A method and application for the recycling of salt mud

Abstract

This invention relates to a method and application for the recovery of salt mud, belonging to the field of chemical process technology. The invention utilizes a chemical reaction between sodium sulfate in mineral brine and calcium chloride in the wastewater discharged from a soda ash plant. The salt mud produced from the refined mineral brine is then mixed with the above reaction solution. After sedimentation and filtration, a mixture of sodium chloride, gypsum, and salt mud is generated. The obtained sodium chloride can be used to produce soda ash, while the gypsum and salt mud mixture can be used as a building material. The gypsum and salt mud mixture obtained by the method of this invention has stable properties and can be directly sold as a semi-finished product. The method of this invention employs multiple processing steps, reducing equipment and pipeline blockage during the recovery process and minimizing corrosion of equipment by raw materials and intermediate products. This significantly reduces operating costs, facilitates extended production cycles, and meets the current high demand in the soda ash market, resulting in high economic benefits.

Description

Technical Field

[0001] This invention relates to the field of chemical process technology, and in particular to a method and application for the recovery of salt mud. Background Technology

[0002] Salt mud is a waste product generated during the brine refining process in soda ash manufacturing. Its main components are CaCO3, Mg(OH)2, CaSO4 precipitates, and nearly saturated NaCl brine. Directly discharging the generated salt mud not only wastes resources but also pollutes the environment. Therefore, the recycling and utilization of salt mud discharged from industry has gradually gained attention.

[0003] Currently, domestic alkali plants typically use either a mixed discharge of salt mud and alkali residue or a pressure filtration method to recover brine. The existing technology employs the following method: saturated crude brine from the salt and nitrate unit is sent to a crude brine distribution tank; diluted lime slurry from the lime slurry process enters a lime slurry tank and is pumped to a causticizing tank; soda ash solution from the calcination process enters a soda ash solution tank and is pumped to the causticizing tank by a hot alkali pump; lime slurry Ca(OH)2 and alkali solution Na2CO3 undergo a causticizing reaction in the causticizing tank at a specific ratio; qualified causticizing solution NaOH is metered into the crude brine distribution tank, mixes with the crude brine, and flows by gravity into the bottom of the reaction tank; the reaction solution overflows from the reaction tank into a curved trough; and qualified polypropylene is prepared in a flocculant preparation tank. Sodium sulfate solution is pumped into the flocculant tank, diluted with refined brine to form a qualified polyacrylamide solution, and then pumped into the flocculant high-level tank. Controlled by a flocculant flow meter, it flows into the curved neck tank and, together with the calcium and magnesium removal brine, into the clarification tank. The salt sludge at the bottom of the clarification tank is then discharged into the intermediate salt sludge tank. Part of the salt sludge is circulated back to the curved neck tank by a salt sludge settling pump, while another part enters the salt sludge thickener via the intermediate pump. The clear liquid in the upper part of the thickener flows by gravity into the thickened brine receiving tank, while the thickened sludge at the bottom is discharged into the salt sludge tank. After dilution with water, it is pumped to the waste liquid tank of the distillation and absorption process by an external mud pump. The qualified refined brine from the top of the clarification tank overflows into the refined brine tank and is pumped to the refined brine high-level tank of the distillation and absorption process for use in the ammonia brine production process. The salt sludge discharged from the clarification tank undergoes thickening and sedimentation treatment. The thickened salt sludge directly enters the distillation waste liquid system and is centrally sent to the purification station for neutralization treatment. The above method involves dewatering the salt mud slurry using a hydraulic differential speed horizontal screw centrifuge in the white mud dewatering process, recovering the brine, and reducing salt consumption in soda ash production. The discharged salt mud has a brine content of 68%. The discharged salt mud is piped with carbon steel pipe at the brine station and sent to the hydraulic differential speed horizontal screw centrifuge dewatering device in the lime purification process. The separated brine is pumped back to the thick brine recovery tank in the heavy soda ash workshop, and then pumped to the curved channel for intermittent operation, processing salt mud for 4 hours a day. This method is prone to resulting in a large amount of industrial wastewater discharge.

