Composite ferrous solution as well as preparation method and application thereof

Abstract

The invention discloses a composite ferrous solution and a preparation method and application thereof, and belongs to the technical field of industrial wastewater treatment. The preparation method comprises the following steps: mixing and stirring the waste sulfuric acid generated in the production of titanium dioxide by a sulfuric acid method and a ferrous raw material at 20-50 DEG C, and purifying to obtain the composite ferrous solution. In the preparation process, the mixing ratio of the waste sulfuric acid to the ferrous raw material is controlled, so that the iron-acid ratio of the final solution is controlled to be 1: 2-1: 5. And heavy metal ions in the composite ferrous solution are further removed through a purification process, so that secondary pollution caused by wastewater treatment is reduced. The waste in the titanium dioxide industry is used as the raw material, the effect of treating waste with waste is achieved, and the agent cost of Fenton treatment is remarkably reduced. The prepared composite ferrous solution can be directly added into the papermaking wastewater, pH adjustment and catalyst addition are completed in one step, the process is simplified, targeted configuration can be performed according to the COD content of the wastewater, treatment is efficient and accurate, and remarkable economic and environment-friendly benefits are achieved.

Description

Technical Field

[0001] This application belongs to the field of industrial wastewater treatment technology, and specifically relates to a composite ferrous solution, its preparation method and application. Background Technology

[0002] Fenton oxidation, as a highly efficient advanced oxidation technology, utilizes ferrous ions (Fe²⁺) to achieve oxidation. 2+ The Fenton process catalyzes the generation of highly oxidizing hydroxyl radicals (·OH) from hydrogen peroxide, and is widely used in the treatment of recalcitrant organic wastewater in industries such as papermaking and dyeing. However, the traditional Fenton process has many drawbacks in practical applications: First, the reagents are expensive and the process is cumbersome. Traditional processes typically involve a three-step method: first, adding concentrated acid to adjust the wastewater pH to an acidic range of 2-4; second, adding commercial ferrous salt as a catalyst; and finally, adding hydrogen peroxide. This process not only consumes large amounts of expensive commercial acid and ferrous salt, but the addition of concentrated sulfuric acid also poses safety hazards and may cause the water temperature to rise excessively, exceeding the optimal temperature range for the Fenton reaction (20℃~40℃), thus accelerating the ineffective decomposition of hydrogen peroxide. Furthermore, the multi-step addition and uneven mixing can easily lead to localized precipitation of ferrous ions, reducing catalytic efficiency.

[0003] Secondly, the disposal of industrial byproducts is costly and poses significant environmental risks. Taking the sulfuric acid process for titanium dioxide production as an example, it generates large quantities of waste sulfuric acid (concentration 15%–25%), high-iron solutions (ferrous content 80 g / L–120 g / L), and solid ferrous sulfate byproducts. Because these byproducts contain high levels of heavy metals, they cannot be directly utilized. Currently, the mainstream disposal method for these byproducts is neutralization and precipitation, which not only consumes large amounts of alkali but also generates massive amounts of difficult-to-treat hazardous waste (such as iron sludge), resulting in resource waste and secondary pollution. Other methods, such as vacuum concentration to recover sulfuric acid, suffer from frequent equipment scaling, high energy consumption, and unstable operation.

[0004] Therefore, how to solve the problem of reagent consumption in the traditional Fenton process in a low-cost and efficient manner, and simultaneously realize the resource utilization of typical wastes from the titanium dioxide industry, is a technical problem that urgently needs to be solved in the field of industrial wastewater treatment. Summary of the Invention

[0005] The purpose of this application is to provide a composite ferrous solution, its preparation method and application. The composite ferrous solution is prepared using by-products from the production of titanium dioxide using the sulfuric acid process. This can solve the problems of high cost, limited efficiency and disposal of titanium dioxide by-products in the traditional Fenton process, achieve the effect of treating waste with waste and improve the Fenton treatment effect and economy.

[0006] To achieve the above objectives, this application provides a method for preparing a composite ferrous solution, comprising the following steps: Waste sulfuric acid and ferrous raw material generated during the sulfuric acid process for titanium dioxide production are mixed and stirred at 20℃~50℃ to obtain a liquid. The ferrous raw material is iron-containing mother liquor or ferrous sulfate by-product. The iron-containing mother liquor is ferrous sulfate monohydrate mother liquor or ferrous sulfate heptahydrate mother liquor. The ferrous sulfate by-product is ferrous sulfate monohydrate and / or ferrous sulfate heptahydrate. The liquid mixture is continuously stirred until it is evenly mixed to obtain a composite ferrous mixture solution. A reducing agent is added to a composite ferrous mixed solution, and a primary solution is obtained through reduction and displacement reactions; A purifying agent was added to the primary solution, and after purification and sedimentation, a composite ferrous solution was obtained.

[0007] Furthermore, the acid concentration in the waste sulfuric acid is 15wt%~25wt%, and the iron concentration is 2wt%~5wt%.

