Preparation of sulfoaluminate cementitious material using harmful titanium gypsum: material properties and heavy metal immobilization characteristics

The production of titanium dioxide (a necessary industrial color additive) can generate massive amount of titanium gypsum, a hard-to-treat solid waste. Diverse metallic impurities, heavy metals and reddish color in titanium gypsum make it difficult to be used in building materials like other by-product gypsums. As a result, most of titanium gypsum in China is just stored and has caused serious environmental issues. In this study, titanium gypsum, which contained high contents of impurities and heavy metals, was synergistically used with other three solid wastes to prepare sulfoaluminate cementitious material (SACM) for the first time. The mass proportion of titanium gypsum in the raw materials exceeded 25%. The chemical, mechanical and heavy metal leaching characteristics of this solid waste-based SACM were tested via XRD, XRF, ICP-OES, etc. The main components and metallic impurities of titanium gypsum could be transformed to the components of the main mineral of SACM, ye'elimite. The compressive strength of the prepared SACM reached 38.2, 59.7 and 95.8 MPa at 1-day, 3-day, and 28-day hydration, respectively, indicating the features of rapidly hardening and high strength. Importantly, the solid waste-based SACM could effectively solidify the heavy metals contained in titanium gypsum and other raw material during thje hydration process. The retention ratio of total Cr reached 97.5%, and other heavy metals were almost not detected in the leachate of SACM. This study provided a feasible approach to utilize titanium gypsum to produce high-performance, green building material, and might promote the massive utilization of this solid waste.