A method and device for preparing an ultra-low heavy metal polymeric ferric sulfate based on complex precipitation

Abstract

The application discloses a kind of based on complex precipitate ultra-low heavy metal polymeric ferric sulfate preparation method and device, it is related to polymeric ferric sulfate preparation process field, comprising the following steps: S1, iron-containing raw material is catalytically oxidized in sulfuric acid medium, preliminary hydrolysis polymerization is carried out, intermediate state acidic polymerization liquid;S2, add precipitator precursor to carry out reaction, precipitator precursor releases active complexing group at controlled rate, gradient complexation reaction occurs, and complex precipitate is formed;S3, solid-liquid separation is carried out, and the clear polymeric ferric sulfate supernatant is obtained;S4, ripening.The application significantly improves the selective precipitation efficiency of heavy metal ions by the controlled slow release of active complexing group, avoids the competition side reaction with iron ions, and obtains high-quality precipitate more easily separated, and process parameters can be dynamically optimized according to real-time data of raw material heavy metal composition and content, so that the production process has self-adaptive ability.

Description

Technical Field

[0001] This invention relates to the field of polyferric sulfate preparation process, specifically to a method and apparatus for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation. Background Technology

[0002] Polyferric sulfate (PFLS) is a high-performance, widely used inorganic polymeric flocculant, playing a crucial role, particularly in drinking water purification, wastewater treatment, and industrial process water treatment. Its excellent flocculation effect, wide pH adaptability, and low risk of residual aluminum make it a significant alternative to traditional aluminum-based flocculants. With increasingly stringent drinking water quality standards, especially the stricter limits on heavy metal impurities (such as lead, cadmium, chromium, and arsenic), the purity of water treatment agents is subject to near-obsessive requirements. Therefore, developing a stable and efficient PFLS preparation technology to remove trace heavy metal impurities from products is of great significance for ensuring drinking water safety and enhancing product competitiveness.

[0003] Currently, the industrial production of polyferric sulfate is mainly based on a catalytic oxidation-polymerization process using ferrous sulfate, iron filings, or iron ore acid solutions as raw materials. To control the heavy metal content in the final product, the industry typically adopts two technical routes: one is to pretreat the raw materials to reduce the introduction of impurities; the other is to remove impurities and purify the product during or after its preparation. Common methods for the latter include adding precipitants such as sulfides and phosphates to the reaction system to form insoluble heavy metals for separation, or using physicochemical methods such as adsorption and ion exchange for deep purification. These methods can reduce the concentration of heavy metals in the finished product to some extent.

[0004] However, traditional precipitants are mostly added directly, which can lead to decreased selectivity in highly acidic polymerization systems with high ferric ion concentrations due to localized overconcentration. This can not only affect the impurity removal efficiency but also cause unnecessary side reactions with ferric ions or produce colloidal precipitates that are difficult to settle, increasing separation difficulty and potentially affecting the stability of the final product. Secondly, due to the diverse sources of raw materials, the types and contents of heavy metal impurities often fluctuate significantly. Existing process parameters (such as precipitant dosage and reaction conditions) are usually set based on experience or are relatively fixed, lacking the ability to adaptively adjust to fluctuations in raw material impurities. This makes it difficult for the process to always operate at its optimal state; either incomplete impurity removal affects the product yield, or over-treatment increases costs and introduces new process control challenges. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a method and apparatus for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation, so as to solve the technical problems in the existing preparation process, such as poor impurity removal selectivity and difficulty in separating precipitates due to direct addition of precipitant, and the inability to achieve stable and adaptive deep impurity removal due to fluctuations in the heavy metal composition of raw materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method and apparatus for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation, comprising the following steps: S1, obtaining iron-containing raw materials, and obtaining the heavy metal impurity composition and content data of the iron-containing raw materials before or simultaneously with obtaining the iron-containing raw materials; S2, based on the heavy metal impurity composition and content data, dynamically optimizing and controlling the process parameters of complexation precipitation impurity removal treatment through an intelligent control system, and performing complexation precipitation impurity removal treatment in one of the following two ways: Method A: first performing complexation precipitation impurity removal treatment on the iron-containing raw materials to obtain purified raw materials, and then oxidizing and polymerizing the purified raw materials to obtain a polymer liquid; Method B: first performing oxidative polymerization on the iron-containing raw materials to obtain an intermediate polymer liquid, and then performing complexation precipitation impurity removal treatment on the intermediate polymer liquid to obtain a polymer liquid; S3, performing solid-liquid separation on the polymer liquid obtained in step S2 to obtain a clear polyferric sulfate solution; S4, aging the clear polyferric sulfate solution to obtain the polyferric sulfate product.

