JP2023506074A - Combined dynamic and static agitation system and process for preparing chromite liquid-phase chromium oxide salts - Google Patents

Abstract

[Solution] The static stirring includes a stirrer (1) and a plurality of static stirring blades (12) installed in parallel with the stirring shaft (2) of the stirrer (1). A combination of dynamic and static blades (12) are installed around the stirring shaft (2), and the stirring blade (4) is attached to the bottom of the stirring shaft (2). Agitation system. The process of liquid-phase oxidation of chromite in this mixed dynamic-static agitation system to prepare chromium salts. Chromite liquid-phase oxidation method to prepare chromium salt to solve the important process problems of solid-liquid separation during chromite leaching, separation of chromium salt in highly alkaline medium and conversion of intermediate products to chromium salt system, The prospects for application in [Selection drawing] Fig. 8

Description

The present invention belongs to the technical field of hydrometallurgical and multi-phase stirred reactions, and specifically relates to a combined dynamic and static stirring system and process for preparing chromite liquid phase chromium oxide salts.

Chromium salt is an important inorganic chemical product. China is the largest producer of chromium salt, with an annual output of 400,000 tons. The traditional chromium salt production process, especially the calcium roasting technology, has a low resource utilization rate and produces a large amount of Cr(VI)-containing toxic chromium slag, so it has been totally abandoned. At present, the chromium salt industry universally uses non-calcium roasting processes, which greatly reduce the amount of chromium slag produced, but the problem of contamination by chromium slag has not been thoroughly resolved. Therefore, the development of chromium salt clean production process technology is highly valued. Among them, the chromite liquid-phase oxidation method (chromite alkaline leaching method) is considered as a clean process with a wide prospect for industrial application.

The method of producing sodium chromate by chromite alkali leaching disclosed in Chinese patent CN201010146648 is a complete chromite clean production process so far, but the reaction temperature (180-320℃) during alkali leaching is high, and then dilute with a large amount of water before solid-liquid separation, so the concentration of unreacted alkali is greatly diluted, and the recycling of alkali in leaching is seriously hindered. , leading to the deposition of calcium-containing slag, which is a serious environmental pollution, and it is difficult to obtain a pure product by evaporation crystallization process for sodium chromate crude product separated from chromium/alkali, at the same time wasting energy and time. leads to There are also the following main problems in the practical application of chromium salt production.

(1) Due to the complexity of the reaction system with high concentration alkali and stable composition of chromite, the conversion efficiency of chromium is low, and the process of mass transfer in the reaction system needs to be strengthened.

(2) A very large amount of alkali is required to achieve high chromium conversion, which is difficult to recover at a later stage and the process is complicated.

(3) Since the alkaline immersion liquid has a high alkali concentration and the particle size of the reaction slag is small, solid-liquid separation is difficult.

(4) The chromium salt and alkali in the leachate are difficult to separate, and the obtained chromium salt contains a large amount of alkali, which complicates the later refining process.

SUMMARY OF THE INVENTION An object of the present invention is to provide an agitation system by combining dynamic and static systems in order to solve the above-mentioned problems in the prior art. The system is simple to configure and rational in design. When the agitator stirs, the reaction fluid in the agitation tank rotates, flows, and mixes, and when it operates stably, it becomes a rotating body centered on the stirring shaft. The formed rotating body mixes each component in the fluid. is unfavorable to Since the present invention installs a plurality of static stirring blades, the originally stable fluid rotating body is disturbed, and the original stable flow field symmetry is broken, so that the fluid rotates, diverts, and the fluid interface. It eliminates the stability, achieves control over the process of fluid mixing in the flow field, and achieves the purpose of mass transfer of fluid mixing.

a plurality of static stirring blades installed parallel to the stirring shaft of the stirrer, wherein the plurality of static stirring blades are centered around the stirring shaft; A combination dynamic and static agitation system comprising an agitator characterized in that it is fitted with a

The above dynamic and static combination agitation system is characterized in that the distances between the plurality of static agitation blades and the agitation shaft are not equal.

The above dynamic and static combination agitation system is characterized in that the static agitation blade is a slat, cylindrical or prismatic agitation blade.

The agitation system by the combination of the above dynamic and static ones has the agitation shaft of the agitator as a circle, and the ratio of the installation radius of the static agitation blade and the radius of the agitation vessel is 1:7.5-1. :16.

The present invention also provides a process for liquid phase oxidation of chromite to prepare chromium salts by a combination of the above dynamic and static agitation systems, characterized by comprising the following steps.

Put chromite, sodium hydroxide and water into an autoclave equipped with a mixing system of dynamic and static stirring. After the pressure is released and cooled, the contents in the autoclave are transferred to a constant temperature box to be kept warm, settled, and kept warm, and the sediment is subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.

The reaction slag is backwashed and then separated to obtain a washing slag liquid and iron slag.

Barium hydroxide is added to the supernatant to cause a precipitation reaction, and separated after the reaction is completed to obtain a sediment A of barium chromate and a lye B containing aluminum.

Barium hydroxide is added to the washing slag liquid to cause a precipitation reaction, and separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.

After dissolving the barium chromate precipitate A and the barium chromate precipitate C with hydrochloric acid, a reducing agent is added, a mixed solution of chromium chloride and barium chloride is obtained by a reduction reaction, and the mixed solution is The pH is adjusted so that chromium is completely precipitated with chromium hydroxide, and the chromium hydroxide product is obtained by solid-liquid separation.

The above method is characterized in that the temperature of the liquid phase oxidation reaction is 180-270° C., the oxygen partial pressure is 1.2-2.6 MPa, the stirring speed is 500-900 rpm, and the reaction time is 1-5 hours.

The above method is characterized in that the mass ratio of sodium hydroxide and chromite is (2-5):1, and the mass of sodium hydroxide is 30-60% of the total mass of sodium hydroxide and water. .

The above method is characterized in that the temperature is 70-150° C. and the time is 120-210 min in the case of the heat retention and sedimentation.

In the above method, when barium hydroxide is added to the supernatant for precipitation reaction, the molar ratio of barium hydroxide and sodium chromate in the supernatant is (1-1.2):1, the reaction time is 1-2 hours, It is characterized by a reaction temperature of 60-80°C.