[0004] In view of the shortcomings of the above-mentioned technical solutions, the current research focus is on developing a salt mud recycling method that can turn sulfate ions in mineral brine into valuable resources and achieve low-cost resource utilization. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and application for the recovery of salt mud. The recovery method of this invention can effectively recover brine and dry salt mud, and the recovery process causes less wear and tear on the equipment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for recovering salt mud, the method comprising the following steps:

[0008] S1. Distill the waste liquid discharged from the soda ash plant and mix it with mineral brine in a reaction tank for 10-30 minutes to obtain a reaction solution;

[0009] S2. Mix and stir the reaction solution obtained in step S1 in a crystallizer to obtain a slurry and a supernatant. Repeat this step 1-2 times to obtain crystals.

[0010] S3. Mix the salt mud with the crystals obtained in step S2 and stir for 2-8 minutes. Add flocculant and continue mixing. Then allow it to settle for 120-180 minutes to obtain the supernatant and precipitate I.

[0011] S4. Separate the precipitate I obtained in step S3 to obtain a dilute liquid and a concentrated liquid. The dilute liquid is returned to the reaction tank in step S1 to continue the reaction, and the concentrated liquid is separated in a filter to obtain filtrate and precipitate II, which can then be sent out.

[0012] In a preferred embodiment of the salt mud recovery method of the present invention, in step S1, the waste liquid includes calcium chloride (CaCl2) and the mineral brine includes sodium sulfate (Na2SO4).

[0013] The main component of the wastewater discharged from the soda ash plant is CaCl2, and the main component of the mineral salt brine is Na2SO4. This invention utilizes the chemical reaction Na2SO4 + CaCl2 + 2H2O = CaSO4·2H2O + 2NaCl to react the wastewater discharged from the soda ash plant with the mineral salt brine to produce sodium chloride and calcium sulfate. The raw materials in step S2 of this invention undergo multiple crystallizations, which can fully utilize the raw materials and greatly improve the recovery efficiency of this invention. The supernatant obtained in step S3 of this invention can be used to produce saturated crude brine through a salt-dissolving device, overcoming the technical problem in the prior art of sending the separated brine back to the thick brine recovery tank and directly sending it to the evaporation and absorption process to absorb ammonia to produce ammonia brine, which affects the ammonia brine index. The filtrate obtained in step S4 of this invention can also be reused. The precipitate II obtained by the method of this invention does not require solid waste disposal and has stable indicators. It can be sold as a semi-finished product or directly used as a building material filler.

[0014] In a more preferred embodiment of the salt mud recovery method of the present invention, in step S1, the concentration of CaCl2 in the waste liquid is >100g / L, and the concentration of Na2SO4 in the mineral brine is 20-30g / L.

[0015] As a more preferred embodiment of the salt mud recycling method of the present invention, in step S1, the volume ratio of the cleaned waste liquid to the mineral salt brine is 1:10; the inventors have conducted a large number of experiments and calculated the optimal volume ratio of the cleaned waste liquid to the mineral salt brine based on the chemical reaction formula: Na2SO4+CaCl2+2H2O=CaSO4·2H2O+2NaCl.

[0016] In a preferred embodiment of the salt mud recovery method of the present invention, in step S1, the flow rate of the clean waste liquid discharged from the soda ash plant is 20-30 m³ / h. 3 The flow rate of the mineral brine is 200-220 m³ / h. 3 / h.

[0017] In a preferred embodiment of the salt mud recycling method of the present invention, in step S1, the reaction tank can be multiple reaction tanks connected in series. The number of reaction tanks can be determined according to the actual production process. The use of multiple reaction tanks can make the raw materials fully mixed and is more suitable for large-scale industrial production.

