A process for preparing chlorides by reducing chlorination of rare metal oxides

Abstract

This invention discloses a process for preparing chlorides by reducing chlorination with rare metal oxides, comprising the following steps: S1, in an inert atmosphere, a mixture containing rare metal oxide powder, a reducing agent, and a chloride salt is subjected to a reduction reaction at a predetermined temperature 1; S2, the temperature is lowered to a predetermined temperature 2, oxygen is introduced, and the concentration of oxygen in the mixed gas is adjusted to carry out a chlorination reaction, and the chlorinated product is condensed and collected. This invention eliminates the need for gaseous chlorinating agents such as chlorine or hydrogen chloride, avoiding the leakage risks of liquid chlorine and compressed hydrogen chloride during storage and transportation; the raw materials can be directly rare metal oxides, with a wide range of sources, good process adaptability, and significantly reduced production costs.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and particularly relates to a process for preparing chlorides by reducing chlorination of rare metal oxides. Background Technology

[0002] Rare metals derive their name from their low abundance in the Earth's crust. In particular, rare metals like tungsten, molybdenum, tantalum, and niobium often possess high melting and boiling points and high hardness. However, contrary to the properties of metals, due to their larger atomic radii, rare metals tend to have weaker binding forces with chlorine. Their chlorides are typically molecular crystalline compounds with low melting and boiling points, low hardness, and high valence states of the metallic components. Therefore, these materials are frequently used as fundamental chemical materials in high-end chemical catalysts, CVD metal vapor deposition materials, and high-end plastic additives. They have a wide range of applications and a broad market prospect. Their applications, especially in ultra-high temperature coatings and chip surface vapor deposition (CVD / PVD), are receiving increasing attention, and their application scope is expanding, leading to a gradual increase in demand.

[0003] Conventional chlorination processes typically use rare metal powders as raw materials and chlorine gas as the chlorine source. The synthesis occurs through the combustion reaction of the metal powder in chlorine. Chlorine itself is a hazardous chemical, highly irritating to human skin and respiratory tract. Furthermore, the chlorination process is exothermic, posing inherent safety risks in both the storage and transportation of chlorine and the reaction itself. Moreover, in rare metal beneficiation, many materials exist in the raw ore as oxides or hydroxides. Obtaining metal powder through intensified reduction smelting of these oxides or hydroxides, followed by chlorination, is not only a lengthy process but also inefficient. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a process for the direct reduction chlorination of rare metal oxides to prepare chlorides, thereby reducing safety risks and production costs, and providing a feasible process technology for the efficient extraction of rare metals from such materials.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A process for preparing chlorides by reduction chlorination of rare metal oxides includes the following steps:

[0007] S1. In an inert atmosphere, a mixture containing rare metal oxide powder, reducing agent and chloride salt is subjected to a reduction reaction at a predetermined temperature 1.

[0008] S2. Cool down to the predetermined temperature 2, introduce oxygen, and adjust the concentration of oxygen in the mixed gas to carry out the chlorination reaction. The chlorination product is then condensed and collected.

[0009] The reducing agent is carbonaceous powder;

[0010] The predetermined temperature 1 is 400-800℃, and the predetermined temperature 2 is 350-600℃;

[0011] The concentration of oxygen in the mixed gas is 50% to 80%.

[0012] As a further improvement, the rare metals include tungsten, molybdenum, tantalum, niobium, hafnium, zirconium, or rhenium.

[0013] As a further improvement, the reducing agent includes one or any combination of graphite powder, coke powder, or wood charcoal powder.

[0014] As a further improvement, the reducing agent is added in excess of 1 to 5 times based on the stoichiometric ratio of the reaction.

[0015] As a further improvement, the chloride salt includes one or any combination of sodium chloride, calcium chloride, magnesium chloride, or aluminum chloride.

[0016] As a further improvement, the ratio of the rare metal oxide to the chloride salt is such that the chloride salt is in excess by 10% to 30% based on the stoichiometric ratio of the reaction.

[0017] As a further improvement, the holding time of S1 at the predetermined temperature is 2 to 6 hours.

[0018] As a further improvement, the inert atmosphere is argon or nitrogen or a mixture thereof.

[0019] As a further improvement, the chlorinated product is carried by the airflow into a constant temperature receiver, the temperature of which is 10-50°C.

[0020] This invention aims to achieve direct chlorination of rare metal oxides without chlorine gas, avoiding the safety risks associated with the use of chlorine or hydrogen chloride in traditional production processes. It also eliminates the need for elemental rare metals, thereby reducing the production cost of chlorides. The invention proposes a two-step chlorination method involving the reduction and separation of chloride salts to achieve safe production of rare metal chlorides.

