Method for preparing ferric phosphate and white gypsum by using waste titanium white acid

Abstract

The present invention discloses a method for preparing iron phosphate and white gypsum by using waste acid from titanium dioxide production, belonging to the field of wastewater treatment. The method for preparing iron phosphate and white gypsum by using waste acid from titanium dioxide production comprises the following steps: A. Freezing and crystallizing the waste acid from titanium dioxide production, followed by solid-liquid separation to obtain ferrous sulfate and waste sulfuric acid; B. Preparation of iron phosphate: Refining the ferrous sulfate obtained in step A, adding auxiliary materials, and carrying out an iron phosphate synthesis reaction to obtain amorphous iron phosphate. The amorphous iron phosphate is subjected to steps of primary washing, aging, secondary washing, drying, calcination dehydration, pulverization, screening, and iron removal to obtain iron phosphate; Preparation of white gypsum: Neutralizing the waste sulfuric acid obtained in step A with lime milk to obtain a calcium sulfate slurry, and subjecting the calcium sulfate slurry to steps of solid-liquid separation, drying, and pulverization to obtain white gypsum. The technical solution of the present invention can resourcefully utilize the waste acid generated in the production process of sulfuric acid process titanium dioxide, reduce energy consumption costs, and achieve sustainable development.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment, and relates to a method for resource utilization of titanium white waste acid, specifically to a method for preparing iron phosphate and white gypsum using titanium white waste acid. Background Art

[0002] In the production process of titanium white by the sulfuric acid method, waste acid containing ferrous sulfate is generated. The waste acid needs to be recycled and neutralized to the maximum extent to meet environmental protection requirements. Currently, common waste acid treatment methods are concentration and recycling, and discharging to the sewage treatment station for neutralization. Among them, waste acid concentration is to concentrate the waste sulfuric acid to about 55% by using steam heating through a multi-effect concentration device or an MVR concentration device and then recycle it to the titanium white production system; the waste acid that cannot be recycled by the system is discharged to the sewage treatment station and neutralized with lime. The qualified wastewater is directly discharged, and the waste residue is stored in the slag yard.

[0003] The deficiencies of the existing waste acid concentration process are as follows: (1) There is a large amount of ferrous in the waste acid. As the concentration of the concentrated acid increases, ferrous precipitates, abrading pumps and pipelines; (2) Ferrous precipitation is prone to fouling, easily blocking pipelines and evaporator tubes, resulting in poor heat transfer effect and increased energy consumption; (3) After the system is fouled and blocked, it needs to be shut down for cleaning. The cleaning cycle is about 10 days, with low system efficiency and high energy consumption; (4) The cleaning cycle is frequent, and the labor intensity of workers is large.

[0004] The deficiencies of the existing waste acid neutralization process are as follows: (1) The waste acid contains ferrous, which consumes lime during neutralization, increasing the neutralization cost; (2) The waste acid contains ferrous, which requires aeration treatment, increasing the neutralization cost; (3) The waste acid contains ferrous. After neutralization, since ferrous becomes ferric, the color of the gypsum is reddish-brown and cannot be reused, and can only be stored in the slag yard, increasing the environmental protection treatment cost. At the same time, the slag yard has also become a factor restricting the production of titanium white by the sulfuric acid method. Summary of the Invention

[0005] In view of the above technical problems, the present invention provides a method for preparing iron phosphate and white gypsum using titanium white waste acid, which comprehensively recycles the waste acid generated in the production process of titanium white by the sulfuric acid method. While obtaining the iron source required for preparing iron phosphate, the purified waste sulfuric acid is concentrated and recycled to the titanium white production system and white gypsum for building use is produced.

[0006] The technical solution adopted by the present invention to solve its technical problems is: A method for preparing iron phosphate and white gypsum using titanium white waste acid, comprising the following steps:

[0007] A. Freeze-crystallize the titanium white waste acid and then separate the solid and liquid to obtain ferrous sulfate and waste sulfuric acid;

[0008] B. Prepare iron phosphate and white gypsum:

[0009] Preparation of iron phosphate: The refined ferrous sulfate obtained in step A is added with auxiliary materials to carry out the iron phosphate synthesis reaction to obtain amorphous iron phosphate. The amorphous iron phosphate is subjected to the steps of primary washing, aging, secondary washing, drying, calcination dehydration, pulverization, screening, and iron removal to obtain iron phosphate;

[0010] Preparation of white gypsum: The waste sulfuric acid obtained in step A is subjected to a neutralization reaction with lime milk to obtain a calcium sulfate slurry. The calcium sulfate slurry is subjected to the steps of solid-liquid separation, drying, and pulverization to obtain white gypsum.

