Metallurgical grade chromium green, its preparation method and application

Abstract

The present application relates to a kind of metallurgical grade chrome green and its preparation method and application.The preparation method of metallurgical grade chrome green includes the following steps: the pH value of hexavalent chromium salt solution is adjusted to acidic, and solution A is obtained;Reducing agent, seed crystal and alkali are mixed and then added to water, and high-dispersion mixed slurry B is obtained;High-dispersion mixed slurry B is heated to boiling, then solution A is added to high-dispersion mixed slurry B, to form fluid microelement, so that solution A and high-dispersion mixed slurry B react at the interface of fluid microelement, continue to react after feeding, so that the product is deposited, crystallized and grown, and intermediate product C is obtained;Intermediate product C is washed and calcined, and high-quality metallurgical grade chrome green product is obtained.The present application also provides a kind of metallurgical grade chrome green prepared by the preparation method as described in the present application.The present application solves the problem that the chromium green produced by the existing process has high impurity content and small particle size, which is difficult to meet the requirements of high-quality metallurgical grade chrome green.

Description

A metallurgical grade chromium green, its preparation method and application Technical Field

[0001] This invention relates to the field of chemical product manufacturing technology, specifically to a metallurgical grade chromium green, its preparation method, and its application. Background Technology

[0002] With economic development, the chromium metal market has been expanding in recent years. While demand is increasing, customers are also demanding higher quality chromium green products, such as those with low silicon, low carbon and sulfur, low iron, high purity, and large, intact grains. Especially high-end chromium metal products like those for aerospace and electronics are seeing growing popularity both domestically and internationally, and have become a key economic growth point in the new materials sector. However, traditional processes for producing chromium metal using the chromium hydroxide and aluminothermic methods suffer from poor purity and high impurity content (mainly iron, sulfur, carbon, and vanadium) in the intermediate products due to the nature of these processes. The smelted chromium metal can only meet national standards, making it difficult to produce higher-quality products. Therefore, the high-end chromium metal product market is essentially nonexistent. Thus, researching and preparing high-quality metallurgical-grade chromium green products with good crystallinity, large particle size, high apparent density, and low impurities is a necessary condition for producing high-quality chromium metal.

[0003] Existing metallurgical-grade chromium green is mainly produced by reducing sodium chromate with sulfur to obtain chromium hydroxide, followed by calcination. This process is complex, with numerous side reactions. The sulfur reduction reaction requires sophisticated equipment, and sulfur utilization is low. The byproducts contain large amounts of chromium and sodium thiosulfate, leading to high costs for subsequent wastewater treatment. Furthermore, the resulting chromium green has a high sulfur content (80 ppm S) and insufficient particle size (D...). 50 It has drawbacks such as a particle size of approximately 7–16 μm. Secondly, there is the ammonium process for producing chromium green, which involves reacting a chromium compound with ammonium sulfate to obtain an intermediate product, which is then calcined to obtain chromium green. However, the chromium green produced by the ammonium process has a finer particle size; typically, the medium particle size D... 50 The initial particle size is less than 4 μm, although some can reach 6-9 μm after high-temperature calcination. Therefore, chrome green prepared by the ammonium method can mostly only be used as pigment-grade chrome green in industries such as ceramics and abrasives. Furthermore, the subsequent processing of pigment-grade chrome green is complex and costly, and in recent years, the market demand for pigment-grade chrome green has been far lower than that for metallurgical-grade chrome green. Therefore, developing a method for preparing high-quality metallurgical-grade chrome green is of great practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide a metallurgical grade chromium green, its preparation method, and its application, in order to solve the problem that chromium green produced by existing processes has high impurity content and small particle size, making it difficult to meet the requirements of high-quality metallurgical grade chromium green.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing metallurgical grade chromium green includes the following steps:

[0007] The pH of the hexavalent chromium salt solution was adjusted to acidity to obtain solution A;

[0008] The reducing agent, seed crystals, and alkali are mixed and then added to water to obtain a highly dispersed mixed slurry B;

[0009] The highly dispersed slurry B is heated to boiling, and then solution A is added to the highly dispersed slurry B to form fluid micro-elements, so that solution A and highly dispersed slurry B react at the fluid micro-element interface to obtain intermediate product C.

[0010] Intermediate product C was washed and calcined to obtain high-quality metallurgical grade chromium green.

[0011] According to the above technical means, an acidic solution A is obtained by adjusting the pH of the hexavalent chromium salt solution with acid. A highly dispersed slurry B is obtained by adding seed crystals to an alkaline solution containing a reducing agent. Then, under boiling conditions, the acidic solution A is added to the highly dispersed slurry B, causing a reaction between solution A and the highly dispersed slurry B at the fluid micro-element interface. This creates a localized high-temperature environment at the interface. This unique high-temperature environment effectively enhances the diffusion of the reducing agent from the highly dispersed slurry B into solution A and promotes the redox reaction between the reducing agent and the hexavalent chromium in the inner liquid film of the fluid micro-element interface to generate trivalent chromium. The trivalent chromium then diffuses into the highly dispersed slurry B. Chromium hydroxide diffuses and forms in the dispersed slurry B. Simultaneously, the newly formed chromium hydroxide deposits and grows with the seed crystals in the highly dispersed slurry B as the core, effectively avoiding the formation of a large number of ultrafine chromium hydroxide particles, thus obtaining a highly crystalline and large-particle chromium hydroxide intermediate product C. Due to the large grain size and high crystallinity of the chromium hydroxide intermediate product C, it is easy to wash away impurities with water, thoroughly removing impurities such as sodium sulfate, and significantly reducing the content of impurities such as sodium and sulfur. After high-temperature calcination, harmful impurities such as C and S are further reduced, ultimately yielding a high-quality metallurgical-grade chromium green product with good crystallinity, large particle size, high apparent density, and low carbon and sulfur content, which can be directly used as a high-quality metallurgical raw material.

[0012] When adding the reducing agent, seed crystals, and alkali to water, thorough stirring is required to obtain a highly dispersed slurry B.

[0013] Preferably, the pH of the hexavalent chromium salt solution is adjusted to acidic using an acid.

