Method and apparatus for extracting high-purity molybdenum oxide powders and nanopowders from low-grade concentrates

Abstract

A method and plant for molybdenum recovery from a low-grade crude ore by low-temperature chlorination, where the molybdenum-bearing fine ore is chlorinated with gaseous chlorine at a temperature of 220-250 C. to form a volatile chloride compound, which after leaving a reactor is directed to a low-temperature nitrogen-oxygen plasma unit having a temperature of 800-1000 C., wherein the said compound decomposes and turns into a high-purity MoO.sub.3 powder or nanopowder, which is cooled with an air stream and collected in a dumping hopper. The invention enables recovery of ultra-high purity MoO.sub.3 (purity of 99.997-99.999%) using an environmental friendly, cost effective, and inexpensive method implemented on an industrial scale.

Claims

1. A method of molybdenum recovery from a fine molybdenum-bearing ore by low-temperature chlorination, comprising: chlorination of the fine molybdenum-bearing ore using gaseous chlorine at a temperature of 220-250 C. to form a volatile chloride compound in a reactor; and decomposing the volatile chloride compound in a low-temperature nitrogen-oxygen plasma unit having a temperature between 800 C. and 1000 C. to produce a MoO.sub.3 powder or nanopowder.

2. The method of claim 1, wherein the particle size of the ore is 30-50 m.

3. The method of claim 1, wherein the reactor is blown down with an inert gas to remove air prior to the chlorination.

4. The method of claim 1, wherein the ore is fed into the reactor through a screw in countercurrent to the gaseous chlorine.

5. The method of claim 1, further comprising filtering the volatile chloride compound through a granular material to remove impurities before the decomposing in the plasma unit.

6. The method of claim 1, further comprising trapping particles of the MoO.sub.3 powder or nanopowder in filtration sleeves.

7. The method of claim 1, further comprising: removing nitrogen or oxygen from chlorine exiting the plasma unit; and transferring the chlorine to the reactor for reuse.

8. The method of claim 1, further comprising generating chlorine leaks; and neutralizing the chlorine leaks with alkali in a scrubber.

9. The method of claim 1, further comprising cooling the MoO.sub.3 powder or nanopowder.

10. An apparatus for the method of claim 1, comprising: a reactor for low-temperature chlorination of molybdenum-bearing ore capable of maintaining a temperature in the range of 220-250 C.; and a low-temperature nitrogen-oxygen plasma unit capable of operating at a temperature between 800 C. and 1000 C. for decomposition of chlorinated molybdenum compound generated in the reactor.

11. The apparatus of claim 10, further comprising a filtration unit between the reactor and the plasma unit for removal of impurities from the chlorinated molybdenum compound.

12. The apparatus of claim 11, wherein the filtration unit comprises at least one reservoir with granular reagents installed in a gas duct and designed specifically for trapping each impurity.

13. The apparatus of claim 10, further comprising a scrubber for alkaline neutralization of chlorine leaks.

14. The apparatus of claim 10, further comprising at least one temperature sensor, at least one pressure sensor, at least one raw material or reagent feed sensor, or at least one finished product discharge sensor for automated control of the apparatus.

15. The apparatus of claim 10, further comprising heater for heating gaseous chlorine up to between 50 C. and 60 C. before the gaseous chlorine enters the reactor.

16. The apparatus of claim 10, wherein the reactor is configured to receive an inert gas for preliminary blowdown.

17. The apparatus of claim 10, further comprising a hopper to collect the MoO.sub.3 powder or nanopowder produced in the plasma unit.

18. The apparatus of claim 10, further comprising a chlorine regenerator for separating gaseous chlorine from gaseous impurities for subsequent use in the chlorination reactor.

19. The method of claim 1, wherein the volatile chloride compound is MoO.sub.2Cl.sub.2.

20. The apparatus of claim 10, wherein the chlorinated molybdenum compound generated in the reactor is MoO.sub.2Cl.sub.2.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The drawing is not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. The FIGURE presents a technological workflow of the example plant, which is one embodiment of the invention.

DETAILED DESCRIPTION

(2) An example embodiment of the invented plant schematically illustrated in the FIGURE operates based on the low-temperature chlorination technology (LTC) and designed for the recovery of high-purity molybdenum dioxydichlorides from any low-grade molybdenum dioxide ores (MoO.sub.2), which form a basis for the recovery of high-purity MoO.sub.3 powders and nanopowders, while the plant's capacity makes up at least 250 tons per annum.

(3) In this embodiment, the whole process runs in a gas environment at T=220-250 C. in a closed cycle with no harmful emissions into the atmosphere as almost all used chlorine is recycled, therefore the process is completely environmental friendly.

(4) In this embodiment, the plant consists of the following assemblies:

(5) The continuously operating LTC reactor, which provides chlorination of MoO.sub.2 ore by gaseous chlorine.

