Method and system for recovering chromium and aluminum from waste chromium catalyst

Abstract

The invention provides a method and a system for recovering chromium and aluminum from a waste chromium catalyst. The method comprises the following steps: carrying out alkali fusion reaction on the waste chromium catalyst and sodium hydroxide to obtain alkali fusion clinker; mixing the alkali fusion clinker with water, pulping, leaching, and carrying out solid-liquid separation to obtain a water leaching solution containing Na2CrO4 and NaAlO2 and a filter cake containing Al2O3; adding a barium salt solution or solid into the aqueous extract containing Na2CrO4 and NaAlO2, reacting to generate a BaCrO4 precipitate, and carrying out solid-liquid separation to obtain a BaCrO4 filter cake and a sodium metaaluminate filtrate; reacting the BaCrO4 filter cake with an inorganic acid, and carrying out solid-liquid separation to obtain a chromic acid solution and a barium sulfate precipitate; and adding an acid solution into the sodium metaaluminate filtrate, adjusting the pH value to 7-8, and carrying out solid-liquid separation to obtain an Al (OH) 3 filter cake. According to the method, Cr (III) in the waste catalyst is directionally converted into Cr (VI) through an alkali fusion oxidation process, then the solubility difference of sodium chromate and sodium metaaluminate in an aqueous solution is fully utilized, the high-selectivity separation characteristic of barium chromate precipitation is combined, the chromium-aluminum separation problem is fundamentally solved, and the finally obtained product is excellent in purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a method and system for recovering chromium and aluminum from waste chromium catalysts. BACKGROUND

[0003] The traditional waste chromium catalyst treatment method is mainly safe landfill, which not only has potential environmental risks, but also causes great waste of valuable metal resources such as chromium and aluminum. Therefore, developing a recovery technology that can realize the harmless and resource utilization of waste chromium catalysts has urgent environmental significance and significant economic value.

[0004] At present, the research on the recovery technology of waste chromium catalysts mainly includes pyrometallurgy and hydrometallurgy. Pyrometallurgy usually involves high-temperature reduction smelting, which not only has high energy consumption, but also is difficult to realize efficient separation of chromium and aluminum; hydrometallurgy mainly transfers metal components to the solution through acid leaching or alkali leaching, and then separates and purifies them, but the existing hydrometallurgical process still has many bottlenecks: first, the acid leaching method needs to use strong acid (such as sulfuric acid), which can cause chromium and aluminum to be dissolved synchronously, not only the solution separation and purification steps are complicated, but also the equipment is seriously corroded; second, the conventional alkali leaching method only uses sodium carbonate or sodium hydroxide solution for leaching, because trivalent chromium is difficult to be effectively extracted in mild alkali solution, the leaching efficiency of Cr2O3 is low; third, chromium and aluminum have similar chemical properties, the separation factor is small, and cross contamination of products is easy to cause, so the purity is difficult to guarantee; fourth, the process flow is long, and multi-step extraction, ion exchange or precipitation operation not only increases the process complexity, but also increases the processing cost.

[0005] Therefore, there is an urgent need in the art for a new recovery process with short process, high separation efficiency, good product purity and environmental friendliness. SUMMARY

[0006] The present application provides a method and system for recovering chromium and aluminum from waste chromium catalysts to solve the problems of long treatment process, low separation efficiency and low product purity in the prior art.

[0007] The technical method of the present application is as follows: A method for recovering chromium and aluminum from waste chromium catalysts, the method comprising the following steps: S1, alkali fusion reaction of waste chromium catalyst and sodium hydroxide to obtain alkali fusion clinker; wherein the alkali fusion reaction converts Cr2O3 in the waste chromium catalyst into Na2CrO4 and Al2O3 into NaAlO2; S2, mixing, beating, leaching and solid-liquid separation of the alkali fusion clinker and water to obtain a water leaching solution containing Na2CrO4, NaAlO2 and an Al2O3-containing filter cake; S3, adding barium salt solution or solid to the Na2CrO4 and NaAlO2 containing water leaching solution to generate BaCrO4 precipitate, solid-liquid separation, obtaining BaCrO4 filter cake and sodium metaaluminate filtrate; S4, reacting BaCrO4 filter cake with inorganic acid, solid-liquid separation, obtaining chromic acid solution and barium sulfate precipitate; adding acid solution to the sodium metaaluminate filtrate, adjusting pH to 7-8, solid-liquid separation, obtaining Al(OH)3 filter cake.

