Method and treatment system for synergetic resource utilization of titanium white waste acid and acid wastewater

Abstract

The invention relates to the technical field of resource recovery, in particular to a titanium white waste acid and acid wastewater collaborative resource utilization method and a treatment system. The method comprises the following steps: carrying out membrane concentration pretreatment on acidic wastewater generated in the titanium dioxide production process to obtain reuse water and concentrated acid water containing sulfuric acid and metal ions; mixing the concentrated acid water with the pretreated titanium dioxide waste acid to obtain mixed waste acid, and feeding the mixed waste acid into a multi-effect evaporation and concentration unit for concentration to obtain concentrated waste acid; the concentrated waste acid is subjected to a pre-pyrolysis drying reaction at the temperature of 250-400 DEG C, and a solid product and sulfur-containing tail gas are obtained; the sulfur-containing tail gas is condensed, concentrated sulfuric acid with the mass concentration not lower than 90% is obtained through recovery, and uncondensed tail gas is discharged after being purified. By precisely regulating and controlling the temperature window of the pre-pyrolysis drying reaction, solid products can be directionally produced, the additional value is remarkably improved, the acid purchasing cost of enterprises can be reduced by recycling high-purity concentrated sulfuric acid, and the overall economic benefit is very remarkable.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a method and treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater. Background Technology

[0002] In the sulfuric acid process for titanium dioxide production, the ore undergoes decomposition, dilution, hydrolysis, and calcination with concentrated sulfuric acid. While producing titanium dioxide, this process inevitably generates a large amount of acidic byproducts, including low-concentration waste sulfuric acid (commonly known as titanium dioxide waste acid) with a sulfuric acid mass fraction of approximately 20%–25%, and acidic wastewater from the washing, filtration, and cooling systems. Besides sulfuric acid, titanium dioxide waste acid also contains large amounts of ferrous sulfate, silica gel, aluminum salts, and unreacted impurities, while the acidic wastewater is also highly acidic and rich in fine, difficult-to-settle particles.

[0003] On the one hand, the industry currently uses limestone or carbide slag to neutralize waste acid, converting the sulfuric acid into calcium sulfate (titanium gypsum) solid. While this most common treatment method is simple, the resulting titanium gypsum has high impurity content and unstable crystal structure, resulting in quality far below that of building gypsum or industrial by-product gypsum. This makes large-scale resource utilization difficult, and most of it is simply stockpiled. With the increase in titanium dioxide production, the stockpiled titanium gypsum continues to rise, occupying a huge area and potentially causing environmental risks such as leachate pollution. Furthermore, this method neutralizes a large amount of sulfuric acid in a single step, making recycling impossible. Companies need to continuously replenish fresh sulfuric acid, resulting in significant resource waste and increased operating costs. On the other hand, acidic wastewater from the production process is typically treated with alkali neutralization and precipitation before discharge. However, this method not only generates large amounts of sludge containing impurities, increasing the wastewater treatment load, but also directly discharges water resources that could be reused, failing to meet the industry's needs for water conservation, emission reduction, and near-zero emissions.

[0004] While there are existing cases of applying the "concentration-pyrolysis" process to treat pickling waste acid in the stainless steel industry, this process relies on high-temperature electric furnace pyrolysis, resulting in a lengthy and energy-intensive process. The final product, a mixed metal oxide, has a complex composition and low value, making it difficult to cover its operating costs. Furthermore, this technology does not consider co-treatment with acidic wastewater, limiting its resource utilization efficiency. More importantly, the composition of titanium dioxide waste acid differs significantly from that of stainless steel pickling waste acid. The large amounts of ferrous sulfate and colloidal silica impurities it contains are highly susceptible to crystallization or gelation on the heat exchange surface during evaporation and concentration, leading to rapid scaling and blockage of the evaporator. This drastically shortens the equipment's operating cycle, and frequent shutdowns for cleaning not only affect production continuity but also significantly increase maintenance costs, making it difficult to practically promote this technology in the titanium dioxide industry. Summary of the Invention

[0005] To address the common technical problems of high energy consumption, low product value, insufficient resource utilization, unstable operation, and inability to achieve internal system circulation in existing waste acid and acidic wastewater treatment methods, this invention provides a method and treatment system for the synergistic resource utilization of waste acid and acidic wastewater from titanium dioxide production. This method enables the synergistic treatment of waste acid and wastewater, features a simple process, low energy consumption, high product value, and long-term stable operation. It fundamentally solves the problem of treating waste acid and acidic wastewater from titanium dioxide production, achieves efficient recycling of sulfuric acid and water resources, and reduces solid waste emissions.

