Treatment method of salt-making byproduct salt gypsum

Abstract

The invention provides a treatment method of salt production by-product salt gypsum, which comprises the following steps: S1, carrying out plate-frame pressure filtration on a gypsum mother solution containing salt to obtain brine and a filter cake, and diluting the filter cake with water to obtain a gypsum sub-solution; s2, adding a carrying type crystal modifier into the gypsum sub-liquid obtained in the S1, controlling the temperature to be 35-55 DEG C, the pH value to be 6-8 and the stirring speed to be 180-220 r / min, and promoting crystal transformation to obtain crystal transformation liquid; the carrying type crystal modifier is prepared by carrying sodium sulfate on cross-linked starch; s3, carrying out solid-liquid separation on the crystal transformation liquid obtained in S2 to obtain dihydrate gypsum and a salt-containing aqueous solution; and S4, drying the dihydrate gypsum obtained in S3 to obtain a final product. The salt content of the final product is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of salt gypsum processing, and in particular relates to a method for processing salt gypsum, a byproduct of salt production. Background Art

[0002] Gypsum is one of the three major cementitious materials today, along with cement and lime. It has many excellent properties and is widely used in many application fields such as construction, building materials, industrial molds and art models, chemical industry and agriculture, food processing and medical beauty. It is an important industrial raw material and occupies an important position in the national economy. Compared with traditional similar new building materials, gypsum is second to none in terms of saving energy, land, wood, human resources, environmental protection, fire prevention and earthquake resistance. For this reason, it is recognized internationally as an energy-saving green building material.

[0003] The main impurities in gypsum-type brine are CaSO4, CaCl2, MgCl2, etc. The NaCl content in the brine is about 300g / L, and the gypsum content is 4-6g / L. During the production, as the brine evaporates and concentrates to precipitate salt particles, the byproduct gypsum is also continuously enriched and precipitated. In order not to affect the quality of the salt product, a part of the gypsum must be discharged, and this part of the discharged gypsum is processed to become the byproduct of salt production - salt gypsum. Most of the gypsum is discharged into the environment through pipelines, causing great pollution. The pressure of environmental governance is very high. Therefore, it is of great significance to comprehensively recycle this type of salt gypsum.

[0004] Calcium sulfate in salt gypsum usually precipitates in three different forms: CaSO4·2H2O, CaSO4·1 / 2H2O, and CaSO4. After testing and analysis, more than 90% is anhydrous gypsum. In addition, due to the high evaporation rate of vacuum salt production, the nucleation rate of calcium sulfate is high, the precipitated gypsum has a small particle size, the median particle size is about 4-6μm, and the specific surface area is large, which makes separation difficult. Gypsum absorbs a lot of salt and water and is difficult to use. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a method for treating salt gypsum, a by-product of salt production, which effectively reduces the salt content of the final product.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0008] S1, filtering the gypsum mother liquor containing salt through a plate and frame filter to obtain brine and filter cake, and then diluting the filter cake with water to obtain gypsum sub-liquid;

[0009] S2, adding a carrier-type crystal-transforming agent to the gypsum liquid obtained in S1, controlling the temperature at 35-55°C, the pH value at 6-8, and the stirring speed at 180-220r / min to promote crystal transformation, and obtaining a crystal transformation liquid; the carrier-type crystal-transforming agent is prepared by cross-linking starch and carrying sodium sulfate;

[0010] S3, performing solid-liquid separation on the crystallization liquid obtained in S2 to obtain dihydrate gypsum and a saline solution;

[0011] S4, drying the dihydrate gypsum obtained in S3 to obtain a final product.

[0012] Furthermore, the preparation method of the carrier-type crystal-transforming agent is as follows:

[0013] A1. Stir cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%;

[0014] A2, add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, the mass of sodium sulfate is 55-65% of the mass of cassava starch, then adjust the pH to 10-11 with sodium hydroxide solution, place in a constant temperature water bath at 35±2°C, stir and react for 2h, and then neutralize with hydrochloric acid to pH 6.5-6.8 to obtain a cross-linked liquid;

[0015] A3. Filter the cross-linked liquid obtained in A2, wash it, dry it at 50±2°C for 10-12h, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

[0016] Furthermore, in A2, the mass fraction of the sodium hydroxide solution is 4-6%.

[0017] Furthermore, in A2, the concentration of the hydrochloric acid is 0.9-1.1 mol / L.

[0018] Furthermore, in S1, the mass ratio of the filter cake to the dilution water is 1:(25-35).

