Preparation method of superfine tungsten powder and high-purity cadmium

Abstract

The invention relates to the technical field of material preparation, and particularly discloses a preparation method of superfine tungsten powder and high-purity cadmium, which comprises the following steps: contacting a crude cadmium salt solution with a sodium hydroxide solution, and carrying out precipitation reaction under the condition that the pH value is greater than 13 to obtain a cadmium hydroxide precipitate and an alkaline leaching solution; dissolving the cadmium hydroxide precipitate in inorganic acid to obtain refined cadmium salt; the method comprises the following steps: mixing tungstate and refined cadmium salt in a solution to carry out precipitation reaction, and carrying out solid-liquid separation to obtain a cadmium tungstate precipitate and a filtrate which is a precipitate mother solution; the obtained cadmium tungstate precipitate is subjected to a reduction reaction under the condition that hydrogen is introduced at the temperature of 650-750 DEG C, superfine tungsten powder and cadmium steam are obtained, and the cadmium steam leaves a reduction reaction zone along with hydrogen flow; and condensing the cadmium steam in a condensing area at the temperature of below 500 DEG C to obtain high-purity metal cadmium. According to the method, cadmium tungstate is used as a precursor, the superfine tungsten powder and the high-purity cadmium are prepared at the same time through the high-temperature reduction method, and the method has the advantages of being simple in process, high in product purity, free of ammonia nitrogen pollution and the like.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, specifically to a method for preparing ultrafine tungsten powder and high-purity cadmium. Background Technology

[0002] Ultrafine tungsten powder and high-purity cadmium, as essential basic materials in modern industry, play an irreplaceable role in national defense and high-end manufacturing. Ultrafine tungsten powder is a key material for preparing ultrafine tungsten carbide-based cemented carbide. Compared to ordinary tungsten powder, ultrafine tungsten powder can lower the carburization and sintering temperatures, which is beneficial for preparing high-density, fine-grained alloys, thereby improving the strength, hardness, and wear resistance of cemented carbides. High-purity cadmium is mainly used in the nuclear industry, special alloys, and functional materials. Cadmium has excellent neutron absorption capabilities and is a key material for manufacturing silver-indium-cadmium alloys for nuclear reactor control rods. In the battery field, high-purity cadmium is an important raw material for producing the positive electrode active material of nickel-cadmium batteries for extreme environment backup power. In addition, high-purity cadmium can also be used to prepare solar cell materials, infrared detector materials, and gas-sensitive materials.

[0003] Currently, ultrafine tungsten powder is typically prepared industrially using the purple tungsten reduction method. This first requires the preparation of ammonium paratungstate, which is then calcined under a reducing atmosphere to obtain purple tungsten oxide (WO3) with rod-shaped fine crystals. 2.72 The process of reducing purple tungsten oxide with hydrogen to obtain ultrafine tungsten powder has the problems of a long process and many control factors. On the other hand, high-purity cadmium requires solving the problem of deep removal of trace impurity elements (such as lead, zinc, aluminum, etc.) during the electrolytic refining process. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ultrafine tungsten powder and high-purity cadmium, which aims to use cadmium tungstate as a precursor to generate ultrafine tungsten powder and cadmium vapor under high-temperature reduction conditions, and then condense and recover to obtain high-purity cadmium.

[0005] To achieve the above objectives, the present invention proposes a method for preparing ultrafine tungsten powder and high-purity cadmium based on cadmium tungstate as a precursor, comprising the following steps: (1) The crude cadmium salt solution produced during the smelting process and / or the precipitate mother liquor obtained in step (3) are contacted with sodium hydroxide solution, and a precipitation reaction is carried out under the condition that the pH value is greater than 13 to obtain cadmium hydroxide precipitate and alkaline leaching solution. (2) Dissolve the cadmium hydroxide precipitate obtained in step (1) in an inorganic acid to obtain refined cadmium salt; (3) Mix tungstate with the refined cadmium salt obtained in step (2) in a solution to undergo a precipitation reaction. The molar ratio of cadmium to tungstate is greater than or equal to 1.2. Maintain the reaction temperature at 20℃~95℃. After reacting for 1~3 hours, separate the solid and liquid to obtain cadmium tungstate precipitate. The filtrate is the mother liquor of the precipitate. (4) The cadmium tungstate precipitate obtained in step (3) is reduced under the condition of hydrogen gas passing through at 650℃~750℃ for 0.5~1.5 hours to obtain ultrafine tungsten powder and cadmium vapor. The cadmium vapor leaves the reduction reaction zone with the hydrogen gas flow. (5) The cadmium vapor obtained in step (4) is condensed in the condensation zone below 500°C to obtain high-purity metallic cadmium.

