Toluene/ter-Butanol Mixed Solvent for the Selective Extraction of Cr(VI) from Divalent Heavy Metals

Abstract

A solvent-extraction system comprising toluene/ter-butanol (ter-BuOH) mixed solvent as the organic phase was developed to selectively extract Cr(VI) from acidic chloride media in the presence of divalent metals, namely Cd(II), Co(II), Cu(II), Ni(II) and Zn(II) under 5 M CaCl2 salting-out conditions. Chromium(VI) was selectively extracted as a solvated ion-pair of [ter-BuOH2+ x CrO3Cl-] at ter-BuOH mole fractions of between 0.1 and 0.6 (9.0-57.2% in volume). Divalent metals were extracted at ter-BuOH mole fraction over 0.6 with extraction percents of Co (< 20%), Cu (< 15%), Ni (< 10%) and Zn (< 20%). The concentrations of Ca2+, water and ter-BuOH in the organic phase and ter-BuOH in the aqueous phase were determined to find out the effects on the extraction of Cr(VI). The chemical species of Cr(VI) in acidic chloride media containing 5 M CaCl2 and 0.1 M HCl was confirmed to be the CrO3Cl- species. The effects of the acid, salt concentrations in the aqueous phase and the solvent composition of a mixed organic solvent on the extraction of Cr(VI) were evaluated. Based on the above studies, the extraction mechanism was elucidated and the optimum extraction conditions were determined.

Cloud point extraction of Cu(II) using a mixture of triton X-100 and dithizone with a salting-out effect and its application to visual determination

“…53 For visually determining trace constituents in environmental water samples, it is 54 necessary to concentrate the sample to a level at which determination is possible. The 55 measurement of heavy metals in water samples requires the use of preconcentration methods, 56 such as coprecipitation, ion exchange, and extraction [7][8][9][10][11][12][13][14][15]. 57 In this study, cloud point extraction (CPE) using a nonionic surfactant [16][17][18] was 58 selected as the preconcentration method for enabling the visual determination of Cu(II).…”

Process Intensification on the Supercritical Carbon Dioxide Extraction of Low-Concentration Ethanol from Aqueous Solutions

“…Moreover, it can be found that the salting effect of ionic liquids is less effective for improving the extraction performance than inorganic solid salt. This may be attributed to the large monovalent ions causing poor salting-out effect . Although the separation ability of ionic liquids is weaker than that of inorganic solid salts, they are in the liquid state at room temperature and thus have no problems of dissolution, tub-jam, and transport brought on by inorganic solid salts in industry.…”

“…This may be attributed to the large monovalent ions causing poor salting-out effect. 38 Although the separation ability of ionic liquids is weaker than that of inorganic solid salts, they are in the liquid state at room temperature and thus have no problems of dissolution, tub-jam, and transport brought on by inorganic solid salts in industry. Therefore, ionic liquids are regarded as green separating agents and suitable for application at industrial scale for intensifying the conventional separation processes.…”

Chemical Speciation of Chromium(III) and (VI) Using Phosphonium Cation Impregnated Polyurethane Foams Prior to Their Spectrometric Determination

“…clay minerals, gelatin, biosorbent, and active carbon, synthetic polymers, C18-bonded silica, silica gel immobilized with Zr(IV) and Zr(VI) phosphate have been used for preconcentration and/or separation of trace and ultra trace amounts of toxic metal ions from complex matrices. [8][9][10][11][12][13][14][15] Determination and chemical speciation of Cr(III) and Cr(VI) at trace levels in welding fumes and in drinking water samples using strong anion ion-exchange, 16 neutral alumina, 17 mini-columns packed with resin immobilized with 8-hydroxyquinoline, 18 activated carbon, 19 leaching procedure with sodium carbonate 5 and drawn and modified lingo cellulosic materials 20,21 have been reported. However, some of these SPE methods [10][11][12][13][14][15] are too expensive or unselective; they require careful experimental conditions, are time consuming and are not compatible with the detection limit of Cr(VI) in various matrices.…”