Efficient Removal of Aqueous Heavy Metal Cd ²⁺ by Alanine Intercalation of MgAl–LDH: Adsorbent Preparation, Characterization, Adsorption Performance, and Mechanisms

Abstract In this work, MgAl‐NO3‐LDH was prepared by co‐precipitation method, and the alanine intercalation of MgAl‐Ala‐LDH was prepared by roasting and recovery method. The structure, morphology and pore size of prepared materials were systematically characterized by XRD, SEM, TEM, BET, XPS, TG‐DTG and FTIR. The (003) diffraction peak of MgAl‐Ala‐LDH shifted from 11.29° to 6.17° and the interlayer spacing of d(003) expanded from 0.79 nm to 1.33 nm, indicating that alanine was successfully inserted into the hydrotalcite interlayer. The effects of solution pH, initial concentration of Cd2+, time, temperature and quality of the adsorbent on Cd2+ adsorption performance were studied. The results indicate that when the pH value of CdCl2 solution is 5–6 and the temperature is 45℃, the Cd2+ adsorption capacity of MgAl‐NO3‐LDH and MgAl‐Ala‐LDH are 39.7 mg/g and 135.5 mg/g, respectively. The adsorption data conforms to the pseudo‐second‐order kinetic and Langmuir model, indicating that the adsorption process is monolayer adsorption and controlled by chemisorption. Thermodynamic investigations indicated that higher temperatures facilitated Cd2+ adsorption and strengthened the affinity with MgAl‐Ala‐LDH. The mechanisms of Cd2+ adsorption mainly include surface complexation, chelation and isomorphic substitution. MgAl‐Ala‐LDH may have a good application prospect in the removal of heavy metal ions.