Method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt

Abstract

The invention provides a method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt, and relates to the technical field of chemical engineering. The method comprises the following steps: mixing sodium sulfate waste salt with water for dissolution, mixing the obtained sodium sulfate waste salt solution with an impurity removal agent for impurity removal, and mixing the obtained impurity removal solution with ammonium bicarbonate for double decomposition reaction to obtain a reaction feed liquid; carrying out primary cold separation on the reaction feed liquid to obtain first filtrate and primary sodium bicarbonate; sequentially washing, drying and roasting the primary sodium bicarbonate to obtain a sodium carbonate product; carrying out secondary cold separation on the first filtrate, carrying out solid-liquid separation to obtain a second filtrate and mixed salt, and reusing the mixed salt in the metathesis reaction; and mixing the second filtrate with an acid adjusting agent to adjust the acid, and carrying out evaporative crystallization on the obtained solution to obtain an ammonium sulfate product and an evaporation mother solution. Industrial-grade sodium carbonate and ammonium sulfate are co-produced by using sodium sulfate waste salt, sodium carbonate and ammonium sulfate meet national standard requirements, and the recovery rate of sodium sulfate is greater than or equal to 90%.

Description

TECHNICAL FIELD

[0001] The application relates to the chemical technology field, in particular to a method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt. BACKGROUND

[0002] A large amount of waste sodium sulfate salt is generated in the chemical and metallurgical industry, the new energy battery material preparation industry and the high-sulfur wastewater treatment process. High-value recycling of waste sodium sulfate salt is an urgent task.

[0003] The preparation of soda ash (sodium carbonate) from waste sodium sulfate salt has always been a key research direction in the soda ash industry. However, the economic benefits of the technology are not good, and the recovery rate of sodium sulfate is generally below 70%, which is difficult to industrialize. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a method for preparing sodium carbonate and co-producing ammonium sulfate from waste sodium sulfate salt. The present application uses waste sodium sulfate salt to prepare industrial-grade sodium carbonate and co-produce ammonium sulfate. The sodium carbonate meets the requirements of the national standard GB / T 210-2022, the ammonium sulfate meets the requirements of the standard HG / T5744-2020, and the recovery rate of sodium sulfate is greater than or equal to 90%.

[0005] In order to achieve the above-mentioned purpose of the application, the following technical solutions are provided:

[0006] The present application provides a method for preparing sodium carbonate and co-producing ammonium sulfate from waste sodium sulfate salt, comprising the following steps:

[0007] Mixing waste sodium sulfate salt with water to dissolve and obtain a waste sodium sulfate salt solution;

[0008] Mixing the waste sodium sulfate salt solution with a decontamination agent to remove impurities, and then performing solid-liquid separation to obtain a decontamination liquid; the decontamination agent comprises an oxidizing agent and an alkaline compound;

[0009] Mixing the decontamination liquid with ammonium bicarbonate to perform a double decomposition reaction and obtain a reaction liquid;

[0010] Performing primary cold separation on the reaction liquid, and then performing solid-liquid separation to obtain a first filtrate and primary sodium bicarbonate;

[0011] Sequentially performing water washing, drying and calcination on the primary sodium bicarbonate to obtain a sodium carbonate product;

[0012] Performing secondary cold separation on the first filtrate, and then performing solid-liquid separation to obtain a second filtrate and a mixed salt, wherein the mixed salt is recycled to the double decomposition reaction;

[0013] Mixing the second filtrate with an acid adjusting agent to adjust the acidity, evaporating and crystallizing the obtained acid adjusting solution, and then performing solid-liquid separation to obtain an ammonium sulfate product and an evaporation mother liquor.

[0014] Preferably, the mass ratio of the sodium sulfate waste salt to water is 1:(1.5-3.5); the temperature of the dissolving is 25-45℃, and the time is 30-40min.

[0015] Preferably, the oxidizing agent comprises sodium hypochlorite and / or hydrogen peroxide, and the basic compound comprises one or more of sodium hydroxide, calcium hydroxide and sodium bicarbonate; the temperature of the impurity removal is 25-45℃, and the time is 15-20min.

[0016] Preferably, the mass ratio of the ammonium bicarbonate to sodium sulfate in the impurity removal solution is (1.0-1.2):1; the temperature of the double decomposition reaction is 20-40℃, and the time is 60-90min.

[0017] Preferably, the temperature of the first cold separation is 5-20℃.

