Method for treating salt-containing wastewater in titanium dioxide production

Abstract

The invention relates to the technical field of titanium dioxide production processes, and discloses a method for treating salt-containing wastewater in titanium dioxide production, which comprises the following steps: carrying out membrane separation treatment on salt-containing wastewater, returning a dilute phase solution to a production process, adding potassium chloride and circulating mother liquor into a concentrated phase solution, carrying out evaporation, concentration and crystallization to obtain glaserite, and separating; sending the glaserite filter cake to a dissolving process, adding potassium chloride to dissolve glaserite to obtain potassium sulfate, separating, and returning the separated mother liquor to the first stage to separate to obtain a potassium sulfate product; and evaporating, concentrating and crystallizing the mother liquor of the glaserite to obtain sodium chloride crystal mush, performing third separation, circulating and returning the mother liquor obtained by the third separation to the first section, and obtaining a sodium chloride product from the solid obtained by the third separation. According to the treatment method provided by the invention, resources in the salt-containing wastewater can be fully recycled and recycled, generation and discharge of wastewater and waste salt are avoided, the resource value and market value in the wastewater are improved, and green development is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide production technology, and in particular to a method for treating salt-containing wastewater in the production of titanium dioxide. Background Art

[0002] Whether titanium dioxide is produced by the sulfuric acid method, the chlorination method or the hydrochloric acid method, in terms of the pigment properties given by the optical and material science, titanium dioxide is produced by preparing titanium dioxide microcrystalline particles with a half-wavelength of visible light in the range of 200 to 350nm. Due to the inherent lattice defects of titanium dioxide, the physical and chemical properties of photocatalytic solids exist. Under the action of ultraviolet light, they produce photocatalytic reactions in downstream application fields such as coatings, plastics, decorative papers, etc., degrading the molecular bonds of these organic materials, resulting in a decrease in service life, decorative effects and color. Therefore, it is necessary to improve the weather resistance of the quality of titanium dioxide products during production, and to carry out surface coating treatment (post-treatment), that is, to coat a layer of inorganic matter or inorganic oxide on the titanium dioxide microcrystalline particles to shield ultraviolet light, thereby improving the weather resistance of titanium dioxide. In the above, the chemical reactions involved are as follows:

[0003] Na2SiO3+H2SO4→SiO2·nH2O↓+Na2SO4+H2O(1)

[0004] Al2(SO4)2+4NaOH→Al2O3·nH2O↓+2Na2SO4(2)

[0005] 2NaAlO2+H2SO4→Al2O3·nH2O↓+Na2SO4(3)

[0006] Zr(SO4)2+4NaOH→ZrO2·nH2O↓+2Na2SO4(4)

[0007] Al2(SO4)3+NaH2PO4→AlPO4·nH2O↓+Na2SO4(5)

[0008] These precipitates adhere to the surface of titanium dioxide particles to shield ultraviolet light. At the same time, a large amount of saline wastewater containing sodium sulfate is also produced during production. After post-treatment, the product is obtained by filtering, washing, drying and crushing. Almost all of the post-treatment saline wastewater from existing titanium dioxide production is incorporated into the acidic wastewater produced. Lime is used to neutralize and enrich impurities in the wastewater. Since the saline wastewater generated by post-treatment is mainly sodium sulfate, it is not precipitated by lime and is discharged into natural water bodies along with the neutralized wastewater. This not only affects the environment, but also does not utilize resources.

[0009] At the same time, in the production of titanium dioxide by sulfuric acid method, a large amount of acidic gas is generated in the acidolysis tail gas and calcination tail gas. The acidic tail gas is absorbed by spraying with alkali solution, which also produces a large amount of sodium sulfate wastewater. In addition, the preparation of rutile crystal seeds by sulfuric acid method requires a large amount of alkali solution and produces sodium sulfate wastewater. As mentioned above, the wastewater is discharged into the natural water body together with the neutralization wastewater, which not only pollutes the water body, but also the sodium and sulfur resources in it are not utilized. Summary of the invention

[0010] The technical problems to be solved by the present invention are:

[0011] At present, in the process of producing titanium dioxide, saline wastewater is mixed into the total sewage and neutralized with lime to achieve the neutralization of the wastewater to meet national emission standards and other requirements. However, for the treatment of saline wastewater generated in the production of titanium dioxide, when lime neutralization and precipitation are used, a pH value of 7 is required, and it is discharged as neutral water. Sodium sulfate salts generated by sodium ions still remain in the external drainage, resulting in a large amount of waste and resources not being utilized, resulting in low economic benefits. In addition, the discharge of saline wastewater violates the concept of sustainable development of green environmental protection.

