Understanding the binding and leaching of Cr(Ⅵ) in calcium aluminate cement based solidified/stabilized pastes

摘要

This study investigated the potential of calcium aluminate cement (CAC) to solidify/stabilize Cr(VI) (Na2CrO4). The hydration and microstructure development of CAC pastes in the presence of Na2CrO4 were examined by means of isothermal calorimetry, XRD, TG/DTG and SEM-EDS. The leaching properties of Cr (VI) were evaluated by TCLP and GANC methods. The results demonstrated that addition Na2CrO4 significantly retarded the early-age hydration of CAC depending on the dosage, while caused an acceleration of long-term hydration. The formations of CAH(10) and C(2)AH(8) were inhibited, instead AH(3), CrO4-C(3)AH(6) and CrO4-U phase were found as the main hydrates. These changes of hydrate assemblages led to a strong decrease in compressive strength. Complying with the TCLP regulatory limit of 5 mg/L, up to 1.0% of Cr(VI) could be effectively immobilized in the CAC paste. Two binding phases, CrO4-C(3)AH(6) and CrO4-U phase, were responsible for controlling Cr(VI) leaching in the CAC pastes. (C) 2020 Elsevier Ltd. All rights reserved.