Molybd?n(VI) und Wolfram(VI)

Ohne Zusammenfassung     

Zur Bestimmung von Molybd?n(VI), Wolfram(VI) und Vanadium(V) mit Thalliumnitrat

Ohne Zusammenfassung     

分光光度法快速测定水中铬(VI)

铬是人体所必需的微量元素之一,但摄入过量会对人体产生危害。铬的毒性与其存在的价态有关,铬(Ⅵ)的毒性比铬(Ⅲ)高100倍,而且铬(Ⅵ)更易为人体吸收并在体内蓄积。科学研究表明,铬(Ⅵ)化合物在人体内具有致癌作用,是水质监测中的重要检测项目。目前铬(Ⅵ)的测定方法有二苯碳酰二肼(DPC)分光光度法[1]、乙酰偶氮胂法[2]、3,3,′5,5′-四甲基联苯胺法[3]等,其中DPC分光光度法测定铬(Ⅵ)具有灵敏度高、特异性好的优点,是目前最常用的方法,但用此法测定时,显色剂DPC需用有机溶剂配制,配好的显色剂需置于冰箱中保存,而且半个月后显色剂即呈暗…     

Cr(VI)吸附剂及其吸附机理研究进展

摘要 重金属污染已成为影响人们生活亟亟待解的问题,它不仅威胁着自然环境的持续发展,更是对人类身体健康提出了严峻的考验。其中,六价铬因为环境污染持续久,危害大,更是得到各国研究者的重视。研究者们研究了各种吸附材料,它们对于六价铬的移除能力以及移除机理不尽相同。本文介绍了Cr(VI)吸附材料分类及其特点,重点分析了聚合物吸附材料在吸附和分离Cr(VI)方面的应用进展。并简要介绍了Cr(VI)吸附过程中的吸附动力学模型和等温方程式,以著名的Langmuir和Freundlich模型为例加以说明,为解决重金属铬离子引起的环境污染尤其水污染问题提供一种借鉴。     

Spectrophotometric Determination of Trace Chromium(VI) in Mass Chromium(III)

There is little conclusive evidence of the toxic effects of Cr(III) so far, but Cr(VI) has carcinogenic activity, so the analysis of the chromine ions is very important in environmental research and the quality control of industry products. Usually Cr(III) and Cr(VI) interfere with each other in the species analysis, the measurement of Cr(VI) of numerous previous papers is related to the Cr(VI) samples, which contain a little Cr(III). When the amount of trivalent chromine exceeds ten …     

Mössbauer study of sodium ferrates(IV) and (VI)

Sodium ferrates(IV) and (VI) were synthesized by the reaction between Fe₂O₃ and Na₂O₂ in a dry oxygen stream. The Mössbauer data for the obtained samples are presented (for Na₂FeO₃–=0.18(2) mm/s; for Na₄FeO₅–=–0.54(2) mm/s). It was shown that pure K₂FeO₄ and Cs₂FeO₄ can be obtained by heating Fe₂O₃ with apropriate alkali metal peroxides.     

Über die Extrahierbarkeit des Wolfram(VI)-rhodanids

Zusammenfassung Die Anwendbarkeit des Wolfram(VI)-komplexes mit Rhodanid für die analytische Praxis wurde untersucht; durch seine Löslichkeit in organischen Lösungsmitteln eignet sich der Komplex gut zur Trennung von anderen Elementen.Unter Zuhilfenahme des radioaktiven Wolframisotopes¹⁸⁵W konnten die optimalen Extraktionsbedingungen, wie Säure- und Rhodanidkonzentration, rasch ermittelt werden. Bei der Untersuchung verschiedener organischer Lösungsmittel zeigte Amylalkohol sowohl in reiner Form als auch in Mischungen mit Chloroform die besten Extraktionseigenschaften.Da der Komplex zu den stärksten des Wolframs gehört, stören bei der Durchführung von Analysen nur wenige Anionen, am meisten Fluorid. Von den Kationen werden nach Reduktion des Eisens, wozu Ascorbinsäure empfohlen wird, nur wenige andere mitextrahiert; am störendsten wirkt Molybdän, das mitausgeschüttelt wird und anschließend entfernt werden muß. Zur Bestimmung des Wolframs eignet sich dann am besten die Hydrochinonmethode.

