Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam

A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l⁻¹, and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis.     

Extractive separation of trace amounts of mercury, cadmium and zinc

A simple solvent extraction procedure is reported for the sequential separation of mercury(II), cadmium(II) and zinc(II). Mercury is separated first using 1,3-diphenyl-2-thiourea in chloroform at an overall acidity of 0.3M HCl. Then cadmium separated using the same reagent at pH 10 into dichloromethane. The zinc which is remaining in the aqueous phase is then quantitatively extracted into toluene-cyclohexanol mixture using 2-mercaptobenzoxazole. Suitable stripping solutions have been proposed for the re-extraction of these metal ions for their subsequent estimations. The method has been made highly selective by the use of appropriate masking agents and has been applied in conjunction with estimation procedures for the determination of these metal ions in city waste incineration ash (CRM 176), mercuric chloride (A. R. grade) and in magnesium alloy samples.     

Synergic extraction of zinc, cadmium and lead with hexafluoroacetylacetone and di-n-butylsulphoxide and tri-n-butyl phosphate, and the gas chromatography of the zinc adduct

The synergic solvent extraction of zinc(II), cadmium(II), and lead(II) with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, H(HFA), and tri-n-butyl phosphate (TBP) or di-n-butylsulphoxide (DBSO) as neutral donors, into cyclohexane has been investigated. Quantitative extraction occurs at pH 4.5-6.0 in extraction times of 10-30 min, depending on the metal species. The optimum pH, equilibration time, stoichiometry and stability of the extracted species, as well as the effect of fluorinated beta-diketone concentration, metal concentration and neutral donor concentration on the extraction are reported. The extracted species was found to be M(HFA)(2).2DBSO or M(HFA)(2).2TBP by mass-action studies. Thermogravimetric analysis of the complexes is reported. The gas chromatographic behaviour of the ternary complexes of the three metals has also been studied. A calibration plot of peak area vs. the amount of zinc injected was linear over the range 40-900 ng of zinc for the Zn(HFA)(2). 2DBSO species; the cadmium and lead species apparently decomposed on the column and useful chromatographic peaks were not observed. The calibration plot for zinc was determined on the basis of the averages of 3-5 replicate determinations for 14 different concentrations over the range stated. The average relative standard deviation was 2.9%.     

Improved separation of cadmium from indium,zinc, gallium and other elements by anion-exchange chromatography in hydrobromic nitric acid mixtures

The separation of cadmium from indium, zinc and many other elements is considerably improved by eluting these elements with 0.1 M hydrobromic–0.5 M nitric acid solution from a column of AG1-X8 resin. Cadmium is retained very strongly and can be eluted with 2 M nitric acid or 1 M ammonia–0.2 M ammonium nitrate solution. Separations are sharp and quantitative and from microgram amounts up to 2 g of indium and zinc are separated from amounts of cadmium ranging from micrograms up to 100 mg on a 2-g (4.6 ml) resin column. Ga(II), Fe(III). Mn(II), Co(II), U(VI) and Ni(II) can be separated quantitatively from cadmium in the same way. The behaviour of numerous elements is discussed, with special attention to lead, and relevant elution curves and results from the analysis of synthetic mixtures are presented.     

Solvent extraction separation of tin (IV) with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A)

Solvent extraction of tin(IV) from hydrochloric acid media was carried out with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) in toluene. Tin(IV) was quantitatively extracted with 2.5x10(-2) M PC-88A in toluene from 0.1-0.3 M HCl when equilibrated for 5 min. Tin(IV) from the organic phase was stripped with 4 M HCl and determined spectrophotometrically by both the morin and pyrocatechol violet method. The nature of the extracted species was determined from the log-log plots. Various other diluents such as xylene, hexane and cyclohexane also gave quantitative extraction of tin. The metal loading capacity of the reagent was found to be 0-15 ppm of tin(IV). The extraction of tin(IV) was carried out in the presence of various ions to ascertain the tolerance limit of individual ions. Tin(IV) was successfully separated from commonly associated metal ions such as antimony(III), bismuth(III), lead(II), thallium(I), copper(II), nickel(II), etc. The method was extended for determination of tin in real samples.     

Gallium(III) Extraction from Hydrochloric Acid Solutions with Diacylated Diethylenetriamine Hydrochloride

Extraction of gallium(III) from hydrochloric acid solutions with hydrochloride of diethylenetriamine [N-(2-aminoethyl)ethane-1,2-diamine] N,N'-diacylated with neodecanoic acid was studied using chloroform as diluent. Gallium(III) can be effectively recovered from 6–10 M HCl solutions and selectively separated from indium(III), aluminum(III), and zinc(II). The concentration constant and thermodynamic parameters of the anion-exchange extraction of gallium(III) from 6 M HCl solutions were evaluated.     

