Method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor

Abstract

The invention discloses a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor, which comprises the following steps of: performing double decomposition reaction on the sodium dichromate mother liquor serving as a raw material and potassium chloride to prepare a crude potassium dichromate semi-finished product and a chromium-containing sodium chloride solution; and carrying out deep processing and purification on the crude potassium dichromate semi-finished product to produce reagent-grade potassium dichromate, carrying out evaporative crystallization on the chromium-containing sodium chloride solution, washing to reduce the chromium content, and adding a reducing agent to remove chromium so as to prepare industrial salt. According to the method, iron and aluminum impurities can be directly removed in the double decomposition reaction procedure, the yield is increased, meanwhile, the yield of the rough potassium dichromate semi-finished product is guaranteed, and a foundation is laid for subsequent production of high-quality reagent-grade potassium dichromate. Meanwhile, the method has the advantages of being high in operability, low in operation cost and easy to industrialize. And wastewater generated in the production process can be recycled, so that resource maximization is realized, and environmental pollution is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of chromium salt preparation, and more specifically, relates to a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor. Background Art

[0002] Sodium dichromate mother liquor is used as raw material, potassium chloride is added to undergo double decomposition reaction to prepare high-quality crude potassium dichromate semi-finished product, and then the crude potassium dichromate semi-finished product is subjected to a series of purification treatments to obtain reagent-grade potassium dichromate.

[0003] Chinese invention patent CN1565979A discloses a method for preparing a crude potassium dichromate semi-finished product, which produces a crude potassium dichromate semi-finished product from potassium chromate crystals. The method includes carbonating potassium chromate slurry, refining the obtained crude potassium dichromate semi-finished product crystals by removing iron and aluminum impurities, cooling and salting out the obtained potassium bicarbonate solution, recovering potassium chromate and co-producing potassium bicarbonate. The process product does not contain Cl - Although Cl pollution is eliminated during the production process and the terminal use of the product, the carbonization rate of the industrial implementation process of this process is only 75-85%. The treatment of iron and aluminum impurities in this process is left to the later stage, and the generated potassium dichromate needs to be dissolved twice, with a low yield. The precipitation condition of potassium carbonate is -5 to -12°C, and the operating cost is considered, making industrial production difficult. Summary of the invention

[0004] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] In order to achieve these purposes and other advantages according to the present invention, a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor is provided, comprising: using sodium dichromate mother liquor as a raw material to carry out double decomposition reaction with potassium chloride to first prepare a crude potassium dichromate semi-finished product and a chromium-containing sodium chloride solution, further processing and purifying the crude potassium dichromate semi-finished product to produce reagent-grade potassium dichromate, evaporating and crystallizing the chromium-containing sodium chloride solution, washing to reduce the chromium content, and then adding a reducing agent to remove the chromium to prepare industrial salt (sodium chloride).

[0006] Preferably, the method specifically comprises the following steps:

[0007] Step 1: Mix the raw materials of sodium dichromate mother liquor and potassium chloride solid, add water to adjust to a suitable concentration, and heat to boiling to obtain a reaction solution;

[0008] Step 2: add alkali to the reaction solution of step 1 to adjust the acidification rate of the solution, add an oxidant to remove trivalent chromium ions in the reaction solution, filter and remove impurities after heat preservation and precipitation, wash the hexavalent chromium doped in the impurities with hot water, and return the washing water to step 1;

[0009] Step 3: Filter and wash the solid obtained after cooling and crystallization of the filtrate in step 2, and the obtained solid is a crude potassium dichromate semi-finished product.