[0019] Furthermore, in S2, the added mass of the carrier-type crystal-changing agent is 0.2-0.5% of the mass of the gypsum liquid.

[0020] Furthermore, in S3, the solid-liquid separation is performed by filtration, centrifugation or flotation.

[0021] Furthermore, in S4, the specific operation of the drying treatment is: drying at a temperature of 80-120° C. under normal pressure.

[0022] This application has the following beneficial effects:

[0023] 1. The present invention uses a carrier-type crystal-changing agent, which is prepared by carrying cross-linked starch with sodium sulfate. The cross-linked starch has higher stability and shear resistance, which means that during the crystal-changing process, it can exist more stably in the solution, reducing the instability of the crystal form caused by environmental changes; sodium sulfate, as a part of the carrier-type crystal-changing agent, has strong solubility and crystallization ability, which helps to separate salt from gypsum during the crystal-changing process; compared with the direct use of sodium sulfate, the carrier-type crystal-changing agent achieves a more uniform and stable crystal growth environment through the carrying effect of cross-linked starch, thereby effectively reducing the salt content of the final product.

[0024] 2. In the preparation of the carrier-type crystal-transforming agent, the phosphate groups on sodium trimetaphosphate can react with the hydroxyl groups on the starch molecular chain to form a phosphate ester bond, so that a network structure is formed between the starch molecular chains, thereby enhancing the mechanical strength and stability; on the one hand, sodium sulfate plays a salting-out role in the reaction system, promoting the aggregation between the starch molecular chains; on the other hand, sodium sulfate can also help stabilize the swelling state of starch granules by increasing the ionic strength of the solution, making it easier for sodium trimetaphosphate to penetrate into the starch granules, thereby improving the uniformity of the cross-linking reaction; and, the mass of sodium sulfate is 50-60% of the mass of cassava starch, and the high addition amount of sodium sulfate makes it easier for it to be trapped inside the starch gel with a network structure, thereby being carried on the cross-linked starch as a crystal-transforming agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , a comparative trend chart of the salt contents of the final products obtained in Examples 1-7 of the present invention and Comparative Examples 1-5. DETAILED DESCRIPTION

[0026] The present application is further described in detail below with reference to the embodiments.

[0027] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0028] Embodiment 1: A method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0029] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:30 to obtain the gypsum liquid.

[0030] S2, adding a crystal-transforming agent to the gypsum liquid obtained in S1, the added mass of the crystal-transforming agent being 0.3% of the mass of the gypsum liquid. Controlling the temperature at 45°C, pH value at 7, and stirring speed at 200 r / min to promote crystal transformation, after 2.5 hours, a crystal transformation liquid is obtained.

[0031] Among them, the preparation method of the carrier-type crystal-transforming agent is as follows:

[0032] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0033] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 60% of the mass of cassava starch. Then adjust the pH to 10.5 with a 5% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.0 mol / L hydrochloric acid to pH 6.7 to obtain a cross-linked liquid.

[0034] A3. Filter the cross-linked liquid obtained in A2, wash it with distilled water for 5 times, dry it at 50°C for 11 hours, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

[0035] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0036] S4. Dry the dihydrate gypsum obtained in S3 at 100° C. under normal pressure for 3 h to obtain the final product.

[0037] The main physical performance indicators of the final product are as follows:

[0038] Standard water consumption / % Initial setting time / min Final setting time / min 2h wet flexural strength / Mpa 0.72 4:30 6:00 2.48

[0039] Meet the GB / T9776-2008 standard for building gypsum.

[0040] Embodiment 2: The difference between this embodiment and embodiment 1 is that: a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0041] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:25 to obtain the gypsum liquid.

[0042] S2, adding a crystal-transforming agent to the gypsum liquid obtained in S1, the added mass of the crystal-transforming agent being 0.2% of the mass of the gypsum liquid. Controlling the temperature at 35°C, pH value at 6, and stirring speed at 180r / min to promote crystal transformation, after 2 hours, a crystal transformation liquid was obtained.

[0043] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0044] S4. Dry the dihydrate gypsum obtained in S3 at 80°C under normal pressure for 3 hours to obtain the final product.

[0045] Embodiment 3: The difference between this embodiment and embodiment 1 is that: a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0046] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:35 to obtain the gypsum liquid.

[0047] S2, adding a crystal-transforming agent to the gypsum liquid obtained in S1, the added mass of the crystal-transforming agent being 0.5% of the mass of the gypsum liquid. Controlling the temperature at 55°C, pH value at 8, and stirring speed at 220 r / min to promote crystal transformation, after 3 hours, a crystal transformation liquid was obtained.

