Cobalt immobilization performance and mechanism analysis of low carbon belite calcium sulfoaluminate cement

Cementitious materials are well acknowledged as one of the most adaptable materials for immobilizing heavy metals. Belite calcium sulfoaluminate cement (BCSA), one of the low-carbon alternative binders to cement with superior properties regarding chemical resistance and mechanical properties, is found with a desirable capability for waste immobilization. In this study, BCSA was used for Co(II) immobilization with a dosage of up to 2.5% by weight of BCSA. The results showed that Co(II) could promote the hydration of BCSA pastes, specifically accelerated the hydration of ye'elimite. More hydration products could be generated in the Co(II)-doped BCSA pastes, leading to the construction of a denser microstructure. The compressive strength of BCSA pastes would be slightly improved when BCSA was used for Co(II) immobilization, and the electrical resistivity would decrease. In terms of Co(II) immobilization, BCSA cement exhibited a desirable capacity for Co(II) immobilization. The majority of the Co(II) could be immobilized within the first 100 min of mixing BCSA with Co(II) solutions. The immobilization degrees of Co(II) in hardened BCSA pastes could approach about 99.99% after 7d. The acquired results indicated that BCSA cement is effective for Co(II) immobilization. Therefore, BCSA has a low-carbon advantage with superior strength development over time and prospective capacity of heavy metals immobilization.