[0010] Step 4, soaking the crude potassium dichromate semi-finished product obtained in step 3 for a period of time and then filtering it, returning the filtrate to step 1, and the solid is reserved;

[0011] Step 5: Dissolve the solid in step 4 in clean water, adjust to a suitable concentration and then filter, and cool the filtered solution for recrystallization;

[0012] Step 6: Filter the solution in step 5, and return the filtered filtrate to step 5 to dissolve the soaked solid. If the filtrate does not meet the physical and chemical indicators of the required solvent, return to step 1, and the filtered solid is dried to obtain reagent-grade potassium dichromate;

[0013] Step 7, evaporating and crystallizing the filtrate from step 3, filtering and washing, the obtained solid is chromium-containing sodium chloride, and the filtrate and washing water are returned to step 1;

[0014] Step eight, dissolving the chromium-containing sodium chloride in step eight, adding a reducing agent to remove chromium, filtering, evaporating and crystallizing to obtain industrial salt.

[0015] Preferably, in the step 1, the content of sodium dichromate mother liquor is ≥1100 g / L as calculated by Na2Cr2O7.2H2O, the content of potassium chloride is ≥60% as calculated by K2O, the sodium dichromate mother liquor and potassium chloride are mixed in a sodium-potassium molar ratio of 1.5 to 2, the concentration of the reaction solution is 35 to 38°Bé, and the reaction temperature is 100 to 110°C.

[0016] Preferably, in step 2, the alkali used is at least one of sodium hydroxide and potassium hydroxide, the insulation time is 1 to 2 hours, the oxidant is at least one of sodium chlorate and sodium hypochlorite, and the acidification rate is 89 to 96%.

[0017] Preferably, in step 3, the cooling crystallization temperature is ≤40°C, and the qualified washing standard is: Cl - ≤0.03%.

[0018] Preferably, in the step 4, the soaking time of the crude potassium dichromate semi-finished product is 24 to 48 hours, and the water used for soaking is at least one of soft water and clean water without chloride.

[0019] Preferably, in step five, the dissolution concentration is controlled at 29-32 Bé, and the fine filtration equipment after dissolution is at least one of plate and frame filtration, single disc filtration, and bag filtration, and the pore size must be ≤10 μm.

[0020] Preferably, in step 6, the solvent selection criteria are: Cl -≤0.002%, the drying equipment is at least one of a boiling dryer and a double cone dryer.

[0021] Preferably, in the step seven, the evaporation concentration of the filtrate is 38-42° Bé, and the hexavalent chromium content in the chromium-containing sodium chloride is ≤0.08%.

[0022] Preferably, the reducing agent in step eight is at least one of sodium pyrosulfite and hydrazine hydrate.

[0023] At the same time, the industrial salt prepared also includes ultrafine processing of the industrial salt, and the specific ultrafine processing method includes:

[0024] S1. The prepared industrial salt is configured into a sodium chloride (industrial salt) aqueous solution with a concentration of 2-4 mol / L, and the temperature is raised to 30-60° C. by stirring, and n-butanol and polyvinyl pyrrolidone are added to the sodium chloride aqueous solution, and the volume ratio of the sodium chloride aqueous solution to n-butanol and polyvinyl pyrrolidone is 4:1-2:1, and ultrasonic dispersion is performed at 50-60 kHz for 10-30 min, and then the mixture is allowed to stand for 4-12 hours; after standing, the mixture is evaporated and concentrated to 40-80 Bé to obtain an industrial salt concentrate;

[0025] S2, adding the industrial salt concentrate to a mixed solvent of glycerol and N,N-dimethylformamide to obtain solution A; the volume ratio of the industrial salt concentrate, glycerol and N,N-dimethylformamide is 1-3:5-8:1-2; after stirring at a speed of 600-2400 rpm for 20-50 min, the solution A is heated to 120-140° C., and n-butanol is distilled off; after standing for 6-12 h, the temperature is continued to be raised, and evaporation is performed to obtain a saturated solution of industrial salt;

[0026] S3. Add triethanolamine to the saturated solution of industrial salt, ultrasonically disperse it at 30-60kHz for 1-2 hours, then let it stand for 2-6 hours, and then spray centrifugal dry the saturated solution of industrial salt; the atomizer speed is 8000-12000rpm, the inlet air temperature is 170-220℃, and the outlet air temperature is 120-150℃ to obtain ultrafine industrial salt; wherein the volume ratio of triethanolamine to the saturated solution of industrial salt is 1-10:50-100.

