The effect of mineral particle size and pulp density on the bioleaching of
pyrite by the acidophilic thermophile Sulfolobus metallicus was investigate
d in a batch bioreactor. Decreasing the particle size from a mean diameter
of 159 micron (size fraction:150-180 micron) to a mean diameter of 29.5 mic
ron (size fraction:25-45 micron) enhanced the bioleaching rate from 0.05 to
0.098 kg m(-3) h(-1). The particle size distribution of the mineral in thi
s range did not influence the morphology and growth kinetics of the cells.
Decreasing the particle size of the mineral to a mean diameter of 0.2 micro
n (size fraction< 25 micron) severely damaged the structure of the cells, r
esulting in their inability to oxidise pyrite. The rate of bioleaching of p
yrite was not influenced by the mineral pulp density in the range 6 to 12%.
With a pulp density of 6%, complete oxidation of pyrite (based on the conc
entration of released iron) was achieved, while with the pulp densities of
10 and 12%, the extent of pyrite oxidation was 67%. The bioleaching rate of
pyrite at a pulp density of 15% was relatively slower than those observed
in the presence of 6 to 12% pyrite and the extent of pyrite oxidation was o
nly 30%.