[0006] Preferably, the crude cadmium salt in step (1) comprises one or more of cadmium chloride, cadmium nitrate, cadmium acetate, and cadmium sulfate, as well as impurity elements, including one or more of lead, zinc, aluminum, arsenic, calcium, magnesium, copper, nickel, and iron.

[0007] Preferably, the precipitation reaction time in step (1) is greater than 0.5 hours.

[0008] Preferably, the inorganic acid in step (2) includes one or more of hydrochloric acid, nitric acid, acetic acid, and sulfuric acid.

[0009] Preferably, the tungstate in step (3) is one or more of sodium tungstate, ammonium tungstate, and potassium tungstate.

[0010] The technical principles employed in this invention are as follows: This invention proposes a tungsten-cadmium co-metallurgical technology, which enables tungstate ions to react with refined cadmium salts to form cadmium tungstate precipitate. Subsequently, under high-temperature reduction conditions, two products are obtained: ultrafine tungsten powder and high-purity metallic cadmium. The main process is as follows: crude cadmium salt is reacted with NaOH solution to form cadmium hydroxide precipitate and maintain a certain alkalinity, so that impurities such as lead, zinc, aluminum, and arsenic are retained in the mother liquor, completing the first stage of purification and impurity removal; then, cadmium hydroxide is dissolved in inorganic acid to obtain refined cadmium salt; the refined cadmium salt reacts with tungstate solution to form cadmium tungstate precipitate, while impurities such as calcium and magnesium are retained in the mother liquor, thus completing the second stage of purification and impurity removal; cadmium tungstate is reacted at high temperature in a hydrogen atmosphere to directionally generate ultrafine tungsten powder and cadmium vapor, while trace impurities such as copper, nickel, and iron do not volatilize, and the third stage of purification and impurity removal is completed during the volatilization and condensation of cadmium vapor. Equations (1) to (5) are examples describing the reaction process, but are not limited to these equations.

[0011] The beneficial effects that this invention can achieve are as follows: This technology employs a multi-stage purification and impurity removal process based on different reaction principles to separate various trace impurities in crude cadmium salt at different stages, thereby obtaining high-purity metallic cadmium with a purity exceeding 99.999%. Furthermore, the cadmium tungstate precursor has a particle size below 2 μm, and after reduction, it yields ultrafine tungsten powder with a primary particle size of approximately 200 nm and below. Through the tungsten-cadmium co-metallurgical technology of this invention, both ultrafine tungsten powder and high-purity metallic cadmium can be prepared. Attached Figure Description

[0012] Figure 1 This is a scanning electron microscope image of the cadmium tungstate precursor prepared in Example 2.

[0013] Figure 2 The image shows the XRD pattern of the cadmium tungstate precursor prepared in Example 2.

[0014] Figure 3 This is a scanning electron microscope image of the ultrafine tungsten powder prepared according to the present invention in Example 2.

[0015] Figure 4 The image shows the XRD pattern of the ultrafine tungsten powder prepared in Example 2.

[0016] Figure 5 This is a scanning electron microscope image of the ultrafine tungsten powder prepared according to the present invention in Example 4.

[0017] Figure 6 The image shows the XRD pattern of the ultrafine tungsten powder prepared in Example 4. Detailed Implementation

[0018] The present invention will be further illustrated by the following examples, but is not limited thereto.

[0019] Example 1 Five portions of crude cadmium salt solution were taken, and NaOH solid was added to each portion to obtain solutions with different equilibrium pH values. The solutions were stirred and reacted for 1.5 hours. Cadmium hydroxide precipitate was obtained after solid-liquid separation. During this precipitation reaction, impurities such as lead, zinc, arsenic, and aluminum tend to remain in the solution under high pH conditions, thus achieving the separation of these impurity elements from cadmium hydroxide. Elemental analysis of the mother liquor and the cadmium hydroxide precipitate was performed to calculate the impurity removal rate. The experimental results are shown in Table 1.

[0020] Table 1. Impurity removal rate at different equilibrium pH values Example 2 Take 1 liter of crude cadmium salt solution, add solid NaOH until the pH value is 13.3, filter and wash with water to obtain cadmium hydroxide precipitate. Dissolve the cadmium hydroxide precipitate with hydrochloric acid to obtain purified cadmium salt. Add the purified cadmium salt to sodium tungstate solution according to a cadmium-tungsten molar ratio of 1.2, react at 60℃ for 2 hours, filter to obtain cadmium tungstate precursor and precipitate mother liquor. The scanning electron microscope image and XRD pattern of the cadmium tungstate precursor powder are attached. Figure 1 and attached Figure 2 As shown in the figure. Dry cadmium tungstate was reduced with hydrogen at 750℃ for 1.5 hours to obtain ultrafine tungsten powder. Scanning electron microscope images and XRD patterns of the ultrafine tungsten powder are attached. Figure 3 and attached Figure 4 As shown.