[0027] The present invention has at least the following beneficial effects:

[0028] (1) Iron and aluminum impurities can be directly removed in the double decomposition reaction process to improve the yield while ensuring the output of crude potassium dichromate semi-finished product, laying the foundation for the subsequent production of high-quality reagent-grade potassium dichromate.

[0029] (2) Wastewater generated during the production process can be recycled to maximize resources and avoid environmental pollution.

[0030] (3) The present invention uses alcohol solvents twice to regulate the morphology and size of the prepared industrial salt (sodium chloride), that is, first using n-butanol with a longer carbon chain length as a solvent, and then using glycerol as a solvent. At the same time, polyvinyl pyrrolidone is mixed in the n-butanol, and N,N-dimethylformamide is added to the glycerol. On the basis of alcohol regulation and the growth of sodium chloride crystals, polyvinyl pyrrolidone and N,N-dimethylformamide are used to further inhibit the ionization and migration of sodium chloride, and the growth of sodium chloride crystals is further refined and regulated. As a result, the surface twice alcohol solvents combined with the regulating effect of polyvinyl pyrrolidone and N,N-dimethylformamide significantly reduce the morphology particle size and particle size distribution range of sodium chloride. Finally, triethanolamine is added as a morphology control agent, and the particle size and particle size distribution range of sodium chloride are further reduced by a spray drying method, thereby obtaining ultrafine sodium chloride. Ultrafine sodium chloride industrial salt is widely used in the fields of chemical industry, agriculture, and environmental protection.

[0031] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a process flow chart of a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0034] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0035] The sodium dichromate mother liquor used in each embodiment is the secondary concentrated mother liquor of Huayi Da sodium dichromate workshop, and the potassium chloride used is imported from Russia. Example 1:

[0036] like Figure 1 As shown, this embodiment provides a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor, comprising the following steps:

[0037] Step 1: Add 4L of water and 0.23L of 1350g / L sodium dichromate mother liquor into the reaction vessel, heat the solution to 100°C, add 150g of potassium chloride, and adjust the solution concentration to 37°Bé. At this time, the potassium dichromate content in the solution is 344.37g / L, the sodium chloride content is 218.17g / L, and the potassium salt ratio is 1.58. Continue to heat the solution to boiling.

[0038] Step 2: Add 25g of sodium hydroxide to the solution, adjust the acidification rate to 94.33%, add 1g of sodium chlorate, keep warm and precipitate for 1 hour, then filter.

[0039] Step 3: Cool the filtered solution to crystallize, filter and wash it when the temperature is cooled to 40°C, and wash the chloride to 0.021%. The obtained solid is the undried crude potassium dichromate semi-finished product.

[0040] Step 4: Soak the undried crude potassium dichromate semi-finished product for 36 hours and then filter it. Change the water twice during the soaking period.

[0041] Step 5: Put the soaked solid into a reaction container, add soft water, stir and heat until the solid is completely dissolved, and use plate and frame filtration to perform fine filtration when the solution concentration is 30°Bé.

[0042] Step 6: The solution after fine filtration is recrystallized and filtered when the temperature drops to 40°C. The obtained solid is dried to obtain reagent grade potassium dichromate.

[0043] Step 7: Evaporate the filtrate after cooling, crystallizing and filtering to a concentration of 40° Bé, filter and wash, and the solid is sodium chloride with a hexavalent chromium content of 0.04%.

[0044] Step 8: Dissolve 350g of solid sodium chloride containing chromium with a hexavalent chromium content of 0.04% (calculated as potassium dichromate) in water, add 0.26g of sodium pyrosulfite to reduce the hexavalent chromium after dissolution, filter after heat preservation and precipitation, evaporate and crystallize the filtrate and then dry it to obtain industrial salt (sodium chloride).

