Method for recovering waste acid in production of titanium dioxide by sulfuric acid method

Abstract

The invention relates to the technical field of production of titanium dioxide by a sulfuric acid method, and particularly discloses a method for recovering waste acid in production of titanium dioxide by the sulfuric acid method, aiming at the problem of resource waste in recovery treatment of acidic wastewater generated in the production of titanium dioxide by the sulfuric acid method. Comprising the following steps: S1, filtering and washing metatitanic acid generated by producing titanium dioxide by a sulfuric acid method, and collecting waste acid separated by filtering and washing; s2, adding a neutralizer into the collected waste acid, controlling the reaction system to be acidic, and performing neutralization precipitation reaction and solid-liquid separation to obtain a titanium filter cake and primary filtrate; s3, taking the primary filtrate, adding a neutralizer, controlling the reaction system to be weakly acidic or neutral or weakly alkaline, and carrying out neutralization precipitation reaction, solid-liquid separation, iron filter cake preparation and secondary filtrate; and S4, evaporating, concentrating and crystallizing the secondary filtrate to obtain sulfur crystals. Almost all resources in the waste acid generated in titanium dioxide production can be recovered or recycled, and resource waste caused by treatment of resources such as ferrotitanium in the waste acid as solid wastes is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of producing titanium dioxide by a sulfuric acid process, and in particular to a method for recovering waste acid in producing titanium dioxide by a sulfuric acid process. Background Art

[0002] In industrial production, the sulfuric acid method is often used to produce titanium dioxide, that is, sulfuric acid is used to acidify the titanium raw material to generate titanyl sulfate, which is then hydrolyzed to generate metatitanic acid, which is then washed, purified, and treated to produce titanium dioxide products through calcination. In the process of producing titanium dioxide by the sulfuric acid method, the filtration and washing and purification process of the hydrolyzed metatitanic acid precipitate is the main process and source of the production of waste acid and acidic wastewater. The chemical reaction process of the hydrolysis is as follows:

[0003] Ti(SO4) 2(液) + H2O + Heat + Seed → TiOSO 4(液) + H2SO 4(液) (1);

[0004] TiOSO 4(液) + 3H2O → Ti(OH) 4(固) + H2SO 4(液) (2).

[0005] The precipitate produced by hydrolysis and the sulfuric acid solution containing impurities need to be separated by impurity removal, that is, filtered and washed after the reaction. However, due to the limitations of the hydrolysis reaction in actual industrial production, the hydrolysis rate is usually only about 95%, so for every ton of titanium dioxide produced, about 40-50 kg of titanium remains in the liquid phase after filtration and washing. The separated liquid after filtration and washing also needs to be washed with water to remove colored impurity ions, such as iron sulfate, etc., so a large amount of waste sulfuric acid will be generated. For every ton of titanium dioxide produced, about 5 tons of waste sulfuric acid will be generated. The total amount of waste sulfuric acid is affected by the production process and equipment, and these waste acids contain a large amount of resources such as iron and titanium.

[0006] In traditional processes, evaporation and concentration are often used to separate and recover the residual titanium in the waste acid. For example, the patent with publication number CN101214931A provides a method for concentrating and removing impurities from dilute sulfuric acid in the process of producing titanium dioxide by sulfuric acid method, wherein the dilute sulfuric acid is first sent to the mixing acid tank, and after the dilute sulfuric acid is concentrated into concentrated sulfuric acid, a part of it is returned to the mixing acid tank, mixed into feed acid, and sent to the steam concentration system for multi-effect evaporation concentration. Another part of the concentrated sulfuric acid material is returned to the mixing acid tank, and the remaining part enters the series-type countercurrent cooling, maturation and crystal growing tank. In the countercurrent cooling, maturation and crystal growing tank, the sulfuric acid material after maturation and crystal growing cooling is sent to a solid-liquid separator for solid-liquid separation, and the filtrate is the concentrated sulfuric acid product.

