Method for recycling stainless steel surface treatment waste liquid

Abstract

The invention discloses a stainless steel surface treatment waste liquid recycling method which comprises the following steps: adding an alkaline compound into stainless steel surface treatment waste liquid to carry out a neutralization precipitation reaction, and carrying out solid-liquid separation after the reaction to obtain a mixed salt solution and a metal hydroxide precipitate; wherein the stainless steel surface treatment waste liquid contains at least one acid selected from hydrochloric acid, sulfuric acid, nitric acid and hydrofluoric acid; mixing the obtained mixed salt solution with a precipitant, carrying out precipitation reaction, and carrying out solid-liquid separation after the reaction to obtain regenerated acid liquor and separated insoluble salt precipitate; and calcining the obtained metal hydroxide precipitate to obtain a composite metal oxide product. According to the method, efficient collaborative recovery of acid and metal components in the waste liquid, source reduction of hazardous wastes, green conversion of valuable byproducts and remarkable reduction of the whole-process treatment cost are realized.

Description

Technical Field

[0001] This invention belongs to the field of waste liquid resource utilization technology, and in particular relates to a method for the resource utilization of waste liquid from stainless steel surface treatment. Background Technology

[0002] Stainless steel surface treatment is a key process for improving the material's corrosion resistance, smoothness, and service life. However, the waste liquid generated during this process contains strong acids such as nitric acid and hydrofluoric acid, as well as heavy metal ions such as iron, chromium, and nickel. Its complex composition and significant hazards are undeniable. Direct discharge of this waste liquid can corrode pipes, cause soil calcification, and its heavy metal ions may accumulate through the food chain, posing a serious threat to human health. Simultaneously, the waste liquid is rich in recyclable resources; for example, nitric acid content can reach 100-300 g / L, and chromium and nickel content can reach 40-50 g / L. Traditional treatment methods have failed to effectively utilize these resources, resulting in resource waste.

[0003] Currently, the mainstream treatment technologies for stainless steel surface treatment wastewater include neutralization precipitation, membrane separation, and pyrolysis, but all have significant limitations. Neutralization precipitation relies on lime or liquid alkali for neutralization, producing 30%-50% of the treated volume as hazardous sludge containing heavy metals. Subsequent disposal costs are high, and the metal recovery rate is less than 60%, failing to recover acid components. While membrane separation technology can partially recover acid (e.g., nitric acid recovery rate of 65%-90%), it suffers from severe membrane fouling, high energy consumption, and poor retention of metal ions. Pyrolysis (e.g., spray roasting) may produce NO during the high-temperature decomposition of the wastewater. x It produces harmful gases, does not meet the requirements of green manufacturing, and also causes problems such as equipment corrosion and high investment costs.

[0004] Existing patented technologies have also failed to completely solve the above problems. For example, the BSTAR technology (involving processes such as aeration-freezing crystallization, nanofiltration, and spray roasting) used in patent CN104250820A is essentially a pyrolysis technology, which suffers from low acid recovery rate and tail gas treatment problems; patent CN107747101B recovers metals from waste acid through organic acid precipitation, but under strong acid conditions, the metals exist in the form of fluorine complexes, resulting in low metal recovery rate and high cost; patent CN114481148B uses adsorption materials to treat pickling waste liquid, but since the acid components in the waste passivation liquid have been basically consumed, the passivation liquid cannot be recycled and regenerated; patent CN118495482A uses concentrated sulfuric acid replacement and vacuum separation technology to recover hydrofluoric acid and nitric acid, but the azeotropic effect of water and acid leads to high energy consumption, and residual sulfates easily clog the equipment.

