Method for preparing sodium sulfate solution and chromic oxide of different grades from chromium-containing sodium hydrogen sulfate

Abstract

The invention discloses a method for preparing a sodium sulfate solution and chromic oxide of different grades from chromium-containing sodium hydrogen sulfate, which comprises the following steps: calcining the chromium-containing sodium hydrogen sulfate at high temperature to obtain a solid product and a gas product; putting the solid product into a pulping tank, adding water, pulping and dissolving until the solid product is completely dispersed, preparing a feed liquid, and carrying out filter pressing to obtain a primary filter-pressed filter cake and an acidic solution; adding alkali into the acidic solution for neutralization, preserving heat and curing, and then carrying out filter pressing to obtain a secondary filter-pressed filter cake and a slightly acidic solution; washing and filter-pressing the primary filter-pressed filter cake, and calcining to obtain low-grade chromium sesquioxide; and washing the secondary filter-pressed filter cake, carrying out filter pressing, and calcining to obtain the high-grade chromium sesquioxide. The invention provides the method for efficiently recycling the by-product chromium-containing sodium hydrogen sulfate in the production process of chromic anhydride, the problem of poison of wastes is solved, the process is simple and easy to operate, environmental protection benefits and economic benefits are considered, and the method is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of by-product utilization, and particularly relates to a method for preparing sodium sulfate solution and different grade chromium sesquioxide from chromium-containing sodium bisulfate. BACKGROUND

[0002] In the process of producing chromic anhydride by the sulfuric acid method, about 1.4 tons of sodium bisulfate containing chromium is discharged for producing 1 ton of chromic anhydride. In order to improve the product quality of chromic anhydride, a large amount of hexavalent chromium is directly discharged with the sodium bisulfate, so that the content of hexavalent chromium in the discharged sodium bisulfate reaches 5-10%, and the acid value (calculated by sulfuric acid) reaches 35-40%.

[0003] At present, the most commonly used method for utilizing the chromium-containing sodium bisulfate in the chromium salt production industry is the recycling method, that is, the chromium-containing sodium bisulfate is used to replace sulfuric acid in the acidification process of sodium chromate solution. This process can effectively recycle the hexavalent chromium and sulfuric acid in the sodium bisulfate, but on the one hand, due to the high impurity content of the sodium bisulfate, a large amount of acid residue is generated, forming a new chromium-containing by-product, and at the same time, the use of sodium bisulfate in the acidification process will cause the concentration of the sodium chromate solution to decrease, increasing the subsequent evaporation cost; on the other hand, part of the impurities (such as aluminum, vanadium and iron) in the sodium bisulfate will enter the chromium salt production system, forming harmful element enrichment, affecting the product quality. In other methods, the chromium-containing sodium bisulfate can be used to produce basic chromium sulfate or chromium black, but due to the high impurity content of the sodium bisulfate, the product has high impurity content, and the industrial value is not high.

[0004] In summary, it is of great significance to study how to more effectively utilize and dispose of the chromium-containing sodium bisulfate, and realize the resourceful and high-value recycling of the chromium-containing sodium bisulfate. SUMMARY

[0005] An object of the present application is to solve at least the above problems and / or defects, and to provide at least the advantages to be described later.

[0006] In order to achieve these objects and other advantages of the present application, a method for preparing sodium sulfate solution and different grade chromium sesquioxide from chromium-containing sodium bisulfate is provided, which comprises the following steps: Step one, high-temperature calcination of the chromium-containing sodium bisulfate to obtain solid product and gaseous product; Step two, the solid product is put into a beating tank, water is added for beating and dissolving until complete dispersion, and then a certain concentration of slurry is prepared, and after pressure filtration, a first pressure filtration cake and an acidic solution are obtained, the first pressure filtration cake is chromium sesquioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate; Step three, neutralization of the acidic solution by adding alkali, heat preservation and aging, and then pressure filtration to obtain a second pressure filtration cake and a slightly acidic solution, the second pressure filtration cake is a chromium hydroxide cake, and the slightly acidic solution is a sodium sulfate solution; Step four, washing, pressure filtration, and calcination of the primary pressure filtration cake to produce low-grade chromium trioxide; Step five, washing, pressure filtration, and calcination of the secondary pressure filtration cake to produce high-grade chromium trioxide.

[0007] Preferably, in step one, the calcination temperature is 600-1000℃, and the calcination time is 10-60 min.

[0008] Preferably, in step one, the gaseous product is a mixture of SO2 and SO3, and the gaseous product is absorbed by a spray washing tower after being drawn by an air draft system to form a mixed liquid of sulfurous acid and sulfuric acid, which is used to treat hexavalent chromium in wastewater from a chromium salt production system.

[0009] Preferably, in step two, the concentration of the feed liquid is 200-410 g / L, and the pressure filtration pressure is 0.1-1.2 MPa.

