Determination of chromium in ores, rocks and related materials, iron, steel and non-ferrous alloys by atomic-absorption spectrophotometry after separation by tribenzylamine-chloroform extraction

A method for determining trace and moderate amounts of chromium in ores, concentrates, rocks, soils and clays is described. After fusion of the sample with sodium peroxide, the melt is dissolved in dilute sulphuric acid. The chromium(III) produced by the hydrogen peroxide formed is co-precipitated with hydrous ferric oxide. The precipitate is dissolved in 0.7M sulphuric acid and chromium oxidized to chromium(VI) with ceric ammonium sulphate. The chromium(VI) is extracted as an ion-association complex into chloroform containing tribenzylamine and stripped with ammoniacal hydrogen peroxide. This solution is acidified with perchloric acid and chromium determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 357.9 nm. Barium and strontium do not interfere. The procedure is also applicable to iron and steel, and nickel-copper, aluminium and zirconium alloys. Up to 5 mg of manganese and 10 mg each of molybdenum and vanadium will not interfere. In the absence of vanadium, up to 10 mg of tungsten will not interfere. In the presence of 1 mg of vanadium, up to 1 mg of tungsten will not interfere.     

Selective separation and determination of dissolved chromium species in natural waters by atomic absorption spectrometry

A procedure for determining the concentrations of dissolved chromium species in natural waters is described. Chromium(III) and chromium(VI), separated by co-precipitation with hydrated iron(III) oxide, and total dissolved chromium are determined separately by conversion to chromium(VI), extraction with APDC into MIBK and determination by a.a.s. The detection limit is 40 ng l^?1 Cr. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In the waters investigated, total concentrations were relatively high (1–5 μg l^?1) with Cr(VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species.     

Characterization of cathodic film formed during reduction of chromic acid: role of sulphuric acid concentration

The surface composition of chromium, electrodeposited from a chromic acid solution with different amounts of sulphuric acid, has been investigated by means of Auger Electron Spectroscopy (AES) and X‐ray Photoelectron Spectroscopy (XPS). The quantity of sulphuric acid is a critical parameter in order to form metallic chromium instead of a non‐reducible chromium (III) oxide layer. The intermediate cathodic film formed on the electrode before the metallic chromium deposition has been investigated and XPS measurements have shown that a chromium oxide film is formed whatever the sulphuric acid concentration. However, in the presence of sufficient amounts of sulphate, this oxide is dissolved or the layer is broken down, giving rise to a free steel surface where the reduction of chromate ions into metallic chromium can take place. Copyright © 2004 John Wiley & Sons, Ltd.     

Enhanced capacity of chitosan for transition-metal ions in sulphate-sulphuric acid solutions

Batch measurements have shown that the collection yields of chitosan for chromium(III), iron(III), nickel, copper(II), zinc and mercury(II) from sulphuric acid solutions are higher when the solutions contain ammonium sulphate, or when chitosan conditioned in ammonium sulphate is used, particularly at pH 3.0 and 5.0. The contrary is verified for the oxy-anions vanadate, chromate and molybdate. Manganese is never collected. At pH 1.0 no collection occurs. A procedure for recycling chromatographic columns includes fixation of Cu or Ni from a sulphate solution at pH 3-5 on sulphate-conditioned chitosan, and elution with 0.1M sulphuric acid/0.1M ammonium sulphate at pH 1.0; the presence of sulphate in the eluent obviates the detrimental effect of sulphuric acid on the next cycle. Sulphate is the favoured counter-ion of the chelated cations and its action produces shorter chromatographic bands. The interaction of sulphate with chitosan is discussed in terms of crystallinity and steric distribution of the protonated amino-groups in the polymer. Data on the new diethylaminohydroxypropylcellulose are included.     

The determination of uranium in alloy systems

A procedure is described for the determination of the uranium content of metallurgical alloys containing this element as a minor constituent. The uranium is first separated from the sample solution by precipitation as uranyl ammonium phosphate in the presence of ethylenediamine-totra-acetic acid. By this means the uranium is separated from many elements including iron, chromium, copper, nickel, vanadium, cerium, ncodymium and bismuth. Tho uranyl ammonium phosphate precipitate is dissolved in hydrochloric acid and the resulting solution is passed through a lead reductor. The tetravalent uranium is titrated with a standard cerie sulphate solution, using ferroin as the indicator. This procedure has proved very suitable for the analysis of bismuthuranium binary alloys containing uranium in amounts up to approximately 20%.     