[0048] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0049] S4. Dry the dihydrate gypsum obtained in S3 at 120°C under normal pressure for 3 hours to obtain the final product.

[0050] Embodiment 4: The difference between this embodiment and embodiment 1 is that: a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0051] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:30 to obtain the gypsum liquid.

[0052] S2, adding a crystal-transforming agent to the gypsum liquid obtained in S1, the added mass of the crystal-transforming agent being 0.2% of the mass of the gypsum liquid. Controlling the temperature at 35°C, pH value at 6, and stirring speed at 220 r / min to promote crystal transformation, after 2.5 hours, a crystal transformation liquid was obtained.

[0053] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0054] S4. Dry the dihydrate gypsum obtained in S3 at 100° C. under normal pressure for 3 h to obtain the final product.

[0055] Example 5: The difference between this example and Example 1 is that the preparation method of the carrier-type crystal-transforming agent is as follows:

[0056] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0057] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 55% of the mass of cassava starch. Then adjust the pH to 10 with a 4% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 0.9 mol / L hydrochloric acid to pH 6.5 to obtain a cross-linked liquid.

[0058] A3. Filter the cross-linked liquid obtained in A2, wash it, dry it at 50°C for 10 hours, grind it, and pass it through a 100-mesh sieve to obtain a carrier-type crystal-transforming agent.

[0059] Example 6: The difference between this example and Example 1 is that the preparation method of the carrier-type crystal-transforming agent is as follows:

[0060] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0061] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 65% of the mass of cassava starch. Then adjust the pH to 11 with a 6% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.1 mol / L hydrochloric acid to pH 6.8 to obtain a cross-linked liquid.

[0062] A3. Filter the cross-linked liquid obtained in A2, wash it, dry it at 50°C for 12 hours, grind it, and pass it through a 100-mesh sieve to obtain a carrier-type crystal-transforming agent.

[0063] Example 7: The difference between this example and Example 1 is that the preparation method of the carrier-type crystal-transforming agent is as follows:

[0064] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0065] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 60% of the mass of cassava starch. Then adjust the pH to 10 with a 4% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.1 mol / L hydrochloric acid to pH 6.8 to obtain a cross-linked liquid.

[0066] A3. The cross-linked liquid obtained in A2 is filtered, washed, dried at 50°C for 11 hours, ground, and passed through a 100-mesh sieve to obtain a carrier-type crystal-transforming agent.

[0067] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the carrier-type crystal-transforming agent, the mass of sodium sulfate is 30% of the mass of cassava starch.

[0068] Specifically, the preparation method of the carrier-type crystal-transforming agent is as follows:

[0069] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0070] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 30% of the mass of cassava starch. Then adjust the pH to 10.5 with a 5% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.0 mol / L hydrochloric acid to pH 6.7 to obtain a cross-linked liquid.

[0071] A3. Filter the cross-linked liquid obtained in A2, wash it with distilled water for 5 times, dry it at 50°C for 11 hours, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

[0072] Comparative Example 2: The difference between this comparative example and Example 1 is that in the preparation of the carrier-type crystal-changing agent, the mass of sodium sulfate is 30% of the mass of cassava starch; and in the method for treating the salt gypsum, a by-product of salt production, the added mass of the carrier-type crystal-changing agent is 0.6% of the mass of the gypsum liquid.

[0073] Specifically, a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0074] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:30 to obtain the gypsum liquid.

[0075] S2, adding a crystal-transforming agent to the gypsum liquid obtained in S1, the added mass of the crystal-transforming agent being 0.6% of the mass of the gypsum liquid. Controlling the temperature at 45°C, pH value at 7, and stirring speed at 200 r / min to promote crystal transformation, after 2.5 hours, a crystal transformation liquid is obtained.

[0076] Among them, the preparation method of the carrier-type crystal-transforming agent is as follows:

[0077] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0078] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 30% of the mass of cassava starch. Then adjust the pH to 10.5 with a 5% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.0 mol / L hydrochloric acid to pH 6.7 to obtain a cross-linked liquid.

[0079] A3. Filter the cross-linked liquid obtained in A2, wash it with distilled water for 5 times, dry it at 50°C for 11 hours, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

[0080] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0081] S4. Dry the dihydrate gypsum obtained in S3 at 100° C. under normal pressure for 3 h to obtain the final product.

[0082] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the carrier-type crystal-transforming agent, the mass of sodium sulfate is 70% of the mass of cassava starch.

