DISSOLUTION OF PARTICLES OF PYRITE MINERAL BY DIRECT ATTACHMENT OF THIOBACILLUS-FERROOXIDANS

Shake flask experiments on the leaching of particles of pyrite mineral with Thiobacillus ferrooxidans indicate that, under conditions of large particle sizes and high pulp density, the dissolution occurs primarily through direct attachment of the micro-organism on the mineral surface. Even though both Fe2+ and the cells are present in the aqueous phase, there is negligible oxidation of Fe2+ to Fe3+ at 20% pulp density. The main products of the reaction are FeSO4 and H2SO4. For particle sizes in the range 150-2830 mu m, the rate of leaching is found to increase as the particle size increases, in spite of the lower surface area available. These unexpected results have been explained by assuming that the bacteria preferentially attach to specific sites, which are formed during grinding. A model incorporating the number of attachment sites and leaching at these sites is proposed to explain the experimental results.