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1.
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. 相似文献
2.
Summary A method for the determination of chromium(VI) in solid materials with a Cr(VI) content at ppm level in the presence of ca. 10% Cr(III) has been devised. Chromium(VI) is extracted with 0.1M NaOH in a double-water bath (97° C) for 90 min. Differential-pulse polarography in 1M NaOH and spectrophotometry with 1,5-diphenylcarbazide have been tested for use in the final determination of Cr(VI). After extraction in the form of dithiocarbamate into methylisobutylketone or ethylacetate, chromium was determined by flame AAS and DPP in an organic extract. 相似文献
3.
A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml-1 and 0.55 μg Fe(III) ml-1 did not interfere with the determination of 0.050 μg Cr(VI) ml-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml-1 to 2.0 μg ml-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml-1. 相似文献
4.
Kunihiko Yokoi Toru Ozeki Iwao Watanabe Shigero Ikeda 《Journal of Electroanalytical Chemistry》1982,133(1):73-78
Reduction mechanisms of polarographic reduction waves of Mo(VI) in 0.1–5 M sulfuric acid solutions are described. Three reduction waves are observed when the concentration of sulfuric acid is >3 M. From the results of coulometry and the catalytic behavior of Mo(V), it is concluded that three different reduction mechanisms of Mo(VI) to Mo(V) are present and that two separate reductions of Mo(VI) to Mo(V) and of Mo(V) to Mo(III) are involved at the potential of the third wave. The presence of three reduction mechanisms of Mo(VI) to Mo(V) in sulfuric acid α 3 M seems to indicate the existence of three different chemical species of Mo(VI). Two of these three species are different from the present in 0.1 M sulfuric acid. 相似文献
5.
W. Żmijewska 《Journal of Radioanalytical and Nuclear Chemistry》1972,10(2):187-196
A method has been developed for the substoichiometric separation of Cr(VI) by extraction with tri-n-octylamine solution in
benzene from 0.1M H2SO4 solution. The method has been applied to the determination of chromium in silicon and aluminium by the neutron activation
method. 相似文献
6.
A. V. Radushev V. Yu. Gusev T. D. Batueva G. S. Bogomazova L. S. Shabalina V. N. Tyryshkina V. I. Karmanov 《Russian Journal of Inorganic Chemistry》2006,51(12):1973-1976
The solubility and acid-base properties of benzoic acid N,N-dihexylhydrazide (BDHH) were studied. The extraction of copper(II), cobalt(II), nickel(II), zinc(II), iron(III), platinum(II), platinum(IV), chromium(III), chromium(VI), palladium(II), and molybdenum(VI) with this reagent was studied. It was shown that BDHH most efficiently extracts copper(II) from ammonia solutions and chromium(VI) from sulfuric acid solutions. In the extraction of copper(II), complexes with the [Cu(II)]: [BDHH] = 1: 1 and 1: 2 stoichiometries were found to form. The structure of the 1: 2 complex was suggested proceeding from its IR spectra. A copper(II) extraction isotherm was plotted. 相似文献
7.
T. Zh. Sadyrbaeva 《Russian Journal of Applied Chemistry》2013,86(9):1392-1398
A study of the process of electrodialytic recovery of chromium(VI) from a solution of 0.01 M K2Cr2O7 in 0.1 M HCl with liquid membranes containing tri-n-octylamine with addition of di(2-ethyl hexyl)phosphoric acid in1,2-dichloroetrhane to dilute solutions of various acids determined the optimal process conditions: electrodialysis current density and the composition of the starting and receiving aqueous solutions and liquid membranes. It was found that all the liquid membranes studied provide a complete recovery of chromium(VI) anions from the starting solution. 相似文献
8.
Fang Kong Jia-li Liao Song-dong Ding Yuan-you Yang Huang Huang Ji-jun Yang Jun Tang Ning Liu 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):651-656
The extraction behavior of U(VI) and Th(IV) with tri-isoamyl phosphate–kerosene (TiAP–KO) from nitric acid medium was investigated in detail using the batch extraction method as a function of aqueous-phase acidity, TiAP concentration and temperature, then the thermodynamic parameters associated with the extraction were derived by the second-law method. It could be noted that the distribution ratios of U(VI) or Th(IV) increased with increasing HNO3 concentration until 6 or 5 M from 0.1 M. However, a good separation factor (D U(VI)/D Th(IV)) of 88.25 was achieved at 6 M HNO3, and the stripping of U(VI) from TiAP–KO with deionized water or diluted nitric acid was easier than that of Th(IV). The probable extracted species were deduced by log D-log c plot at different temperatures as UO2(NO3)2·(TiAP)(1–2) and Th(NO3)4·(TiAP)(2–3), respectively. Additionally, △H, △G and △S for the extraction of U(VI) and Th(IV) revealed that the extraction of U(VI) by TiAP was an exothermic process and was counteracted by entropy change, while the extraction of Th(IV) was an endothermic process and was driven by entropy change. 相似文献
9.