[0012] The technical solution adopted by the present invention is:

[0013] In order to treat the saline wastewater generated in the production of titanium dioxide in a greener way, the present invention provides a method for treating the saline wastewater in the production of titanium dioxide, comprising the following steps:

[0014] S1 sends the salt-containing wastewater in the titanium dioxide production to the nanofiltration membrane for separation and treatment, and the separated dilute phase solution is sent back to the titanium dioxide production process as purified water. The separated concentrated phase solution is added with potassium chloride and the circulating mother liquor for the first stage of evaporation, concentration and crystallization to obtain potassium glauberite slurry, and the first separation is performed;

[0015] The filter cake separated in the first step S2 is sent to the dissolution production process, and then potassium chloride solution is added to dissolve potassium sulfate to obtain potassium sulfate slurry, and then the second separation is performed. The mother liquor separated in the second separation is used as the circulating mother liquor, and the circulating mother liquor is circulated back to the first stage of evaporation, concentration and crystallization, and the solid separated in the second step is obtained to obtain the potassium sulfate product;

[0016] The mother liquor separated for the first time in S3 is subjected to the second stage of evaporation, concentration and crystallization to obtain sodium chloride slurry, which is then subjected to the third separation. The mother liquor separated for the third time is circulated back to the first stage of evaporation, concentration and crystallization, and the solid separated for the third time is used to obtain the sodium chloride product.

[0017] According to some preferred embodiments, membrane separation treatment adopts a membrane separation system, which includes a pretreatment system, an osmosis and reverse osmosis system, and a reverse osmosis membrane multi-stage separation device system composed of auxiliary dosing, cleaning, backwashing, etc. The membrane separation system is composed of high, medium and low pressure reverse osmosis membranes.

[0018] According to some preferred embodiments, in the membrane separation treatment of saline wastewater, a single-stage or multi-stage reverse osmosis membrane filtration separator may be used, preferably a multi-stage reverse osmosis membrane system consisting of low pressure, medium pressure and high pressure.

[0019] According to some preferred embodiments, the salt-containing concentrated water after membrane separation is added with potassium chloride and the recycled mother liquor for separating potassium sulfate and sodium chloride can be filtered and separated before the first stage of evaporation and concentration to separate the water-insoluble matter brought by potassium chloride to meet the high water solubility of the potassium sulfate product.

[0020] According to some preferred embodiments, in step S1, a multi-stage membrane filtration separator is used for membrane separation treatment, and the concentration multiple of the treated saline wastewater is 2-6 times, preferably 3-5 times.

[0021] According to some preferred embodiments, the dilute phase conductivity in the membrane separation process is 10-30 μs / cm, preferably 15-25 μs / cm.

[0022] According to some preferred embodiments, in step S1, the first stage evaporation concentration temperature is 100-150°C, and the potassium sulfate crystallization temperature is 30-50°C.

[0023] According to some preferred embodiments, in step S1, the mother liquor of the first separation of glauberite is composed of: + 2.5~6.0%、Na + 7.5~10.0%、Cl - 13~17%、SO4 2- 1.8~3.5%.

[0024] According to some preferred embodiments, in step S2, the temperature for dissolving and decomposing glauberite is 10 to 90°C, preferably 15 to 50°C.

[0025] According to some preferred embodiments, in step S2, the second separated mother liquor is circulated back to the first stage evaporation concentration before mixing with the added potassium chloride and membrane separated salt-containing concentrated wastewater. The ion concentration composition of the mother liquor after the second separation of potassium sulfate is: K + 3.5~9.0%、Na + 7.5~10.0%;Cl - 15~22%、SO4 2- 0.1~2.5%.

[0026] According to some preferred embodiments, in step S3, the second stage evaporation concentration temperature is 100-150°C, and the sodium chloride crystallization temperature is 30-50°C.

