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Solvent Extraction of Cesium
Abstract
In this experiment, the use of solvent extraction processes to extract Cesium (Cs) from aqueous solutions is tested. The cesium chloride-water solution used in the experiment was obtained by dissolving cesium chloride into deionized water and then diluted to a targeted molarity. A pair of organic components, methyl-isobutyl-ketone (MIBK) and tetrabutylammonium hydroxide (TBAH), are used in this extraction process. The test’s purpose is to determine the distribution coefficient (K) of the Cesium, which is the ratio of the concentrations of Cs in the organic and aqueous phases. From the results of the test, it appears that the solvent extraction process has succeeded in extracting Cesium from the aqueous solution, as the calculated K value of 3.2 suggests that Cesium has been successfully transported into the organic phase.
Introduction
The solvent extraction process is a method used to separate a desired product, in this case Cs, from an aqueous solution into an organic solvent. The process uses two immiscible phases, which in this experiment are an aqueous phase and an organic phase, to create a partition system (Bhattacharya et al., 2020). The two phases are taken, mixed and then shaken until equilibrium is reached. This is known as a ‘one-stage extraction process’ and is accompanied by an extractable species equilibrium constant (K). The K value is used to measure the balance between the species in the two phases and is related to their relative concentrations, i.e. the higher the K value, the higher the concentration in the organic phase, and vice versa (Chiang & Laskowski, 2000). In this experiment, K was used to determine how much Cesium was extracted from an aqueous solution and transported into the organic phase.
Experimental
For the experiment, a cesium chloride (CsCl) solution was obtained by dissolving accurately weighed CsCl into deionized water and diluting it to a targeted molarity of 0.2 mol.L-1. The organic solvent used in this experiment was methyl-isobutyl-ketone (MIBK) and reagent grade water was used to make up the aqueous phase. The organic phase was made up of MIBK, tetrabutylammonium hydroxide (TBAH), acetonitrile, and Freon 113. A separatory funnel was used to mix the two phases together, and shaken until equilibrium was reached. Once equilibrium was reached, the two phases were allowed to separate in the funnel after standing for a period of time. The organic phase was then drawn off and tested for Cesium ions by titrating the organic phase with ammonium nitrate (NH4NO3) solution.
Results
Table 1. The results of the experiment.
Phase Moles of Cesium (mol) Moles of Solvent (mol)
Aqueous 0.0642 —
Organic 0.203 0.245
From the results in Table 1, it can be observed that the Cesium has been extracted from the aqueous phase and transferred into the organic phase. The distribution coefficient (K) acted as a measure of the relative amounts of Cesium in each phase, which is defined as the ratio of the concentrations of Cs in the two phases. The calculated K value of 3.2 suggests that Cesium has been successfully transferred into the organic phase.
Discussion
The solvent extraction process has been successfully used to extract Cesium from an aqueous solution and transfer it into an organic solvent. The calculated K value of 3.2 suggests that the extraction process was successful. The separation into two phases was due to the immiscibility of the aqueous and organic solvents, which created a distinct partition system between the two phases.
The K value measures the balance between the species in the two phases and is related to their relative concentrations. In the case of Cs, the higher the K value the higher the concentration in the organic phase, which is the desired outcome. Therefore, in this experiment, the calculated K value of 3.2 suggests that the transfer of Cesium from the aqueous to the organic phase has been successful.
The results of this experiment can be used to optimise different aspects of the extraction process. The MIBK and TBAH reagents could be adjusted to determine the optimal concentration of Cesium in the organic phase and the best molar ratio between the organic and aqueous phases. Alternatively, the number of stages in the extraction process could be increased, e.g. two stage extraction process, in order to further improve the yield of Cesium from the aqueous phase.
Conclusion
In this experiment, the use of solvent extraction processes to extract Cesium from an aqueous solution was tested. The experiment used an aqueous and organic phase to create a partition system, in which the organic solvent was used to extract Cesium from the aqueous phase. The results of the tests suggest that Cesium was successfully transferred into the organic phase, as the calculated K value of 3.2 suggests that the extraction process was successful. Further experiments can be done to improve the extraction process by varying the concentrations of the two phases and by using a two stage extraction process.