[0018] Preferably, the number of the water washing is 2-4 times, and the temperature of each time is independently 5-20℃; the total mass of the water used in the water washing is 5-15 times of the water content of the primary sodium bicarbonate; the washing solution produced in the first time of the water washing is used in the dissolving.

[0019] Preferably, the temperature of the second cold separation is -6℃-10℃.

[0020] Preferably, the acid regulator is sulfuric acid, and the mass fraction of the sulfuric acid is 98%; the pH value of the acid regulating solution is 5.5-6.

[0021] Preferably, the evaporation mother liquor is used in the second cold separation.

[0022] Preferably, the evaporation condensate water produced in the evaporation crystallization is used in the warming of the acid regulating solution, and is used in the water washing and the dissolving after cooling.

[0023] The present application provides a method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt. The present application uses sodium sulfate waste salt to prepare industrial-grade sodium carbonate and co-produces ammonium sulfate, the sodium carbonate meets the requirements of national standard GB / T 210-2022, the ammonium sulfate meets the requirements of standard HG / T5744-2020, and the recovery rate of sodium sulfate is ≥90%. The present application is beneficial to the rapid industrialization of sodium sulfate waste salt regeneration technology, effectively solves the problem of high-value recycling of sodium sulfate waste salt, and has a very broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The process flow chart of the present application for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt is shown. DETAILED DESCRIPTION

[0025] The application provides a method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt, comprising the following steps:

[0026] The sodium sulfate waste salt is mixed with water for dissolution to obtain a sodium sulfate waste salt solution;

[0027] The sodium sulfate waste salt solution is mixed with a decontamination agent for decontamination, and solid-liquid separation is performed to obtain a decontamination liquid; the decontamination agent comprises an oxidizing agent and an alkaline compound;

[0028] The decontamination liquid is mixed with ammonium bicarbonate for a double decomposition reaction to obtain a reaction liquid;

[0029] The reaction liquid is subjected to primary cold separation, and solid-liquid separation is performed to obtain a first filtrate and primary sodium bicarbonate;

[0030] The primary sodium bicarbonate is sequentially subjected to water washing, drying and calcination to obtain a sodium carbonate product;

[0031] The first filtrate is subjected to secondary cold separation, and solid-liquid separation is performed to obtain a second filtrate and mixed salt, and the mixed salt is recycled to the double decomposition reaction;

[0032] The second filtrate is mixed with an acid adjusting agent for acid adjustment, and the obtained acid adjusting solution is subjected to evaporation crystallization, and solid-liquid separation is performed to obtain an ammonium sulfate product and an evaporation mother liquor.

[0033] Figure 1 The process flow diagram for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt is provided in the application, and the following will be described in detail in combination with Figure 1 .

[0034] The sodium sulfate waste salt is mixed with water for dissolution to obtain a sodium sulfate waste salt solution.

[0035] The application does not have special requirements for the source of the sodium sulfate waste salt, and the sodium sulfate waste salt from a source known to those skilled in the art can be used. In the examples of the application, the sodium sulfate waste salt produced by lithium carbonate enterprises and waste battery recycling enterprises is used, which contains potassium, chlorine, silicon, calcium, magnesium, aluminum, iron and trace amounts of heavy metal elements in addition to sodium sulfate.

[0036] In the application, the water is preferably pure water (the washing solution produced by subsequent water washing and the evaporation condensate water produced by evaporation crystallization are also used for the dissolution step); the mass ratio of the sodium sulfate waste salt to water is preferably 1:(1.5-3.5), which can be 1:2, 1:2.1, 1:2.2, 1:2.5 or 1:3. In the application, the temperature of the dissolution is preferably 25-45 DEG C, which can be 38-42 DEG C, and the time is preferably 30-40 min, which can be 30, 35 or 40 min, and the specific value is determined according to the complete dissolution of the sodium sulfate waste salt; the dissolution is preferably performed under stirring.

[0037] In the embodiment of the present application, the dissolving is performed in a dissolving and impurity removing kettle, and the specific operation is preferably as follows: water is sent into the dissolving and impurity removing kettle by a pump, an electric heating system and a stirrer are started, the electric heating power is adjusted, and the dissolving temperature is controlled to be the set temperature; then sodium sulfate waste salt is added into the dissolving and impurity removing kettle for dissolving.