[0008] Furthermore, the ferrous content in the iron-containing mother liquor, calculated as FeSO4•H2O, is 80 g / L to 120 g / L, and the iron concentration in the ferrous sulfate byproduct is 15 wt% to 30 wt%.

[0009] Furthermore, the mixing and stirring method is as follows: first add waste sulfuric acid or ferrous raw material, heat to 20℃~50℃, and add the remaining raw material while stirring; wherein, the mixing and stirring speed is 60rpm~120rpm, and the mixing and stirring time is 30min~60min.

[0010] Furthermore, the stirring time is 30 to 60 minutes.

[0011] Furthermore, the reducing agent is reduced iron powder, iron flakes, or an organic reducing agent, and the amount of reducing agent added is the theoretical amount of ferric ions in the composite ferrous solution. The reduction and displacement reaction time is 0.5 h to 2 h. The role of the reducing agent added in this application is reduction and displacement.

[0012] Furthermore, the purifying agents include phosphate purifying agents and metatitanic acid separating agents. The amount of phosphate purifying agent added is 0.5‰~2‰ of the primary solution, and the amount of metatitanic acid separating agent added is 5ppm~50ppm of the primary solution; the sedimentation time is 0.5h~2h. The supernatant after sedimentation or the filtrate obtained after filtration is the composite ferrous solution.

[0013] Furthermore, by controlling the mixing ratio of waste sulfuric acid and ferrous raw materials, the ferric acid ratio in the final prepared composite ferrous solution is controlled at 1:2 to 1:5.

[0014] This application also provides a composite ferrous solution prepared by the above method, wherein the concentration of H2SO4 in the composite ferrous solution is 5wt%~15wt%, and the concentration of ferrous ions is 30g / L~80g / L.

[0015] This application also provides the application of the above-mentioned composite ferrous solution in the Fenton treatment of papermaking wastewater, and the method of use is as follows: In the papermaking wastewater to be treated, the calculated amount of composite ferrous solution is directly added according to the ferrous dosage required by the Fenton process. After stirring evenly, the pH of the wastewater is automatically adjusted to the optimal range of 2-4 for the Fenton reaction. Then, hydrogen peroxide is added to carry out the Fenton oxidation reaction. The composite ferrous solution with a corresponding ferric acid ratio can be selected for addition based on the COD content of the papermaking wastewater to achieve targeted treatment.

[0016] In summary, this application has the following advantages: This application achieves high efficiency, low cost, and greening of the Fenton oxidation process through collaborative innovation of waste-to-waste treatment and targeted design of precise control. The principle lies in cleverly using two typical wastes generated during the sulfuric acid process for titanium dioxide production—waste sulfuric acid and ferrous raw materials (ferrous sulfate monohydrate mother liquor or ferrous sulfate heptahydrate mother liquor or ferrous sulfate monohydrate solid by-product or ferrous sulfate heptahydrate solid by-product)—as composite raw materials for preparing Fenton catalysts and acidity regulators. The main technical solution is to precisely control the mixing ratio of these two wastes to prepare a ferric-acid ratio (Fe... 2+ A ferrous complex solution with adjustable H2SO4 was prepared, and the solution quality was improved through purification processes (including reduction, displacement, sedimentation, and separation). The beneficial effects of this application are: 1) Significantly reduced costs: Directly utilizing waste materials to replace expensive commercial sulfuric acid and ferrous salts, turning waste into treasure, and significantly reducing reagent costs and waste disposal expenses; 2) Simplified process flow: The traditional three-step process of adding acid to adjust pH, adding ferrous iron, and adding hydrogen peroxide is simplified to a two-step process of adding this solution and adding hydrogen peroxide. The operation is convenient and avoids the loss of ferrous iron precipitation due to uneven mixing. 3) Precise and efficient treatment effect: The composite ferrous solution with the best ferric acid ratio can be targeted and configured according to the COD content of different wastewaters to ensure that the pH automatically enters the optimal range of Fenton reaction (2-4) after addition and maintains a suitable reaction temperature to maximize catalytic efficiency, thereby achieving precise and efficient treatment of various types of wastewater.

[0017] In summary, this application provides an economical, efficient, and environmentally friendly wastewater treatment solution with significant industrial application value and environmental benefits. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the preparation method of the composite ferrous solution proposed in the embodiments of this application.

[0020] Figure 2 This is a photograph of the dark green, clear composite ferrous solution A presented in the embodiments of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Fenton oxidation technology, as a highly efficient advanced oxidation process, plays an important role in the treatment of recalcitrant organic wastewater and is widely used in industries such as papermaking, printing and dyeing, and chemicals. Its core reaction mechanism involves the reaction of ferrous ions (Fe²⁺) under acidic conditions (typically pH 2-4). 2+ The catalytic reaction of hydrogen peroxide (H2O2) produces highly oxidizing hydroxyl radicals (·OH), and the relevant reaction formula is as follows: Fe 2+ +H₂O₂→Fe 3+ +·OH+OH - Hydroxyl radicals can non-selectively oxidize and decompose organic pollutants in wastewater, thereby achieving the purpose of wastewater purification.