[0014] Preferably, the hexavalent chromium salt solution is selected from at least one of chromate solution, dichromate solution and chromic acid solution, or a corresponding solution prepared from chromate solid, dichromate solid and chromic anhydride.

[0015] Preferably, sulfuric acid is used to adjust the pH of the hexavalent chromium salt solution to below 1.

[0016] Among these factors, considering product quality, production process, equipment protection, and environmental protection, using sulfuric acid to adjust the pH of the hexavalent chromium salt solution is the best option.

[0017] By adjusting the pH of the hexavalent chromium salt solution to below 1, the full reaction between hexavalent chromium and the reducing agent thiosulfate is effectively ensured.

[0018] Preferably, the amount of reducing agent added is the theoretical amount required for the reaction of hexavalent chromium to produce trivalent chromium.

[0019] Preferably, the amount of seed crystals added is 20% to 80% of the amount of chromium hydroxide generated in the reaction;

[0020] Preferably, the amount of alkali added is 90% to 99.9% of the theoretical amount required for the alkali to react completely with the free acid in solution A and the generated chromium sulfate. That is, the amount of alkali added is slightly lower than the theoretical amount required for the alkali to completely react with the free acid in solution A and the generated chromium sulfate.

[0021] By controlling the amount of alkali added to be slightly lower than the theoretical amount required for complete reaction between the alkali and the free acid in solution A and the generated chromium sulfate, the pH value of the slurry after the reaction is kept weakly acidic, while ensuring that the thiosulfate reacts completely with hexavalent chromium.

[0022] To control the subsequent formation of chromium hydroxide, ensure effective deposition and growth rate on the seed crystals, and effectively control the particle size of the chromium hydroxide, the amount of seed crystals added is controlled between 20% and 80%. Adding more seed crystals leads to a faster deposition rate, resulting in finer particle size.

[0023] Preferably, the amount of seed crystals added is 30% to 40% of the amount of chromium hydroxide generated in the reaction.

[0024] Preferably, the reducing agent is selected from thiosulfate or organic reducing agent. Where no other impurities are introduced, thiosulfate can also be replaced by other organic reducing agents with the same function.

[0025] Preferably, the organic reducing agent includes industrial glucose, methanol, or formaldehyde.

[0026] Preferably, the thiosulfate is selected from sodium thiosulfate.

[0027] Preferably, the seed crystal is selected from chromium hydroxide.

[0028] Preferably, the alkali is selected from sodium hydroxide.

[0029] Using sodium hydroxide as an alkali not only has the advantages of strong alkalinity and low cost, but also does not introduce other impurities, ensuring the high purity of the finished product.

[0030] Preferably, the solution A is added to the highly dispersed mixed slurry B to form fluid micro-elements, and the reaction time at the interface of the fluid micro-elements is controlled to be between 0.5 and 1 hour, that is, the feeding time is controlled to be between 0.5 and 1 hour.

[0031] Preferably, after the solution A is added to the highly dispersed mixed slurry B, the mixture is stirred and reacted for 1 to 5 hours to allow chromium hydroxide to crystallize and grow.

[0032] Preferably, the solution A and the highly dispersed mixed slurry B undergo an interfacial reaction, causing chromium hydroxide to crystallize and grow. When the reaction reaches its endpoint, the pH value of the mixed slurry is between 4 and 6.

[0033] In this process, solution A is added to the highly dispersed slurry B at a constant rate.

[0034] By rationally controlling the feeding time of solution A into the highly dispersed slurry B, the feeding rate of solution A into the highly dispersed slurry B is also rationally controlled, allowing the newly generated chromium hydroxide to gradually deposit and grow on the seed crystals, thereby achieving the ideal particle size as much as possible. This is because feeding too quickly will result in an excessive amount of chromium hydroxide being generated too rapidly, leading to poor bonding with the seed crystals and the formation of a large number of fine particles, resulting in a product with a fine particle size defect.

[0035] By controlling the pH of the mixed solution at the reaction endpoint between 4 and 6, the hexavalent chromium in the mixed solution is effectively reduced to chromium hydroxide as completely as possible.

[0036] Preferably, after the solution A is added to the highly dispersed mixed slurry B, the reaction continues, so that the crystallization and growth time of chromium hydroxide is 2 to 3 hours.

[0037] Preferably, the solution A and the highly dispersed slurry B undergo an exothermic acid-base neutralization reaction at the fluid micro-element interface to form a local high-temperature environment in the interface region. This local high-temperature environment can enhance the diffusion of thiosulfate in the highly dispersed slurry B into the solution A and promote the redox reaction between thiosulfate and hexavalent chromium to generate trivalent chromium. The trivalent chromium diffuses into the highly dispersed slurry B and generates chromium hydroxide. At the same time, the generated chromium hydroxide is deposited and grown with the seed crystals in the highly dispersed slurry B as the core, resulting in an intermediate product C with high crystallinity and large particles.

[0038] Preferably, the intermediate product C is washed until the conductivity of the wash water is ≤1 mS / cm.

[0039] Preferably, the roasting temperature is 1200℃~1500℃ and the roasting time is 0.5~3h.

[0040] Preferably, the roasting temperature is 1400℃ and the roasting time is 2h.

[0041] When the acid is selected from sulfuric acid, the base from sodium hydroxide, and the reducing agent from sodium thiosulfate, the main reaction equations that occur during the preparation of metallurgical grade chromium green in this invention are as follows:

[0042] 2Na2CrO4+H2SO4=Na2Cr2O7+H2O+Na2SO4(1)

[0043] H₂SO₄ + 2NaOH = Na₂SO₄ + 2H₂O (2)

[0044] 4Na2Cr2O7+3NaS2O3+13H2SO4=4Cr2(SO4)3+7Na2SO4+13H2O (3)

[0045] Cr2(SO4)3+6NaOH=2Cr(OH)3+3Na2SO4(4)

[0046] Cr(OH)3=Cr2O3+3H2O (5)

[0047] The present invention also provides a metallurgical grade chromium green prepared by the preparation method described herein.

[0048] Preferably, the metallurgical grade chromium green has a purity of 99.5% or higher and a particle size D. 50 Above 22 μm, the bulk density is 1.8 g / cm³. 3 The carbon content is below 32 ppm and the sulfur content is below 28 ppm.