[0045] Among them, the test data of reagent-grade potassium dichromate prepared in this embodiment is shown in Table 1:

[0046] Table 1 Reagent grade potassium dichromate test data

[0047] Potassium dichromate content (%) 99.9466 Water insoluble matter (%) 0.003 Loss on drying (%) 0.02 Chloride (Cl) (%) 0.0008 <![CDATA[Sulfate (SO4) (%)]]> 0.004 Sodium(Na)(%) 0.018 Calcium (Ca) (%) 0.002 Iron (Fe) (%) 0.0008 Copper (Cu) (%) 0.0008 Lead (Pb) (%) 0.004

[0048] As can be seen from the above table, the potassium dichromate content in the reagent-grade potassium dichromate prepared in this embodiment exceeds 99.9%, and the chloride content is controlled at 0.0008%, which is lower than the required 0.001%, and meets the reagent-grade potassium dichromate standard.

[0049] Embodiment 2:

[0050] This embodiment provides a method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor, comprising the following steps:

[0051] Step 1: Add 4L of water and 0.21L of 1420g / L sodium dichromate mother liquor to the reaction vessel, heat the solution to 100°C, add 150g of potassium chloride, and adjust the solution concentration to 37°Bé. At this time, the potassium dichromate content in the solution is 353.20g / L, the sodium chloride content is 212.28g / L, and the potassium salt ratio is 1.66. Continue to heat the solution to boiling.

[0052] Step 2: Add 25g of sodium hydroxide to the solution, adjust the acidification rate to 95.75%, add 1g of sodium chlorate, keep warm and precipitate for 1 hour, then filter.

[0053] Step 3: Cool the filtered solution to crystallize, filter and wash when the temperature is cooled to 40°C, and wash the chloride to 0.023%. The obtained solid is the undried crude potassium dichromate semi-finished product.

[0054] Step 4: Soak the undried crude potassium dichromate semi-finished product for 36 hours and then filter it. Change the water twice during the soaking period.

[0055] Step 5: Put the soaked solid into a reaction container, add soft water, stir and heat until the solid is completely dissolved, and filter when the solution concentration is 30°Bé, with a filter cloth pore size of 0.2 μm.

[0056] Step 6: The solution after fine filtration is recrystallized and filtered when the temperature drops to 40°C. The obtained solid is dried to obtain reagent grade potassium dichromate.

[0057] Step 7: Evaporate the filtrate after cooling, crystallizing and filtering to a concentration of 40° Bé, filter and wash, and the solid is sodium chloride with a hexavalent chromium content of 0.04%.

[0058] Step 8: Dissolve 350g of solid chromium-containing sodium chloride with a hexavalent chromium content of 0.04% (calculated as potassium dichromate) in water, add 0.26g of sodium pyrosulfite to reduce the hexavalent chromium after dissolution, filter after heat preservation and precipitation, evaporate and crystallize the filtrate and then dry it to obtain industrial salt.

[0059] Among them, the test data of the reagent-grade potassium dichromate prepared in this embodiment is shown in Table 2;

[0060] Table 2 Reagent grade potassium dichromate test data

[0061]

[0062]

[0063] It can be seen from the above table that the potassium dichromate content in the reagent-grade potassium dichromate prepared in this example exceeds 99.9%, and the chloride content is controlled at 0.0008%, which is lower than the required 0.001%, and meets the reagent-grade potassium dichromate standard.

