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Experimental Study and Optimization of Calcium Ion Extraction Using Emulsion Liquid Membrane with Isotope Separation Perspective

Abdollahzadeh Khanghah, Fariba | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56630 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghotbi, Cyrus; Karimi Sabet, Javad
  7. Abstract:
  8. The aim of this dissertation is to investigate the extraction of calcium ions using an emulsion liquid membrane (ELM) with an isotopic perspective. Considering the importance of ion extraction as a preliminary step to isotope separation, the factors affecting the extraction of Ca(II) ions in the ELM process were investigated and optimization of the process was performed in this study. Dicyclohexano-18-crown-6 (DC18C6) was used as the carrier due to isotopic considerations. However, its extractability for calcium ions is limited. In order to address this issue, it is possible to introduce an organic acid, specifically di-(2-ethylhexyl) phosphoric acid (D2EHPA), into the membrane phase. This addition serves as a synergistic carrier, facilitating the extraction of calcium ions by a cation exchange mechanism. The type of solvent and the ability of D2EHPA to extract calcium ions were tested within a bulk liquid membrane (BLM). Results showed that kerosene achieved better Ca(II) transport efficiency. In addition, D2EHPA showed good efficacy and significantly facilitated the transport of calcium ions (extraction efficiency (98.9 ± 0.3%) and transport efficiency (97.3 ± 1.2%) at 0.05M D2EHPA). The transport mechanism was investigated by FTIR analysis and measurement of the pH drop of the feed phase. The effect of homogenizer time and speed on the stability of the W/O emulsion was evaluated by the method of phase separation and measurement of emulsion droplet size distribution. It was found that to achieve an instability percentage of less than 5% after 6 hours, the speed of the homogenizer should be higher than 6000 rpm and the time should be longer than 7 minutes. Prior to investigating the factors affecting the ELM, a combination of carriers was tested in the ELM. The results showed that 0.01M D2EHPA-0.05M DC18C6 achieved an extraction efficiency of 78.9%, whereas DC18C6 alone had negligible extractability and D2EHPA achieved an extraction efficiency of 30.3%. This indicates a synergistic effect between the carriers, resulting in an extraction efficiency of 48.6%. Therefore, it can be concluded that the above solution is suitable for addressing the issue of low extractability of DC18C6, and 0.01M D2EHPA was used in the next experiments. In addition, the calcium ion concentration in the feed phase is 100 ppm in all experiments. To optimize the extraction of calcium ions using the ELM, a two-level fractional factorial design (FFD) was initially implemented to screen the key factors. In this step, the effect of 10 factors (feed phase pH, carrier concentration, receiving phase concentration, surfactant concentration, membrane/receiving phase volume ratio, homogenizer time and speed, W/O/W stirring time and speed, and feed/emulsion volume ratio) was investigated. It was found that homogenizer time and speed do not have a significant effect on the response. Of the remaining 8 factors, feed phase pH, carrier concentration, feed/emulsion volume ratio, and W/O/W stirring time have a greater influence on extraction efficiency and were therefore selected as important factors. The selected factors were then optimized using a central composite design (CCD), and a reduced quartic model was fitted to the experimental data appropriately. With the exception of the feed/emulsion volume ratio, which had a negative effect on extraction efficiency, the effect of the other three factors was positive. The only significant interaction between the factors was the interaction between the carrier concentration and feed phase pH. The maximum extraction efficiency was 97.3% under optimum conditions (feed phase pH of 4, carrier concentration of 0.035M, W/O/W stirring time of 23.4min, and feed/emulsion volume ratio of 2.3). It was found that under these conditions, an extraction efficiency of 35.1% was achieved due to the synergistic effect. Furthermore, the ELM exhibited satisfactory stability with a breakage value of 0.6
  9. Keywords:
  10. Emulsion Liquid Membrane ; Diethyl Hexyl Phosphoric Acid (DEHPA) ; Experiments Design ; Synergistic Effect ; Calcium Ion Extraction ; Dicyclohexano-18-Crown-6 (DC18C6)

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