Feasibility of uranium tailings for cemented backfill and its environmental effects

Surface storage of uranium tailings presents a potential threat to the environment and human health. Cemented backfill can be used to dispose of tailings and control the ground pressure of stopes, providing a new approach for the in-situ seal of heap leaching uranium tailings (HLUTs). The backfilling characteristics of HLUTs were investigated by analyzing the release mechanism of sulfuric acid in HLUTs, the rheological properties of backfill slurry, as well as the strength development and microscopic characteristics of cemented HLUTs backfill (CUTB). The environmental effects of the CUTB were also assessed, and a novel filling process was presented. The results showed that the release rate of sulfuric acid in HLUTs decreased logarithmically, and the content of free sulfuric acid in coarse particles surfaces and ultrafine particles is high, which can be pretreated with 0.1 % quicklime. Slurry with a mass concentration of 74 % ~ 76 % can satisfy the requirements for pipeline transport. The CUTB's strength raised quickly in the former 90d, then decreased to a different extent after 150d, adding 50 wt% FA can enhance its later stability. The leaching level of uranium in CUTB cured for 28d is below the stipulated limit (GB 23727-2009) under different test conditions, having little impact on the underground environment. The hydration products of CUTB are mainly gypsum and C-S-H gel. Gypsum causes later degradation in strength; numerous C-S-H gels generated by the secondary hydration of FA enhance the resistance to sulfate corrosion. These findings have demonstrated that cemented backfill has a high inclusion ratio and low cost for HLUTs, which is of great significance to the HLUTs minimization and the safety of mining while promoting the environmentally friendly development of uranium mines and mills.