[0064] Example 3

[0065] In this embodiment, the industrial salt (sodium chloride) prepared in Example 1 is subjected to ultrafine treatment, and the specific ultrafine treatment method includes:

[0066] S1. 234.0 g of the prepared industrial salt is configured into 1 L of a 4 mol / L sodium chloride (industrial salt) aqueous solution, stirred and heated to 60° C., 250 mL of n-butanol and 250 mL of polyvinyl pyrrolidone are added to the sodium chloride aqueous solution, ultrasonically dispersed at 55 kHz for 30 min, and then allowed to stand for 12 h; after standing, evaporate and concentrate to 50 Bé to obtain an industrial salt concentrate;

[0067] S2. Add 200 mL of industrial salt concentrate to a mixed solvent of 500 mL of glycerol and 100 mL of N,N-dimethylformamide to obtain solution A; after stirring at a speed of 1200 rpm for 50 min, heat solution A to 120° C. and distill to remove n-butanol; after standing for 12 h, continue to heat and evaporate to obtain a saturated solution of industrial salt;

[0068] S3. Add 10 mL of triethanolamine to 100 mL of saturated industrial salt solution, disperse under 60 kHz ultrasonic wave for 1 hour, and then let stand for 6 hours. Then, the saturated industrial salt solution is sprayed and centrifugally dried. The atomizer speed is 12000 rpm, the air inlet temperature is 170°C, and the air outlet temperature is 120°C to obtain ultrafine industrial salt.

[0069] Example 4

[0070] In this embodiment, the industrial salt prepared in Example 1 is subjected to ultrafine treatment, and the specific ultrafine treatment method includes:

[0071] S1. 234.0 g of the prepared industrial salt was prepared into 1 L of a 4 mol / L sodium chloride (industrial salt) aqueous solution, stirred and heated to 60° C., 500 mL of n-butanol and 250 mL of polyvinyl pyrrolidone were added to the sodium chloride aqueous solution, and ultrasonic dispersion was performed at 60 kHz for 30 min and then allowed to stand for 12 h; after standing, the solution was evaporated and concentrated to 60 Bé to obtain an industrial salt concentrate;

[0072] S2. Add 200 mL of industrial salt concentrate to a mixed solvent of 600 mL of glycerol and 200 mL of N,N-dimethylformamide to obtain solution A; after stirring at a speed of 1800 rpm for 50 min, heat solution A to 140° C. and distill to remove n-butanol; after standing for 12 h, continue to heat and evaporate to obtain a saturated solution of industrial salt;

[0073] S3. Add 5 mL of triethanolamine to 100 mL of saturated industrial salt solution, disperse by 60 kHz ultrasonic wave for 2 hours, and then let stand for 6 hours, then spray centrifugal drying the saturated industrial salt solution. The atomizer speed is 12000 rpm, the air inlet temperature is 220°C, and the air outlet temperature is 150°C to obtain ultrafine industrial salt.

[0074] Comparative Example 1

[0075] In this comparative example, the industrial salt prepared in Example 1 is subjected to ultrafine treatment, and the specific method includes:

[0076] 234.0 g of the prepared industrial salt was configured into 1 L of a 4 mol / L sodium chloride (industrial salt) aqueous solution, stirred and heated to 60° C., 250 mL of n-butanol and 250 mL of polyvinyl pyrrolidone were added to the sodium chloride aqueous solution, and ultrasonic dispersion was performed at 55 kHz for 30 min and then allowed to stand for 12 h; after standing, evaporation, concentration, crystallization, solid-liquid separation, and drying were performed to obtain ultrafine industrial salt.

[0077] Comparative Example 2

[0078] In this comparative example, the industrial salt prepared in Example 1 is subjected to ultrafine treatment, and the specific method includes:

[0079] 234.0 g of the industrial salt prepared in Example 1 was added to a mixed solvent of 500 mL of glycerol and 100 mL of N,N-dimethylformamide to obtain solution A; after stirring at a speed of 1200 rpm for 50 min, the solution A was heated to 120° C. and n-butanol was distilled off; after standing for 12 h, the temperature was continued to be raised, evaporated, concentrated and crystallized, solid-liquid separated, and dried to obtain ultrafine industrial salt.