When barium hydroxide is added to the washing slag liquid to cause a precipitation reaction, the molar ratio of barium hydroxide and sodium chromate in the washing slag liquid is (1 to 1.2): 1, the reaction time is 1 to 2 hours, and the reaction temperature is is between 60 and 80°C.

The above method is characterized by including the steps of adding sodium silicate pulp to the aluminum-containing lye D to cause a precipitation reaction, and separating after the reaction is completed to obtain a low-aluminum lye and a sodium aluminosilicate precipitate. and

The above method is characterized in that the lye D containing sodium silicate and aluminum has a molar ratio of sodium aluminate of (1-1.2):1.

The above method is characterized by also including the step of adding alkali to the low aluminum lye obtained from the separation and then returning it to the autoclave for recycling.

The above method is characterized in that it also includes the step of returning the aluminum-bearing lye B to the autoclave for recycling.

In the above method, the ratio of the sum of the amounts of the barium chromate precipitate A and the barium chromate precipitate C to the amount of HCl in hydrochloric acid is 1: (2 to 5), The volume of hydrochloric acid is 4 to 8 times the sum of the mass of the barium chromate precipitate A and the barium chromate precipitate C (wherein the volume is in mL and the mass is in g), is a small-molecular alcohol-based organic substance, and the molar mass of the reducing agent is 1 to 5 times the molar mass of the theoretical reaction with barium chromate.

The above method is characterized in that the reduction reaction has a stirring speed of 200-400 rpm, a reaction temperature of 50-80° C., and a reaction time of 1-2 hours.

The above method is characterized by adjusting the pH of the mixed solution to 8-9 with barium hydroxide after the reduction reaction.

The above method is also characterized by including the step of completely precipitating chromium with chromium hydroxide until barium is completely precipitated, and then adding sulfuric acid to the liquid phase obtained by solid-liquid separation to obtain a barium sulfate product. .

Compared with the prior art, the present invention has the following advantages.

1. The stirring system according to the present invention is simple in construction and rational in design. When the agitator stirs, the reaction fluid in the agitation tank rotates, flows, and mixes, and when it operates stably, it becomes a rotating body centered on the stirring shaft. The formed rotating body mixes each component in the fluid. is unfavorable to Since the present invention installs a plurality of static stirring blades, the originally stable fluid rotating body is disturbed, and the original stable flow field symmetry is broken, so that the fluid rotates, diverts, and the fluid interface. It eliminates the stability, achieves control over the process of fluid mixing in the flow field, and achieves the purpose of mass transfer of fluid mixing.

2. The dynamic and static combination agitation system of the present invention can significantly improve the conversion rate of chromium during the liquid phase oxidation of chromite, greatly shorten the reaction time, and provide a fast, efficient and clean production method for chromium salts. can be achieved.

3. The present invention points out a new process route to prepare chromium salt by chromite liquid phase oxidation method, creatively solid-liquid separation during chromite leaching, separation of chromium salt in highly alkaline medium and intermediate product conversion to chromium salt system. It solves important process challenges and has very broad industrial application prospects.

4. This invention relates to the process of chromite liquid-phase oxidative leaching by combining dynamic and static autoclaves equipped with stirring blades. The air phase in the upper part of the autoclave is wound from the original single area, and the mixing method is multi-area. , the process of mass transfer of gas-liquid-solid phase in the reaction system is greatly enhanced, and the efficiency of the leaching reaction process is improved.

5. The present invention creatively points out the separation process of heat preservation and sedimentation of chromite oxidative leaching system in highly alkaline medium, solves the problem of solid-liquid separation, and compares with the traditional dilution filtration, centrifugation and other methods, The solid-liquid separation time and equipment costs are significantly reduced, and the supernatant liquid can keep a low aluminum content and a high alkali content all the time, and the washing slag liquid has a high aluminum content and a low alkali content. Therefore, the original lye concentration is retained to the greatest extent, and the efficiency of the direct recycling of the medium is greatly improved, at the same time, which is highly beneficial to the succeeding circulation and the process of aluminum removal.

6. The present invention points out a new process of separating chromium salts from chromite leachate directly by the barium salt method and a new process of converting barium chromate into chromium salts, thus creatively achieving the separation of chromium and alkali, and chromic acid. Pointing out the method of dissolving and reducing barium in hydrochloric acid and organic matter system, achieving the goal of preparing chromium salt system with barium chromate, and at the same time achieving the recycling of hydrochloric acid medium to obtain pure barium sulfate products. This process has mild reaction conditions, is environmentally friendly, and is highly efficient.

7. The present invention pointed out a novel process for aluminum removal with lye that was creatively subjected to chromium-alkali separation on chromite leachate. That is, sodium silicate is used as a precipitant in the lye to directly precipitate and convert sodium aluminate into sodium aluminosilicate, and further processing can obtain sodium aluminosilicate molecular sieve by-product with high economic value, and the lye can be directly It can be recycled to the leaching reaction process, leading to improved economic efficiency and reduced energy consumption.

Next, the technical solution of the present invention will be described in more detail in conjunction with figures and examples.

Schematic diagram of a stirring system by combining dynamic and static systems according to the present invention. Image of the flow field of a single dynamic stirring blade in operation (Y=0 front view) Image of the flow field of a single dynamic stirring blade in operation (Z=0 overhead view) Image of the field during operation of the stirring system by combining dynamic and static according to the present invention (Y = 0 front view) Image of the place in operation of the stirring system by combining the dynamic and static ones according to the present invention (Z = 0 bird's-eye view) Fig. 1 shows the relationship between the rate of leaching of chromium and the leaching time when chromium salts are prepared by the combination of dynamic and static stirring systems according to the present invention and the liquid-phase oxidation of chromite. Schematic diagram of an autoclave equipped with a stirring system that combines dynamic and static systems according to the present invention. Process chart of the present invention

As shown in FIG. 1, the combined dynamic and static agitation system of the present invention comprises an agitator 1 and a static agitator blade 12 installed parallel to the agitator shaft 2 of said agitator 1. , a plurality of the static stirring blades 12 are installed around the stirring shaft 2 , and a stirring blade 4 is attached to the bottom of the stirring shaft 2 .

In this example, the distances between the plurality of said static stirrer blades 12 and the stirrer shaft 2 are not equal. Said static stirrer blades 12 may be in quantity of 2, 3, 4, 5 or 6 and so on.

