Low-concentration waste acid recovery process

Abstract

The invention relates to the technical field of titanium dioxide waste acid treatment, and provides a low-concentration waste acid recovery process which comprises the following steps: conveying titanium dioxide waste acid to a vacuum evaporation and concentration system for vacuum evaporation and concentration, discharging the concentrated waste acid, crystallizing, concentrating the waste acid to 29%, and separating out yellow ferrous iron, carrying out solid-liquid separation to obtain yellow ferrous precipitate and a concentrated acid solution; dissolving the obtained yellow ferrous precipitate in water, carrying out purification treatment for three times to obtain a yellow ferrous solution, then mixing the yellow ferrous solution with the obtained concentrated acid solution, and cooling to a certain temperature, so that free sulfuric acid and titanyl sulfate in the yellow ferrous are transferred to a liquid phase, and the yellow ferrous is converted into ferrous sulfate heptahydrate; according to the recycling process, the concentration of sulfuric acid in the low waste acid can be increased, yellow ferrous iron can be recycled, comprehensive treatment of by-products is achieved, and the economic benefits and green sustainable development of enterprises are improved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide waste acid treatment, and in particular to a low-concentration waste acid recovery process. Background Art

[0002] Most of my country's titanium dioxide is produced by sulfuric acid process. However, the hydrolysis rate of concentrated titanium solution cannot reach 100%. The sulfuric acid process will produce low-concentration waste acid with a concentration of about 8%. 2 The content is about 0.40-0.50%. This part of titanium resources is almost never recycled. If it is discharged directly, it will not only cause a waste of resources, but also cause great damage to the environment.

[0003] Therefore, how to effectively treat titanium dioxide waste acid is crucial to the green and sustainable development of sulfuric acid method titanium dioxide. The most commonly used method at present is to concentrate and recover titanium dioxide waste acid. Due to the high water content of waste acid, conventional evaporation and concentration requires huge energy consumption, resulting in high operating costs; more importantly, a large amount of ferrous yellow will be produced when titanium dioxide waste acid is concentrated, and the titanium resources in titanium dioxide waste acid are mainly enriched in ferrous yellow. As a result, the treatment of ferrous yellow faces a major problem and causes a waste of titanium resources.

[0004] Therefore, it is particularly important to reuse the ferrous iron in waste acid and recover titanium resources to reduce production costs and alleviate environmental pollution. Summary of the invention

[0005] The purpose of the present invention is to provide a low-concentration waste acid recovery process, which can increase the sulfuric acid concentration in the low-concentration waste acid and realize the reuse of ferrous iron, thereby achieving comprehensive management of by-products, improving the economic benefits of the enterprise and green and sustainable development.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] A low-concentration waste acid recovery process comprises the following steps:

[0008] S1. Preparation of Ferrous Yellow

[0009] Titanium dioxide waste acid (generally FeSO 4 Content 9%~13%, H 2 SO 4The titanium dioxide waste acid (containing 16-25% of the titanium dioxide content and an initial temperature of 40-60°C) is transported to a vacuum evaporation concentration system for vacuum evaporation concentration. Under vacuum and high temperature conditions (generally 0.05-0.1MPa, not less than 60°C), the solution in the titanium dioxide waste acid evaporates. As the solution in the titanium dioxide waste acid volatilizes, the ferrous sulfate and acidity in the titanium dioxide waste acid gradually increase. When reaching a certain level, the concentrated waste acid is discharged and crystallized. The waste acid concentration is concentrated to 29% and yellow ferrous iron is precipitated at 10-20°C. After solid-liquid separation, yellow ferrous iron precipitation and concentrated acid solution are obtained. The sulfuric acid concentration in the concentrated acid solution is about 45-65%.