[0038] After obtaining the sodium sulfate waste salt solution, the sodium sulfate waste salt solution is mixed with an impurity removing agent for impurity removal, and solid-liquid separation is performed to obtain an impurity removing solution; the impurity removing agent comprises an oxidizing agent and an alkaline compound.

[0039] In the present application, the oxidizing agent preferably comprises sodium hypochlorite and / or hydrogen peroxide, and the alkaline compound preferably comprises one or more of sodium hydroxide, calcium hydroxide and sodium bicarbonate; the mass of the oxidizing agent is preferably 1-4 ‰ of the mass of the sodium sulfate waste salt, and the mass of the alkaline compound is preferably 1-4 ‰ of the mass of the sodium sulfate waste salt; the addition amount of the oxidizing agent and the alkaline compound is adjusted according to the impurity content in the sodium sulfate waste salt. In the present application, the temperature for impurity removal is preferably 25-45℃, and can be 38-42℃, and the time is preferably 15-20 min, and can be 15, 16, 17, 18, 19 or 20 min, and the specific value is subject to the sufficient removal of impurities. In the present application, the oxidizing agent and the alkaline compound are used to remove a small amount of organic matter in the sodium sulfate waste salt, change the valence of part of impurity ions, and remove various metal and non-metal impurities. The impurity removing agent is preferably added into the sodium sulfate waste salt solution in the dissolving and impurity removing kettle for the impurity removal.

[0040] In the present application, the solid-liquid separation is preferably filtration. The dissolving and impurity removing pump is preferably used to send the mixed solution obtained by the impurity removal into a filter, and the pump and pipeline are flushed with an appropriate amount of pure water after the mixed solution is sent; after filtration by the filter, an impurity removing solution and impurities are obtained; the impurities are removed from the filter, measured and collected for treatment.

[0041] In the present application, the impurity removal of the sodium sulfate waste salt is the basis for the utilization of the sodium sulfate waste salt.

[0042] After obtaining the impurity removing solution, the impurity removing solution is mixed with ammonium bicarbonate for a double decomposition reaction to obtain a reaction solution.

[0043] In the present application, the ammonium bicarbonate can be of industrial grade or of fertilizer grade. In the present application, the mass ratio of the ammonium bicarbonate to sodium sulfate in the impurity-removing solution is preferably (1.0-1.2):1, can be (1.1-1.2):1, and specifically can be 1.0:1, 1.1:1 or 1.2:1; the temperature of the double decomposition reaction is preferably 20-40℃, and can be 30-40℃, and the time is preferably 60-90 min, and can be 60, 70, 80 or 90 min; the double decomposition reaction is preferably carried out under stirring.

[0044] In the present application, the double decomposition reaction is carried out in a double decomposition kettle, and the specific operation is preferably as follows: the impurity-removing solution is fed into the double decomposition kettle, a stirrer is started, the solution in the double decomposition kettle is warmed to a set temperature, and then the ammonium bicarbonate is slowly added to the double decomposition kettle according to the ratio for the double decomposition reaction.

[0045] After the sodium sulfate waste salt is dissolved and impurities are removed, the double decomposition reaction occurs with the ammonium bicarbonate, the bicarbonate ion combines with the sodium ion to form sodium bicarbonate, and the sulfate ion combines with the ammonium ion to form ammonium sulfate, i.e. after the double decomposition reaction, the reaction solution containing sodium bicarbonate and ammonium sulfate is obtained.

[0046] In the present application, during the double decomposition reaction, the ammonia gas produced by the decomposition of the ammonium bicarbonate is preferably collected and treated for reuse by an absorption tower.

[0047] After the reaction solution is obtained, the reaction solution is subjected to primary cold separation in the present application, and the first filtrate and primary sodium bicarbonate are obtained through solid-liquid separation.

[0048] In the present application, the temperature of the primary cold separation is preferably 5-20℃, and can be 7-11℃, and the time is 15-60 min; in the present application, the primary cold separation is carried out in a double decomposition cold separation kettle. In the present application, the solid-liquid separation is preferably centrifugal separation, and the specific operation is preferably as follows: the completely cold-separated solution is pumped into a centrifuge for separation by a double decomposition cold separation kettle pump, and the first filtrate and primary sodium bicarbonate are obtained; and after the solution is pumped, the pump and pipeline are rinsed with an appropriate amount of pure water.

[0049] After the primary sodium bicarbonate is obtained, the primary sodium bicarbonate is subjected to water washing, drying and calcination in sequence in the present application, and the sodium carbonate product is obtained.

