Mixing of waste rock to lower the release of mg +2 and so 4-2 at Argyle diamond mine

Abstract

The seepage from the Argyle mine waste dumps is mildly acidic and contains high concentrations of magnesium (1400 mg/L) and sulfate (6500 mg/L). Out of the fourteen waste rock types mined, only Pv1 (with relatively low total sulfur content of 0.1 % to 1.0 %) causes a significant release of acidity and solutes. Only Pv5 possesses abundant acid neutralizing capacity and releases significant amount of Ca +2 during neutralization reactions. Experiments conducted in the laboratory have shown that when Pv1 is blended with Pv5 (ratio 2:1) a neutral pH solution, with about 1/10 the Mg +2 and 1/3 the SO 4-2 is released compared to unblended Pv1 or blends made with other waste rock types. Argyle mine has recently implemented controlled co-disposal of these two rock types. The environmental and ecological benefits resulting from of these changes into the waste rock management procedures will be assessed in the coming years.