In this example, the static stirrer blade 12 is a slatted, cylindrical or prismatic stirrer blade.

In this example, the stirring shaft 2 of the stirrer 1 is circular, and the ratio of the installation radius of the static stirring blade 12 to the radius of the stirring vessel is 1:7.5 to 1:16.

The specific operation principle of the agitation system by combining the dynamic and static systems according to the present invention is as follows. In other words, the reaction system (solid/liquid, gas/liquid, liquid/liquid, gas/liquid/solid, etc.) is stirred by a stirrer, and the reaction fluid rotates, flows, and mixes. (Figs. 2-3), and although the formed rotor is disadvantageous for mixing each component in the fluid, the presence of static stirring blades in the flow field makes the fluid rotor stable. is disturbed and the symmetry of the original stable flow field is broken, causing the fluid to rotate and divert (Figs. 4-5), the fluid interface becomes unstable, and the mixing process of the fluid in the flow field becomes Achieving control and achieving the purpose of mass transfer of fluid mixing.

The agitation system by the combination of dynamic and static according to the present invention is applied to the mass transfer reaction system of gas/liquid/solid phase mixture, and the agitation tank by the agitation system by the combination of dynamic and static is applied. The gas at the top of the mixture enters the solid-liquid phase system in the vessel by entrainment due to agitation and participates in the reaction, while the gas phase entrains into the flow field around the original single dynamic stirrer. Changed from the method to the multi-mixing method of the flow field around the dynamic stirrer and the small flow field area near the static stirring blades, the mass transfer area of the gas, liquid and solid phases in the reaction system is greatly expanded. Therefore, the mass transfer between each phase is enhanced. Accelerated gas-liquid-solid phase mass transfer helps reduce system reaction times. For the process of chromite liquid phase oxidation, it also helps to lower the reaction alkali concentration and other process conditions, improving the chromium conversion rate and lowering the energy consumption at the same time. Therefore, this dynamic/static combination agitation system enhances the mixing of fluids in the agitated tank, enhances the entrainment of the gas phase in the gas-liquid-solid phase reaction, and increases the mass transfer between the phases in the reaction system. It can be used in a variety of fluid mixing systems based on stirred tanks, and is particularly suitable for multi-phase reaction systems involving solids that are structurally stable and difficult to decompose. In addition, the system is simple in construction, low in energy consumption, high in efficiency, low in cost, and easy to repair and maintain.

As shown in Figure 7, the autoclave equipped with the combined dynamic and static agitation system of the present invention includes an autoclave 8 with an open top and a sealing cap 3 installed at the opening of the autoclave 8. , the agitator 1 is attached to the sealing cap 3 , the agitator shaft 2 of the agitator 1 is in the autoclave 8 , and the agitator blade 4 is attached to the bottom of the agitator shaft 2 . The sealing cap 3 has a plurality of static stirring blades 12, the plurality of static stirring blades 12 are installed around the stirring shaft 2, and the static stirring blades 12 have a plurality of sealing caps. One end leaving 3 is deep into the autoclave 8.

In this example, the distances between the plurality of said static stirrer blades 12 and the stirrer shaft 2 are not equal. Said static stirrer blades 12 may be in quantity of 2, 3, 4, 5 or 6 and so on.

In this example, the static stirrer blade 12 is a slatted, cylindrical or prismatic stirrer blade.

In this example, a thermocouple 7 is attached to said sealing cap 3 .

In this example, said static stirrer blade 12 has its lower end above the stirrer blade 4 .

In this example, said stirring blade 4 is elliptical in blade shape.

In this example, said sealing cap 3 has an inlet and an outlet, said inlet is fitted with an inlet pipe 9, the inlet pipe 9 is deep into the autoclave 8, and the inlet The bottom of the pipe 9 is close to the bottom of the autoclave 8, the inlet valve 5 is attached to the top of the inlet pipe, the exhaust pipe is attached to the exhaust port, and the exhaust valve 11 is attached to the top of the exhaust pipe.

In this example, said sealing cap 3 is fitted with a pressure gauge 10 for measuring the pressure inside the autoclave 8 .

In this example, there is a heating jacket 6 on the outside of said autoclave 8 and a groove for installing the autoclave 8 in the middle of the heating jacket 6 .

In this example there is a base 13 at the bottom of said heating jacket 6 .

Preparing a chromium salt by liquid phase oxidation of chromite in an autoclave fitted with a single dynamic stirring blade and in an autoclave fitted with a combined dynamic and static stirring system according to the invention, respectively, Chromite powder from South Africa is taken and polished to 300 mesh (48 μm), and the Cr ₂ O _ternary content of about 42.92% is measured by X-ray fluorescence spectroscopy (XRF). 125 g of chromite powder (300 mesh), 500 g of sodium hydroxide and 333 mL of deionized water are mixed and put into an autoclave at a temperature of 250°C, an oxygen partial pressure of 2.4 MPa (total pressure of about 3.2 MPa), and a reaction time of 60 minutes. , 120 min, 180 min, 240 min, and 300 min in an autoclave equipped with a single dynamic stirring blade and an autoclave equipped with a combined dynamic and static stirring system according to the present invention. , to measure the content of chromium in the leachate after the liquid phase oxidation reaction. The leaching rate of chromium in the two autoclaves depends on the reaction time, and as shown in Figure 7, the leaching rate of chromium in the leachate after the reaction is complete in the autoclave using only a single dynamic stirrer blade. The highest, only 90%, requires a long period of about 300min, but in the autoclave with a stirring system of a combination of dynamic and static, the leaching rate of chromium is only 240min after the reaction is completed. has reached 99%, and the leaching rate of chromium in the agitation system with a combination of dynamic and static systems is about twice that of the former in a short period of 60-120 min. The dynamic and static combination agitation system of the present invention achieves high-efficiency leaching by chromite liquid-phase oxidation in a short period of time, and at the same time greatly improves the leaching rate of chromium, secondary recovery and resource saving. Avoiding waste, the dynamic and static combination enhancement method effectively improves the efficiency of mass transfer and reaction process in the system, suitable for various multi-phase reaction systems, new and efficient It is a device that enhances high, multi-phase mass transfer.

The process of liquid-phase oxidation of chromite to prepare chromium salt in an autoclave equipped with the above-described combination of dynamic and static agitation system includes the following steps.