[0007] However, the existing traditional treatment methods such as the above fail to achieve the separation and recovery of various valuable resources such as titanium and iron in acidic wastewater, and thus there are still problems such as waste of resources. Summary of the invention

[0008] The purpose of the present invention is to solve the problem that the various valuable resources such as titanium and iron in the waste acid cannot be fully separated and recovered during the current recovery and treatment of waste acid produced in the production of titanium dioxide by the sulfuric acid method, thereby causing waste of resources.

[0009] The present invention is achieved through the following technical solutions:

[0010] The present invention provides a method for recovering waste acid in the production of titanium dioxide by a sulfuric acid process, comprising the following steps:

[0011] A method for recovering waste acid in the production of titanium dioxide by sulfuric acid method comprises the following steps:

[0012] S1 filters and washes the metatitanic acid produced by the sulfuric acid process in the production of titanium dioxide, and collects the waste acid separated by filtration and washing;

[0013] S2 takes the collected waste acid, adds a neutralizing agent, controls the reaction system to be acidic, performs a neutralization precipitation reaction, and separates the solid and liquid to obtain a titanium filter cake and a primary filtrate;

[0014] S3 takes the primary filtrate, adds a neutralizing agent, controls the reaction system to be weakly acidic, neutral or weakly alkaline, performs a neutralization precipitation reaction, solid-liquid separation, an iron filter cake and a secondary filtrate;

[0015] S4 evaporates, concentrates and crystallizes the secondary filtrate to obtain sulfur crystals.

[0016] Preferably, in step S1, only the waste acid in the initial washing stage is collected, and the mass concentration of sulfuric acid ≥ 7% is used as the dividing node in the initial washing stage.

[0017] Preferably, the initial washing liquid waste acid is mixed with the filtrate waste acid, and the obtained filtrate mixed waste acid is used as the waste acid collected in step S2, and the sulfuric acid mass concentration of the filtrate mixed waste acid is controlled to be ≥10%. By utilizing the change in the concentration of the initial waste acid and the later waste acid of the washing liquid by metatitanic acid, the concentration is differentiated, and the impurities are removed by maintaining a high concentration. The alkaline chemical energy of the ammonia neutralizer can neutralize the sulfuric acid in the acidic washing water and replace the sulfate ions in the metal sulfate. Before and after the neutralization precipitation treatment, the chemical properties of the ammonia neutralizer as a nitrogen fertilizer resource have unchanged characteristics, avoiding the generation of more waste gas or solid waste due to the neutralization precipitation treatment, reducing the subsequent further processing discharge or stacking problems, and avoiding the problem of thin impurities in the recovery of acidic wastewater with low impurity concentration.

[0018] Preferably, the neutralizing agent includes one or more of ammonia gas, ammonia water, green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt.

[0019] Preferably, in step S2, the pH value of the reaction system is controlled to be 1.0-4.0, and the reaction residence time is 0.5-2.5 h.

[0020] Preferably, in step S3, the pH value of the reaction system is controlled to be 6.0-8.0, and the reaction residence time is 1-3 hours.

[0021] Preferably, in step S2 and step S3, while adding the neutralizing agent, air is blown in and graphene is added.

[0022] Furthermore, in step S2, graphene oxide or graphene aerogel and a photocatalyst are added while adding a neutralizing agent; in step S3, air is blown in while adding a neutralizing agent, and magnetic graphene or porous graphene is added.

[0023] In the above-mentioned waste acid recovery process, the following reaction processes are involved:

[0024] H2SO4 + 2NH4OH → (NH4)2SO4 + 2H2O (3);

[0025] TiOSO4 + 2(NH)4OH + H2O → TiO2·2H2O↓ + (NH4)2SO4 (4);

[0026] FeSO4 + (NH)4OH → Fe(OH)2 ↓+ (NH4)2SO4 (5);

[0027] 2Fe(OH)2 + 1 / 2O2 + H2O → 2Fe(OH)3↓ (6).

