【作者】 王仕芳；

【导师】 李在均；

【作者基本信息】 江南大学 ， 分析化学， 2011， 硕士

【摘要】 离子液体是一种绿色溶剂,它作为萃取介质可避免传统湿法冶金因有机溶剂挥发而产生环境污染。采用改进后的无溶剂法和程序升温法合成5种1-烷基-3-甲基咪唑六氟磷酸盐([CxMIm][PF6],其中X=4、6、8、10、12)离子液体。离子液体粗品用丙酮稀释后,活性炭脱色制得无色离子液体,产品在400~800 nm范围内无明显吸收。离子液体理化性质被详细研究。紫外吸收光谱法测定离子液体在水中的溶解度。芘荧光探针测得离子液体极性和短醇类相当,并显示出随着烷基链的增加,极性逐渐降低的规律性。热稳定性、密度、粘度和表面张力等物理化学性质结果表明:离子液体的性能是由阴、阳离子的结构和性质共同决定的。热稳定性、密度、粘度和溶解性主要受阴离子种类影响;随着咪唑阳离子取代基链长的规律性增加,离子液体的热稳定性、密度、极性、水含量和表面张力逐渐降低;热分解温度均高于260 oC;密度介于1.1~1.4g.cm-3之间;表面张力高于传统有机溶剂正己烷,低于水的表面张力。因此离子液体的高稳定性、强憎水性、低表面张力的性质应用于萃取方面有着独特的优势。以制备合成的离子液体(IL)、磷酸三丁酯(TBP)和三氯化铁(FeCl3)分别为萃取介质、萃取剂和协萃剂建立盐湖卤水锂萃取研究模型,考察离子液体性质和不同萃取条件对锂萃取率的影响。结果表明离子液体的粘度、极性和憎水性是影响锂萃取率的主要因素。锂的萃取率随离子液体中烷基碳原子数的增加而增加。然而,当碳原子数超过8时,离子液体室温下呈固态,在萃取过程中出现第三相,不利于萃取分离,因此,1-辛基-3-甲基咪唑六氟磷酸盐被确定为最终萃取介质。该体系的最佳萃取条件是:TBP/IL:9/1(v/v),水相酸度:0.03 mol/L HCl,相比(O/A):1.5:1和Fe/Li:1.3:1。在优化条件下,锂的单次萃取率和反萃率分别是87%和90%。卤水中的钾、钙、镁、钠等主要离子不干扰萃取。卤水中锂的串级萃取实验表明经过三级萃取和二级反萃后,锂的总提取率大于97%,有机相中Mg/Li比降至2.2左右。离子液体-TBP有机相可重复使用10次以上。机理研究表明,Li+与TBP和FeCl3形成极性较小的LiFeCI4·2TBP络合物而被萃取进入有机相,在有机相中加入盐酸因H+极化强于Li+而将Li+置换重新进入水相。因LiFeCl4·2TBP在弱极性的离子液体中溶解度优于非极性的溶剂煤油,离子液体萃取体系具有更高的锂萃取效率和容量。此外,上述体系用于头发中痕量锂的富集测定,线性范围为0.00~2.50μg·L-1,检出限在2.5 ng·L-1,富集倍数在100倍以上,加标回收率在89%~92%之间,实现了简单设备对超复杂体系中超痕量组分的准确测定,结果满意。更多还原

【Abstract】 Ionic liquid is green solvent and as extraction medium can avoid environmental pollution of conventional hydrometallurgy due to volatilization of organic solvent. The modified two-steps method using non-solvent and temperature programmed technologies was developed for synthesis of five ionic liquids 1-alkyl-3-methylimidazolium hexafluorophosphate abbreviated as [CxMIm][PF6], where X=4, 6, 8, 10 and 12. After the crude products were diluted by acetone, it was decolored with activated carbon and almost colorless ionic liquids were obtained. There was no obvious absorption peak in the wavelength range of 400~800 nm.The physical and chemical properties of the ionic liquid such as thermal stability and solubility were investigated in detail. We determined the solubility of ionic liquids in water by ultraviolet absorption spectrum method. Polarity of ionic liquid was determined by pyrene fluorescence probe, and found polarity decreasing with the increasing of alkyl chain length. Besides, the physical properties containing thermal stability, density, viscosity and surface tension were determined. The results showed the properties were decided by both cations and anions of ionic liquids and exhibited how melting point, viscosity, density and surface tension were affected by changes in alkyl chain length. In the series of ionic liquids studied here, the thermal stability, polarity, water content and surface tension of ionic liquids were decreased with the increasing in alkyl chain length. All these ionic liquids exhibited excellent thermal stability of 260 oC; density was of 1.1~1.4g.cm-3; surface tension lower than water and higher than hexane. Therefore, the excellent properties containing high stability, strong hydrophobicity and low surface tension of ionic liquids proved its advantage in extraction.A model for study on extraction lithium from salt lake brine was designed, in which the assayed ionic liquid (IL), tributyl phosphate (TBP) and FeCl3were used as extraction medium, extracting agent and synergic reagent, respectively. The effects of ionic liquid propertied and extraction conditions on the lithium extraction were investigated. The results indicated that the viscosity, polarity and hydrophobicity were the main factors which influenced the extraction efficiency. With increasing number of carbon atom of alkyl group in the ionic liquid the extraction efficiency of lithium will obviously increase. However, the ionic liquid was solid and resulted in appearing a third phase when number of alkyl group exceeded eight. Thus, 1-octyl-3-methylimidazolium hexafluorophosphate ionic liquid was finally selected as extraction medium. Optimal extraction conditions of the system included TBP/IL of 9/1(v/v), 0.03 mol/L HCl, O/A of 1.5:1 and Fe/Li of 1.3:1. Under optimal conditions, single extraction and back-extraction efficiencies are 87% and 90%, respectively. The interference study indicated the determination of lithium was free from the interference of almost all positive and negative ions such as K+, Ca2+, Mg2+ and Na+ found in brine water. Daisy extraction of salt lake brine indicated that total recovery of 97% was obtained by combination of three step extractions with two step back-extraction, and Mg/Li ratio was lower to about 2.2. The reuse of ionic liquid-TPB organic phase was up to 10 times. Study on the mechanism revealed Li+ combines with TBP and FeCl3 to form a low polar LiFeCI4·2TBP and was extracted into organic phase because, and addition of HCl in the organic phase will result that Li+ was again back-extracted into aqueous phase due to strong polarization force of H+. As LiFeCl4·2TBP is more easy to small polar ionic liquid than non-polar solvent paraffin, the system with ionic liquid is of higher extraction efficiency and the capacity of lithium.Moreover, the above system was applied to the preconcentration of ultra trace lithium in hair. Proposed procedure allowed the rapid lithium determination at 2.5μg.L-1 level in hair samples with satisfactory results. The detection limit, calculated using three times the standard error of estimate of the calibration graph, was 2.5 ng of lithium per liter hair sample. The enrichment factor of lithium was more than 100 times. Lithium recoveries between 89 and 92% for samples proof the accuracy of the proposed method.更多还原