The distribution and influence of silver in pyrite bacterial leaching systems

It has been observed that elemental silver occurring in the lattice of pyrite and other sulphide minerals is released during their leaching with mesophilic bacteria. This silver may associate itself with bacteria in the form of silver sulphide particles but may also be observed in particulate form on the surfaces of actively leaching sulphide particles. Experimental results have shown that the silver observed is in a sulphide form and is a reaction product and not the natural form in which the silver may occur in pyrite. The release of elemental silver into solution from pyrite or additions of silver during leaching does not appear to influence the activity of bacteria. Silver additions to ferrous sulphate solutions severely curtail the oxidation of ferrous iron to the ferric form by bacteria. The formation of silver sulphide during the bacterial oxidation of sulphide minerals is most interesting. It counteracts the bacteriacidal influence of silver in the leaching system and also allows for recovery of the element in leach residues. It may also form the basis of a novel method of recovering silver from a number of sulphide minerals. Copyright (C) 1996 Published by Elsevier Science Ltd