Development of advanced pyrite passivation strategies towards sustainable management of acid mine drainage

Acid mine drainage (AMD) is one of the most serious environmental problems encountered in mining areas worldwide. When released into the environment without treatment, AMD pollutes the surrounding water bodies and soils with hazardous and toxic elements like arsenic (As), selenium (Se) and heavy metals such as lead (Pb), cadmium (Cd), copper (Cu) and zinc (Zn) that rapidly destroy affected ecosystems. The most commonly used method to treat AMD is chemical neutralization, a technique whereby basic materials like limestone or lime are mixed with AMD to raise its pH and remove most of the contaminants via precipitation. Although effective, this approach requires the continuous supply of chemicals, energy, and manpower, which makes it unsustainable because AMD generation has been documented to continue for a very long time (up to several centuries to millennia). One promising alternative to chemical neutralization is (micro) encapsulation, a technique that directly treats pyrite, the main mineral responsible for AMD formation, and renders it unreactive by encapsulating the mineral with protective coatings. In this study, we introduced two advanced pyrite passivation techniques to limit AMD formation called "carrier-microencapsulation" (CME) and "galvanic microencapsulation" (GME). CME uses a redox-reactive organic carrier to deliver the coating material on the surface of pyrite. Because the carrier only decomposes oxidatively, the primary strength of this technique is its high selectivity for pyrite even in complex systems like mine tailings and pyrite-rich waste rocks. Meanwhile, GME is based on galvanic interactions between pyrite and metals with lower rest potentials so this technique could be applied directly in a ball mill during ore processing or coal cleaning.