[0008] Optionally, in the S1 step, the particle size of the waste chromium catalyst is not less than 200 mesh; the mass ratio of the waste chromium catalyst to sodium hydroxide is 1:2-4. The conditions of the alkali fusion reaction are: the alkali fusion oxidation reaction is carried out in air at a temperature of 500-550℃, and the holding time is 1-2 hours.

[0009] Optionally, in the S2 step, the liquid-solid mass ratio of the alkali fusion clinker to water is 10-20:1, and in the S2 step, the leaching temperature is 85-95℃, and the leaching time is 2.5-3 hours.

[0010] Optionally, in the S3 step, the barium salt is barium chloride, the reaction temperature for generating BaCrO4 precipitate is 85-95℃, and the reaction time is 2.5-3 hours.

[0011] Optionally, in the S4 step, the inorganic acid is sulfuric acid with a concentration of 30%-40%, the reaction temperature of BaCrO4 filter cake with inorganic acid is 85-95℃, the reaction time is 1.5-2 hours, and the mass concentration of the chromic acid solution is 10%-35%. In the S4 step, the acid solution is sulfuric acid, and the Al(OH)3 filter cake is dried by flash drying to obtain a powder product.

[0012] Optionally, the Al2O3 containing filter cake and BaCrO4 filter cake generated after the solid-liquid separation of the S2 and S3 steps are treated by countercurrent washing.

[0013] Optionally, before the S1 step, it further includes: screening and ball milling the waste chromium catalyst to obtain waste chromium catalyst powder.

[0014] The application also provides a system for recovering chromium and aluminum from waste chromium catalyst, which comprises: a mixing and alkali melting unit for mixing the waste chromium catalyst with sodium hydroxide and reacting in a rotary kiln to obtain alkali melting clinker; a water immersion and solid-liquid separation unit for mixing and beating the alkali melting clinker with water, leaching, solid-liquid separation, obtaining Na2CrO4-containing water immersion liquid, NaAlO2-containing water immersion liquid and Al2O3-containing filter cake; a chromium precipitation and acidification unit for adding a barium salt solution or solid to the Na2CrO4-containing water immersion liquid and NaAlO2-containing water immersion liquid, reacting to generate BaCrO4 precipitate, solid-liquid separation, obtaining BaCrO4 filter cake and sodium aluminate filtrate, reacting the BaCrO4 filter cake with an inorganic acid, solid-liquid separation, obtaining chromic acid solution and barium sulfate precipitate; and an aluminum precipitation unit for reacting the BaCrO4 filter cake with an inorganic acid, solid-liquid separation, obtaining chromic acid solution and barium sulfate precipitate.

[0015] The application has the following advantages: I. The application realizes efficient and selective separation of chromium and aluminum: the application converts Cr(III) in the waste catalyst into Cr(VI) through an alkali melting oxidation process, then fully utilizes the solubility difference between sodium chromate and sodium aluminate in aqueous solution, and combines the high selective separation characteristics of barium chromate precipitation, thus fundamentally solving the separation problem of chromium and aluminum, and finally obtaining products with excellent purity.

[0016] II. The process flow of the application has high integration degree, is short and efficient, and has significant resource value: the application integrates the dispersed multi-step leaching, purification and conversion units in the traditional process into a simple flow of "alkali melting-water immersion-chromium precipitation-acidification", which greatly reduces equipment investment and operation steps and improves production efficiency. At the same time, the resource utilization degree is high and the product added value is outstanding: the final products are chromic acid and aluminum hydroxide, both of which are chemical raw materials with large market demand and high economic value, and compared with the traditional process of recovering metal elements or low added value intermediate chemicals, the economic benefit is significantly improved; in addition, the barium sulfate produced in the process can be recovered as a byproduct, realizing the comprehensive conversion and resource utilization of each component in the waste catalyst.

[0017] III. The application is environmentally friendly and clean production: the process blocks the leaching risk of hexavalent chromium from the source, and fundamentally reduces the environmental hazards. At the same time, the countercurrent washing technology is used in the process, which greatly reduces the wastewater discharge and fresh water consumption, and no toxic and harmful substances are produced throughout the process, which meets the development principles of green chemistry and clean production.