---

Summary A study was made of the use of tungsten(VI) complex with thiocyanate in analytical practice. Because of its solubility in organic liquids the complex is well suited for separation from other elements.By using the radioactive isotope¹⁸⁵W, the optimal extraction conditions, such as the acid- and thiocyanate concentration, could be rapidly determined. When various organic solvents were tried, it was found that amyl alcohol, either by itself or mixed with chloroform, had the best extraction characteristics.Since the complex is one of the most stable formed by tungsten, only a few anions interfere in the analysis; fluoride causes the most trouble. Among the cations, only a few interfere after the iron has been reduced (ascorbic acid is recommended for this purpose). The greatest interference comes from molybdenum, which is co-extracted and has to be removed subsequently. The hydroquinone method is then the best procedure for determining the tungsten.

---

Résumé On a cherché à appliquer le complexe tungstène-VI-thiocyanate à l'analyse. Grâce à sa solubilité dans les solvants organiques, le complexe se prête bien à la séparation d'avec les autres éléments.Au moyen de l'isotope radioactif du tungstène¹⁸⁵W, on a pu trouver rapidement les conditions optimales d'extraction, ainsi que la concentration en acide et en thiocyanate. Après essai de divers agents de dissolution organiques, l'alcool amylique a montré les meilleures propriétés extractives, aussi bien sous sa forme pure qu'en mélange avec le chloroforme.Etant donné que le complexe est l'un des plus robustes du tungstène, seuls quelques anions gênent pour effectuer les analyses, et surtout les fluorures. Parmi les cations, après réduction du fer pour laquelle l'acide ascorbique est recommandé, seuls quelques autres sont extraits avec lui; le molybdène présente l'action la plus gênante, il doit être masqué et séparé complètement. Pour le dosage du tungstène, la méthode à l'hydroquinone convient alors le mieux.

     

Counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) using tris-2-ethyl hexyl phosphate (TEHP)

Evaluation of tris-2-ethyl hexyl phosphate (TEHP) for counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) from nitric acid medium was carried out under wide experimental conditions. Batch extraction studies were carried out to investigate the effect of nitric acid concentration in feed solution, U(VI)/Th(IV) ratio and extractant concentration and the results were compared with established solvent such as tri-n-butyl phosphate (TBP) for separation of U(VI) from nitric acid medium. McCabe–Thiele diagrams for extraction as well as stripping of U(VI) were constructed under simulated conditions. Based on batch experiments, six stage counter-current extraction studies were conducted under various TEHP concentration and it was observed that 0.1 M TEHP/n-paraffin was most suitable for selective recovery of U(VI) from a mixture of U(VI)–Th(IV). An optimized condition, 0.1 M TEHP/n-paraffin, 2 M HNO₃ in feed and six number of stages was evaluated for selective extraction and stripping of U(VI) from a solution containing mixture of U(VI)–Th(IV)–Y(III) in nitric acid medium. The U(VI) in strip solution was precipitated using 30 % H₂O₂ at pH ~3. Average particle size of the final precipitate was found to be ~33 μm.     

Cluster-models for uranyl(VI) adsorption on α-alumina

Aqueous complexation, adsorption, and redox chemistry of actinide species at mineral surfaces have a significant impact on their transport and reactive behavior in chemically and physically heterogeneous environments. The adsorption configurations and energies of microsolvated uranyl dication species, UO(2)(H(2)O)(n)(2+), were determined on fully hydroxylated and proton-deficient α-alumina(0001)-like finite cluster models. The significant size of the models provides faithful representations of features that have emerged from periodic calculations, but most importantly, they afford us a systematic study of the adsorption mechanism, the effect of secondary solvation shells and an explicit treatment of the total charge. Based on this cluster representation, the energetics computed from the difference between the optimized structures and the appropriate reference states point to a preference for an inner-sphere type complex.     

铜(II)-铬(VI)复合均匀胶体粒子的制备

报导在尿素存在下通过均相沉淀法由硝酸铜和重铬酸铵制备复合均匀胶体粒子的结果．研究了一些实验参数对其组成、形态和粒子大小的影响．确定了胶体粒子的制备条件．结果观测到，由硝酸铜和重铬酸铵溶液形成了球形的多刺的粒子，它的组成为水含铅酸铜．     

Dioxomolybdenum(VI) complex with N,N′- ethylenebis(salicylideneimine)

The interaction of N,N′-ethylenebis(salicylideneimine), H₂salen, with ammonium molybdate yielded the molybdenum(VI) complex MoO₂(salen) with the cis-dioxostructure as inferred from IR spectral studies. The ¹H NMR chemical shifts of azomethine protons in the free ligand and the complex are 8.14 and 8.39 δ, respectively, suggesting the bonding of the azomethine nitrogen to MoO₂ group. The thermal decomposition behaviour of the complex is discussed.     

