Solvent extraction of chromium(VI) from base metal ions with diphenyl-2-pyridylmethane as a liquid anion exchanger

The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM) dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase is possible with HCl or HNO₃ at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species was studied in solution. The complexes (DPPMH)⁺HCrO ₄ ⁻ and (DPPMH)₂Cr₂O ₇ ⁻ are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of chromium(VI) from base metal ions.     

Extraction of thiocyanate complexes of cobalt(II) by diphenyl-2-pyridylmethane in benzene from mineral acid solutions

Extraction of Co(II) by diphenyl-2-pyridylmethane (DPPM) in benzene form mineral acid solutions containing potassium thiocyanate has been studied at room temperature (23±2°C). Its extraction from mineral acids alone is rather poor. Optimal aqueous phase composition for the quantitative extraction of Co(II) by 0.1M DPPM is 0.1M acid+0.2M KSCN. Stoichiometric studies indicate that an ionic type complex, (DPPM·H)₂·Co(SCN)₄, is responsible for extraction. The metal can be back-extracted from the organic phase by aqueous acetate, citrate or oxalate solutions. Separation factors from other metals determined under optimal conditions reveal that Co(II) can be quantitatively separated from CsI), Sr(II), Cr(III), Ln(III), Zr(IV), Hf(IV), Cr(VI) and Tc(VII), Mo(VI), Zn(II), Au(III), Hg(II) and U(VI) are, however, coextracted and hence should be previously removed by other techniques or reagents.     

Liquid — Liquid extraction of silver(I) by diphenyl-2-pyridylmethane in benzene from aqueous mineral acid — Thiocyanate solutions

Liquid — liquid extraction of Ag(I) by diphenyl-2-pyridylmethane (DPPM) in benzene from aqueous nitric and sulfuric acid solutions containing thiocyanate ions has been studied at ambient temperature (24±2 °C). The metal is extracted quantitatively from 0.01M HNO₃+0.02M KSCN; or 0.25M H₂SO₄+0.02M KSCN by 0.1M DPPM (optimum extraction conditions). Slope analysis indicates that two types of ion-pair complexes i.e. [(DPPMH)⁺·Ag(SCN) ₂ ^– ] and [(DPPMH) ₂ ⁺ ·Ag(SCN) ₃ ^2– ] are involved in the extraction process. Separation factors determined at optimum conditions reveal the separation of Ag(I) from Cs(I), Br(I), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Fe(III), Au(III) (from HNO₃ solution only), Cr(III), Hf(IV), Ta(V), Sn(IV) and Cr(VI). With the exception of thiosulfate, other complexing anions like ascorbate, acetate, citrate, oxalate do not hinder the extraction of Ag(I) under optimum conditions.     

Preconcentration and separation of silver from neutron poisons and rare earths using diphenyl-2-pyridylmethane as an extractant

The extraction of silver from aqueous thiocyanate-perchlorate solutions using diphenyl-2-pyridylmethane (DPPM) in benzene has been investigated. The variables such as concentrations of perchloric acid, thiocyanate and DPPM influencing the extraction have been optimized. Maximum extraction has been achieved from 0.01 M perchloric acid solution containing 0.01 M potassium thiocyanate in 0.075 M DPPM in benzene. The extraction was found to be independent of silver concentration in the range from 10^–4–10^–6 M. The influence of several anions on the extraction was examined; only thiosulphate interfered seriously and reduced the extraction below 1%. Thus 0.1M potassium thiosulphate was found to back-extract silver quantitatively in one step. Under selected optimal conditions, very small extraction (<1%) was observed for trivalent Gd, Dy, Ho, Tm, Yb, Lu; Cs(I) and Cd(II) and separation factors for these elements were better than 10³. Only Sn(IV) exhibited quantitative extraction (>99%). This extraction procedure can be used for the preconcentration of silver and tin or their separation from rare earths mentioned above.     

N-oxides of 4-(5-nonyl)pyridine and trioctylamine as extractants for cerium(IV) and its separation from thorium(IV)

Trace level cerium has been oxidized to the quadrivalent state with potassium dichromate and shown to be preferentially extracted from very dilute mineral acid solutions and also from moderate nitric acid media by 0.1M solutions of 4-(5-nonyl)pyridine oxide and trioctylamine oxide dissolved in xylene. The dependence of extraction on the type of N-oxide, acid concentration and the N-oxide concentration has been investigated. The influence of the concentration of salting-out agents is described. Separation factors for a number of metal ions relative to cerium(IV) are reported for 0.1 M 4-(5-nonyl)pyridine oxide/xylene-0.1M sulphuric acid system. The ratio of the D for Ce(IV) to that of Ce(III) is greater than 10⁵, and the D for Ce(IV) is much greater than that for thorium(IV). Separation of cerium(IV) from thorium has been achieved from 0.1M sulphuric acid solutions using 0.1M 4-(5-nonyl)pyridine oxide/xylene as an extractant.     