[0010] S2, yellow ferrous purification

[0011] Dissolve the yellow ferrous precipitate obtained in S1 in water and heat it for a period of time under stirring to make it evenly dispersed. Then add an appropriate amount of alkali solution and adjust the pH value of the solution to 2-5 so that the Ti 4+ The ions are precipitated out in a precipitated manner, and after filtration, the first supernatant is obtained.

[0012] Adding an appropriate amount of a chelating agent (such as HEDTA, citric acid, ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, N-acylethylenediamine triacetic acid) to the first supernatant, which can react with various heavy metals in the solution to generate insoluble chelated metal salts and form precipitation, thereby removing heavy metal ions in the solution; after filtering, a second supernatant is obtained;

[0013] Add modified polyacrylamide to the second supernatant to obtain a purified ferrous iron solution; add modified polyacrylamide to adsorb suspended particles in the solution, play a bridging role between particles, so that the particles are adsorbed into agglomerates, and the sedimentation rate can be accelerated, effectively reducing the turbidity of the solution; specifically, the preparation method of modified polyacrylamide includes the following steps:

[0014] (1) Add a certain amount of deionized water to a flask, then add a certain amount of amylose to the deionized water and mix, and stir magnetically at 100-300°C for 1 hour to obtain a first liquid; then add a certain amount of amylopectin to the deionized water and mix, and stir magnetically at 5-20°C for 1 hour to obtain a second liquid; mix the first liquid and the second liquid and cool them to room temperature, add a certain amount of initiator solution to a three-necked flask, and react for 10 minutes under magnetic stirring to fully activate the free radicals. Then continue to add a certain amount of a mixed solution of acrylamide monomer and cationic monomer to the three-necked flask and react for 3 hours. After the polymerization reaction is completed, cool the colloidal product to room temperature, add a certain amount of anhydrous ethanol while stirring, and precipitate a white or light yellow cationic starch-based flocculant. Filter the crude product, put it in a vacuum drying oven at 300°C and dry it to constant weight. After purification, the grafted polymer is obtained;

[0015] Amylose is a linear polysaccharide with a large number of glucose units in its molecular structure. In hot water, amylose dissolves to form a transparent, viscous solution. Amylopectin is a branched polysaccharide with a large number of branches in its molecular structure. In cold water, amylopectin forms a colloid with high viscosity.

[0016] (2) 2.0 g of the grafted polymer was dissolved in 500 mL of deionized water, and the mixture was stirred continuously. After the mixture was completely dissolved, 2.0 g of a di-long chain quaternary ammonium salt was added, and the mixture was stirred at 80° C. for 7 days. The solution was then poured into a dialysis bag, and the dialysis bag was placed in deionized water with a stirring system and stirred for 14 days, so that the unreacted di-long chain quaternary ammonium salt diffused into the deionized water through the dialysis bag. The modified polyacrylamide was then obtained after purification and drying.

[0017] The modified polyacrylamide of the invention is grafted with amylose and amylopectin and then polymerized with a quaternary ammonium salt, so that the polymerization of the modified polyacrylamide is more stable, and a large amount of positive charges can be evenly loaded on the surface, thereby enhancing the bridging effect and adsorption effect thereof, so that the suspended metatitanic acid particles are agglomerated and flocculated, and then precipitated. Meanwhile, a large amount of positive charges of the modified polyacrylamide destroy the stability of the suspended metatitanic acid particles by neutralizing the electrical property, thereby improving the sedimentation effect of the metatitanic acid.

[0018] Furthermore, di-long-chain quaternary ammonium salts include: bis(decyldimethyl)ammonium bromide, bis(decyldimethyl)ammonium chloride, dimethylbenzyl ammonium chloride, bis(dodecyldimethyl)ethylenediammonium bromide, 2-(2-phenoxyethoxy)ethyltrimethylammonium chloride, and a mixture of alkyldimethylbenzylammonium chloride and octyldecyldimethylammonium chloride.

[0019] Furthermore, the initiator is ammonium cerium nitrate, ammonium persulfate, or potassium persulfate.

