QUANTIFICATION OF THE INTRAGRANULAR POROSITY FORMED IN BIOLEACHING OF PYRITE BY THIOBACILLUS-FERROOXIDANS

During the bacterial oxidation of a pure pyrite by Thiobacillus ferrooxidans, a great number of corrosion tunnels appear that are easily revealed by scanning electron microscopy observations. This involves an increase in the surface area without significant granulometric reduction of mineral grains. Thus, the evaluation of intragranular porosity, determined by elution front analysis, allows one to estimate accurately the fraction of oxidized sulphide, because of the development of deep holes (propagating pore mechanism). After 60 days of bioleaching, the intragranular porosity represents about 34% of the initial sulphide volume, which corresponds to 25 km of tunnels (2-mu-m i.d.) per gram of pyrite. On other hand, the granulometric reduction (almost-equal-to 7%) is responsible for a 23% decrease of the initial sulphide volume. The elution front analysis appears as a nondestructive method for measuring the intragranular porosity of the bioleached pyrite.