125 g of chromite (300 mesh), 250 g of sodium hydroxide and 583 g of water are placed in an autoclave equipped with a stirring system combining dynamic and static, and oxygen is introduced into the autoclave while stirring for liquid phase oxidation. React (reaction temperature: 180°C, oxygen partial pressure: 1.2 MPa (total pressure: about 2.4 MPa), stirring speed: 500 rpm, reaction time: 1 hour), release the pressure after the reaction is complete, and allow it to cool. The contents in the autoclave are transferred to a constant temperature box, kept warm, and sedimented (temperature: 70°C, time: 120 min), and the sedimented contents are subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.

The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag.

The content of sodium chromate in the above supernatant liquid and washing slag liquid was measured with industrial sodium chromate (HG/T 4312-2012), and the supernatant liquid contained 11.43 g of sodium chromate and 1.45 g of sodium metaaluminate. g. There are 22.87 g of sodium chromate and 8.68 g of sodium metaaluminate in the washing slag liquid.

12.1 g of barium hydroxide is added to the supernatant so that the molar ratio of sodium chromate is 1:1 between barium hydroxide and the supernatant, and a precipitation reaction is carried out (reaction time: 1 h, reaction temperature: 60 ℃), separated after the reaction is completed to obtain a precipitate A of barium chromate and a lye B containing aluminum. Lye B containing aluminum is returned to the autoclave for recycling.

24.2 g of barium hydroxide was added to the washing slag liquid so that the molar ratio of sodium chromate was 1:1 between the barium hydroxide and the washing slag liquid, and a precipitation reaction was carried out (reaction time: 1 h, reaction temperature: : 60°C), separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.

The content of aluminum in lye D containing aluminum was measured according to "GB/T 5750.6-2006 Standard test method for domestic drinking water metal indicator Chromazurol S spectrophotometric method", and sodium silicate and lye D containing aluminum 21.54 g of sodium silicate pulp with a mass concentration of 60% was added to the lye D containing aluminum so that the sodium molar ratio was 1:1, and a precipitation reaction was carried out (reaction time: 1 hour, reaction temperature: 70 ° C. ), after the reaction is completed, low aluminum lye and sodium aluminosilicate sediment are obtained by separation, the aluminum removal rate reaches 90%, meeting the recycling standard, adding alkali to the low aluminum lye by separation, then autoclaving. to recycle.

The barium chromate precipitate A and the barium chromate precipitate C were combined and measured, and the chromium conversion rate was 90%. (mL:g), the molar ratio of the combined barium chromate to HCl in the hydrochloric acid solution is 1:2, and the chromium dissolution rate is 92% as measured after dissolution, the reducing agent is added and subjected to a reduction reaction (stirring speed: 200 rpm, reaction temperature: 50°C, reaction time: 1 hour). The reducing agent is ethanol, a small-molecular-weight alcohol-based organic substance, and the molar mass of the reducing agent is one times the molar mass of the theoretical reaction with barium chromate to obtain a mixed solution of chromium chloride and barium chloride. , the chromium reduction rate is 72%. Adjust the pH of the mixed solution of chromium chloride and barium chloride to 8 with barium hydroxide so that chromium is completely precipitated with chromium hydroxide, obtain chromium hydroxide products by solid-liquid separation, barium Add dilute sulfuric acid to the centrifuged liquid phase until complete precipitation of barium sulphate to obtain a pure barium sulphate product.

As shown in FIG. 1, the combined dynamic and static agitation system of the present invention comprises an agitator 1 and a static agitator blade 12 installed parallel to the agitator shaft 2 of said agitator 1. , a plurality of the static stirring blades 12 are installed around the stirring shaft 2 , and a stirring blade 4 is attached to the bottom of the stirring shaft 2 .

In this example, the distances between the plurality of said static stirrer blades 12 and the stirrer shaft 2 are not equal. Said static stirrer blades 12 may be in quantity of 2, 3, 4, 5 or 6 and so on.
In this example, the static stirrer blade 12 is a slatted, cylindrical or prismatic stirrer blade.

In this example, the stirring shaft 2 of the stirrer 1 is circular, and the ratio of the installation radius of the static stirring blade 12 to the radius of the stirring vessel is 1:7.5 to 1:16.

The specific operation principle of the agitation system by combining the dynamic and static systems according to the present invention is as follows. In other words, the reaction system (solid/liquid, gas/liquid, liquid/liquid, gas/liquid/solid, etc.) is stirred by a stirrer, and the reaction fluid rotates, flows, and mixes. (Figs. 2-3), and although the formed rotor is disadvantageous for mixing each component in the fluid, the presence of static stirring blades in the flow field makes the fluid rotor stable. is disturbed and the symmetry of the original stable flow field is broken, causing the fluid to rotate and divert (Figs. 4-5), the fluid interface becomes unstable, and the mixing process of the fluid in the flow field becomes Achieving control and achieving the purpose of mass transfer of fluid mixing.

The agitation system by the combination of dynamic and static according to the present invention is applied to the mass transfer reaction system of gas/liquid/solid phase mixture, and the agitation tank by the agitation system by the combination of dynamic and static is applied. The gas at the top of the mixture enters the solid-liquid phase system in the vessel by entrainment due to agitation and participates in the reaction, while the gas phase entrains into the flow field around the original single dynamic stirrer. Changed from the method to the multi-mixing method of the flow field around the dynamic stirrer and the small flow field area near the static stirring blades, the mass transfer area of the gas, liquid and solid phases in the reaction system is greatly expanded. Therefore, the mass transfer between each phase is enhanced. Accelerated gas-liquid-solid phase mass transfer helps reduce system reaction times. For the process of chromite liquid phase oxidation, it also helps to lower the reaction alkali concentration and other process conditions, improving the chromium conversion rate and lowering the energy consumption at the same time. Therefore, this dynamic/static combination agitation system enhances the mixing of fluids in the agitated tank, enhances the entrainment of the gas phase in the gas-liquid-solid phase reaction, and increases the mass transfer between the phases in the reaction system. It can be used in a variety of fluid mixing systems based on stirred tanks, and is particularly suitable for multi-phase reaction systems involving solids that are structurally stable and difficult to decompose. In addition, the system is simple in construction, low in energy consumption, high in efficiency, low in cost, and easy to repair and maintain.

