Reduction Of Molybdate Research Articles

On the aluminothermic reduction of calcium vanadate

In the aluminothermic reduction of m e t a l oxide, calcium oxide is often used as a flux. The calcium oxide instead of forming an extraneous addition can sometimes be present in chemical combination with the m e t a l oxide. A familiar example is the aluminothermic reduction of calcium tungstate for the production of ferrotungsten. It has been stated1 that good coalescence of ferrotungsten is probably due to calcium oxide being an integral part of the tungsten resource, thus being made available essentially on a molecular basis for combining with alumina reaction product and quickly forming a fluid s lag . This can be considered to be a favorable state of affairs in the aluminothermic reduction of metal oxide as tied up with calcium oxide. In this context, reference can also be drawn t o the aluminothermic reduction of calcium molybdate for the production of ferromolybdehum and of molybdenum reported previously from this laboratory.~'3 This communication is an account of the efforts made for the preparation of vanadium and of ferrovanadium from calcium vanadates. The literature has made reference to the precipitation of calcium vanadate from vanadium bearing aqueous solution.4-7 T h e r e is however no information available on any technical use that has been developed for calcium vanadate. Aluminothermic reduction of vanadium pentoxide for the production of ferrovanadium or of vanadium in the industrial practice is known to be c a r r i e d out in presence of lime serving as a flux. This points towards the possibility for calcium vanadate as an alternative starting material for the aluminothermic reduction. For use in the present investigation the calcium vanadates were prepared in the laboratory. The compounds corresponding t o 2 CaO.V205 and to 4 CaO.V2Os were precipitated from alkaline sodium vanadate colution by treatments with CaC12 and lime respectively essentially in accordance with published work.7 The precipitated vanadium salts were dried, calcined at 1123 K and ground predominantly to -100 m e s h . The 2 CaO.V~Os and the 4 CaO.V2Os compounds, as made ready for use, analyzed 59.18 pct VaO5 and 44 pct V2Os respectively. Aluminum powder (grade ' C ' , 1 2 0 mesh) as received from M/s Indian Aluminium Co. was used as the reductant. The proc e d u r e for carrying out the aluminothermic r e d u c tions in refractory lined open vessels was essentially

ChemInform Abstract: ELECTROCHEMICAL REDUCTION OF MOLYBDATE IN THE PRESENCE OF ZINC CHLORIDE IN MOLTEN LITHIUM CHLORIDE‐POTASSIUM CHLORIDE EUTECTIC

AbstractBei der elektrochemischen Reduktion von Molybdat in Gegenwart von ZnCl2 in eutektischer LiCl/KCl‐ Schmelze (450°C) werden 2 chronopotentiometrische Stufen mit Viertelstufenpoten‐ tialen von ‐1,5 und ‐1 ,75 V gegen eine Pt(II)/Pt‐Bezugselektrode beobachtet.

Electrochemical Reduction of Molybdate in the Presence of Zinc Chloride in Molten Lithium Chloride‐Potassium Chloride Eutectic

Two chronopotentiometric waves were observed for the electrochemical reduction of molybdate in the presence of zinc chloride, with quarter‐wave potentials of −1.5V and −1.75V vs. the Pt(II)/Pt reference electrode, respectively. It was observed that an increase in the molybdate concentration causes a decrease of the first transition time indicating a chemical reaction between (which is reduced at −1.5V) and in the melt forming which is sparingly dissociated in eutectic. The equilibrium constant for the observed reaction was calculated. X‐ray powder diffraction patterns of the reduction product of have been obtained.

Oxidation of propene in the absence of gaseous oxygen: II. Bismuth molybdates and iron antimonates

Propene oxidation in the absence of gaseous oxygen has been studied on unsupported bismuth molybdate with atomic ratio Mo Bi = 2.66 , and on unsupported iron antimonates prepared according to various procedures. The study was carried out in a flow reactor: the distribution of the products and the oxygen consumption were followed. The experimental conditions were: temperature, 450–550 °C; C 3H 6 WHSV, 0.1–0.2 hr −1; and C 3H 6 partial pressure, 108 mbar. On bismuth molybdate and iron antimonate with ratio Sb Fe = 2 the main oxidation product was acrolein, whereas for Sb Fe = 1 deep oxidation products were obtained. The structural modifications occurring during the reduction of bismuth molybdate are pointed out and the structure of the intermediate phase was elucidated. The chemical composition of this intermediate is close to 2Bi 2O 3 · MoO 3 and the structure is monoclinic pseudo-tetragonal ( a = b = 5.58 A ̊ ; c = 11.62 A ̊ ; γ = 89.00 ° ). The different behavior of iron-antimony catalysts obtained varying the chemical composition and the thermal treatment of the samples supports the hypothesis that the two phases of the catalyst, FeSbO 4 and Sb 2O 4, cooperate in producing acrolein with a higher selectivity than on each phase alone. A mechanism has been proposed to explain the phenomenon.

