Method for treating and recycling acid wastewater in sulfuric acid method titanium dioxide process

Abstract

The invention discloses a method for treating and recycling acidic wastewater in a sulfuric acid method titanium dioxide process, which comprises the following steps: discharging acidic wastewater generated in a metatitanic acid washing process in sulfuric acid method titanium dioxide production into a wastewater collecting tank, and feeding into a heat exchanger for cooling treatment; feeding into a pretreatment system, intercepting and concentrating large-particle solid titanium dioxide suspended solids in the acid wastewater, and returning intercepted titanium dioxide to a titanium dioxide production line nearby; the vast majority of metal ions in the acid wastewater are intercepted and concentrated through an SNF membrane treatment system; water produced by the SNF membrane treatment system is subjected to concentration and separation of acid and water through an SRO membrane, and an SRO concentrated solution is further concentrated and then returns to the front end of a sulfuric acid method titanium dioxide process; the water produced by the SRO membrane is collected and then reused in a production line, so that the water is recycled.

Description

Technical Field

[0001] This invention relates to the field of acidic wastewater treatment and reuse in the sulfuric acid process for titanium dioxide, and in particular to a method for treating and reusing acidic wastewater from the sulfuric acid process for titanium dioxide. Background Technology

[0002] Titanium dioxide is widely used in coatings, plastics, papermaking, and other fields. With the improvement of living standards, the consumption of titanium dioxide is gradually increasing. Currently, 98% of titanium dioxide is produced using the sulfuric acid process. During the production of titanium dioxide using the sulfuric acid process, 60-100 tons of acidic wastewater with a concentration of 3-6% are generated for every ton of titanium dioxide produced. This wastewater mainly comes from the washing section and the tail gas treatment section, and contains a large amount of SO4. 2- H + Fe 2+ Ions, and also contains some Ti 3+ Ca 2+ Mg 2+ These wastewaters contain trace amounts of metal ions. They are not only produced in large quantities but also have low acid concentrations and contain iron and other salts, making direct reuse of them less valuable. However, due to the presence of certain concentrations of heavy metals and low-concentration acid, direct discharge is not permitted. Currently, both domestically and internationally, acid-base neutralization methods using lime, calcium carbonate, or calcium carbide sludge are primarily employed for treating acidic wastewater from the sulfuric acid process. These methods have several drawbacks: excessive suspended solids, low water reuse rates, and reliance on single treatment methods like lime, calcium carbonate, or calcium carbide sludge. Furthermore, during pH adjustment, Fe... 2+ and Fe 3+ The hydroxyl compounds generated by ions are prone to disproportionation reactions, making it difficult to guarantee the color of the water as the drainage time increases. Furthermore, the high iron content results in poor hydrophobicity and high moisture content in titanium gypsum. Therefore, improving the treatment and reuse methods for acidic wastewater from the sulfuric acid process for titanium dioxide is an urgent problem to be solved. Summary of the Invention

[0003] In view of the above situation and to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for treating and reusing acidic wastewater from the sulfuric acid process for titanium dioxide, which can effectively solve the problems of the prior art, such as the difficulty in ensuring water quality and color, and the poor hydrophobicity and high moisture content of titanium gypsum due to high iron content.

[0004] The technical solution provided by this invention includes the following steps: 1) The acidic wastewater generated during the titanate washing process is stored in a wastewater collection tank; 2) It enters the heat exchanger for cooling; 3) The wastewater enters the pretreatment system's security filter to remove large particles of solid titanium dioxide suspended in the acidic wastewater, and the retained titanium dioxide is recycled. 4) Entering the SNF membrane system, most of the metal ions in the concentrated acidic wastewater are retained to produce by-products such as polyferrous sulfate; 5) The solution enters the SRO concentration membrane system for acid and water concentration and separation; 6) The SRO concentrate is supplied to the evaporation and concentration unit for further concentration to achieve acid balance; the produced water is collected and reused in the production line to achieve water recycling.

[0005] In step 1), the acidic wastewater generated during the titanate washing process meets the following criteria: sulfuric acid content of 2-6%, total iron content of 0.3-0.5%, and temperature of 40-50℃.