电化学传感分析平台测定污水中的Cr(VI)

结合微型电化学仪器,研究了一种快速、便携、灵敏的Cr(VI)电化学传感分析平台,用于污水中Cr(VI)的检测。采用三电极体系,差分脉冲阴极溶出伏安法(DPCSV),记录伏安曲线中Cr(VI)的还原峰。Cr(VI)的溶出峰电流与其浓度在2～500 μmol L-1范围内有良好的线性关系,测得Cr(VI)的检测限为0.55 μmol L-1 (28.60 g L-1),达到了国际卫生组织（WHO）规定的饮用水中Cr(VI)的最高含量50 g L-1。测得镀铬厂废水中Cr(VI)含量为2.03 mol L-1,与国标法中光谱学分析法的结果基本一致。该法重现性好、灵敏度高,使其应用在现场实时监测环境中的Cr(VI)具有很大的潜力。     

氨在丝光沸石位置(VI)上的吸附

The adsorption of NH3 on (AO)3SiO*HAl(OA)2OSi(OA)3 cluster from the structure of site (VI) of mordenite Zeolite has been calculated by an adsorption model of hydrogen-bond form, quantum chemical method, CNDO/2 scheme. Variations of adsorption distance between NH3 and O* in the cluster were directly related to initial adsorption heats of NH3 on O*H group, jump frequency of the proton between NH3 and O* and frequency shift of IR band with O*H group. Adsorption distance of NH3 on O*H group has been calculated, the range was about 2.5 to 2.75A, and the most favourable adsorption distance with strong acid strength was 2.5A. It was related to the maximum initial adsorption heat which was 33.80 kcal/mol, the lowest activation energy of proton mobility between NH3 ane O*, and the largest frequency shift of IR bands with O*H group. This result qualitatively corresponded to experimental observations. It showed that the various representations of acidic strength are equivalent to each other which could be explained on basis of adsorptin model of hydrogen bond form.     

Spectrophotometric Determination of Chromium(VI) with Cr(VI)-o-Cl-PF–TDPC Ternary Complex after Preconcentration on an Organic Solvent-soluble Membrane Filter

Abstract

A simple and rapid preconcentration technique, based on collecting trace hexavalent chromium on an organic soluble membrane filter is described. At pH 5.0, chromium(VI), o-chlorophenyl-fluorone (o-Cl-PF) and tetradecylpyridinium chloride (TDPC) form the ternary ion-associate chelate, which can be collected on a 0.2μm nitrocellulose membrane. The filter is dissolved in a small volume of dimethyl sulfoxide (DMSO) acidified with 0.15 mL 3 mol/L sulfuric acid, and the absorbance of the resulting solution is measured at 545 nm wavelength against the reagent blank. The absorbance is proportional to the content of hexavalent chromium in the range of 0.1–1.8μg, in 5 mL solvent. The sensitivity of the ternary complex reaction is very high with molar absorptivity of 1.2 × 10⁵. A detection limit better than 0.3 μg/L can be achieved. The ions normally present in water do not interfere when mixed masking agents are added. The proposed method has been applied to the analysis of water samples from several sources, the recoveries of the hexavalent chromium added to the samples are quantitative, and results found are satisfactory.     

铬(VI)-O-FPF-CTMAB-酒石酸钠荧光熄灭体系及其应用

铬(ＶＩ)影响人体健康,从而引起人们的注意,近年来建立了许多测定铬(ＶＩ)的新方法。用荧光熄灭法测定铬的方法有:二溴羟基苯基荧光酮 乳化剂ＯＰ[1]、水杨基荧光酮 ＣＴＭＡＢ[2]、二溴苯基荧光酮[3]、间氟苯基荧光酮 ＣＴＭＡＢ[4]等,但以上均为三元体系。本实验发现在ｐＨ4 20～4 80的ＨＡｃ ＮａＡｃ缓冲介质中,Ｃｒ(ＶＩ)与邻氟苯基荧光酮(Ｏ ＦＰＦ)、溴化十六烷基三甲基铵(ＣＴＭＡＢ)及酒石酸钠(Ｔａｒｔｒａｔｅ)可形成一多元混配络合物,使Ｏ ＦＰＦ试剂的荧光显著熄灭。Ｃｒ(ＶＩ) Ｏ ＦＰＦ ＣＴＭＡＢ Ｔａｒｔ荧光体系测定…