Impact of High Alkalinity and Gamma Radiation on the Leaching Stability of Cement-Solidified Heavy Metal Mixed Waste

This study investigated the leaching behavior of cement-solidified waste containing heavy metals (Pb, Cd, and Sb) in a high-alkaline environment, simulating conditions silo-type radioactive waste disposal facilities. The leaching characteristics were evaluated using standardized methods, including the Toxicity Characteristic Leaching Procedure (TCLP), the Korean Elution (KE) test, and ANS 16.1. The results indicated that Pb leaching significantly increased in the high-alkaline leachate environment, whereas Cd did not leach under any tested conditions. Sb exhibited lower leaching compared to Pb, with increased leaching observed under high-alkaline conditions in both TCLP and KE tests. Furthermore, leaching tests conducted under gamma radiation exposure revealed a decrease in Pb and Sb concentrations, while Ca concentrations increased. This phenomenon is primarily attributed to the radiolysis-induced local pH depression, which facilitates the accelerated dissolution of the pH-sensitive portlandite phase. The linear correlation between test results suggests the potential for interchangeability among leaching methods, indicating that disposal regulations for mixed waste could be established by adapting standards from different test methods. Further studies are needed to reflect real disposal conditions and long-term testing to evaluate the impact of environmental factors on the leaching resistance of solidified mixed waste.