M. Ejaz

The extraction of trace amounts of gold from different aqueous mineral acid solutions by diphenyl-2-pyridylmethane dissolved in chloroform

Diphenyl-2-pyridylmethane, a high molecular weight substituted pyridine has been examined and found to be a useful solvent extraction reagent. Its behaviour is similar to amines in that it forms salts with mineral acids. The acid ionization constant (pKBH+) determined spectrophotometrically has a value of 4.41±0.06 at 25 °C. A study of the partition behaviour of trace amounts of gold between mineral acid solutions and 0.1M diphenyl-2-pyridylmethane dissolved in chloroform indicates that the metal can be quantitatively extracted from dilute mineral acid solutions and also from concentrated hydrochloric acid media in a single extraction. Attempts have been made to gain an understanding of factors affecting the extraction of gold. Common anions have little effect on extraction in concentrations upto 1M. Separation factors of a number of metal ions relative to gold are reported for three mineral acid systems; and gold has been estimated in some synthetic samples using neutron activation technique by prior extraction with 0.1M solution of diphenyl-2-pyridylmethane dissolved in chloroform.

Chemical separation of molybdenum from uranium and fission product nuclides

A very rapid method for the separation of molybdenum(VI) from neutron irradiated uranium and its fission products is described. The procedure is based on the selective extraction of molybdenum(VI) by a 0.1M solution of 2-hexylpyridine in benzene from 4M HCl+0.04M KSCN. Decontamination factors were estimated to be >104 for the radionuclides of niobium, zirconium, ruthenium, lanthanum, cerium, promethium, yttrium, strontium and barium.

4-(5-Nonyl)pyridine as an extractant for cobalt thiocyanate complexes from mineral acid solutions

The partition behaviour of cobalt into 4-(5-nonyl)pyridine (NPy) in benzene from aqueous hydrochloric, nitric and sulfuric acid media containing variable amounts of potassium thiocyanate is described. Cobalt is quantitatively extracted by NPy from 0.1–1M KSCN solutions at 0.01 M concentration of the mineral acids. The extraction mechanism and the possible compositions of the extracted species are discussed. The effects of foreign salts on the extraction of cobalt from three mineral acid solutions are reported. Several elements including those which are of some interest in connection with the separation of cobalt were tested for extraction from 0.01 M solutions of mineral acids 0.3 M with respect to KSCN and their factors for separation from cobalt were estimated.

Extraction of iron(III) with diphenyl-2-pyridylmethane dissolved in benzene from aqueous chloride solutions

The mechanism of extraction has been investigated by partition, slope analysis and loading-ratio data. The results obtained give a picture of the mechanism of extraction of FeCl4− ions in relation to the hydration and solvation of the compound extracted. The possible formula of the extracted species is (DPPM)3H3O+(H2O)n−FeCl4−. In dilute aqueous hydrochloric acid systems the influence of the concentration of a number of salts with cations of different electrical potentials (Ze/r), on iron(III) extraction, has been studied. Splitting of the organic phases occurs at high acid and/or high salt concentrations. The phenomenon is explained on the basis of the variability of the hydration number. Investigations have been made to understand the parameters controlling the extraction of the metal and its is shown that the extraction offers a simple, fast and selective separation method of iron from solutions.

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)+HCrO4− and (DPPMH)2Cr2O7− 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.

Investigations of the use of 4-(5-nonyl)pyridine as a liquid anion exchanger for tetrachloroferrate ions in aqueous chloride media

In an attempt to gain an understanding of factors affecting the extraction of iron(III) by 4-(5-nonyl)pyridine, the equilibria between hydrogen chloride and benzene solutions of 4-(5-nonyl)pyridine have been studied. From acid distribution data and visible absorption spectra of the organic phases, it was concluded that FeCl4− ion, with a tetrahedral sp3 configuration is the principal iron containing species. The pyridine extraction of macro and trace amounts of the metal has indicated the formation of 1∶1 and 2∶1 complexes respectively. The 2∶1 complexes are assumed to result from association of a 1∶1 complex with a molecule of the pyridine hydrochloride. The salting-out effect increases in the order, LiCl<NaCl<MgCl2<AlCl3 and these differences in the effect have been attributed to the different degree of hydration of cations of the salts present and to the ionic radii. The effect of various anions including the reducing agents have been described. Separation factors of several metal ions relative to ferric iron, in 6M HCl, are also reported.

Spectrophotometric determination of uranium(VI) with 7-iodo-8-hydroxyquinoline-5-sulfonic acid (ferron)

A new method is introduced to estimate uranium(VI) spectrophotometrically by extraction of its ferron (7-iodo-8-hydroxyquinoline-5-sulfonic acid) complex with 1% tridodecylamine in chloroform at pH 4.5. The optimum absorption wavelength is 380 nm. The stoichiometry of the uranium-ferron complex as indicated by a mole ratio plot is 1:2 and its dissociation constant is 3.24·10−9. The effects of various parameters on the absorption are studied. This method has a sensitivity of 0.028 ppm on Sandells scale. Interferences are described.

Solvation of thiocyanate complexes of mercury(II) by 2-hexylpyridine from aqueous mineral acid solutions

The extraction of trace amounts of mercury(II) by 2-hexylpyridine dissolved in benzene from aqueous mineral acid solutions has been studied. The replacement of chloride, nitrate and sulfate ions by the potentially ambidentate, linear and less basic thiocyanate group offers interestingly high extraction coefficients. The value of the distribution coefficients may be lowered by complexing mercury with oxalate, thiosulfate, acetate or citrate ions in the aqueous phase. The possible mechanism of extraction has been discussed in the light of the results of extraction isotherms and slope analysis data. Distribution coefficients and separation factors of several metal ions relative to mercury(II) are reported for the three mineral acid systems and the possible removal of mercury along with some other inorganic pollutants from aqueous solutions is suggested.

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+(HCrO4−) 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.

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.