Cost-effective fabrication of fluorite tailings-based calcium silicate hydrate for excellent adsorption performance of Cr (III) from aqueous solution.

The rational design and preparation of adsorbents with superior performance are of great significance in mitigating water pollution caused by heavy metal ions (HMIs). In this work, fluorite tailings were used as the silica source to synthesize mesoporous silica (MSi) through alkali fusion. The resulting MSi was then mixed with calcium oxide to prepare calcium silicate hydrate (CSH) via one-step hydrothermal method. The effects of different hydrothermal temperatures on microstructures and the adsorption properties of CSH were investigated. The changes of CSH crystal structure, microscopic morphology, and surface functional groups were analyzed using XRD, BET, SEM, TEM, and FT-IR. The optimal adsorption conditions for Cr3+ were explored by assessing the influence of initial concentration, contact time, and pH. The results showed that the maximum adsorption capacity of CSH could reach 488.56 mg/g under the hydrothermal temperature of 180 °C, initial concentration of 250 mg/L, contact time of 360 min, and pH of 5.5. Besides, the adsorption kinetics, thermodynamics, and isotherm modeling were proposed to reveal the Cr3+ adsorption mechanism, which demonstrated that the Cr3+ adsorption process is mainly dominated by ion exchange and surface complexation. The novel CSH adsorbent prepared in this work has the advantages of low-cost raw materials, simple preparation process, excellent adsorption performance, and no secondary pollution, which provides a viable route to utilize tailings and obtain valuable HMIs adsorbents.