[0049] The present invention also provides an application of the metallurgical grade chromium green prepared by the method described herein, wherein the metallurgical grade chromium green is used in the production of high-quality metallic chromium and refractory materials.

[0050] The beneficial effects of this invention are:

[0051] The method for preparing metallurgical-grade chromium green of the present invention involves adjusting the pH of a hexavalent chromium salt solution with sulfuric acid to obtain an acidic solution A. Seed crystals are then added to an alkaline solution containing a reducing agent to obtain a highly dispersed mixed slurry B. Under boiling conditions, the acidic solution A is fed into the highly dispersed mixed slurry B, causing a reaction between solution A and the highly dispersed mixed slurry B at the fluid micro-element interface. This creates a localized high-temperature environment at the interface, effectively enhancing the diffusion of the reducing agent from the highly dispersed mixed slurry B into solution A. It also promotes the redox reaction between the reducing agent and the hexavalent chromium in the liquid film inside the fluid micro-element interface to generate trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B to generate chromium hydroxide. Meanwhile, the newly generated chromium hydroxide is deposited and grown using the seed crystals in the highly dispersed mixed slurry B as the core, effectively avoiding the formation of a large number of ultrafine chromium hydroxide particles, thus obtaining a highly crystalline and large-particle chromium hydroxide intermediate product C. Due to the large grain size and high crystallinity of the chromium hydroxide intermediate product C, it is easy to wash away impurities with water, thoroughly removing impurities such as sodium sulfate, and significantly reducing the content of impurities such as sodium and sulfur. After high-temperature calcination, harmful impurities such as C and S are further reduced, ultimately yielding a high-quality metallurgical grade chromium green product with good crystallinity, large particle size, high apparent density, and low carbon and sulfur content. It can be directly used as a high-quality metallurgical raw material and has the advantages of simple operation, mild conditions, and easy industrial production. It has promotion and application value in the field of chemical product production technology. Attached Figure Description

[0052] Figure 1 is a material flow diagram of the preparation method of metallurgical grade chromium green;

[0053] Figure 2 shows the particle size determination results of the metallurgical grade chromium green product prepared in Example 1;

[0054] Figure 3 shows the particle size determination results of the metallurgical grade chromium green product prepared in Example 2;

[0055] Figure 4 shows the particle size determination results of the metallurgical grade chromium green product prepared in Example 3;

[0056] Figure 5 shows the particle size determination results of the metallurgical grade chromium green product prepared in Example 4.

[0057] Figure 6 shows the particle size determination results of the metallurgical grade chromium green product prepared in Example 5. Detailed Implementation

[0058] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0059] This application aims to disclose a metallurgical grade chromium green, its preparation method, and its application, in order to solve the problem that chromium green produced by existing processes has high impurity content (mainly including carbon and sulfur) and small particle size, making it difficult to meet the requirements of high-quality metallurgical grade chromium green.

[0060] Metallurgical-grade chromium green has very high requirements for particle size, bulk density, and C and S impurity content. Conventional sulfur reduction and ordinary ammonium methods are insufficient to produce qualified, high-quality metallurgical-grade chromium green products. This invention, based on theories of fluid mixing, chemical process interface strengthening, and crystal growth, designs a specific reaction method, followed by washing and calcination, to obtain high-quality metallurgical-grade chromium green products.

[0061] Specifically, as shown in Figure 1, the preparation method of metallurgical grade chromium green of the present invention includes the following steps:

[0062] The pH of the hexavalent chromium salt solution was adjusted to acidity to obtain solution A;

[0063] The reducing agent, seed crystals, and alkali are mixed and then added to water to obtain a highly dispersed mixed slurry B;

[0064] The highly dispersed slurry B is heated to boiling, and then solution A is added to the highly dispersed slurry B to form fluid micro-elements, so that solution A and highly dispersed slurry B react at the fluid micro-element interface. After further reaction, the product crystallizes and grows to obtain intermediate product C.

[0065] Intermediate product C was washed and calcined to obtain high-quality metallurgical grade chromium green.

[0066] Acidic solution A is obtained by adjusting the pH of a hexavalent chromium salt solution with sulfuric acid. Highly dispersed slurry B is obtained by adding seed crystals to an alkaline solution containing a reducing agent. Then, under boiling conditions, acidic solution A is added to highly dispersed slurry B, causing a reaction between solution A and highly dispersed slurry B at the fluid micro-element interface. This creates a localized high-temperature environment at the interface, effectively enhancing the diffusion of the reducing agent from highly dispersed slurry B into solution A. It also promotes the redox reaction between the reducing agent and the hexavalent chromium in the liquid film inside the fluid micro-element interface, generating trivalent chromium. The trivalent chromium then diffuses into highly dispersed slurry B and forms trivalent chromium. Chromium hydroxide is deposited and grown using the seed crystals in the highly dispersed mixed slurry B as the core, effectively avoiding the formation of a large number of ultrafine chromium hydroxide particles, thus obtaining a highly crystalline and large-particle chromium hydroxide intermediate product C. Due to the large grain size and high crystallinity of the chromium hydroxide intermediate product C, it is easy to wash with water to remove soluble salts adsorbed on its surface and fully wash away impurities such as sodium sulfate, significantly reducing the content of impurities such as sodium and sulfur. After high-temperature calcination, harmful impurities such as C and S are further reduced, ultimately yielding a high-value, high-quality metallurgical-grade chromium green product with good crystallinity, large particle size, high apparent density, and low carbon and sulfur content, which can be directly used as a high-quality metallurgical raw material.

[0067] The above preparation method also has the advantages of simple operation, mild conditions and easy industrial production.

[0068] When adding the reducing agent, seed crystals, and alkali to water, thorough stirring is required to obtain a highly dispersed mixed slurry B.

[0069] In some embodiments, the pH of the hexavalent chromium salt solution is adjusted to acidic using an acid.

[0070] In some embodiments, the hexavalent chromium salt solution is selected from at least one of chromate solution, dichromate solution, and chromic acid solution, or a corresponding solution prepared from solid chromate, solid dichromate, and chromic anhydride. It can be understood that the hexavalent chromium salt solution can be a chromate solution, such as sodium chromate solution, potassium chromate solution, etc., or a dichromate solution, such as sodium dichromate solution, potassium dichromate solution, etc., or a mixed solution of at least two of chromate solution, dichromate solution, and chromic acid solution, or a corresponding solution prepared by dissolving solid chromate, solid dichromate, or solid chromic anhydride.

