Carrier-microencapsulation for preventing pyrite oxidation

The oxidation of pyrite causes the formation of acid mine drainage polluted by heavy metals. This paper proposes carrier-microencapsulation (CME) for preventing pyrite oxidation. In CME, an organic agent is used as an in-situ carrier for transporting Ti from Ti minerals to the pyrite surface through an aqueous phase. Then, the organic carrier is decomposed and Ti(OH)4 or TiO2 film is formed on the pyrite surface as a protective coating against oxidation.To demonstrate the effect of CME on pyrite oxidation, shaking-flask leaching experiments of ground pyrite were performed at 298 K in air for 25 days, with or without anatase (TiO2) and catechol (1,2-dihydroxybenzene) as the organic carrier. The amounts of Fe and S extracted from the pyrite were lower with TiO2 and catechol than without TiO2 or catechol, indicating that CME using TiO2 and catechol is effective in suppressing pyrite oxidation. When TiO2 and catechol coexist, the Ti concentration in the solution phase increased initially and then decreased. SEM-EDX analysis of the CME-treated pyrite showed that Ti and O are present on the pyrite surface. Cyclic voltammogram of catechol showed that catechol was oxidized on pyrite electrode. These results indicate that Ti is extracted from TiO2 by catechol as a Ti-catechol complex and that the complex is adsorbed and oxidized on pyrite to form a Ti(OH)4 or TiO2 coating suppressing pyrite oxidation.