[0010] Preferably, in step three, the addition of alkali for neutralization is the addition of sodium hydroxide to adjust the pH of the acidic liquid to 7-9; the temperature for heat curing is 60-95℃, and the time is 1-4 h; the pressure filtration pressure is 0.1-1.2 MPa; and electrolysis of the slightly acidic solution can obtain sodium hydroxide and sulfuric acid.

[0011] Preferably, in step four, the washing water ratio is 1:1-20, the pressure filtration pressure is 0.1-1.2 MPa, the calcination temperature is 900-1500℃, and the calcination time is 2-4 h.

[0012] Preferably, in step four, the low-grade chromium trioxide is a mixture of chromium trioxide, sodium chromate, and insoluble impurities, which can enter the calcination system of a chromium salt production system and be used as a chromium ore.

[0013] Preferably, in step five, the washing water ratio is 1:1-20, the pressure filtration pressure is 0.1-1.2 MPa, the calcination temperature is 900-1500℃, and the calcination time is 1-4 h.

[0014] Preferably, in step five, the high-grade chromium trioxide can be washed with water to remove chromium to produce metallurgical chrome green.

[0015] Preferably, step two is replaced by: putting the solid product into a pulping tank, adding water to pulp and dissolve until completely dispersed, preparing a material solution of a certain concentration, adding the material solution into a discharge plasma reactor with anode and cathode electrodes, introducing air that has passed through distilled water by an air pump, connecting the power supply, increasing the voltage to 400-700V, the current to 5-15A, and discharging for 20-30 minutes to reduce hexavalent chromium in the material solution to trivalent chromium, and obtaining a primary filter cake and an acidic liquid after pressure filtration. The primary filter cake consists of chromium trioxide and insoluble impurities, and the acidic liquid is a mixed solution of sodium sulfate, sodium bisulfate, and chromium sulfate.

[0016] The present invention has at least the following beneficial effects: It provides a method for the resource utilization of sodium bisulfate, a byproduct of chromic anhydride production, by preparing chromium bisulfate into chromium trioxide and sodium sulfate solutions of different grades, thus solving the toxicity problem of the waste. Simultaneously, a two-stage pressure filtration and fractionation separation technology is employed, enabling the obtained products to be reused, significantly improving recycling efficiency. Furthermore, the preparation method of the present invention yields high-purity chromium trioxide, is simple and easy to operate, and significantly reduces the overall cost of chromium resource recovery and sodium sulfate reuse while avoiding environmental pollution risks, thus balancing environmental and economic benefits and being suitable for industrial production.

[0017] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0018] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0019] The sodium bisulfate containing chromium used in Examples 1-7 is a byproduct of chromium anhydride. By mass fraction, it includes 3.71 wt% sodium dichromate, 3.62 wt% total chromium, 75.8 wt% sulfate, 0.04 wt% Fe2O3, and the remainder is impurities.

[0020] Example 1 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 64.5% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 67.5% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 95.67%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 98.38%.

[0021] Example 2 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 15 minutes to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 65.8% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 71.65% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 96.62%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 98.87%.

[0022] Example 3 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 20 minutes to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 66.6% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 70.34% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 96.57%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 98.61%.

[0023] Example 4 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 850℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 64.5% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 71.65% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 94.07%. Step 5: Wash the filter cake from the secondary filter press with a washing-to-water ratio of 1:10, filter under 0.2 MPa pressure, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 97.33%.

[0024] Example 5 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 850℃ for 20 minutes to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 67.46% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 72.61% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 95.04%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 97.89%.

[0025] Example 6 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 64.5% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 67.5% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing-to-water ratio of 1:5, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 92.36%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:5, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 96.91%.

[0026] Example 7 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into the pulping tank, add water to pulp and dissolve until completely dispersed, and prepare a 250g / L material solution. After filtration at 0.2MPa, a primary filter cake with a total chromium content of 64.5% and an acidic solution are obtained. The primary filter cake contains chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 67.5% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:15, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 96.81%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:15, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 98.97%.

[0027] Example 8 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 800℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into a pulping tank, add water and pulp until completely dispersed, prepare a 250g / L solution, add the solution to a discharge plasma reactor with cathode and anode electrodes, introduce air through distilled water by an air pump, turn on the power, increase the voltage to 500V and the current to 15A, discharge reaction for 30min, reduce hexavalent chromium in the solution to trivalent chromium, filter at 0.2MPa to obtain a primary filter cake with a total chromium content of 66.8% and an acidic solution. The primary filter cake is chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 70.5% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first press filter with a washing water ratio of 1:10, press filter at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 96.89%. Step 5: Wash the filter cake from the secondary pressure filter with a washing-to-water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 99.25%.

