper, lead, zinc, gold, silver, and nickel. Microorganisms are used because they can:

• ·        lower the production costs.
• ·         cause less environmental pollution in comparison to the traditional leaching methods.
• ·         very efficiently extract metals when their concentration in the ore is low.

As high grade ores which contain higher metal content are getting depleted, ores with low metal content are tried for extracting metals. But low grade ores are not suitable for direct smelting (extracting (metal) from its ore by a process involving heating and melting), unlike high grade ores. Hence microorganisms which can act on low grade ores and extract the metal are employed in bioleaching/bio mining.

Microbial recovery of metals is called microbial mining/bio hydro metallurgy. Metals are extracted from sulfide/sulfur containing low grade ores are using the activity of sulfur oxidising bacteria such as Thiobacillus ferroxidans, Sulfolobus etc

This process is commercially used for low grade copper and uranium ores. Can also be uised for recovering nickel zinc, cobalt, tin, cadmium, molybdenum, lead, antimony, arsenic, selenium etc from low grade sulfide ores.

Bioleaching reactions industrially are performed by many bacterial species that can oxidize ferrous iron and sulfur. Sulfur oxidising bacteria such as Thiobacillus ferroxidans, Sulfolobus etc, some fungi (Aspergillus niger and Penicillium simplicissimum) have also been shown to have the ability to dissolute heavy metals. When fungi are used, the leaching mechanism is different. The fungi use the acids that they produce in their metabolic reactions to dissolve the metal.

In general, bioleaching is cleaner and safer for the environment than chemical processing. However environmental pollution with toxic products, like sulfuric acid from the pyrite leaching, and heavy metals is still possible. Another drawback of microbial leaching is the slow rate at which microbes work