Preparation method of salt gypsum

Abstract

The invention relates to a preparation method of salt gypsum. The seed crystal is prepared before the reaction of the mirabilite water and the ammonia distillation waste liquid, the salt gypsum crystallization promoting agent is added in the reaction, and various conditions in the salt gypsum reaction process are controlled, so that the water content of the salt gypsum is reduced from 30% to 15% or below, and meanwhile, the crystal grains of the salt gypsum are increased; therefore, the salt gypsum can be used as a raw material for preparing building gypsum and high-strength gypsum, and a new way is developed for comprehensive utilization, energy conservation and emission reduction of the salt gypsum. The method provided by the invention is suitable for various reactions containing Na2SO4 solution and CaCl2 solution, and can effectively control the water content of the generated salt gypsum.

Description

Technical Field

[0001] The invention belongs to the technical field of chlor-alkali salt gypsum production, and in particular relates to a method for controlling the water content of salt gypsum. Background Art

[0002] The production of soda ash occupies an important position in the process of national economic development and construction. China has become the country with the largest production and consumption in the world. The ammonia-soda process is still the main method for producing soda ash at present, because it has the following advantages: cheap and easy-to-obtain raw materials, high product quality, long history, mature technology, large-scale continuous production, and sufficient recycling of ammonia in production with small loss. The disadvantages of this method are low raw material utilization, mainly low utilization of NaCl and large waste liquid discharge. Ammonia evaporation waste liquid is the largest waste liquid produced in the soda ash preparation process. It is mainly high-salt wastewater, and the main components are inorganic salts such as sodium chloride and calcium chloride. At present, it is concentrated by drying and then enters the calcium chloride preparation plant for crystallization. However, this method is extremely harmful to the environment and requires a large amount of land. In addition, it is affected by the region and climate. The concentrated liquid after drying is unstable and has many impurities, which is not conducive to the evaporation and crystallization of calcium chloride. The disposal of ammonia evaporation waste liquid has always been one of the factors restricting the sustainable development of ammonia-soda process alkali production enterprises.

[0003] Through the comprehensive utilization of mirabilite and ammonia evaporation waste liquid, on the one hand, the storage and disposal problems of mirabilite produced by chlor-alkali plants are solved, and on the other hand, the discharge of ammonia evaporation waste liquid is reduced, and part of sodium chloride is recovered at the same time, which not only has good economic benefits, but also can turn waste into treasure and comprehensively utilize waste. However, the gypsum produced by mirabilite and ammonia evaporation waste liquid has small grains and no strength, so it cannot be used and can only be landfilled. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for controlling the water content of salt gypsum. The method can reduce the water content of salt gypsum from 30% to below 15%, so that the salt gypsum can be used for the preparation of gypsum products, and develop a new method for the comprehensive utilization of ammonia waste liquid and mirabilite water in the chlor-alkali industry and energy conservation and emission reduction.

[0005] A method for preparing salt gypsum comprises the following steps:

[0006] Step 1, stirring and mixing the mirabilite solution, the crystal promoter and the salt gypsum seed crystals;

[0007] Step 2, slowly adding ammonia evaporation waste liquid to perform precipitation crystallization reaction;

[0008] Step 3, separating the solid from the liquid in the crystallized precipitate to obtain salt gypsum.

[0009] In step 1, salt gypsum seed crystals are prepared by the following steps: by mixing Na2 SO 4 Solution with CaCl 2 The solution undergoes a precipitation crystallization reaction, and salt gypsum seed crystals are obtained after crystal separation; the precipitation crystallization reaction temperature is 35-40°C.

[0010] In step 2, the precipitation crystallization reaction temperature is 40-50° C., and the precipitation crystallization reaction time is 0.5-2 hours.

[0011] In step 3, solid-liquid separation is carried out by suction filtration or centrifugation until no mother liquid is discharged, and the water content of the obtained salt gypsum is less than 15%.

[0012] CaCl in ammonia wastewater 2 The content of Na in Glauber's salt water is 60-120 g / l; 2 SO 4 The content is 80-100g / l.

[0013] The amount of salt gypsum seed crystals added is 1 to 4% of the weight of the mirabilite solution.

[0014] The amount of salt gypsum crystal promoter added is 0.01-0.1% of the weight of the sodium sulfate solution.

[0015] The crystal-promoting agent is composed of an inorganic salt and a surfactant in a weight ratio of (1:4) to (4:1).

