The application of coal combustion by-products in mine site rehabilitation

Coal combustion by-products (CCBs) generated from coal-fired power plants have been considered in some circumstances and in some applications as alternatives for natural materials. This review focused on the beneficial use of CCBs for mine sites. The alkaline pH of CCBs has been shown to play a neutralising role for acid mine drainage and the consequent precipitation of metals from solution, mainly as metal hydroxides. Coal combustion by-products have also been used for soil restoration, having been shown to improve one or more of the physical, chemical and biological properties of degraded soils which in turn has led to improvements in revegetation outcomes. In addition, fly ash has been used as a one of the materials in engineered covers that are constructed to encapsulate and isolate potentially hazardous mine wastes. The use of CCBs for mine void backfilling has been considered an opportunity for the bulk utilization of CCBs. Backfilling of underground mine voids with these materials presents the potential to reduce acid mine drainage, limit the risk of land subsidence and minimise and control the likelihood of mine fires. Even though the proactive use of CCBs may eliminate or reduce an environmental burden that remains if separate storage or disposal of these otherwise 'waste' materials is required, there may be adverse side effects that could occur through such uses of CCBs, such as the leaching of deleterious elements. Therefore, in the case of their use in mine backfilling, for example, possible environmental impacts need to be assessed and monitored during a testing phase in the context of other variables, and before backfilling with such materials is used on a large-scale. There is still a lack of well-researched information on the practical use of CCBs, and their potential environmental and health effects, and in their use for mine site rehabilitation purposes, effective guidelines and regulations are also limiting factors. In most countries, government regulations regard CCBs as a waste but not a hazardous waste. However, given the high potential CCBs have in a number of roles and functions relating to mine rehabilitation and mine closure, more research at the practical level, and more engagement at a government level, is required.