Determination of antimony in ores and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A continuous hydride-generation atomic-absorption spectrometric method for determining approximately 0.02 mug/g or more of antimony in ores, concentrates, rocks, soils and sediments is described. The method involves the reduction of antimony(V) to antimony(III) by heating with hypophosphorous acid in a 4.5M hydrochloric acid-tartaric acid medium and its separation by filtration, if necessary, from any elemental arsenic, selenium and tellurium produced during the reduction step. Antimony is subsequently separated from iron, lead, zinc, tin and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 4.5M hydrochloric acid/0.2M sulphuric acid in the presence of ascorbic acid as a reluctant for iron(III). After the extract is washed, if necessary, with 10% hydrochloric acid-2% thiourea solution to remove co-extracted copper, followed by 4.5M hydrochloric acid to remove residual iron and other elements, antimony(III) in the extract is oxidized to antimony(V) with bromine solution in carbon tetrachloride and stripped into dilute sulphuric acid containing tartaric acid. Following the removal of bromine by evaporation of the solution, antimony(V) is reduced to antimony(III) with potassium iodide in approximately 3M hydrochloric acid and finally determined by hydride-generation atomic-absorption spectrometry at 217.8 nm with sodium borohydride as reluctant. Interference from platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide during the iodide reduction step. Interference from gold is avoided by using a 3M hydrochloric acid medium for the hydride-generation step. Under these conditions gold forms a stable iodide complex.     

The determination of beryllium in geological and industrial materials by atomic-absorption spectrometry after cation-exchange separation

A method is described for the determination of beryllium in geological and industrial samples. After dissolution of the sample in mineral acids, beryllium is separated from the matrix elements by chloroform extraction of its acetylacetonate from a solution of pH 7 containing ascorbic acid and EDTA. Beryllium is separated from the organic extract and from co-extracted aluminium by means of a column of the strongly acidic cation-exchanger Dowex 50; beryllium is adsorbed from a medium consisting of 60 % (v/v) tetrahydrofuran, 30 % (v/v) chloroform and 10 % (v/v) methanol containing hydrochloric acid, aluminium is removed with 0.4 M oxalic acid and after elution with 6 M hydrochloric acid, beryllium is determined by atomic-absorption spectrometry with a nitrous oxide-acetylene flame. The method was used to determine p.p.m. and sub-p.p.m. quantities of beryllium in geochemical reference materials, U₃O₃ and yellow cake samples, and manganese nodules.     

Sequential and rapid determination of Po-210, Bi-210 and Pb-210 in natural waters

A sequential and rapid separation method for the determination of radon daughter nuclides, Pb-210, Bi-210 and Po-210 has been developed for application to natural waters. Rapid separation is attained by the use of the same hydrochloric acid solution. After isolation of the three radionuclides from the sample by co-precipitation with added Fe³⁺, polonium isotopes are first spontaneously deposited onto a silver disc from a 0.5N hydrochloric acid solution. Next, bismuth isotopes are electrodeposited onto a platinum net cathode coupled with a platinum coil anode at 1.2 V. Finally, lead isotopes are electrodeposited onto a platinum net cathode at 1.8 V from the remaining solution by adding hydroxylamine hydrochloride as an anodic depolarizer. This method can be applied to meteorological precipitation samples where these three nuclides are separated within 10 hr after the sampling with chemical yields of more than 80% for Po-210 and Bi-210 and more than 70% for Pb-210. This method is applicable to other environmental water samples.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—I: Degradation thermique du chloro-4-hexene-2

This paper describes an extensive kinetic study of thermal dehydrochlorination for 4-chloro-2-hexene (model of an allylic unstable structure in polyvinylchloride) in solution in dichloroethane. di-ethyl-2-hexyl phthalate and other solvents. The reaction, which is reversible, has an ionic mechanism. It is catalysed by a charge transfer complex between hexadiene and hydrochloric acid. It is inhibited by complexing agents for hydrochloric acid, such as tetrahydrofuran. The addition of hydrochloric acid to conjugated dienes has been shown to occur also in the case of β-carotene.     

