INFLUENCE OF IRON OXIDE FORMING CONDITIONS ON PYRITE OXIDATION

Abstract

Iron released from pyrite during oxidation in slightly acid to alkaline conditions is known to produce one or more forms of iron oxide. There is, however, no solid understanding of how, and to what degree, these iron oxides affect pyrite oxidation. This was investigated by leaching pyrite in a chromatographic column with a 1-cm i.d. and a flow rate of 0.43 mL min^-1 at room temperature with a solution containing hydrogen peroxide (H₂O₂) buffered with acetate. When the leaching solution reached pyrite surfaces, H₂O₂ oxidized a small portion of pyrite and released Fe³⁺. The latter hydrolyzed to form an amorphous ferric oxyhydroxide that precipitated as a passive coating on the pyritic surfaces. The rate of pyrite oxidation was shown to be suppressed greatly by these coatings. This suppressive effect was attributed first to the coating's ability to serve as a sink for Fe³⁺, thus making it no longer available to oxidize pyrite, and second to the coating's ability to act as a barrier to the upcoming H₂O₂, thereby physically protecting the pyritic surfaces. It was also shown that the above leaching solution acted as a coating agent when buffered at pH 4.0 to 6.0. Values higher than pH 6 were not investigated.