[0050] In the present application, the water washing is a primary sodium bicarbonate refining process. In the present application, the number of times of the water washing is preferably 2-4, which can be 2, 3 or 4, and the temperature of each time of water washing is independently preferably 5-20℃, more preferably 6-12℃, and the time of single washing is preferably 20 min; each time of water washing is preferably carried out under stirring. In the present application, the total mass of water used in the water washing is preferably 5-15 times of the water content of the primary sodium bicarbonate. In the present application, the water used in the first time of water washing (denoted as first washing water) is preferably pure water (the condensate produced in subsequent evaporation crystallization and the second washing liquid produced in the second time of water washing are also used in the first time of water washing). In the present application, the washing liquid produced in the first time of water washing (denoted as first washing liquid) is preferably used in the dissolving, and the washing liquid produced in other times of water washing is preferably used in the last time of water washing, respectively.

[0051] In the present application, taking the number of times of the water washing as 2 for example, the specific operation of the water washing is preferably as follows: the first washing water is pumped into the double decomposition cold separation kettle according to the proportion, the stirrer is started, the pre-prepared refrigerant (such as calcium chloride freezing liquid) is sent into the double decomposition cold separation kettle cooling layer, the temperature in the kettle is controlled to be constant to the set temperature (if the temperature is lower than the set temperature, the heater needs to be used to adjust the constant temperature to the set temperature), the primary sodium bicarbonate is added, the stirring and washing are carried out for the set time, then the washing liquid is pumped into the separator by the double decomposition cold separation kettle pump, and the pump and pipeline are washed with appropriate pure water after the liquid is sent; the first washing liquid separated by the centrifugal machine is sent into the first washing liquid tank for standby, and the first washing sodium bicarbonate is subjected to the second time of water washing. In the present application, the specific operation of the second time of water washing is preferably as follows: the second washing water is pumped into the double decomposition cold separation kettle according to the proportion, and then the operation of the first time of water washing is the same, and the first washing sodium bicarbonate is added; the second washing liquid separated by the centrifugal machine is sent into the second washing liquid tank for standby, and the bicarbonate separated after is refined sodium bicarbonate.

[0052] In the present application, the temperature of the drying is preferably 40-50℃, which can be 40-45℃; the temperature of the calcination is preferably 200-300℃, which can be 250-270℃. After the calcination, the sodium carbonate product is obtained.

[0053] After the first filtrate is obtained, the first filtrate is subjected to secondary cold separation in the present application, solid-liquid separation is carried out, the second filtrate and mixed salt are obtained, and the mixed salt is used in the double decomposition reaction again.

[0054] In the present application, the temperature of the secondary cold separation is preferably -6℃-10℃, which can be -3℃-1℃. In the present application, the mixed salt includes sodium bicarbonate, sodium sulfate and ammonium sulfate.

[0055] In the embodiment of the present application, the secondary cold separation is carried out in a freezing kettle, and the specific operation is preferably as follows: the first filtrate (which can be used as the evaporation mother liquor later) is fed into the freezing kettle, and the solution in the freezing kettle is cooled to a set temperature to carry out the secondary cold separation. In the present application, the solid-liquid separation method is preferably filtration; and the material liquid after the secondary cold separation is preferably fed into a separator to be filtered and separated, so as to obtain the mixed salt for collection and standby, and the second filtrate is fed into an acid adjusting tank to carry out subsequent operations.

[0056] In the present application, the mixed salt is reused in the metathesis reaction, and the amount of ammonium bicarbonate is increased according to the content of sodium sulfate in the mixed salt. The reuse of the mixed salt can accelerate the metathesis reaction, and the sodium sulfate in the mixed salt participates in the metathesis reaction, the sodium bicarbonate is naturally separated out, and the ammonium sulfate and other materials exist in the solution.

[0057] After obtaining the second filtrate, the second filtrate is mixed with an acid adjusting agent to carry out acid adjustment, and the obtained acid adjusting solution is subjected to evaporation crystallization, solid-liquid separation, to obtain an ammonium sulfate product and an evaporation mother liquor.

[0058] In the present application, the acid adjusting agent is preferably sulfuric acid, the mass fraction of the sulfuric acid is preferably 98%, and the pH value of the acid adjusting solution is preferably 5.5-6; the acid adjustment is carried out at room temperature. In the present application, the acid adjusting agent is added to the second filtrate in the acid adjusting tank to carry out the acid adjustment. In the present application, the acid adjustment functions to supplement sulfate ions and ensure the quality of the ammonium sulfate under the premise that more ammonium sulfate is produced.

