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Chalcopyrite (XX 7mm, Montroc, France)
Chalcopyrite (XX 7mm, Montroc, France)

A golden yellow mineral otherwise known as copper iron sulfide. Its chemical formula is CuFeS2

Leaching of chalcopyrite is tricky

The direct leaching of chalcopyrite and other hypogenic copper sulfide minerals in sulfuric acid solution poses a variety of problems causing slow leach kinetics and incomplete biooxidation. At temperatures below the melting point of sulfur (approximately 118° C.), the rate of copper dissolution has, to date (2007) been uneconomically slow. At temperatures above the melting point of sulfur the chalcopyrite and other hypogenic copper sulfide minerals are passivated by what is believed to be a layer of elemental sulfur which forms over the unreacted sulfide particles. This again renders the extraction of copper uneconomical by this process. Other leaching systems that have been studied over the years for the extraction of copper from chalcopyrite on laboratory or pilot scale include systems employing concentrated solutions of ferric chloride or ammoniacal ammonium as lixiviants.

Efforts to bioleach chalcopyrite and other hypogenic copper sulfides on a commercial scale have also proven unsuccessful to date. Hypogenic copper sulfides such as chalcopyrite are notoriously difficult to bioleach even though bioleaching is now used as the principal production approach to extract copper from supergenic copper sulfide minerals such as chalcocite and covellite at several mining operations around the world.

Any biohydrometallurgical process for treating hypogenic copper sulfides such as chalcopyrite, therefore, will have to address passivation. A number of different additives have been used in an attempt to increase the dissolution of copper from chalcopyrite, presumably by disrupting the passivating layer. These additives include metal salts such as Ag2 SO4, Bi(NO3), graphite and other sulfide minerals. [1]

The microbial cultures presently (2007) used for bioleaching are unable to produce commercially acceptable results for chalcopyrite without either ultra fine milling (P 80 <20 μm) of the ore or concentrate to facilitate microbial oxidation, or the use of very long leach times to achieve oxidation. Times of over 100 days are not uncommon.



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