Liquid-Liquid Extraction Of Gold, Palladium And Platinum Participated By Ionic Liquids

The hypochromic effect of bromocresol green (BCG) resulted by long-chained imidazolium ionic liquids was investigated. The hypochromic effect may be caused by the formation of the neutral complex as [Cnmim] 2[BCG] " via electrostatic interaction and hydrophobic interaction. Based on the spectral characteristics, a new method for determination of long-chained imidazolium ionic liquid is developed. The proposed method can be achieved by a UV-vis spec trop ho to meter, at the optimum λmin. Beer’s law is obeyed in the concentration ranges 0.004 - 0.04 mmol L-1 for [C14mim]Br and [C16mim]Cl, and the detection limits are 0.0011 and 0.00095 mmol L-1 for [C14mim]Br and [C16mim]Cl, respectively. Meanwhile, precision, accuracy and tolerance are also very good. The method is rapid, economical and without using organic solvent, the method can be applied for determination of long-chained imidazolium ionic liquids.The microemulsions consisted of cyclohexane, n-hexylalcohol, hydrochloric acid solutions and the ionic liquid 1-n-tetradecyl-3-methylimidazolium bromide ([C14mim]Br) was investigated for Au(Ⅲ) extraction. In the extraction system, [C14mim]Br bears double functions of surfactant and extractant. The anion-exchange mechanism of Au(Ⅲ) extraction by [C14mim]Br was confirmed by the method of continuous variation and the infrared spectrum analysis. The effects of extraction time and various material concentrations were examined for Au(Ⅲ) extraction. Under the optimum conditions, almost all the Au(Ⅲ) in hydrochloric acid solution was extracted to the microemulsion phase, also has high selectivity for Au(Ⅲ) over base metals (Cu(Ⅱ), Cd(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Sb(Ⅲ), Fe(Ⅲ), Al(Ⅲ), and Sn(Ⅳ)). Therefore, the extraction of Au(Ⅲ) by the [C14mim]Br/cyclohexane/n-hexylalcohol/HCl microemulsion is an efficient and effective approach with high selectivity.The ionic liquid, 1-hexadecyl-3-methylimidazolium chloride/chloroform system was investigated for gold(Ⅲ) extraction. In the extraction system, [C16mim]Cl bears a function of extractant. The effects of extraction time and [C16mim]Cl concentration were examined for Au(Ⅲ) extraction. The anion-exchange mechanism of gold(Ⅲ) extraction by [C16mim]Cl was confirmed by the method of continuous variation, UV-Vis and infrared spectrum analysis. According to the thermodynamics analysis, thermodynamic parameters of the Au(Ⅲ) extraction reaction were obtained, which illustrates that higher temperature show negative effect for the Au(Ⅲ) extraction. Under the experimental conditions, the [C16mim]Cl/chloroform system shows a high extractability for Au(Ⅲ), also has high selectivity over some metals (Cu(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Fe(Ⅲ), A1(Ⅲ) and Sn(Ⅳ)). Moreover, oxalic acid is explored to reduce the gold-IL complex ([C16mim]+[AuCl4]-), by which Au(Ⅲ) is striped in the form of metallic gold precipitate and [C16mim]Cl also can be recycled.The hexadecylpyridinium chloride/chloroform system was employed for the Pd(Ⅱ) extraction from hydrochloric acid medium. The effects of extraction time and material concentrations were examined for Pd(Ⅱ) extraction. The anion-exchange mechanism of Pd(Ⅱ) extraction by [Hpy]Cl was confirmed by Job’s method, UV-Vis, infrared spectrum and 1H NMR analysis. Thermodynamic parameters of the Pd(Ⅱ) extraction reaction were obtained from the thermodynamics analysis, which illustrate that higher temperatures show a negative effect on the Pd(Ⅱ) extraction. When the mole ratio of [Hpy]Cl to Pd(Ⅱ) is above 4, the Pd(Ⅱ) extraction yield (E%) is almost 100%. It also has high selectivity over some metals (Cu(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Fe(Ⅲ), Al(Ⅲ) and Sn(IV)). Moreover, oxalate is explored as a reducing agent for [Hpy]+2[PdCl4]2- complexes, by which Pd(Ⅱ) is striped in the form of palladium powders and [Hpy]Cl also can be recycled. Therefore, the method is an efficient, effective and highly selective approach to extract Pd(Ⅱ) and recover metal palladium.Hydrophilic ionic liquids, 1-alkyl-3-methylimidazolium chloride ([Cnmim]Cl, n =12,14 and 16) are tested to precipitate Pt(IV) from hydrochloric acid medium. Meanwhile the Pt(IV) extractions are performed with hydrophobic ionic liquids, including 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim]PF6, n=4,6 and 8) and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C8mim]NTf2). Based on Job’s method, infrared spectra and 1H NMR analysis, the anion-exchange mechanism is confirmed during the Pt(IV) precipitation. The mixed hydrophilic-hydrophobic ionic liquids ([Cnmim]Cl/[Cgmim]PF6) are developed for Pt(IV) extraction, which significantly increase the Pt(IV) extractability comparing to the single hydrophobic ionic liquid. Under the optimum conditions, the [C16mim]Cl/[Cgmim]PF6 system shows high extractability as well as outstanding selectivity for Pt(Ⅳ) over the base metals (Mn(Ⅱ), Cu(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Fe(Ⅲ) and Al(Ⅲ)). By the reductive stripping, Pt(Ⅳ) in the organic phase can be stripped in the formof platinum powders with using hydrazine hydrate, at the same time [C16mim]Cl is regenerated in the organic phase. The mixed [C16mim]Cl/[C8mim]PF6 ionic liquids can be reused to extract Pt(Ⅳ). Therefore, [C16mim]Cl/[Cgmim]PF6 ionic liquids can recurrently extract Pt(Ⅳ) from hydrochloric acid medium.