[0059] In the present application, the evaporation temperature in the evaporation crystallization is preferably 90-115°C, and can be 95-105°C; the crystallization is preferably carried out when the mass of the evaporation condensate water is 40-60% of the mass of the evaporation original liquid (i.e. the acid adjusting solution); and the crystallization temperature is preferably 50-70°C, and can be 60-70°C. After solid-liquid separation, an ammonium sulfate product and an evaporation mother liquor are obtained, and the ammonium sulfate product is further preferably dried; and the evaporation mother liquor is preferably reused in the secondary cold separation, specifically, the evaporation mother liquor enters a mother liquor buffer tank and is returned to the freezing kettle to be reused in the secondary cold separation. In the present application, the evaporation condensate water generated in the evaporation crystallization is preferably used for heating the acid adjusting solution in the acid adjustment process, and is used in the washing (including each washing) and the dissolving after cooling, and the cooling method is preferably heat exchange with the acid adjusting solution.

[0060] The present application can stably produce industrial-grade sodium carbonate of class II first-grade and qualified industrial-grade ammonium sulfate from sodium sulfate waste salt, the recovery rate of sodium sulfate is ≥90% (theoretically 100%), and all the waste liquid in the production process is recycled. The product quality is good and stable, mainly from the impurity removal process and the refining process; the sodium sulfate recovery rate is high, mainly from the double decomposition process, the recycling of the washing liquid for dissolving the sodium sulfate waste salt, and the recycling of the cold separation mixed salt of the ammonium sulfate evaporation stock solution and the evaporation mother liquor for the double decomposition.

[0061] In order to further illustrate the present application, the method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt provided by the present application is described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0062] Examples

[0063] The method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt is as follows:

[0064] (1) Test conditions

[0065] 1. Test materials: The main raw materials used in the test are sodium sulfate waste salt from the new energy material industry, composite impurity removal agent, ammonium bicarbonate, acid adjusting agent, pure water, etc.

[0066] 2. Test equipment: The test equipment has a batch pilot test line for preparing sodium bicarbonate and ammonium sulfate, has a complete set of detection conditions, and the sodium carbonate is prepared in the laboratory.

[0067] (2) Steps and process of the test

[0068] 1. Raw material preparation

[0069] The raw material analysis is mainly the component analysis of the sodium sulfate waste salt, and the content of sodium sulfate, potassium, chlorine, silicon, calcium, magnesium, aluminum, iron, etc. and trace heavy metals in the sodium sulfate waste salt is detected. The batching scheme in the experimental process is formulated according to the content of sodium sulfate and the content of other materials.

[0070] The ammonium bicarbonate (industrial grade, fertilizer grade), the composite impurity removal agent, and the acid adjusting agent are all industrial grade products, and the pure water is self-made.

[0071] 2. Dissolution and impurity removal process

[0072] 1) Constant temperature liquid preparation: The pure water (including the subsequent condensate and washing liquid) is pumped into the dissolution and impurity removal kettle at a solid-liquid mass ratio of 46:100, the electric heating system and the stirrer are started, the electric heating power is adjusted, and the dissolution liquid is controlled to be constant at a set temperature of 40±2℃.

[0073] 2) Sodium sulfate waste salt dissolution: take sodium sulfate waste salt according to the solid-liquid mass ratio of 46:100, and when the dissolution solution is stable at the set temperature of 40±2℃, add sodium sulfate waste salt into the dissolution and impurity removal kettle.

[0074] 3) Impurity removal: after the complete dissolution of sodium sulfate waste salt, manually add hydrogen peroxide 1.5‰ (1.5‰ relative to the mass of sodium sulfate waste salt) and sodium hydroxide 2‰ (2‰ relative to the mass of sodium sulfate waste salt) into the dissolution and impurity removal kettle according to the proportion, until the reaction is complete.

[0075] 4) Impurity separation: use the dissolution and impurity removal pump to send the impurity-removed solution to the second-floor filter. After the impurity-removed solution is sent, flush the pump and pipeline with appropriate amount of pure water. The impurity-removed solution is directly sent to the double decomposition kettle for standby, and the impurities are removed from the filter for measurement and collection for processing.