[0083] Specifically, the preparation method of the carrier-type crystal-transforming agent is as follows:

[0084] A1. Mix cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%.

[0085] A2. Add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, and the mass of sodium sulfate is 70% of the mass of cassava starch. Then adjust the pH to 10.5 with a 5% sodium hydroxide solution, place it in a constant temperature water bath at 35°C and stir for 2 hours, then neutralize it with 1.0 mol / L hydrochloric acid to pH 6.7 to obtain a cross-linked liquid.

[0086] A3. Filter the cross-linked liquid obtained in A2, wash it with distilled water for 5 times, dry it at 50°C for 11 hours, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

[0087] Comparative Example 4: The difference between this comparative example and Example 1 is that in the method for treating salt gypsum, a by-product of salt production, the carrier-type crystal-changing agent is replaced by sodium sulfate.

[0088] Specifically, a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0089] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:30 to obtain the gypsum liquid.

[0090] S2, adding sodium sulfate to the gypsum liquid obtained in S1, the added mass of sodium sulfate is 0.3% of the mass of the gypsum liquid. Control the temperature at 45°C, pH value at 7, stirring speed at 200r / min to promote crystallization, and after 2.5 hours, obtain the crystallization liquid.

[0091] S3, performing solid-liquid separation on the crystallization liquid obtained in S2, wherein the solid-liquid separation is performed by filtering to obtain dihydrate gypsum and a saline solution.

[0092] S4. Dry the dihydrate gypsum obtained in S3 at 100° C. under normal pressure for 3 h to obtain the final product.

[0093] Comparative Example 5: The difference between this comparative example and Example 1 is that in the method for treating salt gypsum, a by-product of salt production, the carrying type crystal-transforming agent is deleted.

[0094] Specifically, a method for treating salt gypsum, a byproduct of salt production, comprises the following steps:

[0095] S1. The gypsum mother liquor containing salt is filtered through a plate and frame filter to recover the brine. The gypsum is retained on the filter cloth during the filtration process to form a filter cake. The filter cake is then diluted with water, and the mass ratio of the filter cake to the dilution water is 1:30 to obtain the gypsum liquid.

[0096] S2, controlling the temperature at 45°C, pH value at 7, and stirring speed at 200 r / min, treating the gypsum sub-liquid obtained in S1 for 2.5 hours, and then performing solid-liquid separation. The solid-liquid separation is performed by filtration to obtain dihydrate gypsum and a saline solution.

[0097] S3. Under normal pressure, the temperature is controlled at 100° C. to dry the dihydrate gypsum obtained in S3 for 3 hours to obtain the final product.

[0098] Test example: Test item: salt content of final product.

[0099] Test objects: final products obtained from Examples 1-7 and Comparative Examples 1-5.

[0100] Test basis: GBT 5484-2012.

[0101] Test results: See Table 1.

[0102] Table 1. Test data of the experimental example

[0103] Final product salt content / % Example 1 0.7 Example 2 0.8 Example 3 0.8 Example 4 0.5 Example 5 0.6 Example 6 0.5 Example 7 0.7 Comparative Example 1 6.4 Comparative Example 2 6.6 Comparative Example 3 0.8 Comparative Example 4 3.7 Comparative Example 5 9.6

[0104] Result analysis:

[0105] Analyze Examples 1-7 and combine the data in Table 1 and Figure 1 It can be seen that the salt content of the final product obtained by the present invention is as low as below 0.8%.

[0106] Analyze Example 1 and Comparative Examples 1-3 and combine the data in Table 1 and Figure 1 It can be seen that in the preparation of the carrier-type crystal-transforming agent of the present invention, the added mass of sodium sulfate should be 55-65% of the mass of cassava starch; if the added amount of sodium sulfate is too low (such as the mass of sodium sulfate in Comparative Example 1 is 30% of the mass of cassava starch), the salt content of the final product is 6.4%, which is much higher than the salt content of 0.7% of the final product in Example 1 (the mass of sodium sulfate is 60% of the mass of cassava starch), indicating that in the preparation of the carrier-type crystal-transforming agent, the added amount of sodium sulfate is too low, which will directly lead to a significant increase in the salt content of the final product;