[0023] However, the traditional Fenton process has many unavoidable drawbacks in practical industrial applications, which restrict its efficient and economical operation. These drawbacks are as follows: 1. Requires the addition of large amounts of acid to adjust pH: Papermaking wastewater is usually neutral or weakly alkaline, while the Fenton reaction requires an acidic environment of pH 2-4 to proceed efficiently. Therefore, large amounts of sulfuric acid or hydrochloric acid must be added to adjust the pH of the reaction system. This not only directly increases the cost of reagent procurement, but also requires a dedicated acid dosing device when adding high-concentration acids such as 98%, further increasing equipment investment and operation and maintenance costs.

[0024] 2. High Risk of Temperature Control Issues: The Fenton reaction has an optimal temperature range (typically 20℃~40℃). According to Arrhenius's law, while increasing temperature can accelerate molecular motion, it also leads to a sharp increase in the thermal decomposition rate of H2O2, resulting in reagent waste and reduced oxidation efficiency. In actual operation, adding 98% concentrated sulfuric acid releases a large amount of heat, which can easily cause the water temperature to exceed the optimal reaction range, severely affecting the utilization efficiency of hydrogen peroxide.

[0025] 3. Inappropriate dosing method leads to decreased catalytic efficiency: The traditional Fenton process generally adopts a three-step dosing method of adding acid to adjust pH → adding ferrous iron → adding hydrogen peroxide. If the acid and wastewater are not mixed evenly, local pH will be too high, causing ferrous ions to prematurely generate ferrous hydroxide and other precipitates due to the pH exceeding the suitable range, which significantly reduces its catalytic activity. This not only affects the treatment effect, but also increases the cost of reagent consumption due to the reduced utilization rate of ferrous iron.

[0026] 4. High Cost of Ferrous Salts: With the expanding demand in the new energy market, the price of ferrous salts such as ferrous sulfate heptahydrate, used as precursors for cathode materials, continues to rise, and their purchase cost has become one of the major expenses of the Fenton process. Furthermore, solid ferrous salts must be prepared into a liquid before addition, requiring additional preparation tanks and related equipment, which also increases labor costs, further driving up processing costs.

[0027] At the same time, the sulfuric acid process for titanium dioxide production generates a large number of industrial byproducts, mainly including waste sulfuric acid with a concentration of about 15% to 25% and iron-containing solutions (such as ferrous sulfate monohydrate mother liquor or ferrous sulfate heptahydrate mother liquor) with an Fe content of 80 g / L to 120 g / L calculated as FeSO4•H2O, as well as solid ferrous sulfate byproducts (ferrous sulfate monohydrate and / or ferrous sulfate heptahydrate) with an iron concentration of 15 wt% to 30 wt%. These byproducts are highly acidic, have high iron content, and complex impurities, making them difficult and costly to handle. Improper disposal can easily lead to serious environmental pollution, becoming a major bottleneck for the sustainable development of the titanium dioxide industry. The specific current disposal status is as follows: For byproduct waste sulfuric acid, there are currently two main disposal methods in the industry. One is the alkali neutralization method, which involves adding alkaline solutions such as carbide slag, stone powder, caustic soda, and lime to neutralize the waste acid before direct discharge. This method requires a large amount of alkali, resulting in high disposal costs, and improper handling of the neutralization products can easily cause secondary pollution. The other method is the vacuum concentration method to recover sulfuric acid. This method consumes a huge amount of steam, has high operating costs, and the graphite heater is prone to frequent scaling and blockage during the concentration process due to the precipitation of ferrous sulfate crystals. Typically, the machine needs to be shut down for cleaning every 6 to 7 days, with each cleaning session lasting about 36 hours, resulting in low equipment uptime and seriously affecting the normal production of enterprises. For iron-containing solutions (such as ferrous monohydrate mother liquor) produced as a byproduct of titanium dioxide production, which contain various impurities such as Ti, Mn, Cr, and Pb, the current main treatment method is neutralization precipitation. This method involves adding an alkaline agent to convert iron ions into iron sludge precipitate. This method generates a huge amount of hazardous waste (iron sludge), which not only causes a serious waste of iron resources, but also requires additional high costs for the subsequent treatment of iron sludge, further increasing the burden on enterprises.

[0028] In summary, the traditional Fenton process suffers from high reagent costs, complex operation, and susceptibility to reduced processing efficiency. Furthermore, the disposal of waste sulfuric acid and iron-containing solutions, byproducts of the sulfuric acid process in titanium dioxide production, remains a pressing issue. Therefore, this application provides a composite ferrous solution, its preparation method, and its application, which can efficiently utilize byproducts from the titanium dioxide industry while optimizing the Fenton process and reducing processing costs.

[0029] Specifically, in the first aspect, this application provides a method for preparing a composite ferrous solution, such as... Figure 1 As shown, it includes the following steps: S1. Take the waste sulfuric acid and ferrous raw material generated during the sulfuric acid process of titanium dioxide production, mix and stir them at 20℃~50℃ to obtain a liquid; wherein, the ferrous raw material is iron-containing mother liquor or ferrous sulfate by-product, the iron-containing mother liquor is ferrous monohydrate mother liquor or ferrous sulfate heptahydrate mother liquor, and the ferrous sulfate by-product is ferrous sulfate monohydrate and / or ferrous sulfate heptahydrate.

