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题名	液－液－液三相萃取分离金属及调控
作者	谢铿
学位类别	博士
答辩日期	2012-06-02
授予单位	中国科学院研究生院
导师	刘会洲
关键词	液－液－液三相萃取 Ti Fe Mg和Cr 络合剂 功能化聚合物 光还原
其他题名	Three-Liquid-Phase Extraction of Metal: Behavior and Regulation
学位专业	化学工艺
中文摘要	由有机溶剂、聚合物、无机盐和水形成的液－液－液三相体系集成了油－水两相萃取和聚合物－无机盐双水相萃取的优势，是一类具有良好应用前景的新型萃取体系。本论文系统地研究了Ti、Fe、Mg和Cr在三相体系中的分配行为及其影响因素，探讨了添加络合剂或功能化聚合物对三相萃取Ti、Fe和Mg的调控作用，实现了Ti、Fe和Mg的一步萃取分离以及同一种金属的不同价态离子（Cr(III)和Cr(VI)）的分离，建立了光还原耦合三相萃取一步脱除和回收水溶液中Cr(VI)的方法。具体开展的研究工作和取得的研究成果如下： 1.针对Ti、Fe和Mg的分离，构建了三烷基氧化膦（TRPO）－聚乙二醇（PEG）－无机盐三相体系，考察了初始水相pH、无机盐种类和浓度及PEG分子量对Ti(IV)、Fe(III)和Mg(II)在三相体系的分配行为的影响。当初始水相pH由0.5增大到2.0时，Ti(IV)在TRPO上相的萃取率由71.9%逐渐降低到64.8%，Fe(III)在TRPO上相的萃取率从55%增加到了65%；盐析能力强的盐有利于TRPO萃取Ti(IV)和Fe(III)，以Na2SO4替代(NH4)2SO4做成相盐，Ti(IV)和Fe(III)在上相的萃取率增大了15%左右；采用分子量大的PEG做成相物质，可提高Ti(IV)、Fe(III)和Mg(II)在中相的萃取率。实验发现，Ti(IV)和Fe(III)共萃进入上相，PEG中相基本不萃取Ti(IV)、Fe(III)和Mg(II)，Mg(II)全部保持在盐水下相，Ti(IV)和Fe(III)在上相和中相间的分离系数（βTi/Fe, t/m）<4，由此表明，此时不能实现三相萃取分离Ti(IV)、Fe(III)和Mg(II)。 2.通过筛选，发现了添加络合剂EDTA或1,10-邻菲啰啉（phen）可以使Fe定向迁移到PEG中相，TRPO－PEG－(NH4)2SO4三相体系可实现Ti(IV)、Fe(III)和Mg(II)的三相分配。考察了初始水相pH、络合剂添加量、(NH4)2SO4用量、PEG用量、TRPO浓度和金属浓度的影响，发现初始水相pH和络合剂添加量是影响络合剂调控作用的关键因素。EDTA分子中的亚甲基和phen的联苯环结构与PEG链段的疏水相互作用是使金属配位物进入PEG中相的主要推动力。通过优化实验，提供了三相萃取分离Ti(IV)、Fe(III)和Mg(II)的工艺策略。添加EDTA，PEG中相萃Fe(III)是放热反应，焓变∆H为-13 KJ∙mol-1，经四级萃取，Ti(IV)在上相的萃取率（ETi(IV), t）可达到99.1%，Fe(III)在中相的萃取率（EFe(III),m）可达到95.4%；负载上相和中相可分别采用4 mol∙L-1盐酸和pH<0.5的(NH4)2SO4溶液反萃再生。如果预先将水相中的Fe(III)还原为Fe(II)，添加phen，一级萃取，ETi(IV), t和EFe(II),m分别达到86%和100%，Ti(IV)和Fe(II)在上中两相的分离系数β>20000，Mg(II)全部保持在下相。 3.合成了EDTA－PEG功能化聚合物，考察了添加EDTA－PEG时，二（2-乙基己基）磷酸（D2EHPA）－PEG－(NH4)2SO4三相体系对Ti(IV)、Fe(III)和Mg(II)的萃取分离效果。由于EDTA－PEG与PEG结构性质相似度很大且含有EDTA官能团，在分相过程中有利于Fe(III)转入PEG中相。实验表明，全部Fe(III)可富集到PEG中相，与此同时，100%的Ti(IV)被萃入D2EHPA上相，Mg(II)完全保持在(NH4)2SO4水相，EDTA－PEG的反复萃用性能良好。 4.针对Cr(III)和Cr(VI)的分离，构建了D2EHPA－PEG－(NH4)2SO4三相体系，研究了Cr(III)和Cr(VI)在三相体系中的分配行为，发现D2EHPA上相和PEG中相分别对Cr(III)和Cr(VI)具有良好的选择性。Cr(III)以Cr(OH)2+形态通过阳离子交换进入D2EHPA上相，Cr(VI)以HCrO4-形态与质子化的PEG结合生成HCrO4-∙PEGH+离子缔合物萃入PEG中相。通过调节成相剂含量和水相pH，实现了三相萃取一步富集分离Cr(III)和Cr(VI)。 5.实验中发现光照下PEG可以快速还原Cr(VI)，基于此现象，并结合D2EHPA－PEG－(NH4)2SO4三相体系萃取分离Cr(III)和Cr(VI)的性能，提出了光还原耦合液－液－液三相萃取处理含Cr(VI)溶液的方法。采用红外和1H NMR分析探讨了还原机理。研究了Cr(VI)的还原速率的控制方法，结果表明，Cr(VI)还原速率随光照强度和PEG用量的增大而增大，随溶液初始pH、PEG分子量和初始Cr(VI)浓度的减小而增大。用该方法处理含Cr(VI)溶液，高毒性的Cr(VI)先被PEG中相富集并在光照下还原成低毒性的Cr(III)，Cr(III)进一步被萃入D2EHPA上相，上相中的Cr(III)容易用酸液反萃回收。 本论文的工作为液－液－液三相萃取分离金属新工艺的实际应用奠定了基础。
英文摘要	The newly emerging three-liquid-phase system (TLPS), which is constructed by organic solvent, polymer, inorganic salt as well as water, is considered as an integration of an oil-water liquid-liquid system and a polymer-water aqueous-two-phase system and a promising extraction system in industry. The partition behavior of Ti, Fe, Mg and Cr in the TLPSs and the related influencing factors were systematically studied in the dissertation. One-step extraction and separation of Ti, Fe and Mg was realized by addition of a complexing agent or a functionized polymer. Also, one step enrichment and separation of different oxidation states of one metal (Cr(III) and Cr(VI)) using the three-liquid-phase extraction (TLPE) was attained. Moreover, an innovative photochemical reduction combined TLPE for one-pot reduction, detoxication and recovery of Cr(VI) was formulated. The details of the study are as follows 1. Trialkylphosphine oxide (TRPO)-polyethylene glycol (PEG)-inorganic salt TLPSs