Method for treating mother liquor resulting from preparation of soda ash from mirabilite

Abstract

A method for treating a mother liquor resulting from preparation of soda ash from mirabilite, relating to the field of wastewater treatment. The treatment method comprises: subjecting sodium sulfate wastewater and ammonium bicarbonate to double decomposition to obtain sodium bicarbonate; acidifying a double decomposition mother liquor and then evaporating and denitrifying the acidified double decomposition mother liquor to obtain sodium sulfate; cooling and crystallizing a denitration mother liquor to remove a double salt; and mixing a mother liquor from double salt removal with aluminum sulfate and evaporating the mixture to obtain ammonium aluminum sulfate. Co-production of sodium bicarbonate and ammonium aluminum sulfate byproducts from high-concentration sodium sulfate wastewater is achieved. A large amount of high-salinity wastewater produced in industry is rationally utilized. Byproducts with higher value are produced. The process is simple, process products can all be recycled into the system, and no wastewater and waste residues are produced, thus improving economic benefits.

Description

A method for treating mother liquor from sodium sulfate alkali production Technical Field

[0001] The present application relates to the field of wastewater treatment, and in particular to a method for treating mother liquor from sodium sulfate alkali production. Background Art

[0002] Industrial production processes in numerous fields, such as pharmaceuticals, metallurgy, and chemicals, involve the addition of various chemicals, generating vast quantities of wastewater. This includes the introduction of acids and alkalis to adjust the pH of wastewater, resulting in highly saline wastewater. The primary inorganic salt dissolved in this high-salinity wastewater is sodium sulfate. Three common treatment methods are typically used, depending on the salt type, concentration, impurities, and COD content: membrane separation, thermal concentration, and biological treatment.

[0003] The mother liquor from the production of mirabilite is a high-concentration sodium sulfate wastewater. Its main components are (NH4)2SO4, Na2SO4, and small amounts of NaHCO3 and NH4HCO3. Currently, the main treatment methods for high-salt wastewater containing (NH4)2SO4 and Na2SO4 are thermal decomposition and crystallization. Thermal decomposition involves decomposing the (NH4)2SO4 in the mixed salt at temperatures exceeding 400°C. The pyrolysis offgas is desulfurized and NH3 is recovered, leaving the pyrolysis residue primarily as Na2SO4. While this method has advantages in industries with abundant high-temperature waste heat resources, such as smelting, thermal decomposition consumes significant energy and results in a low recovery rate of valuable mixed salt resources. Crystallization separates sodium sulfate and ammonium sulfate by exploiting the solubility differences between sodium sulfate and ammonium sulfate at different temperatures. However, since (NH4)2SO4 and Na2SO4 can form the complex salt Na2SO4·(NH4)2SO4·4H2O at low temperatures, simple evaporation, concentration, and crystallization by cooling cannot completely separate the two salts, resulting in a low salt recovery rate.

[0004] In the current situation of relative water scarcity, finding a process to reduce industrial wastewater emissions and maximize the utilization of salt resources can not only alleviate the shortage of water resources, but also reduce environmental pollution, which has both economic and environmental strategic significance.

[0005] Summary of the Invention

[0006] The present application provides a method for treating the mother liquor of sodium sulfate production to solve the problem of treating the wastewater of sodium sulfate production, purify the mother liquor to obtain sodium sulfate, and process and recover the sodium bicarbonate and ammonium aluminum sulfate products, thereby reducing pollution to the environment.

[0007] In order to solve the above technical problems, the present application provides a method for treating a mother liquor of sodium sulfate alkali production, comprising the following steps:

[0008] Taking the mother liquor of mirabilite alkali production and ammonium bicarbonate for reaction, filtering, and obtaining sodium bicarbonate wet residue and double decomposition mother liquor;

[0009] Acidifying the metathesis mother liquor to convert the ammonium bicarbonate and sodium bicarbonate contained therein into carbon dioxide to obtain an acidified mother liquor;

[0010] The acidified mother liquor is heated and evaporated until the ammonium sulfate is saturated under the temperature condition, and filtered while hot to obtain sodium sulfate by-product and denitrification mother liquor;

[0011] After cooling and crystallizing the denitrification mother liquor, filtering is performed to obtain double salt and denitrification mother liquor;

[0012] The decomplex salt mother liquor is mixed with aluminum sulfate, heated and evaporated until the sodium sulfate is saturated, and filtered to obtain aluminum ammonium sulfate and deammonium mother liquor.