As shown in Figure 7, the autoclave equipped with the combined dynamic and static agitation system of the present invention includes an autoclave 8 with an open top and a sealing cap 3 installed at the opening of the autoclave 8. , the agitator 1 is attached to the sealing cap 3 , the agitator shaft 2 of the agitator 1 is in the autoclave 8 , and the agitator blade 4 is attached to the bottom of the agitator shaft 2 . The sealing cap 3 has a plurality of static stirring blades 12, the plurality of static stirring blades 12 are installed around the stirring shaft 2, and the static stirring blades 12 have a plurality of sealing caps. One end leaving 3 is deep into the autoclave 8.

In this example, the distances between the plurality of said static stirrer blades 12 and the stirrer shaft 2 are not equal. Said static stirrer blades 12 may be in quantity of 2, 3, 4, 5 or 6 and so on.

In this example, the static stirrer blade 12 is a slatted, cylindrical or prismatic stirrer blade.

In this example, a thermocouple 7 is attached to said sealing cap 3 .

In this example, said static stirrer blade 12 has its lower end above the stirrer blade 4 .

In this example, said stirring blade 4 is elliptical in blade shape.

In this example, said sealing cap 3 has an inlet and an outlet, said inlet is fitted with an inlet pipe 9, the inlet pipe 9 is deep into the autoclave 8, and the inlet The bottom of the pipe 9 is close to the bottom of the autoclave 8, the inlet valve 5 is attached to the top of the inlet pipe, the exhaust pipe is attached to the exhaust port, and the exhaust valve 11 is attached to the top of the exhaust pipe.

In this example, said sealing cap 3 is fitted with a pressure gauge 10 for measuring the pressure inside the autoclave 8 .

In this example, there is a heating jacket 6 on the outside of said autoclave 8 and a groove for installing the autoclave 8 in the middle of the heating jacket 6 .

In this example there is a base 13 at the bottom of said heating jacket 6 .

Preparing a chromium salt by liquid phase oxidation of chromite in an autoclave fitted with a single dynamic stirring blade and in an autoclave fitted with a combined dynamic and static stirring system according to the invention, respectively, Chromite powder from South Africa is taken and polished to 300 mesh (48 μm), and the Cr ₂ O _ternary content of about 42.92% is measured by X-ray fluorescence spectroscopy (XRF). 125 g of chromite powder (300 mesh), 500 g of sodium hydroxide and 333 mL of deionized water are mixed and put into an autoclave at a temperature of 250°C, an oxygen partial pressure of 2.4 MPa (total pressure of about 3.2 MPa), and a reaction time of 60 minutes. , 120 min, 180 min, 240 min, and 300 min in an autoclave equipped with a single dynamic stirring blade and an autoclave equipped with a combined dynamic and static stirring system according to the present invention. , to measure the content of chromium in the leachate after the liquid phase oxidation reaction. The leaching rate of chromium in the two autoclaves depends on the reaction time, and as shown in Figure 7, the leaching rate of chromium in the leachate after the reaction is complete in the autoclave using only a single dynamic stirrer blade. The highest, only 90%, requires a long period of about 300min, but in the autoclave with a stirring system of a combination of dynamic and static, the leaching rate of chromium is only 240min after the reaction is completed. has reached 99%, and the leaching rate of chromium in the agitation system with a combination of dynamic and static systems is about three times that of the former in a short period of 60-120 min. The dynamic and static combination agitation system of the present invention achieves high-efficiency leaching by chromite liquid-phase oxidation in a short period of time, and at the same time greatly improves the leaching rate of chromium, secondary recovery and resource saving. Avoiding waste, the dynamic and static combination enhancement method effectively improves the efficiency of mass transfer and reaction process in the system, suitable for various multi-phase reaction systems, new and efficient It is a device that enhances high, multi-phase mass transfer.

The process of liquid phase oxidation of chromite to prepare chromium salt in an autoclave equipped with a combined dynamic and static agitation system as described in Example 2 includes the following steps.

125 g of chromite (300 mesh), 250 g of sodium hydroxide and 583 g of water are placed in an autoclave equipped with a stirring system combining dynamic and static, and oxygen is introduced into the autoclave while stirring for liquid phase oxidation. React (reaction temperature: 180°C, oxygen partial pressure: 1.2 MPa (total pressure: about 2.4 MPa), stirring speed: 500 rpm, reaction time: 1 hour), release the pressure after the reaction is complete, and allow it to cool. The contents in the autoclave are transferred to a constant temperature box, kept warm, and sedimented (temperature: 70°C, time: 120 min), and the sedimented contents are subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.

The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag.

The content of sodium chromate in the above supernatant liquid and washing slag liquid was measured with industrial sodium chromate (HG/T 4312-2012), and the supernatant liquid contained 11.43 g of sodium chromate and 1.45 g of sodium metaaluminate. g. There are 22.87 g of sodium chromate and 8.68 g of sodium metaaluminate in the washing slag liquid.

12.1 g of barium hydroxide is added to the supernatant so that the molar ratio of sodium chromate is 1:1 between barium hydroxide and the supernatant, and a precipitation reaction is carried out (reaction time: 1 h, reaction temperature: 60 ℃), separated after the reaction is completed to obtain a precipitate A of barium chromate and a lye B containing aluminum. Lye B containing aluminum is returned to the autoclave for recycling.

24.2 g of barium hydroxide was added to the washing slag liquid so that the molar ratio of sodium chromate was 1:1 between the barium hydroxide and the washing slag liquid, and a precipitation reaction was carried out (reaction time: 1 h, reaction temperature: : 60°C), separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.

The content of aluminum in lye D containing aluminum was measured according to "GB/T 5750.6-2006 Standard test method for domestic drinking water metal indicator Chromazurol S spectrophotometric method", and sodium silicate and lye D containing aluminum 21.54 g of sodium silicate pulp with a mass concentration of 60% was added to the lye D containing aluminum so that the sodium molar ratio was 1:1, and a precipitation reaction was carried out (reaction time: 1 hour, reaction temperature: 70 ° C. ), after the reaction is completed, low aluminum lye and sodium aluminosilicate sediment are obtained by separation, the aluminum removal rate reaches 90%, meeting the recycling standard, adding alkali to the low aluminum lye by separation, then autoclaving. to recycle.

