Abstract
The reactivity of pyrite with Fe(III) ions in solutions of pH around 2 containing anionic species was evaluated by the determination of released Fe(II) ions, and by surface analysis of pyrite using X-ray photoelectron spectroscopy (XPS). The release of Fe(II) ions decreased with increasing concentration of total anionic species, and the suppression of pyrite dissolution was in the order chloride<sulfate⋘phosphate≈oxalate. The Fe(III)-CDTA and [Fe(CN) 6] 3− complexes did not function as oxidants. For [Fe(CN) 6] 3−, the results were explained by a mechanism based on molecular orbital theory, since the complex is inert and of low-spin type. For the others, the order of suppression was found to be in parallel with the order of potential as oxidant, the standard redox potential, E 0. The redox couples of Fe(III)-CDTA and Fe(III)-oxalate complexes have lower E 0 values and this is considered to be the reason for no oxidation. In the phosphate system, colloid formation and polynucleation of Fe(III) ions were observed and these were additional factors in the suppression. The experimental results and the calculated E 0 values indicate that E 0 for SO 4 2− /pyrite-S may be around 0.3 V. This means that E 0 is an important measure for estimating the ligand effect.
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