[0018] IV. Energy consumption and cost advantage of the present application: the alkali fusion reaction temperature of the present application is moderate, far lower than the pyrometallurgical process, and the energy consumption is significantly reduced; in addition, the process flow is short, further reducing the overall material consumption and energy consumption. In addition, the equipment used in the process are conventional chemical equipment such as reaction kettles and filter machines, without the need to use special corrosion-resistant materials, greatly reducing the equipment investment and long-term operation and maintenance costs, and having strong industrial application feasibility. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A flow chart of the preparation method of the present application is shown; Figure 2 A schematic diagram of the system of the present application is shown. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described below clearly and completely. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] The present application provides a method for recovering chromium and aluminum from waste chromium catalyst, as shown in Figure 1 The method comprises the following steps: S1, alkali fusion reaction of waste chromium catalyst with sodium hydroxide to obtain alkali fusion clinker; wherein the alkali fusion reaction converts Cr2O3 in the waste chromium catalyst into Na2CrO4 and Al2O3 into NaAlO2.

[0022] In this embodiment, the typical composition of the waste chromium catalyst is: Cr2O3 10-20%, Al2O3 80-85%, and a small amount of carbon deposition and alkali metals.

[0023] In this embodiment, before the S1 step, it also includes: screening and ball milling the waste chromium catalyst to obtain waste chromium catalyst powder. The particle size of the waste chromium catalyst is not less than 200 mesh to increase its specific surface area and improve the reaction activity.

[0024] In this embodiment, the mass ratio of the waste chromium catalyst to sodium hydroxide is 1:2~4.

[0025] In this embodiment, the alkali fusion reaction uses a rotary kiln, and the conditions of the alkali fusion reaction are: alkali fusion oxidation reaction in air at a temperature of 500~550℃, and the holding time is 1~2 hours.

[0026] The chemical reaction of the S1 step is: 2Cr2O3+8NaOH+3O2→4Na2CrO4+4H2O This reaction will oxidize insoluble trivalent chromium oxide to water-soluble sodium chromate.

[0027] Al2O3 + 2NaOH → 2NaAlO2 + H2O This reaction converts the carrier alumina into sodium metaaluminate.

[0028] C + O2→ CO2↑ and CmHn+ O2→ CO2↑ + H2O↑ This process removes both carbon and organic matter from the surface of the catalyst.

[0029] S2, mix the alkali fusion clinker with water, pulp, leaching, solid-liquid separation, to obtain a water leaching solution containing Na2CrO4, NaAlO2, and an Al2O3-containing filter cake.

[0030] In this embodiment, the liquid-solid mass ratio of the alkali fusion clinker and water is 10-20:1. Specifically, the pulp is prepared in a dispersing tank, and the leaching is performed in a water leaching kettle.

[0031] In this embodiment, the leaching temperature is 85-95°C, and the leaching time is 2.5-3 hours. Specifically, the pulp is prepared in hot water at 85-95°C, and the mass ratio of water to clinker (liquid-solid ratio) is controlled to be 2:1 to 5:1. Then the slurry is pumped into the water leaching kettle, water is added to make the final liquid-solid ratio reach 10:1 to 20:1, and the reaction is kept for 2.5-3 hours under stirring and heat preservation, so that Na2CrO4 is fully dissolved.

[0032] In this embodiment, the filtrate (water leaching solution) is a solution mainly containing Na2CrO4 and NaAlO2, which is sent to the chromium precipitation process. The filter cake is a solid of unreacted Al2O3 and a small amount of wrapped chromate. The filter cake is washed with clean water using countercurrent washing technology, and the thickest washing solution is returned to the water leaching process, so as to improve the recovery rate of chromium and reduce the amount of new water. The chromium content of the filter cake after washing is analyzed, and if the chromium content is still high, it can be returned to the alkali fusion step.

[0033] S3, add a barium salt solution or solid to the water leaching solution containing Na2CrO4 and NaAlO2, react to generate BaCrO4 precipitate, and solid-liquid separation to obtain BaCrO4 filter cake and sodium metaaluminate filtrate.

