A method for producing high-density metallic chromium by continuous atmosphere carbon reduction

Abstract

The application discloses a method for producing high-density metallic chromium by continuous atmosphere carbon reduction, and belongs to the technical field of metallic chromium preparation, which comprises the following steps: adding chromium oxide green, a carbon reducing agent and a binder into a mixer, uniformly mixing, pressing into blocks, and drying and then putting into a push plate furnace to perform sintering to generate metallic chromium. The method adopts the push plate furnace to perform multi-stage high-temperature solid sintering under inert atmosphere, and can prepare the metallic chromium without harsh conditions such as vacuum environment, and the product quality is stable, the impurity content is small, the metallic chromium density is high, meanwhile, the preparation method is environment-friendly, can be continuously produced, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of metallic chromium preparation technology, and more specifically, this invention relates to a method for producing high-density metallic chromium by continuous atmosphere carbon reduction. Background Technology

[0002] Metallic chromium possesses excellent properties such as high melting and boiling points, high hardness, and strong corrosion resistance, making it widely used in high-temperature alloys, resistance alloys, sputtering targets, aerospace materials, and other fields, with market demand increasing daily. Chromium green (chromium trioxide), as the core raw material for preparing metallic chromium, is widely available and its purity is relatively controllable, making it the preferred precursor in current technologies. The mainstream preparation methods mainly include the aluminothermic method, the carbothermic reduction method, and a small amount of electrolysis.

[0003] In existing technologies, the aluminothermic process is the main method for producing metallic chromium in China. It uses chromium green as a raw material, aluminum powder as a reducing agent, and alkali metal salts as exothermic agents to produce metallic chromium through a self-thermal reaction. However, this method has several insurmountable drawbacks: first, the aluminum content of the product is too high, affecting the purity of the metallic chromium and its subsequent performance; second, the chromium recovery rate is low, only 83%~85%, resulting in raw material waste; third, it has high energy consumption, and the aluminum powder preparation process generates pollutants such as wastewater and red mud, while the exothermic agent produces salt-containing dust, making treatment difficult and costly. Furthermore, the self-thermal reaction temperature is difficult to control, resulting in poor reaction uniformity, further affecting product quality stability. The byproduct chromium corundum is classified as hazardous waste, with high subsequent disposal costs and treatment difficulties, making it neither environmentally friendly nor economically viable.

[0004] Furthermore, existing methods often use chromium green raw materials with high impurity content and uneven particle size, making it difficult to improve the purity of the prepared metallic chromium and meet the requirements of high-end fields such as aerospace and electronics. Although electrolysis can obtain high-purity metallic chromium, it suffers from huge power consumption, severe pollution, and high production costs, making it difficult to promote its widespread application.

[0005] Carbothermic reduction is another commonly used method, which prepares metallic chromium by reacting chromium green with a carbon source at high temperatures. However, this method has significant drawbacks: the resulting metallic chromium contains high and difficult-to-control carbon impurities, which can easily lead to physical fusion of coke and metallic chromium, reducing the mechanical and corrosion resistance properties of the metallic chromium; the reaction requires a high vacuum environment, placing stringent demands on equipment, resulting in low unit capacity, long reaction time, and unsuitability for large-scale industrial production, and also incurring high overall energy consumption. Existing patents such as CN201010124791, CN200310103510, and US2833645A disclose carbon reduction processes that all rely on vacuum furnace sintering, which suffers from limited capacity, low production efficiency, and other problems, making them unsuitable for large-scale industrial production. The resulting metallic chromium also has low density, limiting its application scenarios. In summary, existing methods for preparing metallic chromium using chromium green all suffer from low purity, low recovery rate, high energy consumption, high pollution, low density, or high equipment requirements, failing to balance product quality and production economy. An improved preparation method is urgently needed to address these technical shortcomings. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] To achieve these objectives and other advantages according to the present invention, a method for producing high-density metallic chromium by continuous atmosphere carbon reduction is provided, comprising: Step 1: Add chrome green powder, carbon reducing agent and binder to a mixer, mix evenly and then press it into blocks using a molding device, and then dry it in a drying oven; Step 2: The dried block is subjected to multi-stage high-temperature solid-state sintering in an inert atmosphere in a pusher furnace. After sintering, it is cooled to obtain high-density metallic chromium.

[0008] Preferably, in step one, the chrome green powder has a purity of ≥99wt% and a particle size of 80~200 mesh.

