Adsorption performance and mechanism of Ca–Al-LDHs prepared by oyster shell and pop can for phosphate from aqueous solutions

Abstract

The anion exchange properties of layered composite metal hydroxide (LDHs) make it a significant anion purification material in aquatic environment. Ca–Al-LDHs as a calcium-based adsorbent can significantly improve the removal rate of phosphate. In this manuscript, waste oyster shell was used as the source of calcium and waste cans as the source of aluminum, and compared with the LDHs prepared by chemical reagents. The optimal molar ratio of for both the types of materials prepared from waste material as well as reagents was found to be 4:1 for best adsorption performance, with the waste group and reagent group materials showing similar adsorption capacities of 127.50 mg g−1 and 126.67 mg g−1, respectively. The effects of adsorbent dosage, initial solution pH and presence of coexisting ions on the adsorption capacity were investigated. Langmuir adsorption isotherm, quasi-second-order kinetic equation and mass transfer kinetics was found to describe the phosphorus adsorption process of CAs-4 and CA-4 in better way. The maximum adsorption capacities of Langmuir equation for CAs-4 and CA-4 adsorption process were 126.41 mg g−1 and 127.43 mg g−1, respectively, for CAs-4 and CA-4. The characterization results of FTIR, XRD and ICP showed that the main adsorption mechanisms were intercalation anion exchange, electrostatic attraction and dissolution precipitation. This work not only provides a method to prepare Ca–Al-LDHs for efficient utilization of solid waste, but also provides theoretical significance for controlling water eutrophication and realize waste recycling.