The barium chromate precipitate A and the barium chromate precipitate C were combined and measured, and the chromium conversion rate was 90%. (mL:g), the molar ratio of the combined barium chromate to HCl in the hydrochloric acid solution is 1:2, and the chromium dissolution rate is 92% as measured after dissolution, the reducing agent is added and subjected to a reduction reaction (stirring speed: 200 rpm, reaction temperature: 50°C, reaction time: 1 hour). The reducing agent is ethanol, a small-molecular-weight alcohol-based organic substance, and the molar mass of the reducing agent is one times the molar mass of the theoretical reaction with barium chromate to obtain a mixed solution of chromium chloride and barium chloride. , the chromium reduction rate is 72%. Adjust the pH of the mixed solution of chromium chloride and barium chloride to 8 with barium hydroxide so that chromium is completely precipitated with chromium hydroxide, obtain chromium hydroxide products by solid-liquid separation, barium Add dilute sulfuric acid to the centrifuged liquid phase until complete precipitation of barium sulphate to obtain a pure barium sulphate product.

The process of liquid phase oxidation of chromite to prepare chromium salts in an autoclave equipped with a combined dynamic and static agitation system as described in Example 2 including the following steps.

125 g of chromite (300 mesh), 500 g of sodium hydroxide and 500 g of water are placed in an autoclave equipped with a stirring system combining dynamic and static, and oxygen is introduced into the autoclave while stirring for liquid phase oxidation. Let the reaction (reaction temperature: 240°C, oxygen partial pressure: 2.4 MPa (total pressure about 3.2 MPa), stirring speed: 800 rpm, reaction time: 4 hours), release the pressure after the reaction is completed, and allow it to cool. The contents in the autoclave are transferred to a constant temperature box, kept warm, and sedimented (temperature: 90°C, time: 180 min), and the sedimented contents are subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.

The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag.

The content of sodium chromate in the above supernatant liquid and washing slag liquid was measured with industrial sodium chromate (HG/T 4312-2012), and the supernatant liquid contained 21.95 g of sodium chromate and 2.02 g of sodium metaaluminate. g. There are 87.83 g of sodium chromate and 25.17 g of sodium metaaluminate in the washing slag liquid.

23.2 g of barium hydroxide was added to the supernatant so that the molar ratio of sodium chromate in the barium hydroxide and the supernatant was 1.1:1, and the precipitation reaction was carried out (reaction time: 1.5 h, reaction temperature: 70 ℃), separated after the reaction is completed to obtain a precipitate A of barium chromate and a lye B containing aluminum. Lye B containing aluminum is returned to the autoclave for recycling.

92.9 g of barium hydroxide was added to the washing slag liquid so that the molar ratio of sodium chromate in the barium hydroxide and the washing slag liquid was 1.1:1, and the precipitation reaction was carried out (reaction time: 1.5 h, reaction temperature: : 70°C), separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.

The content of aluminum in lye D containing aluminum was measured according to "GB/T 5750.6-2006 Standard test method for domestic drinking water metal indicator Chromazurol S spectrophotometric method", and sodium silicate and lye D containing aluminum 46.85 g of sodium silicate pulp with a mass concentration of 80% was added to the lye D containing aluminum so that the sodium molar ratio was 1.1:1, and a precipitation reaction was carried out (reaction time: 2 hours, reaction temperature: 80 °C), after the reaction is complete, a low aluminum lye and a sodium aluminosilicate precipitate are obtained by separation. The aluminum removal rate reaches 92%, meeting the recycling standard. Alkali is added to the low aluminum lye from separation and then returned to the autoclave for recycling.

The combined measurement of barium chromate precipitate A and barium chromate precipitate C gives a chromium conversion of 94%. Dissolve combined barium chromate in hydrochloric acid solution, liquid-solid ratio is 6:1 (mL:g), molar ratio of combined barium chromate and HCl in hydrochloric acid solution is 1:4, dissolve The chromium dissolution rate is 96%. A reducing agent is added and a reduction reaction is carried out (stirring speed: 300 rpm, reaction temperature: 80°C, reaction time: 1.5 hours). The reducing agent is a small-molecular alcohol-based organic ethanol whose molar mass is twice the molar mass of the theoretical reaction with barium chromate. A mixed solution of chromium chloride and barium chloride is obtained, and the chromium reduction rate is 96%. Adjust the pH of the mixed solution of chromium chloride and barium chloride to 8.5 with barium hydroxide, so that chromium is completely precipitated with chromium hydroxide, obtain chromium hydroxide product by solid-liquid separation, barium Add dilute sulfuric acid to the centrifuged liquid phase until complete precipitation of barium sulphate to obtain a pure barium sulphate product.

The process of liquid phase oxidation of chromite to prepare chromium salts in an autoclave equipped with a combined dynamic and static agitation system as described in Example 2 including the following steps.

125 g of chromite (300 mesh), 625 g of sodium hydroxide and 416 g of water are put into an autoclave equipped with a stirring system combining dynamic and static, and oxygen is introduced into the autoclave while stirring for liquid phase oxidation. Let the reaction (reaction temperature: 270°C, oxygen partial pressure: 2.6 MPa (total pressure about 3.5 MPa), stirring speed: 900 rpm, reaction time: 5 hours), release the pressure after the reaction is completed, and allow it to cool. The contents in the autoclave are transferred to a constant temperature box, kept warm, and sedimented (temperature: 150°C, time: 210 min), and the sedimented contents are subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.

The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag.

The content of sodium chromate in the above supernatant liquid and washing slag liquid was measured with industrial sodium chromate (HG/T 4312-2012), and the supernatant liquid contained 22.64 g of sodium chromate and 1.73 g of sodium metaaluminate. g. There are 90.57 g of sodium chromate and 26.04 g of sodium metaaluminate in the washing slag liquid.

28.7 g of barium hydroxide was added to the supernatant so that the molar ratio of sodium chromate in the barium hydroxide and the supernatant was 1.2:1, and a precipitation reaction was carried out (reaction time: 2 hours, reaction temperature: 80 ℃), separated after the reaction is completed to obtain a precipitate A of barium chromate and a lye B containing aluminum. Lye B containing aluminum is returned to the autoclave for recycling.