[0080] Comparative Example 3

[0081] In this comparative example, the industrial salt (sodium chloride) prepared in Example 1 is subjected to ultrafine treatment, and the specific ultrafine treatment method includes:

[0082] S1. 234.0 g of the prepared industrial salt is configured into 1 L of a 4 mol / L sodium chloride (industrial salt) aqueous solution, stirred and heated to 60° C., 250 mL of n-butanol and 250 mL of polyvinyl pyrrolidone are added to the sodium chloride aqueous solution, ultrasonically dispersed at 55 kHz for 30 min, and then allowed to stand for 12 h; after standing, evaporate and concentrate to 50 Bé to obtain an industrial salt concentrate;

[0083] S2. Add 10 mL of triethanolamine to 100 mL of industrial concentrated solution, disperse under 60 kHz ultrasonic wave for 1 hour, and then let stand for 6 hours. Then, spray centrifugal drying is performed on the saturated industrial salt solution. The atomizer speed is 12000 rpm, the air inlet temperature is 170°C, and the air outlet temperature is 120°C to obtain ultrafine industrial salt.

[0084] Comparative Example 4

[0085] In this comparative example, the industrial salt prepared in Example 1 is subjected to ultrafine treatment, and the specific method includes:

[0086] S1. Add 234.0 g of the industrial salt prepared in Example 1 to a mixed solvent of 500 mL of glycerol and 100 mL of N,N-dimethylformamide to obtain solution A; after stirring at a speed of 1200 rpm for 50 min, heat solution A to 120° C., distill off n-butanol, and let stand for 12 h;

[0087] S2. Add 10 mL of triethanolamine to 100 mL of solution A, disperse under 60 kHz ultrasonic wave for 1 hour, and then let stand for 6 hours. Then, spray centrifugal drying is performed on the saturated industrial salt solution. The atomizer speed is 12000 rpm, the air inlet temperature is 170°C, and the air outlet temperature is 120°C to obtain ultrafine industrial salt.

[0088] Comparative Example 5

[0089] In this comparative example, the industrial salt prepared in Example 1 is subjected to ultrafine treatment. The difference between this comparative example and Example 3 is that triethanolamine is not added, and the process parameters of the remaining steps are the same as those of Example 3.

[0090] Comparative Example 6

[0091] In this comparative example, the industrial salt prepared in Example 1 is subjected to ultrafine treatment. The difference between this comparative example and Example 3 is that an equal amount of glycine is used to replace triethanolamine, and the process parameters of the remaining steps are the same as those of Example 3.

[0092] The industrial salt samples of Examples 1-2 and the industrial salts after ultrafine treatment of Examples 3-4 and Comparative Examples 1-6 were scanned and the particle size distribution was calculated using a scanning electron microscope, and Table 3 was obtained:

[0093] Table 3 Particle size data of industrial salt in various embodiments and comparative examples

[0094] D10(μm) D50(μm) D90(μm) Example 1 64.51 256.02 409.14 Example 2 59.34 242.92 411.83 Example 3 12.26 23.54 38.77 Example 4 14.19 28.08 41.60 Comparative Example 1 46.52 157.10 325.47 Comparative Example 2 52.33 227.46 318.02 Comparative Example 3 28.12 110.55 265.34 Comparative Example 4 39.15 134.31 310.96 Comparative Example 5 19.25 101.59 210.44 Comparative Example 6 16.53 85.42 143.29

[0095] It can be seen from the above table that the particle size of the industrial salt after ultrafine treatment in Example 3 is concentrated in the range of 12.23 μm to 38.77 μm, and the particle size of the industrial salt after ultrafine treatment in Example 4 is concentrated in the range of 14.19 μm to 41.60 μm. The particle size and distribution range are not only significantly improved compared with Examples 1 and 2, but also better than the industrial salts obtained by the treatment of Comparative Examples 1 to 6.

