High efficiency and mechanisms of Cd2+, Cu2+, Mn2+ removal from aqueous solution by modified tobermorite

Abstract

In this work, nanoscale magnesium oxide and activated carbon were simultaneously loaded on tobermorite through a gelation-calcination method. The new composite (TOB@C@MgO) was used as an effective adsorbent to remove Cd2+, Cu2+, and Mn2+ from aqueous solution and actual wastewater. Its specific surface area was determined to be 146.90 m2/g, and its sedimentation property was found to be satisfactory. At an initial ion concentration of 500 mg/L, a solution pH of 5.2 ± 0.2, an adsorbent dosage of 1.5 g/L, and a temperature of 25 °C, the adsorption equilibrium for Cd2+, Cu2+, and Mn2+ was reached within 2 h, 4 h, and 6 h, with a removal efficiency of 100 %, 90 %, and 64 %, respectively. The pseudo-second-order model and Langmuir model fitted the kinetic and isothermal adsorption data well. The maximum adsorption capacity for Cd2+, Cu2+, and Mn2+ by TOB@C@MgO, as calculated from the Langmuir model, was 1000.00 mg/g, 526.32 mg/g, and 416.67 mg/g, respectively. The selective sequence of metal ions by TOB@C@MgO was in the order of Cd2+ > Cu2+ > Mn2+. Besides, TOB@C@MgO demonstrated effective treatment of actual wastewater, and exhibited reasonably good reusability and stability. Different characterizations revealed that Cd2+, Cu2+, and Mn2+ removal by TOB@C@MgO was primarily dominated by ion exchange. Surface precipitation/complexation, interaction with π electrons, and physical adsorption also contributed to the fixation of Cd2+, Cu2+, and Mn2+ onto the surface of TOB@C@MgO.