Extraction of metals by neutral sulfur-containing extractants: Part I. o-isopropyl-n-ethylthiocarbamate

The formation of neutral mixed complexes of the MX_mS_p type (where M is a metal ion with m⁺ charge, X the inorganic anion, and S the sulfur-containing extractant) allows a selective extraction of various elements. The extraction of many metals from mineral acid solutions or from halide-sulfuric acid mixtures by 0.05 M O-isopropyl-N-ethylthiocarbamate(IPETC) solution in chloroform has been studied. (IPETC) possesses very high selectivity for silver and mercury ions in extractions from HNO₃, H_{2)SO4, HClO4 and HCl solutions. In addition to silver and mercury, Cu, Au, Tl and Se are readily extracted from solutions containing bromide. From iodide solutions, copper, gold and thallium ions may be selectively extracted because silver and mercury cannot be extracted at concentrations of iodide above 0.1 M.(IPETC} extracts metals as mixed complexes, containing the halide and apparently the extractant in the molecular form.     

Selective solvent extraction of chromium(VI) using 2-hexylpyridine

The extraction behaviour of trace and macroamounts of chromium(VI) from different mineral acid solutions by 2-hexylpyridine in chloroform has been investigated. In the chloride system, the extracted species is apparently (HPyH⁺)₂ (Cr₂O₇)²⁻ or HPy⁺(HCrO ₄ ⁻ ) for macro and trace amounts of chromium(VI), respectively. Among the common anions chloride and sulphate have little effect on extraction up to 1M concentration, while in the case of nitrate there is a continuous decrease in the extraction with the increase of salt concentration in the aqueous phase. The effect of ascorbate, acetate, citrate, oxalate, thiosulphate, thiocyanate ions on the extraction from 1M HCl was also examined. Separation factors of several elements relative to chromium(VI) have been described and the separation of chromium(IV) from a large number of elements has been achieved.     

Solvation of cobalt-thiocyanate complexes by 2-hexylpyridine from aqueous mineral acid solutions

A study of the distribution of cobalt between mineral acid solutions containing potassium thiocyanate and 0.1M 2-hexylpyridine in benzene has been undertaken. Cobalt can be quantitatively extracted as its thiocyanate complex from very dilute acid solutions containing 0.1–1M KSCN. Variation of the distribution coefficient D_Co in terms of the ligand concentration in the organic phase has allowed the formula of the extracted species to be determined as Co(HPy)₄ (SCN)₂. The effects of oxalate, acetate, fluoride, ascorbate, sulphate and thiosulphate ions on the extraction of cobalt from three mineral acid solutions have been reported. The extraction coefficients of several elements are given for the 0.1M 2-hexylpyridine in three systems containing 0.5M KSCN with 0.25M HNO₃, 0.05M HCl and 0.05M H₂SO₄ respectively; and their factors for separation from cobalt are estimated.     

Investigation of the use of diphenyl-2-pyridylmethane in benzene as an extractant for palladium from aqueous thiocyanate-nitrate solutions

The extraction of palladium/II/ with diphenyl-2-pyridylmethane /DPPM/ in benzene has been investigated from thiocyanate-nitrate media and optimized. Thiosulphate ions showed strong interference and reduced the extraction below 1%. Separation factors determined for most of the elements were better than 10³. This extraction method affords palladium preconcentration and its separation from Sc/III/, Co/II/, Cu/II/, Zn/II/, Se/IV/, Sr/II/, Ru/III/, Cd/II/, Cs/I/ and Eu/III/. Few possible applications of such separations have been cited.     

Extraction of gold(III) with (RS)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1H-1,2,4-triazol-1-yl-methyl)-pentan-3-ol from hydrochloric acid solutions

Extraction of gold(III) with (RS)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)-pentan-3-ol from 3 M hydrochloric acid solutions (with chloroform as a diluent) has been studied. Optimal extraction conditions have been found. The reagent has been shown to extract efficiently metal ion from solutions containing 3 M hydrochloric acid due to formation of coordination bond between gold(III) and the N4 atom of the triazole ring. The coordination mechanism of gold(III) extraction has been proposed on the basis of the data obtained. Concentration constants of extraction have been calculated, and the thermodynamic parameters of extraction have been determined.     