[0027] According to some preferred embodiments, the temperature for the third separation is 30-60° C. to obtain a third separated sodium chloride product, and the mother liquor after separation is circulated back to the mixed solution before the first stage evaporation and concentration.

[0028] According to some preferred embodiments, the first stage evaporation concentration and the second stage evaporation concentration can be concentrated by using multi-stage evaporation, heat pump and mechanical compression MVR, etc., preferably MVR concentration.

[0029] The treatment principle of the present invention for the salt-containing wastewater in the production of titanium dioxide is as follows:

[0030] 4Na2SO4+6KCl→Na2SO4·3K2SO4+6NaCl(1)

[0031] Na2SO4·3K2SO4+2KCl→4K2SO4+2NaCl(2)

[0032] That is, the saline wastewater produced by titanium dioxide production is first separated by membrane, and the concentrated brine and circulating mother liquor after membrane separation are added with potassium chloride to form a mixed salt solution. After the first stage of evaporation and concentration, sodium potassium sulfate complex salt (glauberite) crystals are produced, and the separated crystals are dissolved in potassium chloride to obtain potassium sulfate products; the mother liquor after separating the glauberite is subjected to the second stage of evaporation, concentration and crystallization to produce sodium chloride products. The dilute phase water and concentrated evaporation condensed water obtained by membrane separation are returned to the titanium dioxide production process together, which can replace the original process water and realize the recycling of water resources; the potassium sulfate product produced makes high-value use of the sulfate resource ions in the saline wastewater, and at the same time, the sodium resource ions in the saline wastewater are accepted by the huge market as the basic raw material products of the sodium chloride industry.

[0033] The beneficial effects achieved by the present invention are:

[0034] Compared with the existing mixed sewage neutralization treatment method, the method for treating saline wastewater in the production of titanium dioxide of the present invention can effectively realize the efficient resource utilization and recycling of saline wastewater in the production of titanium dioxide. The dilute phase water in the saline wastewater is recycled by membrane separation as a process desalted water, and the separated saline concentrated phase is added with potassium chloride to replace sodium sulfate to form two products, potassium sulfate and sodium chloride, thereby increasing the resource and market value of sulfate in the saline wastewater. It is the best method to replace the existing "Mannheim" sulfuric acid plus potassium chloride to produce potassium sulfate and waste resource coupling, and is also an effective way to produce potassium sulfate, a highly water-soluble drip irrigation fertilizer required by the market. Through sodium-potassium conversion, a huge market is also opened up for sodium resource products in saline wastewater, reducing the indirect discharge of saline wastewater into natural water bodies through the neutralization of wastewater in the production of titanium dioxide, polluting the water environment, and realizing sustainable production of resource reuse and environmental protection to a greater extent; and the treated water can be used to produce titanium dioxide, reducing the large demand for raw water in the production stage, realizing the recycling and reuse of water resources, and improving the economic benefits of the production process.

[0035] The present invention adopts membrane separation to separate saline wastewater, thereby enriching sodium sulfate in the wastewater, and the separated water can be recycled; potassium sulfate products are produced by directly adding potassium chloride to the enriched sodium sulfate brine, thereby avoiding the lengthy production steps of separately concentrating and crystallizing sodium sulfate, reducing production energy consumption and operating costs, and increasing the market value of resources while recovering resources in saline wastewater; and effective recovery and high-value processing and utilization of resources in saline wastewater are achieved by processing sodium chloride, a byproduct of potassium sulfate products, thereby solving the problem that a large amount of treated water is generated by existing treatment technologies and is difficult to be recycled, and also solving the impact of a large amount of saline wastewater discharged to the outside and the like on natural water bodies.

[0036] Specifically, since the titanium dioxide acidic wastewater and saline wastewater are treated differently in the present invention, and the sodium sulfate salt in the saline wastewater is processed with high value, the solubility characteristics and market value characteristics of sulfate in sodium sulfate and potassium sulfate are utilized to exchange sodium and potassium, produce highly water-soluble potassium sulfate (drip irrigation) fertilizer products, and improve resource value; at the same time, the sodium in the sodium sulfate is converted into an industrial salt product with a huge market (returning to the initial raw material stage of sodium salt), rather than the limited market of the existing industrial by-product sodium sulfate (glauber's salt); multiple goals are achieved at one stroke, and the problem of resource utilization of saline wastewater in titanium dioxide production is fully solved.