[0071] For example, sulfuric acid is used to adjust the pH of the hexavalent chromium salt solution to below 1. The sulfuric acid can be dilute sulfuric acid, concentrated sulfuric acid, or other inorganic acids. Considering factors such as product quality, production process, equipment protection, and environmental protection, using concentrated sulfuric acid to adjust the pH of the hexavalent chromium salt solution is the best approach.

[0072] In some embodiments, in order to ensure the complete reaction of the reducing agent, the amount of reducing agent added is controlled to be the theoretical amount required for the reaction of hexavalent chromium to produce trivalent chromium.

[0073] In some embodiments, the amount of seed crystals added is 20% to 80% of the amount of chromium hydroxide generated in the reaction. Preferably, the amount of seed crystals added is 30% to 40% of the amount of chromium hydroxide generated in the reaction.

[0074] In some embodiments, in order to control the subsequent generation of chromium hydroxide, to effectively deposit and grow the crystals on the seed crystals, and to effectively control the particle size of the chromium hydroxide, the amount of alkali added is 90% to 99.9% of the theoretical amount for the reaction with the free acid in solution A and the generated chromium sulfate. That is, the amount of alkali added is slightly less than the theoretical amount for the alkali to completely react with the free acid in solution A and the generated chromium sulfate.

[0075] In some embodiments, the reducing agent is selected from thiosulfates or organic reducing agents.

[0076] For example, thiosulfate is selected from sodium thiosulfate.

[0077] For example, the organic reducing agent is selected from industrial glucose, methanol, or formaldehyde, etc.

[0078] In some embodiments, the seed crystals are selected from chromium hydroxide.

[0079] In some embodiments, sodium hydroxide is selected as the alkali based on considerations such as strong alkalinity, readily available raw materials, low price, no introduction of impurities, and high product purity.

[0080] In some embodiments, solution A is added to highly dispersed mixed slurry B, so that the two react at the fluid micro-element interface, and the reaction time at the fluid micro-element interface is controlled to be 0.5 to 1 hour, that is, the feeding time is controlled to be between 0.5 and 1 hour.

[0081] In some embodiments, after solution A is added to highly dispersed mixed slurry B, the reaction is continued for 1 to 5 hours to allow chromium hydroxide to deposit, crystallize and grow on the surface of the crystal nucleus.

[0082] For example, after solution A is added to highly dispersed mixed slurry B, the reaction continues for 2 to 3 hours, allowing chromium hydroxide to deposit, crystallize, and grow on the surface of the crystal nuclei.

[0083] In some embodiments, in order to ensure that hexavalent chromium is reduced to chromium hydroxide as completely as possible, solution A reacts with highly dispersed mixed slurry B at the fluid micro-element interface, and the pH value of the mixed slurry is between 4 and 6 when the reaction reaches its endpoint.

[0084] In some embodiments, solution A and highly dispersed mixed slurry B undergo an exothermic acid-base neutralization reaction at the fluid micro-element interface to form a local high-temperature environment in the interface region. This local high-temperature environment can enhance the diffusion of thiosulfate in highly dispersed mixed slurry B into solution A and promote the redox reaction between thiosulfate and hexavalent chromium to generate trivalent chromium. The trivalent chromium diffuses into highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the generated chromium hydroxide is deposited and grown with the seed crystals in highly dispersed mixed slurry B as the core, resulting in an intermediate product C with high crystallinity and large particles.

[0085] In some embodiments, in order to fully wash away soluble impurities on the surface of intermediate product C and to significantly reduce the content of impurities such as sodium and sulfur, the washing of intermediate product C is terminated when the conductivity of the washing water is ≤1 mS / cm.

[0086] In some embodiments, in order to further reduce harmful impurities such as carbon and sulfur, the washed intermediate product C is calcined at a temperature of 1200°C to 1500°C for a time of 0.5 to 3 hours.

[0087] For example, the calcination temperature is 1400℃ and the calcination time is 2h.

[0088] Actual testing revealed that the metallurgical-grade chromium green prepared by the above method has a purity of over 99.5% and a particle size D. 50 Above 20 μm, the bulk density is 1.8 g / cm³. 3 The carbon content is below 32 ppm and the sulfur content is below 28 ppm, which meets the quality requirements of high-quality metallurgical grade chromium green.

[0089] The metallurgical grade chromium green prepared by the above method can be used in the production of high-quality metallic chromium and refractory materials.

[0090] The preparation method of metallurgical grade chromium green of the present invention will be further described below with reference to specific embodiments.

[0091] Example 1

[0092] As shown in Figure 1, a method for preparing metallurgical grade chromium green includes the following steps:

[0093] S1. Dissolve 104g of sodium dichromate containing chromium (calculated as Cr) in water to prepare a solution containing 17g / L of chromium (calculated as Cr) (i.e., a hexavalent chromium salt solution). Then adjust the pH of the solution (i.e., the hexavalent chromium salt solution) to below 1 with sulfuric acid to obtain a sodium dichromate solution (i.e., solution A) with an acid value (428.2g of H2SO4) of approximately 70g / L.

[0094] S2. Based on the amount of hexavalent chromium contained in the sodium dichromate solution (i.e., solution A) obtained in S1, weigh 120g of sodium thiosulfate according to the chemical reaction formula of sodium thiosulfate; weigh 41.2g of chromium hydroxide according to the 20% seed coefficient ratio; weigh 320g of sodium hydroxide according to 97% of the theoretical amount required to produce chromium hydroxide by reacting with sulfuric acid and chromium sulfate in the sodium dichromate solution (i.e., formula (2) and formula (4));

[0095] S3. Mix 120g of sodium thiosulfate, 41.2g of chromium hydroxide and 320g of sodium hydroxide to obtain a mixture. Add the mixture to water under thorough stirring to prepare a solution of about 35 Baume degrees, and obtain a highly dispersed mixed slurry B.