were developed for enrichment and separation of Ti(IV), Fe(III) and Mg(II), The effects of pH value, inorganic salt amount and types, and PEG molecular weight on the partition behavior of Ti(IV), Fe(III) and Mg(II) in the TLPSs were investigated. Extraction percentage of Ti(IV) by the top phase was 71.9% at pH 0.5 and slightly deceased to 64.8% at pH 2.0, while that of Fe(III) increased from 55% at pH 0.5 to nearly 65% at pH 2.0. The salt with a higher salt-outing ability can induce more incompatibility between the bottom phase and the upper two phases and increases the affinity of Ti(IV) and Fe(III) for the TRPO-rich top phase. When Na2SO4 was used instead of (NH4)2SO4 as the phase-forming salt, an increase of 15% or so in the metal extraction was found at 20 wt.% salt concentration and pH 0.5. The salinity and acidity of the solution together with the PEG molecular weight directly influences the equilibrium of the systems and furtherly the metal ions’ partition behaviors. Under such conditions with lower salinity (or higher acidity or higher PEG molecular weight), more water was incorporated into the PEG-rich middle phase and metals accompanied free water to the middle phase. However, the increments in the metal extraction percentages are small. Ti(IV) and Fe(III) were co-extracted into the TRPO-rich top phase and the maximum was only 4. TLPE of Ti(IV), Fe(III) and Mg(II) could not be realized in this situation. 2. Ethylenediaminetetraacetate acid (EDTA) and 1,10-phenanthroline (phen) were screened to be effective in transferring Fe to the PEG-rich middle phase. They played both the roles of a masking agent and an extractant. By the masking effect, Fe(III), which interfered in the extraction of Ti(IV), was removed from the TRPO-rich top phase. Acting as an extractant, each is capable of transferring Fe(III) to the middle phase. The solution pH and the amount of complexing agent are two key factors influencing the complexation. Hydrophobic interaction was the main driving force for the enrichment of the metal complexes in the PEG-rich middle phase. The extraction of Fe(III) by the PEG-rich middle phase is exothermic with a enthalpy (∆H) value of -13 kJ/mol with EDTA. The extraction percentage of Ti(IV) in the TRPO-rich top phase(ETi(IV), t) was 99.1% and the extraction percentage of Fe(III) in the PEG 2000-rich middle phase (EFe(III), m) was 95.4% after four extraction procedures with EDTA. The loaded TRPO-rich phase and the loaded PEG 2000-rich phase could be stripped by 4 mol∙L-1 HCl acid and pH<0.5 (NH4)2SO4 solution, respectively, and regenerated. Nearly 86% of titanium were extracted into the top phase while 100% of iron(II) was distributed into the middle phase, without interference between each other, and the separation factor of titanium and iron in the upper two phases was greater than 20000 with addition of phen after reduction of iron(III) to iron(II) by hydroxylammonium chloride. Mg(II) tended to remain in the bottom phase. The present work highlights a new approach by using TLPE technique to enhance the separation of multimetal system and prevent the mutual interference resulting from coextraction of components. The characteristic of complete transfer of iron into the PEG-rich middle phase of TLPS in the presence of phen suggests a potential use of TLPE for separation of iron and other target metals as iron is ubiquitous