[0028] Example 9 A method for preparing sodium sulfate solution and chromium trioxide of different grades from chromium-containing sodium bisulfate includes the following steps: Step 1: Calcine sodium bisulfate containing chromium at 850℃ for 10 min to obtain solid and gaseous products; Step 2: Put the solid product into a pulping tank, add water and pulp until completely dispersed, prepare a 250g / L solution, add the solution to a discharge plasma reactor with anode and cathode electrodes, introduce air through distilled water by an air pump, turn on the power, increase the voltage to 500V and the current to 15A, discharge reaction for 30min, reduce hexavalent chromium in the solution to trivalent chromium, filter at 0.2MPa to obtain a primary filter cake with a total chromium content of 67.52% and an acidic solution. The primary filter cake is chromium trioxide and insoluble impurities, and the acidic solution is a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. Step 3: Neutralize the acidic solution with sodium hydroxide, adjust the pH to 7, and keep it at 80℃ for 2 hours. Then filter it under 0.2MPa pressure to obtain a secondary filter cake with a total chromium content of 73.16% and a slightly acidic solution. The secondary filter cake is a chromium hydroxide filter cake, and the slightly acidic solution is a sodium sulfate solution. Step 4: Wash the filter cake from the first filter press with a washing water ratio of 1:10, filter under 0.2 MPa pressure, and calcine at 1300℃ for 3 hours to obtain low-grade chromium trioxide with a total chromium content of 96.07%. Step 5: Wash the filter cake from the secondary pressure filter with a washing water ratio of 1:10, filter under pressure at 0.2 MPa, and calcine at 1300℃ for 3 hours to obtain high-grade chromium trioxide with a total chromium content of 99.12%.

[0029] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium characterized in that, The method comprises the following steps: Step one, calcining sodium bisulfate containing chromium at high temperature to obtain solid product and gas product; Step two, putting the solid product into a beating tank, adding water to beat and dissolve until completely dispersed, then preparing a certain concentration of slurry, and obtaining primary filter cake and acidic solution through pressure filtration, the primary filter cake being chromium trioxide and insoluble impurities, and the acidic solution being a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate; Step three, neutralizing the acidic solution with alkali, keeping warm and aging, then obtaining secondary filter cake and slightly acidic solution through pressure filtration, the secondary filter cake being chromium hydroxide filter cake, and the slightly acidic solution being sodium sulfate solution; Step four, washing and pressure filtering the primary filter cake, then calcining to obtain low-grade chromium trioxide; Step five, washing and pressure filtering the secondary filter cake, then calcining to obtain high-grade chromium trioxide.

2. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step one, the calcination temperature is 600-1000℃, and the calcination time is 10-60 min.

3. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step one, the gas product is a mixed gas of SO2 and SO3, the gas product is absorbed by a spray washing tower after being drawn by a system, forming a mixed liquid of sulfurous acid and sulfuric acid, which is used to treat hexavalent chromium in wastewater of a chromium salt production system.

4. The process for preparing sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step two, the concentration of the slurry is 200-410 g / L, and the pressure filtration pressure is 0.1-1.2 MPa.

5. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step three, the neutralization with alkali is adding sodium hydroxide to adjust the pH of the acidic solution to 7-9; the temperature for keeping warm and aging is 60-95℃, and the time is 1-4 h; the pressure filtration pressure is 0.1-1.2 MPa; the slightly acidic solution can be electrolyzed to obtain sodium hydroxide and sulfuric acid.

6. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step four, the washing water ratio is 1:1-20, the pressure filtration pressure is 0.1-1.2 MPa, the calcination temperature is 900-1500℃, and the calcination time is 2-4 h.

7. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step four, the low-grade chromium trioxide is a mixture of chromium trioxide, sodium chromium sulfate and insoluble impurities, which can be used in the calcination system of the chromium salt production to serve as chromium ore. ​ 8. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step five, the washing water ratio is 1:1-20, the pressure filtration pressure is 0.1-1.2 MPa, the calcination temperature is 900-1500℃, and the calcination time is 1-4 h.

9. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step five, the high-grade chromium trioxide can be washed with water to remove chromium to prepare metallurgical chrome green.

10. The process for the preparation of sodium sulfate solution and different grades of chromium trioxide from sodium bisulfate containing chromium as claimed in claim 1 wherein, In step two, the solid product is put into a beating tank, water is added to beat and dissolve until completely dispersed, then a certain concentration of slurry is prepared, the slurry is added to a discharge plasma reactor with negative and positive electrodes, air passing through distilled water is introduced by an air pump, the power is turned on, and the discharge reaction is carried out for 20-30 min, hexavalent chromium in the slurry is reduced to trivalent chromium, and primary filter cake and acidic solution are obtained through pressure filtration, the primary filter cake being chromium trioxide and insoluble impurities, and the acidic solution being a mixed solution of sodium sulfate, sodium bisulfate and chromium sulfate. ​