CONICET | Buscador de Institutos y Recursos Humanos

Pollutant releases into the environment is a dramatic problem related to modern life. Industries such as metallurgical, petrochemical, electronic, paint and pigment, together with other human activities are a very important sources of heavy metals contamination in effluents. The pollution originated in these environmental matrices should be detected at early stage and, if necessary, different remediation techniques must be taken into account [1]. In particular, cesium, cobalt and strontium are heavy metals that can be released into the environment during accidents in nuclear reactors. Their high toxicity makes essential to remove them from contaminated effluents.Widely extended remediation technologies are based on the process of sorption of the contaminants. Among the sorbent materials, clay minerals such as montmorillonite (MMT), are well ranked [2]. Montmorillonite clays are 2:1 layered structures which in natural state may allocate different hydrated cations such as M-nH2O (M=Na, Ca, Fe, etc.) in its interlayer spacing. The present work resumed the preliminary results of a theoretical-experimental approach study of Sr sorption in Na-MMT, Na0.41[(MgAl3O8(OH)4 (Si8O12)]2 .n(H2O). For the determination of the Sr adsorption, the experiments were carried out under batch conditions (V = 25 mL, Sr concentration 100 mg/L, pH = 6, S/L=5 g/L). After the test, solid and liquid phases were separated by centrifugation and the solid one were analyzed using X-ray diffraction (Cu-Kα) to determine the position of the reflection peak d001 (partial diffractograms-semioriented samples). Sr adsorption was quantify by the difference between the initial and the equilibrium concentration, using ICP- masses. The obtained adsorption percentage was 80 ± 4%.Also, a modelization of the sortion procces has been performed in the framework of the Density Functional Theory. For the calculations, the pseudopotential and plane-wave method was used. (Quantum Espresso code [3]), and the exchange-correlation interaction has been described with GGA-PBE, and also van der Waals correction was considered (rVV10). In order to evaluate if the Sr sorption is favored, total energies and formation energies were calculated. Furthermore, we have determined the electric field gradient and NMR parameters in different atoms using the GIPAW method [4]. We started from pristine MMT (Na-MMT), and we explored the replacement of Na atoms located into the interlayers spacing by Sr atoms coordinated with n.H2O molecules (n=4, 6, 8, 10). For each case, atomic positions and cell parameters has been optimized in order to obtain the formation energy at equilibrium. The basal spacing d001 for the optimized structures was calculated and compared with the experimental one, obtaining a good agreement with this last. Comparison of Sr sorption with Co sorption [5] (previous study) was also discussed.[1]. J. Hofmann, R. Leicht, H.J. Wingender, J. Wörner, Natural radionuclide concentrations in materials processed in the chemical industry and the related radiological impact, European Commision; Nuclear Safety and the Environment Report EUR 19264, (2000).[2]. S.S. Gupta, K.G. Bhattacharyya, Adsorption of heavy metals on kaolinite and montmorillonite: a review, Phys. Chem. Chem. Phys. 14 (2012) 6698.[3]. C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101.[4]. P. Giannozzi, et al., Advanced capabilities for materials modelling with Quantum-ESPRESSO, J. Phys.: Condens. Matter. 29 (2017) 462901.[5]. A.V. Gil Rebaza, M.L Montes, M.A. Taylor, L.A. Errico, R.E. Alonso, Experimental and theoretical study of Co sorption in clay montmorillonites, Mater. Res. Express 5 (2018) 035519.