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卤素离子是自然界江河湖海及工业生产中常见的阴离子。氟离子常常作为有害杂质存在于各种溶液中，针对酸性高氟溶液，现有除氟技术要么效率低，要么成本高。氯盐体系是重要的湿法冶金反应体系，许多矿物或二次资源在处理过程中都会产生含高浓度氯离子的溶液，而且往往需要和其他阴离子进行分离。传统除氯工艺主要针对低氯的脱除，尚无经济高效的高氯分离方法。溴碘都是有价的元素，但我国溴碘资源匮乏，提取工艺落后，产供矛盾突出，亟需开发新的溴碘资源和先进的生产工艺。针对卤素离子面临的上述难题，本论文利用卤素离子的易络合性，系统研究了卤素离子与中心离子的络合规律，并以Alamine336为萃取剂，详细研究了卤素离子络阴离子的萃取规律。在卤素离子络合萃取规律基础上，开发了新型高效除氟技术、萃氯技术以及提碘技术。取得的主要研究成果如下：（1）卤素离子络合规律、萃取规律以及卤素离子高效分离研究。卤素离子与中心离子形成络合物的稳定常数主要与它们的离子势有关，离子势越相近的离子形成的络合物越稳定。离子的水化能可用来表征离子与萃取剂的接触几率，离子所带电荷越低，半径越大，水化能越小，与萃取剂接触的几率越大，越易被萃取。从离子液体、萃合物空间位阻、碰撞理论、萃取能等方面阐释了络阴离子价态越低，与Alamine336形成的中性萃合物越稳定。通过选择合适的络合试剂，使目标元素形成低价态络阴离子或使杂质元素形成高价态络阴离子，从而提高目标元素的萃取效率和选择性。（2）氟离子的络合萃取工艺及机理研究。通过引入硼离子，形成了易被萃取的硼氟酸根离子，有机相饱和容量相比萃取单一氟离子增加了4倍。通过红外光谱分析负载有机相，在1040 cm-1处发现了硼氟酸根离子的特征吸收峰。氟离子的萃取效率随着硼氟摩尔比、Alamine336浓度、萃取相比增加而显著增加。当初始氟浓度为5 g/L时，经过两级错流萃取，氟萃取效率达到99%。二价金属离子铜、锌、镍对氟萃取基本没有影响，可用于铜、锌、镍等电解液的除氟。通过热力学研究可知萃取过程是放热反应。当温度为298 K时，萃取硼氟酸根离子和氟离子的分别为-2.93 kJ/mol和-0.92 kJ/mol。前者小于后者，意味着萃取硼氟酸根离子的反应是优先的。（3）氯离子的络合萃取工艺及机理研究。通过引入锌离子形成锌氯配合物，实现了氯离子的高效萃取。氯离子的萃取效率随着锌氯摩尔比、Alamine336浓度和萃取相比增大而显著增大。温度和初始pH对氯离子的萃取效率影响很小。经两级逆流萃取，氯离子浓度可由100 g/L降至10 g/L。根据锌氯配合物的逐级络合常数可以计算，当锌氯摩尔比为0.23时，被萃物应以ZnCl3-为主。该预测结果与饱和容量法和斜率法所得结果一致。通过热力学研究可知萃取过程为吸热反应。根据吉布斯-骇姆霍兹公式可以求得萃取过程的主要热力学参数。（4）碘离子的络合萃取工艺及机理研究。通过氧化碘离子形成碘三负离子，实现了碘的高效萃取。碘萃取效率随着双氧水用量、萃取相比和Alamine336浓度增大而增大，随着温度和平衡pH增大而减小。经过一级萃取，碘萃取效率达到91%。负载有机相中碘氯摩尔比为1.68，相比初始溶液提高了600倍，说明该萃取体系对碘的选择性较高。由于碘三负离子形成的平衡常数较大，当水相中碘离子比例大于10%时，I3-的比例始终高于I2，意味着直接回收I-和I3-相比I2更容易。根据饱和容量实验可知，I-和I3-均按摩尔比1:1与萃取剂(R3NH+)结合。根据紫外光谱分析可知，当加入双氧水后，形成了I3-。365 nm处的吸收峰应为萃取剂(R3NH+)与I-的相互作用产生的，485-535 nm处的吸收峰应为萃取剂(R3NH+)与I3-的相互作用产生的。;Halide ions are common anions in nature and industrial production. Fluoride ion is harmful impurity in a variety of solutions. For acidic high-fluoride solutions, conventional de?uoridation technologies are either inefficient or costly. Chloride system is an important hydrometallurgical medium, and high-chloride solutions are usually generated by utilizing these minerals or secondary resources containing chloride. The typical processes are mainly aimed at the removal of low-chloride, so economical and efficient methods are urgent for high-chloride solution. Bromine and iodine are valuable elements, but the resources are scarce, the technologies are backward, and the contradiction between production and supply is acute, hence it is critical to explore new resources and develop advanced process. In view of the above-mentioned problems, the complexation regulations between halide ions and central ions have been studied, and the extraction regulation of halide complex anions have also been investigated by using Alamine336 as the extractant. On the basis of the obtained regulations, efficient processes for fluoride removal, chloride separation and iodine extraction have been developed. The main results are as follows:The stability constants of the complexes formed by halide ions and central ions are mainly related to their ionic potentials. The more close the ionic potentials are, the more stable the complexes can be formed. The hydration energy of ions can be used to characterize the contact probability of ions with extractants. The lower the charge and the larger the radius of ions, the