[0030] In the specific implementation, the acid concentration in the waste sulfuric acid is 15wt%~25wt%, and the iron concentration is 2wt%~5wt%. The ferrous content in the iron-containing mother liquor, calculated as FeSO4•H2O, is 80g / L~120g / L, and the iron concentration in the ferrous sulfate byproduct is 15wt%~30wt%. The waste sulfuric acid in this application is a byproduct of the sulfuric acid process for titanium dioxide production. Its waste sulfuric acid solution contains only sulfuric acid. The iron-containing mother liquor is also a byproduct of the sulfuric acid process for titanium dioxide production, and its iron ions are mainly present as ferrous ions, with a small amount of trivalent iron ions also present. This application uses byproducts of the sulfuric acid process for titanium dioxide production (waste sulfuric acid, ferrous monohydrate mother liquor, ferrous sulfate heptahydrate mother liquor, or byproduct ferrous sulfate) as raw materials, eliminating the need to purchase industrial-grade acid and ferrous salts. This solves the environmental pain points of high acidity and difficult disposal of byproducts in the titanium dioxide industry, achieving resource utilization through waste treatment, and significantly reducing raw material costs. Meanwhile, the waste sulfuric acid contains only a single acid solution, and the iron ions in the iron-containing mother liquor and by-product ferrous sulfate are mainly ferrous, which reduces the interference of impurities and ions on subsequent reactions.

[0031] In a specific embodiment, the mixing and stirring method is as follows: first, waste sulfuric acid or ferrous raw material is added, and the temperature is raised to 20℃~50℃. While stirring, the remaining raw material is added. The mixing and stirring speed is 60rpm~120rpm, and the mixing and stirring time is 30min~60min. The reaction temperature in this application is room temperature to 50℃, and the hot reaction temperature can be achieved by heating methods such as a water bath. Limiting the reaction temperature to 20℃~50℃ can be achieved by conventional heating methods such as a water bath, without the need for high-temperature and high-pressure equipment, resulting in low energy consumption and safe operation. Optimizing the stirring speed (60rpm~120rpm) and time (30min~60min) parameters ensures that the raw materials are fully contacted and mixed, avoiding reaction deviations caused by uneven local concentrations, while also preventing energy waste or solution splashing due to excessively high speed.

[0032] S2. Continue stirring the liquid until it is evenly mixed to obtain a composite ferrous mixture solution.

[0033] In this specific embodiment, the continuous stirring time is 30-60 minutes. Continuous stirring for 30-60 minutes can further eliminate any remaining local concentration differences from step S1, ensuring that the H+ in the waste sulfuric acid is properly controlled. + Fe in molten iron 2+ The solution is fully dispersed to form a thermodynamically stable composite ferrous mixture, thus avoiding incomplete treatment due to uneven local component distribution in subsequent reduction and purification steps.

[0034] S3. Add a reducing agent to the composite ferrous mixed solution, and obtain a first-stage solution through reduction and displacement reactions.

[0035] In a specific implementation, the reducing agent is reduced iron powder, iron flakes, or an organic reducing agent. The amount of reducing agent added is the theoretical amount of ferric ions in the solution, quantified as 0.5‰~1‰ of the mass of the composite ferrous solution. This is for the purpose of addressing the small amount of ferric ions (Fe3+) in the iron-containing mother liquor. 3+ To address the issue of factors affecting the efficiency of the Fenton reaction, this application addresses this by adding a reducing agent (such as reduced iron powder) to reduce Fe... 3+ Directional reduction to Fe 2+ This directly increases the content of the core catalytic components in the composite ferrous solution, enhancing its subsequent Fenton treatment efficiency. This application preferentially selects reduced iron powder as the reducing agent, which can not only reduce Fe... 3+ Furthermore, it can remove heavy metal ions (such as Pb and Cr) that may be present in the solution through displacement reactions, further purifying the system and reducing the risk of secondary pollution from heavy metals to subsequent wastewater treatment, achieving the dual effects of reduction and impurity removal. The theoretical amount and theoretical reduction amount referred to in this application, taking iron powder as an example: 1 mol of iron powder can reduce 2 mol of ferric iron to ferrous iron. Based on test results, if the ferric iron content is 1.61g, approximately 0.0288mol, then 0.0144mol of iron powder is needed for reduction. The mass of 0.0144mol of iron powder is 0.804g. Based on product characteristics, this is quantified to: the amount of reducing agent added is approximately 0.5‰~1‰ of the total mass of the composite ferrous solution.

[0036] S4. Add a purifying agent to the primary solution, purify and settle, and then separate to obtain a composite ferrous solution.