Separation of trace concentrations of tantalum from niobium and some other heavy metal ions by extraction with N-oxide of trioctylamine

The distribution of tantalum(V) between 0.1M trioctylamine oxide dissolved in xylene and sulphuric acid solutions has been studied. On the basis of results on the distribution, it is concluded that at sulphuric acid concentration 0.5M, tantalum is probably extracted by a solvate mechanism as the complex Ta(OH) (SO₄)₂·3TOAO. It has also been shown that tantalum can be quantitatively separated from niobium, uranium, thorium and rare earth elements by extraction with N-oxide of trioctylamine from 0.5M sulphuric acid solution.     

Determination of gold by atomic absorption spectrometry after extraction into the non-desulphurized fraction of crude oil distillate

The extraction of gold from aqueous chloride solutions into non-desulphurized fractions of crude oil distillates, especially paraffin oil, is described. The fraction boiling at 150–220°C exhibited optimum properties. The extraction is tested for solutions containing chlorides, dissolved chlorine and 0.1–3 M hydrochloric acid. Nitric acid should be absent. The distribution coefficient of gold varies from 400 to 900. Extracts containing ? 0.3 g l^?1 gold are stable for at least 12 months. The organic extract is sprayed into a lean acetylene/air flame with measurement at 242.8 nm (background correction). The calibration graph has linear portions over the ranges 0–2.5 and 2.5–16 mg l^?1. The limit of detection is 0.03 mg l^?1 gold in the extract (0.001 mg l^?1 in the aqueous phase). The minimum measurable concentration for gold in auriferous rocks and ores is 0.018 g per ton with 25-g samples.     

Solvation of thiocyanate complexes of tungsten(VI) by 5-(4-pyridyl) nonane from aqueous hydrochloric acid solutions

5-(4-Pyridyl)nonane has been evaluated as a solvent for trace amounts (<5·10^–5 M) of tungsten(VI) from aqueous chloride-thiocyanate solutions. Remarkable enhancements in metal extractability are observed on the addition of SCN^– to aqueous hydrochloric acid solutions. Extremal partition coefficients are obtained from 0.1 M HCl in 0.2 M KSCN. Diminutions of the metal extractability are produced by relatively high (>0.5 M) SCN^– concentrations and increased concentration of the supporting acid. Slope analysis data, under optimal parameters, indicates the most probable composition of the extractable species as WO₂(SCN)₂·2P_YN. Neutral anions do not have any significant effect on the D values. Behaviour of a number of metal ions has been checked using optimal aqueous conditions of extraction. The investigation shows that the reagent has a great potential for the preconcentration of a number of metal ions including the common toxins.     

Enrichment of51Cr through Szilard—Chalmers effect

Enrichment of⁵¹Cr has been made by recoil enrichment using potassium chromate as the target material. Irradiation of four days at a neutron flux of 2·10¹³n·cm⁻²·sec⁻¹ in the core of PARR, followed by a chemical separation using a new liquid-anion exchanger, diphenyl-2pyridylmethane (0.1M in chloroform) gives a product of high specific activity (>30 Ci per gram), suitable for medical diagnostic applications.     

Investigations on the use of 4-(5-Nonyl) pyridine as an extractant for chlorocomplexes of gallium(III)

A study of the distribution of gallium(III) between hydrochloric acid solutions and 0.1M 4-(5-nonyl)-pyridine in benzene has been undertaken. Gallium can be quantitatively extracted from moderate to concentrated acid solutions and also from dilute acid solutions containing high concentrations of neutral cations of high charge density. The effects of acidity, the solvent concentration and diverse ions on the extraction have been investigated. An attempt has been made to elucidate the stoichiometry of the extracted species. The formulation of (NP_y H)⁺ GaCl ₄ ⁻ ) and (NP_y−H−NP_y)⁺ GaCl ₄ ⁻ is expected at macro and trace concentrations of the metal. The extraction coefficients of several elements have been recorded under conditions optional for the extraction of gallium; and their factors for separations are estimated.     

Synergistic extraction of Ce(III), Eu(III) and Tm(III) with a mixture of picrolonic acid and benzo-15-crown-5 in chloroform

Summary The synergistic mixture comprising picrolonic acid (HPA) and benzo-15-crown-5 (B15C5) in chloroform has been used for the extraction of Ce(III), Eu(III) and Tm(III) as representatives of lanthanide(III) ions from pH 1-2 solutions having ionic strength of 0.1 mol^. dm^-3(K⁺/H⁺, Cl^-). The composition of the extracted species has been determined as M(PA)₃^. nB15C5 where M is Ce, Eu and Tm and n=1 or 2. The influence of various anions and cations on the extraction of these ions has also been studied and only oxalate, cyanide and tartrate have some deleterious effect. The extraction equilibrium constants have been evaluated and discussed.     