[0020] Furthermore, the cationic monomer is dimethyldiallylammonium chloride, allyltrimethylammonium chloride and 3-acrylamidopropyltrimethylammonium chloride.

[0021] S3, crystallization

[0022] The ferrous yellow solution purified by S2 is mixed with the concentrated acid solution obtained by S1 and cooled to 10-30°C, which can increase the sulfuric acid concentration in the acidic wastewater, thereby increasing the recycling rate of sulfuric acid and reducing the amount of titanium gypsum generated. The amount of ferrous yellow added and the cooling temperature are controlled to mix and cool with low-concentration waste acid, and the free sulfuric acid and titanyl sulfate in the ferrous yellow are transferred to the liquid phase waste acid solution. The ferrous yellow is converted into ferrous sulfate heptahydrate, which can be directly used in downstream applications, such as the preparation of ferric phosphate or polyferric, thereby further increasing the sulfuric acid concentration in low-concentration waste acid and realizing the reuse of ferrous yellow, realizing comprehensive management of by-products, improving the economic benefits of enterprises and green sustainable development.

[0023] Through research, it is found that the conversion of ferrous iron to ferrous sulfate heptahydrate is an exothermic reaction. The amount of ferrous iron / acidic wastewater is 80%, the crystallization time is 2-3h, and the crystallization temperature is 30℃. The titanium content of ferrous iron will not affect the crystallization process. The titanium content and free sulfuric acid content of ferrous iron heptahydrate after crystallization are relatively high. The crystallized ferrous iron needs to be washed for export. When the waste acid for crystallization adopts the acid preparation process, the iron and titanium content of the concentrated waste acid is high. It is advisable to adopt the direct concentration process. The color of ferrous iron gradually changes from yellow to earthy brown as the titanium content increases. Using the secondary crystallization process, under the current conditions, 71,500 tons of ferrous iron can be processed annually, 126,300 tons of 8% acidic wastewater can be recycled, 68,200 tons of ferrous sulfate heptahydrate can be produced, and 14,300 tons of titanium can be recycled (100%), which can create a benefit of 35.06 million yuan. During the crystallization process, about 95% of the titanium in ferrous iron enters the waste acid. If the titanium is recycled, the annual cost saving is expected to be nearly 420,000 yuan.

[0024] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0025] 1. The present invention utilizes ferrous yellow produced as a byproduct of titanium dioxide to react with low-concentration waste acid to achieve waste acid concentration; and realizes low-temperature crystallization of ferrous yellow to prepare ferrous sulfate heptahydrate, thereby saving the cost of waste acid concentration, reducing the production cost of titanium dioxide, realizing the reuse of ferrous yellow, and recovering titanium resources, significantly reducing production costs, turning waste into treasure, bringing huge economic benefits to enterprises, and reducing pollution to the environment, thereby achieving green and sustainable development.

[0026] 2. The present invention adopts a secondary crystallization process, which can treat 71,500 tons of ferrous iron per year, recycle 126,300 tons of high-concentration acidic wastewater, produce 68,200 tons of ferrous sulfate heptahydrate, recycle 14,300 tons of titanium (100%), and create benefits of 35.06 million yuan. During the crystallization process, about 95% of the titanium in the ferrous iron enters the waste acid. If the titanium is recycled, the annual cost is expected to save nearly 420,000 yuan.

[0027] 3. The modified polyacrylamide of the present invention is grafted with amylose and amylopectin and then polymerized with a quaternary ammonium salt, so that the polymerization of the modified polyacrylamide is more stable, and a large amount of positive charges can be evenly loaded on the surface, thereby enhancing its bridging effect and adsorption effect, so that the suspended metatitanic acid particles are agglomerated and flocculated, and then settled. At the same time, the large amount of positive charges of the modified polyacrylamide destroy the stability of the suspended particles by neutralizing the electrical properties, thereby improving the sedimentation effect on the suspended particles. DETAILED DESCRIPTION

[0028] 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.

