چكيده به لاتين
The rare earth elements have an ever growing variety of applications in the modern technology such as hybrid vehicles, night vision cameras and wind turbines. Because of proximity of these elements in the nature, their extraction and separation from each other is the most important challenges. In this thesis, the extraction and separation of samarium and lutetium from aqueous acidic solutions were investigated by solvent extraction method. On the basis of the stability diagram of these elements in acidic media drawn by Medusa software, the optimized conditions were obtained and applied for extraction and separation of Lu from Sm by acidic extractants of D2EHPA, PC88A and their mixtures from nitric and sulfuric acidic solutions. . In order to maximize the extraction efficiency of Sm and Lu from acidic solution, the effective parameters such as initial aqueous pH, time, concentration of D2EHPA and PC88A were optimized so that the optimum values of above parameters were obtained for Sm and Lu extraction as, 2.5, 10 min, 0.05 M and 0.4 M, and 1.5, 5 min, 0.03 M and 0.05 M, respectively. Based on the results obtained at this stage, it was found that the tendency to extraction of lutetium is much higher than samarium in all systems. The main reason for this is the smaller ionic radius of lutetium compared to samarium and the consequent increase in the electric charge density of this element. Furthermore, the stoichiometric coefficients of reaction equations, equilibrium constants and thermodynamic functions were calculated for two extractants and their mixture for extraction of these elements from nitric and sulfuric acid solutions. The thermodynamic results showed that the order of priority of the various systems studied in order to achieve the maximum extraction efficiencies of samarium and lutetium metals was from the D2EHPA in nitric medium to the PC88A in sulfuric medium, respectively. Therefore, the extraction ability of PC88A was lower compared to D2EHPA due to the presence of excess oxygen bond in the molecular structure of D2EHPA.
The synergistic enhancement factor showed that the mixture of extractants provided better extraction efficiency, especially in the case of samarium and the effective stripping of metals, especially in the case of lutetium, in comparison with single D2EHPA or PC88A, due to the formation of a novel dimer that combined with the PC88A and D2EHPA unimers based on the results of FT-IR, in certain proportions. The most synergistic effect was observed for samarium extraction equal to 5.71, which was obtained in a 2: 3 ratio of PC88A to D2EHPA extractants while the most synergistic effect of these two extractants was obtained at the extractants ratio of 1 to 4 for lutetium extraction which was determined as 1.6. By investigating the reaction of samarium extraction by the mixture of extractants, the stoichiometric coefficients in both aqueous solutions for D2EHPA and PC88A were 2 and 1, respectively. In the final stage, in order to determine the optimal separation conditions of samarium and lutetium elements from the aqueous solution, experiments were designed and carried out using Design expert software taking into account the variables of initial pH of the aqueous solution (A), total concentration of extractants (B), mole fraction of D2EHPA in the organic phase (C), and aqueous solution type (D). The R-squares of the actual and predicted data values for Samarium and Lutetium extraction were 97.87% and 98.36%, respectively, indicating a good agreement between the experimental data and the proposed model prediction. Finally, in order to achieve maximum separation between the two elements, the optimal values for parameters A, B, C and D were determined as 0.85, M 0.05, 0.2 and sulfuric solution, respectively, under which the separation coefficient was 272.