[0006] The specific technical solution is as follows: In a first aspect, the present invention provides a method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater, comprising the following steps: (1) The acidic wastewater generated during the production of titanium dioxide is pretreated by membrane concentration to obtain recycled water and concentrated acid water containing sulfuric acid and metal ions; (2) Mix concentrated acid water with pretreated titanium dioxide waste acid to obtain mixed waste acid, which is then sent to a multi-effect evaporation concentration unit for concentration to obtain concentrated waste acid; (3) The concentrated waste acid is preheated and dried at a temperature of 250~400℃ to obtain solid products and sulfur-containing tail gas; (4) The sulfur-containing tail gas is condensed and recovered to obtain concentrated sulfuric acid with a mass concentration of not less than 90%. The uncondensed tail gas is purified and then discharged.

[0007] Furthermore, in step (3), the reaction temperature is controlled at 350~400℃, and the solid product obtained is ferrous sulfate monohydrate.

[0008] Furthermore, in step (3), the reaction temperature is controlled at 250~300℃, and the obtained solid product is an intermediate containing ferrous sulfate and sulfuric anhydride; the intermediate is subjected to a pyrolysis reaction at 450~650℃ to generate crude iron oxide.

[0009] Furthermore, in step (1), the membrane used for membrane concentration pretreatment is a nanofiltration membrane or a reverse osmosis membrane; the recovery rate of recycled water is ≥70%, the rejection rate of metal ions is ≥95%; and the mass concentration of sulfuric acid in concentrated acid water is increased to 15%~25%.

[0010] Furthermore, in step (2), the mixing volume ratio of titanium dioxide waste acid to concentrated acid water is (3~5):1; multi-effect evaporation concentration is converted to triple-effect evaporation, the temperature of the first effect evaporation is controlled at 130~150℃, and the temperature of the last effect evaporation is 60~80℃.

[0011] Furthermore, in step (2), the pretreatment of titanium dioxide waste acid includes sedimentation and filtration; the mass concentration of the concentrated waste acid is 38%~42%.

[0012] Furthermore, the purification process in step (4) is a three-stage purification process, which consists of acid washing with 20wt%~30wt% dilute sulfuric acid, water washing with deionized water, and alkaline washing with 5%~10% sodium hydroxide solution.

[0013] Secondly, the present invention also provides a processing system for implementing the above-mentioned method, including a membrane concentration pretreatment unit, which is provided with a recycled water outlet and a concentrated acid water outlet. The concentrated acid water outlet is connected to the inlet of a mixing tank, and the outlet of a mixing pipe is connected to the inlet of a multi-effect evaporation concentration unit. The concentrated waste acid outlet of the multi-effect evaporation concentration unit is connected to the inlet of a controllable pyrolysis drying unit via a corrosion-resistant high-pressure pump. The tail gas outlet of the controllable pyrolysis drying unit is connected to the inlet of a tail gas resource utilization unit, and the solid product outlet of the controllable pyrolysis drying unit is connected to a solid product collection device.

[0014] Furthermore, the membrane concentration pretreatment unit includes a raw water tank, a feed pump, a pretreatment filter, and a membrane separation device, which is an acid-resistant nanofiltration membrane or a reverse osmosis membrane system.

[0015] Furthermore, the controllable pyrolysis drying unit is a spray dryer, which includes a tower body, an atomizer at the top of the tower body, a hot air inlet connected to a hot air distributor at the side or top of the tower body, and a solid product outlet connected to a product collection system at the bottom of the tower body.

