RU2354726C1 - Method of receiving molybdenum dioxide - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes reduction of molybdenum trioxide carbon monoxidom during heating. Before reduction initial molybdenum trioxide is molten at temperature 820-850°C, it is transferred into the gaseous state. Reduction is implemented in recovery reactor by carbon monoxide (CO) with heating up to the temperature higher 1200°C with molar correlation1:2÷3 of molybdenum trioxide in the mixture with carbon monoxide (CO) and with following sedimentation of molybdenum dioxide without the access of air in close volume.

EFFECT: low activity and productivity improvement of the process.

2 cl, 1 dwg, 1 ex

Description

The invention relates to the metallurgy of refractory rare metals, in particular to a method for producing molybdenum dioxide.

There is a method in which molybdenum dioxide is deposited from a solution of sodium molybdate by reduction with hydrogen under pressure [Z.M. Lapina, A.N. Zelikman. Precipitation of molybdenum dioxide from sodium molybdate solutions by reduction with hydrogen under pressure. Izv. Universities, Tsv. Metallurgy, 1959, N 3, p. 93-98]. The method is as follows. A solution of sodium molybdate containing 5-40 g / l of molybdenum at pH 2.0 is poured into an autoclave, heated to 200 ° C, hydrogen is supplied. The process is carried out at a partial pressure of hydrogen of 60 atm (P _total = 80 atm). To accelerate the process, metal molybdenum is supplied in an amount of 7% of the stoichiometrically necessary for the complete reduction of molybdate ions to dioxide. MoO ₂ particles resulting from this reaction serve as crystallization centers; a large, well-filtered precipitate containing up to 74.6% molybdenum falls out of solution.

The disadvantages of the method include the need to work with hydrogen at high pressure and temperature, which requires special quality of the material from which the equipment is made, the need to use expensive metal molybdenum.

The method of deposition of molybdenum dioxide from a solution of sodium molybdate with metallic molybdenum [S.I. Sobol, V.I. Spiridonova, I.M. The processing technology of sulfide molybdenum feedstock using oxidative autoclave leaching] is carried out at a temperature of 200 ° C during mixing of the initial solution, the pH of which is 2.5-3.0, with molybdenum powder taken in the amount stoichiometrically necessary for the complete recovery of molybdate ions to dioxide. Precipitation takes 1-1.5 hours. Part of the dioxide powder (35%) is reduced by hydrogen at 850–900 ° С to molybdenum, which returns to the process.

The disadvantages include the need to restore part of the dioxide to metal, which makes the process more expensive and complicates, since it requires additional equipment to prevent secondary oxidation of the metal.

As a prototype of the selected method of producing molybdenum dioxide by reducing molybdenum trioxide with hydrogen [A.N. Zelikman, B.G. Korshunov. Metallurgy of rare metals. M., Metallurgy, 1991, 432 pp.]. The process is as follows. In multi-tube horizontal furnaces in boats made of NIMO alloy or in a furnace with an inclined rotating tube, MoO _{3 is} reduced to hydrogen to MoO ₂ with a gradual increase in temperature from 400-450 to 650 ° C.

The disadvantages of the method are the high activity of the powder, which leads to its secondary oxidation during long-term storage, the low productivity of the unit due to the fact that the process is slow at the temperatures used for reducing firing.

The technical result of the invention is to obtain a molybdenum dioxide powder having low activity, increasing productivity.

The specified technical result is achieved by the fact that in the method of producing molybdenum dioxide from trioxide, including reducing it with gas by heating, according to the invention, before restoration, the initial molybdenum trioxide is melted at a temperature of 820-850 ° C, it is transferred to a gaseous state, and the reduction is carried out in a reactor reduction with carbon monoxide (CO) when heated to a temperature above 1200 ° C with a molar ratio of molybdenum trioxide and carbon monoxide (CO) 1: 2 ÷ 3 and subsequent precipitation of molybdenum dioxide without additional stupid air in a closed volume.

