极谱法测定化探样品中钨钼的技术改进

针对传统极谱法测定化探样品中钨钼时操作手段繁琐问题加以改进。试样以硫酸-二苯乙醇酸-二苯胍-氯酸钠体系为混合底液,将经过碱熔融后的样品以甲基橙为指示剂,用硫酸(1+1)调酸度后,加入固定比例的混合底液,摇匀,无需定容,放置25~30min后直接测定。采用二次倒数波测定,钨峰电位在-660mV左右,钼峰电位在-30mV左右,钨钼的质量浓度在0.02~1.0μg/mL内呈线性关系,钨检出限为0.5μg/g,钼检出限为0.3μg/g。方法灵敏度高,快捷、简单,适用于大批量化探样品的测定。     

催化极谱法同时测定岩石、矿物中微量钨和钼

关于钨和钼的催化极谱法测定已有许多文献报导。为了满足地球化学地质样品分析低达1ppm钨、钼的要求,本文着重研究了提高钨催化极谱测定灵敏度。在前人工作的基础上,提出在硫酸-二苯羟乙酸辛可宁8羟基喹啉-氯酸钾体系中进行钨钼连测。在该体系中钨、钼的峰电位分别约为-0.75伏和-0.45伏     

催化极谱法连续测定岩石中钨和钼

本文提出了在二苯基乙醇酸-二苯胍-氯酸钠催化极谱体系测钨后,加入少许钛铁试剂,使钼产生一个极灵敏的导数波。谊波形尖锐、对称,便于测量钼。建立的连测体系简便灵敏,用于岩石样品中钨和钼的测定,取得了满意的效果。     

在CTMAB存在下钨的催化极谱波及海水中超痕量钨的测定方法

研究了硫酸-二苯羟乙酸-氯酸钾-CTMAB体系中钨的极谱催化性质.证实了该极谱波是吸附催化波.发现了CTMAB能改善波形,增加灵敏度,同时能消除较大量钼的干扰。利用CHCl_3萃取钨与氯化6,7-二羟基-2,4-二苯基苯并吡喃的络合物,以浓缩海水中超痕量的钨,然后用催化极谱法测定.水中钨的测定灵敏度为5×10~(-11)M.方法选择性好,简便、快速.除能测定海水外,还可用于测定江水、湖水、温泉水以及自来水等,均取得了满意的结果.     

极谱法快速测定化探试样中钼钨

硫酸-苯羟乙酸-氯化钾体系催化极谱测定钼、钨已有报导。本文在此底液中加入适量辛可宁,提高了钼钨的测定灵敏度;改用盐酸-硝酸-氢氟酸-高氯酸混合酸于聚四氟乙烯烧杯中分解试样,钼、钨可定量溶解,且降低了空白,与碱在刚玉坩埚中分解试样的分析结果对照颇为一致;共存干扰元素,可借硫酸冒烟或用氢氧化钠沉淀分离予以消除;底液混合后一次     

流动型膜电极催化伏安连续扫描测定微量钨钼

催化极谱测定钨、钼,在引用二苯乙醇酸取代苦杏仁酸后,稳定性和灵敏度都大为改善。而面对成千上万化探试样的定量分析,应用流动型膜电极以避免汞毒害是很可取的。但是,钨、钼分开测量,速度太慢。我们试验了流动型膜电极法,在改善流动状况和统一钨、钼清洗液的同时,利用主机有较宽的电压扫描范围及自动取样,在同一份试液中完成钨、钼一次连续扫描记录。並且对钨、钼标准溶液的浓度、扫描速度和清洗润湿时间作了适当调整,使方法的稳定性、速度和灵敏度都大有改善。本法已成功地用于大批化探试样中钨、钼的测定。     

