Molybdic Oxide Research Articles

Determination of optimal conditions for pressure oxidative leaching of Sarcheshmeh Molybdenite concentrate using Taguchi method

The present research work is based on finding the optimum conditions for pressure oxidative leaching of the molybdenite concentrate to produce technical-grade molybdic oxide (MoO3) with high recovery through further treatment of the filtrate solution. The Taguchi method was used to design and minimize the number of experiments. By using Taguchi orthogonal (L25) array, five parameters (time, temperature, oxygen pressure, pulp density and acid concentration) at five levels were selected for 25 experiments. The experiments were designed and carried out in a high-pressure reactor in the presence of nitric acid as solvent and oxidizing agent for the molybdenite concentrate and its ReS2 content. The optimum conditions for pressure leaching of molybdenite were obtained through using Signal to Noise analysis and modified by using Minitab software prediction tool. Furthermore, the optimum condition for an economical pressure leaching of rhenium sulfide (ReS2) was achieved with the same process. Analysis of variance (ANOVA) showed that the pulp density is of paramount importance in this process.

Kinetics of pressure oxidative leaching of molybdenite concentrate by nitric acid

The current study was carried out to investigate the kinetics of reactions for the pressure oxidative leaching of a molybdenite concentrate in less than one hour. The effects of oxygen pressure, stirring speed, pulp density, acid concentration and temperature on the leaching rate of the molybdenum were studied. It was found that about 85% of molybdenite was oxidized to molybdic oxide precipitate with remaining molybdenum dissolved in the leaching liquor. Analysis of experimental data showed that the reaction is chemically controlled with activation energy of 68.8 kJ/mol. Furthermore SEM images showed no significant boundary diffusion layer and it was noted that the molybdic oxide precipitates were of fibrous shape.

Molybdenite alkali fusion and leaching: reactions and mechanism

The production of MoO3 from Sarcheshmeh molybdenite concentrate via a pyro-hydrometallurgical process was studied. The molybdenite concentrate and sodium carbonate were premixed and fused under air atmosphere. Then the fused products were leached in water and the dissolved molybdenum was recovered as ammonium molybdate. The ammonium molybdate was then calcined to produce molybdic oxide. At the fusion stage, the effect of the mass ratio of carbonate to sulfide on the reaction products and the solubility of the products was investigated. The results show that during the fusion, sodium molybdate and sodium sulfate are the final reaction products and sodium sulfide is detected as an intermediate reaction product. By melting at 850°C with 5wt% excess carbonate, the maximum solubility of the products is obtained. The molybdenum is recovered from the solutions as ammonium molybdate.

Using metal/organic junction engineering to prepare an efficient organic base-modulation triode and its inverter

In this study, we investigated the influence of a buffer layer of molybdic oxide (MoO 3) at the metal/organic junction on the behavior of organic base-modulation triodes. The performance of devices featuring MoO 3/Al as the emitter electrode was enhanced relative to that of corresponding devices with Au and Ag, presumably because of the reduced in the contact barrier and the prevention of metal diffusion into the organic layer. The device exhibited an output current of −16.1 μA at V B = −5 V and a current ON/OFF ratio of 10 3. Using this architecture, we constructed resistance–load inverters that exhibited a calculated gain of 6.

Utilization of mill scale and recycled MoO 3 from spent acid for economic synthesis of nanocrystalline intermetallic Fe–Mo alloys

This paper deals with an economic and clean route for the synthesis of ferro-alloys through utilization of waste materials (mill scale and spent acid). The molybdic oxide, MoO 3 is successfully synthesized from the spent acid by ammonia gas neutralization method. MoO 3/mill scale powder mixture was isothermally reduced in pure hydrogen at 700–1100 °C. Based on thermogravimetric analysis, the reduction behavior of the synthesized Fe–Mo alloy and the kinetics reaction mechanism were studied. The initial oxides powder and the various reduction products were characterized by XRD and SEM to reveal the effect of hydrogen reduction on composition, microstructure and reaction kinetics of synthesized ferro-alloys. The activation energy values were calculated using the Arrhenius equation. The approved mathematical formulations for the gas–solid reaction were applied to confirm the estimated rate controlling reaction mechanism. Complete reduction of mixed oxides powder was achieved with synthesis of nanocrystalline Fe–Mo alloys.

Recovery of Molybdenum from Spent Acid by Ammonia Gas Neutralization

The present work reports the commercialization of a recycling process of spent acid to recover molybdenum. The process consists of ammonia gas neutralization of spent acid containing molybdenum, crystallization and filtration of ammonium molybdate, roasting and hydrogen reduction of molybdic oxide to produce a commercial grade molybdenum metal powder. The mother liquor, highly nitrogeneous residual solution after the filtration of ammonium molybdate, can be utilized to produce chemical fertilizers.