[0009] Preferably, in step one, the carbon reducing agent is one or a mixture of several of activated carbon, carbon black powder, graphite, coke, semi-coke and organic carbon, and the molar ratio of chrome green powder to carbon reducing agent is 1:1.2~1.5, based on the oxygen in chrome green and the carbon in the carbon reducing agent.

[0010] Preferably, in step one, the adhesive is at least one of water, starch, phenolic resin, polyacrylamide, polyethylene glycol, polyvinyl alcohol, and cassava flour; the mass ratio of chrome green powder to adhesive is 100:2~20.

[0011] Preferably, in step one, the mixing process uses one of the following: a dual-motion mixer, a three-dimensional mixer, a ribbon mixer, a trough mixer, a CR high-intensity mixer, or a double-cone mixer, with a mixing time of 30–180 min. The pressing process uses one of the following: a press or a double-roller briquetting machine, with a molding pressure of 15–40 MPa, a drying temperature of 50–100 °C, and a drying time of 3–10 h.

[0012] Preferably, in step two, the inert atmosphere is at least one of helium or argon, and the amount of inert gas used is ≥0.05L / kg of block material.

[0013] Preferably, in step two, the pressure inside the inert atmosphere sintering furnace in the pusher furnace is 0.1 Pa to 0.03 MPa.

[0014] Preferably, in step two, during the multi-stage high-temperature solid-state sintering, the temperature is first uniformly raised to 1300℃ and held for 3-5 hours, then raised to 1500-1600℃ and held for 10-20 hours, then raised to 1700-1900℃ and held for 3-10 hours, and finally cooled to 50℃.

[0015] Preferably, the chromium green powder is pretreated before step one: the chromium green powder is placed in a crucible and transferred to a high-temperature tube furnace. It is first heated to 600-800°C in an argon atmosphere, and then methane is introduced at a flow rate of 5-10 mL / min. The heating is maintained for 5-10 min to obtain surface-carbonized chromium green powder. Preferably, in step two, after multi-stage high-temperature solid-state sintering, the inert gas is stopped, and then hydrogen is introduced at 0.01~0.02L / kg of block material, and the temperature is raised again to 1100~1200℃ for calcination for 1~2 hours. After cooling, high-density metallic chromium is obtained.

[0016] The present invention has at least the following beneficial effects: (1) This invention is based on metallurgical grade chrome green. It uses a mixer to mix materials and utilizes a three-dimensional mixing + shear dispersion mode to effectively improve mixing efficiency, break up agglomerated materials, and ensure the uniformity of powder. (2) The present invention uses a pusher furnace for multi-stage high-temperature solid sintering under an inert atmosphere, which can prepare metallic chromium without the need for harsh conditions such as vacuum environment. The product quality is stable, with low impurity content and high metallic chromium density. At the same time, the preparation method is environmentally friendly, can be continuously produced, and is suitable for large-scale industrial production. (3) The present invention uses one or a mixture of activated carbon, carbon black powder, graphite, coke, semi-coke and organic carbon as carbon reducing agent to carry out high-temperature reduction reaction in an inert atmosphere in a pusher furnace for continuous production, reducing production energy consumption, and the product obtained has extremely low impurity elements. (4) At high temperatures, the presence of inert gas increases the saturated vapor pressure of the material, greatly reduces the amount of volatilization of the material, and allows the material to react fully at higher temperatures, resulting in a stable quality of the metallic chromium product. (5) The present invention also pre-treats the chromium green powder by carbonization, so that a small amount of carbon is first coated on the surface of the chromium green, which helps the reduction reaction to proceed during subsequent high-temperature sintering. At the same time, it can avoid the accumulation of carbon reducing agent during sintering, thus improving the quality of the metal chromium. Furthermore, after multi-stage high-temperature solid sintering, hydrogen is introduced for heat treatment to further remove carbon, oxygen and other elements brought in by the raw materials, thereby significantly improving the quality and density of the metal chromium.

