Environmental impact assessment of tailings storage facilities focuses on defining the reactivity and potential for acid rock drainage and metal leaching (ARDML) through geochemical testing of representative samples and numerical predictive calculations. The acid generation potential of tailings is dependent on the reactivity of their sulphide content which is directly proportional to the oxygen concentration within the material. As such, predicting the oxygen concentration as a function of time and depth is critical to understand the acid generation potential of tailings material.
The aim of this study was to predict the oxygen flux and concentration as a function of time and depth within the San Manuel flotation copper tailings in Arizona, USA. This flow was combined with mineralogical data, including the presence of encapsulated sulphide, oxygen and moisture content to model oxidation and metal release in the tailings.
Numerical simulations, using reactive transport code MIN3P, correctly reproduced the San Manuel field and analytical results when the sulphide reactivity was controlled by reducing the effective sulphide mass within the numerical models from total sulphide to available sulphide. These calculations effectively demonstrated that an effective control minimizing sulphide oxidation exists within a portion of the San Manuel tailings.