[0016] Concentrated waste acid is pumped to the atomizer by a corrosion-resistant high-pressure pump, causing it to be immediately atomized into fine droplets upon entering the tower. A hot air distributor connects to the hot air inlet of the tower, evenly distributing hot air at a specific temperature into the tower, creating a co-current contact with the droplets falling from the top. During this direct contact between the droplets and the hot air within the tower, moisture evaporates rapidly, and ferrous sulfate undergoes simultaneous dehydration and pyrolysis. The resulting solid product is collected by the product collection system and transported to a solid product collection device via the solid product outlet. The exhaust gas outlet at the top of the tower connects to the inlet of the exhaust gas resource recovery unit, used to remove sulfur-containing exhaust gas generated during drying and pyrolysis. The entire spray drying process achieves rapid liquid-to-solid conversion through the synergistic action of the atomizer, hot air distributor, and the internal space of the tower, realizing the drying and controlled pyrolysis of the concentrated waste acid.

[0017] Furthermore, the processing system also includes a pyrolysis furnace, which can be a rotary kiln, a fluidized bed furnace, or a multi-stage series suspension roasting system. The feed inlet of the pyrolysis furnace is connected to the solid product outlet of the controllable pyrolysis drying unit to receive intermediates and carry out pyrolysis reactions.

[0018] Furthermore, the exhaust gas resource recovery unit includes a condenser and an exhaust gas purification tower connected thereto; the bottom of the condenser is equipped with a concentrated sulfuric acid outlet, and the exhaust gas purification tower is a three-stage packed tower, which includes an acid washing section, a water washing section and an alkaline washing section.

[0019] The beneficial effects of this invention are as follows: 1. This invention discloses a method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater. By precisely controlling the temperature window of the controllable pyrolysis drying unit, ferrous sulfate monohydrate can be directly obtained at 350-400℃, or an intermediate can be prepared at 250-300℃ followed by pyrolysis at 450-650℃ to obtain crude iron oxide, thus achieving targeted production of solid products. Compared with the extremely low-value and difficult-to-utilize titanium gypsum in traditional processes, the added value of the products obtained by this invention is significantly increased, and the recovery of high-purity concentrated sulfuric acid can greatly reduce the amount and cost of fresh acid purchased by enterprises, resulting in significant overall economic benefits.

[0020] 2. This invention provides a treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater. By deeply coupling units such as membrane concentration pretreatment, multi-effect evaporation concentration, controlled pyrolysis drying, and tail gas resource utilization, the synergistic treatment of titanium dioxide waste acid and acidic wastewater is achieved. Compared with the existing mode of decentralized treatment of the two types of waste, this invention not only achieves a high degree of process chain unification, but also achieves efficient enrichment of recyclable components in acidic wastewater through the introduction of membrane technology. This allows sulfuric acid, metal ions, and water resources in the waste acid system to be recycled within the system, thus forming a closed-loop process of material and energy coupling. This synergistic mode significantly improves the overall resource utilization level of the system, ultimately obtaining multiple high-value products such as recycled water, ≥90wt% concentrated sulfuric acid, and ferrous sulfate monohydrate or ferric oxide, completely overcoming the limitations of traditional processes that can only produce low-value-added titanium gypsum or mixed metal oxides.

[0021] 3. Regarding energy consumption, this invention avoids the electric furnace pyrolysis stage at up to 1100℃ found in existing concentration-pyrolysis technologies. By employing triple-effect evaporation to reduce phase change energy consumption and utilizing membrane pretreatment to lower the evaporation load, the overall energy consumption of the system is reduced by more than 30% compared to traditional technologies. The process is more compact, and operating costs are significantly reduced. Simultaneously, by rationally controlling the final evaporation concentration and the ratio of ferrous sulfate to colloidal silica in the waste acid, this invention significantly inhibits evaporation scaling and heat exchanger blockage. Combined with optimized corrosion-resistant equipment configuration, the entire system can achieve long-term stable operation, significantly improving reliability. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of a treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater according to Embodiment 1 of this application; wherein, 101, membrane concentration pretreatment unit; 201, mixing tank; 301, triple-effect evaporation concentration unit; 401, spray dryer; 501, tail gas resource utilization unit; 501a, condenser; 501b, tail gas purification tower; 601, solid product collection device.

[0024] Figure 2 This is a schematic flowchart of a method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater in Embodiment 1 of this application.

[0025] Figure 3 This is a schematic diagram of the structure of a treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater according to Embodiment 2 of this application; wherein, 101, membrane concentration pretreatment unit; 201, mixing tank; 301, triple-effect evaporation concentration unit; 401, spray dryer; 501, tail gas resource utilization unit; 501a, condenser; 501b, tail gas purification tower; 601, solid product collection device; 701, multi-stage series suspension roasting system.