[0017] Other advantages, objectives and features of the present invention will be apparent in part from the following description, and in part from the understanding of those skilled in the art through study and practice of the invention. Detailed Implementation The present invention will now be described in further detail with reference to embodiments, so that those skilled in the art can implement it based on the description. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0018] Example 1 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Mix 10 kg of Cr2O3 (99.19 wt%) that has passed through a 200-mesh sieve, 2.3 kg of carbon black powder (98 wt% fixed carbon), 0.26 kg of cassava flour, and 1.32 kg of water in a three-dimensional mixer for 80 minutes, then press the mixture into blocks with a diameter of 20 mm and a density of 2.95 g / cm³, and then dry them in a vacuum drying oven at 80 °C. Step 2: Load the material blocks into a graphite crucible and push it into a pusher furnace filled with argon gas at a flow rate of 0.5 L / min. Heat the furnace at a uniform rate to 1300℃ and hold for 3 hours, then to 1500℃ and hold for 10 hours. Next, heat to 1750℃ and hold for 3 hours. Cool to 50℃ and remove from the furnace. The density of metallic chromium reaches 6.79 g / cm³. 3 The purity reaches 99.75%.

[0019] Example 2 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Mix 10 kg of Cr2O3 (99.19 wt%) that has passed through a 100-mesh sieve, 2.3 kg of carbon black powder (98 wt% fixed carbon), and 1.32 kg of water in a three-dimensional mixer for 100 min, then press the mixture into blocks with a diameter of 20 mm and a density of 2.95 g / cm³, and then dry them in a vacuum drying oven at 80 °C. Step 2: Load the material blocks into a graphite crucible and push it into a pusher furnace filled with argon gas at a flow rate of 0.8 L / min. Heat the furnace at a uniform rate to 1300℃ and hold for 5 hours, then to 1500℃ and hold for 15 hours. Next, heat to 1850℃ and hold for 3 hours. Cool to 50℃ and remove from the furnace to obtain a high-density metallic chromium product with a density of 6.9 g / cm³. 3 The purity reaches 99.78%.

[0020] Example 3 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Add 10 kg of Cr2O3 (content 99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (fixed carbon 98 wt%), and 1.32 kg of water to a double-motion mixer and mix for 30 minutes. Press the mixture into blocks with a diameter of 20 mm and a density of 2.95 g / cm³. Then dry the blocks in a vacuum drying oven at 90°C. Step 2: Load the material blocks into a graphite crucible and push it into a pusher furnace filled with argon gas at a flow rate of 0.6 L / min. Heat the furnace at a uniform rate to 1300℃ and hold for 5 hours, then to 1500℃ and hold for 20 hours. Finally, heat to 1900℃ and hold for 3 hours. Cool to 50℃ and remove from the furnace to obtain a high-density metallic chromium product with a density of 7.02 g / cm³. 3 The purity reaches 99.68%.

[0021] Example 4 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Place 10 kg of chromium green powder into a crucible and transfer it into a high-temperature tube furnace. First, heat the furnace to 800°C in an argon atmosphere, then introduce methane at a flow rate of 10 mL / min and maintain the heating for 5 min to obtain surface-carbonized chromium green powder. Step 2: Add 10 kg of surface-carbonized Cr2O3 (content 99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (fixed carbon 98 wt%), and 1.32 kg of water to a double-motion mixer, mix for 30 minutes, press into blocks, and then dry in a vacuum drying oven at 90℃. Step 3: Load the material blocks into a graphite sagger and push them into a pusher furnace filled with argon gas at a flow rate of 0.6 L / min. Heat the material at a uniform rate to 1300℃ and hold for 5 hours, then to 1500℃ and hold for 20 hours. Next, heat to 1900℃ and hold for 3 hours. Stop the inert gas supply, then introduce hydrogen gas at a rate of 0.02 L / kg of material. Calcination is then carried out again at 1200℃ for 2 hours. Cool to 50℃ and remove from the furnace to obtain a high-density metallic chromium product with a density of 7.15 g / cm³. 3The purity reaches 99.95%.

[0022] Example 5 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Place 10 kg of chromium green powder into a crucible and transfer it into a high-temperature tube furnace. First, heat the furnace to 800°C in an argon atmosphere, then introduce methane at a flow rate of 10 mL / min and maintain the heating for 5 min to obtain surface-carbonized chromium green powder. Step 2: Add 10 kg of surface-carbonized Cr2O3 (content 99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (fixed carbon 98 wt%), and 1.32 kg of water to a double-motion mixer, mix for 30 minutes, press into blocks, and then dry in a vacuum drying oven at 90℃. Step 3: Load the material blocks into a graphite crucible and push it into a pusher furnace filled with argon gas at a flow rate of 0.6 L / min. Heat the furnace at a uniform rate to 1300℃ and hold for 5 hours, then to 1500℃ and hold for 20 hours. Finally, heat to 1900℃ and hold for 3 hours. Cool to 50℃ and remove from the furnace to obtain a high-density metallic chromium product with a density of 7.08 g / cm³. 3 The purity reaches 99.91%.

