Extractive separation of metal ions with inorganic ligands such as halide ion into supercritical carbon dioxide

用超临界流体代替传统有机溶剂的超临界流体萃取技术是近年来研究的热点，用于去除水溶液和固体材料中的金属离子。在超临界流体中，二氧化碳因其具有较低的临界温度和压力、无毒、不可燃性和高纯度而得到广泛应用，尽管其溶剂化能力低于氯仿等有机溶剂，但由于要求金属离子的电荷中和，很难将大多数金属离子从液体和固体样品中提取到高度非极性的超临界流体二氧化碳(SF-CO2)中。然而，不带电荷的络合物的形成使金属离子能够被萃取到SF-CO_2中，以及传统的溶剂萃取。因此，选择合适的络合萃取剂是超临界CO_2萃取剂的关键。本工作对2-甲基-8-喹啉(HMQ)和2-甲基-5-丁氧甲基-8-喹啉(HMO_4Q)从弱酸性溶液中萃取镓(III)到超临界流体二氧化碳中进行了基础研究。在45℃、8.6-20.4 Mpa和I=0.1M(H，Na)NO3条件下，测定了HMO4Q在水相和SF-CO2相间的分配常数。在45℃和15.3 Mpa下，在pH=2.20-2.84范围内，HMO4Q几乎不能将镓(III)萃取到SF-CO2中，而用HMO4Q定量萃取。用HMO4Q测定了镓(III)的萃取常数K&lt；ex-CO2&gt；([Ga(OH)(MO_4Q)_2]_&lt；SF-CO_2&gt；[H^+]^3[Ga^&lt；3+&gt；]^&lt；-1&gt；[HMO_4Q])在45℃时，I=0.1M(H，Na)NO_3时为15.7 Mpa，是正庚烷中45℃和0.10 Mpa时的63倍。加入3，5-二氯苯酚作为增效剂，提高了镓(III)与HMO_4Q在SF-CO_2中的萃取率。

A supercritical fluid extraction (SFE) by a supercritical fluid instead of a conventional organic solvent has recently been focused on the advanced method to remove the metal ions from aqueous solutions and solid materials. Among the supercritical fluids used in SFE, a carbon dioxide has been widely used because of its desirable properties, i.e. relatively low critical temperature and pressure, non-toxicity, non-flammability and high purity, although its solvating power is lower than those of organic solvents, such as chloroform.Extraction of most metal ions into supercritical fluid carbon dioxide (SF-CO_2), which is highly nonpolar as a solvent, from liquid and solid samples is difficult due to the requirement of charge neutralization of metal ions. The formation, however, of an uncharged complex enabled the extraction of metal ions into SF-CO_2, as well as a conventional solvent extraction. To select a suitable chelating extractants, therefore, is essential in the SF-CO_2 extraction.This work performed fundamental studies for the extraction of gallium(III) with 2-methyl-8-quinolinol (HMQ) and 2-methyl-5-butyloxymethyl-8-quinolinol (HMO_4Q) into supercritical fluid carbon dioxide from a weakly acidic solution. The distribution constants of HMO_4Q between aqueous and SF-CO_2 phases were determined at 45℃, 8.6-20.4 MPa and I = 0.1 M (H, Na)NO_3. At 45℃ and 15.3 MPa, gallium(III) was hardly extracted with HMQ into SF-CO_2, but was quantitatively extracted with HMO_4Q in the pH range of 2.20-2.84. The extraction constant, K_<ex-co2> ( [Ga(OH)(MO_4Q)_2]_<SF-CO_2>[H^+]^3[Ga^<3+>]^<-1> [HMO_4Q])^<-2>_<SF-CO2>), of gallium(III) with HMO_4Q was determined to be 10^<-2.6> at 45℃, 15.7 MPa and I = 0.1 M(H, Na)NO_3, which was 63 times larger than that in heptane at 45℃ and 0.10 MPa. It was also found that the addition of 3 ,5-dichlorophenol as a synergist enhanced the extractability of gallium(III) with HMO_4Q into SF-CO_2.