[0096] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0097] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor, characterized in that: include: Sodium dichromate mother liquor is used as raw material to carry out double decomposition reaction with potassium chloride to first prepare crude potassium dichromate semi-finished product and chromium-containing sodium chloride solution. The crude potassium dichromate semi-finished product is subjected to deep processing and purification to produce reagent-grade potassium dichromate. The chromium-containing sodium chloride solution is evaporated and crystallized, washed to reduce the chromium content, and then a reducing agent is added to remove the chromium to prepare industrial salt.

2. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 1, characterized in that: The specific steps include: Step 1: Mix the raw materials of sodium dichromate mother liquor and potassium chloride solid, add water to adjust to a suitable concentration, and heat to boiling to obtain a reaction solution; Step 2: add alkali to the reaction solution of step 1 to adjust the acidification rate of the solution, add an oxidant to remove trivalent chromium ions in the reaction solution, filter and remove impurities after heat preservation and precipitation, wash the hexavalent chromium doped in the impurities with hot water, and return the washing water to step 1; Step 3, filtering and washing the solid obtained after cooling and crystallization of the filtrate in step 2, and the obtained solid is a crude potassium dichromate semi-finished product; Step 4, soaking the crude potassium dichromate semi-finished product obtained in step 3 for a period of time and then filtering it, returning the filtrate to step 1, and the solid is reserved; Step 5: Dissolve the solid in step 4 in clean water, adjust to a suitable concentration and then filter, and cool the filtered solution for recrystallization; Step 6: Filter the solution in step 5, and return the filtered filtrate to step 5 to dissolve the soaked solid. If the filtrate does not meet the physical and chemical indicators of the required solvent, return to step 1, and the filtered solid is dried to obtain reagent-grade potassium dichromate; Step 7, evaporating and crystallizing the filtrate from step 3, filtering and washing, the obtained solid is chromium-containing sodium chloride, and the filtrate and washing water are returned to step 1; Step eight, dissolving the chromium-containing sodium chloride in step eight, adding a reducing agent to remove chromium, filtering, evaporating and crystallizing to obtain industrial salt.

3. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step 1, the content of Na2Cr2O7.2H2O in the sodium dichromate mother liquor is ≥1100 g / L, the content of potassium chloride is ≥60% as calculated by K2O, the sodium dichromate mother liquor and potassium chloride are mixed in a sodium-potassium molar ratio of 1.5 to 2, the concentration of the reaction solution is 35 to 38° Bé, and the reaction temperature is 100 to 110°C.

4. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step 2, the alkali used is at least one of sodium hydroxide and potassium hydroxide, the insulation time is 1-2 hours, and the acidification rate is 89-96%; the oxidant is at least one of sodium chlorate and sodium hypochlorite, and the molar ratio of the oxidant to trivalent chromium is 1-3:

2.

5. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step 3, the cooling crystallization temperature is ≤40°C, and the qualified washing standard is: Cl - ≤0.03%.

6. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step 4, the crude potassium dichromate semi-finished product is soaked for 24-48 hours, and the water used for soaking is at least one of soft water and clean water without chloride.

7. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step 5, the dissolution concentration is controlled at 29-32 Bé, and the fine filtration equipment after dissolution is at least one of plate and frame filtration, single disc filtration, and bag filtration, and the pore size must be ensured to be ≤10 μm.

8. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In step 6, the solvent selection criteria are: Cl - ≤0.002%, the drying equipment is at least one of a boiling dryer and a double cone dryer.

9. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: The evaporation concentration of the filtrate in step seven is 38-42° Bé, and the hexavalent chromium content in the chromium-containing sodium chloride is ≤0.08%.

10. The method for preparing reagent-grade potassium dichromate and industrial salt from sodium dichromate mother liquor according to claim 2, characterized in that: In the step eight, the reducing agent is at least one of sodium pyrosulfite and hydrazine hydrate, and the molar ratio of the reducing agent to hexavalent chromium is 1-2:3-4.

Images