NET NEUTRALISATION POTENTIAL (NNP) IN KIMBERLEY DIAMOND TAILINGS AND SLIMES WASTE MATERIALS

摘要

Recent studies suggest that sulphide minerals are insignificant in the tailings and slimes of diamond mines. Other studies indicate that sulphide minerals are in fact present. An overabundance of neutralisation potential is also reported, suggesting that long term environmental risks associated with acidity and leaching of heavy metals is insignificant. The knowledge of acid generation potential and metal mobility in the slimes and tailings conditions is therefore necessary. The objective of this study was to evaluate the potential for acid generation and to assess if conventional pyrite oxidation occurs in the slimes and tailings materials. This was assessed using standard geochemical testing techniques such as Acid Base Accounting (ABA) and accelerated weathering testing by means of humidity cell experiments. A total of 131 samples, representing 35 tailings and 5 slimes facilities were sampled, tested and analysed using static tests. Six samples (three tailings and three slimes) were selected based on Neutralization potential (NP): Acid Potential (AP) ratios and subjected to humidity cell testing.ABA results show that paste pH ranges from 7.5 to 10. Neutralisation Potential Ratio (NPR) was found to be greater than 4 for all tailings and slime samples, indicating that the materials are non acid generating. The deionised water leachate metal concentrations in alkaline conditions did not indicate elevated concentrations relative to the NAG leachate concentrations especially for metals like Zn that could be soluble in neutral pH. However, sulphate and sodium occurred at concentrations indicating that they may require further consideration with respect to the impact on site water quality.Long term leaching using column leaching cells is recommended to quantify the long term sulphide oxidation and neutralization depletion rates. This will lend insight into metal leaching rates under ambient conditions.