[0107] Even if the amount of the carrier-type crystal-changing agent added is increased in the method for treating the salt production byproduct salt gypsum, such as in Comparative Example 2 (the added mass of the carrier-type crystal-changing agent is increased from 0.3% to 0.6% of the mass of the gypsum liquid on the basis of Comparative Example 1), the salt content of the final product is 6.6%, which is very close to Comparative Example 1 and much higher than the salt content of 0.7% of the final product in Example 1. This shows that in the preparation of the carrier-type crystal-changing agent, too low an amount of sodium sulfate added will directly lead to a significant increase in the salt content of the final product. Even if the amount of the carrier-type crystal-changing agent is increased in subsequent use, the salt content of the final product cannot be reduced;

[0108] If the amount of sodium sulfate added is too high (such as the mass of sodium sulfate in Comparative Example 3 is 70% of the mass of cassava starch), the salt content of the final product is 0.7%, which is the same as the salt content of 0.7% in the final product of Example 1 (the mass of sodium sulfate is 60% of the mass of cassava starch). This shows that in the preparation of the carrier-type crystal-transforming agent, excessive addition of sodium sulfate will only increase the amount of sodium sulfate used and increase the cost, and will not further reduce the salt content of the final product.

[0109] Analyze Example 1 and Comparative Examples 4-5 and combine the data in Table 1 and Figure 1 It can be seen that when the loaded crystal-changing agent is not used (such as in Comparative Example 5), the oxygen content of the final product is 9.6%, and when the loaded crystal-changing agent is replaced by sodium sulfate, that is, when the sodium sulfate is not loaded with cross-linked starch (such as in Comparative Example 4), the salt content of the final product is 3.7%, indicating that the use of sodium sulfate in the process of treating the salt production by-product salt gypsum can itself reduce the salt content of the final product, and the use of cross-linked starch to load sodium sulfate before use can further reduce the salt content of the final product.

[0110] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0111] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for treating salt gypsum, a byproduct of salt production, characterized in that: The following steps are involved: S1, filtering the gypsum mother liquor containing salt through a plate and frame filter to obtain brine and filter cake, and then diluting the filter cake with water to obtain gypsum sub-liquid; S2, adding a carrier-type crystal-transforming agent to the gypsum liquid obtained in S1, controlling the temperature at 35-55°C, the pH value at 6-8, and the stirring speed at 180-220r / min to promote crystal transformation, and obtaining a crystal transformation liquid; the carrier-type crystal-transforming agent is prepared by cross-linking starch and carrying sodium sulfate; S3, performing solid-liquid separation on the crystallization liquid obtained in S2 to obtain dihydrate gypsum and a saline solution; S4, drying the dihydrate gypsum obtained in S3 to obtain a final product.

2. The method for treating salt gypsum, a byproduct of salt production, according to claim 1, characterized in that: The preparation method of the carrier-type crystal-transforming agent is as follows: A1. Stir cassava starch and distilled water to prepare a starch emulsion with a mass fraction of 40%; A2, add sodium trimetaphosphate and sodium sulfate to the starch emulsion obtained in A1, the mass of sodium trimetaphosphate is 0.1% of the mass of cassava starch, the mass of sodium sulfate is 55-65% of the mass of cassava starch, then adjust the pH to 10-11 with sodium hydroxide solution, place in a constant temperature water bath at 35±2°C, stir and react for 2h, and then neutralize with hydrochloric acid to pH 6.5-6.8 to obtain a cross-linked liquid; A3. Filter the cross-linked liquid obtained in A2, wash it, dry it at 50±2°C for 10-12h, grind it, and pass it through a 100-mesh sieve to obtain the carrier-type crystal-transforming agent.

3. The method for treating salt gypsum, a byproduct of salt production, according to claim 2, characterized in that: In A2, the mass fraction of the sodium hydroxide solution is 4-6%.

4. The method for treating salt gypsum, a byproduct of salt production, according to claim 1, characterized in that: In A2, the concentration of the hydrochloric acid is 0.9-1.1 mol / L.

5. The method for treating salt gypsum, a byproduct of salt production, according to claim 1, characterized in that: In S1, the mass ratio of filter cake to dilution water is 1:(25-35).

6. The method for treating salt gypsum, a byproduct of salt production, according to any one of claims 1 to 5, characterized in that: In S2, the added mass of the carrier-type crystal-changing agent is 0.2-0.5% of the mass of the gypsum liquid.

7. The method for treating salt gypsum, a byproduct of salt production, according to claim 1, characterized in that: In S3, the solid-liquid separation is performed by filtration, centrifugation or flotation.

8. The method for treating salt gypsum, a byproduct of salt production, according to claim 1, characterized in that: In S4, the specific operation of the drying treatment is: drying at a temperature of 80-120° C. under normal pressure.

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