ChemInform Abstract: ELECTROCHEMICAL REDUCTION OF MOLYBDENUM(VI) COMPOUNDS IN MOLTEN LITHIUM CHLORIDE‐POTASSIUM CHLORIDE EUTECTIC

AbstractMoO3 reagiert mit dem geschmolzenen LiCl‐KCl‐Eutektikum bei 450°C zu MoOgClg, das in der Schmelze wahrscheinlich als MoOzClä′ und MozOä′ vorliegt.

Electrochemical Reduction of Molybdenum(VI) Compounds in Molten Lithium Chloride‐Potassium Chloride Eutectic

Molybdenum (VI) oxide reacts with molten eutectic at 450° to form , which probably is present as an anion , and pyromolybdate, . Both of these species are electrochemically reduced to , which can be reoxidized to by current reversal. A second reduction step, observed whether or is added to the melt, can be attributed to the reduction of , formed as a secondary reaction product in the first step. The reduction of molybdate proceeds in two steps, the first at −0.85V and the second at −1.75V vs. the 1M Pt(II)/Pt reference electrode. The first step shows an abnormally short transition time, attributable to a slow equilibrium. The second step corresponds to a diffusion‐controlled reduction with , yielding a product of the empirical formula .

Molybdenum metal by the aluminothermic reduction of calcium molybdate

This investigation deals with a process for extracting molybdenum metal in well consoli-dated form and in good yield from calcium molybdate, by open aluminothermic reduction. Aluminothermic molybdenum has been further processed both by electron-beam melting and by molten salt electrorefining for the removal of aluminum. The final metal compares very favorably with commercial molybdenum obtainable by other routes.

Extraction-Polarograpy Applied to the Microdetermination of Phosphate

Phosphate ion can be polarographically determined by adding a known amount of molybdate and measuring the diffusion current due to the reduction of the excess molybdate. This method, however, is disadvantageous to the spectrophotometric one, because the polarographic procedure is less sensitive and interfered by several other constituents. In the present study a new method is developed in which the phosphate ion is extracted as phosphomolybdate into methyl isobutyl ketone and to the organic extract is added aqueous electrolyte solution and methylcellosolve, resulting in a homogeneous solution, in which the hexavalent molybdenum shows prominent and well-defined a.c.polarographic peaks. Fujinaga and others, employed a ternary mixture of chloroform-hydrochloric acidmethylcellosolve system as a polarographic . electrolyte-solvent and succeeded elegantly in the microdetermination of lead by means of diethyldithiocarbamate extraction. In the present study the Takeuchi-Ishii method for the phosphomolybdate extraction into methyl isobutyl ketone was utilized and the polarographic behavior of molybdate ion in the ternary electrolyte-solvent composed of methyl isobutyl ketone, methylcellosolve and an aqueous solution of various electrolytes is investigated. The a.c. polarographic method by Breyer has shown in this case an excellent result. Thus, about hundred microgram quantity of phosphate can easily be determined a.c. polarographically after the phosphomolybdate extraction.

Comparison of Several Methods of Determining Inorganic Phosphate in Sea Water

Five methods of estimating dissolved inorganic phosphate in sea water are compared. Membrane-filtered inshore water from the Menai Straits was used in the study.Wooster and Rakestraw's method gave higher results than Harvey's procedure. This was caused by some unidentified factor resulting in a non-sensitized reduction of molybdate in the former method.

Thiocyanate Complexation of Molybdenum in Solutions of Reduced Molybdate

A frequently used method for the determination of trace amounts of molybdenum utilizes the ability of this element in one of its oxidation states to form an intensely colored complex, or complexes, with thiocyanate. This method requires the reaction of an acid solution of molybdate with a suitable reducing agent, such as stannous tin, then the addition of alkali thiocyanate to develop a characteristic red color. Since the aqueous mixture of thiocyanate, reducing agent, and reduced molybdate is not in a state of equilibrium under optimum conditions for the development of maximum color, it is necessary, for analytical purposes, to stabilize the system by the addition of a homogeneous organic solvent, such as acetone, or to extract the thiocyanate-complexed molybdenum into an immiscible solvent, such as diethyl ether. It is the purpose of this investigation to establish, unequivocally, the oxidation state of molybdenum in the thiocyanate complex, or complexes, so formed, and to evaluate the molybdenum to thiocyanate ratio for the predominating colored specie. Suitable experimental conditions for the spectrophotometric determination of molybdenum with thiocyanate have been developed recently by Crouthamel and Johnson (2). The mechanism which was suggested for the reduction of molybdate by stannous tin is as follows: Mo(VI) + Sn(II) --+ Mo(IV) + Sn(IV) 2 Mo(IV) --+ Mo(V) + Mo(III). From a comparison of the absorption spectrum of the molybdenum thiocyanate complex formed when using copper(I), a one-electron reducing agent, with that using tin(II), it was concluded that the oxidation state of molybdenum in its red thiocyanate complex is plus five. This conclusion is in agreement with the findings of other investigators (1, 3).

The Effect of Hydrochloric Acid Concentration on the Reduction of Molybdate in the Silver Reductor

The Effect of Hydrochloric Acid Concentration on the Reduction of Molybdate in the Silver Reductor