[0076] 3、Double decomposition process

[0077] 1) Double decomposition reaction: start the stirrer when the impurity-removed solution enters the double decomposition kettle. Slowly add ammonium bicarbonate into the double decomposition kettle according to the mass ratio of sodium sulfate in sodium sulfate waste salt to ammonium bicarbonate of 1:1.113, and control the temperature at 35±5℃, until the reaction is complete.

[0078] 2) First cold separation: use the double decomposition pump to send the completely reacted solution to the double decomposition cold separation kettle for cold separation, control the cold separation temperature at 9±2℃, and the cold separation time is 15 minutes.

[0079] 3) Solid-liquid separation: use the double decomposition cold separation kettle pump to send the completely cold-separated solution to the centrifuge for separation. After the solution is sent, flush the pump and pipeline with appropriate amount of pure water. The separated double decomposition filtrate is sent to the double decomposition freezing kettle for standby. The separated solid, primary sodium bicarbonate, is packaged and transported to the second floor for measurement standby.

[0080] 4、Sodium bicarbonate refining and rinsing

[0081] 1) First washing and separation: take first washing water (pure water, condensed water or second washing solution) according to the proportion and send it into the double decomposition cold separation kettle using a pump. Start the stirrer and send the pre-prepared refrigerant (calcium chloride freezing solution) into the double decomposition cold separation kettle cooling layer at the same time. Control the kettle temperature at 9±2℃ (if the temperature is lower than the set temperature, use the heater to adjust and control the temperature at the set temperature). Add primary sodium bicarbonate and stir for a set time for washing. Then use the double decomposition cold separation kettle pump to send the washing solution to the separator. After the solution is sent, flush the pump and pipeline with appropriate amount of pure water. The first washing solution separated by the centrifuge is sent to the first washing solution tank for standby, and the first washing sodium bicarbonate separated is packaged and transported to the second floor for measurement standby.

[0082] 2) Second washing separation: according to the proportion, second washing water (pure water or condensate water) is pumped into the double decomposition cold analysis kettle. The same as the washing operation, the second washing liquid separated by the centrifuge is used for the next first washing water.

[0083] 5. Preparation of sodium carbonate

[0084] The refined sodium bicarbonate is dried at 40°C and calcined at 270°C to obtain sodium carbonate product (in the pilot test, the drying and calcining device is not configured, and the sample is dried and calcined in the laboratory for detection of sodium carbonate or submission).

[0085] 6. Preparation of ammonium sulfate

[0086] 1) Second cold analysis: double decomposition filtrate and evaporation mother liquor freezing: the double decomposition filtrate and evaporation mother liquor enter the freezing kettle, the solution temperature of the freezing kettle is frozen to -1±2°C, and the frozen liquid is sent to the separator for filtration and separation to obtain mixed salt for collection; the frozen filtrate is sent to the acid adjusting tank.

[0087] 2) Acid adjustment of frozen filtrate: 98wt% sulfuric acid is added to the frozen filtrate to adjust the pH value to 5.5-6, and the adjusted solution (i.e. acid-adjusted solution) is sent to the evaporator.

[0088] 3) Preparation of ammonium sulfate: the acid-adjusted solution enters the evaporator at an evaporation temperature of 100±5°C, and when about 50% of the condensate water is discharged, crystallization separation (crystallization separation temperature 65±5°C) and drying are carried out to obtain ammonium sulfate (laboratory detection or submission); the evaporation mother liquor enters the mother liquor buffer tank, and the evaporation mother liquor returns to the freezing kettle.

[0089] 7. Other supporting processes

[0090] 1) Condensate water utilization: the evaporation condensate water waste heat is used for warming the acid-adjusted solution, and then part of the condensate water is used for rinsing water, and part of the condensate water is returned to the dissolution process.

[0091] 2) Washing liquid utilization: the first washing liquid in the first washing tank is used for sodium sulfate dissolution, and the second washing liquid in the second washing tank is used as the first washing water for the next time.

[0092] 3) Freezing mixed salt utilization: the freezing mixed salt is directly used for double decomposition reaction.

[0093] 4) Ammonia gas produced by adding ammonium bicarbonate in the production process is collected and treated for reuse. However, due to the small amount of ammonia gas in the pilot test, the ammonia gas absorption tower is not configured.

