Highly Efficient Cd Removal Using Tobermorite with pH Self-Adjustment Ability from Aqueous Solution.

Cadmium (Cd), as a type of heavy metal, can increase the incidence of many diseases, even in low concentrations. In this study, tobermorite was hydrothermally synthesized and then applied to adsorb Cd from an aqueous solution. The physicochemical characteristics of the synthesized tobermorite were detected, and the results indicated that the well-crystallized tobermorite had a lot of mesopores and a large specific surface area of 140.92 m/g. It acquired a pH self-adjustment ability via spontaneously releasing Ca and OH into the aqueous solution. The effects of different factors on Cd removal were investigated. For Cd, the removal efficiency could reach 99.71% and the maximum adsorption capacity was 39.18 mg/g using tobermorite. The adsorption data was best fitted with the pseudo-second-order kinetic and Langmuir isotherm models. In addition, there was no strict limit on the solution pH in Cd adsorption because the tobermorite could adjust the solution pH to an alkaline atmosphere spontaneously. The efficient removal of Cd using tobermorite was a result of surface complexation and ion exchange.