[0037] In a specific implementation, the purifying agent comprises a phosphate purifying agent and a metatitanic acid separating agent. The amount of phosphate purifying agent added is 0.5wt‰~2wt‰ of the primary solution, and the amount of metatitanic acid separating agent added is 5ppm~50ppm of the primary solution; the sedimentation time is 0.5h~2h. The supernatant after sedimentation or the filtrate obtained after filtration is a composite ferrous sulfate solution. The phosphate purifying agent (0.5wt‰~1wt‰) can form insoluble phosphate precipitates with the residual heavy metal ions such as Ti, Mn, Mg, and Al in the primary solution, specifically addressing the problem of residual heavy metal impurities in the original mother liquor; the metatitanic acid separating agent (5ppm~50ppm, usually prepared as a 1‰ concentration solution for use) continuously and efficiently flocculates and removes metatitanic acid suspended impurities in the system. The two complement each other, eliminating the interference of heavy metals on Fenton catalytic activity and avoiding the risk of equipment scaling caused by metatitanic acid, significantly improving the purity of the composite ferrous sulfate solution. After dual purification, the Fe in the solution... 2+ The effective concentration is more stable, avoiding the reaction of impurity ions with Fe. 2+Competing reaction sites or catalytic decomposition of ineffective hydrogen peroxide ensure the high efficiency of subsequent Fenton reactions; simultaneously, deep removal of heavy metals and suspended impurities reduces the risk of secondary pollution in treated papermaking wastewater, improving the environmental friendliness of the application. Preferably, the metatitanic acid purifier in this application is the N800 metatitanic acid purifier for waste acid from Sichuan Kerui Environmental Protection Technology Co., Ltd., whose main component is nonionic polyacrylamide. The phosphate purifier in this application includes at least one of sodium phosphate salts, ammonium phosphate salts, and phosphoric acid, including sodium monohydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and 85% phosphoric acid, etc.

[0038] In this application, the reduction and displacement reaction in step S3 focuses on improving Fe 2+ The core activity indicator is content, while also removing heavy metal impurities; step S4, purification and sedimentation, targets the specific impurity metatitanic acid. The two steps have clear divisions of labor and complement each other. Specifically, step S3 removes ionic impurities (Fe...). 3+ (Heavy metals), step S4 removes solid suspended impurities (metatinic acid), forming a dual purification system of ion-level purification and solid-state impurity removal. This synergy ensures that the final product has both high catalytic activity and high purity, avoiding the drawbacks of high activity but many impurities or high purity but low activity.

[0039] Preferably, this application controls the mixing ratio of waste sulfuric acid with iron-containing mother liquor or ferrous sulfate byproducts to achieve a ferric acid ratio of 1:2 to 1:5 in the final prepared composite ferrous solution. In the preparation of the composite ferrous solution in this application, the ferric acid ratio (i.e., the mass ratio of ferrous ions to sulfuric acid in the solution) is a core control parameter determining the product performance and the subsequent Fenton treatment effect. Its value directly relates to the acid concentration, ferrous ion concentration, and reactivity of the final composite ferrous solution. Therefore, it is necessary to precisely control the mixing ratio of the iron-containing solution and waste sulfuric acid to achieve the target ferric acid ratio. The optimization of this parameter essentially matches the dual requirements of the Fenton reaction for an acidic environment and catalytically active components, ensuring that the composite ferrous solution can fully exert its synergistic effect during application. If the ferric acid ratio is too high, it means that the relative content of sulfuric acid in the composite ferrous solution is too high, while the ferrous ions (Fe2+) that are the core catalyst of the Fenton reaction... 2+The concentration of ferrous ions is relatively low. When such solutions are used for Fenton treatment of papermaking wastewater, although the high acid content can help adjust the pH of the wastewater, the insufficient total amount of ferrous ions leads to a significant reduction in the number of effective catalytic active sites participating in the ·OH generation reaction due to the dilution effect of the wastewater system. Simultaneously, subsequent adjustments to stabilize the wastewater pH within the optimal range for the Fenton reaction further dilute the ferrous ion concentration in the system, resulting in a significant decrease in the decomposition efficiency of hydrogen peroxide, ultimately weakening the Fenton oxidation capacity and making it difficult to achieve efficient degradation of organic pollutants. Conversely, if the ferric-acid ratio is too low, there is a relative excess of ferrous ions and insufficient sulfuric acid content in the solution. Since the efficient conduct of the Fenton reaction strictly depends on an acidic reaction environment of 2-4, when such low ferric-acid ratio solutions are added, the sulfuric acid they carry cannot provide sufficient acidity support for the wastewater system. Even with external auxiliary adjustments, it is difficult to accurately and stably control the pH of the reaction system within the aforementioned optimal range. More importantly, when the pH of the system exceeds the stable range of ferrous ions, the ferrous ions in the solution are prone to hydrolysis to generate precipitates such as ferrous hydroxide, which have no catalytic activity. This process not only causes ineffective loss of the core catalytic component, but the precipitate products may also adsorb onto the surface of organic pollutants, forming a mass transfer barrier and further reducing the overall efficiency of the Fenton reaction. Through extensive experimental verification and process optimization, this application more preferably controls the ferric acid ratio of the composite ferrous solution within the range of 1:(2-5). This ratio range was determined by precisely matching the kinetic requirements of the Fenton reaction and the actual working conditions of wastewater treatment, ensuring that the final composite ferrous solution simultaneously meets the following core indicators: the sulfuric acid concentration is stable at 5%~15% (w / w), and the ferrous ion (Fe) ratio is stable at 5%~15% (w / w). 2+ The concentration is controlled between 30 g / L and 80 g / L. This combination of parameters allows the composite ferrous solution to be directly adapted to the Fenton process for papermaking wastewater treatment without additional adjustments. It ensures sufficient active components for the catalytic reaction while precisely constructing the optimal acidic reaction environment, effectively avoiding problems such as ferrous ion waste and reaction efficiency degradation. Specifically, the mass ratio of waste acid:ferrous mother liquor:water is 1:(0.25~0.8):(0~0.3), and the mass ratio of waste acid:ferrous sulfate byproduct:water is 1:(0.1~0.4):(0~0.5). In actual production, the specific product concentration and the final ferric-acid ratio are the main quantitative standards.

