A cleaner production strategy for acid mine drainage prevention of waste rock: A porphyry copper case

An in-process technology approach is proposed to identify the source of acid mine drainage (AMD) generation and prevent its formation in a porphyry copper waste rock (WR). Adopting actions before stockpiling the WR enables the establishment of potential contaminants and predicts the more convenient method for AMD prevention. A WR sample was separated into size fractions, and the WR’s net acid-generating potential was quantified using chemical and mineralogical characterization. The diameter of physical locking of sulfides (DPLS) was determined, and the fractions below the DPLS were desulfurized using flotation. Finally, the WR fractions and tailing from the flotation test were submitted to acid-base accounting and weathering tests to evaluate their acid-generating potential. Results show that the WR’s main sulfide mineral is pyrite, and the DPLS was defined as 850 µm. A sulfide recovery of 91% was achieved using a combination of HydroFloat® and Denver cells for a size fraction lower than DPLS. No grinding was conducted. The results show that size fractions greater than DPLS and the desulfurized WR are unlikely to produce AMD. The outcomes show that in-processing technology can be a more proactive approach and an effective tool for avoiding AMD in a porphyry copper WR.