[0034] In this embodiment, a reaction kettle is used for the reaction. The barium salt is barium chloride. The reaction temperature for generating BaCrO4 precipitate is 85-95°C, and the reaction time is 2.5-3 hours. Specifically, the above water leaching solution is pumped into the reaction kettle, barium chloride (BaCl2·2H2O) solid or saturated solution is slowly added under the conditions of 85-95°C and stirring, and the reaction is kept for 2.5-3 hours. The following precipitation reaction occurs: BaCrO4 + BaCl2→ BaCrO4↓ (yellow) + 2NaCl Barium chromate (BaCrO4) has very low solubility (Ksp≈1.2×10 -10 ), which can realize high selective precipitation of chromium. After the reaction is completed, the second solid-liquid separation is performed.

[0035] The separation result is that the filter cake is yellow BaCrO4precipitate, which is washed by countercurrent washing with pure water and then enters the acidification process. The filtrate is a solution mainly containing NaAlO2and NaCl, which is sent to the aluminum precipitation process.

[0036] In this embodiment, the BaCrO4filter cake produced after the solid-liquid separation of the S3 step is treated by countercurrent washing.

[0037] S4, the BaCrO4filter cake is reacted with an inorganic acid, solid-liquid separation is performed, and a chromic acid solution and a barium sulfate precipitate are obtained; acid liquid is added to the sodium metaaluminate filtrate, the pH is adjusted to 7-8, solid-liquid separation is performed, and an Al(OH)3filter cake is obtained.

[0038] In this embodiment, the inorganic acid is sulfuric acid, and the concentration is 30%-40%. The temperature for the reaction of the BaCrO4filter cake with the inorganic acid is 85-95°C, and the reaction time is 1.5-2 hours. Specifically, the washed BaCrO4filter cake is placed in an acid-resistant reactor, and a sulfuric acid solution with a concentration of 30%-40% (preferably 34%) is added under stirring and at a temperature of 85-95°C. The reaction is performed for 1.5-2 hours, and a double decomposition reaction occurs: BaCrO4+ H2SO4→ BaSO4↓ (white) + H2CrO4 The solubility of barium sulfate (BaSO4) (Ksp≈1.1×10 -10 ) is even lower, and the reaction is driven to the right to be complete. After the reaction is completed, the third solid-liquid separation is performed.

[0039] The separation result is that the filtrate is the target product, a chromic acid (H2CrO4) solution, and the concentration can be adjusted to 10%-35% by controlling the amount of acid added and the amount of washing water, and the solution is stored in a chromic acid intermediate tank. The filter cake is a byproduct, barium sulfate, which is washed and sold as an industrial raw material or used in building materials.

[0040] In this embodiment, the acid liquid is sulfuric acid, and the Al(OH)3filter cake is dried by flash drying to obtain a powder product. Specifically, the sodium metaaluminate filtrate produced after the chromium precipitation is transferred to a neutralization reactor, and a sulfuric acid solution with a concentration of 30%-40% is slowly added under stirring, and the end point pH value is precisely controlled to be between 7 and 8. At this time, the sodium metaaluminate undergoes a hydrolysis precipitation reaction: 2NaAlO2+ H2SO4+ 2H2O→ Na2SO4+ 2Al(OH)3↓ At the same time, a small amount of free NaOH remaining in the filtrate is also neutralized. After the reaction is completed, a fourth solid-liquid separation is performed, and the filter cake is a white aluminum hydroxide precipitate. After the filter cake is washed with pure water, it is sent to a flash dryer, and after drying, a high-purity aluminum hydroxide (Al(OH)3) powder product is obtained. The filtrate is mainly a sodium sulfate solution, which can be recovered as sodium sulfate by evaporation crystallization or sent to a sewage treatment station.

[0041] The present application also provides a system for recovering chromium and aluminum from waste chromium catalyst, comprising: a mixing and alkali melting unit for mixing the waste chromium catalyst with sodium hydroxide and reacting in a rotary kiln to obtain an alkali melting clinker; a water immersion and solid-liquid separation unit for mixing and beating the alkali melting clinker with water, leaching, and solid-liquid separation to obtain a water leaching solution containing Na2CrO4 and NaAlO2 and a filter cake containing Al2O3; a chromium precipitation and acidification unit for adding a barium salt solution or solid to the water leaching solution containing Na2CrO4 and NaAlO2 to react to generate a BaCrO4 precipitate, and solid-liquid separation to obtain a BaCrO4 filter cake and a sodium metaaluminate filtrate, and reacting the BaCrO4 filter cake with an inorganic acid to obtain a chromic acid solution and a barium sulfate precipitate; and an aluminum precipitation unit for reacting the BaCrO4 filter cake with an inorganic acid to obtain a chromic acid solution and a barium sulfate precipitate.