[0029] It should be noted that FeSO 4 Content 10%, H 2 SO 4 Content 20%, initial temperature 50℃.

[0030] Example 1

[0031] A low-concentration waste acid recovery process comprises the following steps:

[0032] S1. Preparation of Ferrous Yellow

[0033] The titanium dioxide waste acid is transported to a vacuum evaporation concentration system for vacuum evaporation concentration. Under the conditions of 0.095 MPa and 100° C., the solution in the titanium dioxide waste acid evaporates. As the solution in the titanium dioxide waste acid volatilizes, the ferrous sulfate and acidity in the titanium dioxide waste acid gradually increase. After vacuum evaporation concentration for 1 hour, the concentrated waste acid is discharged, cooled and crystallized at 15° C., the waste acid concentration is concentrated to 29%, and yellow ferrous iron is precipitated. After solid-liquid separation, yellow ferrous iron precipitation and concentrated acid solution are obtained, and the sulfuric acid concentration in the concentrated acid solution is about 50%;

[0034] S2, yellow ferrous purification

[0035] The yellow ferrous precipitate obtained in S1 was dissolved in water, heated for 1 h under stirring, and then ammonia water was added to adjust the pH value of the solution to 3, so that the titanium ions in the solution were precipitated out in the form of precipitation. After filtering, the first supernatant was obtained.

[0036] Adding an appropriate amount of ethylenediaminetetraacetic acid to the first supernatant to generate an insoluble chelated metal salt precipitate; after filtering, obtaining a second supernatant;

[0037] Add modified polyacrylamide to the second supernatant to obtain a purified ferrous yellow solution; specifically, the preparation method of modified polyacrylamide comprises the following steps:

[0038] (1) Add 500 mL of deionized water to a flask, then add 10 g of amylose to the deionized water and mix, and stir magnetically at 150°C for 1 hour to obtain a first liquid; then add 10 g of amylopectin to 500 mL of deionized water and mix, and stir magnetically at 15°C for 1 hour to obtain a second liquid; mix the first liquid and the second liquid and cool them to room temperature, add 30 g of initiator solution to the flask, react under magnetic stirring for 10 minutes, and then continue to add a mixed solution of 5 g of acrylamide monomer and 5 g of cationic monomer to the flask to react for 3 hours. After the polymerization reaction is completed, cool to room temperature, add 50 mL of anhydrous ethanol while stirring, precipitate the starch-based flocculant, filter, put it in a vacuum drying oven at 300°C and dry it to constant weight, and obtain a grafted polymer after purification;

[0039] (2) 2.0 g of the grafted polymer was dissolved in 500 mL of deionized water, and the mixture was stirred continuously. After the mixture was completely dissolved, 2.0 g of dimethylbenzyl ammonium chloride was added, and the mixture was stirred at 80° C. for 7 days. The solution was then poured into a dialysis bag, and the dialysis bag was placed in deionized water with a stirring system and stirred for 14 days, so that the unreacted dimethylbenzyl ammonium chloride diffused into the deionized water through the dialysis bag. The modified polyacrylamide was then obtained after purification and drying.

[0040] S3, crystallization

[0041] The purified ferrous sulfate solution from S2 was mixed with the concentrated acid solution from S1 in a mass ratio of 0.8:1, cooled to 30°C for 2.5 hours, and finally 68,200 tons of ferrous sulfate heptahydrate precipitate and 126,300 tons of concentrated acid product were obtained. The concentration of sulfuric acid in the concentrated acid could reach 65%. 14,300 tons of titanium (100% off) were recovered, creating a benefit of 35.06 million yuan.