[0005] Against the backdrop of increasingly stringent environmental protection requirements and the continuous promotion of chromium-free passivation technology by international standards, the resource-based treatment of stainless steel surface treatment waste liquid shows enormous market demand. It is estimated that my country's annual stainless steel production exceeds 30 million tons, with a corresponding annual generation of approximately 1.5 million tons of passivation waste liquid, indicating a huge market potential for its resource recovery. However, existing treatment methods still have significant shortcomings in terms of resource utilization, process stability, and energy consumption, failing to meet the urgent need for efficient, low-consumption, and synergistic recovery processes. This restricts the simultaneous resource recovery of acid and metal components in the waste liquid and has become a key challenge for technological upgrading in the industry. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the resource utilization of stainless steel surface treatment waste liquid, which solves the problems of low resource utilization, serious secondary pollution, high treatment cost and poor process stability in the prior art. It realizes the efficient synergistic recovery of acid and metal components in waste liquid, the source reduction of hazardous waste, the green conversion of valuable by-products, and a significant reduction in the overall treatment cost.

[0007] The technical solution adopted in this invention is a method for resource recovery of stainless steel surface treatment waste liquid, comprising the following steps: S1: Add an alkaline compound to the stainless steel surface treatment waste liquid to carry out a neutralization and precipitation reaction. After the reaction, perform solid-liquid separation to obtain a mixed salt solution and a metal hydroxide precipitate. S2: The mixed salt solution obtained in step S1 is mixed with a precipitant to carry out a precipitation reaction. After the reaction, solid-liquid separation is performed to obtain regenerated acid solution and precipitated insoluble salt precipitate. S3: Calcine the metal hydroxide precipitate obtained in step S1 to obtain a composite metal oxide product.

[0008] Further, in step S1, the alkaline compound is sodium hydroxide or potassium hydroxide, and the pH value of the neutralization precipitation reaction system is adjusted to 6-10.

[0009] Furthermore, when the alkaline compound is potassium hydroxide, the precipitant in step S2 is tartaric acid or fluorosilicic acid; when the alkaline compound is sodium hydroxide, the precipitant is fluorosilicic acid.

[0010] Further, in step S2, the amount of precipitant added is such that the molar ratio of the precipitant to all alkali metal ions in the mixed salt solution is (0.5~0.8):1.

[0011] Furthermore, in step S2, the precipitation reaction is carried out at room temperature and the stirring time is 2 to 3 hours.

[0012] Further, in step S3, the metal hydroxide precipitate is calcined for 2 hours at a temperature of 600℃~1200℃ under an inert atmosphere.

[0013] The beneficial effects of this invention are: This invention achieves efficient resource recovery of stainless steel surface treatment wastewater by neutralizing and precipitating metal precipitates from the wastewater, then adding a specific acid to the filtrate to regenerate the pickling and passivation solution and produce a specific salt as a byproduct. The metal precipitates are then calcined to convert them into ceramic additives. Under optimal conditions, this method can increase the recovery rate of mixed acid radicals to over 99%, while simultaneously achieving a similarly high recovery rate of metal ions, successfully producing high-value-added specific acid salt products. This method completely solves the wastewater pollution problem while significantly reducing raw material costs and process energy consumption, improving overall process economics, effectively reducing carbon emissions from the stainless steel industry, and realizing the recycling of elements within the region. Attached Figure Description

[0014] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the process flow of the method of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 A method for resource recovery of stainless steel surface treatment waste liquid, such as Figure 1 As shown, it includes the following steps: (1) Take 1000g of stainless steel surface treatment waste liquid that has been actually sampled. The waste liquid mainly contains two inorganic acids, nitric acid and hydrofluoric acid, as well as metal ions such as chromium, iron and nickel. Add potassium hydroxide solid to the stainless steel surface treatment waste liquid and stir to make it react fully. Adjust the pH value of the system to 6. Under this condition, the metal ions such as chromium, iron and nickel in the waste liquid form hydroxide precipitates. Fluoride ions partially form metal fluoride precipitates or complexes, and partially combine with potassium ions in a free state to form potassium fluoride. Then filter and separate to obtain a mixed potassium salt solution filtrate mainly composed of potassium nitrate and potassium fluoride and metal hydroxide precipitate. The metal hydroxide precipitate needs to be pretreated according to the product use and with reference to industry conventional methods (such as washing and purification) to remove soluble impurity ions such as potassium and sodium, so as to ensure the purity of the subsequent calcination product.