[0013] The mother liquor of the present application's mirabilite alkali production is high-concentration sodium sulfate wastewater. For high-concentration sodium sulfate wastewater, it can be directly evaporated and concentrated to achieve zero wastewater discharge, but a large amount of sodium sulfate solid is produced. The domestic market capacity of sodium sulfate is limited and there are great environmental risks in stacking. The sodium sulfate in the mother liquor of the present application's mirabilite alkali production can undergo a double decomposition reaction with ammonium bicarbonate to convert it into sodium bicarbonate precipitate. The sodium bicarbonate wet residue can be dried or the wet residue can be reused according to process requirements. The reaction equation is as follows: Na2SO4+2NH4HCO3=NaHCO3+(NH4)2SO4. The double decomposition mother liquor is acidified to convert the sodium bicarbonate dissolved in the reaction and the unreacted ammonium bicarbonate into sodium sulfate and ammonium sulfate, which is convenient for subsequent salt separation. The acidified mother liquor is mainly composed of sodium sulfate, ammonium sulfate and water. According to the solubility of ammonium sulfate, the sodium bicarbonate in the mother liquor can be converted into sodium sulfate and ammonium sulfate. The solubility is greater than the solubility of sodium sulfate. Under high-temperature evaporation, sodium sulfate is preferentially supersaturated and precipitates first. The concentration of ammonium sulfate is nearly saturated at high temperature, and hot filtration is performed to obtain a denitrification mother liquor. When the temperature is lowered, the saturation of sodium sulfate and ammonium sulfate in the solution increases sharply, and they precipitate together to form a complex salt (Na2SO4·(NH4)2SO4·4H2O). The reaction equation is as follows: Na2SO4+(NH4)2SO4+4H2O=(Na2SO4(NH4)2SO4·4H2O). The denitrification mother liquor is a highly saturated ammonium sulfate solution. Aluminum sulfate is added to react to form ammonium aluminum sulfate, which crystallizes and precipitates under high-temperature evaporation to achieve the purpose of deammoniation. The reaction equation is as follows: Al2(SO4)3+(NH4)2SO4+24H2O=2[AlNH4(SO4)2]·12H2O.

[0014] In another embodiment, sodium sulfate is added to the sodium sulfate mother liquor prepared from mirabilite at a heating temperature of 40-60° C. under stirring to achieve a sodium sulfate concentration of 2.6-4.8 mol / L, and then the temperature is lowered to 35-50° C. to obtain a supersaturated sodium sulfate mother liquor, which is mixed with ammonium bicarbonate for reaction and filtered to obtain sodium bisulfate and a double decomposition mother liquor.

[0015] In the present application, under the condition of supersaturation of sodium sulfate, ammonium bicarbonate is added at a uniform speed, so that the sodium sulfate consumed in the solution can be replenished in time, which is conducive to the reaction moving towards the generation of sodium bicarbonate and further improving the precipitation rate of sodium sulfate conversion into sodium bicarbonate; at the same time, the purity of the sodium sulfate obtained in the present application reaches more than 90%, and can be recycled into the mother liquor of mirabilite alkali production to adjust the sodium sulfate concentration, thereby achieving a recycling effect.

[0016] In another embodiment, sodium sulfate is added to the mother liquor of mirabilite alkali production at a heating temperature of 40-60° C. and a stirring speed of 300-450 rpm / min to achieve a sodium sulfate concentration of 2.6-4.8 mol / L, the mixture is cooled to 35-50° C., and mixed with ammonium bicarbonate for reaction for 1-3 hours.

[0017] In another embodiment, the molar ratio of sodium in the supersaturated sodium sulfate mother liquor to ammonium in the ammonium bicarbonate is 1:(1-2).

[0018] In another embodiment, the sodium sulfate by-product is circulated and added to the sodium sulfate mother liquor under stirring conditions at a heating temperature of 40-60°C to achieve a sodium sulfate concentration of 2.6-4.8 mol / L, and then cooled to 35-50°C and mixed with ammonium bicarbonate for reaction.