and separation of iron is often needed in the analytical scale and the hydrometallurgical industry as well. 3. A functionized polymer EDTA-PEG was synthesized, characterized and added into the di-2-ethyl-hexyl phosphoric acid (D2EHPA)-PEG with molecular mass 2000 (PEG 2000)-(NH4)2SO4 TLPS. As expected, immobilization of functional group on the polymer chain can entitle the polymer extractability and selectivity for the target metals owing to its PEG-like structure and complexing ability for metals. The PEG 2000-rich middle phase extracted Fe(III) quantitatively upon the addition of EDTA-PEG and almost all Fe(III) was distributed into the PEG 2000-rich middle phase. Meanwhile, 100% of Ti(IV) and all of Mg(II) were concentrated in the D2EHPA-rich top phase and (NH4)2SO4-rich bottom phase, respectively. Obviously, one-step extraction and separation of Ti(IV), Fe(III) and Mg(II) was achieved in the TLPS. The extraction and back-extraction properties of EDTA-PEG remain good after reuse for 6 times. The employment of functionized polymer in the TLPE provided a new route for separation techniques. 4. A D2EHPA-PEG-(NH4)2SO4 TLPS was developed for enrichment and separation of Cr(III) and Cr(VI). The organic top phase and the polymer-rich middle phase exhibited a high separation selectivity for Cr(III) and Cr(VI), respectively. Cr(III) preferred the D2EHPA-rich top phase through a cation exchange reaction while Cr(VI) was enriched into the PEG-rich middle phase according to an ion-pair formation route. Thorough separation of metals can be easily achieved by adjusting the parameters such as the initial solution pH and the concentration of the phase-forming substances. Both Cr(III) and Cr(VI) can be removed or recovered from aqueous solutions in a single extraction procedure, reducing the risk of releasing toxic metals into the environment and increasing the profit from recycling the total chromium as much as possible. The characteristic of distribution of different oxidation states into respective phases of TLPS suggests an extensive application of TLPE in dealing with the metals and non-metal elements that have variable oxidation states. 5. The photoreduction of Cr(VI) by PEG was discovered. Based on this, an innovative photochemical reduction combined TLPE was formulated. Use of this method to treat Cr(VI) in the D2EHPA-PEG-(NH4)2SO4 TLPS, Cr(VI) would enrich in the PEG-rich middle phase and was reduced under irradiation. The photoreduction process is based on such a mechanism that Cr(VI)-PEG ester formation, photo-excitation and then decomposition with electron transfer from the oxygen atoms of PEG molecular chain to the Cr(VI) anions. The reduction rate of Cr(VI) increases with the increase of light intensity or PEG dosage and the decrease of solution pH or PEG molecular weight or the initial Cr(VI) concentration. All the produced Cr(III) could form complexes with D2EHPA and distributed into the D2EHPA-rich top phase and further be completely stripped by acid solution. The future design and implementation of TLPE in the enrichment and separation of metals can be benefited by the theoretical and experimental results from this dissertation.
语种	中文
公开日期	2013-09-25
内容类型	学位论文
源URL	[http://ir.ipe.ac.cn/handle/122111/1796]
专题	过程工程研究所_研究所（批量导入）
推荐引用方式 GB/T 7714	谢铿. 液－液－液三相萃取分离金属及调控[D]. 中国科学院研究生院. 2012.

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