Carbonate Form of Mg,Al-Layered Double Hydroxides for Concentrating Eu(III) and Its Subsequent Analytical Determination in Natural Aqueous Media

Abstract

The efficiency of the sorption of Eu(III) by various forms of Mg,Al- and Zn,Al-layered double hydroxides (LDH) from model and natural waters at various pH was estimated for concentrating this metal ions and its subsequent spectrophotometric determination. It was found that the almost complete extraction of Eu(III) is reached on the carbonate form of Mg,Al-LDH by a deposition mechanism because of the formation of poorly soluble compounds of this element (carbonate and hydroxide of Eu(III) at pH ≥ 6.2, which correlates with the calculated Eu(III) speciation in aqueous solution in the presence of carbonate ions. The distribution coefficients of Eu(III) are 1.4 × 106 cm3/g (the pH of the initial solution is ≥7.0; the pH of the solution after the sorption is ≥ 6.87), which is indicative of a high efficiency of this sorbent with respect to this metal ion. For Mg,Al- and Zn,Al-LDH intercalated with organic complex-forming ligands—citrate and ethylenediaminetetraacetate ions, the dominant mechanism Eu(III) extraction from aqueous media is the complex formation. The distribution coefficients of Eu(III) on these sorbents are (0.26—22.71) × 103 cm3/g. For concentrating Eu(III) and its spectrophotometric determination in natural waters, it was proposed to use the carbonate form of Mg,Al-LDH with its subsequent decomposition by a nitric acid solution after the sorption. It was shown that the major components of natural waters and the constituents of this sorption materials do not affect the correctness and accuracy of the determination of Eu(III) by this method with arsenazo III (at pH 2.6 ± 0.1). The linearity range of the calibration graph is 1–50 μg Eu(III) in 50 cm3 of the final solution cm3 (λ = 650 nm). The proposed method of concentrating and determining Eu(III) was tested on samples of model, tap, and surface waters (the sorbent weight is 0.100 g, and the water sample volume is 500 cm3).