[0011] In the above step A, the titanium white waste acid is the waste acid containing 20-30% sulfuric acid concentration generated in the production of titanium white by the sulfuric acid method; the freeze crystallization is carried out under stirring conditions, and the temperature of the waste acid is lowered to below the crystallization temperature of ferrous sulfate through circulating chilled water until ferrous sulfate is fully crystallized and precipitated.

[0012] In the above step B, the preparation of iron phosphate specifically includes the following steps:

[0013] a. The ferrous sulfate obtained in the above step A is added to pure water for pulping treatment, and then ammonia water is added to adjust the pH to 2-4. After full reaction, it is filtered, and the concentration of the filtrate is adjusted so that the content of ferrous sulfate in terms of iron is 7-8% to obtain a refined ferrous sulfate solution;

[0014] b. Hydrogen peroxide, ammonia water, and industrial monoammonium phosphate solution are added to the refined ferrous sulfate solution obtained in step a. After full reaction, amorphous iron phosphate precipitate is formed. After solid-liquid separation, amorphous iron phosphate is obtained;

[0015] c. The amorphous iron phosphate obtained in step b is subjected to primary washing and then filtered. Then it is added to pure water for pulping treatment, and then phosphoric acid is added and mixed evenly. Then it is heated to 90-98 °C for aging. After full reaction, shaped iron phosphate is obtained;

[0016] d. The shaped iron phosphate obtained in step c is subjected to secondary washing and then pressure filtration to obtain an iron phosphate filter cake. The iron phosphate filter cake is subjected to drying and calcination dehydration treatment. The dehydrated iron phosphate is pulverized, screened, and iron-removed according to actual application requirements to obtain iron phosphate.

[0017] In the above step a, the mass ratio of ferrous sulfate to pure water is 1:4-4.5.

[0018] In the above step b, the mass ratio of hydrogen peroxide: ammonia water: industrial monoammonium phosphate solution: refined ferrous sulfate solution is 19:39:127:152.

[0019] In the above step c, the mass ratio of amorphous iron phosphate to pure water is 1:4-4.5; the mass ratio of amorphous iron phosphate to phosphoric acid is 152:10-12.

[0020] In the above step c, the primary washing is to wash the amorphous iron phosphate obtained in step b with pure water 20 times the mass of the iron phosphate.

[0021] In the above step c, the aging reaction time is 3 - 4 h.

[0022] In the above step d, the secondary washing is to wash the shaped iron phosphate obtained in step c with pure water 20 times the mass of the iron phosphate.

[0023] In the above step d, the drying is carried out in a flash dryer at 100 - 110 °C for 30 - 40 s, and the calcination dehydration is carried out in a calcination kiln at 700 - 800 °C for 3 - 4 h for dehydration.

[0024] In the preparation of white gypsum in the above step B, the neutralization reaction is as follows: under stirring conditions, slaked lime is slowly added to the waste sulfuric acid obtained in step A for neutralization reaction until precipitation is complete to obtain a calcium sulfate slurry.

[0025] In the preparation of white gypsum in the above step B, the specific steps of solid - liquid separation, drying and pulverization are as follows: the calcium sulfate slurry is pumped into a plate - and - frame filter press for solid - liquid separation to obtain a gypsum filter cake, the gypsum filter cake is sent to a drum dryer for drying and then pulverized according to actual application needs to obtain white gypsum.

[0026] The beneficial effects of the present invention are as follows: the technical solution of the present invention can recycle the waste acid generated in the sulfuric acid process titanium dioxide production process, use the ferrous iron separated from the waste acid to produce iron phosphate, and realize the recycling of waste by - products; while obtaining the iron source required for preparing iron phosphate, the purified waste sulfuric acid is concentrated and recycled to the titanium dioxide production system, improving the waste acid concentration efficiency, reducing the cleaning cycle and lowering the energy consumption cost; the purified waste sulfuric acid is made into white gypsum powder for construction use, which can realize the full recycling of waste acid, reduce the generation amount of sulfuric acid process titanium dioxide waste residue, lower the enterprise environmental protection cost and achieve sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow schematic diagram of the technical solution of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The technical solution of the present invention can be specifically implemented in the following manner.