[0018] In a preferred embodiment of the salt mud recycling method of the present invention, in step S2, the crystallizer can be multiple crystallizers connected in parallel. The number of crystallizers can be determined according to the actual production process. The use of multiple crystallizers can make the raw materials fully mixed and is more suitable for large-scale industrial production.

[0019] In a preferred embodiment of the salt mud recycling method of the present invention, in step S3, the volume ratio of the mixture obtained in step S2 to the salt mud is 8:1. The inventors have found through a large number of experiments that at this volume ratio, each raw material can be utilized more fully.

[0020] In a preferred embodiment of the salt mud recycling method of the present invention, in step S3, the flocculant is a commonly used flocculant in the art, and the present invention uses an aqueous solution of polyacrylamide.

[0021] In a preferred embodiment of the salt mud recovery method of the present invention, in step S4, the filter cloth used for separating the concentrated liquid in the filter is a polypropylene filter cloth.

[0022] In a more preferred embodiment of the salt mud recovery method of the present invention, the filter cloth has a pore size of 40-60 μm. Through numerous experiments, the inventors have found that selecting a filter cloth with the above-mentioned pore size increases the filtration accuracy, reduces the liquid penetration resistance, increases the filtration rate, and increases the processing capacity, thus better meeting production needs. At the same time, the above-mentioned filter cloth selection is beneficial to the control of moisture in the final gypsum and salt mud mixture, which can ensure that the content of adhering water in the product obtained in the present invention is ≤25%.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention provides a method and application for the recovery of salt mud. It utilizes the reaction between sodium sulfate in mineral brine and calcium chloride in the wastewater discharged from a soda ash plant. The salt mud generated from the refined mineral brine is then mixed with the reaction solution. After sedimentation and filtration, a mixture of sodium chloride, gypsum, and salt mud is produced. The obtained sodium chloride can be used for soda ash production, while the gypsum and salt mud mixture can be used as building materials. The product obtained using this method has stable performance indicators and can be sold directly as a semi-finished product. This method employs multiple processing steps, reducing equipment and pipeline blockage during the recovery process and minimizing corrosion from raw materials, significantly lowering operating costs and facilitating extended production cycles. This method meets the current high demand in the soda ash market and offers high economic benefits. Attached Figure Description

[0025] Figure 1 The flowchart is a process for recovering salt mud according to one embodiment of the present invention; (1): reaction tank, (2): crystallizer, (3): settling tank, (4): filter, (5): reaction pump, (6): intermediate pump, (7): mixing tank, (8): mixing pump, (9): mixing baffle, (10): low nitrate brine tank, (11): calcium slurry material tank, (12): calcium slurry pump, (13): filtrate tank, (14): filtrate pump. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the raw materials, methods and equipment used in this invention are all conventional raw materials, methods and equipment in this technical field.

[0028] Example 1

[0029] The process flow chart for the recovery of salt mud described in Embodiment 1 of this invention is as follows: Figure 1 As shown, (1): reaction vessel, (2): crystallizer, (3): settling tank, (4): filter, (5): reaction pump, (6): intermediate pump, (7): mixing tank, (8): mixing pump, (9): mixing baffle, (10): low nitrate brine tank, (11): calcium slurry material tank, (12): calcium slurry pump, (13): filtrate tank, (14): filtrate pump.

[0030] It should be noted that in this embodiment, there are 4 reaction vessels (1). Figure 1 The reaction vessel (1) in the flowchart shown does not represent the actual number of reaction vessels in production.

[0031] The recycling method described in this embodiment includes the following steps:

[0032] S1. Discharge the wastewater from the soda ash plant at a rate of 25m³. 3 A flow rate of / h is fed into reactor #1 (1), and then at 210m 3 The brine is added at a flow rate of / h and passed through reaction tank 2 (1), reaction tank 3 (1), and reaction tank 4 (1) in sequence. The mixture is thoroughly mixed and stirred for 20 minutes to obtain the reaction solution. The volume ratio of the waste liquid to the brine is 1:10.

