Improved mine waste characterisation through static blended test work

Prediction of the geoenvironmental characteristics of mine waste materials typically relies on the static and kinetic testing of individual waste units. In reality, waste rock piles are heterogeneous landforms containing potentially acid forming (PAF) units juxtaposed with non-acid forming (NAF) units. Despite this, predictive geoenvironmental test work programs rarely characterise blends of waste materials. Through undertaking laboratory-based blended static testing and mineralogical assessments, a first insight into the leachate chemistry of a waste landform can be ascertained. This was tested using three waste units (Type A - alkaline, B - neutral and D - PAF; n = 31) obtained from the Savage River mine, Western Tasmania. Seven daughter blend types (1-7; n = 42) were prepared using different ratios of the individual waste types, and characterised by acid base accounting and mineralogical techniques. Blend types were NAF when a maximum of 20% of Type D was used, with daughter blend 4 (90% Type A + 10% Type D) the most inert when screened against ANZECC (2000) aquatic protection trigger values. This study demonstrates that through first-pass static blended testing, opportunities exist to improve waste-rock handling practices and design NAF waste piles once field trials, involving a range of particle sizes, have been conducted.