[0029] A method for preparing iron phosphate and white gypsum using titanium dioxide waste acid includes the following steps:

[0030] (1) Waste acid freezing crystallization: The waste acid is pumped into a crystallization kettle with stirring and cooling jacket by a pump, and the reaction kettle jacket is passed through with chilled water to cool the material; under slow stirring, the material temperature gradually drops to 5 °C, and the cooling time is maintained for 4 h to ensure that ferrous sulfate in the waste acid fully crystallizes out;

[0031] (2) Separation of ferrous sulfate and waste sulfuric acid: The crystallized material is pumped into a plate and frame filter press through a pump for solid-liquid separation. Ferrous sulfate and waste sulfuric acid are reserved as raw materials for the next step.

[0032] (3) Production of iron phosphate using ferrous sulfate:

[0033] a. Refinement of ferrous sulfate: Ferrous sulfate and pure water are slurried at a mass ratio of 1:4. Ammonia water is added to adjust the pH value to 3 for precipitation. Then, it is filtered through a filter press to remove impurities. The concentration of the refined ferrous sulfate solution is adjusted to 7-8% (calculated as iron) for standby.

[0034] b. Oxidation of ferrous sulfate and synthesis of iron phosphate: The refined ferrous sulfate solution is pumped into a synthesis kettle. Hydrogen peroxide, ammonia water, industrial monoammonium phosphate solution are added in a mass ratio of hydrogen peroxide: ammonia water: industrial monoammonium phosphate: ferrous sulfate = 19:39:127:152 for the iron phosphate synthesis reaction to produce amorphous iron phosphate precipitate.

[0035] c. Primary washing of iron phosphate: The synthesized iron phosphate precipitate is pumped into a diaphragm filter press for filtration, and then 20 times the mass of pure water of iron phosphate is passed through for washing to remove impurities and salts in the system.

[0036] d. Aging of iron phosphate: The washed iron phosphate filter cake is sent to an aging kettle, slurried with 4 times the mass of pure water of iron phosphate, heated to 95°C, and phosphoric acid is added in a mass ratio of iron phosphate: phosphoric acid = 152:10 for aging to convert amorphous iron phosphate into crystalline iron phosphate.

[0037] e. Secondary washing of iron phosphate: The aged iron phosphate material is pumped into a diaphragm filter press for filtration, and then 20 times the mass of pure water of iron phosphate is passed through for washing to remove impurities and salts in the system.

[0038] f. Drying and dehydration of iron phosphate: The iron phosphate slurry qualified for secondary washing is pumped into a filter press for solid-liquid separation. The iron phosphate filter cake enters a flash dryer and is dried at 105°C for 30 s to remove free water. The material dried by flash drying enters a calcination kiln and is calcined at 750°C for 3.5 h to remove crystal water.

[0039] g. Crushing, screening, iron removal, and packaging of iron phosphate: The iron phosphate material after calcination and dehydration is crushed by a mechanical mill. The crushed material is recovered by a system bag filter and then enters a vibrating screen for screening. After passing the screening, the material is de-ironed and then enters an automatic packaging system for packaging, warehousing, and sales.

[0040] (4) Concentrate the waste acid after iron removal and recycle it to the titanium dioxide system: Pump the waste acid after iron removal into a multi-effect concentration system, concentrate the waste acid to 50%-55% and recycle it to the acid preparation and leaching of the titanium dioxide production line;

[0041] (5) Produce white gypsum using the waste acid after iron removal:

[0042] a. Neutralize the waste acid: Pump the waste acid after iron removal into a neutralization tank, gradually add lime milk for neutralization reaction until the pH reaches 7.5 to form calcium sulfate precipitate;

[0043] b. Filter press the gypsum: Pump the neutralized calcium sulfate slurry into a plate and frame filter press for solid-liquid separation. The filtrate is discharged after being treated qualified, and the gypsum filter cake enters the next process;

[0044] c. Dry the gypsum: The gypsum filter cake enters a drum dryer and is dried at 100°C for 15 minutes to remove moisture;

[0045] d. Crush the gypsum: The dried gypsum enters a crushing device for crushing treatment, and the crushed material enters the packaging system for packaging, warehousing, and sales.