矿石中钼的催化示波极谱测定——钼(Ⅵ)-硫酸-苯羟乙酸-柠檬酸-氯酸钠体系

钼(Ⅵ)在硫酸-苯羟乙酸-氯酸钾底液中形成的吸附催化波已应用于矿石中痕量钼的测定。一般是在普通极谱仪上测定矿石中含量为0.000x%的钼,而在示波极谱仪上阴极极化扫描所得图形欠佳。通常选矿试样要求测定含量0.00x～0.0x%的钼,且要求分析方法简便、快速。为此,本实验在钼(Ⅵ)-硫酸-苯羟乙酸-氯酸钠体系中加入柠檬酸以降低钼催化波的灵敏度,并进行阳极极化导数示波极谱测定。使方法的灵敏度和     

钨基中微量钼的直接催化极谱测定

钨基中微量钼的催化极谱测定,多采用苦杏仁酸-氯酸钾-硫酸体系。据资料报导,在该体系中,当钨量高于钼量500倍时,严重干扰钼的测定,故测定前需分离除钨,因此费时,精密度又差。我们通过试验,改用柠檬酸络合钨,用标准加入法抵消钨的干扰。对钼量0.00077—0.39%的试样,经不同分析人员操作,证明:钨量比钼量大100000倍,亦可直接进行钼的测定。本法勿需采用冗长的分离步骤,仅将试样用碱和过氧化氢分解后,分取试液即可直接测定。方法具有简便、快速、准确、成本低等优点,测定下限为0.000x%。     

X射线荧光光谱法同时测定矿石中钨钼锡

提出了X射线荧光光谱法同时测定钨钼锡矿石中钨、钼、锡元素含量的分析方法。方法选择四硼酸锂作熔剂,熔融制成样片,通过PW2403型X射线荧光光谱仪自带Super Q系统软件,以经验α系数法和Rh康普顿散射线内标法校正基体效应。以标准样品建立工作曲线,同时测量样品中钨、钼、锡元素含量。方法准确度和精密度能满足规范要求,钨、钼、锡的分析方法检出限分别为0.0042%、0.0026%、0.0072%。采用本法同时测定矿石中钨、钼、锡元素含量结果与传统分析方法测定结果相吻合,样品检测结果能满足矿区地质勘查的工作要求。     

电感耦合等离子体质谱（ICP-MS）法测定炭质页岩中的钨钼钪

炭质页岩中含有大量的炭化有机质,其中钨钼在单一盐酸溶液中易水解,样品的完全消解及有效防止钨酸、钼酸的形成是准确测定炭质页岩中钨、钼和钪含量的关键。采用HCl-HF-HNO_3-HClO_4四酸体系消解样品,加盖形成蒸气回流;采用酒石酸-盐酸体系浸取,有效防止钨酸、钼酸沉淀导致结果偏低问题。建立了电感耦合等离子体质谱(ICP-MS)法测定炭质页岩中的钨、钼、钪的分析方法。测定结果表明,各元素在0.01～200.0μg/L范围内线性关系良好,相关系数均在0.999 9以上,方法检出限为0.011～0.045μg/g。按照实验方法测定炭质页岩中的钨、钼、钪,结果的相对标准偏差(RSD,n=11)为0.77%～2.6%,加标回收率在94.0%～107%。能满足炭质页岩中钨、钼和钪含量的测定。     

Mo,W电极在MgCl_2-KCl-NaCl-CaCl_2熔盐中电解镁的钝化行为

应用循环伏安法和计时电流法研究了Mg(Ⅱ)在MgCl2-KCl-NaCl-CaCl2四元熔盐体系中于(Mo、W)阴极上的放电过程及其钝化行为.结果表明,W电极放电反应的可逆性比Mo电极的好.后者的计时电流曲线偏离线性特征,且其阴极钝化比W严重.     