[0019] In another embodiment, the metathesis mother liquor is acidified by adding 10-20% dilute sulfuric acid to the metathesis mother liquor and reacting for 1-2 hours to stabilize the pH value, and the pH value of the acidified mother liquor is less than 4.

[0020] The reaction equation for the acidification treatment of the double decomposition mother liquor in this application is as follows: 2NaHCO3+H2SO4=Na2SO4+2H2O+2CO2; 2NH4HCO3+H2SO4=(NH4)2SO4+2H2O+2CO2; the sodium bicarbonate dissolved back in the double decomposition reaction and the ammonium bicarbonate that has not reacted completely are decomposed by adding dilute sulfuric acid.

[0021] In another embodiment, the double salt is circulated and mixed with the acidified mother liquor, and then heated and evaporated until the sodium sulfate is saturated under the temperature conditions, wherein the acidified mother liquor and the double salt are mixed in a volume ratio of 1: (0.05-0.1).

[0022] The double salt (Na2SO4·(NH4)2SO4·4H2O) obtained in the present application can be recycled into the acidified mother liquor. During the heating and evaporation process, the double salt is decomposed again into Na2SO4, NH4HCO3 and H2SO4. The Na2SO4 component can be evaporated and precipitated with the sodium sulfate in the acidified mother liquor, which can reduce the sodium sulfate and ammonium sulfate outlet of the entire system, maximize the recycling of sodium sulfate, and increase the subsequent aluminum ammonium sulfate production.

[0023] In another embodiment, the deammonium mother liquor is circulated and mixed with the denitrification mother liquor, and the volume ratio of the denitrification mother liquor to the deammonium mother liquor is 1:(0.5-1), followed by cooling and crystallization.

[0024] The deammonium mother liquor and denitrification mother liquor obtained in the present application are circulated for double salt removal treatment, which can increase the yield of double salt. The process products can be recycled into the system without the output of wastewater and waste residue, thus reducing the amount of treated water after wastewater treatment.

[0025] In another embodiment, the acidified mother liquor is heated to 70-85° C. and evaporated until the ammonium sulfate is saturated under the temperature condition.

[0026] In another embodiment, the denitrification mother liquor is cooled to 20-30° C. for crystallization.

[0027] In another embodiment, the denitrification mother liquor is cooled and crystallized at 20-30° C. for 1-3 hours.

[0028] In another embodiment, the denitrification mother liquor is cooled and crystallized under stirring conditions at a stirring speed of 100-300 rpm / min.

[0029] In another embodiment, the decomplexed salt mother liquor is mixed with aluminum sulfate and then heated to 75-85° C. for evaporation.

[0030] In another embodiment, the decomplex salt mother liquor contains ammonium sulfate, and the decomplex salt mother liquor is mixed with aluminum sulfate in a molar ratio of ammonium sulfate to aluminum sulfate of 1:(1-1.2).

[0031] In another embodiment, the sodium bicarbonate wet residue is washed with water to remove impurities, and the amount of water used is 30-50% of the mass of the sodium bicarbonate wet residue.

[0032] Compared with the existing technology, this application has the following beneficial effects:

[0033] 1. This application adopts a high-concentration sodium sulfate wastewater solution to produce sodium bicarbonate and co-produce ammonium aluminum sulfate as a by-product. By disposing of sodium sulfate as a resource and using Glauber's salt to make alkali, sodium bicarbonate and ammonium aluminum sulfate with higher added value can be produced, thereby realizing the recycling of sodium resources, rationally utilizing a large amount of high-salt wastewater produced by industry, and producing higher-value by-products. The process is simple, and all process products can be reused in the system. No wastewater or waste residue is produced, thereby improving economic benefits.

[0034] 2. Compared with the conventional use of a deamination tower to remove ammonium bicarbonate and sodium bicarbonate, the present application uses acidification to decompose ammonium bicarbonate and sodium bicarbonate, converting them into sodium sulfate and ammonium sulfate, the main components in the wastewater, thereby reducing the steam usage of the deamination tower and saving costs; most of the sodium sulfate is separated by evaporation and cooling crystallization, so that ammonium sulfate can be converted with aluminum sulfate into a higher-purity ammonium aluminum sulfate by-product for recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a process flow chart of a method for treating a mother liquor from sodium sulfate production in an embodiment of the present application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] Example 1

[0038] A method for treating a mother liquor from sodium sulfate alkali production comprises the following steps:

