Planning for waste management and disposal in minerals processing using life cycle assessment

Abstract

Good environmental performance in mining and minerals processing operations relies on effective waste management. In turn, the generation of waste, both its quality and quantity, is a direct function of technology choice and is limited further by the thermodynamic constraints under which the industry operates. It is only over the former that operating companies can exercise any control. We argue that improvements in environmental performance are realised primarily by changes in technology—not simply hardware choice, but also operating and management practice. Whilst such changes are driven by environmental concerns expressed by society (often in the form of legislative guidelines), it is operating companies alone which can effect such change. Current environmental management systems offer little in the way of technical guidance for mining and minerals processing companies intent on improving their environmental performance. They tend to reflect a static operating condition, in which the domain of influence is seen as external to the mining or minerals process. Generally, opportunities for improved process development and design are overlooked. There is little attempt to relate environmental impacts from, for example, waste generation, to the processes that generate these wastes. This ‘closed box’ view of technology is limiting in another way also. It restricts opportunities to see environmental performance in the same context as economic performance. The latter is driven by measures of efficiency—capital, labour, and technology. So too is the former. The ability to reconcile these two aspects of company performance, and so make explicit any trade‐offs between the two that are required as part of operational strategy, arises naturally when a causative link is made between technology choice/operation and waste generation. This becomes clearer when it is recognised that ‘avoidable’ wastes represent process inefficiency, which directly affects economic performance. In this instance an ‘avoidable’ waste can be defined as the difference between the optimal and the actual waste generated by the technology in place. We have developed a systemic model of mining and minerals processing, which reflects all environmental issues arising from resource extraction and minerals beneficiation, including waste generation. The model is dynamic and processbased; critical resource consumption and waste flows are linked directly to unit operations. We have adopted the methodology of Life Cycle Assessment (LCA) to relate resource and waste issues to environmental impacts. This reverse‐mapping exercise, in which impacts can be traced back to particular wastes or emissions, which, in turn, are related to specific unit technologies, allows companies to target strategic improvements in environmental performance by reviewing their process design and operation philosophies. This approach is consistent with pro‐active ‘planning for closure’. In this way, issues of waste management and disposal are brought to the fore. We propose that this approach will assist operating companies in identifying their long‐term liability associated with waste disposal. Rehabilitation of waste deposits on cessation of mining and minerals processing can be guided by the above and implemented cost effectively. The model provides a basis upon which to explore in detail the relationship between income generation and waste generation potential for a given process requirement, specifically in terms of technology selection and operation. In this way, it may be possible to identify constraints on the part of operating companies to fund closure management practices. Equally, the model gives some guidance on how best to apply regulatory mechanisms to closure planning. We have explored the use of this generic modelling approach to the South African minerals industry, which has been analysed on a sectoral basis vis‐à‐vis gold, coal, base metals, platinum group metals, mineral sands and ferro‐alloys. Case studies from the base metals sector have been used to demonstrate how structural features of the industry dictate systemic environmental performance. The value of the model in an expanded environmental management programme framework is highlighted in the context of the prevailing regulatory regime.