[0016] The inorganic salt is one or two of sodium thiosulfate, sodium carbonate and ferric sulfate.

[0017] The surfactant is one or two of sodium dodecylbenzene sulfonate, dodecylbenzene sulfonic acid, sodium xylene sulfonate and dodecyl dimethyl ammonium oxide.

[0018] Beneficial Effects

[0019] The present invention generates CaSO by crystallization through reaction of mirabilite water and ammonia distillation waste liquid in the chlor-alkali industry. 4 ·2H 2 O, and by adding crystal seeds and salt gypsum crystal promoters during the reaction and controlling the reaction, the water content of the salt gypsum is reduced from 30% to below 15%. At the same time, the grain size of the salt gypsum is enlarged and can be used to prepare building gypsum and high-strength gypsum, which not only reduces the production of dihydrate salt gypsum, but also creates certain economic benefits and good environmental benefits, opening up a new way for the comprehensive utilization of salt gypsum and energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the salt gypsum crystal form prepared by the present invention.

[0021] Figure 2This is the raw salt gypsum crystal form obtained in Control Example 1.

[0022] Figure 3 This is the salt gypsum crystal form obtained in Control Example 2.

[0023] Figure 4 This is the salt gypsum crystal form obtained in Control Example 3.

[0024] Figure 5 This is the process flow chart of salt gypsum crystal growth. DETAILED DESCRIPTION

[0025] A method for controlling the water content of salt gypsum provided in this patent specifically comprises the following steps:

[0026] Preparation of salt gypsum seed crystals: temperature 35-40℃, while adding Na 2 SO 4 Solution with CaCl 2 Solution, salt gypsum (CaSO 4 ·2H 2 O) as seed crystal

[0027] Separation of salt gypsum crystal seeds: Separate the salt gypsum, use solid-liquid separation equipment to increase the concentration of salt gypsum in the solution, and send the resulting clear liquid to the next process;

[0028] Salt gypsum crystal growth: Add Na into the neutralization reaction tank 2 SO 4 The solution, the crystal promoter and the obtained seed crystals are stirred at a temperature of 40-50°C. Slowly add the distilled ammonia waste liquid into the pool and stir the solution evenly. The reaction time is 0.5-2 hours;

[0029] Salt gypsum separation: The solution obtained by the above reaction is initially separated by solid-liquid separation equipment, the supernatant enters the next process, and the concentrated solution enters a three-legged centrifuge for centrifugation to obtain salt gypsum with a water content of less than 15%. The supernatant obtained by separation at the same time enters the same process as the supernatant obtained by cyclone separation.

[0030] Further technical solutions: Na in mirabilite water 2 SO 4 The content is 80-100 g / l;

[0031] Further technical solution: CaCl in ammonia evaporation wastewater 2 The content is 60-120 g / l;

[0032] The solid concentration of salt gypsum seed after concentration should be between 40% and 60%;

[0033] The amount of salt gypsum seed added is 1-4%;

[0034] Further technical solution: the amount of salt gypsum crystal promoter added is 0.01-0.1% of Glauber's salt solution.

[0035] A further technical solution: the inorganic salt in the crystal-promoting agent is one or two of sodium thiosulfate, sodium carbonate and ferric sulfate.

[0036] A further technical solution: the organic matter in the crystal-promoting agent is one or two of sodium dodecylbenzene sulfonate, dodecylbenzene sulfonic acid and sodium xylene sulfonate.

[0037] Example 1

[0038] The used materials are the mirabilite solution and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of the mirabilite solution is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl 2 Content: 104.81g / L.

[0039] The steps adopted by the present invention are as follows:

[0040] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H 2 O) as a seed crystal;

[0041] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 2% (about 21.6 g) is taken as the seed crystals for the next step reaction;

[0042] Salt gypsum crystal growth reaction: heat 1L of Glauber's salt solution, control the temperature to 45°C, add 0.8g of salt gypsum crystal promoter (mass ratio of sodium thiosulfate: sodium dodecylbenzene sulfonate = 2:1), 15g of the seed crystals prepared in the previous step, stir evenly with a stirring paddle, control the temperature of the reaction system to 45°C, take 660ml of ammonia waste liquid and add it to the Glauber's salt water within 1h using a peristaltic pump, and maintain the temperature after the addition is completed. Continue the reaction time for 2 hours;

[0043] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 95g of salt gypsum, and the water content was 11.64%. The sodium chloride content in the filtered wastewater can be reused in the process.