115.0 g of barium hydroxide was added to the washing slag liquid so that the molar ratio of sodium chromate in the barium hydroxide and the washing slag liquid was 1.2:1, and a precipitation reaction was carried out (reaction time: 2 hours, reaction temperature: : 80°C), separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.

The content of aluminum in lye D containing aluminum was measured according to "GB/T 5750.6-2006 Standard test method for domestic drinking water metal indicator Chromazurol S spectrophotometric method", and sodium silicate and lye D containing aluminum 43.08 g of sodium silicate pulp with a mass concentration of 90% was added to the lye D containing aluminum so that the sodium molar ratio was 1.2: 1, and a precipitation reaction was carried out (reaction time: 3 hours, reaction temperature: 90 °C), after the reaction is complete, a low aluminum lye and a sodium aluminosilicate precipitate are obtained by separation. Aluminum removal rate is 95%, meeting recycling standards. Alkali is added to the low aluminum lye from separation and then returned to the autoclave for recycling.

The combined measurement of barium chromate precipitate A and barium chromate precipitate C gives a chromium conversion of 97%. Dissolve combined barium chromate in hydrochloric acid solution, liquid-solid ratio is 4:1 (mL:g), molar ratio of combined barium chromate and HCl in hydrochloric acid solution is 1:5, dissolve After that, the dissolution rate of chromium was 99%, and the reducing agent was added for reduction reaction (agitation speed: 400 rpm, reaction temperature: 80°C, reaction time: 2 hours), and the reducing agent was a small molecular alcohol. system organic matter methanol, the molar mass of the reducing agent is five times the theoretical reaction molar mass with barium chromate, to obtain a mixed solution of chromium chloride and barium chloride, the chromium reduction rate is 99% . The mixed solution of chromium chloride and barium chloride is adjusted with barium hydroxide until the pH reaches 9, so that the chromium is completely precipitated in the chromium hydroxide, and the chromium hydroxide product is obtained by solid-liquid separation. Add dilute sulfuric acid to the centrifuged liquid phase until the barium is completely precipitated to obtain a pure barium sulfate product.

According to the process of Example 5, the chromium conversion rate is 99%, measured after liquid-phase oxidation reaction, incubation, settling and solid-liquid separation. The molar ratio of barium hydroxide and sodium chromate in the supernatant liquid is 1.2:1. Add barium hydroxide to the supernatant liquid, stir at 80 ° C for 2 hours, and separate after the reaction is complete. A barium chromate precipitate A and aluminum-bearing lye B were measured to give a chromium conversion of 97%. The lye B containing aluminum is returned to the autoclave for recycling, supplemented with a small amount of sodium hydroxide and water, subjected to liquid phase oxidation reaction under the same conditions, and after the reaction is completed, the pressure is released and cooled. The material in the autoclave was transferred from the autoclave to a constant temperature box, kept warm, settled (temperature: 150 ° C, time: 210 min), and measured after solid-liquid separation. Lye B containing
(Comparative example 1)

According to the process of Example 5, the chromium conversion rate is 99%, measured after liquid-phase oxidation reaction, incubation, settling and solid-liquid separation. The supernatant liquid after solid-liquid separation is directly circulated into the autoclave, supplemented with sodium hydroxide and water, and subjected to liquid phase oxidation reaction under the same conditions. After the reaction is completed, the pressure is released and cooled. After that, the contents in the autoclave were transferred to a constant temperature box, kept warm, settled (temperature: 150 ° C, time: 210 min), solid-liquid separation was performed, and the chromium conversion rate was 82%. It shows that if the content of sodium chromate in the liquor is too high, it may inhibit the leaching of chromium in the chromite.

According to the process of Example 5, liquid-phase oxidation reaction, incubation, sedimentation, solid-liquid separation, and measurement of the supernatant liquid and reaction slag obtained show that the chromium conversion rate is 99%. The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag. Barium hydroxide is added to the washing slag liquid so that the molar ratio of sodium chromate is 1.2:1 between the barium hydroxide and the washing slag liquid, and the precipitation reaction is carried out (reaction time: 2 hours, reaction temperature: 80°C ), the sediment C of barium chromate and the lye D containing aluminum obtained by separation after the completion of the reaction were measured, and the conversion of chromium was 97%. The lye D containing sodium silicate and aluminum has a sodium aluminate molar ratio of 1.2:1, and a sodium silicate pulp having a mass concentration of 90% is added to the lye D containing aluminum to cause a precipitation reaction ( Reaction time: 3h, reaction temperature: 90°C), low aluminum lye and sodium aluminosilicate precipitate are obtained by separation after the reaction is completed. The aluminum removal rate reaches 95% and meets the recycling standard. Alkali is added to the low aluminum lye from separation and then returned to the autoclave for recycling. Let the liquid phase oxidation reaction under the same conditions, release the pressure after the reaction is completed, let it cool down, transfer the contents in the autoclave to a constant temperature box to keep warm and settle (temperature: 150 ° C, time: 210 min ), after solid-liquid separation, the chromium conversion rate is 99%, so the lye D containing aluminum is treated with sodium silicate, and the low-aluminum lye obtained has no effect on chromium leaching. indicates that
(Comparative example 2)

According to the process of Example 5, the liquid-phase oxidation reaction, incubation, settling, solid-liquid separation, and then the supernatant liquid and the reaction slag obtained are measured, and the chromium conversion rate is 99%. The reaction slag is subjected to back washing with water and then separated to obtain a washing slag liquid and iron slag. Barium hydroxide is added to the washing slag liquid so that the molar ratio of sodium chromate is 1.2:1 between the barium hydroxide and the washing slag liquid, and the precipitation reaction is carried out (reaction time: 2 hours, reaction temperature: 80°C ), the sediment C of barium chromate and the lye D containing aluminum obtained by separation after the completion of the reaction were measured, and the conversion of chromium was 97%. Alkali is added to the lye D containing aluminum and then returned to the autoclave for recycling. Let the liquid phase oxidation reaction under the same conditions, release the pressure after the reaction is completed, let it cool down, transfer the contents in the autoclave to a constant temperature box to keep warm and settle (temperature: 150 ° C, time: 210 min ), the conversion rate of chromium is 88% when measured after solid-liquid separation, indicating that the lye D containing untreated aluminum can suppress the leaching of chromium.

