Adsorption of high concentration perchlorate from aqueous solution onto Mg/Fe magnetic hydrotalcite calcined product (MAG@CHT): kinetics and isotherm study

In this study, the calcined Mg/Fe magnetic hydrotalcite (MAG@CHT) was synthesized for the first time by co-precipitation and calcination method. MAG@CHT with the destructive layered structure is effective in adsorbing perchlorate in water to recover its original layered structure by Mg/Fe magnetic hydrotalcite (MAG@HT). In addition, MAG@CHT can be quickly separated by the applied magnetic field. The pseudo-second-order kinetics model was a better description of the adsorption kinetics process. The Langmuir model was more satisfactory than the Freundlich model for fitting the isotherm experimental data. The maximum adsorption capacities obtained Langmuir model at 25°C, 30°C, and 35°C were 93.17, 103.54, and 110.88 mg/g, respectively. The detrimental effect order of co-existing anion was: Cl– < NO2– < NO3– < SO42– < PO43–. The Fe(III)/Fe(II) ratio of the MAG@CHT is 5.33, which is close to the theoretical value (4.70); the saturation magnetic strength value (Ms) was 9.10 emu/g, which is easy to achieve solid–liquid separation. Combined with the detailed characterization of MAG@CHT, absorption mechanism of perchlorate on MAG@ CHT likely includes: (1) adsorption on the surface of adsorbent by electrostatic interactions; (2) restoration of the layered structure by using ClO4– as an anion interlayer.