[0033] S2. The reaction solution obtained in step S1 is sent to the crystallizer (2) by reaction pump (5) and mixed and stirred to obtain slurry and supernatant. Then, the slurry and supernatant are pumped into the crystallizer (2) by intermediate pump (6) and mixed and stirred again to obtain crystals.

[0034] S3. The salt mud from the refined brine system and the crystals obtained in step S2 are mixed and stirred in a mixing tank (7) for 20 minutes. Then, the mixture is pumped into a mixing baffle tank (9) by a mixing pump (8). Flocculant is added to the mixing baffle tank (9) and mixing continues. Then, the mixture is stirred at a speed of 25 m 3The flow rate is / h into the settling tank (3) for settling. After settling for 150min, the supernatant and precipitate I are obtained. The supernatant flows into the low nitrate brine tank (10).

[0035] The mass ratio of the mixture obtained in step S2 to the salt mud is 8:1.

[0036] S4. The precipitate I obtained in step S3 is sent to the calcium slurry material tank (11) for separation to obtain a dilute solution and a concentrated solution. The dilute solution is returned to the reaction tank (1) in step S1 by the calcium slurry pump (12) to continue the reaction. The concentrated solution is pumped at 60m... 3 The flow rate is fed into the filter (4) at a rate of / h to separate the filtrate and precipitate II. The filtrate is pumped into the mixing baffle (9) by the filtrate pump (14) through the filtrate tank (13), and the precipitate II can be discharged.

[0037] In this embodiment, the concentration of NaCl in the mineral brine is ≥295g / L, and the concentration of Na2SO4 is 20-30g / L; the concentration of CaCl2 in the waste liquid in step S1 is 100g / L, and the concentration of NaCl is ≥40g / L; in step S3, the concentration of CaCO3 in the salt mud transported from the refined brine system is 21.59g / L, and the concentration of Mg(OH)2 is 0.508g / L.

[0038] In this embodiment, in step S4, the filter cloth in the filter press is a PP filter cloth, and the pore size of the filter cloth is 40-60μm.

[0039] Example 2

[0040] The process flow chart for the recovery of salt mud described in Embodiment 2 of this invention is as follows: Figure 1 As shown, the recycling method includes the following steps:

[0041] S1. Dispose of the wastewater discharged from the soda ash plant at a rate of 20m³. 3 A flow rate of / h is fed into reactor #1 (1), and then at 220m 3 The brine is added at a flow rate of / h and passed through reaction tank 2 (1), reaction tank 3 (1), and reaction tank 4 (1) in sequence. The mixture is thoroughly mixed and stirred for 20 minutes to obtain the reaction liquid. The volume ratio of the waste liquid to the brine is 1:10.

[0042] S2. The reaction solution obtained in step S1 is sent to the crystallizer (2) by reaction pump (5) and mixed and stirred to obtain slurry and supernatant. Then, the slurry and supernatant are pumped into the crystallizer (2) by intermediate pump (6) and mixed and stirred again to obtain crystals.

[0043] S3. The salt mud from the refined brine system and the crystals obtained in step S2 are mixed and stirred in a mixing tank (7) for 20 minutes. Then, the mixture is pumped into a mixing baffle tank (9) by a mixing pump (8). Flocculant is added to the mixing baffle tank (9) and mixing continues. Then, the mixture is stirred at a speed of 25 m 3 The flow rate is / h into the settling tank (3) for settling. After settling for about 150 minutes, the supernatant and precipitate I are obtained. The supernatant flows into the low nitrate brine tank (10).

[0044] The mass ratio of the mixture obtained in step S2 to the salt mud is 8:1.

[0045] S4. The precipitate I obtained in step S3 is sent to the calcium slurry material tank (11) for separation to obtain a dilute solution and a concentrated solution. The dilute solution is returned to the reaction tank (1) in step S1 by the calcium slurry pump (12) to continue the reaction. The concentrated solution is pumped at 60m... 3 The flow rate is fed into the filter (4) at a rate of / h to separate the filtrate and precipitate II. The filtrate is pumped into the mixing baffle (9) by the filtrate pump (14) through the filtrate tank (13), and the precipitate II can be discharged.