[0039] (1) Taking the filtered sodium sulfate mother liquor of 2.5 mol / L as the stock solution, adding commercially available sodium sulfate at 50°C and stirring at 400 rpm / min to reach a sodium sulfate concentration of 2.7 mol / L, reacting for 0.5 h, cooling to 40°C, adding ammonium bicarbonate at a sodium / ammonium molar ratio of 1:1.2, reacting for 1 h, filtering and separating to obtain a double decomposition mother liquor and sodium bicarbonate wet residue, wherein the sodium precipitation rate (by mole) is 64.5%, eluting the sodium bicarbonate wet residue with pure water, and drying to obtain sodium bicarbonate with a purity of 98.7%;

[0040] (2) adding 10% dilute sulfuric acid to the metathesis mother liquor to adjust the pH to 3.5, and reacting for 1 hour to stabilize the pH to obtain an acidified mother liquor;

[0041] (3) The acidified mother liquor is evaporated at 75° C. until the ammonium sulfate reaches saturation, and the sodium sulfate and the denitrification mother liquor are separated by hot filtration to obtain sodium sulfate with a purity of >96%, wherein the sodium precipitation rate (by mole) is 24.3%. The sodium sulfate can be used for addition in step (1) of the next treatment cycle;

[0042] (4) The denitrification mother liquor is cooled and crystallized at 20° C., with a stirring speed of 250 rpm / min. After the temperature stabilizes, the reaction is carried out for 1 hour, and the double salt and the denitrification mother liquor are separated by filtration. The double salt can be used for addition in step (3) of the next treatment cycle;

[0043] (5) Aluminum sulfate was added to the decomplex salt mother liquor in an equal molar amount to ammonium sulfate, and the mixture was evaporated at 78° C. and a stirring speed of 200 rpm / min until saturation with sodium sulfate was achieved. The decomplex salt mother liquor was filtered to obtain ammonium aluminum sulfate with a dry basis content of 99.36% and a deammonium mother liquor. The precipitation rate of ammonium (by mole) was 20.6%. The deammonium mother liquor could be used for addition in step (4) of the next treatment cycle.

[0044] Example 2

[0045] A method for treating a mother liquor from sodium sulfate production, as shown in FIG1 , comprises the following steps:

[0046] (1) Taking the filtered sodium sulfate mother liquor of 2.5 mol / L as the stock solution, adding the sodium sulfate obtained in Example 1 at 50° C. and a stirring speed of 400 rpm / min to reach a sodium sulfate concentration of 2.7 mol / L, reacting for 0.5 h, cooling to 40° C., adding ammonium bicarbonate at a sodium / ammonium molar ratio of 1:1.2, reacting for 1 h, filtering and separating to obtain a double decomposition mother liquor and sodium bicarbonate wet residue, wherein the sodium precipitation rate (by mole) is 64.3%, eluting the sodium bicarbonate wet residue with pure water, and drying to obtain sodium bicarbonate with a purity of 98.8%;

[0047] (2) adding 10% dilute sulfuric acid to the metathesis mother liquor to adjust the pH to 3.5, and reacting for 1 hour to stabilize the pH to obtain an acidified mother liquor;

[0048] (3) 50 g of the double salt obtained in Example 1 was added to every 1000 mL of the acidified mother liquor, and the mixture was evaporated at 75° C. until the ammonium sulfate reached saturation. The sodium sulfate and the denitrification mother liquor were separated by hot filtration to obtain sodium sulfate with a purity of >96%, wherein the sodium precipitation rate (by mole) was 32.1%. The sodium sulfate can be used for addition in step (1) in the next treatment cycle;

[0049] (4) The denitrification mother liquor is mixed with the deammonium mother liquor obtained in Example 1, which accounts for 50% by volume of the denitrification mother liquor, and cooled and crystallized at 20° C. with a stirring speed of 250 rpm / min. After the temperature stabilizes, the mixture is reacted for 1 hour, and filtered to separate the double salt and the decomplex salt mother liquor. The double salt can be used for addition in step (3) of the next treatment cycle;

[0050] (5) Aluminum sulfate was added to the decomplex salt mother liquor in an equal molar amount to ammonium sulfate, and the mixture was evaporated at 78° C. and a stirring speed of 200 rpm / min until the sodium sulfate reached saturation. The aluminum ammonium sulfate with a dry basis content of 99.52% and the deammonium mother liquor were filtered to obtain the precipitation rate of ammonium (by mole) of 18.2%. The deammonium mother liquor can be used for the addition of step (4) in the next treatment cycle.

