INVESTIGATION OF EFFECTIVE NEUTRALIZATION POTENTIAL IN ANTAMINA MINE WASTE ROCK USING NUMERICAL MODELING

Neutralization potential (NP) of waste rock material is a key aspect for environmental planning at mines that host sulfide minerals. Predictive measures such as estimation of the time that it will take for a waste rock dump to transition from neutral to acidic drainage depend on the this parameter. The neutralization potential is commonly measured using acid-base accounting (ABA), however, results from these tests are often not representative of the effective neutralizing potential within waste rock dumps. This study focuses on the estimation of the effective NP in intrusive waste rock material from one of the constructed experimental piles at the Antamina Mine using numerical modeling. The measured NP by the unmodified Sobek et al. (1978) method indicates the presence of 0.7 % calcite in one of the most reactive tipping phases in this experimental pile, and solid phase elemental analysis indicates the presence of 0.4% of calcite. Observed drainage water chemistry data from the experimental test pile under investigation in combination with quantitative analysis using the MIN3P code indicate an effective field buffering capacity lower than the value from the lab measured results. The modeling study includes the investigation of buffering mechanisms along with representing the processes controlling the drainage chemistry such as oxidation/reduction, dissolution/precipitation and degassing in the unsaturated zone. The study includes a sensitivity analysis to evaluate lab data and provide a constraint on effective NP. These results confirm effects of reactive grain size fractions, representativeness of the tested samples, and passivation of carbonate minerals due to coatings by precipitates on neutralization potential in waste rock material.