Waste material placement options during construction and closure risk reduction - quantifying the how, the why and the how much

摘要

Technical aspects of waste rock characterisation and assessment have been the focus of considerable research over the past decade, with many guidance documents being published on the subject internationally and within Australia. While these documents provide detailed information on how to characterise waste rock, there is not a great amount of guidance on how the placement of waste rock can be optimised to account for the results of the characterisation studies. In this respect it could be reasonably concluded that the science has progressed to a more advanced stage for waste classification in comparison to how to manage it. This has lead in many cases to site specific waste characterisations being followed up with generic waste management solutions such as widespread adoption of the ubiquitous potential acid forming cell as a management solution. The net result of this mismatch is that although acid and metalliferous drainage (AMD) assessments are undoubtedly being carried out to a higher level of detail than in the past, there is not a definitive correlation with site management practices and, therefore, effective closure risk reduction over this time. The net effect of this trend has been that site operators are being given better information on AMD risks, but not better solutions on how to manage these risks. That is to say site operators are being told why they should manage risks but not how to achieve this, and by how much risks can effectively be managed (if at all). Questions that site engineers and operators may ask about the relative benefit of one placement solution over another have for the most not been adequately addressed by research. Examples include assessment of the quantitative benefit of paddock dumping vs end tipping, determining the optimal tip head height for waste placement in a storage facility, and how sulphide grade control should be carried out. A detailed risk-based investigation of the influence of factors common to waste placement is presented herein and has been completed as part of a wider research initiative to investigate the technical aspects of developing a quantitative assessment tool. Applying a numerical modelling approach to assessment of the different waste material placement strategies allows for the graphical presentation and communication of the variation in risk through risk matrices and histograms.