smaller the hydration energy, the easier it is to contact with extractants and the easier it is to be extracted. From the aspects of ionic liquid, steric hindrance, collision theory and extraction energy, it is explained that the lower valence of complex anion is, the more stable the neutral extraction complexation is. In order to improve the extraction efficiency and selectivity, suitable complex reagents were selected to form low valence complex anions for target elements, or to form high valence complex anions for impurity elements.Boric acid was selected as the complexation reagent since boron coordinated with fluoride strongly, and the generated borofluoride ion with low hydration energy is an easily extracted species. The extraction ratio was found to increase with the increase in the boron fluoride molar ratio, Alamine336 concentration, and phase volume ratio. Fluoride decreased from 5 g/L to 0.05 g/L after two-stage cross-flow extraction alone; with an extraction efficiency of 99%. For the simulated electrolyte, the majority of metallic ions were insensitive to the extraction, with the exception of Al3+ and Fe3+. The loading capacity was 43.4 g/L, and increased by four times, when boric acid was added. FT-IR spectroscopic analysis was utilized for describing the extraction mechanism, and the peak appeared at 1040 cm-1 was the characteristic peak of BF4-. It was found that the extraction process was exothermic, and the main thermodynamic parameters were obtained by Gibbs-Helmholtz equation.Zinc sulfate was selected as the complexation reagent since zinc coordinated with chloride strongly. The extraction ratio increased with increases in Alamine336 concentration, phase volume ratio and Zn/Cl molar ratio. However, temperature and initial pH had negligible effects on the extraction ratio. After a two-stage counter-current extraction, the concentration of Cl in the raffinate could be reduced from 100 g/L to 10 g/L. Chloride was mainly extracted as ZnCl3- when Zn/Cl molar ratio was 0.23, as predicted by theoretical calculations based on the cumulative stability constants. The result was confirmed experimentally by saturated method and slope method. It was found that the extraction process was endothermic, and the main thermodynamic parameters were obtained by Gibbs-Helmholtz equation.An efficient process was proposed for the recovery of iodine via solvent extraction of triiodide (I3-) and iodide (I-). The extraction ratio increased with the increasing of H2O2 dosage, phase volume ratio and Alamine336 concentration, whereas it decreased with the increase in equilibrium pH and temperature. The extraction ratio reached up to 91% after only one stage extraction. High selectivity was found since the molar ratio of I/Cl in the loaded organic phase increased by 600 times compared with the initial aqueous. When the distribution ratio of I- was more than 10%, the distribution ratio of I3- was always more than that of I2, indicating that the recovery of I- and I3- was easier than I2. UV–vis spectra analysis was also utilized for describing the extraction mechanism.
|李建. 卤素阴离子络合萃取机理及选择性分离研究[D]. 中国科学院大学,2020.|
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