[0042] In the present embodiment, the system further comprises a pretreatment unit for screening and ball milling the waste chromium catalyst.

[0043] Specifically, as shown in Figure 2 The mixing and alkali melting unit uses a mixer and a rotary kiln. The water immersion and solid-liquid separation unit uses a dispersing tank, a water immersion kettle, and a 1# filter-washing integrated machine. The chromium precipitation and acidification unit uses a reaction kettle and a 2# filter-washing integrated machine. The aluminum precipitation unit uses an acidification device (for sodium metaaluminate acidification), a belt filter, and a flash drying device (for flash drying).

[0044] In the present application, all the preparation raw materials are commercially available products well known to those skilled in the art unless otherwise specified.

[0045] The present application is described in detail below through examples and experimental examples. However, these are only examples and do not limit the present application in any form.

[0046] Example 1 The present embodiment provides a method for recovering chromium and aluminum from waste chromium catalyst, comprising the following steps: (1) Pretreatment Take 1.0 tons of waste chromium catalyst (dry basis) from a certain PDH device, and analyze that the Cr2O3 content is 15.2% and the Al2O3 content is 82.5%. Crush and grind it to pass through a 200-mesh screen.

[0047] (2) Alkali melting and oxidation The waste chromium catalyst of the PDH device passing through a 200-mesh screen was mixed with 2.8 tons of solid sodium hydroxide, and then was sent into a rotary kiln and was calcined at 520°C for 1.5 hours to obtain an alkali melting clinker.

[0048] (3) Water immersion and solid-liquid separation The alkali melting clinker obtained in step (2) was slurried (3 tons of water was added) at 90°C, and then was transferred into a water immersion kettle, water was added to a total amount of 15 tons, and was kept at 90°C for 3 hours of stirring and immersion. After pressure filtration, 13.5 tons of a water immersion liquid (containing Cr ~12.5 g / L) and an aluminum-containing filter cake were obtained. 3 (4) Precipitation and acidification conversion of chromium, and recovery of aluminum

[0049] (4) Precipitation and acidification conversion of chromium, and recovery of aluminum The precipitation and acidification conversion of chromium included that 1.1 tons of barium chloride dihydrate was added into the water immersion liquid obtained in step (3) at 90°C, and was reacted for 3 hours. After filtration, about 0.98 tons of a barium chromate wet filter cake (calculated on a dry basis) and a sodium metaaluminate filtrate were obtained. After the barium chromate filter cake was washed with pure water, 0.65 tons of 34% sulfuric acid was added into a reaction kettle, and was reacted for 2 hours at 90°C. After filtration, about 1.2 tons of a chromium acid solution with a concentration of 10%~25% (calculated on H2CrO4) and about 0.95 tons of a barium sulfate wet cake were obtained.

[0050] The recovery of aluminum included that the sodium metaaluminate filtrate after chromium precipitation was slowly neutralized to pH=7.5 with 34% sulfuric acid under stirring to precipitate aluminum hydroxide. After filtration and washing, the wet filter cake was dried by flash drying to obtain about 0.78 tons of white and loose aluminum hydroxide powder.

[0051] It was calculated that the recovery rate of chromium was ≥92% and the recovery rate of aluminum was ≥88% in the embodiment. The chromium acid solution product met the industrial grade standard, and the aluminum hydroxide product reached the chemical raw material grade.

[0052] The method provided by the application successfully converts the hazardous waste waste chromium catalyst into chromium acid and aluminum hydroxide products with high economic value, the process route is reasonable, the technology is feasible, the separation effect is good, the environmental and economic benefits are significant, and a reliable technical scheme is provided for large-scale industrial application.

[0053] Various embodiments of the application can take form in a range of permutations; it is to be understood that the description in the form of a range is used merely for the sake of convenience and brevity, and should not be construed as a strict limitation of the scope of the application; therefore, it is to be understood that the description of a range has specifically disclosed all possible sub-ranges as well as individual numerical values within that range. For example, a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within the range, for example 1, 2, 3, 4, 5, and 6, regardless of the boundaries of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any cited number(s) within the specified range (fractional or integral).

