There is a general trend towards more responsible water management across the minerals industry. Two important strategies to improve water efficiency have been implementation of water reuse and sourcing of alternative water supplies. Both strategies have been shown to result in an increased tendency for water quality to vary. Variation in water quality is undesirable in the sense that it could complicate operating conditions for mineral separation processes and also dictate environmental consequences of non-compliant discharge events. They are intimately linked through the site water system. However, there is a lack of a systematic tool that considers water management decisions and their impacts as an integrated system as opposed to dealing with each impact separately. This might lead to unintended impacts from water management decisions that only consider one objective. The aim of this study was to develop and test the potential of a systematic management tool to assist the industry in organising, understanding and dealing with water quality problems in a structured manner.
A risk-based approach was developed as a water quality management tool which might allow specific situations to be considered in a generic manner. The approach combines risk quantification and system-wide risk control options. The latter allows opportunities to be identified from the entire water system as opposed to separately dealing with each impact in its local area. To test the applicability of the approach, two flotation case studies of different complexity were selected to demonstrate whether the approach was likely to be applicable in complex situations or only constrained to simple situations.
The first case study tested the potential of the approach to be applied to a simple situation. It analysed the previously published data to quantify the risk posed to coal washing by water conductivity variation and to assess the value of a simple mitigation strategy outside the processing plant. The successful implementation of this mitigation strategy in production could ensure that the environmental consequences of both freshwater withdrawal and saline water discharge were minimised.
The second case study attempted to apply the approach to a more complicated situation. It focused on the current research gap that there was a lack of understanding on the impacts and processes associated with biotic water constituents, including bacteria. Experiments were carried out to quantify the effect of bacteria on flotation and investigate the underlying mechanisms using a representative system consisting of E. coli as the model bacterium and three kinds of chalcopyrite-containing minerals, i.e. high-purity chalcopyrite, a simulated ore with controlled gangue, and a real ore. Experiments were then carried out to explore system-wide solutions to deal with the effect. The experimental results show that E. coli cells negatively affected flotation efficiency of chalcopyrite in all three systems. The bacterial cells also negatively affected the flotation efficiency of pyrite in the simulated ore system, and gold in the porphyry ore system. The bacterial attachment to mineral surfaces reduced surface hydrophobicity and also changed properties of the froth phase. The solution of increasing reagent dosage could partly counter the negative effect. An innovative water management solution of using tailings as the adsorbent was found to be effective in reducing the bacterial concentration and thus mitigating the negative effect. Successfully dealing with the negative effect by coupling different solutions shows the potential for mine sites to use bacteria-containing water for flotation, thereby minimising freshwater use and avoiding the undesirable consequences of increasing its use.
The risk-based approach was tested to study its potential as a management tool to improve water quality management on mines sites operating within different contexts. Findings in this research can contribute to the sustainable development of the minerals industry in terms of improving water management.