[0051] Example 3

[0052] A method for treating a mother liquor from sodium sulfate production, as shown in FIG1 , comprises the following steps:

[0053] (1) The sodium sulfate mother liquor of 2.65 mol / L sodium sulfate concentration after filtration was taken as the stock solution, and the sodium sulfate obtained in Example 2 was added under the conditions of heating at 55°C and stirring at a speed of 350 rpm / min to reach a sodium sulfate concentration of 4.7 mol / L. After reacting for 1 hour, the temperature was lowered to 43°C, and ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1. The reaction was continued for 2 hours, and the mixture was filtered and separated to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 60.5%. The sodium bicarbonate wet residue was washed with pure water and dried to obtain sodium bicarbonate with a purity of 98.5%;

[0054] (2) The metathesis mother liquor was adjusted to pH 3 by adding 20% ​​dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0055] (3) 65 g of the double salt obtained in Example 2 was added to every 1000 ml of the acidified mother liquor, and the mixture was evaporated at 80° C. until the mixture was saturated with ammonium sulfate. The mixture was filtered while hot to obtain sodium sulfate with a purity of >96% and a denitrification mother liquor, wherein the sodium sedimentation rate (by mole) was 33.6%. The sodium sulfate could be used for addition in step (1) of the next treatment cycle;

[0056] (4) The denitrification mother liquor was mixed with the deammonium mother liquor obtained in Example 2, which accounted for 50% by volume of the denitrification mother liquor, and then cooled and crystallized at 30° C. with a stirring speed of 200 rpm / min. After the temperature stabilized, the mixture was reacted for 2 h, and filtered to separate the double salt and the decomplex salt mother liquor. The double salt can be used for addition in step (3) of the next treatment cycle;

[0057] (5) The decompound mother liquor was added with aluminum sulfate at a molar amount of 1.05 times that of ammonium sulfate, and evaporated at 82° C. and a stirring speed of 150 rpm / min until saturated with sodium sulfate. The aluminum ammonium sulfate and the deammonium mother liquor having a dry basis content of 99.74% were obtained by filtration, wherein the sedimentation rate of ammonium (by mole) was 22.5%. The deammonium mother liquor could be used for addition in step (4) of the next treatment cycle.

[0058] Example 4

[0059] A method for treating a mother liquor from sodium sulfate production, as shown in FIG1 , comprises the following steps:

[0060] (1) The sodium sulfate mother liquor of 2.49 mol / L sodium sulfate concentration after filtration was taken as the stock solution, and the sodium sulfate obtained in Example 3 was added under the conditions of heating at 45° C. and stirring at 450 rpm / min to reach a sodium sulfate concentration of 3.25 mol / L. After reacting for 1.5 hours, the temperature was lowered to 35° C., and ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1.5. The reaction was continued for 3 hours, and the mixture was filtered and separated to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 68.4%. The sodium bicarbonate wet residue was washed with pure water and dried to obtain sodium bicarbonate with a purity of 98.6%;

[0061] (2) The metathesis mother liquor was adjusted to pH 3 by adding 15% dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0062] (3) 80 g of the double salt obtained in Example 3 was added to every 1000 ml of the acidified mother liquor, and the mixture was evaporated at 85° C. until the ammonium sulfate was saturated. The sodium sulfate and the denitrification mother liquor were separated by hot filtration to obtain sodium sulfate with a purity of >96%, wherein the sodium sedimentation rate (by mole) was 37.8%. The sodium sulfate can be used for addition in step (1) of the next treatment cycle;

[0063] (4) The denitrification mother liquor was mixed with the deammonium mother liquor obtained in Example 3, which accounted for 50% by volume of the denitrification mother liquor, and then cooled and crystallized at 25° C. with a stirring speed of 180 rpm / min. After the temperature stabilized, the mixture was reacted for 3 h, and filtered to separate the double salt and the decomplex salt mother liquor. The double salt can be used for addition in step (3) of the next treatment cycle;

[0064] (5) The decompound mother liquor was added with aluminum sulfate according to 1.12 times the molar amount of ammonium sulfate, and evaporated at 80° C. and a stirring speed of 220 rpm / min until the sodium sulfate was saturated. The aluminum ammonium sulfate with a dry basis content of 99.89% and the deammonium mother liquor were obtained by filtration, wherein the sedimentation rate of ammonium (by mole) was 25.8%. The deammonium mother liquor can be used for the addition of step (4) in the next treatment cycle.