Selective transport of zirconium (IV) and niobium (V) from hydrochloric media through a bulk liquid membrane

The selective transport of zirconium/niobium from hydrochloric medium has been investigated through a bulk liquid membrane (BLM) using tri-n-butyl-phosphate (TBP), tri-n-octylamine and dibenzo-18-crown-6 (DBC-6) as the extractants (carriers). The Optimization studies have been carried out by scrutinizing the effect of variables such as the hydrochloric acid concentration in the feed solution, membrane type and hydrochloric acid concentration in the strip solution using the Taguchi approach. The Quantitative transport of zirconium/niobium has been observed by 30% (v/v) TBP in 1200 min from the feed composed of a 9.0 M hydrochloric acid solution of Zr(IV), Nb(V) and lanthanide cations, while the transport of other cations, which have been presented along with Zr/Nb are less than 3% during the same time. Moreover, the possible mechanism of Zr(IV)/Nb(V) ion transport through the BLM has also been discussed and the results show a consecutive, irreversible second-order reaction at the interfaces. Transfer kinetics studies show that niobium transfer process exhibits slightly faster kinetics than zirconium.     

Chemical analysis of manganese nodules : Part II. Determination of uranium and thorium after anion-exchange separation

A method is described for the determination of uranium and thorium in manganese nodules. After dissolution of the sample in a mixture of perchloric and hydrofluoric acids, uranium is adsorbed on the strongly basic anion-exchange resin Dowex 1 (chloride form) from 6 M hydrochloric acid. The effluent is evaporated and the residue is taken up in 7 M nitric acid—0.25 M oxalic acid; thorium is then isolated quantitatively by anion-exchange on Dowex 1 (nitrate form). Thorium is eluted with 6 M hydrochloric acid and determined spectrophotometrically by the arsenazo III method. Uranium is eluted from the resin in the chloride form with 1 M hydrochloric acid and then separated from iron, molybdenum and other co-eluted elements on a column of Dowex 1 (chloride form); the medium consists of 50% (v/v) tetrahydrofuran, 40% (v/v) methyl glycol and 10% (vv) 6 M hydrochloric acid. After removal of iron and molybdenum by washing the resin with a mixture of the same composition and with pure aqueous 1 M hydrochloric acid, the adsorbed uranium is eluted with 1 M hydrochloric acid and determined by fluorimetry. The method was used successfully for the determination of ppm-quantities of uranium and thorium in 60 samples of manganese nodules from the Pacific Ocean.     

The separation of W(V) from HCl-KSCN medium on polyurethane foam sorbents for its spectrophotometric determination in steels and silicates

A simple procedure for selective sorption of tungsten is described. The method involves reduction of W(VI) to W(V) with tin(II) chloride (2%, w/v) at 8-9M hydrochloric acid, formation of the W(V)-SCN complex with 0.2M KSCN and its sorption on polyurethane foam within 20 min. The sorbed complex is then eluted with acidified acetone (1 ml of 1M hydrochloric acid and 8 ml of acetone) followed by addition of 1 ml of 0.1M KSCN to the eluent. The method has been applied to the spectrophotometric determination of tungsten in steels and silicates by measuring the absorbance of the eluted solution at 400 nm. Beer's law is obeyed for the range 0.1-12 mug W/ml. Other elements, e.g., Co(III) (50 mug/ml), Cu(II) (10 mug/ml), Ti(IV) (20 mug/ml), V(V) (10 mug/ml) and Mo(VI) (0.5 mug/ml) have no effect on the method. Interference of copper, up to 100 mug/ml has been eliminated by masking with thiourea and that due to molybdenum by prior separation with thioglycollic acid on PUF. The method has been verified with standard samples.     