[0096] S4. Under appropriate stirring conditions, the highly dispersed mixed slurry B is heated to boiling. Then, a sodium dichromate solution (i.e., solution A) is added to the highly dispersed mixed slurry B over 0.5–0.6 hours to form fluid micro-elements. This allows the sodium dichromate solution (i.e., solution A) and the highly dispersed mixed slurry B to undergo an exothermic acid-base neutralization reaction at the interface of the fluid micro-elements, creating a localized high-temperature environment at the interface. This localized high-temperature environment enhances the diffusion of sodium thiosulfate from the highly dispersed mixed slurry B into the sodium dichromate solution (i.e., solution A) and promotes the diffusion of sodium thiosulfate into the solution. Sodium sulfate reacts with hexavalent chromium in a redox reaction to produce trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the newly generated chromium hydroxide is deposited and grown with chromium hydroxide seed crystals in the highly dispersed mixed slurry B as the core, thus obtaining a highly crystalline and large-particle chromium hydroxide product. After the addition of the feed is completed, the reaction continues for 2 hours, allowing the chromium hydroxide to deposit, crystallize and grow. When the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6, which allows the hexavalent chromium to be completely reduced to chromium hydroxide. After filtration and separation, intermediate product C is obtained.

[0097] S5. Wash intermediate product C thoroughly with water to remove soluble salts adsorbed on the surface of intermediate product C. The washing is completed when the conductivity of the washing water is ≤1mS / cm. Then, calcine the washed intermediate product C at 1450℃ for 2.5h to obtain high-quality metallurgical grade chromium green product.

[0098] Example 2

[0099] As shown in Figure 1, a method for preparing metallurgical grade chromium green includes the following steps:

[0100] S1. Dissolve 104g of sodium dichromate containing chromium (calculated as Cr) in water to prepare a solution containing 17g / L of chromium (calculated as Cr) (i.e., a hexavalent chromium salt solution). Then adjust the pH of the solution (i.e., the hexavalent chromium salt solution) to below 1 with sulfuric acid to obtain a sodium dichromate solution (i.e., solution A) with an acid value (calculated as H2SO4) of about 70g / L.

[0101] S2. Based on the amount of hexavalent chromium contained in the sodium dichromate solution (i.e., solution A) obtained in S1, weigh 120g of sodium thiosulfate according to the chemical reaction formula of sodium thiosulfate; weigh 61.8g of chromium hydroxide according to the 30% seed coefficient ratio; weigh 320g of sodium hydroxide according to 97% of the theoretical amount required for the reaction of sulfuric acid and chromium sulfate in the sodium dichromate solution (i.e., formula (2) and formula (4)) to generate chromium hydroxide.

[0102] S3. Mix 120g of sodium thiosulfate, 61.8g of chromium hydroxide and 320g of sodium hydroxide to obtain a mixture. Add the mixture to water under thorough stirring to prepare a solution of about 35 Baume degrees, and obtain a highly dispersed mixed slurry B.

[0103] S4. Under appropriate stirring conditions, the highly dispersed mixed slurry B is heated to boiling. Then, a sodium dichromate solution (i.e., solution A) is added to the highly dispersed mixed slurry B over 0.6–0.7 hours to form fluid micro-elements. This allows the sodium dichromate solution (i.e., solution A) and the highly dispersed mixed slurry B to undergo an exothermic acid-base neutralization reaction at the interface of the fluid micro-elements, creating a localized high-temperature environment at the interface. This localized high-temperature environment enhances the diffusion of sodium thiosulfate from the highly dispersed mixed slurry B into the sodium dichromate solution (i.e., solution A) and promotes the diffusion of sodium thiosulfate into the solution. Sodium sulfate reacts with hexavalent chromium in a redox reaction to produce trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the newly generated chromium hydroxide is deposited and grown with chromium hydroxide seed crystals in the highly dispersed mixed slurry B as the core, thus obtaining a highly crystalline and large-particle chromium hydroxide product. After the addition of the feed is completed, the reaction continues for 3 hours, allowing the chromium hydroxide to deposit, crystallize and grow. When the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6, which allows the hexavalent chromium to be completely reduced to chromium hydroxide. After filtration and separation, intermediate product C is obtained.

[0104] S5. Wash intermediate product C thoroughly with water to remove soluble salts adsorbed on the surface of intermediate product C. The washing is completed when the conductivity of the washing water is ≤1mS / cm. Then, calcine the washed intermediate product C at 1450℃ for 2.5h to obtain high-quality metallurgical grade chromium green product.

[0105] Example 3

[0106] As shown in Figure 1, a method for preparing metallurgical grade chromium green includes the following steps:

[0107] S1. Dissolve 104g of sodium dichromate containing chromium (calculated as Cr) in water to prepare a solution containing 17g / L of chromium (calculated as Cr) (i.e., a hexavalent chromium salt solution). Then adjust the pH of the solution (i.e., the hexavalent chromium salt solution) to below 1 with sulfuric acid to obtain a sodium dichromate solution (i.e., solution A) with an acid value (calculated as H2SO4) of about 70g / L.

[0108] S2. Based on the amount of hexavalent chromium contained in the sodium dichromate solution (i.e., solution A) obtained in S1, weigh 120g of sodium thiosulfate according to the chemical reaction formula of sodium thiosulfate; weigh 82.4g of chromium hydroxide according to the 40% seed coefficient ratio; weigh 320g of sodium hydroxide according to 97% of the theoretical amount required for the reaction of sulfuric acid and chromium sulfate in the sodium dichromate solution (i.e., formula (2) and formula (4)) to generate chromium hydroxide.

[0109] S3. Mix 120g of sodium thiosulfate, 82.4g of chromium hydroxide and 320g of sodium hydroxide to obtain a mixture. Add the mixture to water under thorough stirring to prepare a solution of about 35 Baume degrees, and obtain a highly dispersed mixed slurry B.

