Magnetic nanocomposites based on Zn,Al-LDH intercalated with citric and EDTA groups for the removal of U(vi) from environmental and wastewater: synergistic effect and adsorption mechanism study

Abstract

The efficient removal of U(VI) ions from contaminated natural waters and wastewaters of industrial processing plants by novel magnetic nanocomposites based on magnetite and Zn,Al-layered double hydroxides intercalated with citric and EDTA groups (Fe₃O₄/Zn,Al-LDH/Cit and Fe₃O₄/Zn,Al-LDH/EDTA) was shown. These adsorbents were obtained using co-precipitation and ion-exchange techniques. The infrared spectroscopy confirmed the existence of O-containing groups on the surfaces of Fe₃O₄/Zn,Al-LDH/Cit and Fe₃O₄/Zn,Al-LDH/EDTA, which could provide active sites in the interlayer of the adsorbents for the pollutants removal. The intercalation of Zn,Al-LDH with chelating EDTA-groups significantly increased the adsorption capacity toward U(VI) ions (131.22 mg g⁻¹) compared to citric moieties in a wide range of pH (3.5–9.0). The maximum adsorption capacities of U(VI) at pH 7.5 were 81.12 mg g⁻¹ for Fe₃O₄/Zn,Al-LDH/EDTA and 21.6 mg g⁻¹ for Fe₃O₄/Zn,Al-LDH/Cit. The higher adsorption capacity of Fe₃O₄/Zn,Al-LDH/EDTA vs. the citric sample might be explained by high affinity of LDH-supports and high-activity of the chelating groups in formation of the complexes in the interlayer space of the magnetic nanocomposite. The removal of U(VI) by the magnetic nanocomposites occurred due to interlayer complexation and electrostatic interactions. The cations (Na⁺, K⁺, Ca²⁺), HCO₃⁻ and fulvic acid anions being typical for natural waters were practically not affected upon the removal of U(VI) from aqueous media. The adsorption performance of Fe₃O₄/Zn,Al-LDH/EDTA nanocomposites was evaluated in the analysis of environmental and wastewater samples with recoveries in the range of 95.8–99.9%. This superior intercalation performance of LDH-supports provides simple and low-cost adsorbents, providing a strategy for decontamination of radionuclides from wastewater.