[0026] Figure 4 This is a schematic flowchart of a method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater in Embodiment 2 of this application. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0028] The raw materials processed in the following examples are from the following sources: Acidic wastewater: taken from the washing section of the titanium dioxide production workshop, pH=1.5, sulfuric acid content 3wt%, total iron content approximately 500mg / L, flow rate 2.0m³ / h. 3 / h.

[0029] Titanium dioxide waste acid: taken from the acidolysis waste acid of the main titanium dioxide production line, with a sulfuric acid concentration of 23wt%, a ferrous sulfate content of approximately 18wt%, and a flow rate of 8.0 m³ / h. 3 / h.

[0030] Example 1: Co-processing method and system for ferrous sulfate monohydrate as the target product like Figure 1 As shown, a treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater includes a membrane concentration pretreatment unit 101, a mixing tank 201, a triple-effect evaporation concentration unit 301, a spray dryer 401, a tail gas resource utilization unit 501, and a solid product collection device 601.

[0031] The membrane concentration pretreatment unit 101 includes a raw water tank, a feed pump, a protective filter, and an acid-resistant nanofiltration membrane system. The membrane material of the acid-resistant nanofiltration membrane system is sulfonated polyethersulfone. The acid-resistant nanofiltration membrane system is equipped with a recycled water outlet and a concentrated acid water outlet. The concentrated acid water outlet is connected to the inlet of the mixing tank 201, and the outlet of the mixing tank 201 is connected to the inlet of the triple-effect evaporation concentration unit 301.

[0032] The triple-effect evaporation and concentration unit 301 includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator connected in sequence. The concentrated waste acid outlet of the triple-effect evaporation and concentration unit 301 is connected to the feed inlet of the spray dryer 401 via a corrosion-resistant high-pressure pump. The heating element of the triple-effect evaporation and concentration unit 301 is made of graphite.

[0033] The spray dryer 401 includes a tower body made of 316L stainless steel with an acid-resistant brick lining. A centrifugal atomizer is installed at the top of the tower body, along with a hot air inlet connected to a hot air distributor. A product collection system is located at the bottom of the tower body, with a solid product outlet connected to a solid product collection device 601. An exhaust gas outlet is also located at the top of the tower body, connected to the air inlet of an exhaust gas resource recovery unit 501.

[0034] The exhaust gas resource recovery unit 501 includes a condenser 501a, with a concentrated sulfuric acid outlet at the bottom and a non-condensable gas outlet at the top. The non-condensable gas outlet is connected to an exhaust gas purification tower 501b. In this embodiment, the exhaust gas purification tower 501b is a three-stage packed purification tower, which includes an acid washing section, a water washing section, and an alkaline washing section. A demister is installed at the top of the three-stage packed purification tower.

[0035] A method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater includes the following steps: (1) Wastewater membrane concentration treatment and titanium dioxide waste acid pretreatment Acidic wastewater stored in the raw water tank is pumped into a 5μm pore size security filter to remove suspended solids, and then enters an acid-resistant nanofiltration membrane system with an operating pressure set at 1.5MPa. Under these conditions, 1.45m³ of recycled water is produced. 3 The recovery rate was 72.5% at a rate of [per hour]. Testing showed that the conductivity of the recycled water was <100 μS / cm and the total iron concentration was <1 mg / L, making it suitable for direct reuse in production. Simultaneously, 0.55 m³ of concentrated acid water was obtained. 3 / h, the sulfuric acid concentration is increased to approximately 16.5wt%.

[0036] The waste acid from the acidolysis of the main titanium dioxide production line is pumped into a sedimentation tank for natural settling. Then, the supernatant is sent to a plate and frame filter press for filtration to obtain pretreated titanium dioxide waste acid.