Spectrophotometric and spectrofluorometric determination of zinc and cadmium with 2,2'-pyridil bis(2-quinolylhydrazone)

The chelating ligand, 2,2'-pyridil bis(2-quinolylhydrazone), has been used for the spectrophotometric determination of zinc and cadmium in synthetic samples. The molar absorptivities of these metal complexes in 80% ethanol-water solution at pH 8 were found to be 4.60 x 10(4) and 5.10 x 10(4) 1.mole(-1).cm(-1) for zinc and cadmium respectively. Beer's law was obeyed for metal-ion concentrations between 1.0 x 10(-6) and 2.5 x 10(-5)M. The limits of detection were found to be 52 and 79 ng ml for zinc and cadmium respectively. The complexes fluoresced in 80% ethanol-water at pH 8 for zinc and at pH 10 for cadmium. The linear range for fluorescence as a function of metal-ion concentration was found to be 5 x 10(-7)-5 x 10(-6)M for both zinc and cadmium. Transition-metal ions interfere severely with both the spectrophotometric and fluorimetric determinations, and must be removed beforehand. An ion-exchange procedure is suitable for this.     

Analytical applications of a liquid anion-exchanger for the separation of uranium(IV) in malonate solution

Uranium was quantitatively extracted with 4% Amberlite LA-1 in xylene at pH 2.5-4.0 from 0.001 M malonic acid. It was stripped from the organic phase with 0.01 M sodium hydroxide and determined spectrophotometrically at 530 nm as its complex with 4-(2-pyridylazo) resorcinol. Of various liquid anion-exchangers tested, Amberlite LA-1 was found to be best. Uranium was separated from alkali and alkaline earth metal ions, thallium(I), iron(II), silver, arsenic(III) and tin(IV) by selective extraction, and from zinc, cadmium, nickel, copper(II), cobalt(II), chromium(III), aluminium, iron(III), lead, bismuth, antimony(III) and yttrium by selective stripping. The separation from scandium, zirconium, thorium and vanadium(V) was done by exploiting differences in the stability of chloro-complexes.     

Extraction and separation of mercury from toxic elements arsenic,cadmium, antimony and thallium,and other metal ions

Extraction of mercury with 3-methyl-1-phenyl-4-trifluoroacetyl-pyrazolin-5-one /FAP/ in chloroform has been described. Maximum extraction /97.3%/ and a distribution coefficient /D/ of 36.5 have been achieved at pH 8. Among the anions tested, thiourea, thiosulphate and cyanide mask the extraction of mercury. Solution of O. 2M KCN was found most suitable stripping agent for mercury. Decontamination data show that mercury can be separated from toxic elements arsenic, cadmium, antimony and thallium; and from other metal ions i. e. Ga/III/, In/III/, Ge/IV/, Sn/II/, Fe/II/, Ir/IV/ and Pt/IV/. A few separations of analytical and radiochemical importance have been discussed.     

Kinetically controlled separation of cadmium(II) from zinc(II) with dithizone in the presence of nitrilotriacetic acid.

The extraction rates of cadmium(II) and zinc(II) with dithizone (H2dz) in the presence of nitrilotriacetic acid (NTA) were measured, and the possible kinetic separation of cadmium(II) from zinc(II) was investigated. Upon the addition of NTA, the difference in the extraction rate between cadmium(II) and zinc(II) became large. Based on the observed rate constant under the condition [NTA] = 1 x 10(-2) mol dm-3, [H2dz]org = 1 x 10(-3) mol dm-3, and pH = 7.0, the shaking time required for the quantitative separation of cadmium(II) from zinc(II) was calculated to be between 326 and 995 s. The experimental results agreed with the prediction, and the quantitative separation of cadmium(II) from zinc(II) was performed within the above-mentioned range of shaking times.     

Ion-exchange foam chromatography : Part II. Rapid separations on heterogeneous cation-exchange foams

The possibility of using polyurethane-Varion KS heterogeneous cation-exchange foam for rapid separations in aqueous and alcoholic solutions was investigated. The exchange equilibria on the ion-exchange foam were attained rapidly and the break-through capacity of columns packed with the foam material was quite acceptable. Relatively high flow-rates could be applied without any appreciable loss in column performance. With foam columns, microgram and milligram amounts of copper could be retained and eluted quantitatively with hydroxyammonium chloride solution. The overall capacity of the examined ion-exchange foams was about 40% of the original capacity of beads. Cation-exchange distribution coefficients of cadmium(II), zinc(II), iron(III) and calcium-(II) were determined for foam material and conventional bead exchanger; the selectivity of both was about the same.     