[0006] In step 2), after cooling by the heat exchanger, the sulfuric acid concentration is 3-6%, the total iron content is 0.3-0.5%, and the temperature is less than 35°C.

[0007] In step 3), the acidic wastewater, after passing through the pretreatment system, has a sulfuric acid concentration of 3-6%, a total iron content of 0.3-0.5%, a temperature of less than 35°C, an SDI of less than 5, and a turbidity of less than 1.

[0008] In step 4), after passing through the SNF membrane system, the following parameters are met: sulfuric acid concentration is 3-6%, total iron content is less than 0.05%, and temperature is less than 35℃.

[0009] In step 5), after concentration and separation by the SRO membrane device, the concentrated liquid meets the following specifications: sulfuric acid concentration of 20-25% and product water meets the deionized water standard.

[0010] In step 6), the SRO concentrate is provided to the evaporation and concentration unit, where the sulfuric acid is further concentrated. The concentrate specifications meet the following: sulfuric acid concentration of 40-50%.

[0011] The beneficial effects of this invention are as follows: This invention sequentially processes acidic wastewater generated during the metatitanic acid washing process through a heat exchanger, a pretreatment system, SNF membrane separation, and SRO membrane concentration to obtain concentrated sulfuric acid and metatitanic acid washing water that meets near-deionized water standards. The treated water meets the requirements for metatitanic acid washing water, and the reuse production line achieves water recycling, saving water resources and effectively protecting the environment. Furthermore, the sulfuric acid concentration reaches 40-50%, and after mixing with high-concentration sulfuric acid, it can be used in the upstream of the sulfuric acid process for titanium dioxide production. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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. Example 1

[0014] Depend on Figure 1 The present invention, in its specific implementation, includes the following steps: 1) The acidic wastewater generated during the titanate washing process is stored in a wastewater collection tank. The acidic wastewater contains 3% sulfuric acid, 0.37% total iron, and is at a temperature of 45℃. 2) After entering the heat exchanger for cooling, the sulfuric acid concentration is 3%, the total iron content is 0.37%, and the temperature is 30℃; 3) After entering the pretreatment system security filter, the sulfuric acid concentration is 3%, the total iron content is 0.37%, the temperature is 30℃, the SDI is 4, and the turbidity is 0.8. Large particles of solid titanium dioxide suspended in the acidic wastewater are removed, and the retained titanium dioxide is recycled. 4) The sulfuric acid concentration is 3%, the total iron content is 0.0045%, and the temperature is 30℃ when the SNF membrane system is entered; most of the metal ions in the concentrated acidic wastewater are retained to produce by-products such as polyferrous sulfate. 5) After entering the SRO concentration membrane system for acid and water concentration and separation, the concentrated liquid meets the following specifications: sulfuric acid concentration of 21% and product water specifications meet deionized water standards. 6) The SRO concentrate is supplied to the evaporation and concentration unit. After further concentration, the concentrate has the following specifications: sulfuric acid concentration of 49%. The produced water is collected and reused in the production line to achieve water recycling. Example 2

[0015] Depend on Figure 1 The present invention, in its specific implementation, includes the following steps: 1) The acidic wastewater generated during the titanate washing process is stored in a wastewater collection tank. The acidic wastewater contains 4% sulfuric acid, 0.39% total iron, and is at a temperature of 44℃. 2) After entering the heat exchanger for cooling, the sulfuric acid concentration is 4%, the total iron content is 0.39%, and the temperature is 28℃; 3) After entering the pretreatment system security filter, the sulfuric acid concentration is 3-6%, the total iron content is 0.3-0.5%, the temperature is less than 35℃, SDI<5, and turbidity<1. Large particles of solid titanium dioxide suspended in the acidic wastewater are removed, and the intercepted titanium dioxide is recycled. 4) The sulfuric acid concentration is 4%, the total iron content is 0.0046%, and the temperature is 28℃ when it enters the SNF membrane system. This system retains most of the metal ions in the concentrated acidic wastewater and produces by-products such as polyferrous sulfate. 5) After entering the SRO concentration membrane system for acid and water concentration and separation, the concentrated liquid meets the following specifications: sulfuric acid concentration of 23% and product water specifications meet deionized water standards. 6) The SRO concentrate is supplied to the evaporation and concentration unit. After further concentration, the concentrate has the following specifications: sulfuric acid concentration of 51%. The produced water is collected and reused in the production line to achieve water recycling.