[0018] (2) Add tartaric acid to the mixed potassium salt filtrate obtained in step (1) at a molar ratio of potassium ions to tartaric acid of 1:0.5 and stir at room temperature for 2 hours; tartaric acid reacts with potassium nitrate, potassium fluoride and other substances in the filtrate to form potassium hydrogen tartrate precipitate; after filtration, crude potassium hydrogen tartrate product and regenerated acid solution are obtained; the crude potassium hydrogen tartrate product is purified according to industry conventional methods (such as washing and recrystallization) to obtain industrial grade potassium hydrogen tartrate product; the regenerated acid solution contains recovered nitric acid, hydrofluoric acid and other effective components, and the acid recovery efficiency is not less than 90%. After testing and adjusting the key indicators (such as free acid concentration and specific metal ion content) to meet the requirements of stainless steel pickling and passivation process, it can be directly reused in the stainless steel pickling and passivation process.

[0019] (3) The metal hydroxide precipitate obtained in step (1) and after washing and purification is calcined at 800°C for 2 hours under an inert gas (such as nitrogen) atmosphere. Under this condition, the chromium element can be effectively prevented from being converted into hexavalent chromium. After calcination, a chromium, iron and nickel composite metal oxide with a stable structure is obtained. This product can be used as a high-performance ceramic additive.

[0020] Example 2 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: (1) Take 1000g of stainless steel surface treatment waste liquid that has been actually sampled. The waste liquid mainly contains two inorganic acids, nitric acid and hydrofluoric acid, as well as metal ions such as chromium, iron and nickel. Add sodium hydroxide solid to the stainless steel surface treatment waste liquid and stir to make it react fully. Adjust the pH value of the system to 6. Under this condition, the metal ions such as chromium, iron and nickel in the waste liquid form hydroxide precipitates and generate corresponding mixed hydroxide precipitates. Fluoride ions partially form metal fluoride precipitates or complexes, and partially combine with sodium ions in a free state to form sodium fluoride. Then filter and separate to obtain a mixed sodium salt solution filtrate mainly composed of sodium nitrate and sodium fluoride and metal hydroxide precipitates. The metal hydroxide precipitates may contain soluble impurity ions such as sodium and potassium. In order to ensure the purity and structural stability of the subsequent calcination products, it is necessary to carry out corresponding pretreatment according to the product use and with reference to industry conventional methods (such as washing and purification).

[0021] (2) Add fluorosilicic acid to the mixed sodium salt filtrate obtained in step (1) at a molar ratio of sodium ions to fluorosilicic acid of 1:0.5 and stir at room temperature for 3 hours. The fluorosilicic acid reacts with the sodium ions in the filtrate to generate sodium fluorosilicate precipitate, and at the same time, nitric acid and hydrofluoric acid are regenerated. After filtration, crude sodium fluorosilicate product and regenerated acid solution are obtained. The crude sodium fluorosilicate product can be purified by referring to the industry's conventional methods (such as washing and recrystallization). The regenerated acid solution contains the recovered nitric acid, hydrofluoric acid and other effective components, and the acid recovery efficiency is not less than 90%. Since the regenerated acid solution may contain impurities such as silicon-containing compounds introduced by raw materials or side reactions, it needs to be tested and the key indicators (such as free acid concentration, specific metal ions and silicon content) adjusted. It can be directly reused after meeting the process requirements of stainless steel pickling and passivation solution.

[0022] (3) The metal hydroxide precipitate obtained in step (1) and after washing and purification is calcined at 900°C for 2 hours under an inert gas (such as nitrogen) atmosphere. This condition can effectively prevent chromium from being converted into hexavalent chromium. After calcination, a chromium, iron and nickel composite metal oxide with a stable structure is obtained. This product can be used as a high-performance ceramic additive.