[0037] (2) Waste acid mixing and triple-effect evaporation concentration The concentrated acid solution and pretreated titanium dioxide waste acid were mixed in a mixing tank, with the volume ratio of waste acid to concentrated acid solution controlled at 4:1, to obtain mixed waste acid. This mixed waste acid was then fed into a triple-effect evaporation concentration unit. The first-effect evaporator was heated with saturated steam at 0.5 MPa (gauge pressure) and the temperature was controlled at 142°C. The second-effect evaporator used secondary steam from the first effect and the temperature was controlled at 98°C. The third-effect evaporator used secondary steam from the second effect and operated under a vacuum of -0.086 MPa, with the temperature controlled at 68°C. By precisely controlling the inlet and outlet flow rates, a concentrated waste acid with a concentration of 40.5% was finally obtained from the bottom of the triple-effect evaporator.

[0038] (3) Controlled pyrolysis drying Concentrated waste acid is pumped to a spray dryer via an acid-resistant high-pressure pump. The temperature of the hot air entering the tower is controlled by adjusting the natural gas burner, maintaining a stable temperature of (380±5)℃ in the reaction zone. The concentrated waste acid is atomized into tiny droplets by a centrifugal atomizer, which come into full contact with the hot air, causing rapid evaporation of moisture and direct crystallization of ferrous sulfate monohydrate. This monohydrate is collected by a product collection system, yielding a light green powder, which is then transported to a solid product collection device via a solid product outlet.

[0039] Sampling analysis showed that the light green powder product met the requirements of GB 34462-2017 "Feed Additives Ferrous Sulfate" for ferrous sulfate monohydrate, with a main content (FeSO4·H2O) ≥98.5% and a yield of 96.2% based on iron content.

[0040] (4) Exhaust gas resource utilization and purification The sulfur-containing exhaust gas from the spray dryer first enters the condenser, where it is indirectly cooled by circulating cooling water at 30°C. Concentrated sulfuric acid with a concentration of 92.5% is recovered from the condensation, with an average yield of approximately 0.20 t / h, which can be reused in the titanium dioxide acidolysis process. The uncondensed exhaust gas then enters a three-stage packed purification tower filled with polypropylene Pall rings. It sequentially passes through an acid washing section, sprayed with 25% dilute sulfuric acid; a water washing section, sprayed with demineralized water; and an alkaline washing section, sprayed with 8% sodium hydroxide solution. After purification, the exhaust gas passes through a demister and is then exhausted by an FRP (fiberglass reinforced plastic) induced draft fan. Online monitoring shows that the SO2 concentration in the exhaust gas is consistently below 50 mg / Nm³. 3 It is far below the national emission standards.

[0041] Example 2: Co-processing method and system for iron oxide as the target product A treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater, such as... Figure 3 As shown, it includes a membrane concentration pretreatment unit 101, a mixing tank 201, a triple-effect evaporation concentration unit 301, a spray dryer 401, a tail gas resource utilization unit 501, a solid product collection device 601, and a multi-stage series suspension roasting system 701.

[0042] A treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater includes a membrane concentration pretreatment unit 101, a mixing tank 201, a triple-effect evaporation concentration unit 301, a spray dryer 401, and a tail gas resource utilization unit 501.

[0043] The membrane concentration pretreatment unit 101 includes a raw water tank, a feed pump, a protective filter, and an acid-resistant nanofiltration membrane system. The membrane material of the acid-resistant nanofiltration membrane system is sulfonated polyethersulfone. The acid-resistant nanofiltration membrane system is equipped with a recycled water outlet and a concentrated acid water outlet. The concentrated acid water outlet is connected to the inlet of the mixing tank 201, and the outlet of the mixing tank 201 is connected to the inlet of the triple-effect evaporation concentration unit 301.

[0044] The triple-effect evaporation and concentration unit 301 includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator connected in sequence. The concentrated waste acid outlet of the triple-effect evaporation and concentration unit 301 is connected to the feed inlet of the spray dryer 401 via a corrosion-resistant high-pressure pump.

[0045] The spray dryer 401 includes a tower body made of 316L stainless steel with an acid-resistant brick lining. A centrifugal atomizer is installed at the top of the tower body, and a hot air inlet connected to a hot air distributor is also located at the top. A product collection system is located at the bottom of the tower body, with a solid product outlet connected to the inlet of a multi-stage series suspension roasting system 701. The outlet of the multi-stage series suspension roasting system 701 is connected to a solid product collection device 601. In this embodiment, the multi-stage series suspension roasting system 701 includes a three-stage cyclone preheater, a suspension roasting furnace, and a two-stage cyclone cooler.