[0046] In this embodiment, the concentration of NaCl in the mineral brine is ≥295g / L, and the concentration of Na2SO4 is 20-30g / L; the concentration of CaCl2 in the waste liquid in step S1 is 100g / L, and the concentration of NaCl is ≥40g / L; in step S3, the concentration of CaCO3 in the salt mud transported from the refined brine system is 21.59g / L, and the concentration of Mg(OH)2 is 0.508g / L.

[0047] In this embodiment, in step S4, the filter cloth in the filter press is a PP filter cloth, and the pore size of the filter cloth is 40-60μm.

[0048] Example 3

[0049] The process flow chart for the recovery of salt mud described in Embodiment 3 of this invention is as follows: Figure 1 As shown, the recycling method includes the following steps:

[0050] S1. Dispose of the waste liquid discharged from the soda ash plant at a rate of 30m³. 3 A flow rate of / h is fed into reactor #1 (1), and then at a rate of 200m 3 The brine is added at a flow rate of / h and passed through reaction tank 2 (1), reaction tank 3 (1), and reaction tank 4 (1) in sequence. The mixture is thoroughly mixed and stirred for 20 minutes to obtain the reaction solution. The volume ratio of the waste liquid to the brine is 1:10.

[0051] S2. The reaction solution obtained in step S1 is sent to the crystallizer (2) by reaction pump (5) and mixed and stirred to obtain slurry and supernatant. Then, the slurry and supernatant are pumped into the crystallizer (2) by intermediate pump (6) and mixed and stirred again to obtain crystals.

[0052] S3. The salt mud from the refined brine system and the crystals obtained in step S2 are mixed and stirred in a mixing tank (7) for 20 minutes. Then, the mixture is pumped into a mixing baffle tank (9) by a mixing pump (8). Flocculant is added to the mixing baffle tank (9) and mixing continues. Then, the mixture is stirred at a speed of 15 m 3 The flow rate is / h into the settling tank (3) for settling. After settling for about 150 minutes, the supernatant and precipitate I are obtained. The supernatant flows into the low nitrate brine tank (10).

[0053] The mass ratio of the mixture obtained in step S2 to the salt mud is 8:1.

[0054] S4. The precipitate I obtained in step S3 is sent to the calcium slurry material tank (11) for separation to obtain a dilute solution and a concentrated solution. The dilute solution is returned to the reaction tank (1) in step S1 by the calcium slurry pump (12) to continue the reaction. The concentrated solution is pumped at 60m... 3 The flow rate is fed into the filter (4) at a rate of / h to separate the filtrate and precipitate II. The filtrate is pumped into the mixing baffle (9) by the filtrate pump (14) through the filtrate tank (13), and the precipitate II can be discharged.

[0055] In this embodiment, the concentration of NaCl in the mineral brine is ≥295g / L, and the concentration of Na2SO4 is 20-30g / L; the concentration of CaCl2 in the waste liquid in step S1 is 100g / L, and the concentration of NaCl is ≥40g / L; in step S3, the concentration of CaCO3 in the salt mud transported from the refined brine system is 21.59g / L, and the concentration of Mg(OH)2 is 0.508g / L.

[0056] In this embodiment, in step S4, the filter cloth in the filter press is a PP filter cloth, and the pore size of the filter cloth is 40-60μm.

[0057] Test Example 1

[0058] 1. Determination of adsorbed water content

[0059] Accurately weigh the precipitate II1 ± 0.0002 g (m0) recovered in Examples 1-3 into a weighing bottle, and then place the weighing bottle in a drying oven at 55-60℃ to dry it. Record the mass of the dried precipitate II as m1. The content of attached water in precipitate II can be calculated according to the following formula. The results are shown in Table 1 below.