[0110] S4. Under appropriate stirring conditions, the highly dispersed mixed slurry B is heated to boiling. Then, a sodium dichromate solution (i.e., solution A) is added to the highly dispersed mixed slurry B over 0.7–0.8 hours to form fluid micro-elements. This allows the sodium dichromate solution (i.e., solution A) and the highly dispersed mixed slurry B to undergo an exothermic acid-base neutralization reaction at the interface of the fluid micro-elements, creating a localized high-temperature environment at the interface. This localized high-temperature environment enhances the diffusion of sodium thiosulfate from the highly dispersed mixed slurry B into the sodium dichromate solution (i.e., solution A) and promotes the diffusion of sodium thiosulfate into the solution. Sodium sulfate reacts with hexavalent chromium in a redox reaction to produce trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the newly generated chromium hydroxide is deposited and grown with chromium hydroxide seed crystals in the highly dispersed mixed slurry B as the core, thus obtaining a highly crystalline and large-particle chromium hydroxide product. After the addition of the feed is completed, the reaction continues for 4 hours, allowing the chromium hydroxide to deposit, crystallize and grow. When the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6, which allows the hexavalent chromium to be completely reduced to chromium hydroxide. After filtration and separation, intermediate product C is obtained.

[0111] S5. Wash intermediate product C thoroughly with water to remove soluble salts adsorbed on the surface of intermediate product C. The washing is completed when the conductivity of the washing water is ≤1mS / cm. Then, calcine the washed intermediate product C at 1450℃ for 2.5h to obtain high-quality metallurgical grade chromium green product.

[0112] Example 4

[0113] As shown in Figure 1, a method for preparing metallurgical grade chromium green includes the following steps:

[0114] S1. Measure 1040 mL of a sodium dichromate acidification solution with a pH of 2.6-3, containing approximately 100 g / L of chromium (Cr) (i.e., a hexavalent chromium salt solution), and a sodium sulfate content of 120 g / L. Then adjust the pH of the solution (i.e., the hexavalent chromium salt solution) to below 1 with sulfuric acid to obtain a sodium dichromate solution (i.e., solution A) with an acid value (428.2 g of H2SO4) of approximately 411.7 g / L.

[0115] S2. Based on the amount of hexavalent chromium contained in the sodium dichromate solution (i.e., solution A) obtained in S1, weigh 120g of sodium thiosulfate according to the chemical reaction formula of sodium thiosulfate; weigh 123.6g of chromium hydroxide according to the 60% seed coefficient ratio; weigh 326.6g of sodium hydroxide according to 99% of the theoretical amount required for the reaction of sulfuric acid and chromium sulfate in the sodium dichromate solution (i.e., formula (2) and formula (4)) to generate chromium hydroxide;

[0116] S3. Mix 120g of sodium thiosulfate, 123.6g of chromium hydroxide and 326.6g of sodium hydroxide to obtain a mixture. Add the mixture to water under thorough stirring to prepare a solution with a Baume degree of about 35, and obtain a highly dispersed mixed slurry B.

[0117] S4. Under appropriate stirring conditions, the highly dispersed mixed slurry B is heated to boiling. Then, a sodium dichromate solution (i.e., solution A) is added to the highly dispersed mixed slurry B over 0.8–0.9 hours to form fluid micro-elements. This allows the sodium dichromate solution (i.e., solution A) and the highly dispersed mixed slurry B to undergo an exothermic acid-base neutralization reaction at the interface of the fluid micro-elements, creating a localized high-temperature environment at the interface. This localized high-temperature environment enhances the diffusion of sodium thiosulfate from the highly dispersed mixed slurry B into the sodium dichromate solution (i.e., solution A) and promotes the diffusion of sodium thiosulfate into the solution. Sodium sulfate reacts with hexavalent chromium in a redox reaction to produce trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the newly generated chromium hydroxide is deposited and grown with chromium hydroxide seed crystals in the highly dispersed mixed slurry B as the core, thus obtaining a highly crystalline and large-particle chromium hydroxide product. After the addition of the feed is completed, the reaction continues for 5 hours, allowing the chromium hydroxide to deposit, crystallize and grow. When the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6, which allows the hexavalent chromium to be completely reduced to chromium hydroxide. After filtration and separation, intermediate product C is obtained.

[0118] S5. Wash intermediate product C thoroughly with water to remove soluble salts adsorbed on the surface of intermediate product C. The washing is completed when the conductivity of the washing water is ≤1mS / cm. Then, calcine the washed intermediate product C at 1450℃ for 2.5h to obtain high-quality metallurgical grade chromium green product.

[0119] Example 5

[0120] As shown in Figure 1, a method for preparing metallurgical grade chromium green includes the following steps:

[0121] S1. Use 945 mL of sodium chromate solution (i.e., hexavalent chromium salt solution) with a chromium concentration (104 g as Cr) of about 110 g / L. Then adjust the pH of the solution (i.e., hexavalent chromium salt solution) to below 1 with sulfuric acid to obtain a sodium dichromate solution (i.e., solution A) with an acid value (428.2 g as H2SO4) of about 453 g / L.

[0122] S2. Based on the amount of hexavalent chromium contained in the sodium dichromate solution (i.e., solution A) obtained in S1, weigh 120g of sodium thiosulfate according to the chemical reaction formula of sodium thiosulfate; weigh 164.8g of chromium hydroxide according to the 80% seed coefficient ratio; weigh 303.5g of sodium hydroxide according to 92% of the theoretical amount required for the reaction of sulfuric acid and chromium sulfate in the sodium dichromate solution (i.e., formula (2) and formula (4)) to generate chromium hydroxide.

[0123] S3. Mix 120g of sodium thiosulfate, 164.8g of chromium hydroxide and 303.5g of sodium hydroxide to obtain a mixture. Add the mixture to water under thorough stirring to prepare a solution with a Baume degree of about 35, and obtain a highly dispersed mixed slurry B.

[0124] S4. Under appropriate stirring conditions, the highly dispersed mixed slurry B is heated to boiling. Then, a sodium dichromate solution (i.e., solution A) is added to the highly dispersed mixed slurry B over 0.9–1 hour to form fluid micro-elements. This allows the sodium dichromate solution (i.e., solution A) and the highly dispersed mixed slurry B to undergo an exothermic acid-base neutralization reaction at the interface of the fluid micro-elements, creating a localized high-temperature environment at the interface. This localized high-temperature environment enhances the diffusion of sodium thiosulfate from the highly dispersed mixed slurry B into the sodium dichromate solution (i.e., solution A) and promotes the diffusion of sodium thiosulfate into the sodium dichromate solution (i.e., solution A). Sodium reacts with hexavalent chromium in a redox reaction to produce trivalent chromium. The trivalent chromium diffuses into the highly dispersed mixed slurry B and generates chromium hydroxide. At the same time, the newly generated chromium hydroxide is deposited and grown with chromium hydroxide seed crystals in the highly dispersed mixed slurry B as the core, thus obtaining a highly crystalline and large-particle chromium hydroxide product. After the addition of the feed is completed, the reaction continues for 1.5 hours to allow the chromium hydroxide to deposit, crystallize and grow. When the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6, which allows the hexavalent chromium to be completely reduced to chromium hydroxide. After filtration and separation, intermediate product C is obtained.