A new volumetric method for the determination of molybdenum(VI)

Summary A new volumetric method has been developed for the determination of molybdenum(VI). The method consists in the reduction of molybdenum(VI) by heating with a slight excess of hydrazine sulphate in 1 to 2 M hydrochloric acid medium for ten minutes on a water bath. The mixture is cooled and the molybdenum(V) obtained determined by titration with a standard solution of ceric sulphate at an overall acidity of 4 N hydrochloric acid, using diphenyl benzidine as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the mixture. Alternately the molybdenum(V) can be titrated with a standard solution of ceric sulphate at an overall acidity of 3 N hydrochloric acid using ferroin as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the titration mixture. The molybdenum(V) can also be titrated with a standard solution of sodium vanadate in 8 N sulphuric acid medium, using N-phenyl anthranilic acid as indicator. Alternately, the titration with sodium vanadate can be made with diphenyl benzidine as indicator in 4 N acid medium, adding 5 ml of syrupy phosphoric acid and 1 ml of 1.0 M oxalic acid to catalyse the indicator action. The method now proposed is much more convenient than the methods currently available. It is simple because it does not require any costly chemicals or complicated apparatus. Furthermore, it has the advantages of great rapidity and excellent precision.     

Atomic-absorption determination of beryllium in liquid environmental samples

A method is described for the atomic-absorption determination of beryllium in liquid environmental samples after separation by solvent extraction and cation-exchange. The beryllium is first isolated from natural waters and beverages by chloroform extraction of its acetylacetonate from a solution at pH 7 and containing EDTA. The chloroform extract is then mixed in the ratio of 3:6:1 with tetrahydrofuran and methanol containing nitric acid, and passed through a column of Dowex 50 x 8 (H(+)-form). After removal of acetylacetone, chloroform and tetrahydrofuran by washing the resin bed with methanol-HNO(3), beryllium is eluted with 6M hydrochloric acid and determined by atomic-absorption spectroscopy. The method was successfully applied to determine beryllium in tap-, river- and sea-water samples, mineral waters and wines. Beryllium contents in the range from < 0.01 to 2.3 microg/l were found in these materials.     

Determination of arsenic in ores, concentrates and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A recent graphite-furnace atomic-absorption method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates, rocks, soils and sediments, after separation from matrix elements by cyclohexane extraction of arsenic(III) xanthate from approximately 8-10M hydrochloric acid, has been modified to include an alternative hydride-generation atomic-absorption finish. After the extract has been washed with 10M hydrochloric acid-2% thiourea solution to remove co-extracted copper and residual iron, arsenic(III) in the extract is oxidized to arsenic(V) with bromine solution in carbon tetrachloride and stripped into water. Following the removal of bromine by evaporation of the solution, arsenic is reduced to arsenic(III) with potassium iodide in approximately 4M hydrochloric acid and ultimately determined to hydride-generation atomic-absorption spectrometry at 193.7 nm, with sodium borohydride as reductant. Interference from gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide before the iodide reduction step. The detection limits for ores and related materials is approximately 0.1 mug of arsenic per g. Results obtained by this method are compared with those obtained previously by the graphite-furnace method.     

Ionic equilibria in aqueous organic solvent mixtures the dissociation constants of acids and salts in tetrahydrofuran/water mixtures

The dissociation constants of several acids (perchloric, hydrochloric, phosphoric, acetic and benzoic acids) and of some sodium salts (chloride, acetate and benzoate) have been conductometrically determined in tetrahydrofuran/water mixtures up to a 90% of tetrahydrofuran in volume. The results demonstrate that conductometry can be successfully applied to determine the dissociation constants of salts and moderately weak and strong acids in the studied mixtures. The dissociation constants of the acids and some bases taken from the literature have been fitted to solvent composition through a previously derived equation, which is based on a preferential solvation model. The fitting parameters obtained allow calculation of the dissociation constant for any solvent composition inside the applicability solvent composition range. From the pK value, the pH of any buffered solution, such as those used in liquid chromatography, can be calculated for the particular tetrahydrofuran/ water composition of interest. Appreciable ion-pairing for sodium salts and strong acids has been observed for tetrahydrofuran contents higher than 60% in volume. Therefore, the accurate calculation of the pH values of buffers in tetrahydrofuran-rich solutions must take into account the pK values of the acid and salt.     