[0060]

[0061] 2. Determination of CaSO4·2H2O content

[0062] Accurately weigh the precipitate II1 ± 0.0002 g (m0) recovered in Examples 1-3 into a weighing bottle, and then place the weighing bottle in a high-temperature furnace at 380°C to dry it. Record the mass of the dried precipitate II as m1. The content of CaSO4·2H2O in precipitate II can be calculated according to the following formula. The results are shown in Table 1 below.

[0063]

[0064]

[0065] 3. Determination of chloride content (calculated as NaCl)

[0066] Accurately weigh 20 ± 0.0002 g (m) of precipitate II recovered in Examples 1-3, dissolve it in deionized water in a 250 mL volumetric flask, shake well, and let it stand for 30 min. Then transfer 50 mL of the supernatant to an Erlenmeyer flask, adjust the pH to 6.5-10.5 with 80 g / L NaOH solution, add 4 drops of potassium chromate indicator solution, and use silver nitrate standard titration solution as the endpoint when it turns reddish-brown. The volume of silver nitrate standard titration solution consumed is V. The chloride content in precipitate II can be calculated according to the following formula. The results are shown in Table 1 below.

[0067]

[0068] 4. Determination of acid-insoluble matter content

[0069] Detection principle: The residue that cannot be dissolved after the sample is heated and fully dissolved in hydrochloric acid is the acid-insoluble substance.

[0070] Detection method: Accurately weigh the precipitate II1 ± 0.0002 g (m) recovered in Examples 1-3, add a small amount of distilled water to moisten it, slowly add hydrochloric acid under electric furnace heating, dissolve it and boil for 5 min, then remove it and filter it with filter paper and wash it. Then transfer the filter paper and filter residue into a pre-weighed porcelain crucible, and finally dry and ignite it. The content of acid insoluble matter can be calculated using the following formula. The results are shown in Table 1 below.

[0071] In the following formula, m1 is the total mass of the porcelain crucible and insoluble matter after ignition, and m0 is the net weight of the porcelain crucible, both in g.

[0072]

[0073] 5. Determination of iron and aluminum oxide content

[0074] Collect the filtrate obtained from the above determination of acid-insoluble matter content, add 3 drops of nitric acid solution, heat to boiling, and add ammonia water while stirring. When the pH of the solution is neutral, continue boiling, remove the solution and let it stand until the precipitate settles. Filter and wash the solution with filter paper, and then transfer the filter paper and filter residue into a pre-weighed porcelain crucible. Finally, dry and ignite the crucible. The content of acid-insoluble matter can be calculated using the following formula, and the results are shown in Table 1 below.

[0075] In the following formula, m1 is the total mass of the porcelain crucible and iron and aluminum oxides after calcination, and m0 is the net weight of the porcelain crucible, both in g.

[0076]

[0077] 6. Determination of CaCO3 content

[0078] Accurately weigh precipitate II1 ± 0.0002 g (m) recovered from Examples 1-3, add 100 mL of distilled water, then add 1 mL of 30% hydrogen peroxide. After reacting for 2 min, standardize with 1000 mol / L hydrochloric acid, heat in a 50-70℃ water bath for 15 min, cool, add a small amount of water and stir for 5 min, add 2 drops of phenolphthalein indicator, and then standardize with 0.1 mol / L NaOH solution until the solution becomes colorless. The volume of NaOH solution consumed is V. The content of CaCO3 can be calculated using the following formula, and the results are shown in Table 1 below.

[0079]

[0080] 7. Determination of CaSO3·1 / 2H2O content

[0081] Principle: In a weakly acidic solution, iodine is used to oxidize sulfite to sulfate, and starch is used as an indicator to titrate excess iodine with a standard sodium thiosulfate titration solution.

