Method for cyclic neutralization of carbonation liquid in sodium chromate production

Abstract

The invention discloses a method for circularly and continuously neutralizing a carbonization solution in sodium chromate production, which comprises the following steps: adding the carbonization solution into a sodium chromate alkaline solution or slurry for continuous neutralization, and then washing with a filter to obtain a sodium chromate neutral solution and filter residues; adding a carbonization solution into the sodium chromate neutral solution for acidification pretreatment to obtain a pretreatment solution, evaporating the pretreatment solution, introducing CO2 for carbonization, filtering a carbonization product with a filter, and washing with hot water to obtain a carbonization solution and sodium bicarbonate; and adding the carbonized solution into a new sodium chromate alkaline solution or slurry, carrying out continuous neutralization and washing with a filter to obtain a sodium chromate neutral solution, and repeating the operation to realize cyclic continuous neutralization of the carbonized solution in sodium chromate production. The method is simple to operate, the generation of chromium-containing sodium sulfate in the existing sodium bichromate production process can be reduced, the environmental protection risk and the production cost are reduced, the produced by-product sodium bicarbonate returns to a calcium-free roasting system to replace part of sodium carbonate to participate in batching, and industrial green production is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of comprehensive utilization of chromium salt, and particularly relates to a method for recycling neutralization of carbonization liquid in sodium chromate production. BACKGROUND

[0002] Chromium salt is one of main varieties of inorganic salt, and calcium-free roasting is a main process for producing red prussiate of sodium, a basic product of chromium salt production. The calcium-free roasting technology has been developed, but the existing neutralization and acidification process at the end of the red prussiate of sodium production process is still the mature and stable sulfuric acid process, and the disposal of sodium bisulfate containing chromium is involved, so a large amount of sodium sulfate containing chromium is generated, which needs to be disposed as hazardous waste. CN111115685A discloses a kind of intermittent neutralization method for treating sodium chromate alkaline liquid, and the acidifying agent involves sulfuric acid and sodium bisulfate; sodium sulfate is generated in the neutralization process of sodium carbonate or sodium hydroxide in the sodium chromate alkaline liquid, and the production of sodium sulfate containing chromium is increased in the red prussiate of sodium production process. SUMMARY

[0003] An object of the present application is to solve at least the above problems and / or deficiencies, and to provide at least the advantages described hereinafter.

[0004] To achieve these objects and other advantages of the present application, a method for recycling continuous neutralization of carbonization liquid in sodium chromate production is provided, comprising the following steps:

[0005] Step one, adding carbonization liquid to the sodium chromate alkaline liquid or slurry for continuous neutralization, then performing belt filtration washing to obtain sodium chromate neutral liquid and filter residue;

[0006] Step two, adding carbonization liquid to the sodium chromate neutral liquid for acidification pretreatment to obtain pretreated liquid, evaporating the pretreated liquid, then introducing CO2 for carbonization, and performing belt filtration and washing with hot water on the carbonization product to obtain carbonization liquid and sodium bicarbonate;

[0007] Step three, adding the carbonization liquid to new sodium chromate alkaline liquid or slurry for continuous neutralization, then performing belt filtration washing to obtain sodium chromate neutral liquid, and then repeating steps one to three to realize recycling continuous neutralization of carbonization liquid in sodium chromate production.

[0008] Preferably, in step one, the temperature during continuous neutralization is 80-95℃, and the pH of the sodium chromate neutral liquid is 6.8-7.2 after continuous neutralization; only when the carbonization liquid is first added to the sodium chromate alkaline liquid or slurry, the carbonization liquid is replaced by red prussiate of sodium dehydration mother liquor, and the main component of the red prussiate of sodium dehydration mother liquor is Na2Cr2O7.

[0009] Preferably, in step two, when the carbonization liquid is added for acidification pretreatment, the acid value of the liquid is detected, and the acidification rate of the liquid is controlled at 10-20%, wherein the acidification rate is the proportion of the conversion of sodium chromate to red prussiate of sodium during acidification pretreatment.

[0010] Preferably, in the second step, the evaporation is carried out by using an mvr evaporator, and the concentration of the feed liquid is controlled at 700-900 g / L in terms of sodium dichromate.