The spectrophotometric determination of chromium in sea water

The coprecipitation of chromium from sea water by several precipitates was examined. With hydrous iron(III) oxide a recovery of chromium of >99% was obtained within the pH range 7.0–9.0 at a chromium level of ca. 0.4 μg/l. Chromium was separated from iron by anion exchange and determined spectrophotometrically using diphenylcarbazide. The method showed a precision of ±0.02 μg Cr/1. Chromium occurs in sea water in the 3+ oxidation state.     

The spectrophotometric determination of chromium in ilmenite

A new diphenylcarbazide procedure free from iron interference is described for the determination of chromium in low-chrome ilmenite. After fusion of the sample, chromium is oxidised with permanganate and most of the iron is eliminated by extraction of chromium(VI) with MIBK Residual iron causes fading of the final colour, this can be avoided by using a phosphoric acid medium at temperatures below 15°. When iron levels are less than 200 μg, temperature control (10°) suffices to prevent iron interference if the concentration of the usual sulphuric acid medium is increased to 0.2 M. However, the phosphoric acid-low temperature method gives wider tolerance to acidity variations and maximum stability with time.     

Determination of total chromium in fresh water by atomic absorption spectrometry following flotation preconcentration

A flotation method is proposed for the quantitative preconcentration and determination of total chromium by electrothermal atomic absorption spectrometry in fresh water samples, without previous reduction or oxidation of the chromium ion state. Hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate were used as precipitating collectors. The detection limit of the method is 0.01 g/L.     

Rapid estimation of metallization in reduced iron oxide ores

A simple and accurate method is described for the determination of degree of metallization in reduced iron oxide ores. Both metallic iron and total iron are determined in a single sample. The metallic iron is selectively dissolved in copper sulphate solution and the oxides are filtered off. The filtrate is titrated with potassium dichromate solution. The residue is dissolved in dilute sulphuric acid in presence of excess of copper powder and after filtration is titrated with the same dichromate solution. The first value gives the metallic iron content and the second value gives the iron content of the oxide residue. From these two values, the degree of metallization is computed.     

A rapid complexometric scheme for analysis of iron, aluminium, calcium and magnesium in slags

A simple and rapid complexometric method has been developed for the simultaneous determination of iron, aluminium, calcium and magnesium in a single solution in slags. Phosphorous and small amounts of chromium (1.5 mg) and vanadium (1 mg) do not interfere in the titration. Titanium and manganese are suitably masked with lactic acid and tetra sodium pyrophosphate, respectively. In a suitable aliquot, iron is titrated at pH 2 with EDTA, using sulphosalicylic acid as indicator. To this solution, excess disodium 1,2-cyclohexane diamine tetra acetic acid (DCTA) is added and aluminium is titrated by titrating the excess DCTA with standard copper sulphate solution at pH 3.5, using 1-(2-pyridylazo)-2-naphthol (PAN) as an indicator. A known excess of EDTA is added, the pH is raised to 10 and calcium and magnesium are jointly titrated by titrating the excess EDTA with copper sulphate solution, using PAN indicator. The Ca-EDTA complex is demasked with ammonium oxalate at pH 5 and the released EDTA equivalent to calcium is titrated with copper sulphate solution at pH 10 with PAN indicator. Results of analysis compare favourably with certified values and values obtained by standard methods for BCS and other slags. A set of five samples can be analysed for iron, aluminium, calcium and magnesium in four hours as compared to three days by the classical conventional method.     

Nm-sized crystallites embedded in single crystalline films of magnesium oxide

Composite films of magnesium oxide embedding metals such as gold, iron and chromium are prepared by the simultaneous deposition technique onto cleavage surfaces of sodium chloride and characterized by high resolution electron microscopy. These metals grow epitaxially and uniformly inside magnesium oxide films as crystallites of a few nm in size. The thickness of the crystallites is estimated to be a few atomic layers. The observation of isolated single atoms or atomic clusters is attempted under an off-Bragg condition. For composite films of iron and magnesium oxide, a heat treatment at 500°C for two hours brings about the growth ofγ-iron crystallites. A strain field at the periphery of theγ-iron crystallites is analysed. For composite films of chromium and magnesium oxide, chromium crystallites of around 1 nm in size grow epitaxially inside magnesium oxide films with two kinds of orientation.     

A new method for the direct precipitation of aluminium in the presence of iron

It is shown that aluminium can be precipitated as benzoate from solutions containing up to 1 gram of iron in the presence of thioglycollic acid, which reduces the iron and forms a soluble complex with ferrous iron. Very large amounts of such salts as ammonium chloride, sulphate and perchlorate, and sodium chloride do not interfere, nor do other divalent metals. Molybdates and tungstates are without effect, but chromium, vanadium and titanium interfere. This limits the direct application of the method in metallurgical analysis, but in many cases this speedy and complete separation will have many uses.     