[0037] Therefore, the method for treating saline wastewater in the production of titanium dioxide of the present invention can not only recycle and reuse almost all resources in the saline wastewater, but also increase the production value and use value of the resources during the treatment process, improve the economic effect of production, and promote green and sustainable production development. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the solution phase diagram of Na2SO4 / 2NaCl / K2SO4 / 2KCl / H2O system at 0℃, 25℃ and 100℃ respectively.

[0039] Figure 2 It is a schematic diagram of the process of the acidic wastewater treatment method of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0041] Example 1

[0042] 136 kg of saline wastewater (3.75% sodium sulfate) produced in the three-wash process of titanium dioxide production was used. After pretreatment and ultrafiltration to remove suspended matter, two nanofiltrations were performed to obtain 35 kg of concentrated brine (14.5% sodium sulfate) and 101 kg of dilute desalted water (20 μs / cm).

[0043] 4.8 kg of potassium chloride (containing 61.6% K2O) was added to the concentrated phase for dissolution and mixing, and the mixture was sent to the first stage evaporation concentrator for evaporation and concentration. 19.0 kg of water was evaporated to remove 20.8 kg of material. After cooling to 30° C., the mixture was filtered and separated for the first time to obtain 6.3 kg (95%) of glauberite filter cake and 14.5 kg of the first mother liquor (the composition is shown in Table 1).

[0044] The 6.3 kg of glauberite obtained by the first filtration separation was added with 5 kg of 40% potassium chloride solution at 30° C. to stir and decompose the glauberite, and then filtered and separated for the second time to obtain 6.6 kg (94%) of potassium sulfate and 4.7 kg of mother liquor (composition is shown in Table 1). The filter cake was washed three times with 0.6 kg of clean water to obtain 6.33 kg of potassium sulfate (containing 1.8% water and 0.2% chlorine) and 0.87 kg of second filtration washing water.

[0045] The 14.5 kg mother liquor separated by the first filtration was concentrated by the second evaporation, and 10 kg of water was evaporated to remove the remaining 4.5 kg of material, which was separated by the third filtration to obtain 1.40 kg of sodium chloride solid and 3.10 kg of filtrate (composition see Table 1).

[0046] Table 1. Composition of separation mother liquor

[0047] composition / % Potassium sodium chlorine Sulfate First stock solution 2.19 8.47 13.12 1.92 Second mother liquor 6.80 8.82 19.67 0.14 The third mother liquor 10.08 15.72 33.61 8.83 Second filter wash water 1.5 2.19 3.31 1.84

[0048] Example 2

[0049] The three-wash process after the production of titanium dioxide produces 123 kg of saline wastewater (4.15% sodium sulfate) per hour. After pretreatment and ultrafiltration to remove suspended matter, two nanofiltrations are performed to obtain 33.55 kg of concentrated brine (15.2% sodium sulfate) and 89.45 kg of dilute desalted water (18 μs / cm).

[0050] 33.55 kg of concentrated brine was dissolved by adding 3.50 kg of potassium chloride (containing 62.1% K2O), and 4.7 kg of the second separated mother liquor and 3.1 kg of the third separated mother liquor were added and mixed to obtain 44.85 kg of mixed solution, the composition of which is shown in Table 2. The mixture was sent to the first stage evaporation concentrator for evaporation and concentration, 24.05 kg of water was evaporated and 20.8 kg of material remained. After cooling to 30 ° C, the mixture was filtered and separated for the first time to obtain 6.37 kg (94%) of potassium glauberite filter cake and 14.43 kg of mother liquor (the composition is shown in Table 2).

[0051] The 6.37 kg of glauberite obtained by the first separation was added with 5 kg of a 40% concentration of potassium chloride solution prepared by adding process water to the second filtered washing water at a temperature of 30° C. After stirring to decompose the glauberite, it was filtered and separated for the second time to obtain 6.67 kg (93%) of potassium sulfate and 4.7 kg of mother liquor (composition is shown in Table 2). The filter cake was washed three times with 0.6 kg of clean water to obtain 6.36 kg of potassium sulfate (containing 2.2% water and 0.3% chlorine) product and 0.91 kg of secondary filtered washing water.