[0011] Preferably, in the second step, the carbonization is carried out in a carbonizer, the CO2 pressure is 0.8-1.2 MPa, the carbonization temperature is 20-80℃, the carbonization time is 0.5-1 h, and the carbonization rate is controlled at 70-85% by detecting the acid value of the carbonized liquid, wherein the carbonization rate is the proportion of sodium chromate converted into sodium dichromate during carbonization.

[0012] Preferably, in the second step, the obtained sodium bicarbonate can be used for returning to the calcium-free roasting system after drying.

[0013] Preferably, in the first and third steps, the alkalinity of the sodium chromate alkaline liquid or slurry is 80-110 g / L in terms of Na2CO3.

[0014] Preferably, the filter residue obtained in the first step can be used for returning to the calcium-free roasting system.

[0015] Preferably, the main component of the carbonization liquid used in the first to third steps is Na2Cr2O7.

[0016] Preferably, in the second step, a high-pressure-resistant carbonizer is used for carbonization, and the CO2 is replaced by supercritical CO2, the carbonization temperature is 30-80℃, and the pressure during carbonization is controlled at 7.4-8.5 MPa.

[0017] The present application at least has the following beneficial effects: the present application can reduce the production of chromium-containing sodium sulfate in the existing sodium dichromate production process, reduce the environmental protection risk and production cost, and make the entire sodium dichromate production process more green, circular and sustainable; the present application is simple to operate, the by-product sodium bicarbonate produced is returned to the calcium-free roasting system to replace part of the pure soda for batching, which is beneficial to the green production of industry; and the present application also uses supercritical CO2 for carbonization, CO2 has good diffusion performance in the supercritical state, which can effectively improve the reaction rate.

[0018] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following description, and will be understood by those skilled in the art upon reading and understanding the specification. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The process flow chart of the present application. DETAILED DESCRIPTION

[0020] The present application will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the specification.

[0021] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0022] Example 1

[0023] A method for recycling and neutralizing sodium chromate carbonization liquid, the process flow chart is shown as Figure 1 The method comprises the following steps:

[0024] Step one, sodium dichromate dehydrated mother liquor is added to sodium chromate alkaline liquid slurry with a basicity of 86.22 g / L (calculated as Na2CO3) for continuous neutralization to pH 7.0, and then filter washing is carried out to obtain sodium chromate neutral liquid and filter residue;

[0025] Step two, carbonization liquid is added to the sodium chromate neutral liquid for acidification pretreatment, and the acid value of the liquid is detected during the process until the acidification rate (the proportion of sodium chromate converted into sodium dichromate) of the liquid is 15.14%, and a pretreated liquid is obtained. The pretreated liquid is evaporated to a liquid concentration of 736.61 g / L (calculated as sodium dichromate), and then CO2 is introduced for carbonization. The carbonization temperature is 35℃, the carbonization pressure is 1.0 MPa, the carbonization product is filtered and washed with hot water, and the acid value of the carbonization liquid is detected to obtain carbonization liquid with a carbonization rate (the proportion of sodium chromate converted into sodium dichromate) of 78.54% and sodium bicarbonate;

[0026] Step three, the carbonization liquid is added to new sodium chromate alkaline liquid or slurry for continuous neutralization, and after filter washing, sodium chromate neutral liquid is obtained, which meets the process requirements, the Al2O3 in the sodium chromate neutral liquid is less than 5 mg / L, and the sodium chromate content (calculated as sodium dichromate) is greater than 250 g / L; then steps one to three are repeated to realize the recycling and continuous neutralization of sodium chromate carbonization liquid.

[0027] Example 2

[0028] A method for recycling and neutralizing sodium chromate carbonization liquid, the method comprises the following steps:

[0029] Step one, sodium dichromate dehydrated mother liquor is added to sodium chromate alkaline liquid slurry with a basicity of 86.22 g / L (calculated as Na2CO3) for continuous neutralization to pH 7.0, and then filter washing is carried out to obtain sodium chromate neutral liquid and filter residue;

[0030] Step two, add carbonization liquid to the sodium chromate neutral liquid, and perform acidification pretreatment, detect the acid value of the liquid during the process, until the acidification rate (the proportion of sodium chromate converted to sodium bichromate) of the liquid is 16.62%, obtain the pretreated liquid, evaporate the pretreated liquid, evaporate to a liquid concentration of 761.81 g / L (calculated by sodium bichromate), then pass in CO2 for carbonization, the carbonization temperature is 38℃, the carbonization pressure is 1.1 MPa, the carbonization product is filtered and washed with hot water, and the acid value of the carbonization liquid is detected, to obtain a carbonization liquid with a carbonization rate (the proportion of sodium chromate converted to sodium bichromate) of 78.35% and sodium bicarbonate;