[0125] S5. Wash intermediate product C thoroughly with water to remove soluble salts adsorbed on the surface of intermediate product C. The washing is completed when the conductivity of the washing water is ≤1mS / cm. Then, calcine the washed intermediate product C at 1450℃ for 2.5h to obtain high-quality metallurgical grade chromium green product.

[0126] Comparative Example 1

[0127] Chromium green products commercially available via the sulfur process.

[0128] Comparative Example 2

[0129] Chromium green products commercially available via the ordinary ammonium process.

[0130] Detection and Analysis

[0131] 1) Purity testing of chrome green products

[0132] The purity of chromium trioxide in the chromium green products of Examples 1 to 5, as well as Control Examples 1 and 2, was tested according to the HGT 2775-2010 industry standard. The test results are shown in Table 1.

[0133] Table 1. Purity test results of chrome green products

[0134]

[0135] 2) Particle size D of chrome green products 50 Detection

[0136] The particle size D of the chrome green products in Examples 1 to 5, as well as Control Examples 1 and 2, was determined using a Malvern laser particle size analyzer APA-2000. 50 The test results are shown in Figures 2 to 6 and Table 2.

[0137] Table 2 Particle size D of Chrome Green products 50 Test results

[0138]

[0139] 3) Bulk density testing of chrome green products

[0140] The specific operation is as follows: Weigh about 100g of the chromium green product from Examples 1 to 5, as well as Control Examples 1 and 2, accurate to 0.02g, and place it in a 100mL graduated cylinder. Place the graduated cylinder containing the sample on a table (the table is covered with a rubber pad about 5mm thick) and let it fall from a height of about 2cm onto the table. Repeat this operation several times until the volume reading remains unchanged, and record the sample volume V.

[0141] Result Calculation

[0142] Bulk density ρ (g / cm³) 3 ), calculate according to the following formula

[0143] ρ=m / V

[0144] In the formula: V—the volume occupied by the sample in the graduated cylinder, cm³ 3;

[0145] m — mass of the sample, in grams.

[0146] The test results are shown in Table 3.

[0147] Table 3. Bulk density test results of chrome green products

[0148]

[0149] 4) Detection of carbon content in chrome green products

[0150] The specific operation is as follows: Follow the operating procedures of the infrared carbon-sulfur analyzer. Specifically, weigh approximately 0.2g of the chromium green product from Examples 1 to 5, and Control Examples 1 and 2, accurate to 0.0001g, and place it in a porcelain crucible preheated to constant weight at 1200℃. Heat and burn the crucible in an oxygen stream within a high-frequency induction furnace to fully oxidize sulfur and carbon, generating sulfur dioxide and carbon dioxide. These are then passed into the infrared measuring cell along with the oxygen. Sulfur dioxide and carbon dioxide absorb energy as they pass through the infrared measuring cell. The concentrations of sulfur dioxide and carbon dioxide are measured based on the energy changes received by the detector. The instrument is calibrated using standard samples (or reference materials) with known sulfur and carbon contents, directly displaying the percentage content of sulfur and carbon. The detection results are shown in Tables 4 and 5.

[0151] Table 4. Detection results of carbon content in chrome green products.

[0152]

[0153] Table 5. Detection results of sulfur content in chrome green products.

[0154]

[0155] 5) Detection of hexavalent chromium content in chrome green products

[0156] The specific operation is as follows: Weigh 0.10g of the chromium green product from Examples 1 to 5, as well as from Control Examples 1 and 2, accurate to 0.0001g. Place the sample in a 30mL silver crucible, add about 0.2g of potassium nitrate and 2.0g of sodium hydroxide, cover with the silver crucible lid, and melt in a high-temperature furnace at 600-650℃ for 10min. Remove and cool to obtain the melt.

[0157] Place the molten material in a 250mL PTFE beaker, add 80-100mL of boiling water to leach out the molten material, wash the crucible and lid with hot water, transfer it to a 500mL Erlenmeyer flask, add 20mL of sulfuric acid (water to concentrated sulfuric acid volume ratio of 1:1), 5mL of phosphoric acid (concentration of 1.70g / mL), and 10mL of silver nitrate solution (concentration of 25g / L), and adjust the volume to about 130mL;

[0158] Add 4-5g of ammonium persulfate (analytical grade), heat to boiling until large bubbles appear in the solution, continue boiling for 2-3 minutes, remove and cool slightly, add 5mL of sodium chloride solution (concentration of 5%), boil for 5 minutes, remove and cool to room temperature;

[0159] Titrate with ferrous ammonium sulfate standard solution (C[(NH4)2Fe(SO4)2·6H2O] = 0.2 mol / L) until the solution changes from orange-yellow to yellow-green. Add 1 mL of phenyl-o-aminobenzoic acid solution (concentration 1 g / L) and continue titrating until the solution changes from purple-red to green, which is the endpoint.

[0160] The chromium trioxide content, expressed as the quality inspection score w1 of chromium trioxide (Cr2O3), is calculated using the following formula:

[0161]

[0162] Where: V—the volume of ferrous ammonium sulfate standard titration solution consumed in the titration test solution, mL;

[0163] c—The actual concentration of the ferrous ammonium sulfate standard titration solution, in mol / L;

[0164] m—sample mass, g;

[0165] M – The numerical value of the molar mass of chromium trioxide (1 / 6Cr2O3), in grams per mole (g / mol) (M = 25.33).

[0166] The arithmetic mean of the parallel measurement results shall be taken as the measurement result, and the absolute difference between two parallel measurement results shall not be greater than 0.2%.

[0167] The detection and calculation results are shown in Table 6.