[0040] Secondly, based on a general inventive concept, this application provides a composite ferrous solution obtained by the above preparation method, wherein the concentration of H2SO4 in the composite ferrous solution is 5wt%~15wt%, the concentration of ferrous ions is 30g / L~80g / L, and the remainder is water.

[0041] Thirdly, based on a general inventive concept, this application provides the application of the above-mentioned composite ferrous solution in the Fenton treatment of papermaking wastewater, and the method of use is as follows: In the papermaking wastewater to be treated, the calculated amount of composite ferrous solution is directly added according to the ferrous dosage required by the Fenton process. After stirring evenly, the pH of the wastewater is automatically adjusted to the optimal range of 2-4 for the Fenton reaction. Then, hydrogen peroxide is added to carry out the Fenton oxidation reaction. The composite ferrous solution with a corresponding ferric acid ratio can be selected for addition based on the COD content of the papermaking wastewater to achieve targeted treatment.

[0042] The composite ferrous solution of this application is simple and efficient to operate when used in Fenton treatment of papermaking wastewater. It can be directly added according to the ferrous dosing requirements of the Fenton process, without the need to purchase additional acid or matching acid addition equipment. After addition, it can automatically stabilize the pH of the wastewater within the optimal range of 2-4 for the Fenton reaction, eliminating the cumbersome step of separate acid adjustment in traditional processes. It also avoids the problem of premature precipitation of ferrous ions due to uneven acid mixing, ensuring the effective utilization of the catalytically active components. Furthermore, it achieves targeted and precise treatment. Based on the COD content of the papermaking wastewater to be treated, a composite ferrous solution with a corresponding ferric-acid ratio can be selected, ensuring that the ratio of ferrous ions to acid in the solution is precisely adapted to the wastewater pollution load. This avoids waste caused by excessive reagents and ensures efficient Fenton reaction for the complete degradation of organic pollutants. Moreover, the application method of this application aligns with the concept of waste-to-waste treatment. The solution is prepared from by-products of the titanium dioxide industry. Its application not only reduces the reagent costs of the Fenton process but also provides an effective path for the resource utilization of industrial by-products, achieving both economic and environmental benefits.

[0043] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0044] Example 1 This embodiment provides a method for preparing a composite ferrous solution, including the following steps: (1) Waste sulfuric acid and ferrous monohydrate mother liquor generated during the production of titanium dioxide by sulfuric acid method were tested and their components are shown in Table 1 and Table 2.

[0045] Table 1. Waste acid detection data from a titanium dioxide plant.

[0046] Table 2. Test data of mother liquor from a titanium dioxide factory.

[0047] The TFe% in the table mainly represents the total iron content (including ferric and ferrous iron), and TFe% is related to Fe. 2+ The percentage difference represents the ferric trivalent content, and the reducing agent used in this application is mainly used to reduce this portion of ferric trivalent.

[0048] (2) In a 1L beaker with a stirrer, first add 350g of ferrous monohydrate mother liquor, and stir at 100rpm at room temperature. Slowly add 700g of waste sulfuric acid. After about 30 minutes, when the addition is complete, add 100g of water. When the ferric acid ratio of the mixture is measured to be about 1:3, add 0.8g of reduced iron powder and continue stirring. After reacting for 1 hour, add 1g of sodium dihydrogen phosphate (0.8‰ of the total mass). After reacting for 0.5 hours, add 10ppm of 1‰ concentration metatitanic acid purifying agent. After settling for 40 minutes, a dark green and clear composite ferrous solution A is obtained, as shown in the figure. Figure 2 As shown in Table 3, the composition of the composite ferrous solution A was determined.

[0049] Table 3 Test data for composite ferrous solution

[0050] Example 2 This embodiment provides a method for preparing a composite ferrous solution, including the following steps: (1) Take 150 mL of waste sulfuric acid (concentration 20.05%) and 600 mL of ferrous monohydrate mother liquor (FeSO4•H2O content 80 g / L). Their components are shown in Table 4 and Table 5, respectively.

[0051] Table 4. Waste acid detection data from a titanium dioxide plant.

