Experimental-theoretical study of Sr sorption in Na-montmorillonite

A.V. GIL REBAZA; V.L. DÍAZ DE ROSA; L.M. MONTES; R. BASTIDAS BRICEÑO; L.A. ERRICO; R.E. ALONSO; M.A. TAYLOR

Cartagena

Otro; ICTP Caribbean School on Materials for Clean Energy; 2019

Pollutantreleases into the environment is a dramatic problem related to modernlife. Industries such as metallurgical, petrochemical, electronic,paint and pigment, together with other human activities are a veryimportant sources of heavy metals contamination in effluents. Thepollution originated in these environmental matrices should bedetected at early stage and, if necessary, different remediationtechniques must be taken into account [1]. Inparticular, cesium, cobalt and strontium are heavy metals that can bereleased into the environment during accidents in nuclear reactors.Their high toxicity makes essential to remove them from contaminatedeffluents.Widelyextended remediation technologies are based on the process ofsorption of the contaminants. Among the sorbent materials, clayminerals such as montmorillonite (MMT), are well ranked [2].Montmorillonite clays are 2:1 layered structures which in naturalstate may allocate different hydrated cations such as M-nH2O(M=Na,Ca, Fe, etc.)inits interlayer spacing. Thepresent work resumed the preliminary results of atheoretical-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 werecarried out under batch conditions (V = 25 mL, Sr concentration 100mg/L, pH = 6, S/L=5 g/L). After the test, solid and liquid phaseswere separated by centrifugation and the solid one were analyzedusing X-ray diffraction (Cu-Kα) to determine the position of thereflection peak d001(partial diffractograms-semioriented samples). Sr adsorption wasquantify by the difference between the initial and the equilibriumconcentration, using ICP- masses. The obtained adsorption percentagewas 80 ± 4%.Also,a modelization of the sortion procces has been performed in theframework of the Density Functional Theory. For the calculations, thepseudopotential and plane-wave method was used. (Quantum Espressocode [3]), and the exchange-correlation interaction has beendescribed with GGA-PBE, and also van der Waals correction wasconsidered (rVV10). In order to evaluate if the Sr sorption isfavored, total energies and formation energies were calculated.Furthermore, we have determined the electric field gradient and NMRparameters in different atoms using the GIPAW method [4]. We startedfrom pristine MMT (Na-MMT), and we explored the replacement of Naatoms located into the interlayers spacing by Sr atoms coordinatedwith n.H2Omolecules (n=4, 6, 8, 10). For each case, atomic positions and cellparameters has been optimized in order to obtain the formation energyat equilibrium. The basal spacing d001for the optimized structures was calculated and compared with theexperimental one, obtaining a good agreement with this last.Comparison of Sr sorption with Co sorption [5] (previous study) wasalso discussed.p { margin-bottom: 0.1in; direction: ltr; color: rgb(0, 0, 0); line-height: 120%; }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; }p.cjk { font-family: "Noto Sans CJK SC Regular"; font-size: 12pt; }p.ctl { font-family: "FreeSans"; font-size: 12pt; }a:link { }