Effects of temperature and damage degree on the uranium leaching levels of uranium tailings filling materials and their S/S mechanism

Environmental pollution aroused by the discharge of heap leaching uranium tailings (HLUTs) is a significant issue in uranium-producing countries. This study presented a new formulation for filling material that utilized few clinker (CL) and phosphorus slag (PS) as binders blended with HLUTs to achieve dual goals of dealing with hazardous waste and managing mined-out areas. The mechanical properties, pore characteristics, U occurrence forms, and U(VI) leaching behavior of filling materials under various conditions were all investigated, and the S/S mechanism for U(VI) and SO₄^2- were also elucidated. The results showed that elevating the curing temperature from 20 °C to 30 °C resulted in an advancement of rapid strength development from 7–90 d to 0–28 d and a reduction in porosity. The U occurrence forms were less affected by curing temperature and soaking environment. In weak acid environments, the leaching levels of U(VI) in damaged backfill were lower than prescribed limits. Moreover, components such as Ca(OH)₂, C₃A in CL, and orthophosphate in PS could promote the formation of gypsum, ettringite (AFt), and newborn U minerals and other phases in the system, respectively, the latter were adsorped and encapsulated by calcium silicate hydrate (C-S-H) gels, achieving solidification/stabilization (S/S) for U(VI) and SO₄^2-. The findings present a robust theoretical framework and compelling empirical evidence for the sustainable management of HLUTs and other solid waste, with the goal of achieving minimal emissions.