[0028] That is, in the process of washing the titanic acid produced by the sulfuric acid method for producing titanium dioxide, the initial washing liquid is collected in sections, that is, the washing liquid produced in the initial washing process of the titanic acid is recovered and mixed with the filtrate, and the sulfuric acid and ammonia therein are neutralized to form ammonium sulfate. As the neutralization acidity gradually decreases, the soluble titanium therein begins to be precipitated. After separating and recovering the precipitated titanium, the weakly acidic solution is further added with ammonia for neutralization and precipitation reaction, and hydroxides of iron and trace metals are precipitated. Precipitation and separation are then carried out to recover metal resources such as iron, and the obtained ammonium sulfate solution is evaporated, concentrated and crystallized to produce ammonium sulfate products.

[0029] In addition, the titanium recovered by precipitation can be returned to the production system, reducing the consumption of titanium raw materials and increasing economic benefits. It can also be directly used for high-value processing of nano-titanium. The iron recovered by precipitation can be processed as a low-performance iron-based pigment or reduced to produce metallic iron powder for its own titanium dioxide production, etc., saving the purchase of external metallic iron powder raw materials. The condensed water from the concentrated and evaporated secondary filtrate can be sent back to the titanium dioxide production process to replace the original process water, thereby realizing the recycling of water resources.

[0030] The technical solution of the present invention has the following beneficial effects:

[0031] The invention performs multi-stage separation and recovery of the acidic wastewater metatitanic acid washing liquid generated by the sulfuric acid method for producing titanium dioxide, adopts an ammonia neutralizer, blows in air to accelerate the precipitation of iron elements, and is supplemented with separation media such as graphene. The neutralizer reacts with sulfuric acid and sulfate in the acidic wastewater to form an ammonium sulfate solution, and can recover iron and titanium elements respectively, thereby achieving effective recovery and utilization of all key titanium iron resources remaining in the liquid phase after the metatitanic acid is hydrolyzed. This not only solves the problem that the existing treatment technology discards all resources in the hydrolysis liquid phase as waste, generates a large amount of solid and liquid wastes without recycling, but also recovers titanium iron water and sulfur resources, reduces resource waste, and alleviates the impact on the natural environment caused by the discharge of a large amount of solid waste and neutralization wastewater. DETAILED DESCRIPTION

[0032] 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. Where specific conditions are not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents and raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0033] The present invention provides a method for recovering waste acid in the production of titanium dioxide by a sulfuric acid process, comprising the following steps: (1)

[0035] The metatitanic acid produced in the process of producing titanium dioxide by the sulfuric acid method is filtered and washed, and the initial washing liquid waste acid is recovered in stages, and the initial washing liquid waste acid and the hydrolyzed metatitanic acid filtrate waste acid are mixed to obtain the filtered and washed mixed waste acid;

[0036] The specific process of segmented recycling mainly includes:

[0037] About one third of the initial waste acid of the titanate acid washing liquid is recovered, and the mass concentration of sulfuric acid in the initial waste acid of the titanate acid washing liquid is controlled to be not less than 7% as the segmentation standard. The recovered initial titanate acid washing liquid is then mixed with the waste acid of the hydrolyzed titanate acid filtrate, and the mass concentration of sulfuric acid in the mixed liquid is controlled to be not less than 10%. (2)

[0039] The filtrate and wash mixed liquid is sent to a titanium recovery tank, a neutralizer is added, the pH value of the reaction system is controlled to be 1.0-4.0, and a titanium recovery neutralization precipitation reaction is performed. The reaction residence time is 0.5-2.5 hours. After the reaction, the slurry is solid-liquid separated to obtain a titanium filter cake and a primary filtrate respectively;

[0040] The neutralizer can be selected from one or more of ammonia, ammonia water, green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt, etc. At the same time, graphene oxide or graphene aerogel is added, and titanium is adsorbed and separated through the action of photocatalyst. (3)

[0042] The separated titanium filter cake is sent back to the titanium dioxide production process, the primary filtrate is sent to the iron recovery tank, and a neutralizer is added to the iron recovery tank, air is blown in, and the pH value of the reaction system is controlled to be 6.0-8.0, and an iron recovery neutralization precipitation reaction is performed. The reaction residence time is 1-3 hours. After the reaction, the slurry is solid-liquid separated to obtain an iron filter cake and a secondary filtrate respectively, and the iron filter cake is dried to obtain a ferric hydroxide product;

[0043] During the neutralization and precipitation process in this step, air is blown in and magnetic graphene or porous graphene is added to assist in more complete separation of the iron element and improve the recovery rate of iron resources. (4)

[0045] The secondary filtrate is collected and evaporated, concentrated and crystallized using an MVR device to recover the sulfur resources in the secondary filtrate to obtain ammonium sulfate products.