[0031] Step three, add the carbonization liquid to the new sodium chromate alkaline liquid or slurry, and perform continuous neutralization, and after filtration and washing, obtain the sodium chromate neutral liquid, which meets the process requirements, the Al2O3 in the sodium chromate neutral liquid is less than 5 mg / L, and the sodium chromate content (calculated by sodium bichromate) is greater than 250 g / L; then repeat steps one to three to realize the continuous neutralization of the carbonization liquid in the production of sodium chromate.

[0032] Example 3

[0033] A method for continuous neutralization of carbonization liquid in the production of sodium chromate, comprising the following steps:

[0034] Step one, add the carbonization liquid obtained in step two of example 1 to the sodium chromate alkaline liquid slurry with a basicity of 89.77 g / L (calculated by Na2CO3) for continuous neutralization to pH 7.0, and then perform filtration and washing to obtain a sodium chromate neutral liquid;

[0035] Step two, add carbonization liquid to the sodium chromate neutral liquid, and perform acidification pretreatment, detect the acid value of the liquid during the process, until the acidification rate (the proportion of sodium chromate converted to sodium bichromate) of the liquid is 18.23%, obtain the pretreated liquid, evaporate the pretreated liquid, evaporate to a liquid concentration of 782.76 g / L (calculated by sodium bichromate), then pass in CO2 for carbonization, the carbonization temperature is 35℃, the carbonization pressure is 1.05 MPa, the carbonization product is filtered and washed with hot water, and the acid value of the carbonization liquid is detected, to obtain a carbonization liquid with a carbonization rate (the proportion of sodium chromate converted to sodium bichromate) of 82.36% and sodium bicarbonate;

[0036] Step three, add the carbonization liquid to the new sodium chromate alkaline liquid or slurry, and perform continuous neutralization, and after filtration and washing, obtain the sodium chromate neutral liquid, which meets the process requirements, the Al2O3 in the sodium chromate neutral liquid is less than 5 mg / L, and the sodium chromate content (calculated by sodium bichromate) is greater than 250 g / L; then repeat steps one to three to realize the continuous neutralization of the carbonization liquid in the production of sodium chromate.

[0037] Example 4

[0038] The difference between this embodiment and embodiment 1 is that in step two, a high-pressure resistant carbonator is used for carbonization, and supercritical CO2 is continuously introduced into the evaporated feed liquid, and the carbonization pressure is controlled at 8.0 MPa, and the carbonization temperature is 32℃, and the other steps are the same as those in embodiment 1.

[0039] In this embodiment, CO2 is replaced by supercritical CO2 based on embodiment 1. Since CO2 has good diffusion performance in the supercritical state, it can effectively improve the reaction rate of carbonated sodium chromate neutral liquid. Under the same conditions, the carbonation rate reaches 92.14%, which can effectively reduce the generation of by-product sodium bicarbonate, and the purity of the obtained carbonated liquid is higher, which is conducive to reducing the amount of carbonated liquid used in the subsequent recycling of sodium chromate alkaline liquid, thereby reducing the amount of other reagents used in the recycling process to reduce costs.

[0040] Example 5

[0041] The difference between this embodiment and embodiment 2 is that in step two, a high-pressure resistant carbonator is used for carbonization, and supercritical CO2 is continuously introduced into the evaporated feed liquid, and the carbonization pressure is controlled at 8.0 MPa, and the carbonization temperature is 32℃, and the other steps are the same as those in embodiment 1.

[0042] In this embodiment, CO2 is replaced by supercritical CO2 based on embodiment 2. Since CO2 has good diffusion performance in the supercritical state, it can effectively improve the reaction rate of carbonated sodium chromate neutral liquid. Under the same conditions, the carbonation rate reaches 91.86%, which can effectively reduce the generation of by-product sodium bicarbonate, and the purity of the obtained carbonated liquid is higher, which is conducive to reducing the amount of carbonated liquid used in the subsequent recycling of sodium chromate alkaline liquid, thereby reducing the amount of other reagents used in the recycling process to reduce costs.