[0065] Example 5

[0066] A method for treating a mother liquor from sodium sulfate production, as shown in FIG1 , comprises the following steps:

[0067] (1) Taking high-concentration sodium sulfate wastewater with a sodium sulfate concentration of 2.49 mol / L after filtration as the stock solution, ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1.5, reacting for 3 hours, filtering and separating to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 64.8%, and the sodium bicarbonate wet residue was washed with pure water and dried to obtain sodium bicarbonate with a purity of 98.5%;

[0068] (2) The metathesis mother liquor was adjusted to pH 3 by adding 15% dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0069] (3) 80 g of the double salt obtained in Example 3 was added to every 1000 ml of the acidified mother liquor, and the mixture was evaporated at 85° C. until the mixture was saturated with ammonium sulfate. The mixture was filtered while hot to obtain sodium sulfate with a purity of >96% and a denitrification mother liquor, wherein the sodium sedimentation rate (by mole) was 35.7%. The sodium sulfate could be used for addition in step (1) of the next treatment cycle;

[0070] (4) The denitrification mother liquor was mixed with the deammonium mother liquor obtained in Example 3, which accounted for 50% by volume of the denitrification mother liquor, and then cooled and crystallized at 25° C. with a stirring speed of 180 rpm / min. After the temperature stabilized, the mixture was reacted for 3 h, and filtered to separate the double salt and the decomplex salt mother liquor. The double salt can be used for addition in step (3) of the next treatment cycle;

[0071] (5) The decompound mother liquor was added with aluminum sulfate according to 1.12 times the molar amount of ammonium sulfate, and evaporated at 80° C. and a stirring speed of 220 rpm / min until the sodium sulfate was saturated. The aluminum ammonium sulfate and the deammonium mother liquor with a dry basis content of 99.66% were obtained by filtration, wherein the sedimentation rate of ammonium (by mole) was 24.7%. The deammonium mother liquor can be used for the addition of step (4) in the next treatment cycle.

[0072] Example 6

[0073] A method for treating a mother liquor from sodium sulfate production, as shown in FIG1 , comprises the following steps:

[0074] (1) The sodium sulfate mother liquor of 2.49 mol / L sodium sulfate concentration after filtration was taken as the stock solution, and the sodium sulfate obtained in Example 3 was added under the conditions of heating at 45° C. and stirring at a speed of 450 rpm / min to reach a sodium sulfate concentration of 3.25 mol / L. After reacting for 1.5 hours, the temperature was lowered to 25° C., and ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1.5. The reaction was continued for 3 hours, and the mixture was filtered and separated to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 70.01%. The sodium bicarbonate wet residue was rinsed with pure water and dried to obtain sodium bicarbonate with a purity of 82.9%;

[0075] (2) The metathesis mother liquor was adjusted to pH 3 by adding 15% dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0076] (3) 80 g of the double salt obtained in Example 3 was added to every 1000 ml of the acidified mother liquor, and the mixture was evaporated at 85° C. until the mixture was saturated with ammonium sulfate. The mixture was filtered while hot to obtain sodium sulfate with a purity of >96% and a denitrification mother liquor, wherein the sodium sedimentation rate (by mole) was 37.5%. The sodium sulfate could be used for addition in step (1) of the next treatment cycle;

[0077] (4) The denitrification mother liquor was mixed with the deammonium mother liquor obtained in Example 3, which accounted for 50% by volume of the denitrification mother liquor, and then cooled and crystallized at 25° C. with a stirring speed of 180 rpm / min. After the temperature stabilized, the mixture was reacted for 3 h, and filtered to separate the double salt and the decomplex salt mother liquor. The double salt can be used for addition in step (3) of the next treatment cycle;

[0078] (5) The decompound mother liquor was added with aluminum sulfate according to 1.12 times the molar amount of ammonium sulfate, and evaporated at 80° C. and a stirring speed of 220 rpm / min until the sodium sulfate was saturated. The aluminum ammonium sulfate with a dry basis content of 99.34% and the deammonium mother liquor were obtained by filtration. The sedimentation rate of ammonium (by mole) was 23.7%. The deammonium mother liquor could be used for the addition of step (4) in the next treatment cycle.