[0094] (Three) Test data

[0095] The pilot test was carried out from February 12 to March 12, and the test process was completed on March 13. The first phase of the pilot test was completed on March 30, and the second phase of the pilot test was carried out from April. The main test results of the pilot test are as follows:

[0096] Raw material detection data

[0097] The sodium sulfate waste salt used in the test was sourced from New Energy Sodium Sulfate Waste Salt, and was detected by Changsha Mining and Metallurgy Institute Detection Technology Co., Ltd. The composition of sodium sulfate waste salt is shown in Table 1 (in Table 1, "old Hui Cheng" and "new Hui Cheng" are two branches of Guizhou Dalong Hui Cheng New Material Co., Ltd., and "Xingmao" is Dalong Xingmao New Material Co., Ltd.).

[0098] Table 1 Detection and analysis results of sodium sulfate waste salt and impurities composition (unit: wt%)

[0099] Enterprise Na2SO4 K Cl Si Al Fe Ca Mg Cu Cs Old 96.6 0.748 0.842 0.115 0.141 0.017 0.028 0.057 — 0.034 New 95.49 0.863 0.725 0.148 0.126 0.018 0.045 0.065 0.003 — Star 95.51 0.76 0.845 0.112 0.236 0.028 0.064 0.075 — — Average 95.86 0.790 0.804 0.125 0.168 0.021 0.046 0.066 — —

[0100] The experiment was carried out using sodium sulfate waste salt produced by Guizhou Dalong Hui Cheng New Material Co., Ltd.

[0101] The ammonium bicarbonate used in the test was sourced from Hubei Dengrui Fertilizer Co., Ltd., and the composition of ammonium bicarbonate was detected by Dengrui Fertilizer Co., Ltd., as shown in Table 2.

[0102] Table 2 Detection results of industrial grade ammonium bicarbonate of Dengrui Fertilizer Co., Ltd.

[0103]

[0104] All of the impurity removal agents 1, impurity removal agents 2 and acid adjusting agents used in the test were industrial grade, and pure water was self-made.

[0105] The main process parameters and detection data during the test process are shown in Tables 3-7.

[0106] Table 3 Main process parameters of sodium bicarbonate test

[0107]

[0108]

[0109] Note: All reaction times are calculated after charging.

[0110] Table 4 Ammonium sulfate test process parameters (in Table 4, "Hebei Shiku Detection Technology Service Co., Ltd." is "Hebei Shiku Detection Technology Service Co., Ltd.")

[0111]

[0112] Table 5: Test results of sodium carbonate product

[0113]

[0114]

[0115] Note: In Table 5, sodium sulfate waste salt was dissolved using a washing solution on March 27 and 28, and frozen mixed salt was used during the double decomposition on March 30.

[0116] As shown in Table 5, the qualified rate of the first washing product was 100% from March 13 to 30, and the second washing product was above the first-class product of category II.

[0117] On April 24, the same water was used for washing, and the sodium carbonate product was qualified after one washing, and the sodium carbonate product was excellent after two washings.

[0118] Table 6: Test data statistics of industrial-grade ammonium sulfate

[0119]

[0120] Note: In Table 6, the ammonium sulfate solution is the filtrate after the first cold separation of the double decomposition, and 1#, 2#, and 3# are three ammonium sulfate solution samples taken during production.

[0121] Table 7: Test data statistics of sodium sulfate recovery rate

[0122]

[0123]

[0124] Note: In Table 7, the ammonium sulfate solution is the filtrate after the first cold separation of the double decomposition.

[0125] Explanation:

[0126] (1) The above-mentioned ammonium sulfate solution and the sodium bicarbonate solution dissolved by the first washing solution are converted to the recovery rate at 10°C according to the temperature during the test, and the loss during the test is not included.

[0127] (2) In the actual production process, the sodium bicarbonate dissolved by the first washing solution is recovered when dissolving sodium sulfate, and the sodium bicarbonate dissolved by the ammonium sulfate solution is obtained from the mixed salt after the cold separation of the ammonium sulfate solution, and the mixed salt is recovered during the double decomposition reaction.

[0128] (3) From the table, it can be seen that: using a washing solution for dissolving sodium sulfate can correspondingly reduce the amount of sodium sulfate used, and the sodium bicarbonate in the washing solution after the reaction is effectively recovered; the cold-analyzed mixed salt is used in the double decomposition reaction, and the useful components of the mixed salt after the reaction are efficiently recovered; in the actual production process, by comprehensively adopting a washing solution, cold-analyzed mixed salt recycling and other measures, the recovery rate of sodium sulfate can reach 95%. If fine management and other means are implemented, the recovery rate of sodium sulfate can reach ≥98%.

