Open-pit unclassified cemented paste backfilling (OPUCPB) methods have not only addressed the disposal problems of tailings but also eliminated geological hazards of high and steep open pit slopes and created conditions for ecological restoration of the open pit in the future. In this paper, slope safety simulations, heavy metal leaching, groundwater monitoring, and pollutant diffusion predictions were examined to evaluate the slope safety pattern and environmental protection enabled by OPUCPB. The results showed that: (1) The safety factor of the open pit slope was proportional to the height of OPUCPB operation. Under the condition of seismic force and seepage field, the safety factor of slope B was increased from 1.188 to 1.574 by OPUCPB. (2) The toxic and harmful components in tailings were significantly stabilized by the OPUCPB. Under the conditions of acid leaching and water leaching, the quality of the leaching solution met the requirements of the class III limit of groundwater (GB/T14848-2017). (3) The monitoring results of groundwater quality around the open pit showed that the OPUCPB had no effect on groundwater, and the water quality met the requirements of the class III limit of groundwater (GB/T14848-2017). (4) Considering the diffusion prediction of pollutants and groundwater under extreme conditions, it was found that the pollution process is slow, and the shortest time required for pollutants to reach the standard limit is 232 d at a distance of 50 m from the leakage point. Therefore, the influence of OPUCPB can be controlled, and this method can achieve improved reclamation of open pits and safety treatment of tailings. It was worth popularizing and applying in mining enterprises.
Keywords: groundwater monitoring; heavy metal leaching; open pit; slope safety simulation; unclassified cemented paste backfill.