A novel and recyclable silica gel-modified biochar to remove cadmium from wastewater: Model application and mechanism...

Water pollution caused by heavy metals is a major environmental problem, threatening water production, food safety, and human health. Cadmium (Cd) pollution is particularly serious because of food-chain biomagnification at toxic concentrations. Modified biochar is promising for heavy metal removal; however, efficient adsorbents for Cd removal are lacking. In the present study, a novel adsorbent, silica gel-modified biochar (SGB), was prepared and applied to treat sewage polluted by Cd. Through the batch adsorption experiments, it is known that SGB possessed outstanding Cd removal ability and recycleability. Furthermore, the adsorption behavior and mechanisms were analyzed by the application of kinetic and isotherm models. The maximum Cd²⁺ adsorption capacity of SGB was 38.08 mg g^-1, and after five recycling processes, the Cd²⁺ removal rate was still 86.89 %. When the pH of the solution was 7.0, SGB showed the strongest Cd²⁺ adsorption capacity (29.06 mg g^-1). When competitive ions existed, biochar also had high Cd removal efficiency, although the effect of Pb²⁺ was greater than those of Cu²⁺ and Zn²⁺, indicating that SGB was applicable to complex polluted water. Additionally, the main Cd²⁺ adsorption mechanisms by SGB were electrostatic interactions, π-π interactions, complexation, and co-precipitation. These results showed that SGB can effectively treat Cd-contaminated wastewater as a new adsorbent.