Radiation reduction of Cr, Mo and W isopolymetalates in aqueous system

The radiation-chemical processes in aqueous solutions of dichromates, isopolymolybdates and isopolytungstates have been studied. The radiation reduction of Cr(VI) to Cr(III), Mo(VI) to Mo(V) and W(VI) to W(V) takes place. Molybdenum and tungsten blues are the products of the last two processes in acid solutions. The yields of reduction decrease significantly with the increase of pH. The mechanisms of the processes have been discussed. The photochemical reduction of Mo(VI) and W(VI) for the production of corresponding 5-valent states have been used to the study of their electron scavenging efficiencies. It has been shown that these efficiencies decrease in the order: Mo(V)>W(V)>Cr(VI)>Mo(VI)>W(VI).     

Redox potentials of tungsten and its alloying partners-fundamentals of tungsten determination by redox titration

The fundamentals of tungsten determination by redox titration in hydrochloric acid medium are describe. Conditional redox potentials are given for W, Cr, V, Fe, Ti, Mo, Cu and Sn as a function of HCl concentration. The basic experimental conditions and the difference in conditional potentials required for consecutive titrations are discussed. Any mixture of tungsten with other metals can be analysed without separation if it does not contain both Cr and Ti or both Mo and V.     

Reduction pathway of end-on terminally coordinated dinitrogen. V. N-N bond cleavage in Mo/W hydrazidium complexes with diphosphine coligands. Comparison with triamidoamine systems

N-N cleavage of the dialkylhydrazido complex [W(dppe)2(NNC5H10)] (B(W)) upon treatment with acid, leading to the nitrido/imido complex and piperidine, is investigated experimentally and theoretically. In acetonitrile and at room temperature, B(W) reacts orders of magnitude more rapidly with HNEt3BPh4 than its Mo analogue, [Mo(dppe)2(NNC5H10)] (B(Mo)). A stopped-flow experiment performed for the reaction of B(W) with HNEt3BPh4 in propionitrile at -70 degrees C indicates that protonation of B(W) is completed within the dead time of the stopped-flow apparatus, leading to the primary protonated intermediate B(W)H+. Propionitrile coordination to this species proceeds with a rate constant k(obs(1)) of 1.5 +/- 0.4 s(-1), generating intermediate RCN-B(W)H+ (R = Et) that rapidly adds a further proton at Nbeta and then mediates N-N bond splitting in a slower reaction (k(obs(2)) = 0.35 +/- 0.08 s(-1), 6 equiv of acid). k(obs(1)) and k(obs(2)) are found to be independent of the acid concentration. The experimentally observed reactivities of B(Mo) or B(W) with acids in nitrile solvents are reproduced by DFT calculations. In particular, geometry optimization of models of solvent-coordinated, Nbeta-protonated intermediates is found to lead spontaneously to separation into the nitrido/imido complexes and piperidine/piperidinium, corresponding to activationless heterolytic N-N bond cleavage processes. Moreover, DFT indicates a spontaneous cleavage of nonsolvated B(W) protonated at Nbeta. In the second part of this article, a theoretical analysis of the N-N cleavage reaction in the Mo(III) triamidoamine complex [HIPTN3N]Mo(N2) is presented (HIPTN3N = hexaisopropylterphenyltriamidoamine). To this end, DFT calculations of the Mo(III)N2)triamidoamine complex and its protonated and reduced derivatives are performed. Calculated structural and spectroscopic parameters are compared to available experimental data. N-N cleavage most likely proceeds by one-electron reduction of the Mo(V) hydrazidium intermediate [HIPTN3N]Mo(NNH3)+, which is predicted to have an extremely elongated N-N bond. From an electronic-structure point of view, this reaction is analogous to that of Mo/W hydrazidium complexes with diphos coligands. The general implications of these results with respect to synthetic N2 fixation are discussed.     

