Revisiting the super-stable mineralization mechanism of CaAl-LDHs for Cu²⁺ and complete removal of Cu²⁺ by structured CaAl-LDHs

The in-situ mineralization is regarded as one of the most promising remediation technologies for heavy metals removal. Herein, the CaAl-LDHs (LDHs = layered double hydroxides) with the particle size of similar to 3 mu m were successfully synthesized, which exhibited the saturated mineralization capacity of 588.23 mg/g and a removal efficiency of >99 % for Cu2+ ions in aqueous solution. The mineralization equilibrium can be reached in 150 min. Detailed quasi-situ XRD and HRTEM results revealed that besides the isomorphic substitution mechanism, the dissolution-recombination mechanism can be observed, as evidenced by the co-existence of CaAl-LDHs and CuAl-LDHs in only 5 min. Meanwhile, the CaAl-LDHs can be packaged into the polyacrylonitrile (PAN) membranes and the resultant CaAl-LDHs/PAN showed removal efficiency of 95 % towards Cu2+ in 7 days of column leaching experiment. Such filter bags can be easily taken away, resulting in the complete removal of Cu2+ from soil.