[0052] The 14.43 kg mother liquor separated by the first filtration was concentrated by the second evaporation, and 10 kg of water was removed by evaporation, leaving 4.43 kg of material, which was separated by the third filtration to obtain 1.45 kg of sodium chloride solid and 2.98 kg of filtrate (composition see Table 2).

[0053] Table 2. Composition of separation mother liquor

[0054] composition / % Potassium sodium chlorine Sulfate Mixture components 5.45 5.69 8.05 8.43 First stock solution 2.20 8.78 13.18 1.93 Second mother liquor 6.80 8.82 19.67 0.14 The third mother liquor 10.08 15.72 33.61 8.83 Secondary filtration wash water 1.56 2.28 3.44 1.91

[0055] Example 3

[0056] The three-wash process of post-treatment for titanium dioxide production produces 13.6 tons of saline wastewater (3.75% sodium sulfate) per hour. After pretreatment and ultrafiltration to remove suspended matter, two nanofiltrations are performed to obtain 3.55 tons of concentrated brine (14.3% sodium sulfate) and 10.05 tons of dilute desalted water (20μs / cm).

[0057] 0.48 T of potassium chloride (containing 61.6% K2O) is added to dissolve 3.55 T of concentrated brine per hour, and a filter is used to filter out mechanical impurities brought by potassium chloride and flotation agents added during potassium chloride production.

[0058] The filtered solution was sent to the first stage evaporation concentrator for evaporation and concentration. 1.95 kg of water was evaporated per hour, leaving 2.08 T of material. After cooling to 30 ° C, the first filtration separation was carried out to obtain 0.63 T (95%) of potassium glauberite filter cake and 1.45 T of the first mother liquor (composition is shown in Table 3).

[0059] 0.09T of the second filtered washing water, process water and 0.2T of potassium chloride returned in circulation per hour are made into a potassium chloride solution with a concentration of 35%, and after dissolving and filtering to remove mechanical impurities and flotation agents, 0.57T per hour and 0.63T of glauberite obtained by the first filtration separation are stirred and decomposed at a temperature of 30°C, and then filtered and separated for the second time to obtain 0.66T (94%) of potassium sulfate and 0.54T of mother liquor (composition is shown in Table 3), and the filter cake is washed three times with 0.06T of clean water to obtain 0.63T of potassium sulfate (containing 1.8% water and 0.2% chlorine) and 0.09T of the second filtered washing water.

[0060] The 1.45T mother liquor separated by the first filtration was subjected to the second stage of evaporation and concentration, and 1.0T of water was evaporated away, leaving 0.45T of material, which was then subjected to the third filtration and separation to obtain 0.14T of sodium chloride solid and 0.31T of filtrate (composition see Table 3)

[0061] Table 3. Composition of separation mother liquor

[0062] composition / % Potassium sodium chlorine Sulfate First stock solution 2.19 8.47 13.12 1.92 Second mother liquor 5.92 7.68 17.12 0.12 The third mother liquor 10.08 15.72 33.61 8.83 Second filter wash water 1.5 2.19 3.31 1.84

[0063] Then the mother liquor circulation operation is carried out, 3.55T of concentrated brine is produced by membrane separation of the dense phase per hour, 0.54T of the second filtration separation circulating mother liquor and 0.31T of the third filtration separation mother liquor are incorporated into the concentrated brine per hour, and 0.36T of potassium chloride is added for dissolution, and then filtered through a filter to remove mechanical impurities and insolubles brought in by the potassium chloride raw material.

[0064] The filtered solution was sent to the first stage evaporation concentrator for evaporation and concentration. 1.95 kg of water was evaporated per hour, leaving 2.08 T of material. After cooling to 30 ° C, the first filtration separation was carried out to obtain 0.63 T (95%) of potassium glauberite filter cake and 1.45 T of the first mother liquor.