[0046] Example 1

[0047] Step 1: Wash and filter the metatitanic acid produced in the process of producing titanium dioxide by sulfuric acid method, and take the initial washing liquid after washing for the first 70 minutes, the volume of which is about 10 tons / ton of titanium dioxide. The sulfuric acid content of the collected initial washing liquid is tested, and the results are shown in Table 1:

[0048] Table 1 Initial washing liquid composition in Example 1

[0049] Components <![CDATA[H2SO4]]> FeO <![CDATA[TiO2]]> MgO <![CDATA[Al2O3]]> CaO content(%) 8.51 2.06 0.27 0.14 0.10 0.02

[0050] The initial washing liquid and the hydrolyzed metatitanic acid filtrate were mixed at a volume ratio of 2:1 to obtain a filtrate-washing mixed liquid, and the content of sulfuric acid and the like in the filtrate-washing mixed liquid was tested. The results are shown in Table 2 below:

[0051] Table 2 Filtration and washing mixed liquor composition in Example 1

[0052]

[0053]

[0054] Step 2: 50m 3 The mixed liquid is sent to 80m 3 The titanium recovery tank is provided with a stirring mechanism and an ammonia pipe is provided at the bottom of the titanium recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe, and graphene oxide and nano-TiO2 are added to allow the filtrate and wash mixed liquid to fully contact and react with ammonia. During this period, the pH value of the slurry is controlled at about 2.5, and the slurry reaction residence time is maintained at 1 hour to neutralize the titanium oxysulfate in the filtrate and wash mixed liquid.

[0055] Step 3: After the neutralization and precipitation reaction in the titanium recovery tank is completed, the slurry is sent to the tubular filter through the delivery pump for filtration. After filtration, the thick slurry is continuously sent to the filter press through the filter press pump tank for filter press separation, and washed with 1T of circulating MVR evaporation and concentration condensate water. About 455.5kg of titanium filter cake with a water content of about 55% is obtained per hour. The filtrate after filtration by the tubular filter and the filter press washing liquid are combined to obtain 50.50m 3 The titanium is recovered from the primary filtrate.

[0056] Step 4: Recover the above titanium to obtain 50.50m 3 The first filtrate is sent to 80m 3 The iron recovery tank is of large capacity and is provided with a stirring mechanism. An ammonia pipe and an air pipe are distributed at the bottom of the iron recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe, and air is blown into the air pipe. Magnetic graphene is added to allow the filtrate-washing mixed liquid to fully contact and react with ammonia. During this period, the pH value of the slurry is controlled at about 6.5, and the slurry reaction residence time is maintained at 1.5 hours to neutralize ferrous sulfate and other metal sulfates in the primary filtrate.

[0057] Step 5: After the neutralization and precipitation reaction in the iron recovery tank is completed, the slurry is sent to the filter press through the filter press pump tank for filter press separation, and washed with 4T circulating MVR evaporation and concentration condensate water, and about 3898.5kg of iron filter cake with a water content of about 50% is obtained per hour. After drying, iron hydroxide is obtained; the filtrate and washing liquid after filter press are combined to obtain 52.6m 3 The ammonium sulfate solution with a mass content of 16.52% is sent to the MVR concentration and evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation to obtain 9.14t of ammonium sulfate with a water content of about 5% and 42m 3 Evaporate the condensed water.