[0023] Example 3 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: (1) Take 1000g of stainless steel surface treatment waste liquid that has been actually sampled. The waste liquid mainly contains two inorganic acids, nitric acid and hydrofluoric acid, as well as metal ions such as chromium, iron and nickel. Add potassium hydroxide solid to the stainless steel surface treatment waste liquid and stir to make it react fully. Adjust the pH value of the system to 7. Under these conditions, the metal ions such as chromium, iron and nickel in the waste liquid form hydroxide precipitates. Fluoride ions partially form metal fluoride precipitates or complexes, and partially combine with potassium ions in a free state to form potassium fluoride. Then filter and separate to obtain a mixed potassium salt solution filtrate mainly composed of potassium nitrate and potassium fluoride and metal hydroxide precipitate. The metal hydroxide precipitate needs to be pretreated according to the product use and with reference to industry conventional methods (such as washing and purification) to remove soluble impurity ions such as potassium and sodium, so as to ensure the purity of the subsequent calcination product. (2) Add tartaric acid to the mixed potassium salt filtrate obtained in step (1) at a molar ratio of potassium ions to tartaric acid of 1:0.6 and stir at room temperature for 2 hours; tartaric acid reacts with potassium nitrate, potassium fluoride and other substances in the filtrate to form potassium hydrogen tartrate precipitate; after filtration, crude potassium hydrogen tartrate product and regenerated acid solution are obtained; the crude potassium hydrogen tartrate product is purified according to industry conventional methods (such as washing and recrystallization) to obtain industrial grade potassium hydrogen tartrate product; the regenerated acid solution contains recovered nitric acid, hydrofluoric acid and other effective components, and the acid recovery efficiency is not less than 90%. After testing and adjusting the key indicators (such as free acid concentration and specific metal ion content) to meet the requirements of stainless steel pickling and passivation process, it can be directly reused in the stainless steel pickling and passivation process; (3) The metal hydroxide precipitate obtained in step (1) and after washing and purification is calcined at 900°C for 2 hours under an inert gas (such as nitrogen) atmosphere. Under this condition, the chromium element can be effectively prevented from being converted into hexavalent chromium. After calcination, a chromium, iron and nickel composite metal oxide with a stable structure is obtained. This product can be used as a high-performance ceramic additive.

[0024] Example 4 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the following adjustments, the raw materials, proportions, and steps are the same as in Example 2: In step (1), the pH of the neutralization precipitation reaction system is adjusted to 8.

[0025] Example 5 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the following adjustments, the raw materials, proportions, and steps are the same as in Example 1: In step (1), the pH value of the neutralization precipitation reaction system is adjusted to 9.

[0026] Example 6 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the following adjustments, the raw materials, proportions, and steps are the same as in Example 3: In step (1), the pH value of the neutralization precipitation reaction system is adjusted to 10.

[0027] Example 7 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for adjusting the calcination temperature to 1200℃ in step (3), the other raw materials, proportions and steps are the same as in Example 2.

[0028] Example 8 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), in which the amount of tartaric acid added as the precipitant is adjusted to 1:0.8 based on the molar ratio of potassium ions to tartaric acid, all other raw materials, proportions and steps are the same as in Example 1.

[0029] Example 9 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), in which the amount of precipitant fluorosilicic acid added is adjusted to 1:0.6 based on the molar ratio of sodium ions to fluorosilicic acid, the other raw materials, proportions and steps are the same as in Example 2.

[0030] Example 10 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), in which the amount of precipitant fluorosilicic acid added is adjusted to 1:0.8 based on the molar ratio of sodium ions to fluorosilicic acid, the other raw materials, proportions and steps are the same as in Example 2.

[0031] Example 11 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for adjusting the calcination temperature of the metal hydroxide precipitate to 600°C in step (3), the other raw materials, proportions and steps are the same as in Example 1.