[0082] Accurately weigh the precipitate II1 ± 0.0002 g (m) recovered in Examples 1-3, place it in an iodine flask pre-filled with 10 mL of iodine standard titration solution and 50 mL of distilled water, adjust the pH to 5-6 with hydrochloric acid solution, mix thoroughly, place in the dark for 5 min, titrate with sodium thiosulfate standard titration solution until the solution turns pale yellow, add 3 mL of starch indicator, and continue titrating until the blue color disappears. The volume of sodium thiosulfate standard titration solution consumed is V.

[0083] Blank experiment: Weigh 10 mL of iodine standard titration solution and 50 mL of distilled water into an iodine flask, adjust the pH to 5-6 with hydrochloric acid solution, mix thoroughly, and place in the dark for 5 min. Titrate with sodium thiosulfate standard titration solution until the solution turns pale yellow. Add 3 mL of starch indicator and continue titrating until the blue color disappears. The volume of sodium thiosulfate standard titration solution consumed is V.

[0084] The content of CaSO3·1 / 2H2O can be calculated using the following formula, and the results are shown in Table 1 below. In the table, C is the concentration of the sodium thiosulfate standard titration solution in mol / L, and the molecular weight of CaSO3·1 / 2H2O is 129.14 g / mol.

[0085]

[0086] Table 1

[0087] Inspection Items (Percentage of Quality) Example 1 Example 2 Example 3 Adhering water 18.24 23.17 24.84 <![CDATA[CaSO4·2H2O]]> 45.96 40.24 47.4 Chloride (calculated as NaCl) 6.85 8.24 8.33 Acid-insoluble matter 0.5 0.1 0.2 iron and aluminum oxides 0.5 0.1 0.2 <![CDATA[CaCO3]]> 27.94 27.44 17.71 <![CDATA[CaSO3·1 / 2H2O]]> 0 0 0.1

[0088] According to the data in Table 1, the mass percentage of adhering water in the gypsum and salt mud mixture recovered by the method of the present invention in Examples 1-3 is all <25%, and the various indicators in the recovered material are stable.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for recycling salt mud, characterized in that, The method includes the following steps: S1. Distill the waste liquid discharged from the soda ash plant and mix it with mineral brine in a reaction tank for 10-30 minutes to obtain a reaction solution; S2. Mix and stir the reaction solution obtained in step S1 in a crystallizer to obtain a slurry and a supernatant. Repeat this step 1-2 times to obtain crystals. S3. Mix the salt mud with the crystals obtained in step S2 and stir for 2-8 minutes. Add flocculant and continue mixing. Then allow it to settle for 120-180 minutes to obtain the supernatant and precipitate I. S4. Separate the precipitate I obtained in step S3 to obtain a dilute solution and a concentrated solution. The dilute solution is returned to the reaction tank in step S1 to continue the reaction, and the concentrated solution is separated in a filter to obtain filtrate and precipitate II, which can then be sent out. In step S1, the waste liquid contains calcium chloride, and the mineral brine contains sodium sulfate; the concentration of calcium chloride is >100g / L, and the concentration of sodium sulfate is 20-30g / L. In step S1, the volume ratio of the waste liquid to the mineral brine is 1:

10. In step S3, the volume ratio of the mixture obtained in step S2 to the salt mud is 8:

1.

2. The method for recovering salt mud as described in claim 1, characterized in that, In step S1, the flow rate of the clean waste liquid discharged from the soda ash plant is 20-30 m³ / h. 3 The flow rate of the mineral brine is 200-220 m³ / h. 3 / h.

3. The method for recovering salt mud as described in claim 1, characterized in that, In step S1, the number of reaction vessels is ≥1, and the reaction vessels are connected in series.

4. The method for recovering salt mud as described in claim 1, characterized in that, In step S2, the number of crystallizers is ≥2, and the crystallizers are connected in parallel.

5. The method for recovering salt mud as described in claim 1, characterized in that, In step S4, the filter cloth used for separating the concentrated liquid in the filter is a polypropylene filter cloth.

6. The method for recovering salt mud as described in claim 5, characterized in that, The filter cloth has a pore size of 40-60 μm.

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