[0042] Example 2

[0043] A low-concentration waste acid recovery process comprises the following steps:

[0044] S1. Preparation of Ferrous Yellow

[0045] The titanium dioxide waste acid is transported to a vacuum evaporation concentration system for vacuum evaporation concentration. Under the conditions of 0.085 MPa and 90° C., the solution in the titanium dioxide waste acid evaporates. As the solution in the titanium dioxide waste acid volatilizes, the ferrous sulfate and acidity in the titanium dioxide waste acid gradually increase. After vacuum evaporation concentration for 1 hour, the concentrated waste acid is discharged, cooled and crystallized at 20° C., the waste acid concentration is concentrated to 29%, and yellow ferrous acid is precipitated. After solid-liquid separation, yellow ferrous acid precipitation and concentrated acid solution are obtained, and the sulfuric acid concentration in the concentrated acid solution is about 48%;

[0046] S2, yellow ferrous purification

[0047] The yellow ferrous precipitate obtained in S1 was dissolved in water, heated for 1 h under stirring, and then ammonia water was added to adjust the pH value of the solution to 4, so that the titanium ions in the solution were precipitated out in the form of precipitation. After filtering, the first supernatant was obtained.

[0048] Adding an appropriate amount of N-acylethylenediaminetriacetic acid to the first supernatant to generate an insoluble chelated metal salt precipitate, and filtering to obtain a second supernatant;

[0049] Add modified polyacrylamide to the second supernatant to obtain a purified ferrous yellow solution; specifically, the preparation method of modified polyacrylamide comprises the following steps:

[0050] (1) Add 500 mL of deionized water to a flask, then add 10 g of amylose to the deionized water and mix, and stir magnetically at 130°C for 1 hour to obtain a first liquid; then add 10 g of amylopectin to 500 mL of deionized water and mix, and stir magnetically at 10°C for 1 hour to obtain a second liquid; mix the first liquid and the second liquid and cool them to room temperature, add 40 g of initiator solution to the flask, and react for 10 minutes under magnetic stirring. Then continue to add a certain amount of a mixed solution of acrylamide monomer and cationic monomer to the three-necked flask and react for 3 hours. After the polymerization reaction is completed, cool to room temperature, add 50 mL of anhydrous ethanol while stirring, precipitate the starch-based flocculant, filter, put it in a vacuum drying oven at 300°C and dry it to constant weight, and after purification, obtain a grafted polymer;

[0051] (2) 2.0 g of the grafted polymer was dissolved in 500 mL of deionized water, and the mixture was stirred continuously. After the mixture was completely dissolved, 2.0 g of dimethyl ammonium chloride was added, and the mixture was stirred at 80° C. for 7 days. The solution was then poured into a dialysis bag, and the dialysis bag was placed in deionized water with a stirring system and stirred for 14 days, so that the unreacted dimethyl ammonium chloride diffused into the deionized water through the dialysis bag. The modified polyacrylamide was then obtained after purification and drying.

[0052] S3, crystallization

[0053] The purified ferrous sulfate solution from S2 was mixed with the concentrated acid solution from S1 in a mass ratio of 0.75:1, cooled to 20°C for 2 hours, and finally 65,000 tons of ferrous sulfate heptahydrate precipitate and 124,000 tons of concentrated acid product were obtained. The concentration of sulfuric acid in the concentrated acid could reach 63%. 14,300 tons of titanium (100% off) were recovered, creating a benefit of 35.06 million yuan.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that the polyacrylamide in S3 is not modified, that is, ordinary polyacrylamide is used.

[0056] By analyzing the purified ferrous yellow solution, it was found that the quality of recoverable titanium was extremely low, and it can be concluded that the purified ferrous yellow solution cannot meet the requirements for recycling titanium.