[0052] Table 5. Test data of mother liquor from a titanium dioxide factory.

[0053] (2) Under 40℃ water bath conditions, 760g of waste sulfuric acid was slowly added to 200g of ferrous monohydrate mother liquor under stirring (stirring speed 120rpm). The final ferric acid ratio was approximately 1:4. 0.25g of reduced iron powder was added and the reaction was continued with stirring. After 1.5h of reaction, the reaction was complete. 0.5g of ammonium dihydrogen phosphate (0.5‰ of the total mass) and 20ppm of 1‰ concentration metatitanic acid purifying agent were added. After settling for 60min, a dark green and clear composite ferrous solution B was obtained. Its composition is shown in Table 6.

[0054] Table 6 Test data for composite ferrous solution

[0055] Example 3 This embodiment provides a method for preparing a composite ferrous solution, including the following steps: (1) Take waste sulfuric acid from a titanium dioxide plant and solid by-product of ferrous sulfate heptahydrate from the plant to prepare a solution. The composition and content are shown in Table 7 and Table 8.

[0056] Table 7. Waste acid detection data from a titanium dioxide plant.

[0057] Table 8. Ferrous Fe Content Detection Data of a Titanium Dioxide Factory

[0058] (2) In a 1L beaker with a stirrer, 600g of waste sulfuric acid was added first, and the stirring was started at room temperature (stirring speed of 80rpm). 200g of ferrous sulfate heptahydrate was slowly added. After the addition was completed and the solution was completely dissolved, the ferric acid ratio of the mixture was measured to be approximately 1:2. 0.1g of reduced iron powder was added and the reaction was continued with stirring. After reacting for 0.5h until the reaction was complete, 1.2g of sodium monohydrogen phosphate (1.5‰ by weight) and 10ppm of 1‰ concentration metatitanic acid purifying agent were added. After settling for 30 minutes, a dark green and clear composite ferrous solution C was obtained. Its composition and content are shown in Table 9.

[0059] Table 9 Test data for composite ferrous solution

[0060] Comparative Example This comparative example uses commercially available concentrated sulfuric acid (98%) and ferrous sulfate heptahydrate (FeSO4•7H2O) as reagents.

[0061] Experimental Example 1 Wastewater from the biochemical treatment process of a paper mill was taken, with a chemical oxygen demand (COD) of 280 mg / L and a pH of 7.5. Two parallel experimental groups were set up: (1) Experimental group: Take 500 mL of wastewater and directly add 9.1 mL of the composite ferrous solution A prepared in Example 1 with a ferric-acid ratio of 1:3 (this amount of addition is equivalent to introducing Fe). 2+ (50 mg / L). After addition, the pH of the wastewater immediately dropped to 3.0. Then, 0.46 mL of 30% hydrogen peroxide (equivalent to 140 mg / L of H2O2) was added, and the reaction was allowed to proceed for 30 minutes.

[0062] (2) Control group: Take 500 mL of the same wastewater, first add about 0.3 mL of concentrated sulfuric acid to adjust the pH to 3.0, then add the dissolved ferrous sulfate heptahydrate solution (containing Fe) 2+ 50 mg / L), and finally add an equal amount of hydrogen peroxide, reacting for 30 minutes.

[0063] After the reaction was completed, both groups used NaOH solution to adjust the pH to 8-9 for flocculation and sedimentation. The supernatant was then used to measure COD, and the results are shown in Table 10.

[0064] Table 10 Comparison of COD Treatment Results for Wastewater

[0065] Experimental Example 2 Wastewater from the biochemical treatment process of a paper mill was taken, with a COD of 180 mg / L and a pH of 7.0. Two parallel experimental groups were set up: (1) Experimental group: Take 500 mL of wastewater and directly add 7 mL of the composite ferrous solution prepared in Example 2 (this amount of addition is equivalent to introducing Fe). 2+ (30 mg / L). After addition, the pH of the wastewater immediately dropped to 2.5. Then, 0.3 mL of 30% hydrogen peroxide (equivalent to 100 mg / L of H2O2) was added, and the reaction was allowed to proceed for 30 minutes.

[0066] (2) Control group: Take 500 mL of the same wastewater, first add about 0.4 mL of concentrated sulfuric acid to adjust the pH to 2.5, then add the dissolved ferrous sulfate heptahydrate solution (containing Fe) 2+ 30 mg / L), and finally add an equal amount of hydrogen peroxide, and react for 30 minutes.

[0067] After the reaction was completed, both groups used NaOH solution to adjust the pH to 8-9 for flocculation and sedimentation, and the supernatant was taken to measure COD.

[0068] Table 11 Comparison of COD Treatment Results for Wastewater

[0069] Experimental Example 3 Wastewater from the biochemical treatment process of a paper mill was taken, with a COD of 450 mg / L and a pH of 7.0. Two parallel experimental groups were set up: (1) Experimental group: Take 500 mL of wastewater and directly add 10 mL of the composite ferrous solution A prepared in Example 3 with a ferric-acid ratio of 1:2 (this amount of addition is equivalent to introducing Fe). 2+ (80 mg / L). After addition, the pH of the wastewater immediately dropped to 3.5. Then, 0.75 mL of 30% hydrogen peroxide (equivalent to 225 mg / L of H2O2) was added, and the reaction was allowed to proceed for 30 minutes.