A Coulometric Analysis Method and an Ion-exclusion Chromatographic Method for the Determination of Antimony(V) in Large Excess of Antimony(III)

A coulometric analysis method and an ion-exclusion chromatographic method were developed for the determination of antimony(V) in a large excess of antimony(III). Antimony(V) reacted with potassium iodide in a high concentration hydrochloric acid; the liberated iodine was determined by the standard-addition method using coulometrically generated iodine. Using a Dionex ICE-AS1 ion-exclusion column, antimony(V) was eluted with 40 mmol/L sulfuric acid; on the other hand, antimony(III) was strongly retained on the column. The content, expressed as the amount ratio of antimony(V) to antimony(III), was 0.035% in a 10 g/kg antimony(III) solution prepared from an antimony(III) oxide reagent by the coulometric analysis method and 0.036% in a 1 g/kg antimony(III) solution prepared from the same antimony(III) oxide by the ion-exclusion chromatographic method. The results of both methods were in good agreement with each other. The detection limit of antimony(V) in antimony(III) oxide by the former method was 0.004% of antimony(III), and that by the latter method was 0.002% of antimony(III).     

Application of ultrasound-assisted acid leaching procedures for major and trace elements determination in edible seaweed by inductively coupled plasma-optical emission spectrometry

A new method using diluted reagents (nitric and hydrochloric acids and oxygen peroxide) and ultrasound energy to assist metals acid leaching with from edible seaweed was optimized. The method uses a first sonication at high temperature with hydrochloric acid as a previous stage to an ultrasound-assisted acid leaching with 7 ml of an acid solution containing nitric acid, hydrochloric acid and hydrogen peroxide at concentrations of 3.7, 3.0 and 3.0 M, respectively. Optimum conditions for the first sonication step were ultrasound energy at 17 kHz, sonication temperature at 65 °C, an acid volume of 2 ml, an hydrochloric acid concentration of 6.0 M and a sonication time of 10 min. It has been found that the first sonication stage at high temperature with hydrochloric acid is necessary to obtain quantitative recoveries for As, Ba, Fe and V. Otherwise quantitative recoveries were reached for the other elements investigated (Ca, K, Na, Mg, Cd, Cr, Cu, Mn, Ni, Pb and Zn). The repeatability of the ultrasound-assisted acid leaching method was around 10% for all elements. Adequate limit of detection and limit of quantification were reached by using inductively coupled plasma-optical emission spectrometry (ICP-OES) for measurements. The method resulted accurate after analysing several seaweed certified reference materials (IAEA-140/TM, NIES-03 and NIES-09). The method was finally applied to the multi-element determination in edible seaweed samples.     

原子荧光光谱法测定固体废弃物——氧化皮中的砷

建立了固体废弃物——氧化皮中砷的测定方法。氧化皮粉末样品经盐酸溶解,在溶液中添加硫脲和抗坏血酸预还原砷,以盐酸(2+98)为载流,硼氢化钠(10g/L)和氢氧化钾(5g/L)混合溶液为还原剂,砷与硼氢化钠、盐酸反应生成砷化氢,砷化氢利用氩气导入石英炉原子化器中原子化,以空心阴极灯为激发光源,测量砷产生的荧光强度。测试氧化皮中砷含量的相对标准偏差为不大于4.8%,检出限为0.12μg/L,回收率为97%～103%,结果准确度较好。方法具有试剂消耗少、快速、检出限低的优点。     

Determination of uranium in natural waters after anion-exchange separation

A method is described for the determination of uranium by fluorimetry and spectrophotometry in samples of natural non-saline waters. After acidification with hydrochloric acid, the water sample is filtered and, following the addition of ascorbic acid and potassium thiocyanate, passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (thiocyanate form). On this exchanger uranium is adsorbed as an anionic thiocyanate complex. After removal of iron and other coadsorbed elements by washing first with a mixture consisting of 50 vol.% tetrahydrofuran, 40 vol.% methyl glycol and 10 vol.% 6 M hydrochloric acid, and then with pure aqueous 6 M hydrochloric acid, the uranium is eluted with 1 M hydrochloric acid. In the eluate, uranium is determined fluorimetrically or by means of the spectrophotometric arsenazo III method. The procedure was used for the routine determination of uranium in water samples collected in Austria.     