[0021] Example 3 Two liters of crude cadmium salt solution were taken, and solid NaOH was added until the pH value reached 13.2. After filtration and washing with water, cadmium hydroxide precipitate was obtained. The precipitate was dissolved in nitric acid to obtain refined cadmium salt. The refined cadmium salt was added to sodium tungstate solution at a cadmium-to-tungsten molar ratio of 1.25 and reacted at 92℃~95℃ for 1 hour. The mixture was then filtered to obtain the cadmium tungstate precursor and the precipitate mother liquor. Elemental analysis of the precipitate mother liquor and the cadmium tungstate precipitate revealed that calcium and magnesium remained in the solution and were thus separated from the cadmium tungstate. The removal rates of calcium and magnesium were calculated to be 93.8% and 99.4%, respectively. The dried cadmium tungstate was divided into four equal portions and subjected to hydrogen reduction at 650℃, 700℃, 750℃, and 800℃ for 1 hour, respectively, to obtain tungsten powder. Chemical analysis revealed that the cadmium residue rates of the tungsten powder obtained at hydrogen reduction temperatures of 650℃, 700℃, 750℃, and 800℃ were 0.0009%, 0.0003%, <0.0001%, and <0.0001%, respectively.

[0022] Example 4 One liter of crude cadmium salt solution was taken, and solid NaOH was added until the pH value reached 14.1. After filtration and washing with water, cadmium hydroxide precipitate was obtained. The precipitate was dissolved in acetic acid to obtain refined cadmium salt. The refined cadmium salt was added to ammonium tungstate solution at a cadmium-to-tungsten molar ratio of 1.3 and reacted at 20℃~24℃ for 3 hours. The mixture was then filtered to obtain the cadmium tungstate precursor and the precipitate mother liquor. Elemental analysis of the precipitate mother liquor and the cadmium tungstate precipitate revealed that calcium and magnesium remained in the solution and were thus separated from the cadmium tungstate. The removal rates of calcium and magnesium were calculated to be 98.7% and 99.9%, respectively. The dried cadmium tungstate was reduced with hydrogen at 750℃ for 0.5 hours to obtain ultrafine tungsten powder. Scanning electron microscopy and XRD images of the tungsten powder are attached. Figure 5 and attached Figure 6 As shown, cadmium vapor condenses into a solid at the condenser end at 480℃~490℃. Chemical analysis shows that the purity of the condensed metallic cadmium is above 99.999%, while the purity of copper, nickel, and iron is less than 1ppm.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine tungsten powder and high-purity cadmium, characterized in that, The method comprises the following steps: (1) contacting a crude cadmium salt solution produced in a smelting process or / and a precipitate mother liquor obtained in step (3) with a sodium hydroxide solution to perform a precipitation reaction under a pH value greater than 13, to obtain a cadmium hydroxide precipitate and an alkali leaching solution; (2) dissolving the cadmium hydroxide precipitate obtained in step (1) in an inorganic acid to obtain a refined cadmium salt; (3) mixing a tungstate with the refined cadmium salt obtained in step (2) in a solution to perform a precipitation reaction, with a cadmium-tungsten molar ratio greater than or equal to 1.2, and maintaining the reaction temperature at 20-95 DEG C, and after 1-3 hours of reaction, performing solid-liquid separation to obtain a cadmium tungstate precipitate and a precipitate mother liquor as a filtrate; (4) performing a reduction reaction on the cadmium tungstate precipitate obtained in step (3) under the condition of passing hydrogen into the precipitate at 650-750 DEG C, and maintaining the temperature for 0.5-1.5 hours to obtain ultrafine tungsten powder and cadmium vapor, and the cadmium vapor leaves the reduction reaction zone along with the hydrogen flow; (5) condensing the cadmium vapor obtained in step (4) in a condensing zone below 500 DEG C to obtain high-purity metallic cadmium.

2. The method of claim 1, wherein, The crude cadmium salt in step (1) comprises one or more of cadmium chloride, cadmium nitrate, cadmium acetate and cadmium sulfate, and impurity elements, wherein the impurity elements comprise one or more of lead, zinc, aluminum, arsenic, calcium, magnesium, copper, nickel and iron.

3. The method of claim 1, wherein, The precipitation reaction time in step (1) is greater than 0.5 hours.

4. The method of claim 1, wherein, The inorganic acid in step (2) comprises one or more of hydrochloric acid, nitric acid, acetic acid and sulfuric acid.

5. The method of claim 1, wherein, The tungstate in step (3) is one or more of sodium tungstate, ammonium tungstate and potassium tungstate.

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