[0016] This invention addresses the issue of acidic wastewater generated during the metatitanic acid washing process in the sulfuric acid process for titanium dioxide production. The wastewater is discharged into a wastewater collection tank and then sent to a heat exchanger for cooling. It is then fed into a pretreatment system to concentrate and remove large particles of suspended titanium dioxide, which are then returned to the titanium dioxide production line. Next, an SNF membrane treatment system is used to concentrate and remove most of the metal ions in the acidic wastewater. The wastewater from the SNF membrane treatment system is then further concentrated and separated into acid and water using an SRO membrane. The SRO concentrate is then returned to the upstream of the sulfuric acid process for titanium dioxide production. The SRO membrane wastewater is collected and reused in the production line, achieving water recycling. Practical application has proven that this method effectively solves the problems of large acid emissions, environmental impact from the accumulation of titanium dioxide gypsum, and water waste associated with the traditional lime-based acid-base neutralization process used in this industry.

[0017] It should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any modifications or alterations made by those skilled in the art without departing from the scope of the present invention to create equivalent embodiments based on the disclosed technical content shall fall within the protection scope of the present invention.

Claims

1. A method for treating and recycling acid wastewater in a sulfuric acid process for titanium dioxide, characterized in that, The method comprises the following steps: 1) acidic wastewater produced in metatitanic acid washing process is stored in a wastewater collecting tank; 2) the wastewater is cooled in a heat exchanger; 3) the wastewater is filtered by a pretreatment system security filter to remove large-particle solid titanium dioxide suspension in the wastewater, and the intercepted titanium dioxide is recycled; 4) the wastewater is treated in an SNF membrane system to intercept most of metal ions in the concentrated acidic wastewater and produce by-products such as polymeric ferrous sulfate; 5) the wastewater is treated in an SRO concentration membrane system to separate acid and water; 6) SRO concentrated liquid is provided to an evaporation concentration device for further concentration to achieve acid balance, and the produced water is collected and reused in the production line to achieve water recycling.

2. The method according to claim 1, wherein the method is characterized by, In the step 1), the acidic wastewater produced in metatitanic acid washing process meets the following indexes: sulfuric acid content of 2-6%, total iron content of 0.3-0.5%, and temperature of 40-50℃.

3. The method according to claim 1, wherein the method is characterized by, In the step 2), after cooling in the heat exchanger, the sulfuric acid concentration is 3-6%, the total iron content is 0.3-0.5%, and the temperature is less than 35℃.

4. The method for treating and recycling the acid wastewater of the sulfuric acid method titanium dioxide process according to claim 1, characterized in that, In the step 3), after the pretreatment system, the sulfuric acid concentration is 3-6%, the total iron content is 0.3-0.5%, the temperature is less than 35℃, the SDI is less than 5, and the turbidity is less than 1.

5. The method for treating and recycling the acid wastewater of the sulfuric acid process titanium dioxide process according to claim 1, characterized in that, In the step 4), after the SNF membrane system, the indexes meet: sulfuric acid concentration of 3-6%, total iron content of less than 0.05%, and temperature of less than 35℃.

6. The method for treating and recycling the acid wastewater of the sulfuric acid process titanium dioxide process according to claim 1, characterized in that, In the step 5), after the SRO membrane device concentration separation, the concentrated liquid indexes meet: sulfuric acid concentration of 20-25%, and the produced water indexes meet the deionized water standard.

7. The method for treating and recycling the acid wastewater of the sulfuric acid process titanium dioxide process according to claim 1, characterized in that, In the step 6), the SRO concentrated liquid is provided to the evaporation concentration device, and the sulfuric acid is further concentrated, and the concentrated liquid indexes meet: sulfuric acid concentration of 40-50%.

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