[0070] (2) Control group: Take 500 mL of the same wastewater, first add about 0.3 mL of concentrated sulfuric acid to adjust the pH to 3.5, then add the dissolved ferrous sulfate heptahydrate solution (containing Fe) 2+ (80 mg / L), and finally add an equal amount of hydrogen peroxide, and react for 30 minutes.

[0071] After the reaction was completed, both groups used NaOH solution to adjust the pH to 8-9 for flocculation and sedimentation, and the supernatant was taken to measure COD.

[0072] Table 12 Comparison of COD Treatment Results for Wastewater

[0073] The experimental results from Examples 1-3 show that when treating wastewater with low COD content, the combined ferrous solution and the conventional treatment method (i.e., a mixture of ferrous heptahydrate solution and sulfuric acid) are not significantly different in effectiveness. However, when treating wastewater with high COD content, the combined ferrous solution of this application is superior to the conventional treatment method. Furthermore, the combined ferrous solution used in this application saves all fresh sulfuric acid, and the ferrous iron is derived from waste materials, indicating that the method of this application can save on raw material usage and reduce costs. Simultaneously, the ferrous iron does not need to be dissolved and prepared during use, reducing manpower and material resources, and lowering the accuracy risks associated with the preparation process.

[0074] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of this application.

[0075] Finally, it should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes the element.

[0076] This application uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a composite ferrous solution, characterized in that, The preparation method comprises the following steps: The waste sulfuric acid produced in the production process of titanium dioxide by sulfuric acid method and ferrous raw material are mixed and stirred at 20-50 DEG C to obtain a liquid; wherein the ferrous raw material is ferrous-containing mother liquor or ferrous sulfate by-product, the ferrous-containing mother liquor is ferrous sulfate heptahydrate or ferrous sulfate monohydrate, and the ferrous sulfate by-product is ferrous sulfate monohydrate and / or ferrous sulfate heptahydrate; The liquid is continuously stirred to obtain a composite ferrous mixed solution; A reducing agent is added to the composite ferrous mixed solution to obtain a primary solution through reduction and displacement reaction; A purifying agent is added to the primary solution, and the composite ferrous solution is obtained after purification and sedimentation.

2. The method for preparing a composite ferrous solution according to claim 1, characterized in that, The acid concentration of the waste sulfuric acid is 15-25 wt%, and the iron concentration is 2-5 wt%.

3. The method of claim 1, wherein the composite ferrous solution is prepared by, The ferrous content in the ferrous-containing mother liquor is 80-120 g / L of FeSO4•H2O, and the iron concentration in the ferrous sulfate by-product is 15-30 wt%.

4. The method of claim 1, wherein the composite ferrous solution is prepared by, The mixing and stirring mode is as follows: the waste sulfuric acid or the ferrous raw material is first added, heated to 20-50 DEG C, and the remaining raw materials are added while stirring is maintained; wherein the stirring speed is 60-120 rpm, and the stirring time is 30-60 min.

5. The method of claim 1, wherein the composite ferrous solution is prepared by, The continuous stirring time is 30-60 min.

6. The method of claim 1, wherein the composite ferrous solution is prepared by, The reducing agent is reduced iron powder, iron block or organic reducing agent, and the addition amount of the reducing agent is 0.5-1 ‰ of the composite ferrous solution, and the reaction time after the reducing agent is added is 0.5-2 h.

7. The method of claim 1, wherein the composite ferrous solution is prepared by, The purifying agent comprises a phosphate purifying agent and a metatitanic acid separating agent, the addition amount of the phosphate purifying agent is 0.5-2 ‰ of the primary solution, the addition amount of the metatitanic acid separating agent is 5-50 ppm of the primary solution, and the sedimentation time is 0.5-2 h.

8. The method of claim 1, wherein the composite ferrous solution is prepared by, The mixing ratio of the waste sulfuric acid and the ferrous raw material is controlled to control the ferric acid ratio in the finally prepared composite ferrous solution to 1:2-1:

5.

9. A composite ferrous solution, characterized in that, The preparation method according to any one of claims 1-8, wherein the concentration of H2SO4 in the composite ferrous solution is 5-15 wt%, and the concentration of ferrous ion is 30-80 g / L.

10. Use of the composite ferrous solution according to claim 9 in Fenton treatment of papermaking effluents, characterized by the fact that, The use method is as follows: The calculated amount of the composite ferrous solution is directly added to the papermaking wastewater to be treated according to the required ferrous dosage of Fenton process, and the wastewater pH is automatically adjusted to the optimal range 2-4 of Fenton reaction after stirring; then hydrogen peroxide is added for Fenton oxidation reaction; According to the COD content of the papermaking wastewater to be treated, the composite ferrous solution with a corresponding ferric acid ratio is selected for addition to realize targeted treatment.

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