[0058] Example 2

[0059] Step 1: Wash and filter the metatitanic acid produced in the process of producing titanium dioxide by sulfuric acid method, and take the initial washing liquid after washing for the first 60 minutes, the volume of which is about 9 tons / ton of titanium dioxide. The sulfuric acid content of the collected initial washing liquid is tested, and the results are shown in Table 3:

[0060] Table 3 Initial washing liquid composition in Example 1

[0061] Components <![CDATA[H2SO4]]> FeO <![CDATA[TiO2]]> MgO <![CDATA[Al2O3]]> CaO content(%) 9.62 2.33 0.31 0.22 0.11 0.02

[0062] The initial washing liquid and the hydrolyzed metatitanic acid filtrate were mixed at a volume ratio of 2:1 to obtain a filtrate-washing mixed liquid, and the content of sulfuric acid and the like in the filtrate-washing mixed liquid was tested. The results are shown in Table 4 below:

[0063] Table 4 Filtration and washing mixed liquor composition in Example 1

[0064] Components <![CDATA[H2SO4]]> FeO <![CDATA[TiO2]]> MgO <![CDATA[Al2O3]]> CaO content(%) 13.58 3.29 0.43 0.21 0.16 0.03

[0065] Step 2: 50m 3 The mixed liquid is sent to 80m 3 The titanium recovery tank is provided with a stirring mechanism and an ammonia pipe is provided at the bottom of the titanium recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe. Graphene aerogel and nano-TiO2 are added to allow the filtrate and wash mixed liquid to fully contact and react with ammonia. During this period, the pH value of the slurry is controlled at about 2.5, and the slurry reaction residence time is maintained at 1 hour to neutralize the titanium oxysulfate in the filtrate and wash mixed liquid.

[0066] Step 3: After the neutralization and precipitation reaction in the titanium recovery tank is completed, the slurry is sent to the tubular filter through the delivery pump for filtration. After filtration, the thick slurry is continuously sent to the filter press through the filter press pump tank for filter press separation, and washed with 1T of circulating MVR evaporation and concentration condensate water. About 477.7kg of titanium filter cake with a water content of about 55% is obtained per hour. The filtrate after filtration by the tubular filter and the filter press washing liquid are combined to obtain 50.50m 3 The titanium is recovered from the primary filtrate.

[0067] Step 4: Recover the above titanium to obtain 50.50m 3 The first filtrate is sent to 80m 3 The iron recovery tank is of large capacity and is provided with a stirring mechanism. An ammonia pipe and an air pipe are distributed at the bottom of the iron recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe, and air is blown into the air pipe. Porous graphene is added to allow the filtrate-washing mixed liquid to fully contact and react with ammonia. During this period, the pH value of the slurry is controlled at about 6.5, and the slurry reaction residence time is maintained at 1.5 hours to neutralize ferrous sulfate and other metal sulfates in the primary filtrate.

[0068] Step 5: After the neutralization and precipitation reaction in the iron recovery tank is completed, the slurry is sent to the filter press through the filter press pump tank for filter press separation, and washed with 4T circulating MVR evaporation and concentration condensate water, and about 4124.1kg of iron filter cake with a water content of about 50% is obtained per hour. After drying, iron hydroxide is obtained; the filtrate and washing liquid after filter press are combined to obtain 52.4m 3 The ammonium sulfate solution with a mass content of 17.45% is sent to the MVR concentration and evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation to obtain 9.73t of ammonium sulfate with a water content of about 6% and 42.6m 3 Evaporate the condensed water.

[0069] Example 3

[0070] Step 1: Wash and filter the metatitanic acid produced in the process of producing titanium dioxide by sulfuric acid method, and take the initial washing liquid after washing for the first 50 minutes, the volume of the washing liquid is about 6.5 tons / ton of titanium dioxide. The sulfuric acid content of the collected initial washing liquid is tested, and the results are shown in Table 5:

[0071] Table 5 Initial washing liquid composition in Example 1

[0072] Components <![CDATA[H2SO4]]> FeO <![CDATA[TiO2]]> MgO <![CDATA[Al2O3]]> CaO content(%) 11.62 2.42 0.38 0.27 0.13 0.02

[0073] Step 2: 50m 3 Initial washing liquid is sent to 80m 3 The titanium recovery tank is provided with a stirring mechanism and an ammonia pipe is provided at the bottom of the titanium recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe so that the filtrate and wash mixed liquid can fully contact and react with the ammonia. During this period, the pH value of the slurry is controlled at about 2.5, and the slurry reaction residence time is maintained at 1 hour to neutralize the titanium oxysulfate in the filtrate and wash mixed liquid.