[0044] Example 2

[0045] The used materials are sodium sulfate and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of sodium sulfate is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl2 Content: 104.81g / L.

[0046] The steps adopted by the present invention are as follows:

[0047] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H 2 O) as a seed crystal;

[0048] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 1% (about 11.8 g) is taken as the seed crystals for the next step reaction;

[0049] Salt gypsum crystal growth reaction: heat 1L of Glauber's salt solution, control the temperature to 45°C, add 0.8g of salt gypsum crystal promoter (mass ratio of sodium thiosulfate: sodium dodecylbenzene sulfonate = 1:1), 20g of the seed crystals prepared in the previous step, stir evenly with a stirring paddle, control the temperature of the reaction system to 45°C, take 660ml of ammonia waste liquid and add it to the Glauber's salt water within 1h using a peristaltic pump, and maintain the temperature after the addition is completed. Continue the reaction time for 2 hours;

[0050] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 98g of salt gypsum, and the water content was 14.37%. The sodium chloride content in the filtered wastewater can be reused in the process.

[0051] Example 3

[0052] The used materials are sodium sulfate and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of sodium sulfate is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl 2 Content: 69.87g / L.

[0053] The steps adopted by the present invention are as follows:

[0054] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H 2 O) as a seed crystal;

[0055] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 2% (about 21.6 g) is taken as the seed crystals for the next step reaction;

[0056] Salt gypsum crystal growth reaction: heat 1L of Glauber's salt solution, control the temperature to 45°C, add 0.4g of salt gypsum crystal promoter (mass ratio of sodium thiosulfate: sodium dodecylbenzene sulfonate = 1:2), 15g of the seed crystals prepared in the previous step, stir evenly with a stirring paddle, control the temperature of the reaction system to 45°C, take 660ml of ammonia waste liquid and add it to the Glauber's salt water within 1h using a peristaltic pump, and maintain the temperature after the addition is completed. Continue the reaction time for 2 hours;

[0057] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 102g of salt gypsum, and the water content was 13.29%. The filtered wastewater can be reused in the process due to the sodium chloride content.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that no salt gypsum crystallization promoter is added during the precipitation and crystallization process.

[0060] The used materials are the mirabilite solution and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of the mirabilite solution is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl 2 Content: 104.81g / L.

[0061] The steps adopted by the present invention are as follows:

[0062] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H 2 O) as a seed crystal;

[0063] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 2% (about 21.6 g) is taken as the seed crystals for the next step reaction;

[0064] Salt gypsum crystal growth reaction: heat 1L of Glauber's salt solution and control the temperature to 45°C. Add 15g of the seed crystals prepared in the previous step, stir evenly with a stirring paddle and control the temperature of the reaction system to 45°C. Take 660ml of ammonia waste liquid and add it to the Glauber's salt water by a peristaltic pump within 1 hour. After the addition is completed, maintain the temperature and continue the reaction for 2 hours.

[0065] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 86g of salt gypsum, and the water content was 35.22%. The filtered wastewater can be reused in the process due to the sodium chloride content.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that the salt gypsum crystal-promoting agent contains only sodium thiosulfate.

[0068] The used materials are the mirabilite solution and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of the mirabilite solution is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl 2 Content: 104.81g / L.

[0069] The steps adopted by the present invention are as follows:

[0070] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H 2 O) as a seed crystal;

[0071] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 2% (about 21.6 g) is taken as the seed crystals for the next step reaction;

[0072] Salt gypsum crystal growth reaction: Heat 1L of Glauber's salt solution and control the temperature to 45°C, add 0.8g of sodium thiosulfate and 15g of the seed crystals prepared in the previous step, stir evenly with a stirring paddle and control the temperature of the reaction system to 45°C, take 660ml of ammonia waste liquid and add it to the Glauber's salt water within 1 hour using a peristaltic pump, and maintain the temperature after the addition is completed and continue the reaction time for 2 hours;

[0073] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 90g of salt gypsum, and the water content was analyzed to be 32.13%.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that the salt gypsum crystal-promoting agent contains only sodium dodecylbenzene sulfonate.

[0076] The used materials are the mirabilite solution and ammonia distillation waste liquid provided by the chlor-alkali plant. The main component of the mirabilite solution is Na 2 SO 4 The content is 89.32g / L. The main component of ammonia wastewater is CaCl 2 Content: 104.81g / L.

