Abstract
This paper describes quantitative evaluation of pyrite leaching with Leptospirillum ferrooxidans, an iron-oxidizing chemoautotroph without sulfur-oxidizing ability.
Leaching experiments were carried out in shaking flasks. Massive pyrite was ground and sieved to obtain the size fraction between 20 and 37 micro meters. A pure culture of L. ferrooxidans (ATCC29047) and an enrichment culture of Thiobacillus ferrooxidans were used for inoculum. Several sets of flasks containing inorganic nutrient medium, 1 % of the pyrite and the inoculum were prepared for each experiment. Every two days, one flask of the series was removed from the shaker for analysis. In the case of L. ferrooxidans, the bacterium grew in this condition and solubilized pyrite. Over 90 % of iron were dissolved from pyrite within 400 hours. With the progress of iron extraction, notable amount of sulfur particles was observed in SEM photomicrograph. Those particles attached to residual pyrite, but did not prevent pyrite dissolution. The major products of sulfur species in the pyrite degradation with L. ferrooxidans were elemental sulfur and sulfuric acid. Total amount of these two products corresponded with the amount of degraded sulfur calculated from dissolved iron in every sampling point. The molar fraction of elemental sulfur in total degraded sulfur was approximately 1 / 4 throughout the experiment. In contrast, the major product of sulfur species was sulfuric acid, and no elemental sulfur was detectable in the case of pyrite leaching by T. ferrooxidans.