[0065] 0.09T of second filtration washing water, process water and 0.2T of potassium chloride which are circulated back every hour are used to prepare a potassium chloride solution with a concentration of 35%, and after dissolving and filtering to remove mechanical impurities and flotation agents, 0.57T of 0.63T of glauberite obtained by first filtration separation is stirred and decomposed at a temperature of 30°C, and then filtered and separated for a second time to obtain 0.66T (94%) of potassium sulfate and 0.54T of mother liquor; the mother liquor is circulated back to the mixed solution before the first stage of evaporation and concentration, and the filter cake is washed three times with 0.06T of clean water to obtain 0.63T of potassium sulfate (containing 1.8% water and 0.2% chlorine) and 0.09T of second filtration washing water; the second filtration washing water is returned to the preparation of a 35% potassium chloride solution.

[0066] The 1.45T mother liquor separated by the first filtration was subjected to the second stage of evaporation and concentration, and 1.0T of water was evaporated to remove, leaving 0.45T of material, which was subjected to the third filtration and separation to obtain 0.14T of sodium chloride solid and 0.31T of filtrate. The third filtrate was recycled back to the mixed liquor before the first stage of evaporation and concentration.

[0067] Through the records and verification of the above embodiments, the acidic wastewater treatment method in the production of titanium dioxide proposed by the invention can effectively avoid the discharge of a large amount of waste salt and wastewater gas into natural water bodies and the environment, and realize the recycling and reuse of resources such as water to a greater extent, bringing significant economic benefits to producers and promoting the green and sustainable development of titanium dioxide production technology.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating saline wastewater in titanium dioxide production, characterized in that: The steps include: S1: The salt-containing wastewater generated in the production of titanium dioxide is treated by membrane separation, and the separated dilute phase solution is sent back to the titanium dioxide production process as purified water. The separated concentrated phase solution is added with potassium chloride and circulating mother liquor for the first stage of evaporation, concentration and crystallization to obtain potassium glauberite slurry, and the first separation is performed; S2 The glauberite filter cake separated for the first time is sent to the dissolution production process, and then potassium chloride solution is added to dissolve the glauberite to obtain potassium sulfate crystal slurry, and then the second separation is carried out. The separated mother liquor obtained by the second separation is circulated back to the first evaporation concentration crystallization process, and the solid separated for the second time is obtained to obtain the potassium sulfate product; S3 performs a second stage of evaporation, concentration and crystallization on the mother liquor of the first separation of glauberite to obtain sodium chloride slurry, and performs a third separation. The mother liquor obtained by the third separation is circulated back to the first stage of evaporation, concentration and crystallization process, and the solid separated for the third time obtains the sodium chloride product.

2. The method for treating saline wastewater in the production of titanium dioxide according to claim 1, characterized in that: Membrane separation uses one or more stages of nanofiltration membranes and reverse osmosis membranes. The concentration multiple of saline wastewater is 2-6 times. The dilute phase conductivity in membrane separation treatment is 10-30μs / cm.

3. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S1, the concentrated phase solution obtained by separation is filtered and separated from the mixed solution to which potassium chloride and circulating mother liquor are added, so as to separate the insoluble substances brought in by potassium chloride.

4. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1 or 2, characterized in that: In step S1, the first stage of evaporation, concentration and crystallization: the evaporation and concentration temperature is 110-150°C, and the crystallization temperature is 30-50°C.

5. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid method according to claim 4, characterized in that: In step S2, the filtrate of the first separation of glauberite has the following composition: potassium 2.5-6.0%; sodium 7.5-10.0%; chlorine 13-17%; sulfate 1.5-3.5%.

6. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S2, potassium chloride is added to dissolve glauber's salt to crystallize potassium sulfate product at a temperature of 15 to 90°C.

7. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step S3, the second stage of evaporation, concentration and crystallization: the evaporation and concentration temperature is 100-150°C, and the sodium chloride crystallization temperature is 30-50°C.

8. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid method according to claim 5, characterized in that: In step S3, the filtrate of the second separation of potassium sulfate comprises: 3.5-9.0% potassium, 7.5-10.0% sodium, 15-22% chlorine, and 0.1-2.5% sulfate.

9. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid method according to claim 1, characterized in that: The temperature of the third separation is 30-60°C, and the third separated sodium chloride product is obtained. The mother liquor after separation is circulated back to the mixed solution before the first stage evaporation and concentration.

10. The method for treating saline wastewater in the production of titanium dioxide by sulfuric acid method according to claim 1, characterized in that: The condensed water from the first and second evaporation stages is recycled back to the titanium dioxide process.

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