Influence of iron oxide forming conditions of pyrite oxidation

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 Co 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 4.8 to 6.0. Values higher than pH 6 were not investigated.