[0057] The above are only preferred embodiments of the present invention and are 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 low-concentration waste acid recovery process, characterized in that: The following steps are involved: S1. Preparation of Ferrous Yellow The titanium dioxide waste acid is transported to a vacuum evaporation concentration system for vacuum evaporation concentration, the waste acid obtained after concentration is discharged, and then crystallized, the waste acid concentration is concentrated to 29%, and ferrous iron is precipitated, and after solid-liquid separation, ferrous iron precipitate and concentrated acid solution are obtained; S2, yellow ferrous iron purification The yellow ferrous precipitate obtained in S1 is dissolved in water, heated for a period of time under stirring, and then an appropriate amount of alkali solution is added to adjust the pH value of the solution to 2-5, so that the titanium ions in the solution are precipitated. After filtering, a first supernatant is obtained. Adding an appropriate amount of chelating agent to the first supernatant to produce insoluble chelated metal salt and form a precipitate; after filtering, obtaining a second supernatant; adding modified polyacrylamide to the second supernatant to obtain a purified ferrous yellow solution; S3, crystallization The purified ferrous yellow solution obtained in S2 is mixed with the concentrated acid solution obtained in S1, and cooled to a certain temperature so that the free sulfuric acid and titanyl sulfate in the ferrous yellow are transferred to the liquid phase, and the ferrous yellow is converted into ferrous sulfate heptahydrate.

2. The low-concentration waste acid recovery process according to claim 1, characterized in that: When crystallizing in S1, the crystallization is cooled at 10-20°C for 1 to 2 hours; in S3, the crystallization is cooled to 20-30°C for 2 to 3 hours.

3. The low-concentration waste acid recovery process according to claim 1, characterized in that: In S2, the chelating agent is any one or more of HEDTA, citric acid, ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, and N-acylethylenediamine triacetic acid.

4. The low-concentration waste acid recovery process according to claim 1, characterized in that: In S3, the added mass of ferrous iron is 75-85% of the mass of the concentrated acid solution.

5. The low-concentration waste acid recovery process according to claim 1, characterized in that: The preparation method of the modified polyacrylamide comprises the following steps: (1) adding a certain amount of amylose to water, mixing, and magnetically stirring for a period of time under high temperature conditions to obtain a first liquid; then adding a certain amount of amylopectin to deionized water, mixing, and magnetically stirring for a period of time under low temperature conditions to obtain a second liquid; mixing the first liquid and the second liquid and cooling to room temperature to obtain a colloidal solution; adding a certain amount of initiator solution to the colloidal solution, stirring for a period of time, and then adding a certain amount of a mixed solution of acrylamide monomer and cationic monomer to react for a period of time, after the polymerization reaction is completed, adding a certain amount of anhydrous ethanol to the colloidal product while stirring, precipitating a starch-based flocculant, and drying and purifying to obtain a graft polymer; (2) The grafted polymer is dissolved in water, and then a di-long chain quaternary ammonium salt is added. After stirring for a period of time, the solution is dialyzed, and then purified and dried to obtain modified polyacrylamide.

6. The low-concentration waste acid recovery process according to claim 5, characterized in that: The reaction temperature of step (1) under high temperature conditions is 100-300°C, and the reaction temperature under low temperature conditions is 5-20°C.

7. The low-concentration waste acid recovery process according to claim 5, characterized in that: The mass ratio of the amylose, amylopectin, initiator, acrylamide monomer and cationic monomer is 1:1:2-4:0.5-1:0.5-1.

8. The low-concentration waste acid recovery process according to claim 5, characterized in that: The di-long-chain quaternary ammonium salt includes any one or more of bis(decyldimethyl)ammonium bromide, bis(decyldimethyl)ethylenediammonium bromide, 2-(2-phenoxyethoxy)ethyltrimethylammonium chloride, and a mixture of alkyldimethylbenzylammonium chloride and octyldecyldimethylammonium chloride.

9. The low-concentration waste acid recovery process according to claim 5, characterized in that: The initiator is ammonium cerium nitrate, ammonium persulfate, and potassium persulfate.

10. The low-concentration waste acid recovery process according to claim 5, characterized in that: The cationic monomers are dimethyldiallylammonium chloride, allyltrimethylammonium chloride and 3-acrylamidopropyltrimethylammonium chloride.