Automated environmental analysis: multiple size fraction analysis of kinetic tests and implications for adjusted NNP and NPR values

Kinetic tests are a routine analytical tool for assessing the long-term variation in sulfide oxidation kinetics within potential mine waste. The need to understand the role that mineral texture plays in controlling kinetic test behaviour is integral, and analytical protocols for this are the subject of current research. One of the challenges with mineral texture analysis of kinetic test samples is the large size range of the sample, and therefore the need for multiple size fractions along with the time and cost implications of this.

This paper presents image processing tools using in conjunction with multiple size fractions that have been utilised in the analysis of kinetic test feed samples from the Savage River iron-ore mine, Australia and an IOCG deposit in Scandinavia. These tools allow for the comparatively rapid assessment of sulfide liberation, by combining a bright phase search with the analysis of a dilation zone around the target of interest to ascertain either partial perimeter or area grade liberation. These tools have the potential for widespread application across process mineralogy assessments, presenting the potential for cost and time savings in the analysis of mineral liberation.

From this study, these liberation assessments are used to calculate a reconstructed locking value for the proportion of the sulfides and the carbonates within the sample that can be considered as locked, and are therefore, for textural reasons very slow or very unlikely to react. This locking proportion can be multiplied by the grades of the sulfides and the carbonates to obtain a texturally adjusted Net-Neutralisation Potential, and Neutralisation Potential Ratio value based on mineral exposure that better explains how the kinetic test is currently behaving, and will likely behave in the future. Quantifying the textural controls in this manner are a powerful tool for understanding kinetic tests and provides the overseeing geochemist with sufficient information and confidence to interpret current and likely future kinetic test behaviour.