[0074] Step 3: After the neutralization precipitation reaction in the titanium recovery tank is completed, the slurry is sent to the tubular filter through the delivery pump for filtration. After filtration, the thick slurry is continuously sent to the filter press through the filter press pump tank for filter press separation, and washed with 1T of circulating MVR evaporation and concentration condensate water. About 422.2kg of titanium filter cake with a water content of about 55% is obtained per hour. The filtrate after filtering by the tubular filter and the filter press washing liquid are combined to obtain 50.73m 3 The titanium is recovered from the primary filtrate.

[0075] Step 4: Recover the above titanium to obtain 50.73m 3 The first filtrate is sent to 80m 3The slurry is placed in an iron recovery tank with a capacity of 1.5 m / s and is provided with a stirring mechanism. An ammonia pipe and an air pipe are provided at the bottom of the iron recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe, and air is blown into the air pipe so that the filtrate-washing mixed liquid can fully contact and react with the ammonia. During this period, the pH value of the slurry is controlled at about 6.5, and the slurry reaction residence time is maintained at 1.5 h to neutralize the ferrous sulfate and other metal sulfates in the primary filtrate.

[0076] Step 5: After the neutralization and precipitation reaction in the iron recovery tank is completed, the slurry is sent to the filter press through the filter press pump tank for filter press separation, and washed with 4T circulating MVR evaporation and concentration condensate water, and about 3033.5kg of iron filter cake with a water content of about 50% is obtained per hour. After drying, iron hydroxide is obtained; the filtrate and washing liquid after filter press are combined to obtain 53.21m 3 The ammonium sulfate solution with a mass content of 14.71% is sent to the MVR concentration and evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation to obtain 8.15t of ammonium sulfate with a water content of about 4% and 45.06m 3 Evaporate the condensed water.

[0077] Example 4

[0078] Step 1: Wash and filter the metatitanic acid produced in the process of producing titanium dioxide by the sulfuric acid method, and control the volume of the washing liquid to be about 5 tons / ton of titanium dioxide. The sulfuric acid content of the collected washing liquid is tested, and the results are shown in Table 1 below:

[0079] Table 1 Initial washing liquid composition in Example 1

[0080] Components <![CDATA[H2SO4]]> FeO <![CDATA[TiO2]]> MgO <![CDATA[Al2O3]]> CaO content(%) 21.5 5.20 0.68 0.36 0.25 0.043

[0081] Step 2: 43.5m 3 Washing liquid is fed to 80m 3 The titanium recovery tank is provided with a stirring mechanism and an ammonia pipe is provided at the bottom of the titanium recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe so that the filtrate and wash mixed liquid can fully contact and react with the ammonia. During this period, the pH value of the slurry is controlled at about 2.5, and the slurry reaction residence time is maintained at 1 hour to neutralize the titanium oxysulfate in the filtrate and wash mixed liquid.

[0082] Step 3: After the neutralization and precipitation reaction in the titanium recovery tank is completed, the slurry is sent to the tubular filter through the delivery pump for filtration. After filtration, the thick slurry is continuously sent to the filter press through the filter press pump tank for filter press separation, and washed with 1T of circulating MVR evaporation and concentration condensate water. About 755.5kg of titanium filter cake with a water content of about 55% is obtained per hour. The filtrate after filtration by the tubular filter and the filter press washing liquid are combined to obtain 50.58m 3 The titanium is recovered from the primary filtrate.