In this case, the exhaust gases are regenerated and heated to a temperature above 1200 ° C.

The drawing shows a diagram of units that implement the proposed method.

The method is as follows. Molybdenum trioxide from the hopper 1 enters the melting furnace 2, where it melts at a temperature of 820-850 ° C. At temperatures below 820 ° C, supercooling of the melt and its partial crystallization are possible. At temperatures above 850 ° C, intensive evaporation of molybdenum trioxide (MoO ₃ ) begins, which requires additional costs for its capture. Using a siphon, the melt is fed to the evaporator 3, where it evaporates at the boiling point (1150 ° C). The evaporation rate is controlled by the intensity of heat supply so that the overpressure of the gas in the reactor is 0.1-0.3 atm. At an excess pressure below 0.1 atm, the gas flow rate to the reduction reactor 4 will be low, which reduces productivity. At an overpressure of more than 0.3 atm, the gas flow rate will be high, which will lead to underreduction of the trioxide, as well as extrusion of the melt from the heating zone. Molybdenum trioxide converted to a gaseous state is fed to reduction reactor 4, where at temperatures above 1200 ° C it is reduced by carbon monoxide (CO) coming from gas generator 6. At a lower temperature of reactor 4, condensation of molybdenum oxides on its walls and formation of accretions are possible . The ratio of MoO ₃ : CO fed to the reactor 4 is 1: 2 ÷ 3 mol: mol. If the supplied amount of CO is below the lower limit, then due to the low recovery rate, part of the molybdenum in the product will be in the form of molybdenum trioxide, if higher than the upper, then part of the molybdenum dioxide can be reduced to metal. The resulting molybdenum dioxide is deposited on the filters 5, and the exhaust gas enters the gas generator 6, where it is heated to a temperature of 1200 ° C and regeneration of CO ₂ to CO due to coal conversion. Hot CO is fed to the reduction reactor 4.

Example

A quartz reactor 900 mm long, 50 mm in diameter, 2/3 filled with 2-4 mm quartz chips, was placed in a coal resistance furnace (Tamman furnace). A crucible with molybdenum trioxide (50 grams of MoO ₃ ) was fixed in the upper part of the reactor. The crucible is a closed quartz cylinder, from which a tube for the removal of gaseous molybdenum trioxide is withdrawn, the open end of which is located above the quartz layer. The reactor was purged with argon and heated at a rate of 50 ° / min. When the temperature in the center of the furnace reached 900 ° C, and the temperature in the zone of the crucible with molybdenum trioxide was 820 ° C, CO was fed into the reactor at a rate of 0.5 l / min. Reducing gas was supplied to the upper part of the reactor and removed from the bottom. The furnace was heated to a temperature above 1200 ° C (in the center). Under these conditions, exposure was carried out for 30 minutes. The reactor was cooled with a furnace in a neutral atmosphere. After cooling, the quartz chips were washed from molybdenum dioxide in ethanol (to exclude the possibility of secondary oxidation). The resulting suspension was filtered and dried at a temperature of 80 ° C. The resulting product contained 99% MoO ₂ with a yield of 97%.

Thus, the proposed method allows efficiently with high performance to obtain pure molybdenum dioxide. The material is suitable for use in various industries, for example, the manufacture of elements of electronic devices.

Claims (2)

1. A method of producing molybdenum dioxide from molybdenum trioxide, including reducing it with gas during heating, characterized in that before the reduction, the initial molybdenum trioxide is melted at a temperature of 820-850 ° C, it is transferred to a gaseous state and reduction is carried out in a carbon monoxide reduction reactor (СО ) when heated to a temperature above 1200 ° C with a molar ratio of 1: 2 ÷ 3 molybdenum trioxide mixed with carbon monoxide (CO) and subsequent precipitation of molybdenum dioxide without air in a closed volume. 2. The method according to claim 1, characterized in that the exhaust gases during the deposition of molybdenum dioxide are subjected to regeneration and heating to 1200 ° C.