MMIJ Annual Meeting

The oxidative dissolution of pyrite is the main cause of acid mine drainage (AMD) formation in tailings dams and underground workings of closed and abandoned mines. Without treatment, AMD pollutes the receiving river and groundwater systems, destroying affected ecosystems and negatively affecting the health of individuals living around the contaminated sites. One emerging new approach in mitigating AMD is to passivate pyrite by encapsulating it with an unreactive coating. In this study, two new techniques to passivate pyrite by encapsulation is introduced: (1) ferric-catechol enhanced microencapsulation, and (2) galvanic microencapsulation. Ferric-catechol complex is a redox reactive compound, which could aid in the encapsulation of pyrite by supplying ferric ions and forming an organic-like coating. In the second technique, zero-valent iron (ZVI), a metal that is anodically more reactive than pyrite, was used not only to supply ferrous/ferric ions but also to protect pyrite via galvanic interactions. The results showed that both ferric-catechol and ZVI suppressed the oxidation of pyrite around pH 4-6, and when phosphate was added, suppression of pyrite oxidation was even more dramatic. DRIFTS and SEM-EDX results indicate that an organic-iron-phosphate coating was formed in the presence of ferric-catechol. Similarly, ZVI addition passivated pyrite by intensifying the formation of the iron phosphate coating.