[0046] The top of the tower is also equipped with a tail gas outlet, which is connected to the inlet of the tail gas resource utilization unit 501. The tail gas resource utilization unit 501 includes a condenser 501a, with a concentrated sulfuric acid outlet at the bottom and a non-condensable gas outlet at the top, which is connected to the tail gas purification tower 501b. In this embodiment, the tail gas purification tower 501b is a three-stage packed purification tower, which includes an acid washing section, a water washing section, and an alkaline washing section. A demister is installed at the top of the three-stage packed purification tower.

[0047] The raw materials processed in this embodiment are the same as those in Embodiment 1.

[0048] A method for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater includes the following steps: (1) Wastewater membrane concentration treatment and titanium dioxide waste acid pretreatment: The operation is the same as in Example 1.

[0049] (2) Waste acid mixing and triple-effect evaporation concentration: The operation is the same as in Example 1, and 40.5% concentrated waste acid is obtained.

[0050] (3) Controlled pyrolysis drying preparation of intermediates: Concentrated waste acid is transported to a spray dryer via an acid-resistant high-pressure pump. The temperature of the hot air entering the tower is controlled by adjusting the natural gas burner, so that the temperature of the reaction zone inside the tower is stably controlled at (270±5)℃. The concentrated waste acid is atomized into tiny droplets by a centrifugal atomizer, which come into full contact with the hot air, and the moisture evaporates rapidly, resulting in a brownish-yellow powdery intermediate with extremely low water content. Its main component is ferrous sulfate and contains a small amount of incompletely decomposed ferric bisulfate. The powdery intermediate is collected by a product collection system and transported from the solid product outlet to a multi-stage series suspension roasting system.

[0051] (4) Pyrolysis to prepare iron oxide: The powdered intermediate enters a three-stage cyclone preheater, where it is preheated to above 500°C by the high-temperature flue gas (approximately 700°C) from the suspension roaster, greatly recovering the waste heat of the flue gas. The preheated material enters the suspension roaster and remains there for 5-8 minutes, where it undergoes a rapid decomposition reaction at 580°C, producing reddish-brown, uniformly sized iron oxide powder and high-temperature sulfur-containing flue gas. The iron oxide powder enters a two-stage cyclone cooler, where it undergoes countercurrent heat exchange with the cold air entering the system. The iron oxide powder is cooled to below 80°C and then enters the solid product collection device through the discharge port. The cold air is preheated to approximately 450°C and sent to the burner of the suspension roaster as combustion air, significantly reducing fuel consumption.

[0052] The reddish-brown, uniformly sized iron oxide powder, as determined by XRD analysis, is primarily composed of hematite phase and can be used as a raw material for pigments or soft magnetic materials. Furthermore, compared to traditional rotary kiln pyrolysis, it reduces overall energy consumption by more than 40%.

[0053] (5) Waste Gas Resource Utilization and Purification: The high-temperature sulfur-containing flue gas generated by the multi-stage series suspension roasting system and the sulfur-containing tail gas from the spray dryer are combined and then enter the waste gas resource utilization unit together. The treatment process is the same as in Example 1. Since the high-temperature sulfur-containing flue gas contains SO2, the load of the alkaline washing section will increase accordingly, and the concentration of sodium hydroxide solution will increase to 10%. Online monitoring shows that the SO2 concentration in the exhaust gas is consistently below 50 mg / Nm³. 3 It is far below the national emission standards.

[0054] Comparative Example 1 Acidic wastewater and titanium dioxide waste acid of the same scale as those in Examples 1 and 2 were treated using the traditional lime neutralization method.

[0055] Treatment process: Acidic wastewater (2.0m³) 3 / h) and titanium dioxide waste acid (8.0m 3 After mixing ( / h), the mixture is placed in a large neutralization tank, where quicklime slurry is continuously added and stirred until the pH value is ≥9. The reaction produces a large amount of calcium sulfate precipitate, i.e., titanium gypsum. After a long period of sedimentation, the supernatant is discharged, and the bottom sludge is filtered to form titanium gypsum slag with a water content of approximately 40%. Approximately 240 tons of wet-based titanium gypsum slag are generated daily, requiring transport to a dedicated slag yard for storage or landfill disposal. The annual storage area is enormous, and there is a long-term environmental risk of leachate contamination of groundwater.

