Kinetics and Reaction Products of Aerobic Pyrrhotite (FeS) Hydrolysis at Ambient Temperatures

摘要

The product distributions and mechanisms of FeS hydrolysis were examined in reference to acid mine drainage, as a function of pH, NH sub 4+ ion concentration, and SO sub 2 /sulfite concentrations in aqueous suspensions. Products in the solution phase as well as precipitates and starting material residues were examined by pH and redox potentiometry, x-ray diffraction, x-ray fluorescence, scanning electron microscopy, infrared spectrometry, and wet chemical methods. Principal products of pyrrhotite hydrolysis included soluble SO sub 4 /sup =/, Fe exp 2+ , and lepidocrocite (FeOOH). In an unbuffered acid medium, equimolar leaching of iron and sulfur from FeS gives these plus some evolved H sub 2 S as the only products. Hydrolysis in unbuffered water yields the same products with the exception of H sub 2 S, with an atom ratio of Fe:S leached of 3.5 to 1. Surface pyrite (FeS sub 2 ), S exp 0 , and S-rich sulfides are not observed. Hydrolysis in ammonia at pH = 9 gives rise to equimolar FeS leaching to form Fe(OH) sub 2 , FeO(OH), and SO sub 4 /sup =/ as the only products. Hydrolysis in a bisulfite buffer (pH = 6) gives Fe exp 2+ plus lesser amounts of FeO(OH), FeO, and Fe sub 2 (SO sub 4 ) sub 3 . Thermodynamic and kinetic considerations, extended to present conditions, predict FeO(OH), Fe exp 2+ and SO sub 4 /sup =/ as the principal products. The kinetics of iron sulfide hydrolysis are exceedingly slow. In no case did more than 2 percent of the original FeS leach even after 6 days. (ERA citation 04:042234)