OXIDATION RATE OF IRON SULFIDES AS AFFECTED BY SURFACE AREA, MORPHOLOGY, OXYGEN CONCENTRATION, AND AUTOTROPHIC BACTERIA

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Abstract
In this study we sought to determine the relationship between surface area and rate of oxidation of Fe sulfides (pyrite and marcasite) separated from Texas lignite. We evaluated the reaction kinetics with respect to Fe sulfide morphology and particle size. The oxygen concentration and the presence of autotrophic Fe- and S-oxidizing bacteria (Thiobacillus ferrooxidans) on the rate of oxidation were also evaluated.The formation of sulfate from Fe sulfide was selected to measure the rate of oxidation. Relative reaction rates for different morphological forms of Fe sulfide were: marcasite > framboidal pyrite > massive pyrite. The rate of oxidation of marcasite was much higher than for pyrite at an equivalent surface area. As the surface area of pyrite doubled, reaction rate increased by a factor of 1.5. Sulfate production at optimum reaction conditions in this experiment for the 5− to 2-μm fraction was twice that of the 50− to 20-μm fraction. Reaction rate was ∼fivefold greater for noninoculated treatments at 20% oxygen, compared with 0% O2, and was ∼ninefold greater for the same treatments inoculated with T. ferrooxidans. In this study we sought to determine the relationship between surface area and rate of oxidation of Fe sulfides (pyrite and marcasite) separated from Texas lignite. We evaluated the reaction kinetics with respect to Fe sulfide morphology and particle size. The oxygen concentration and the presence of autotrophic Fe- and S-oxidizing bacteria (Thiobacillus ferrooxidans) on the rate of oxidation were also evaluated. The formation of sulfate from Fe sulfide was selected to measure the rate of oxidation. Relative reaction rates for different morphological forms of Fe sulfide were: marcasite > framboidal pyrite > massive pyrite. The rate of oxidation of marcasite was much higher than for pyrite at an equivalent surface area. As the surface area of pyrite doubled, reaction rate increased by a factor of 1.5. Sulfate production at optimum reaction conditions in this experiment for the 5− to 2-μm fraction was twice that of the 50− to 20-μm fraction. Reaction rate was ∼fivefold greater for noninoculated treatments at 20% oxygen, compared with 0% O2, and was ∼ninefold greater for the same treatments inoculated with T. ferrooxidans. © Williams & Wilkins 1984. All Rights Reserved.

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