Claims

1. A method for preparing iron phosphate and white gypsum using waste titanium white acid, characterized in that It includes the following steps: A. Freeze-crystallize the titanium white waste acid and then perform solid-liquid separation to obtain ferrous sulfate and waste sulfuric acid; B. Prepare iron phosphate and white gypsum: The preparation of iron phosphate specifically includes the following steps: a. Add the ferrous sulfate obtained in step A to pure water for pulping, then add ammonia water to adjust the pH to 2-4. After fully reacting, filter, and adjust the concentration of the filtrate so that the content of ferrous sulfate in terms of iron is 7-8%, obtaining a refined ferrous sulfate solution; b. Add hydrogen peroxide, ammonia water, and industrial monoammonium phosphate solution to the refined ferrous sulfate solution obtained in step a. After fully reacting, form amorphous iron phosphate precipitate. After solid-liquid separation, obtain amorphous iron phosphate; c. Wash the amorphous iron phosphate obtained in step b once and then filter. Add pure water for pulping again, then add phosphoric acid and mix well. Heat to 90-98°C for aging. After fully reacting, obtain shaped iron phosphate; d. Wash the shaped iron phosphate obtained in step c twice and then press-filter to obtain an iron phosphate filter cake. Dry and calcine the iron phosphate filter cake for dehydration. After dehydration, perform crushing, screening, and iron removal treatment on the iron phosphate according to actual application needs to obtain iron phosphate; In step a, the mass ratio of ferrous sulfate to pure water is 1∶4-4.5; In step b, the mass ratio of hydrogen peroxide∶ammonia water∶industrial monoammonium phosphate solution∶refined ferrous sulfate solution is 19∶39∶127∶152; In step c, the mass ratio of amorphous iron phosphate to pure water is 1∶4-4.5; the mass ratio of amorphous iron phosphate to phosphoric acid is 152:10-12; The preparation of white gypsum: Neutralize the waste sulfuric acid obtained in step A with lime milk to obtain a calcium sulfate slurry. The calcium sulfate slurry is subjected to solid-liquid separation, drying, and crushing steps to obtain white gypsum.

2. The method for preparing iron phosphate and white gypsum using waste titanium white acid according to claim 1, characterized in that: In step A, the titanium white waste acid is the waste acid containing 20-30% sulfuric acid produced in sulfuric acid process titanium white production; the freeze-crystallization is to lower the temperature of the waste acid below the ferrous sulfate crystallization temperature through circulating chilled water under stirring conditions until ferrous sulfate fully crystallizes and precipitates.

3. The method for preparing iron phosphate and white gypsum using waste titanium white acid according to claim 1, characterized in that: In step c, the first washing is to wash the amorphous iron phosphate obtained in step b with 20 times the mass of iron phosphate of pure water; in step d, the second washing is to wash the shaped iron phosphate obtained in step c with 20 times the mass of iron phosphate of pure water.

4. The method for preparing iron phosphate and white gypsum using waste titanium white acid according to claim 1, characterized in that: In step d, the drying is carried out in a flash dryer at 100-110°C for 30-40 s, and the calcination dehydration is carried out in a calcination kiln at 700-800°C for 3-4 h for dehydration.

5. The method for preparing iron phosphate and white gypsum using waste titanium white acid according to claim 1, characterized in that: In the preparation of white gypsum in step B, the neutralization reaction is: Under stirring conditions, slowly add lime milk to the waste sulfuric acid obtained in step A for neutralization reaction until the precipitation is complete to obtain a calcium sulfate slurry.

6. The method for preparing iron phosphate and white gypsum using waste titanium white acid according to claim 1, characterized in that: In the preparation of white gypsum in step B, the specific steps of solid-liquid separation, drying, and crushing are: Pump the calcium sulfate slurry into a plate and frame filter press for solid-liquid separation to obtain a gypsum filter cake. Send the gypsum filter cake into a drum dryer for drying and then perform crushing treatment according to actual application needs to obtain white gypsum.

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