Studies on Processing of Low Grade Indian Molybdenum Sulphide Concentrate

In India, a low grade molybdenum sulphide concentrate containing 25–30% molybdenum is recovered as a by-product of uranium operations at Jaduguda. This concentrate contains a high association of copper and nickel. If it is processed by the conventional route, both copper and nickel would decrease molybdenum recovery. Such concentrates need a different processing route. Various processes such as soda ash roasting, lime roasting, oxychlorination, and electro-oxidation have been studied. The processes aimed at converting molybdenum into a soluble form, then purified by chemical processing as well as by carbon adsorption-desorption route to yield pure molybdic oxide. The oxide was then reduced to metal with hydrogen. In an alternate scheme, molybdenum values in solution have been converted into molybdenum intermediates such as calcium molybdate/ferrimolybdate. This paper presents the result of these investigations.

Recovery of molybdenum from spent acid of lamp making industries

The paper reports studies on recovery of molybdic oxide from the molybdenum containing spent acid generated in lamp manufacturing industries. It first gives an account of the efforts made to modify the direct ammonia neutralisation process. Next a new process is described involving adsorption of molybdenum from spent acid on activated carbon and its subsequent desorption with ammonia. Ammonium molybdate crystals are recovered from the eluted liquor by a crystallization/acidification technique. The influence of acidity, molybdenum concentration, amount of carbon, contact time and amount of ammonia as eluant on the process of molybdenum recovery has been studied. A process flowsheet characterised by a large saving in ammonia consumption is presented.

Computer simulation of a molybdenite leaching process using dilute nitric acid

A computer model has been developed to simulate the major part of a proposed hydrometallurgical process for the leaching of molybdenite concentrates. The leaching is achieved with dilute nitric acid (1–6 M) under conditions that permit precipitation of high-purity MoO 3 · 1 2 H 2O from filtered leach solutions. Because the leaching rate is low under these conditions, unleached molybdenite is recycled in a circulating load, after regrinding and reflotation. The leach takes place in several cocurrent stages at a pulp density enhanced by the circulating load, and overall recovery of the order of 98% is predicted, based on losses in the reflotation step rather than on poor extraction in the leach. The computer model is based on a set of material balances and incorporates data obtained from batch leaching and grinding tests to characterize the major kinetic phenomena. Input variables include: (a) nitric acid flow rates, (b) leach-solution strength, (c) solids input rate, (d) leach tank volumes, (e) number of cocurrent leaching stages and (f) degree of bypass of recycle solids around reflotation. The primary output variable is the ratio of recycle to new solids in the feed, and the model also predicts the value of strategic variables such as overall recovery and daily production rate of purified molybdic oxide.

Catalytic anisotropy of MoO 3 in oxidation reactions in the light of bond-strength model of active sites

Catalytic anisotropy of molybdic oxide in oxidation of propylene has been observed by Volta et al. (7th Int. Congr. Catal. Commun. C4, Tokyo, 1980; Faraday Disc. 72/13, Selectivity in Heterogeneous Catalysis, Nottingham, 1981). High selectivity to acrolein in the indicated reaction was ascribed to the (100) plane while the (010) plane was found to yield CO 2. The critical discussion of Volta's experimental data, performed in this paper, has shown that they may be interpreted in three alternative ways, differing in the ascription of the reaction products to the crystallographic planes. Different crystallographic planes exposed by the grains of MoO 3 have been analyzed in terms of the bond-strength model of active sites (Ziółkowski, J. Catal., submitted) developed under the following main assumptions: (i) the reaction path depends on the number and configuration of the active oxygen atoms in the vicinity of the adsorption site, and (ii) the individual catalytic activity of a given surface oxygen atom is proportional to the reciprocal sum of the strength of the bonds to it from the adjacent cations. The analysis provided the arguments to indicate the most probable reaction pattern. According to it the main products expected to be formed in oxidation of propylene on different planes of MoO 3 are (100), CO, CO 2; (001), acrolein (acrylic acid, C 2O, CO, CO 2 mainly at longer contact time); (101) and (101), acrolein; (010), inactive (possible minor yield of hexadiene and benzene).

Nitric acid leaching of molybdenite concentrates

Molybdenite (MoS 2) has been found to leach slowly in dilute (1–4 M) nitric acid at room temperature, to yield solutions of molybdic acid (H 2MoO 4) and sulphuric acid. The solutions are supersaturated with respect to MoO 3 β 1 2 H 2O , which is easily precipitated from the filtered pregnant solution as a fibrous crystalline solid having the consistency of paper pulp. A complete process, which is based on removal of sulphate as gypsum (CaSO 4 • 2H 2O) by limestone addition, and regeneration of most of the required nitric acid from gaseous nitric oxide produced during the leach, has been proposed. The process is potentially economic if relatively pure molybdic oxide has a value moderately higher than roasted calcines. This paper describes the process steps, as they performed in bench scale tests.