(6) A specific nature of chlorination reactions at low temperatures in comparison with standard reactions (700-900 C.) poses certain requirements to the design of the reactor and its operational mode.

(7) The reactor 1 is a cylindrical horizontally mounted chamber made of nickel, Monel, or other material, resistant to such aggressive medium as chlorine at operational temperatures. The feedstock is supplied continuously by portions through a feed-control device, which automatically supplies a set amount of the feedstock to the reactor, depending on the desired output.

(8) A pure-nickel screw rotates in the reactor and mixes the loaded MoO.sub.2 ore to evenly heat powders and avoid agglomeration of powders.

(9) The system is preliminary blown down by argon or gaseous nitrogen at a rate of 300 l/min for air removal from the system, and all plant assemblies are simultaneously heated up to 220-250 C. The heating is provided by panel folding heaters equipped with embedded heating elements made of heat-resistant materials.

(10) External heaters make it possible to easily replace heating elements if necessary without a need to dismantle the reactor's housing.

(11) Gaseous chlorine is supplied to the reactor 1 from a liquid chlorine bulb after passing through a heater/evaporator 11 with a capacity of 50 l, where chlorine is heated to the temperature required for chlorination (approximately 60 C.). Gaseous chlorine is supplied in excess at a preferable rate of 75 l/min for the most complete chlorination process.

(12) The chlorination process is carried out between gaseous reagents and solid feedstock; therefore, its effectiveness depends on the contact area between these phases, i.e. on the fineness degree of the raw material. The feedstock must be finely divided with a particle size of 30-50 m to ensure effectiveness of the process. The fine-dispersed raw material is fed into the reactor in countercurrent to chlorine.

(13) As a result, chlorination of MoO.sub.2 takes place in the reactor 1. A temperature of at least 200 C., preferably 220-250 C., is required for the reaction. In this case the reaction changes molybdenum only to MoO.sub.2Cl.sub.2:
MoO.sub.2(solid)+Cl.sub.2(gas)=MoO.sub.2Cl.sub.2(gas)

(14) This is an exothermic reaction, taking place with minor heat release.

(15) Given the specified temperatures, MoO.sub.2Cl.sub.2 vapors having a sublimation temperature of 157.6 C. are mainly sublimated.

(16) It should be pointed out that some other elements, such as iron, vanadium, etc., presented in the crude ore are also sublimated along with the target molybdenum product. Such raw material components as non-ferrous metals, silicon, etc. do not react at process temperatures and remain in the charge.

(17) The chlorination process is characterized by the following parameters corresponding to the technology implemented by its authors in practice:

(18) operating flow rate of feedstock (MoO.sub.2 powder)30 kg/h;

(19) feedstock fineness <900 m;

(20) molybdenum dioxydichloride recovery rate (MoO.sub.2Cl.sub.2)46 kg/h;

(21) product fineness1-15 m; and

(22) system pressure15-20 mm Hg.

(23) Further, the obtained chlorination product MoO.sub.2Cl.sub.2 is sublimated and enters the gas duct 2, where the gas mixture is purified from contaminating impurities with the sublimate going through filters filled with granules of the corresponding reagents. Every filter is a cylinder made of pure nickel, having one side open and a mesh bottom on the other side. The preferred configuration of the system has three filters sequentially arranged in the gas duct 2 vertically one above the other.

(24) A pure granulated salt NaCl is used to purify the gas mixture from iron impurities and other components. NaCl turns into a non-volatile compound and settles on salt granules when reacting with iron chloride vapors.

(25) Fine copper chips are used to purify the mixture from vanadium impurities. When reacting with the chips, vanadium chloride vapors also turn into a non-volatile compound and settle on the copper chips.

(26) A granular zeolite (such as rhionite) is used for final purification of impurities, which purifies gaseous molybdenum dioxychloride from mechanical impurities and moisture.

(27) Reagents in the filters should be replaced in the course of production, depending on the amount of impurities contained in the feedstock. On average, the replacement takes place once every 15 days of plant operation.

(28) After passing through the filtration system, the gaseous MoO.sub.2Cl.sub.2 purified of all impurities flows through the gas duct to the low-temperature arc plasma unit 3, where MoO.sub.2Cl.sub.2 decomposes in the low-temperature nitrogen-oxygen plasma (800-1500 C.) and turns into high-purity MoO.sub.3 powder or nanopowder. The type of the powder depends on the temperature, mode, and residence time of the gas flow in the plasma unit.

(29) The decomposition process using the low-temperature plasma is characterized by the following parameters:

(30) high-purity MoO.sub.3 powder recovery rate33 kg/h; and

(31) product fineness20 to 30 m, depending on the task, the fineness is regulated in the low-temperature plasma unit by adjusting the residence time of particles in the cooling reactor and the plasma temperature; and

(32) system pressure1 atm or 760 mm Hg.