[0032] Example 12 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: (1) Take 1000g of stainless steel surface treatment waste liquid that has been actually sampled. The waste liquid mainly contains two inorganic acids, nitric acid and hydrofluoric acid, as well as metal ions such as chromium, iron and nickel. Add potassium hydroxide solid to the stainless steel surface treatment waste liquid and stir to make it react fully. Adjust the pH value of the system to 6.5. Under this condition, the metal ions such as chromium, iron and nickel in the waste liquid form hydroxide precipitates. Fluoride ions partially form metal fluoride precipitates or complexes, and partially combine with potassium ions in a free state to form potassium fluoride. Then filter and separate to obtain a mixed potassium salt solution filtrate mainly composed of potassium nitrate and potassium fluoride and metal hydroxide precipitate. The metal hydroxide precipitate needs to be pretreated according to the product use and with reference to industry conventional methods (such as washing and purification) to remove soluble impurity ions such as potassium and sodium, so as to ensure the purity of the subsequent calcination product.

[0033] (2) Add fluorosilicic acid to the mixed potassium salt filtrate obtained in step (1) at a molar ratio of potassium ions to fluorosilicic acid of 1:0.5, stir at room temperature for 2.5 hours, and react to generate potassium fluorosilicate precipitate; after filtration, obtain crude potassium fluorosilicate product and regenerated acid solution; wherein, the crude potassium fluorosilicate product can be purified by referring to industry conventional methods (such as washing and recrystallization); the regenerated acid solution contains recovered nitric acid, hydrofluoric acid and other effective components, and the acid recovery efficiency is not less than 90%. After testing and adjusting the key indicators (such as free acid concentration, specific metal ions and silicon content, etc.) to meet the requirements of stainless steel pickling and passivation solution process, it can be directly reused in the stainless steel pickling and passivation process.

[0034] (3) The metal hydroxide precipitate obtained in step (1) and after washing and purification is calcined at 950°C for 2 hours under an inert gas (such as nitrogen) atmosphere. This condition can effectively prevent chromium from being converted into hexavalent chromium. After calcination, a chromium, iron and nickel composite metal oxide with a stable structure is obtained. This product can be used as a high-performance ceramic additive.

[0035] Comparative Example 1 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the use of calcium hydroxide as a neutralizing agent, the other raw materials, proportions and steps are the same as in Example 1.

[0036] The introduction of calcium hydroxide brings calcium ions, which combine with acid radicals in the waste liquid to form insoluble calcium salt precipitates, making it impossible to effectively recover valuable acid radicals in the form of soluble salts. The insoluble calcium salts formed will form complex co-precipitates with metal hydroxides, which not only increases the sludge volume but also reduces the metal recovery rate.

[0037] Comparative Example 2 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the pH value adjusted to 2 in the neutralization precipitation reaction in step (1), the other raw materials, proportions and steps are the same as in Example 1.

[0038] Under strongly acidic conditions of pH=2, most of the target metal ions such as iron, chromium, and nickel in the waste liquid still exist in the solution in the form of soluble ions and fail to form hydroxide precipitates. As a result, the subsequent filtration steps cannot achieve effective separation of metals, and the metal recovery rate is low.

[0039] Comparative Example 3 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), where oxalic acid is used as a precipitant to react with potassium ions to generate oxalate precipitate, the other raw materials, proportions and steps are the same as in Example 1.

[0040] Oxalic acid reacts with potassium ions to mainly form potassium oxalate, which is easily soluble in water, or acid salts with poor solubility. It is difficult to achieve efficient and selective separation of potassium ions and acid radicals through precipitation. This characteristic means that potassium ions in the mixed potassium salt filtrate cannot be effectively removed, which in turn hinders the recovery of acid radicals and reduces the acid recovery efficiency.

[0041] Comparative Example 4 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for the calcination temperature of the metal hydroxide precipitate in step (3) being 400°C, the other raw materials, proportions and steps are the same as in Example 1.