[0021] This invention uses rare metal oxides as raw materials, carbonaceous powder as a reducing agent, and chloride salts such as sodium chloride, calcium chloride, and magnesium chloride as chlorine sources. Through a two-step high-temperature reaction, rare metal oxides are directly chlorinated to chlorides. Taking hafnium oxide as an example, the overall chemical reaction equation is as follows:

[0022] HfO2 + C = Hf + CO2

[0023] Hf + 2MgCl₂ + O₂ = HfCl₄ + 2MgO

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. No gaseous chlorinating agents such as chlorine or hydrogen chloride are required, and the production process avoids the risk of leakage of liquid chlorine and compressed hydrogen chloride during storage and transportation;

[0026] 2. The production process is a double decomposition reaction, the reaction rate is controllable, the reaction does not have obvious exothermic effects, the operation is simple, safe and reliable;

[0027] 3. Rare metal oxides can be used directly as raw materials, which are widely available, have good process adaptability, and significantly reduce production costs. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is the XRD diffraction pattern of the hafnium tetrachloride product from Example 1;

[0030] Figure 2 This is a photograph of the hafnium tetrachloride product from Example 1;

[0031] Figure 3 This is the XRD diffraction pattern of the tungsten hexachloride product from Example 2;

[0032] Figure 4 This is a photograph of the tungsten hexachloride product from Example 2. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] The method for preparing high-purity chloride by reducing chlorination of rare metal oxides according to some specific embodiments of the present invention includes the following steps:

[0037] S1. In an inert atmosphere, a mixture containing rare metal oxide powder, reducing agent, and chloride salt is subjected to a reduction reaction at a predetermined temperature 1.

[0038] In some embodiments, the rare metals include, but are not limited to, tungsten, molybdenum, tantalum, niobium, hafnium, zirconium, and rhenium.

[0039] In some embodiments, the reducing agent includes, but is not limited to, high-purity graphite powder, coke powder, and charcoal powder. In some embodiments, the reducing agent is added in excess of 1 to 5 times based on the stoichiometric ratio of the reaction. An excess of reducing agent can prevent oxygen from oxidizing the rare metals during chlorination, thus helping to improve the chlorination rate.

[0040] In some embodiments, the chloride salt includes, but is not limited to, sodium chloride, calcium chloride, magnesium chloride, aluminum chloride, etc., with magnesium chloride being preferred. The ratio of rare metal oxide to chloride salt is 10% to 30% excess chloride salt based on the stoichiometric ratio of the reaction.

[0041] In some embodiments, a traditional horizontal tube furnace can be used as the reaction equipment, and the reaction device is made of high-purity quartz to ensure product purity.

[0042] In some embodiments, the inert atmosphere may be argon or nitrogen and a mixture thereof.

[0043] In some embodiments, the predetermined temperature 1 is 400–800°C, preferably 500–750°C. If the temperature is too high, the sintering of chloride salts at high temperatures intensifies, which deteriorates the mass transfer of the subsequent chlorination reaction, resulting in a low chlorination rate. Preferably, the holding time at the predetermined temperature 1 is 2–6 hours.

[0044] S2. Cool down to the predetermined temperature 2, introduce oxygen, and adjust the concentration of oxygen in the mixed gas to a certain range to carry out the chlorination reaction. The chlorination product is then condensed and collected.

[0045] During the reaction, the chlorinated product is carried by the gas flow into a collector (preferably a thermostatic collector) for condensation and collection. Unreacted raw materials remain in the tubular furnace, and the tail gas enters the tail gas absorption device. The collected product must be removed in an oxygen-free environment.

[0046] In some embodiments, the predetermined temperature 2 is 350–600°C, preferably 350–550°C. The predetermined temperature 2 is lower than the predetermined temperature 1. If chlorination is performed at excessively high temperatures, oxygen will enter the chloride, forming chlorine oxides and reducing product purity. Furthermore, excessively high temperatures are detrimental to the subsequent condensation and powdering of the chloride product, potentially leading to the formation of chloride sintered lumps. If the temperature is too low, the reaction rate will be too low, and the reaction time too long.

[0047] In some embodiments, the concentration of oxygen in the mixed gas is 50% to 80% (by volume). Excessive oxygen can cause chloride products to form chlorine oxides, reducing product purity.

[0048] In some embodiments, the temperature of the receiver is 10–50°C.

[0049] The present invention provides a chlorine-free direct chlorination process for rare metal oxides, which not only ensures the safety and controllability of the chlorination process, but also directly converts rare metal oxides into chlorides, reducing the steps of smelting oxides into metals and then chlorinating the metal element, thus greatly saving production costs.