Liquid – liquid extraction behavior of V(IV) using phosphinic acids as extractants

The extraction behavior of V(IV) in the presence of Mo(VI), W(VI), U(VI), V(V), Ti(IV), Al(III), Cr(III), Fe(III), Mn(II), Zn(II) and Pb(II) has been studied using two alkylphosphinic acid extractants, Cyanex 272 and 301. The effect of various parameters, such as the nature of diluent, the type of mineral acid and the concentration of the acid, and metal ions has been investigated. The loading and recycling capacity of the extractants has been assessed. Based on the distribution data some binary separations from V(IV) were achieved. Received: 24 October 1996 / Revised: 2 July 1997 / Accepted: 5 July 1997     

Liquid – liquid extraction behavior of V(IV) using phosphinic acids as extractants

The extraction behavior of V(IV) in the presence of Mo(VI), W(VI), U(VI), V(V), Ti(IV), Al(III), Cr(III), Fe(III), Mn(II), Zn(II) and Pb(II) has been studied using two alkylphosphinic acid extractants, Cyanex 272 and 301. The effect of various parameters, such as the nature of diluent, the type of mineral acid and the concentration of the acid, and metal ions has been investigated. The loading and recycling capacity of the extractants has been assessed. Based on the distribution data some binary separations from V(IV) were achieved. Received: 24 October 1996 / Revised: 2 July 1997 / Accepted: 5 July 1997     

Solid-state synthesis of molybdenum and tungsten porphyrins and aerial oxidation of coordinated benzenethiolate to benzenesulfonate

A new route is developed for the synthesis of molybdenum and tungsten porphyrins using [M(NO)(2)py(2)Cl(2)] (M = Mo, W) as the metal source and TPP (dianion of 5,10,15,20-meso-tetraphenylporphyrin) in the benzoic acid melt. Complexes [Mo(V)O(TPP)(OOCPh)] (1) and [W(V)O(TPP)(OOCPh)] (2) are isolated in almost quantitative yield. These are characterized by single-crystal X-ray structure analysis, electron paramagnetic resonance, electronic and IR spectroscopy, and magnetic moment measurements. Benzenethiol substitutes for PhCOO(-) in 1, forming an intermediate thiolato complex that responds to the intramolecular redox reaction across the Mo(V)-SPh bond to yield [Mo(IV)O(TPP)] (3). Under an excess of benzenethiol, PhS(-) is coordinated to the vacant site in 3, which under aerial oxidation is oxidized to benzenesulfonate to form [Mo(V)O(TPP)(O(3)SPh)] (4). 2 undergoes similar aerial oxidation chemistry albeit slowly.     

Investigation of removal of Cr(VI), Mo(VI), W(VI), V(IV), and V(V) oxy-ions from industrial waste-waters by adsorption and electrosorption at high-area carbon cloth

Adsorption and electrosorption of Cr(VI), Mo(VI), W(VI), V(IV), and V(V) ions from water samples at low concentration were studied at high-area C-cloth electrodes. The concentrations of ions in the solution were monitored using in situ UV spectroscopy. All the investigated ions, except V(IV), showed better adsorption in acidic media. Positive polarization of the C-cloth caused increased adsorption of Cr(VI), Mo(VI), and V(V) ions. When previously adsorbed, Mo(VI) and V(V) ions were shown to be largely desorbable by negative polarization of the C-cloth. Since V(IV) does not become adsorbed significantly at the C-cloth in acidic media, the method provides an interesting means for separation of V(V) and V(IV) species in solution.     

Polarographic study of Mo(VI) in 0.1–5 M sulfuric acid solutions

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.     

Separation of the Oxyanions of Re(VII), Mo(VI), Cr(VI), W(VI), and V(V) from a Multicomponent Solution at pH 6 by foam Fractionation

Abstract

An experimental investigation is presented of the foam separation of the oxyanions of Re(VII), Mo(VI), Cr(VI), W(VI), and V(V). The pH 6.0, multicomponent aqueous solutions are 1.0 × 10 ^?6 M in each metal. The effect of chloride competition with the metal oxyanions for the cationic surfactant is determined with NaCl concentrations up to 0.3 M. With proper NaCl concentration adjustments, V(V) can be separated completely from the other four metals, and Re(VII) and Mo(VI) from the other three. Pulsed surfactant dosage is investigated for 1.0 × 10 ^?6 M Mo(VI) solutions at pH 6.0 and 3.1.