[0042] At a calcination temperature of 400℃, the metal hydroxide failed to completely transform into oxide, and the product still contained some bound water or hydroxyl groups; resulting in unstable product quality and failure to completely transform into structurally stable composite metal oxide.

[0043] Comparative Example 5 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (1), in which sodium carbonate is used as a neutralizing alkali instead of potassium hydroxide, the other raw materials, proportions and steps are the same as in Example 1.

[0044] When sodium carbonate reacts with acid in waste liquid, it releases a large amount of carbon dioxide gas, which easily leads to excessive foaming and splashing in the reaction system, causing instability and uneven and incomplete precipitation of metal ions. Simultaneously, carbonate ions react with some metal ions to form carbonate or basic carbonate precipitates. These precipitates are often colloidal or fine particles, making solid-liquid separation difficult and resulting in metal loss during filtration.

[0045] Comparative Example 6 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for adjusting the pH of the neutralization precipitation reaction system to 11 in step (1), the other raw materials, proportions and steps are the same as in Example 2.

[0046] Under strongly alkaline conditions of pH=11, some heavy metal ions with amphoteric properties in the waste liquid will form soluble complex ions and redissolve, resulting in incomplete metal precipitation and a decrease in metal recovery rate. At the same time, the strongly alkaline environment promotes the adsorption or co-precipitation of some acid radical ions with the metal precipitate, which cannot be effectively retained in the filtrate, resulting in a decrease in acid radical recovery rate.

[0047] Comparative Example 7 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), in which perchloric acid is used as a precipitant instead of tartaric acid, the other raw materials, proportions and steps are the same as in Example 1.

[0048] Perchloric acid is a strong oxidizing agent. When it comes into contact with trace organic matter or reducing substances that may remain in the mixed potassium salt filtrate, there is a risk of violent redox reactions, which may pose serious safety hazards. At the same time, the strong oxidizing property of perchloric acid can destroy the chemical form of the target acid anions or change the valence state of trace metal ions in the filtrate. This not only leads to the introduction of new impurity ions, but also complicates the composition of the regenerated acid solution and contaminates it, making it unable to meet the requirements for reuse.

[0049] Comparative Example 8 A method for resource recovery from waste liquid from stainless steel surface treatment includes the following steps: Except for step (2), where tartaric acid is used as a precipitant instead of fluorosilicic acid when the alkaline compound is sodium hydroxide, the other raw materials, proportions and steps are the same as in Example 2.

[0050] Because sodium hydrogen tartrate, formed by the reaction of tartaric acid and sodium ions, has high solubility in water, it is difficult to form an effective precipitate. Therefore, after stirring at room temperature, no significant precipitate is formed in the solution system, making it impossible to effectively remove sodium ions through solid-liquid separation. A large amount of sodium salt remains in the filtrate, which seriously hinders the regeneration and recovery of effective acid components such as hydrofluoric acid and nitric acid, and significantly reduces the acid recovery efficiency. This result proves that tartaric acid is not an effective precipitant in sodium salt systems, highlighting the necessity of the technical feature in this invention that "when the alkaline compound is sodium hydroxide, the precipitant is fluorosilicic acid".

[0051] To evaluate the overall performance of the resource recovery method of this invention, the nitrate (NO3) in the waste liquid was analyzed. - ), fluoride ions (F) -The total recovery rate of the ceramic additives and the recovery rates of metal ions such as chromium (Cr), iron (Fe), and nickel (Ni) were determined, and the results are shown in Table 1.