(33) The obtained high-purity MoO.sub.3 powders or nanopowders are cooled in the reactor 4, which is cooled by cold running water circulating through a cooling circuit. Then, the powder settles in the receiving hopper 5, while smaller unsettled particles are removed with the gas stream and trapped in the filtration sleeves 6 made of heat-resistant material and the cyclone filters 7. Fineness of the MoO.sub.3 powder is regulated by the residence time in the cooling reactor, which is usually in hundredths of a second. The main high-purity MoO.sub.3 powder settles under the action of a centrifugal force initiated by a stream of purified air.

(34) The waste gas mixture containing chlorine derived from the decomposition of molybdenum dioxychloride, as well as nitrogen and oxygen, enters the chlorine regeneration assembly 8, where gaseous chlorine is separated from nitrogen and oxygen and reused in the reactor 1. For safety purposes, the fiberglass scrubber 9 equipped with a pump 10 and containing a solution of NaOH to neutralize chlorine is also provided at the outlet to catch chlorine, which may be released in emergencies or as a result of a breakthrough.

(35) The plant enables recovery of high-purity molybdenum dioxydichlorides MoO.sub.2Cl.sub.2 whose purity may reach 99.997-99.999% that are further used to produce high-purity MoO.sub.3 powders and nanopowders with the same purity of 99.997-99.999% by means of the low-temperature plasma.

(36) The proposed method makes it possible to use basic process equipment (such as chlorination reactor, sublimation filters, and finished product condensers) made of heat-resistant glass or inexpensive grades of stainless steel to realize the process. Power consumption of the plant makes up a maximum of 165 kW/h. The plant requires the area of 300 m.sup.2 at most with a ceiling height of 3.5 m. Due to its small size the equipment does not have any significant requirements to the installation area. Moreover, the plant does not require to be connected to the sewage and water supply system and does not emit harmful substances into the atmosphere as it operates based on a fully closed cycle.

(37) Industrial tests of the equipment were conducted. The product samples were analyzed using the inductively coupled plasma mass spectrometry. Table 1 shows test results involving different samples (LCM1-LCM6).

(38) A plant constructed as an embodiment of the invention enables production of high-purity MoO.sub.3 powders with a capacity of 250 tons per annum and even up to 500 tons per annum, which is an unprecedented result having no analogues in the world.

(39) TABLE-US-00001 TABLE 1 PGSICP- LCM1 LCM2 LCM3 LCM4 LCM5 LCM6 MS Actual/ Actual/ Actual/ Actual/ Actual/ Actual/ Element DL/g/g g/g g/g g/g g/g g/g g/g Al 0.1 3 3 6 0.4 0.3 0.2 As 0.1 0.1 0.1 0.1 0.1 0.1 0.1 B 0.1 0.1 0.1 0.1 1 1 1 Ba 0.5 0.26 0.5 1 0.5 0.7 1 Be 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Bi 0.1 0.1 0.1 0.1 0.1 0.1 0.11 Ca 1 1 1 1 2 1 1 Cd 0.1 3 2 0.1 0.1 0.1 0.1 Co 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Cr 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Cu 0.1 0 0.1 0.1 0.1 0.1 0.1 Fe 1 8 5 10 2.6 1.7 1.9 Ge 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Hf 0.1 0.1 0.1 0.1 0.1 0.1 0.1 K 0.2 1 1 3 0.6 0.4 0.6 Li 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Mg 0.1 0.1 0.1 1 0.7 0.7 0.5 Mn 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Na 1 2 2 7 5 5 5 Nb 0.1 0.1 0.1 0.1 0.2 0.1 0.1 Ni 0.1 0.1 0.1 1 0.6 0.6 0.6 Pb 0.1 1 1 1 0.1 0.1 0.1 Re 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Sn 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Ta 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Ti 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Tl 0.1 0.1 0.1 0.1 0.1 0.1 0.1 V 0.1 0.1 0.1 0.1 0.1 0.1 0.1 W 1 1 1 1 1 1 1 Zn 0.5 4 5 3 0.7 0.6 0.7 Zr 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Total 26 24 37 17 15 16 Purity 0.99997 0.99998 0.99996 0.99998 0.99999 0.99998

(40) These results confirm the ultra-high purity of all samples taken from different lots and having a different mass.

(41) Many embodiments of the invented method have the shortest process flow, which excludes a number of operations associated with the molybdenum recovery and purification. Moreover, the technology doesn't include stages associated with the hydrometallurgy of rare metals. This made it possible to achieve a very low cost of high-purity and ultra-high purity MoO.sub.3 powders and nanopowders, which is several times lower than the cost of methods now being used in the world.

(42) While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.