Sustainable Methods of Dewatering and Disposal of Processing Plant Tailings

Mineral processing is carried out on low-grade ore to recover valuable minerals as concentrate and reject unwanted minerals as waste, generally termed tailings. Mineral separation when done by dry processing (without using water media) either employing gravity or magnetic separation techniques, the tailings are generated in a dry state and can be transported by conveyor belts or closed tube conveyors to designated tailing dumps. In such cases, there may not be many environmental control issues except for using some dust suppression measures. But, in case mineral separation is carried out by wet methods of processing (using water media in flotation, fine gravity, and wet magnetic separations) the tailings generated are a mixture of water and solids in the form of slurry. In general practices, the tailings in the form of slurry are pumped to designated tailing ponds or tailing Dams for long storage. The disposal of tailings as a slurry with large quantities of water has many environmental concerns and is one of the major problems facing the mineral industry in maintaining environmental controls and safety standards. Impoundment of tailings into tailing dams along with large quantities of water has environmental concerns such as water conservation, and pollution of ground and surface water which are regular immediate concerns, and hazards of dam breaches and land degradation have a long-term impact. In view of the water scarcity expected in coming years, the water contained in tailings needs to be recovered and recirculated. Now several regulations are promulgated at the Government level to restrict the use of water and also to reclaim and recirculate slurry water. Secondly, make-up water to compensate for the losses of water at various stages of processing should be lower as far as possible. This depends on the type of ores processed and may vary between 10 and 30% of feed water to the plant. For this reason, permissions to establish mineral processing units are given only when these guidelines are adhered to. Recently environmental regulations also restrict the disposal of tailings as slurry into natural or artificial ponds. In this regard, it is recommended to adopt and use several methods of dewatering equipment like high capacity and efficient thickeners, vacuum or pressure filters, etc. Secondly, dry methods of processing as well as pre-concentration by dry methods are encouraged. Many mining companies in the world are now making efforts to reduce water consumption and reuse and also financing R&D projects to develop dry methods of ore process. Tailing management is considered one of the major environmental challenges for the mining industry. Under the Sustainable Development Framework (SDF), there are many new guidelines for handling and disposing of mining waste and plant tailings. More emphasis is given to the recovery of water from tailings prior to its disposal. Presently, several methods of dewatering and safe disposal of tailings have evolved in recent years and the industry is keen to adopt sustainable methods. In this paper, some of these methods are discussed.