[0052] Table 1. Acid and metal recovery rates for each embodiment

[0053] The technical solution of this invention achieves simultaneous and efficient resource recovery of acid and metal components from stainless steel surface treatment wastewater through a three-stage synergistic process of "neutralization precipitation—acid regeneration—calcination". As shown in Table 1, under the process parameter combinations covered in Examples 1-12, this method achieves excellent recovery results. Examples 1-3 are particularly representative; under optimized conditions of using potassium hydroxide or sodium hydroxide as a neutralizing agent, controlling the pH of the reaction system to 6-7, selecting tartaric acid or fluorosilicic acid as a precipitant, and calcining at 800-900℃ in an inert atmosphere, the acid recovery rate and metal recovery rate can reach over 99.2% and 99.0%, respectively, demonstrating the optimal resource recovery performance of this process.

[0054] The experimental results of Comparative Examples 1-8, from the opposite perspective, verified the necessity and intrinsic correlation of each key process condition. When the neutralizing agent was replaced with calcium hydroxide (Comparative Example 1), the reaction pH deviated from strong acidity (Comparative Example 2, pH=2), the precipitant was replaced with oxalic acid (Comparative Example 3), or the calcination temperature was significantly lower (Comparative Example 4, 400℃), the recovery efficiency of acid and / or metal all decreased significantly. These systematic comparisons show that the type of neutralizing agent, pH control range, selection of specific precipitants, and suitable calcination temperature used in the examples are not simply a superposition of processes, but constitute a holistic technical solution that supports each other and synergistically enhances efficiency. Any change in key conditions leads to a decrease in overall recovery efficiency, thus demonstrating the unique inventiveness and technical advantages of the present invention in achieving efficient resource recovery.

[0055] Therefore, the resource recovery method provided by this invention can stably and efficiently recover acid components and valuable metals from waste liquid under the aforementioned process conditions, producing reusable recycled acid, high-purity acid salt products (such as potassium hydrogen tartrate and sodium / potassium fluorosilicate), and composite metal oxides that can be used as ceramic additives. This method not only achieves near-zero discharge and high-value utilization of all components of waste liquid from the source, significantly reducing raw material consumption, hazardous waste disposal pressure, and related process energy consumption and carbon emissions, but also provides the stainless steel industry with an economically feasible and environmentally friendly green circular technology path, possessing significant application value and promising prospects for promotion.

[0056] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for resource recovery of waste liquid from stainless steel surface treatment, characterized in that, Includes the following steps: S1: Add an alkaline compound to the stainless steel surface treatment waste liquid to carry out a neutralization and precipitation reaction. After the reaction, perform solid-liquid separation to obtain a mixed salt solution and a metal hydroxide precipitate. S2: The mixed salt solution obtained in step S1 is mixed with a precipitant to carry out a precipitation reaction. After the reaction, solid-liquid separation is performed to obtain regenerated acid solution and precipitated insoluble salt precipitate. S3: Calcine the metal hydroxide precipitate obtained in step S1 to obtain a composite metal oxide product.

2. The method for resource utilization of stainless steel surface treatment waste liquid according to claim 1, characterized in that, In step S1, the alkaline compound is sodium hydroxide or potassium hydroxide, and the pH value of the neutralization precipitation reaction system is adjusted to 6-10.

3. The method for resource recovery of stainless steel surface treatment waste liquid according to claim 2, characterized in that, When the alkaline compound is potassium hydroxide, the precipitant in step S2 is tartaric acid or fluorosilicic acid; when the alkaline compound is sodium hydroxide, the precipitant is fluorosilicic acid.

4. A method for resource recovery of stainless steel surface treatment waste liquid according to claim 1 or 3, characterized in that, In step S2, the amount of precipitant added is such that the molar ratio of the precipitant to all alkali metal ions in the mixed salt solution is (0.5~0.8):

1.

5. The method for resource recovery of stainless steel surface treatment waste liquid according to claim 1, characterized in that, In step S2, the precipitation reaction is carried out at room temperature and the stirring time is 2 to 3 hours.

6. The method for resource recovery of stainless steel surface treatment waste liquid according to claim 1, characterized in that, In step S3, the metal hydroxide precipitate is calcined for 2 hours at a temperature of 600℃~1200℃ under an inert atmosphere.

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