BIOLEACHING

BY SREEREMYA

Introduction• Future sustainable development requires measures to

reduce the dependence on nonrenewable raw materials and the demand for

primary resources. New resources for metals must be developed with the aid of novel technologies. in addition, improvement of alredy

existing mining techniques can result in metal recovery from sources that have not been of economical interest until today. Metal-winning processes based on the activity of microorganisms offer a possibility to obtain metals from mineral resources not accessible by conventional mining

• Bioleaching is a process that employs microorganisms to dissolve (leach) sulphide

minerals. It finds application in the extractionof metals from their ores.

An industrial bioleaching plant for the treatment of arefractory gold concentrate. At the Beaconsfield GoldMine in Tasmania, Australia, about 70 t per day of arefractory pyrite-arsenopyrite concentrate per day areprocessed through this plant, which comprises sixmechanically-agitated reactors each with a volume of380 m3.

Bioleach bacteria are characterised by their optimaloperating temperatures. Mesophiles (top) operate bestbetween 30 and 42 °C, and are rod-shaped bacteria withdimensions of about 0.5 ´ 2.0 μm. Moderatethermophiles (middle) have a similar morphology to themesophiles, and operate at 45 to 55 °C. The extremethermophiles (bottom), which are often spherical andhave a diameter of 1 to 2 μm, operate at elevatedtemperatures of between 60 and 90 °C.