Separation and determination of some trivalent metal ions using rhodamine B grafted polyurethane foam

The incorporation of rhodamine B into polyurethane foam matrix was prepared by mixing the rhodamine B with polyol (polyether) prior to the addition of diisocyanate reagent to form the polyurethane foam material. Rhodamine B grafted polyurethane foam (Rod.B-PUF) was found to be very suitable for the separation and preconcentration of trivalent metal ions e.g. bismuth (III), antimony (III) and iron (III) from thiocyanate solutions. Bismuth and antimony were separated from concentrated acid medium (1–6 M H₂SO₄). Iron (III) was separated from pH 1 to 3. The kinetics of sorption of the Bi (III), Sb (III) and Fe (III) onto the Rod.B-PUF was found to be fast, the extraction is accomplished from 5 to 10 min with average values of half-life of sorption (t_1/2) of 2.9 min. The average values of the Gibbs free energy (ΔG) for the sorption of metal ions onto Rod.B-PUF are ?6.6 kJ mol^?1, which reflect the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Rod.B-PUF was also discussed.     

Improved separation of cadmium-109 from silver cyclotron targets by anion-exchange chromatography in nitric acid—hydrobromic acid mixtures

A method is presented for improved separation of ¹⁰⁹Cd from silver cyclotron targets. After dissolution of the target material in nitric acid and removal of silver by precipitation with copper metal, at pH 5, the cadmium is separated from zinc, copper and other elements by anion exchange chromatography. The solution in 0.5 M nitric acid plus 0.1 M hydrobromic acid is percolated through a column containing 4 ml of AG1-X8 anion-exchange resin (100–200 mesh), equilibrated with the same acid mixture. Zinc, copper(II) and other elements are eluted with 50 ml of this mixture. Cadmium is retained and finally eluted with 50 ml of 3 M nitric acid. The cadmium is retained much more strongly from the hydrobromic acid mixture than from the 0.02 M hydrochloric acid used for such separations previously; the presence of the strongly absorbed nitrate anion in fairly high concentration completely eliminates the tailing of zinc observed in 0.02 M hydrochloric acid. A typical elution curve and results of quantitative separations are presented.     

Synthesis,crystal structure,and electroluminescent properties of zinc and cadmium tetradentate azomethine complexes

Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetradentate Schiff bases (H₂L¹ and H₂L²) resulting from condensation of 2-tosylaminobenzaldehyde with 3,6-dioxa-1,8-octanediamine or 4,9-dioxa-1,12-dodecanediamine were performed. The structure, composition, and properties of the complexes were studied by elemental analysis, IR, ¹H NMR, and UV spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction. The zinc(II) and cadmium(II) complexes luminesce in a DMF solution in the blue spectral region (λ_PL = 425–433 nm), the photoluminescence quantum yield φ being 0.25–0.30. Multilayer zinc(II)- and cadmium(II)-based electroluminescent structures with green-blue emission of the exciplex nature were fabricated.     

Application of chelate forming resin Amberlite XAD-2-o-vanillinthiosemicarbazone to the separation and preconcentration of copper(II), zinc(II) and lead(II)

A very stable chelating resin matrix was synthesized by covalently linking o-vanillinthiosemicarbazone (oVTSC) with the benzene ring of the polystyrene-divinylbenzene resin Amberlite XAD-2 through a -NN- group. The resin was used successfully for the separation and preconcentration of copper(II), zinc(II) and lead(II) prior to their determination by atomic absorption spectrophotometry. The total sorption capacity of the resin was 850, 1500 and 2000 mug g(-1) of the resin for Cu(II), Zn(II) and Pb(II), respectively. For the quantitative sorption and recovery of Cu(II), Zn(II) and Pb(II), the optimum pH and eluants were pH 2.5-4.0 and 4 M HCl or 2 M HNO(3) for Cu(II), pH 5.5-6.5 and 1.0-2.0 M HCl for Zn(II) and pH 6.0-7.5 and 3 M HCl or 1 M HNO(3) for Pb(II). Both, the uptake and stripping of these metal ions were fairly rapid, indicating a better accessibility of the chelating sites. The t (1 2 ) values for Cu(II), Zn(II) and Pb(II) were also determined. Limit of tolerance of some electrolytes like NaCl, NaF, NaNO(3), Na(2)SO(4) and Na(3)PO(4) have been reported. The preconcentration factor for Cu(II), Zn(II) and Pb(II) was 90, 140 and 100 respectively. The method was applied for the determination of Cu(II), Zn(II) and Pb(II) in the water samples collected from Sabarmati river, Ahmedabad, India.     