[0077] The steps adopted by the present invention are as follows:

[0078] Preparation of salt gypsum seed crystals: 660 ml of distilled ammonia waste liquid and 1 L of mirabilite solution were added into a beaker at the same time, the temperature was controlled at 45 °C, and stirred to obtain salt gypsum (CaSO 4 ·2H2 O) as a seed crystal;

[0079] Concentration of salt gypsum seed crystals: The prepared seed crystal solution is filtered with a suction filtration bottle, and 2% (about 21.6 g) is taken as the seed crystals for the next step reaction;

[0080] Salt gypsum crystal growth reaction: Heat 1L of Glauber's salt solution and control the temperature to 45°C, add 0.8g of sodium dodecylbenzene sulfonate and 15g of the seed crystals obtained in the previous step, stir evenly with a stirring paddle and control the temperature of the reaction system to 45°C, take 660ml of ammonia waste liquid and add it to the Glauber's salt water within 1 hour using a peristaltic pump, and maintain the temperature after the addition is completed and continue the reaction time for 2 hours;

[0081] Separation of salt gypsum: The reaction slurry was filtered with a suction bottle, and the obtained gypsum was washed and separated again with tap water for 3 times to obtain 86g of salt gypsum, and the water content was analyzed to be 31.34%.

[0082] The microscope photo of the salt gypsum prepared in Example 1 is as follows: Figure 1 As shown, it can be seen that the crystal particles are large and uniform in morphology; while the salt gypsum prepared in Control Example 1 has a significantly different morphology, showing a fine fiber shape, and there is almost no obvious crystal particle morphology; at the same time, in Control Examples 2 and 3, anionic surfactants and sodium thiosulfate were used separately, respectively, and their regulatory effects on the crystal formation process were also limited, and the crystal morphology of the particles was still significantly inferior to the addition conditions of Example 1. At the same time, because sodium thiosulfate and anionic surfactants can effectively control the mass transfer and reaction process on the interface of sodium sulfate and calcium chloride through the electrostatic effect of surface charges, the crystallization process is affected, making the crystal particles fuller, and the water content in the crystals is significantly reduced after filtration and separation.

Claims

1. A method for preparing salt gypsum, characterized in that: The steps include: Step 1, stirring and mixing the mirabilite solution, the crystal promoter and the salt gypsum seed crystals; Step 2, slowly adding ammonia evaporation waste liquid to perform precipitation crystallization reaction; Step 3, separating the solid from the liquid in the crystallized precipitate to obtain salt gypsum.

2. The method for preparing salt gypsum according to claim 1, characterized in that: In step 1, salt gypsum seed crystals are prepared by the following steps: a precipitation crystallization reaction is carried out by mixing a Na2SO4 solution and a CaCl2 solution, and the salt gypsum seed crystals are obtained after crystal separation; the precipitation crystallization reaction temperature is 35-40°C.

3. The method for preparing salt gypsum according to claim 1, characterized in that: In step 2, the precipitation crystallization reaction temperature is 40-50° C., and the precipitation crystallization reaction time is 0.5-2 hours.

4. The method for preparing salt gypsum according to claim 1, characterized in that: In step 3, solid-liquid separation is carried out by suction filtration or centrifugation until no mother liquid is discharged, and the water content of the obtained salt gypsum is less than 15%.

5. The method for preparing salt gypsum according to claim 1, characterized in that: The content of CaCl2 in ammonia waste liquid is 60-120 g / l; the content of Na2SO4 in mirabilite water is 80-100 g / l.

6. The method for preparing salt gypsum according to claim 1, characterized in that: The amount of salt gypsum seed crystals added is 1 to 4% of the weight of the mirabilite solution.

7. The method for preparing salt gypsum according to claim 1, characterized in that: The amount of salt gypsum crystal promoter added is 0.01-0.1% of the weight of the sodium sulfate solution.

8. The method for preparing salt gypsum according to claim 1, characterized in that: The crystal-promoting agent is composed of an inorganic salt and a surfactant in a weight ratio of (1:4) to (4:1).

9. The method for preparing salt gypsum according to claim 8, characterized in that: The inorganic salt is one or two of sodium thiosulfate, sodium carbonate and ferric sulfate.

10. The method for preparing salt gypsum according to claim 8, characterized in that: The surfactant is one or two of sodium dodecylbenzene sulfonate, dodecylbenzene sulfonic acid, sodium xylene sulfonate and dodecyl dimethyl ammonium oxide.

Images