Determination of lead by the precipitation of lead molybdate from a homogeneous solution by the diffusion method

A satisfactory quantitative method for the determination of lead as lead molybdate by precipitation from a homogeneous solution has been developed. The method employs the diffusion of ammonia into a solution containing lead and sodium molybdate in nitric acid medium. The precipitation of lead in the range of 28·0–280·0 mg is complete within 8–9 hours. Anions like sulphate, arsenate, phosphate, tungstate and chromate in moderate concentrations and cations such as Zn (II), Cu (II), Ni (II), Co (II), Mn (II), Cd (II), Hg (II), Ag (I), Ti (IV), As (V), Mg (II) and Al (III) do not contaminate the precipitate. The precipitate gets constant weight at 120°. This eliminated the ignition of the precipitate,i.e., the contamination of molybdic oxide by the precipitate was reduced.

Electrolytic recovery of molybdenum from molybdic oxide and molybenum sesquisulfide

An electrolytic process for molybdenum extraction in a KCl−K3MoCl4 electrolyte (containing approximately 7.5 wt pct molybdenum) was investigated using three types of anode feed —namely, molybdic oxide-graphite, molybdenum sesquisulfide-graphite, and molybdenum sesquisulfide without graphite. In the case of molybdic oxide-graphite anode, a maximum current efficiency of 99 pct was achieved at an operating voltage of 0.35V, a cathode current density of 5000 A/m2 (450 A/f2) and a bath temperature of 1223 K. Electrolysis with molybdenum sesquisulfide-graphite, at an operating voltage of 1.2V, a cathode current density of 13,900 A/m2 (1250 A/f2) and a bath temperature of 1173 K, yielded a maximum current efficiency of 84 pct. Electrolysis of molybdenum sesquisulfide without graphite incorporation, yielded under almost similar conditions, a maximum current efficiency of 87 pct. Extended electrolysis was carried out using molybdic oxide-graphite and molybdenum sesquisulfide cell charges and yielded metal with purity over 99.9 pct.

Precipitation of lead as lead molybdate from homogeneous solution

Lead molybdate can be precipitated in a granular form from a homogeneous solution by taking advantage of the long induction period for the formation of the precipitate in strong acid solution. The rate of precipitation is probably controlled by the rate at which the polymolybdate species depolymerize to yield simple molybdate ions. Although the bulk (90%) of the precipitate forms at pH ca. 1.0, quantitative recovery requires final adjustment of the pH of the digested solution, either homogeneously (urea hydrolysis) or heterogeneously (dropwise addition of ammonia), to pH 3.0. Contamination by molybdic oxide occurs but both methods yield reliable results if the excess of molybdate is limited to 5% and the precipitate is ignited to 725°. Contamination by copper and cadmium was also studied.

The Lubricating Performance of an“in Situ”Process MoS2Film in Air and in Liquids

The performance of a synthetic MoS2 film, produced by electrodeposition of molybdic oxide followed by a temperature-pressure H2S conversion to a molybdenum sulfide compound, is examined under extreme pressure conditions immersed in various fluids. Friction wear and EP characteristics, measured on various test machines, are compared to those of the fluids alone and also to conventional bonded films. The fluids examined include: mineral oil, jet fuel, hydraulic fluid, silicone fluid. The dry films include: burnished MoS2 powder, MIL-L-8937 resin bonded film, MIL-L-8129 silicate bonded film and the synthetic “in situ” MoS2 film. The performance of the synthetic MoS2 film on titanium and stainless steel is also examined. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

AMAX starts up plant to recover molybdic oxide

AMAX starts up plant to recover molybdic oxide

Identification of tungstic and molybdic “acids” by X-ray powder diffraction

Standard X-ray powder diffraction data are presented for the tungstic and molybdic oxide hydrates, and for water-insoluble polysalts often confused with the hydrates.

Hydrogen reduction of molybdic oxide

Hydrogen reduction of molybdic oxide

The state of molybdenum (VI) in perchloric acid solutions

Solubility measurements of molybdic oxide and of the molybdic oxide hydrates were made to determine the nature of the ionic species formed in 0–6 N perchloric acid solutions. Both hydrates produce the same molybdic acid in water and the same monovalent cation in 0·1-1·0 N perchloric acid. Each hydrate forms its own unique molybdic acid in perchloric acid more concentrated than 2 N. Solubility equilibrium was not observed for molybdic oxide which produced different ions than the hydrates.

Solubility of Molybdic Oxide and Its Hydrates in Nitric Acid, Nitric Acid-Ferric Nitrate, and Nitric Acid-Uranyl Nitrate Solutions.

Solubilities of hydrous molybdic oxide in HNO/sub 3/ at 26 deg C and of the dihydrate and white monohydrate in H/sub 2/0, HNO/sub 3/, and HNO/sub 3/- Fe(NO/sub 3/)/sub 3/ solutions between 26 and 55 deg C were determined. Solubilities at 26 deg C in solutions containing uranyl nitrate were also obtained. (M.C.G.)