[0129] From the test results, it can be seen that: the sodium sulfate waste salt preparation sodium bicarbonate, sodium carbonate co-production ammonium sulfate technology, the process flow is simple, the process route is perfect, the process is controllable, and meets the requirements of green chemical production. Using the method of the present application, industrial-grade sodium bicarbonate, sodium carbonate and industrial-grade ammonium sulfate can be stably prepared, sodium carbonate meets the requirements of national standard GB / T 210-2022, ammonium sulfate meets the requirements of standard HG / T5744-2020, and the recovery rate of sodium sulfate is ≥90%.

[0130] The sodium sulfate waste salt resource treatment technology provided by the present application can be quickly industrialized in the new energy material industry chain, and can effectively realize high-value recycling of sodium sulfate waste salt in new energy material industry and waste battery processing industry. The present application provides inspiration and reference for resource utilization of sodium-based waste salt in different industries. As long as different impurity removal processes and impurity removal agents are studied according to the different impurities contained in sodium-based waste salt, sodium-based waste salt treated by impurity removal can basically realize high-value recycling of sodium-based waste salt by using the present application, and the present application has wide application prospect.

[0131] The above only describes the preferred embodiments of the present application, and does not limit the present application in any form. It should be noted that for ordinary skilled persons in the art, without departing from the principles of the present application, some improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing sodium carbonate and co-producing ammonium sulfate from sodium sulfate waste salt, characterized in that: The following steps are involved: mixing sodium sulfate waste salt with water to dissolve the mixture to obtain a sodium sulfate waste salt solution; The sodium sulfate waste salt solution is mixed with an impurity remover to remove impurities, and solid-liquid separation is performed to obtain an impurity-removed liquid; the impurity remover includes an oxidant and an alkaline compound; Mixing the impurity removal liquid with ammonium bicarbonate to perform double decomposition reaction to obtain a reaction liquid; The reaction liquid is subjected to a first cooling separation and solid-liquid separation to obtain a first filtrate and primary sodium bicarbonate; The primary sodium bicarbonate is sequentially washed, dried and roasted to obtain a sodium carbonate product; The first filtrate is subjected to secondary cold precipitation and solid-liquid separation to obtain a second filtrate and a mixed salt, and the mixed salt is reused in the double decomposition reaction; The second filtrate is mixed with an acid regulating agent to adjust the acidity, and the obtained acid regulating solution is evaporated and crystallized, and solid-liquid separation is performed to obtain an ammonium sulfate product and an evaporated mother liquor.

2. The method according to claim 1, characterized in that The mass ratio of the sodium sulfate waste salt to water is 1:(1.5-3.5); the dissolution temperature is 25-45° C., and the dissolution time is 30-40 minutes.

3. The method according to claim 1, characterized in that The oxidant includes sodium hypochlorite and / or hydrogen peroxide, and the alkaline compound includes one or more of sodium hydroxide, calcium hydroxide and sodium bicarbonate; the impurity removal temperature is 25-45° C. and the time is 15-20 minutes.

4. The method according to claim 1, wherein The mass ratio of the ammonium bicarbonate to the sodium sulfate in the impurity removal liquid is (1.0-1.2):1; the temperature of the double decomposition reaction is 20-40° C., and the time is 60-90 minutes.

5. The method according to claim 1, wherein The temperature of the first cold separation is 5-20°C.

6. The method according to claim 1, characterized in that The number of water washings is 2 to 4 times, and the temperature of each water washing is independently 5 to 20° C.; the total mass of water used in the water washings is 5 to 15 times the water content of the primary sodium bicarbonate; and the washing liquid generated in the first water washing is used in the dissolution.

7. The method according to claim 1, characterized in that The temperature of the secondary cold separation is -6°C to 10°C.

8. The method according to claim 1, characterized in that The acid regulating agent is sulfuric acid, and the mass fraction of the sulfuric acid is 98%; the pH value of the acid regulating solution is 5.5-6.

9. The method according to claim 1, characterized in that The evaporated mother liquor is recycled for the secondary cold separation.

10. The method according to claim 1, 2, 6 or 8, characterized in that The evaporated condensed water generated by evaporation in the evaporative crystallization is used to heat the acid adjustment solution, and is used in the water washing and the dissolution after cooling.

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