[0043] Example 6

[0044] The difference between this embodiment and embodiment 3 is that in step two, a high-pressure resistant carbonator is used for carbonization, and supercritical CO2 is continuously introduced into the evaporated feed liquid, and the carbonization pressure is controlled at 8.0 MPa, and the carbonization temperature is 32℃, and the other steps are the same as those in embodiment 1.

[0045] In this embodiment, CO2 is replaced by supercritical CO2 based on embodiment 3. Since CO2 has good diffusion performance in the supercritical state, it can effectively improve the reaction rate of carbonated sodium chromate neutral liquid. Under the same conditions, the carbonation rate reaches 94.23%, which can effectively reduce the generation of by-product sodium bicarbonate, and the purity of the obtained carbonated liquid is higher, which is conducive to reducing the amount of carbonated liquid used in the subsequent recycling of sodium chromate alkaline liquid, thereby reducing the amount of other reagents used in the recycling process to reduce costs.

[0046] Comparative Example 1

[0047] The sodium chromate alkaline liquid slurry is neutralized by using the sulfuric acid method in the prior art:

[0048] Step one, sulfuric acid is added to the sodium chromate alkaline liquid slurry with a basicity of 86.22 g / L (calculated as Na2CO3) for continuous neutralization to pH 7.0, then belt filtration washing is performed to obtain a sodium chromate neutral liquid; the neutralization reaction equation is: Na2CO3+H2SO4=Na2SO4+H2O+CO2, the obtained sodium chromate neutral liquid contains a process by-product sodium sulfate, because the sodium chromate neutral liquid contains sodium sulfate, it cannot enter the subsequent circulation process, and because it contains hazardous waste hexavalent chromium, the sodium chromate neutral liquid needs additional subsequent disposal.

[0049] Although the embodiments of the present application have been disclosed as above, it is not limited to the application listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A method for continuous neutralization of sodium chromate production carbonization liquid, characterized in that, Includes the following steps: Step 1: Add carbonization liquid to sodium chromate alkaline solution or slurry for continuous neutralization, and then perform washing with filter to obtain sodium chromate neutral solution and filter residue; Step 2: Add carbonization solution to the neutral sodium chromate solution for acidification pretreatment to obtain a pretreated solution. Evaporate the pretreated solution and then pass CO2 through it for carbonization. Filter the carbonization product with a filter and wash it with hot water to obtain carbonization solution and sodium bicarbonate. Step 3: Add the carbonized liquid to a new sodium chromate alkaline solution or slurry for continuous neutralization. After filtration and washing, obtain a neutral sodium chromate solution. Then repeat steps 1 to 3 to achieve continuous neutralization of the carbonized liquid in sodium chromate production.

2. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step one, the temperature during continuous neutralization is 80-95°C, and the pH of the sodium chromate neutral solution is 6.8-7.

2. Only when carbonization solution is added to the sodium chromate alkaline solution or slurry for the first time is the carbonization solution replaced with sodium dichromate dehydration mother liquor, whose main component is Na2Cr2O7.

3. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step two, when adding carbonization liquid for acidification pretreatment, the acid value of the liquid is detected, and the acidification rate of the liquid is controlled at 10-20%. The acidification rate is the ratio of sodium chromate to sodium dichromate during acidification pretreatment.

4. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step two, during evaporation, an MVR evaporator is used, and the concentration of the liquid is controlled at 700-900 g / L, based on sodium dichromate.

5. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step two, carbonization is carried out in a carbonizer with a CO2 pressure of 0.8–1.2 MPa, a carbonization temperature of 20–80°C, and a carbonization time of 0.5–1 h. The acid value of the obtained carbonization liquid is detected, and the carbonization rate is controlled at 70–85%. The carbonization rate is the proportion of sodium chromate converted to sodium dichromate during carbonization.

6. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step two, the obtained sodium bicarbonate, after drying, can be returned to the calcium-free roasting system.

7. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In steps one and three, the alkalinity of the sodium chromate alkaline solution or slurry, expressed as Na2CO3, is 80–110 g / L.

8. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, The filter residue obtained in step one can be used as return residue from calcium-free roasting.

9. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, The main component of the carbonization liquid used in steps one to three is Na2Cr2O7.

10. The method for continuous neutralization of sodium chromate production carbonization liquid as described in claim 1, characterized in that, In step two, a high-pressure resistant carbonizer is used for carbonization, and the introduced CO2 is replaced with supercritical CO2. The carbonization temperature is 30-80℃, and the pressure is controlled at 7.4-8.5MPa during carbonization.

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