[0083] Step 4: Recover the above titanium to obtain 50.58m 3 The first filtrate is sent to 80m 3 The slurry is placed in an iron recovery tank with a capacity of 1.5 m / s and is provided with a stirring mechanism. An ammonia pipe and an air pipe are provided at the bottom of the iron recovery tank. Ammonia is continuously blown into the tank through the ammonia pipe, and air is blown into the air pipe so that the filtrate-washing mixed liquid can fully contact and react with the ammonia. During this period, the pH value of the slurry is controlled at about 6.5, and the slurry reaction residence time is maintained at 1.5 h to neutralize the ferrous sulfate and other metal sulfates in the primary filtrate.

[0084] Step 5: After the neutralization and precipitation reaction in the iron recovery tank is completed, the slurry is sent to the filter press through the filter press pump tank for filter press separation, and washed with 4T circulating MVR evaporation and concentration condensate water, and about 6518.3kg of iron filter cake with a water content of about 50% is obtained per hour. After drying, iron hydroxide is obtained; the filtrate and washing liquid after filter press are combined to obtain 51.32m 3 The ammonium sulfate solution with a mass content of 28.21% is sent to the MVR concentration and evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation to obtain 15.40t of ammonium sulfate with a water content of about 6% and 35.92m 3 Evaporate the condensed water.

[0085] Through the treatment results of the above embodiments 1-4, it can be verified that the waste acid recovery method in the production of titanium dioxide by the sulfuric acid method proposed in the present invention can effectively recover the titanium iron resources in the waste liquid, and for every acidic wastewater generated by the production of 1 ton of titanium dioxide, hundreds of kilograms of titanium iron sulfur resources can be recovered, and a large amount of waste gas and solid waste emissions into natural water bodies and the environment can be avoided, and the recycling and reuse of resources such as water can be achieved to a greater extent, which brings significant economic benefits to producers and promotes the green and sustainable development of titanium dioxide production technology.

[0086] 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 method for recovering waste acid in the production of titanium dioxide by sulfuric acid method, characterized in that: The following steps are involved: S1 filters and washes the metatitanic acid produced by the sulfuric acid process in the production of titanium dioxide, and collects the waste acid separated by filtration and washing; S2 takes the collected waste acid, adds a neutralizing agent, controls the reaction system to be acidic, performs a neutralization precipitation reaction, and separates the solid and liquid to obtain a titanium filter cake and a primary filtrate; S3 takes the primary filtrate, adds a neutralizing agent, controls the reaction system to be weakly acidic, neutral or weakly alkaline, performs a neutralization precipitation reaction, solid-liquid separation, an iron filter cake and a secondary filtrate; S4 evaporates, concentrates and crystallizes the secondary filtrate to obtain sulfur crystals.

2. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S1, only the waste acid in the initial stage of washing is collected, and the mass concentration of sulfuric acid ≥ 7% is used as the division node in the initial stage of washing.

3. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 2, characterized in that: The initial washing liquid waste acid is mixed with the hydrolyzed metatitanic acid filtrate waste acid to obtain the filtration and washing mixed waste acid as the collected waste acid for step S2, and the sulfuric acid mass concentration of the filtration and washing mixed waste acid is controlled to be ≥10%.

4. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid method according to any one of claims 1 to 3, characterized in that: The neutralizing agent includes one or more of ammonia gas, ammonia water, green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt.

5. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 4, characterized in that: In step S2, the pH value of the reaction system is controlled to be 1.0-4.0, and the reaction residence time is 0.5-2.5h.

6. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 4, characterized in that: In step S3, the pH value of the reaction system is controlled to be 6.0-8.0, and the reaction residence time is 1-3 hours.

7. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 4, characterized in that: In step S2 and step S3, while adding the neutralizing agent, air is blown in and graphene is added.

8. The method for recovering waste acid in the production of titanium dioxide by sulfuric acid process according to claim 7, characterized in that: In step S2, graphene oxide or graphene aerogel and photocatalyst are added while adding the neutralizer; in step S3, air is blown in while adding the neutralizer, and magnetic graphene or porous graphene is added.