The extraction of mercury(II), silver(I), cobalt(II) and cadmium(II) by dioctylarsinic acid in chloroform

Dioctylarsinic acid (HDOAA) in chloroform solution has been investigated as a reagent for the extraction of Hg(II), Ag(I), Co(II), and Cd(II). Silver, cobalt and cadmium are not extracted below pH 7. An extraction coefficient of 1.1, constant over the pH range 1–6.5, was observed for Hg(II). With HCl concentrations of 1–8 M the extractability of mercury decreased slowly, reaching E_a⁰ = 0.05 at 8 M HCl. Silver formed a silver dioctylarsinate precipitate which collected at the interface. The extraction coefficients for Hg(II), Co(II) and Cd(II) increased above pH 7 to values of 20 (pH 9.1), 30 (pH 8.0), and 23 (pH 10), respectively. Reagent- and pH-dependence studies indicated that Co(II) and Cd(II) are extracted as M(DOAA)₂ or M(DOAA)Cl through interaction of HDOAA with M(OH)₂ or M(OH)⁺. Mercury was extracted from solutions of pH 1–6.5 as HgCl₂ (HDOAA)_2.5.     

Extractive separation and spectrophotometric determination of tungsten as phosphotungsten blue

Phosphotungsten blue is produced by tin(II) reduction of tungstate solution complexed with phosphate at a w/w ratio of W/P = 5, in 4M hydrochloric acid medium, and extracted with isoamyl alcohol; thus tungsten is separated from Fe(III), Ni, Co, Cr(III), V(V), As(V), Sb(III), Bi, Si, U(VI), Ca and Cu(II). In presence of bismuth (0.5 mg/ml), 99.7% W is separated in a single extraction. After alkaline back-extraction, tungsten is determined spectrophotometrically as phosphotungsten blue; it is measured at 930 nm in aqueous solution or at 900-960 nm after isoamyl alcohol extraction, the Beer's law ranges being 0.08-0.6 and 0.16-0.72 mg/ml respectively. The methods are shown to give satisfactory results in the analysis of practical samples containing some milligrams of tungsten.     

Liquid-liquid extraction of zinc from aqueous thiocyanate solutions with 5-(-4-pyridyl)nonane in benzene

5-(4-Pyridyl)nonane dissolved in benzene has been applied to the extraction of zinc, down to very low concentration (< 10(-6)M), from aqueous thiocyanate solutions. The metal can be quantitatively extracted from neutral and acidic thiocyanate solutions (up to 5M HCl, 0.25M HNO(3) or 0.25M H(2)SO(4)) in a single extraction. Equilibration times of 5 min are sufficient for almost complete extraction. The optimum thiocyanate concentration range is 0.05-0.5M. Among the common anions chloride exerts a slight depressing effect on extraction from neutral solution when present in high concentration. The extraction mechanism and the composition of the extracted complexes of zinc are discussed. The metal is predominantly extracted by means of a solvate mechanism. The effect of chloride, nitrate, sulphate, acetate, citrate, oxalate and ascorbate ions on the extraction of zinc is described. Several elements, including those of interest in separation of zinc, have been tested for extraction from O.1M KSCN at the optimal concentrations of the mineral acids, and the separation factors estimated.     

Preconcentration of trace metal ions by combined complexation-anion exchange : Part 2. Cobalt,zinc, cadmium and lead with 8-hydroxyquinoline-5-sulfonic acid [1]

The ligand, 8-hydroxyquinoline-5-sulfonic acid, forms anionic complexes with cobalt(II), zinc(II), cadmium(II), and lead(II), each resulting complex showing a high affinity for anion-exchange resins. The effect of pH, ligand/metal ratio, volume, and concentration on percent retention of the anionic complexes by an anion-exchange resin are reported. At optimum conditions, all four metals are quantitatively retained by the column. Zinc, cadmium and lead(II) ions are completely eluted with 11 ml or less of 2 M HN0₃; cobalt(II) is totally removed by 12 M HCl and 2 M HNO₃. Concentration enhancements of 100-fold are easily achieved. All four anionic complexes can be left on the column for 7 days and still be quantitatively (99%) recovered. A ligand-loaded resin column can also remove all four metals quantitatively. Distribution coefficients for the metal complexes and their ligand/metal ratios were determined by using batch methods that may also serve as the isolation procedure.     

Complexation of N-acyl-N′-(p-toluenesulfonyl)hydrazines with nonferrous metal ions in ammoniac media

The complexation of N-acyl-N′-(p-toluenesulfonyl)hydrazines (ASHs) with copper(II), cobalt(II), nickel(II), zinc(II), cadmium(II), and silver(I) ions in ammoniac media was studied. The reagents were shown to form compounds with [M]: [ASH] ratios of 1: 1 and 1: 2 in solutions. ASH complexes with metal ions were preparatively separated and identified. The quantitative characteristics of complexation equilibria—the solubility products of precipitates—were found. The effects of ammonium salts and the length of a radical on the completeness of precipitation of M(II) cations with ASH were studied.