[0079] Comparative Example 1

[0080] A method for treating a mother liquor from sodium sulfate alkali production comprises the following steps:

[0081] (1) The sodium sulfate mother liquor of 2.49 mol / L sodium sulfate concentration after filtration was taken as the stock solution, and the sodium sulfate obtained in Example 3 was added under the conditions of heating at 45°C and stirring at a speed of 450 rpm / min to reach a sodium sulfate concentration of 3.25 mol / L. After reacting for 1.5 hours, the temperature was lowered to 35°C, and ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1.5. The reaction was continued for 3 hours, and the mixture was filtered and separated to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 68.4%. The sodium bicarbonate wet residue was washed with pure water and dried to obtain sodium bicarbonate with a purity of 98.6%;

[0082] (2) The metathesis mother liquor was adjusted to pH 3 by adding 15% dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0083] (3) 80 g of the double salt obtained in Example 3 was added to every 1000 ml of the acidified mother liquor, and the mixture was evaporated at 85° C. The evaporation was stopped when the condensed water reached 300 ml. The sodium sulfate and the denitrification mother liquor were separated by hot filtration to obtain sodium sulfate with a purity of >96% and a sodium sedimentation rate (by mole) of 37.7%.

[0084] (4) The denitrification mother liquor was mixed with the deammonium-depleted mother liquor obtained in Example 3, which accounted for 50% by volume of the denitrification mother liquor. Aluminum sulfate was added according to a molar amount of 1.12 times that of ammonium sulfate, and the mixture was evaporated at 80° C. and a stirring speed of 220 rpm / min to obtain ammonium aluminum sulfate with a dry basis content of 37.8% and a deammonium-depleted mother liquor, wherein the sedimentation rate of ammonium (by mole) was 6.4%.

[0085] Comparative Example 2

[0086] A method for treating a mother liquor from sodium sulfate alkali production comprises the following steps:

[0087] (1) The sodium sulfate mother liquor of 2.49 mol / L sodium sulfate concentration after filtration was taken as the stock solution, and the sodium sulfate obtained in Example 3 was added under the conditions of heating at 45° C. and stirring at 450 rpm / min to reach a sodium sulfate concentration of 3.25 mol / L. After reacting for 1.5 hours, the temperature was lowered to 35° C., and ammonium bicarbonate was added at a sodium / ammonium molar ratio of 1:1.5. The reaction was continued for 3 hours, and the mixture was filtered and separated to obtain a double decomposition mother liquor and sodium bicarbonate, wherein the sodium precipitation rate (by mole) was 68.4%. The sodium bicarbonate wet residue was washed with pure water and dried to obtain sodium bicarbonate with a purity of 98.6%;

[0088] (2) The metathesis mother liquor was adjusted to pH 3 by adding 15% dilute sulfuric acid and reacted for 1.5 h to stabilize the pH, thereby obtaining an acidified mother liquor;

[0089] (3) The acidified mother liquor was mixed with the deammonium mother liquor obtained in Example 3, which accounted for 50% by volume of the acidified mother liquor, and then cooled and crystallized at 25° C. with a stirring speed of 180 rpm / min. After the temperature stabilized, the reaction was carried out for 3 hours, and the double salt and the decomplex salt mother liquor were separated by filtration;

[0090] (4) The decomplex salt mother liquor was added with aluminum sulfate in an amount of 1.12 times the molar amount of ammonium sulfate, and evaporated at 80° C. and a stirring speed of 220 rpm / min to obtain ammonium aluminum sulfate with a dry basis content of 43.5% and a deammonium mother liquor, wherein the sedimentation rate of ammonium (by mole) was 8.2%.

[0091] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the scope of protection of the present application.