Determination of cobalt,molybdenum and vanadium in austrian mineral waters by ICP-AES after ion-exchange separation and preconcentration

A method is described for the determination of cobalt, molybdenum and vanadium in mineral water samples by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) after separation of these elements from the matrix by ion exchange. The samples are acidified with concentrated hydrochloric acid (10 ml/l) and the elements are adsorbed as thiocyanate complexes. Elution is performed with a mixture 2M in perchloric acid and 1M in hydrochloric acid and subsequently with 1M hydrochloric acid. After evaporation of the eluates and dissolution of the residue the volume of the measuring solution for ICP-AES is 10 ml. The recoveries for Co, Mo and V at a concentration level of 1 g/1 in mineral waters were approximately 99%. A concentration factor of 100 is achieved by this procedure.     

Determination of tungsten with iron(III) after reduction with mercury in thiocyanate medium

Tungsten(V) is formed by shaking for 2 min sodium tungstate solution in 0.4 M potassium thiocyanate-4M hydrochloric acid medium, with mercury. It is titrated with standard iron(III) solution. The thiocyanate present stabilizes W(V) to aerial oxidation and also acts as indicator. The W(V) can also be titrated potentiometrically in 7M hydrochloric acid, a tungsten wire electrode being used. Fe, Ni, Cr, Zr, Bi, Sb, Ce, Al, Pb, Ca and U do not interfere. Cu, V and As can be tolerated up to 5 mg. Co, Mo, Re, Nb and Mn interfere, but not in the potentiometric determination. The method is direct, simple, rapid, accurate and reproducible.     

Spectrophotometric determination of arsenic in concentrates and copper-base alloys by the molybdenum blue method after separations by iron collection and xanthate extraction

A method for determining 0.0001-1% of arsenic in copper, nickel, molybdenum, lead and zinc concentrates is described. After sample decomposition, arsenic is separated from most of the matrix elements by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Following reprecipitation of arsenic and iron, the precipitate is dissolved in approximately 2 M hydrochloric acid and the solution is evaporated to a small volume to remove water. Arsenic(V) is reduced to the tervalent state with iron(II) and separated from iron, lead and other co-precipitated elements by chloroform extraction of its xanthate from an 11M hydrochloric acid medium. After oxidation of arsenic(III) in the extract to arsenic(V) with bromine-carbon tetrachloride solution, it is back-extracted into water and determined by the molybdenum blue method. Small amounts of iron, copper and molybdenum, which are co-extracted as xanthates, and antimony, which is co-extracted to a slight extent as the chloro-complex under the proposed conditions, do not interfere. The proposed method is also applicable to copper-base alloys.     

Determination of uranium after its selective extraction as phenylacetate

The method described is based on the extraction of uranium with a chloroform solution of phenylacetic acid from slightly acidic solution containing nitrilotriacetic acid, which masks all interfering metals. After stripping into very dilute hydrochloric acid, uranium is reduced with ascorbic acid and determined complexometrically. The method permits reliable determination of uranium in the presence of all quadri-, ter- and bivalent metals investigated, molybdenum(VI), tungsten(VI), and vanadium(V).     

Potentiometric titration of molybdenum(V) with ferric alum

Summary The potentiometric titration of molybdenum(V) with ferric alum has now been investigated. The results show that the potentiometric titration of molybdenum(V) is possible at 98–100 C in a carbon dioxide or other inert gas atmosphere in a medium which is 0.5 to 1.0 N in hydrochloric acid. At higher concentrations of hydrochloric acid, there is no steep jump in potential at the end point. In titrations carried out in 0.5 N hydrochloric acid, the potential jump is about 50 mv per 0.1 ml of 0.05 M ferric alum; when the hydrochloric acid concentration is increased to 1.0 N, the potential jump is about 30 mv per 0.1 ml of 0.05 molar ferric alum solution; in titrations with decinormal solutions of the reactants in 0.5 N hydrochloric acid, the potential jump at end point is about 90 mv per 0.1 ml of iron (III) solutionOne of us, Dr. M. Suryanarayana, desires to thank the Ministry of Education Govt. of India for the award of research scholarship.