A procedure was developed for determining chromium(VI) in the soil organic fraction; it consisted of three steps: the preparation of a soil solution; the isolation and separation of chromium(VI) and chromium(III); and the determination of chromium(VI). Soil solutions were prepared by leaching soil samples with a Na4P2O7 solution (the Rudd method). Chromium(VI) was extracted from the soil solution with a solution of sodium diethyldithiocarbamate in n-amyl alcohol; the conditions of the extraction and separation of chromium(VI) and chromium(III) were optimized. Chromium(VI) in solutions was determined after back extraction by spectrophotometry with diphenylcarbazide or by flame atomic absorption spectrometry. The procedure was validated using a reference soil sample, and the material balance of chromium in the systems under study was calculated. 相似文献
10.
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. 相似文献
11.
Molybdenum (V) was generated at a platinum cathode from 0.7 M molybdenum(VI) in 4 M sulfuric acid. A current efficiency of 99.9% was attained. A limiting current density of 0.05 mA/cm2/mM was found. The formal potential of the Mo(VI)–Mo(V) couple in 4 M sulfuric acid was determined to be ca. 0.55 V vs. N.H.E. Chromium(VI) solutions were titrated over a wide range of sample size and generating current. Amperometric titration curves were interpreted from current-voltage curves. Titrations could be performed in the presence of oxygen at the 1μeq. level. The effect of nitrate, perchlorate, orthophosphate, and chloride ions on the titration was determined. 相似文献
12.
A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities
were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was
retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L−1 HCl and 0.1 mol L−1 NaOH. Detection limits of 0.05 and 0.04 μg mL−1 were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using
250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption
of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide
complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial
water samples. 相似文献
13.
The liquid-liquid extraction of rare-earth elements (REE) by 0.75 M di-(2-ethylhexyl) phosphoric acid (HDEHP) in cyclohexane from perchloric acid (1–12M) has been investigated. At moderate perchloric acid molarities (1–6 M), the distribution coefficient, E, has an inverse third-power dependency upon the acid concentration in the aqueous phase. However, at higher perchloric acid concentrations, the slope of the resulting curve is about +18, which means a change in the extraction mechanism. In 12 M perchloric acid medium, REE are quantitatively and selectively extracted from apatite minerals, in the organic phase. In order to strip out all the lanthanides, back-extractions were carried out with 9 M hydrochloric acid solutions. 相似文献
14.
The metal complexes of uranium(VI) with disodiuM 2-naphthol-3,6-disulphonate and 7-amino-1-naphthol-3,6-disulphonic acid were studied by the established potentiometric techniques of Bjerrum and Irving and Rossotti. The step-wise protonation constants of the ligands and the step-wise stability constants of the uranyl complexes were deterMined in 0.1 M sodiuM perchlorate Media at 25°. 相似文献
15.
M. K. Shehata S. El-Bayoumy M. El-Garhy 《Journal of Radioanalytical and Nuclear Chemistry》1971,8(2):231-234
The distribution of Mo(VI) and the interfering radiocontaminants U(VI), Zr(IV) and Nb(V) have been investigated between chromatographic
alumina and aqueous hydrochloric acid solutions of concentrations ranging from 0.5M to 11M. At low acidities (less than 1M HCl) the distribution coefficients increase with the decrease of acid concentration, while in the region of 2–4M they increase with the increase of the acid concentration. Above 4M HCl, the increase inK
D continues with the acid concentration for both Zr(IV) and Nb(V), but constant values are reached for U(VI) and Mo(VI). 相似文献
16.
Hydrazine sulphate is proposed as a primary standard reagent for the direct titrimetric determination of vanadium(V) and chromium(VI) alone and in mixtures with potentiometric and photometric end-points, in 9–12 M phosphoric acid medium. The methods proposed possess advantages over those currently available. The use of phosphoric acid as a reaction medium not only accelerates the hydrazine-vanadium(V) reaction very much but also makes it follow an accurate stoichiometric path. 相似文献
17.
The current efficiency for the electrogeneration of chromium(II) for use as a coulometric titrant was studied for several supporting electrolytes. With a mercury cathode and a 0.1 M chromic sulfate-0.1 M potassium chloride medium, 0.8 to 2.8 mg of copper (II) in 110 ml of solution can be titrated using potentiometric end-point detection. 相似文献
18.
M. S. Bhatti Shamasud Zuha M. A. Qureshi 《Journal of Radioanalytical and Nuclear Chemistry》1984,82(1):45-52
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. 相似文献
19.
《Journal of Electroanalytical Chemistry》1987,217(2):305-311
The electrochemical behaviour of molybdenum(VI) in sulphuric acid solutions was investigated by cyclic voltammetry. In the reduction of Mo(VI) to Mo(III) a dimerization reaction of Mo(V) is involved; the rate constant for the reaction was estimated to be 2.79×102 M−1 s−1 and the activation energy was ca. 35 kJ mol−1 in 0.1 M H2O4. Oxidation of the monomer and dimer Mo(V) species take place at −0.31 and +0.18 V (vs. SCE), respectively. 相似文献
20.
Mohammad Ali Karimi Rasul Shahin Sayed Zia Mohammadi Abdolhamid Hatefi‐Mehrjardi Javad Hashemi Javad Yarahmadi 《中国化学会会志》2013,60(11):1339-1346
A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H2O2. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H2O2 concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL?1, 0.1‐10.0 ng mL?1 and 4.6% (for 5.0 ng mL?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained. 相似文献