[0050] Example 1

[0051] 1000g of hafnium oxide, 285g of high-purity graphite powder (excess ratio 5), and 1176g of analytical grade magnesium chloride (excess 30%) were mixed evenly and dried to constant weight in an oven at 110℃. The dried material was loaded into a quartz boat, which was then placed in a tube furnace. Argon gas was introduced at a flow rate of 0.5L / min, and the reaction temperature was set to 750℃ for 2 hours. The gas flow rate was kept constant, and the furnace was allowed to cool naturally to 550℃. The argon gas flow rate was then reduced to 0.1L / min, and the oxygen flow rate was turned on at 0.4L / min. Simultaneously, the water bath temperature of the collector was set to 10℃ until the reaction was complete. A total of 1480g of hafnium tetrachloride powder was obtained, with a yield of 97%. A very small amount of product adhered to the wall and could not be collected. The remaining product, including residual reactants, totaled 723g. Figure 1 and Figure 2 The images show the XRD diffraction pattern and physical image of the prepared hafnium tetrachloride product. The trace element analysis results for HfCl4 are as follows: the purity of hafnium tetrachloride obtained by the metal impurity removal method is 99.95%.

[0052] Table 1. Trace element analysis of hafnium tetrachloride (ppm)

[0053]

[0054]

[0055] Example 2:

[0056] 1000g of tungsten oxide powder and 155g of high-purity graphite powder (excess ratio 1) were mixed evenly, and then 1579g of analytical grade magnesium chloride (excess 10%) were added. The mixture was dried to constant weight in an oven at 110℃. The dried material was then loaded into a quartz boat, which was placed in a tube furnace. Argon gas was introduced at a flow rate of 0.4L / min, and the reaction temperature was set to 500℃ for 6 hours. The gas flow rate was kept constant, and the furnace was allowed to cool naturally to 350℃. While maintaining the argon gas flow rate, oxygen was introduced at a flow rate of 0.4L / min, and the water bath temperature of the collector was set to 50℃ until the reaction was complete. A total of 1642g of tungsten hexachloride powder was obtained, with a yield of 96%. A very small amount of product adhered to the walls and could not be collected. The remaining product, including residual reactants, totaled 889g. Figure 3 and Figure 4 The images show the XRD diffraction pattern and a photograph of the prepared tungsten hexachloride product. The trace element analysis results for the WCl6 product are as follows:

[0057] Table 2. Trace element analysis of tungsten hexachloride (ppm)

[0058] element content Ca 52.40 Al 0.99 B 1.14 Si 9.00 Bi 12.40 Co 3.42 Cu 0.41 Mo 40.46 Ti 0.10 V 5.25 Cr 10.80 Mn 0.18 Fe 33.96

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A process for the production of chlorides by the reduction chlorination of a rare metal oxide, characterized in that, The method comprises the following steps: S1, under inert atmosphere, a mixture comprising rare metal oxide powder, reducing agent and chloride salt is subjected to reduction reaction at a predetermined temperature 1; S2, the temperature is lowered to a predetermined temperature 2, oxygen is introduced, and the concentration of oxygen in the mixed gas is adjusted, a chlorination reaction is carried out, and the chlorination product is condensed and collected; The reducing agent is carbonaceous powder; The predetermined temperature 1 is 400-800 ℃, and the predetermined temperature 2 is 350-600 ℃; The concentration of oxygen in the mixed gas is 50%-80%.

2. Process for the preparation of chlorides by reduction chlorination of a rare metal oxide according to claim 1, characterized in that, The rare metal comprises tungsten, molybdenum, tantalum, niobium, hafnium, zirconium or rhenium.

3. The process for the production of chlorides by the reduction chlorination of a noble metal oxide according to claim 1, characterized in that, The reducing agent comprises one or any combination of graphite powder, coke powder or wood carbon powder.

4. Process for the production of chlorides by reduction chlorination of a rare metal oxide according to claim 3, characterized in that, The adding proportion of the reducing agent is 1-5 times more than the stoichiometric ratio.

5. Process for the preparation of chlorides by reduction chlorination of a rare metal oxide according to any one of claims 1 to 4, characterized in that, The chloride salt comprises one or any combination of sodium chloride, calcium chloride, magnesium chloride or aluminum chloride.

6. Process for the production of chlorides by reduction chlorination of a rare metal oxide according to claim 5, characterized in that, The ratio of the rare metal oxide to the chloride salt is that the chloride salt is 10%-30% more than the stoichiometric ratio.

7. Process for the preparation of chlorides by reduction chlorination of a precious metal oxide according to any one of claims 1 to 4, characterized in that, The holding time of S1 at the predetermined temperature 1 is 2-6 hours.

8. Process for the preparation of chlorides by reduction chlorination of a precious metal oxide according to any one of claims 1 to 4, characterized in that, The inert atmosphere is argon or nitrogen or a mixture thereof.

9. Process for the preparation of chlorides by reduction chlorination of a precious metal oxide according to any one of claims 1 to 4, characterized in that, The chlorination product enters a constant-temperature collector with gas flow, and the constant-temperature temperature of the collector is 10-50 ℃.

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