[0056] The entire process produced no valuable products, and the total cost of purchasing quicklime, electricity for filter press, transportation, and hazardous waste disposal amounted to tens of millions of yuan.

[0057] As can be seen from Examples 1-2 and Comparative Example 1, the method and treatment system for the synergistic resource utilization of titanium dioxide waste acid and acidic wastewater provided by this invention, through ingenious process design and system integration, successfully achieves the synergistic, efficient, and high-value resource utilization of titanium dioxide waste acid and acidic wastewater. Example 1 demonstrates a low-cost, short-process direct resource utilization path; Example 2 demonstrates a high-value, low-energy-consumption advanced technology path. The products produced by both paths have clear market demand and high economic value, while completely solving the environmental bottleneck problem. This provides a practical and selectable advanced technology solution for the green, sustainable, and high-quality development of the titanium dioxide industry, with extremely significant comprehensive advantages.

[0058] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for synergistic resource utilization of titanium white waste acid and acid waste water, characterized in that, The method comprises the following steps: (1) membrane concentration pretreatment is performed on the acidic wastewater generated in the production process of titanium white to obtain reused water and concentrated acid water containing sulfuric acid and metal ions; (2) the concentrated acid water is mixed with the pretreated titanium white waste acid to obtain mixed waste acid, which is sent to a multi-effect evaporation concentration unit for concentration to obtain concentrated waste acid; (3) the concentrated waste acid is subjected to a pre-pyrolysis drying reaction at a temperature of 250-400 DEG C to obtain a solid product and a sulfur-containing tail gas; (4) the sulfur-containing tail gas is condensed to recover concentrated sulfuric acid with a mass concentration of not less than 90%, and the uncondensed tail gas is discharged after purification treatment.

2. The method of claim 1, wherein, In step (3), the reaction temperature is controlled to be 350-400 DEG C, and the obtained solid product is ferrous sulfate monohydrate.

3. The method of claim 1, wherein, In step (3), the reaction temperature is controlled to be 250-300 DEG C, and the obtained solid product is an intermediate containing ferrous sulfate and sulfuric acid anhydride; the intermediate is subjected to a cracking reaction at 450-650 DEG C to generate crude iron oxide.

4. The method of claim 1, wherein, In step (1), the membrane used for the membrane concentration pretreatment is a nanofiltration membrane or a reverse osmosis membrane; the recovery rate of the reused water is greater than or equal to 70%, and the rejection rate of the metal ions is greater than or equal to 95%; the mass concentration of sulfuric acid in the concentrated acid water is increased to 15%-25%.

5. The method of claim 1, wherein, In step (2), the volume ratio of the titanium white waste acid to the concentrated acid water is (3-5):1; the multi-effect evaporation concentration is three-effect evaporation, and the evaporation temperature of the first effect is controlled to be 130-150 DEG C, and the evaporation temperature of the last effect is 60-80 DEG C.

6. The method of claim 1, wherein, In step (2), the pretreatment of the titanium white waste acid comprises sedimentation and filtration; the mass concentration of the concentrated waste acid is 38%-42%.

7. The method of claim 1, wherein, The purification treatment of step (4) is three-stage purification treatment, which comprises, in sequence, acid washing treatment using 20wt%-30wt% dilute sulfuric acid, water washing treatment using desalted water, and alkali washing treatment using 5%-10% sodium hydroxide solution.

8. A processing system for implementing the method according to any one of claims 1 to 7, characterized in that The system comprises a membrane concentration pretreatment unit, a multi-effect evaporation concentration unit, a controllable pyrolysis drying unit, and a tail gas resource utilization unit.

9. The processing system of claim 8, wherein, The controllable pyrolysis drying unit is a spray dryer, which comprises a tower body, an atomizer arranged at the top of the tower body, a hot air inlet communicated with a hot air distributor arranged at the side or top of the tower body, and a solid product outlet communicated with a product collection system arranged at the bottom of the tower body.

10. The processing system of claim 8, wherein, The treatment system further comprises a cracking furnace, which is a rotary kiln, a fluidized bed furnace or a multi-stage series suspension calcination furnace, and the solid product outlet of the controllable pyrolysis drying unit is connected with the feeding port of the cracking furnace for receiving the intermediate and performing a cracking reaction.

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