Claims

1. A method for treating the mother liquor of soda ash production from mirabilite, characterized in that, It includes the following steps: Take the mother liquor of mirabilite alkali production and mix it with ammonium bicarbonate for reaction, then filter to obtain wet sodium bicarbonate residue and double decomposition mother liquor; Acidify the double decomposition mother liquor to convert ammonium bicarbonate and sodium bicarbonate contained therein into carbon dioxide to obtain acidified mother liquor; Heat and evaporate the acidified mother liquor until ammonium sulfate is saturated under this temperature condition, then filter while it is hot to obtain by-product sodium sulfate and denitrification mother liquor; Cool and crystallize the denitrification mother liquor, then filter to obtain double salt and mother liquor after removing double salt; Mix the mother liquor after removing double salt with aluminum sulfate, then heat and evaporate until sodium sulfate is saturated, and filter to obtain ammonium aluminum sulfate and mother liquor after removing ammonium; 2. The treatment method of mirabilite-based alkali mother liquor according to claim 1, characterized in that, Take the mother liquor of mirabilite alkali production, add sodium sulfate under the conditions of heating temperature of 40 - 60 °C and stirring to reach a sodium sulfate concentration of 2.6 - 4.8 mol / L, then cool down to 35 - 50 °C to obtain supersaturated sodium sulfate mother liquor, and mix it with ammonium bicarbonate for reaction, then filter to obtain sodium bisulfate and double decomposition mother liquor.

3. The treatment method of the mother liquor for making soda ash with mirabilite as claimed in claim 2, characterized in that, Take the mother liquor of mirabilite alkali production, add sodium sulfate under the conditions of heating temperature of 40 - 60 °C and stirring speed of 300 - 450 rpm / min to reach a sodium sulfate concentration of 2.6 - 4.8 mol / L, cool down to 35 - 50 °C, and mix it with ammonium bicarbonate for reaction for 1 - 3 h.

4. The treatment method of mirabilite-based alkali mother liquor according to claim 2, characterized in that, The molar ratio of sodium in the supersaturated sodium sulfate mother liquor to ammonium in ammonium bicarbonate is 1:(1 - 2).

5. The treatment method of the sodium sulfate mother liquor according to claim 2, characterized in that, The by-product sodium sulfate is cyclically added to the mother liquor of mirabilite alkali production under the conditions of heating temperature of 40 - 60 °C and stirring to reach a sodium sulfate concentration of 2.6 - 4.8 mol / L, then cool down to 35 - 50 °C, and mix it with ammonium bicarbonate for reaction.

6. The treatment method of the mother liquor for making soda ash from mirabilite as claimed in claim 1, characterized in that, The acidification treatment of the double decomposition mother liquor is to add dilute sulfuric acid with a concentration of 10 - 20% to the double decomposition mother liquor, react for 1 - 2 h to stabilize the pH, and the pH value of the acidified mother liquor < 4.

7. The treatment method of the mother liquor for making soda ash from mirabilite as claimed in claim 1, wherein, The double salt is cyclically mixed with the acidified mother liquor, and then heated and evaporated until sodium sulfate is saturated under this temperature condition, wherein the acidified mother liquor and the double salt are mixed according to a volume ratio of 1:(0.05 - 0.1).

8. The treatment method of the mother liquor for making soda ash from mirabilite as claimed in claim 1, characterized in that, The mother liquor after removing ammonium is cyclically mixed with the denitrification mother liquor, the volume ratio of the denitrification mother liquor to the mother liquor after removing ammonium is 1:(0.5 - 1), and then cooled and crystallized.

9. The treatment method of the mother liquor for making soda ash from mirabilite as claimed in claim 1, characterized in that, Meet at least one of the following conditions a) - e): a) Heat the acidified mother liquor to 70 - 85 °C for evaporation until ammonium sulfate is saturated under this temperature condition; b) Cool the denitrification mother liquor to 20 - 30 °C for crystallization; c) Cool and crystallize the denitrification mother liquor at 20 - 30 °C for 1 - 3 h; d) Cool and crystallize the denitrification mother liquor under stirring conditions, and the stirring speed is 100 - 300 rpm / min; e) After mixing the mother liquor after removing double salt with aluminum sulfate, heat it to 75 - 85 °C for evaporation.

10. A method for treating mother liquor of glauber's salt for soda production according to claim 1, characterized in that, The mother liquor after removing double salt contains ammonium sulfate, and the mother liquor after removing double salt is mixed with aluminum sulfate according to a molar ratio of ammonium sulfate to aluminum sulfate of 1:(1 - 1.2).

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