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

超临界流体萃取（SFE）是近年来从水溶液和固体物质中去除金属离子的一种新方法。在超临界流体中，CO2具有较低的临界温度和临界压力、无毒、不燃、纯度高等优点，但其溶剂化能力低于氯仿等有机溶剂，因而得到了广泛的应用。由于需要金属离子的电荷中和，从液体和固体样品中分离是困难的。然而，不带电荷的络合物的形成使得金属离子能够被SF-CO_2萃取，以及常规的溶剂萃取。本文研究了2-甲基-8-羟基喹啉（HMQ）和2-甲基-5-丁氧基甲基-8-羟基喹啉（HMO_4Q）在超临界CO_2流体中从弱酸性溶液中萃取镓（III）的性能。在45℃，8.6- 20.4MPa和I = 0.1M（H，Na）NO_3条件下，测定了HMO_4Q在SF-CO_2和水相中的分配常数。在45℃、15.3MPa条件下，HMQ几乎不萃取镓，而HMO_4Q在pH2.20 -2.84范围内可定量萃取镓。在45℃、15.7 MPa、I = 0.1 M（H，Na）NO_3条件下，HMO_4Q对镓（III）的萃取常数K_<ex-co2>（[Ga（OH）（MO_4Q）_2]_<SF-CO_2>[H^+]^[Ga^&lt;3+]^ [HMO_4Q]）^ _= 10^，比45 ℃、0.10 MPa时的庚烷萃取常数K_（[Ga（OH）（MO_4Q）_2]_ [H^+]^[Ga <-1>^&lt;3 +]^ [HMO_4Q]<-2><SF-CO2><-2.6>）^_= 63倍。实验还发现，3，5-二氯苯酚作为萃取剂的加入增强了HMO_4Q在SF-CO_2中萃取镓（III）的能力。

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.