[0023] Example 6 A method for producing high-density metallic chromium by continuous atmosphere carbon reduction includes the following steps: Step 1: Add 10 kg of Cr2O3 (content 99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (fixed carbon 98 wt%), and 1.32 kg of water to a double-motion mixer, mix for 30 minutes, press into blocks, and then dry in a vacuum drying oven at 90℃. Step 2: Load the material blocks into a graphite sagger and push them into a pusher furnace filled with argon gas at a flow rate of 0.6 L / min. Heat the material at a uniform rate to 1300℃ and hold for 5 hours, then to 1500℃ and hold for 20 hours. Next, heat to 1900℃ and hold for 3 hours. Stop the inert gas supply, then introduce hydrogen gas at a rate of 0.02 L / kg of material. Calcination is then carried out again at 1200℃ for 2 hours. Cool to 50℃ and remove from the furnace to obtain a high-density metallic chromium product with a density of 7.06 g / cm³. 3 The purity reaches 99.86%.

[0024] Comparative Example 1: Step 1: Add 10 kg of Cr2O3 (content 99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (fixed carbon 98 wt%), and 1.32 kg of water to a double-motion mixer and mix for 30 minutes. Press the mixture into blocks with a diameter of 20 mm and a density of 2.95 g / cm³. Then dry the blocks in a vacuum drying oven at 90 °C. Step 2: Load the material blocks into the graphite sagger and push them into the pusher furnace. Do not introduce any inert gas. The furnace atmosphere is air. Heat the material at a uniform rate to 1300℃ and hold for 5 hours. Then heat it to 1500℃ and hold for 20 hours. Finally, heat it to 1900℃ and hold for 3 hours. Cool it to 50℃ and remove it from the furnace.

[0025] In the sintering process of Comparative Example 1, due to the presence of oxygen in the furnace, the carbon reducing agent rapidly reacted with oxygen at high temperatures to generate CO / CO2, resulting in a severe deficiency of the effective carbon content involved in the reduction of chromium green. Simultaneously, the air atmosphere caused some of the reduced metallic chromium to undergo secondary oxidation, resulting in a grayish-green surface and a large amount of unreacted chromium oxide embedded within the product. The final product was primarily a mixture of unreduced Cr2O3 and a small amount of chromium carbide, failing to yield a dense metallic chromium bulk, with a density of only 3.12 g / cm³ (close to the density of the raw material briquettes). This comparative example demonstrates that an inert atmosphere is a necessary condition for achieving the carbothermic reduction reaction and obtaining high-density metallic chromium in this scheme.

[0026] Comparative Example 2: Step 1: Add 10 kg of Cr2O3 (99.19 wt%) that has passed through a 160-mesh sieve, 2.3 kg of carbon black powder (98 wt% fixed carbon), and 1.32 kg of water to a double-motion mixer. Mix for 30 minutes, then press into blocks with a diameter of 20 mm and a density of 2.95 g / cm³. 3 Then, dry them in a vacuum drying oven at 90℃; Step 2: Load the material blocks into a graphite sagger and push them into a pusher furnace filled with argon gas at a flow rate of 0.6 L / min. Heat the material directly to 1900°C at a rate of 10°C / min and hold it at that temperature for 23 hours (the total high-temperature time is consistent with the cumulative holding time of the three stages in Example 3). Cool the material to 50°C and remove it from the furnace.

[0027] During the rapid heating process in Comparative Example 2, the carbothermic reduction reaction on the surface of the bulk material was intense, generating a large amount of CO gas. Due to the excessively rapid heating, the gas could not escape from the interior of the bulk material in time, resulting in numerous pores and microcracks inside the product. Simultaneously, the single-stage high-temperature sintering resulted in insufficient pre-reduction and material diffusion processes in the low-temperature zone (1300-1500℃), leading to uneven grain growth. Although the obtained metallic chromium product was mainly composed of metallic chromium, its internal structure was porous, with a density of only 5.21 g / cm³. 3 It is significantly lower than 7.02 g / cm³ in Example 3. 3This comparative example demonstrates that the multi-stage high-temperature solid-state sintering process of the present invention plays a crucial role in controlling the reaction rate, promoting gas escape, and improving product density.