还原温度对氧化铁吸附性能的影响

利用脉冲气相色谱保留体积法测定了不同还原温度的氧化铁样品对水的吸附特性并和Ｘ光衍射结果进行了关联,同时测定了含铬氧化铁对水的吸附特性。结果表明,中温还原样品有比较均匀的表面,低温和高温还原样品的表面均有一定程度的不均匀性且符合焦姆金吸附方程。铬的加入降低了氧化铁对水的吸附热,并增加吸附中心的数量     

The use of neutron activation for routine analysis of pure iron and chromium

A method is presented for the routine analysis of high-purity iron and chromium by neutron activation analysis. The impurities determined are those which are significant in the control of the purification processes. Nine elements are determined in iron without separation; Co, Cr and Mo can also be determined after an anion-exchange separation. In chromium, a single elution on an anion exchanger allows the detection of nine significant impurities. For the determination of nickel a special method is used. All these methods were chosen to obtain the most comprehensive analytical procedure at the lowest cost.     

Colorimetric determination of chromium in titanium alloys

Chromium-titanium alloys are becoming increasingly important because of their strength and corrosion, resistance. Therefore, accurate methods for the determination of chromium in this type of alloy are needed. A colorimetric procedure for the determination of chromium in titanium alloys is proposed. In this method the chromium is oxidised to the chromate state by means of ammonium persulfate and potassium permanganate in the presence of silver nitrate as a catalyst. Diphenylcarbazide is then added to an aliquot of the solution, and the violet color read in 10 to 40 minutes at 580 millimicrons. None of the elements found in commercial titanium alloys, including iron, vanadium, molybdenum, and tungsten, interferes with the method. The proposed method is superior to the volumetric method for the determination of small amounts of chromium. The method is designed for titanium. alloys containing 0.02 to 4 per cent chromium.     

The application of differential pulse polarography to the determination of a pharmacologically active benzhydrylpiperazine derivative and its major electroactive metabolites in the plasma and urine of animals.

A method for the determination of 1–500 p.p.m. of acid-soluble aluminium and 2–500 p.p.m. of acid-insoluble aluminium in low-alloy and stainless steels by flameless atomic absorption with a HGA 74 graphite furnace is described. A typical value of the relative standard deviation for acid-soluble aluminium at concentrations larger than 10 p.p.m. was 5 %. The steel sample was dissolved in hydrochloric and nitric acid and filtered. Ammonium sulphate was added to the filtered sample in order to overcome interferences caused by hydrochloric acid. No concentration steps were used. Acid-soluble aluminium was determined within 20 min. The influence of iron, chromium, nickel, molybdenum, hydrochloric acid, nitric acid and ammonium sulphate respectively was investigated.     

Thenoyltrifluoroacetone as a reagent for cobalt

Summary An indirect method is proposed for the determination of cobalt (II) with 2-thenoyltrifluoroacetone at the milligram level. The orange cobalt-TTA chelate can be quantitatively precipitated over the p_H range 4.0–8.0. It is dissolved in acid and estimated as cobalt sulphate. Cobalt(II) can be estimated in presence of silver, mercury(II), strontium, iron(III), chromium (III), thorium, zirconium, uranium, citrate and tartrate. The method is reproducible to within ±1 per cent.     

Effects of various washing procedures on the chromium content of human scalp hair

The effects of four wash procedures on the concentration of chromium in a pooled sample of human scalp hair are compared. The wash solutions examined are Triton X-100, sodium lauryl sulphate, acetone, and a mixture (1 + 1) of hexane and ethanol. The plateaux reached for hair chromium concentration are functions of the number of washings, and are characteristic for each wash solution. The wash procedure recommended involves two 20-min washes with aqueous 1% sodium lauryl sulphate solution after a hexane rinse.     

Determination of manganese at ng ml levels in natural waters by differential pulse polarography

A procedure based on differential pulse polarography is described for the determination of manganese at ng/ml levels in fresh, estuarine and sea-water buffered at pH 9.5 with a citrate-borate solution that also serves as supporting electrolyte. The procedure is unaffected by the potentially interfering compounds most likely to occur in natural waters. Furthermore, iron (in ascorbate-borate buffer, pH 9.5) or chromium (in ascorbate-ammonia-ammonium-chloride buffer, pH 9.8) can be determined together with manganese. Some results for the concentration of manganese, iron and chromium in the River Arno are reported.     

Catalysts for methane transformation in the absence of oxygen, II. Nature of active centers

The activity of supported manganese oxide catalysts doped with copper, chromium and iron oxides in methane to higher hydrocarbons transformation in non-oxidizing atmosphere has been studied. Chromium and iron oxides are more effective promoters than copper oxide. Redox centers of dehydrogenation ability are active in methane transformations.