Adsorption of Eu(III) from Aqueous Solutions of Zn,Al- and Mg,Al-Layered Double Hydroxides, Intercalated by Citrate Ions, and Their Magnetic Forms

Abstract

We studied the adsorption extraction of Eu(III) from aqueous media by Zn,Al- and Mg,Al-layered double hydroxides (LDHs), intercalated by citrate ions, and their composites with magnetic properties. Cations typical of natural waters (Na+, K+, Ca2+, Mg2+) do not affect the efficiency of water purification from Eu(III), and humic acids even increase it when using composite materials. The following conditions for the extraction of Eu(III) were determined: pH of the aqueous medium, adsorption kinetics, adsorbent dose, and the effect of organic and inorganic macrocomponents of aqueous media. The adsorption equilibrium is achieved for the studied citrate forms of LDH and their magnetic composites after 1 h of contact of the aqueous solution with the solid phase of the adsorbents. Based on the parameters of kinetic models and linear correlation coefficients, we demonstrated that Eu(III) adsorption with these LDH forms is most reliably described by a pseudosecond order model in the entire range of adsorption durations, in contrast to the pseudofirst-order model. This indicates the prevailing mechanism for the extraction of Eu(III) due to chemisorption, and the equilibrium adsorption values calculated theoretically from the pseudosecond-order model are in good agreement with the experimental ones. The adsorption isotherms of Eu(III) on the citrate forms of Zn,Al- and Mg,Al-LDHs and their magnetic composites were processed using the Freundlich and Langmuir equations; these adsorption models satisfactorily describe the experimental data (correlation coefficients ≥0.99). The forms of the presence of Eu(III) in aqueous solutions are calculated at different pH values in the presence of citrate ions and natural organic ligands (fulvic acids). We propose the mechanism of removal of Eu(III) from aqueous media. The results give grounds to recommend the studied materials as effective adsorbents of radionuclide-complexing agents for the purification of contaminated surface water and liquid radioactive waste using adsorption technology with magnetic separation of sludge.