Liquid-liquid extraction of copper (II) with dialkyl sulphoxides

The extraction behaviour of Cu(II) from hydrochloric acid and lithium chloride solutions with di-n-pentyl sulphoxide (DPSO) and di-n-octyl sulphoxide (DOSO) has been investigated over a wide range of conditions. At a given strength of the extradant, the extraction increases with increase in HCl and LiCl concentrations. The extraction of the metal also increases with increase in extractant concentration at constant [HCl] or [LiCl]. The species extracted would appear to be CuCl₂·2DPSO/2DOSO and CuCl ₄ ²⁻ ·2DPSO. The extraction of the metal decreases with increase in initial aqueous metal concentration and also with increase in temperature. The extraction also depends on the nature of the diluent employed.     

The extraction of iron(III) by dioctylarsinic acid in chloroform

Dioctylarsinic acid, HDOAA, in chloroform solution has been investigated as a reagent for the extraction of iron(III) chloride. The extraction coefficient reaches two maxima, one of 1.5 at 8.5 M hydrochloric acid and another of 7 at pH 2.3. Experiments in the range 4–8 M for sulfuric, nitric and perchloric acids showed no extraction of iron(III) from these solutions for extraction times of 6 h. Evidence for the extraction of H₃FeCl₆ from 4–9 M hydrochloric acid solutions as [(H₂DOAA)⁺]₃FeCl₆^3- is presented. The species extracted from aqueous solutions of pH 1–2.3 is probably a hydroxy complex of the composition [Fe₂(DOAA)₂(HDOAA)X₄(H₂0)₂ ](X = OH and/or Cl).     

Determination of gold in geological samples by x-ray fluorescence spectrometry after extraction with tributyl phosphate

The behaviour of gold and elements impeding its x-ray fluorescence spectrometric (XRF) determination, namely zinc, lead and arsenic, was studied during their extraction from hydrochloric acid, nitric acid, and aqua regia solutions using tributyl phosphate as a solid extractant [SE(TBP)]. Extraction of gold from pulps after aqua regia leaching was found to be the most favourable approach for the quantitative and selective recovery of gold. The gold distribution ratio, D_Au, is ca. 10⁴ ml g^?1. For extraction from hydrochloric acid solutions the D_Au value also exceeds 10⁴ in the whole range of gold concentrations studied (10^?8?10^?4 M), but it decreases substantially with increasing extraction temperature, from 5 × 10⁵ ml g^?1 at 20°C to 9 × 10³ ml g^?1 at 70°C. An anomalously high distribution ratio of lead, D_Pb ≈ 10³ ml g^?1, was observed during extraction from hydrochloric solutions in the presence of chlorine. This could be explained by the formation of the chloro complexes of lead(IV). An XRF method for the determination of gold in natural samples was developed, which includes back-extraction of gold from SE(TBP) using a hot 0.025 M thiourea solution, providing a thin sample layer for secondary XRF. For 25 g of sample material the limit of determination is 10 ng g^?1 (10^?6%). The accuracy of the technique was checked using different reference materials. The results agreed within 10%.     

Extraction of molybdenum(VI) by 4-(5-nonyl)pyridine in benzene from aqueous mineral acid solutions containing thiocyanate ions

Extraction of Mo(VI) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiocyanate ions has been investigated at room temperature (23±2°C). From mineral acid (HCl, HNO₃, and H₂SO₄) solutions alone Mo(VI) is not extracted quantitatively while the presence of small amounts of KSCN in the system augments the extraction by a large factor. Stoichiometric studies indicate that ion-pair type complexes (NPyH)₂·[MoO₂(SCN)₄] are responsible for the extraction. Separation factors determined at fixed extraction conditions (0.1M Npy/C₆H₆–0.1M acid +0.2M KSCN) reveal that Ag(I), Cu(II), Co(II), Zn(II), Hg(II) and U(VI) are co-extracted while a clean separation from alkali metals, alkaline earths and some transition metals like Ln(III), Zr(IV), Hf(IV), Cr(III), Cr(VI) and Ir(III) is possible. Some of the complexing anions like oxalate, citrate, acetate, thiosulfate or ascorbate do not affect the degree of extraction of Mo(VI) allowing it to be recovered from diverse matrices.