[0028] Table 1 shows the density of metallic chromium obtained in Examples 1-6.

[0029] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 <![CDATA[Density / g / cm 3 > 6.79 6.9 7.02 7.15 7.08 7.06 As can be seen from the data in Table 1, Examples 1-3 of this invention, based on metallurgical-grade chromium green, use a mixer to mix materials and employ a three-dimensional mixing + shear dispersion mode, which can effectively improve mixing efficiency, break up agglomerated materials, and ensure the uniformity of powder. Then, a pusher furnace is used for multi-stage high-temperature solid-state sintering under an inert atmosphere. Metallic chromium can be prepared without harsh conditions such as a vacuum environment, and the product quality is stable, with low impurity content and high metallic chromium density. Example 4, based on Example 3, first performs carbonization pretreatment on the chromium green powder, so that a small amount of carbon is first coated on the powder. The chrome green surface facilitates the reduction reaction during subsequent high-temperature sintering and prevents the accumulation of carbon reducing agent during sintering, thus improving the quality of the obtained metallic chromium. Furthermore, after multi-stage high-temperature solid-state sintering, hydrogen gas is introduced for heat treatment to further remove carbon, oxygen, and other elements introduced from the raw materials, significantly improving the quality and density of the obtained metallic chromium. In Example 5, only chrome green was subjected to carbonization pretreatment, and the density of the obtained metallic chromium was slightly lower than that in Example 4. In Example 6, only hydrogen gas was introduced for heat treatment after multi-stage high-temperature solid-state sintering, and the density of the obtained metallic chromium was also slightly lower than that in Example 4.

[0030] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for producing high-density metallic chromium by continuous atmospheric carbon reduction, characterized in that, include: Step 1: Add chrome green powder, carbon reducing agent and binder to a mixer, mix evenly and then press it into blocks using a molding device, and then dry it in a drying oven; Step 2: The dried block is subjected to multi-stage high-temperature solid-state sintering in an inert atmosphere in a pusher furnace. After sintering, it is cooled to obtain high-density metallic chromium.

2. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step one, the purity of the chrome green powder is ≥99wt%, and the particle size of the chrome green powder is 80~200 mesh.

3. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step one, the carbon reducing agent is one or a mixture of several of activated carbon, carbon black powder, graphite, coke, semi-coke and organic carbon. The molar ratio of chrome green powder to carbon reducing agent is 1:1.2~1.5, based on the oxygen in chrome green and the carbon in the carbon reducing agent.

4. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step one, the adhesive is at least one of water, starch, phenolic resin, polyacrylamide, polyethylene glycol, polyvinyl alcohol, and cassava flour; the mass ratio of chrome green powder to adhesive is 100:2~20.

5. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step one, the mixing process uses one of the following: a dual-motion mixer, a three-dimensional mixer, a ribbon mixer, a trough mixer, a CR high-intensity mixer, or a double-cone mixer. The mixing time is 30–180 min. The pressing process uses one of the following: a press or a double-roller briquetting machine. The molding pressure parameters are 15–40 MPa. The drying temperature is 50–100 °C, and the drying time is 3–10 h.

6. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step two, the inert atmosphere is at least one of helium or argon, and the amount of inert gas used is ≥0.05L / kg of block material.

7. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step two, the pressure inside the inert atmosphere sintering furnace in the pusher furnace is 0.1 Pa to 0.03 MPa.

8. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step two, during the multi-stage high-temperature solid-state sintering, the temperature is first uniformly raised to 1300℃ and held for 3-5 hours, then raised to 1500-1600℃ and held for 10-20 hours, then raised to 1700-1900℃ and held for 3-10 hours, and finally cooled to 50℃.

9. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, Pretreatment of chromium green powder before step one: Place chromium green powder in a crucible and transfer it to a high-temperature tube furnace. First, heat it to 600~800℃ in an argon atmosphere, then introduce methane at a flow rate of 5~10mL / min and maintain heating for 5~10min to obtain surface-carbonized chromium green powder.

10. The method for producing high-density metallic chromium by continuous atmosphere carbon reduction as described in claim 1, characterized in that, In step two, after multi-stage high-temperature solid-state sintering, the inert gas is stopped, and then hydrogen is introduced at 0.01~0.02L / kg of block material. The temperature is raised again to 1100~1200℃ and calcined for 1~2 hours. After cooling, high-density metallic chromium is obtained.