[0168] Table 6. Detection results of sulfur content in chrome green products.

[0169]

[0170] A comprehensive analysis of Tables 1 to 6 shows that the purity and particle size D of the metallurgical-grade chromium green product obtained by the method of this invention are... 50The purity and particle size of the metallurgical grade chromium green produced by the method of the present invention are greater than those produced by the ordinary ammonium method and the traditional sulfur method. At the same time, the metallurgical grade chromium green product produced by the method of the present invention has a higher apparent density and lower carbon, sulfur impurities and hexavalent chromium content. This proves that the quality of the metallurgical grade chromium green product produced by the method of the present invention is greatly improved compared with the ordinary ammonium method and the traditional sulfur method. Practical application shows that the metallurgical grade chromium green product produced by the method of the present invention is a high-quality metallurgical grade chromium green.

[0171] In summary, the method for preparing metallurgical-grade chromium green of the present invention involves adjusting the pH of a hexavalent chromium salt solution with sulfuric acid to obtain an acidic solution A. Seed crystals are then added to an alkaline solution containing a reducing agent to obtain a highly dispersed mixed slurry B. Under boiling conditions, the acidic solution A is fed into the highly dispersed mixed slurry B, causing a reaction between solution A and the highly dispersed mixed slurry B at the fluid micro-element interface. This creates a localized high-temperature environment at the interface, effectively enhancing the diffusion of the reducing agent from the highly dispersed mixed slurry B into solution A. Furthermore, it promotes the redox reaction between the reducing agent and the hexavalent chromium in the liquid film inside the fluid micro-element interface to generate trivalent chromium. The trivalent chromium then diffuses into the highly dispersed mixed slurry B and generates hydroxide. Meanwhile, the newly generated chromium hydroxide is deposited and grown using the seed crystals in the highly dispersed mixed slurry B as the core, effectively avoiding the formation of a large number of ultrafine chromium hydroxide particles, thus obtaining a highly crystalline and large-particle chromium hydroxide intermediate product C. Due to the large grain size and high crystallinity of the chromium hydroxide intermediate product C, it is easy to wash away impurities with water, thoroughly removing impurities such as sodium sulfate, and significantly reducing the content of impurities such as sodium and sulfur. After high-temperature calcination, harmful impurities such as C and S are further reduced, ultimately yielding a high-quality metallurgical grade chromium green product with good crystallinity, large particle size, high apparent density, and low carbon and sulfur content. It can be directly used as a high-quality metallurgical raw material and has the advantages of simple operation, mild conditions, and ease of industrial production. It has promotion and application value in the field of chemical product production technology.

[0172] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing metallurgical-grade chromium green, characterized in that, Includes the following steps: The pH of the hexavalent chromium salt solution is adjusted to acidity to obtain solution A. A reducing agent, seed crystals, and alkali are mixed and added to water to obtain a highly dispersed slurry B. The reducing agent is selected from thiosulfate or an organic reducing agent; the seed crystals are selected from chromium hydroxide; the alkali is selected from sodium hydroxide; the amount of reducing agent added is the theoretical amount required for the reaction of hexavalent chromium to trivalent chromium; the amount of seed crystals added is 20%–80% of the amount of chromium hydroxide produced; the amount of alkali added is 90%–99.9% of the theoretical amount required for the reaction with the free acid and the generated chromium sulfate in solution A. The highly dispersed slurry B is heated to boiling, and then solution A is added to the highly dispersed slurry B at a uniform rate to form fluid micro-elements, allowing solution A and the highly dispersed slurry B to react at the fluid micro-element interface to obtain intermediate product C. Intermediate product C was washed and calcined to obtain high-quality metallurgical grade chromium green.

2. The method for preparing metallurgical-grade chromium green according to claim 1, characterized in that, The pH of the hexavalent chromium salt solution is adjusted to acidic using an acid; and / or, the hexavalent chromium salt solution is selected from at least one of chromate solution, dichromate solution, and chromic acid solution; and / or, the pH of the hexavalent chromium salt solution is adjusted to below 1 using sulfuric acid.

3. The method for preparing metallurgical-grade chromium green according to claim 1, characterized in that, Solution A is added to highly dispersed mixed slurry B to form fluid micro-elements, and the reaction time at the fluid micro-element interface is controlled, i.e., the feeding time is controlled between 0.5 and 1 hour; and / or, after solution A is added to highly dispersed mixed slurry B, the reaction is continued to be stirred for 1 to 5 hours to allow chromium hydroxide to crystallize and grow; and / or, solution A and highly dispersed mixed slurry B react at the fluid micro-element interface to allow chromium hydroxide to crystallize and grow, and when the reaction reaches the endpoint, the pH value of the mixed slurry is between 4 and 6.

4. The method for preparing metallurgical-grade chromium green according to claim 1, characterized in that, The solution A and the highly dispersed slurry B undergo an exothermic acid-base neutralization reaction at the fluid micro-element interface to form a local high-temperature environment in the interface region. This local high-temperature environment can enhance the diffusion of the reducing agent in the highly dispersed slurry B into the solution A and promote the redox reaction between the reducing agent and hexavalent chromium to generate trivalent chromium. The trivalent chromium diffuses into the highly dispersed slurry B and generates chromium hydroxide. At the same time, the generated chromium hydroxide is deposited and grown with the seed crystals in the highly dispersed slurry B as the core, resulting in an intermediate product C with high crystallinity and large particles.

5. The method for preparing metallurgical-grade chromium green according to claim 1, characterized in that, The intermediate product C is washed until the conductivity of the washing water is ≤1 mS / cm; and / or the calcination temperature is 1200℃~1500℃ and the calcination time is 0.5~3h.

6. A metallurgical grade chromium green prepared by the preparation method according to any one of claims 1 to 5.

7. The metallurgical grade chromium green according to claim 6, characterized in that, The metallurgical-grade chromium green has a purity of over 99.5% and a particle size D. 50 Above 22 μm, the bulk density is 1.8 g / cm³. 3 The carbon content is below 32 ppm and the sulfur content is below 28 ppm.

8. An application of the metallurgical-grade chromium green prepared by the method according to any one of claims 1 to 5, characterized in that, The metallurgical-grade chromium green is used in the production of high-quality metallic chromium and refractory materials.

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