Mg-Al layered double hydroxides derived from secondary aluminum ash for soil remediation contaminated with Cd(Ⅱ) and...

Cation and oxyanion heavy metals possess opposite physical and chemical properties, which could be hard to simultaneous remediate in soil. In this study, layered double hydroxides from secondary aluminum ash (SAA-LDH) has been synthesized for soil remediation contaminated with heavy metals. The as-obtained SAA-LDH exhibit strong affinity for heavy metals, which could remove 193.50 mg‧g^-1 of Cr(Ⅵ) and 175.84 mg‧g^-1 of Cd(Ⅱ) within 2 h. Optimum acid-base resistance and selectivity guarantee the practice potential of SAA-LDH, which could remove above 85 % of Cd(Ⅱ) and Cr(Ⅵ) under widely pH range (from 4.00 to 10.00), capturing above 90 % of Cd(Ⅱ) and Cr(Ⅵ) under the interference of seven coexisting ions. Soil remediation tests and column leaching experiments further demonstrate that SAA-LDH could immobilize 98.32 % of Cd(Ⅱ) and 97.71 % of Cr(Ⅵ), preventing its migration. Density functional theory (DFT) manifests that SAA-LDH could remove Cd(Ⅱ) and Cr(Ⅵ) through isomorphic substitution and ion exchange respectively under single system. Under compound system, Cd(Ⅱ) fixed with isomorphic substitution could promote the immobilization of Cr(Ⅵ) onto SAA-LDH, constructing hyper-stable coordination structure. This study provides an effective approach to simultaneously recycle hazardous waste and remediate heavy metals contamination in soil.