The above are only preferred examples of the present invention, and do not limit the present invention in any way. belong to the claims of the invention.

The present invention points out a new process route to prepare chromium salt by chromite liquid phase oxidation method, creatively solid-liquid separation during chromite leaching, separation of chromium salt in highly alkaline medium and intermediate product conversion to chromium salt system. It solves important process challenges and has very broad industrial application prospects. This invention relates to the process of chromite liquid-phase oxidative leaching by combining dynamic and static autoclaves equipped with stirring blades. The air phase in the upper part of the autoclave is wound from the original single area, and the mixing method is multi-area. , the process of mass transfer of gas-liquid-solid phase in the reaction system is greatly enhanced, and the efficiency of the leaching reaction process is improved. The present invention points out the separation process of heat preservation and sedimentation of chromite oxidative leaching system in highly alkaline medium, solves the problem of solid-liquid separation, and compares with the traditional dilution filtration, centrifugation and other methods, solid-liquid separation Time and equipment costs are significantly reduced, and a low aluminum content and high alkali content in the supernatant can be maintained all the time. circulation and the process of aluminum removal, while at the same time the original lye concentration is retained to the greatest extent, greatly enhancing the efficiency of direct recycling of the medium.

Claims (17)

a stirrer (1) and a plurality of static stirring blades (12) installed parallel to the stirring shaft (2) of said stirrer (1), wherein said plurality of static stirring blades (12) are A stirring system with a combination of dynamic and static systems, characterized in that it is installed around a stirring shaft (2) and a stirring blade (4) is attached to the bottom of the stirring shaft (2). . The combined dynamic and static stirring system according to claim 1, characterized in that the distances between the plurality of static stirring blades (12) and the stirring shaft (2) are unequal. The combined dynamic and static agitation system according to claim 1 or 2, characterized in that said static agitator blade (12) is a slat, cylindrical or prismatic agitator blade. The stirring shaft (2) of the stirrer (1) is circular, and the ratio of the installation radius of the static stirring blade (12) to the radius of the stirring vessel is 1:7.5 to 1:16. The agitation system by combination of dynamic and static according to claim 2. A process for liquid-phase oxidation of chromite to prepare chromium salts in a combined dynamic and static agitation system according to claim 1, 2 or 4, characterized in that it comprises the steps of:
Put chromite, sodium hydroxide and water into an autoclave equipped with a mixing system of dynamic and static stirring. After the pressure is released and cooled, the contents in the autoclave are transferred to a constant temperature box to be kept warm, settled, and kept warm, and the sediment is subjected to solid-liquid separation to obtain supernatant liquid and reaction slag.
The reaction slag is backwashed and then separated to obtain a washing slag liquid and iron slag.
Barium hydroxide is added to the supernatant to cause a precipitation reaction, and separated after the reaction is completed to obtain a sediment A of barium chromate and a lye B containing aluminum.
Barium hydroxide is added to the washing slag liquid to cause a precipitation reaction, and separated after the reaction is completed to obtain a precipitate C of barium chromate and a lye D containing aluminum.
After dissolving the barium chromate precipitate A and the barium chromate precipitate C with hydrochloric acid, a reducing agent is added, a mixed solution of chromium chloride and barium chloride is obtained by a reduction reaction, and the mixed solution is The pH is adjusted so that chromium is completely precipitated with chromium hydroxide, and the chromium hydroxide product is obtained by solid-liquid separation. 6. The liquid phase oxidation reaction according to claim 5, wherein the temperature is 180-270° C., the oxygen partial pressure is 1.2-2.6 MPa, the stirring rotation speed is 500-900 rpm, and the reaction time is 1-5 hours. Method. According to claim 5, wherein the mass ratio of sodium hydroxide and chromite is (2-5):1, and the mass of sodium hydroxide is 30-60% of the total mass of sodium hydroxide and water. described method. The method according to claim 5, characterized in that the temperature is between 70 and 150°C and the time is between 120 and 210 min for said incubation and sedimentation. When barium hydroxide is added to the supernatant for precipitation reaction, the molar ratio of barium hydroxide and sodium chromate in the supernatant is (1-1.2):1, the reaction time is 1-2 hours, and the reaction temperature is 60. 6. The method of claim 5, wherein the temperature is ~80°C.
When barium hydroxide is added to the washing slag liquid to cause a precipitation reaction, the molar ratio of barium hydroxide and sodium chromate in the washing slag liquid is (1 to 1.2): 1, the reaction time is 1 to 2 hours, and the reaction temperature is is between 60 and 80°C. A step of adding sodium silicate pulp to the lye D containing aluminum to cause a precipitation reaction, and separating after the reaction is completed to obtain a low-aluminum lye and a sodium aluminosilicate precipitate. The method described in 5. 11. Process according to claim 10, characterized in that the lye D containing sodium silicate and aluminum has a molar ratio of sodium aluminate of (1-1.2):1. 11. Process according to claim 10, characterized in that it also includes the step of adding alkali to the low aluminum lye obtained from the separation and then returning it to the autoclave for recycling. 6. Process according to claim 5, characterized in that it also includes the step of returning the aluminum-bearing lye B to the autoclave for recycling. The ratio of the sum of the amounts of the barium chromate precipitate A and the barium chromate precipitate C and the amount of the substance of HCl in hydrochloric acid is 1: (2 to 5), and the volume of hydrochloric acid is 4 to 8 times the sum of the mass of the barium chromate precipitate A and the barium chromate precipitate C (in which the volume is in mL and the mass is in g), and the reducing agent is 6. Process according to claim 5, characterized in that it is a small-molecular alcoholic organic and the molar mass of the reducing agent is 1-5 times the molar mass of the theoretical reaction with barium chromate. 6. The method according to claim 5, wherein the reduction reaction has a stirring rotation speed of 200 to 400 rpm, a reaction temperature of 50 to 80° C., and a reaction time of 1 to 2 hours. 6. The method according to claim 5, characterized in that following the reduction reaction, the pH of the mixed solution is adjusted to 8-9 with barium hydroxide. 6. The method according to claim 5, further comprising the step of completely precipitating chromium with chromium hydroxide until barium is completely precipitated, and then adding sulfuric acid to the liquid phase obtained by solid-liquid separation to obtain a barium sulfate product. described method.

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