Controlled Low-Strength Materials Containing Solid Waste from Minerals Bioleaching

Abstract

Sustainable treatment and disposal of mine waste is a serious environmental issue faced by the mining industry worldwide. Conventional methods of mine waste management predominantly involve indefinite retention in engineered tailings dams. The cost and liability of such surface storage facilities have increased significantly in recent years as an outcome of stringent environmental legislation and mine closure requirements gradually transforming the economics of mine waste disposal. Backfill methods, particularly cemented paste backfill, are increasingly perceived as sustainable, environmentally friendly and cost-effective alternatives as they put waste material to practical use. Controlled low-strength materials (CLSM) offer an effective and practical alternative to similar analogues – requiring minimal compaction, being self-levelling and excavatable in the future if necessary. The aim of this research was to develop and evaluate CLSM, previously un-tested at mines, in which novel utilisation of bioleach waste is maximised and Portland cement content minimised while satisfying performance requirements for classification as CLSM. Leachability of toxic substances was minimised through encapsulating CLSM within a coating of relatively inert CLSM. Formulation and optimisation of CLSM using statistical mixture design and response surface analysis has ensured proper understanding of component interactions and influence on mechanical strength with a minimum amount of experiments. Optimised CLSM formulations were tested for their mechanical, physical, micro-structural, mineralogical and chemical properties. Effects of encapsulation were determined by assessing chemical leaching. The work indicated that bioleach waste could be beneficially reformed as CLSM of appropriate compressive strength for application in groundwork as loadbearing materials. Porosity and hydraulic conductivity were correspondingly high. Leachability of arsenic, barium, chromium, lead and zinc was significant (levels varied depending on waste type). Encapsulation significantly reduced leachability indicating promising potential for implementation of this technology in the mining industry. The research presented in this thesis substantiated the need for, and potential of, sustainable novel alternative technologies such as CLSM to augment future waste management strategies in the mining industry via safe emplacement of solid bioleach waste in the sub-surface.