[0054] While the embodiments of the application have been shown and described, it is to be understood that the embodiments described are only by way of example and are not limiting of the scope of the application. Accordingly, many modifications, well known per se to those skilled in the art, can be made without departing from the spirit and scope of the application, which is limited only by the scope of the appended claims and their equivalents.

Claims

1. A method for recovering chromium and aluminum from spent chromium catalyst, characterized in that, The method includes the following steps: S1. The waste chromium catalyst is subjected to an alkaline fusion reaction with sodium hydroxide to obtain alkaline fused clinker; wherein, the alkaline fusion reaction converts Cr2O3 in the waste chromium catalyst into Na2CrO4 and Al2O3 into NaAlO2. S2. Mix the alkali-fused clinker with water, slurry, extract, and separate the solid and liquid components to obtain an aqueous extract containing Na2CrO4 and NaAlO2, and a filter cake containing Al2O3. S3. Add barium salt solution or solid to the aqueous extract containing Na2CrO4 or NaAlO2. BaCrO4 precipitate is generated by reaction. Solid-liquid separation is performed to obtain BaCrO4 filter cake and sodium aluminate filtrate. S4. React the BaCrO4 filter cake with an inorganic acid, and separate the solid and liquid to obtain a chromic acid solution and a barium sulfate precipitate. Add acid to the sodium aluminate filtrate, adjust the pH to 7-8, and separate the solid and liquid to obtain Al(OH)3 filter cake.

2. The method according to claim 1, characterized in that, In step S1, the particle size of the waste chromium catalyst is not less than 200 mesh. The mass ratio of waste chromium catalyst to sodium hydroxide is 1:2~4.

3. The method according to claim 1, characterized in that, The conditions for the alkali fusion reaction are: alkali fusion oxidation reaction is carried out in air at a temperature of 500~550℃ for 1~2 hours.

4. The method according to claim 1, characterized in that, In step S2, the liquid-solid mass ratio of alkali-fused clinker to water is 10~20:

1.

5. The method according to claim 1, characterized in that, In step S2, the immersion temperature is 85~95℃ and the immersion time is 2.5~3 hours.

6. The method according to claim 1, characterized in that, In step S3, the barium salt is barium chloride.

7. The method according to claim 1, characterized in that, In step S3, the reaction temperature for generating BaCrO4 precipitate is 85~95℃, and the reaction time is 2.5~3 hours.

8. The method according to claim 1, characterized in that, In step S4, the inorganic acid is sulfuric acid with a concentration of 30% to 40%, the reaction temperature between the BaCrO4 filter cake and the inorganic acid is 85 to 95°C, the reaction time is 1.5 to 2 hours, and the mass concentration of the chromic acid solution is 10% to 35%. The acid solution is sulfuric acid, and the Al(OH)3 filter cake is flash-dried to obtain a powder product.

9. The method according to claim 1, characterized in that, The filter cakes containing Al2O3 and BaCrO4 produced after solid-liquid separation in steps S2 and S3 are treated by countercurrent washing.

10. A system for recovering chromium and aluminum from spent chromium catalyst, characterized in that, The system includes: The mixing and alkali fusion unit is used to mix waste chromium catalyst with sodium hydroxide and react them in a rotary kiln to obtain alkali-fused clinker. The water immersion and solid-liquid separation unit is used to mix alkali-fused clinker with water, slurry, immerse, and separate solids and liquids to obtain water immersion liquid containing Na2CrO4 and NaAlO2, as well as filter cake containing Al2O3. The chromium precipitation and acidification unit is used to add barium salt solution or solid to an aqueous leaching solution containing Na2CrO4 or NaAlO2, react to generate BaCrO4 precipitate, separate the solid and liquid to obtain BaCrO4 filter cake and sodium aluminate filtrate, react the BaCrO4 filter cake with inorganic acid, separate the solid and liquid to obtain chromic acid solution and barium sulfate precipitate. The aluminum precipitation unit is used to react BaCrO4 filter cake with inorganic acid, separate the solid and liquid phases, and obtain chromic acid solution and barium sulfate precipitate.

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