[0007] In a preferred embodiment of the present invention, step S2 adopts method A, wherein the treatment of iron-containing raw materials by complexation precipitation for impurity removal includes: dissolving or slurrying the iron-containing raw materials, adding a precipitant precursor, and reacting under stirring conditions at 30-70°C. The precipitant precursor releases active complexing groups at a controlled rate, which undergo a gradient complexation reaction with heavy metal ions in the raw material solution to form heavy metal complex precipitates. Then, solid-liquid separation is performed to obtain purified raw material solution. The purified raw material solution is then catalytically oxidized in sulfuric acid medium to perform hydrolysis polymerization to obtain a polymer solution.

[0008] In another preferred embodiment of the present invention, step S2 adopts method B, wherein the oxidative polymerization of iron-containing raw materials to obtain intermediate polymer solution includes: catalytically oxidizing the iron-containing raw materials in sulfuric acid medium to perform preliminary hydrolysis polymerization, thereby obtaining an intermediate acidic polymer solution with pH < 2.5; the complexation precipitation and impurity removal treatment of the intermediate polymer solution includes: adding a precipitant precursor to the intermediate acidic polymer solution, and reacting it at 50-70°C under stirring conditions, wherein the precipitant precursor releases active complexing groups at a controlled rate, and undergoes a gradient complexation reaction with heavy metal ions in the liquid to form heavy metal complex precipitates.

[0009] Furthermore, in the above two methods, the precipitant precursor is a substance that can alleviate the release of dithiocarbamate groups, organophosphonate groups, or thio-functional groups under the temperature and acidity conditions of the reaction system, and the precipitant precursor is selected from one or more of the following: microencapsulated heavy metal scavengers, heavy metal scavengers supported on porous or layered carriers, or polymers with active groups linked by hydrolyzable chemical bonds.

[0010] Furthermore, in both of the above methods, in step S2, the pH value of the reaction is controlled to be 1.5-2.2.

[0011] Furthermore, in both of the above methods, in step S2, the release rate of the active complexing group is controlled by adjusting the addition rate, physical morphology, or dispersion state of the precipitant precursor in the reaction system.

[0012] Furthermore, the intelligent control system calculates and adjusts in real time the total dosage of the precipitant precursor, the addition rate, and the reaction temperature and time of step S2 based on the heavy metal impurity composition and content data through a built-in process optimization model; the process optimization model also decides whether to adjust the redox potential of the oxidation stage in step S2 based on the types and proportions of different metal ions in the heavy metal impurity composition, so as to optimize the valence state of the heavy metal ions.

[0013] Furthermore, the acquisition of heavy metal impurity composition and content data of iron-containing raw materials is accomplished by using an online heavy metal analyzer or a rapid digestion-detection device.

[0014] Furthermore, in step S3, the solid-liquid separation is carried out under a heat preservation condition of 40-65℃.

[0015] The present invention also includes an apparatus for implementing the above method, comprising: The raw material processing unit is used to perform dissolution, slurry preparation, or oxidative polymerization operations on iron-containing raw materials. A gradient complexation precipitation reaction system, connected to the raw material processing unit, is used to receive iron-containing raw material solutions or intermediate polymerization liquids and complete the gradient complexation precipitation reaction; it is equipped with a precipitant precursor addition unit. A solid-liquid separation system, connected to the gradient complexation precipitation reaction system, is used to separate heavy metal complex precipitates from polyferric sulfate solution. A product maturation system, connected to the solid-liquid separation system, is used to mature the polyferric sulfate solution into the final product. An intelligent control center is connected to the raw material component detection unit, the precipitant precursor addition unit, and the key parameter detection and control units in the raw material processing unit and the gradient complexation precipitation reaction system, respectively, to receive raw material heavy metal data and output control commands according to a preset model to dynamically optimize process parameters.

[0016] In summary, the present invention has the following main beneficial effects: This invention introduces a precipitant precursor for gradient complexation precipitation, combined with intelligent closed-loop control based on raw material impurity fingerprints. This not only significantly improves the selective precipitation efficiency of heavy metal ions through the controlled, slow release of active complexing groups, avoiding competitive side reactions with iron ions and obtaining higher-quality precipitates that are easier to separate, but also dynamically optimizes process parameters based on real-time data on the heavy metal composition and content of the raw materials, enabling the production process to be adaptive. This invention provides two optional impurity removal routes: raw material pre-removal or intermediate removal, which can be flexibly selected according to actual production conditions and raw material characteristics. Therefore, even with fluctuations in raw material sources, it can still stably and efficiently produce polyferric sulfate products with extremely low heavy metal content and consistent quality, while achieving an optimal balance between treatment effect and production cost. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a diagram showing the system composition and connection relationships of the present invention; Figure 3 This is a schematic diagram of the gradient complexation precipitation mechanism of the present invention; Figure 4 This is a block diagram of the intelligent control logic of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] The embodiments of the present invention will now be described.

[0020] A method for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation, such as... Figures 1 to 4 As shown, an innovative gradient complexation precipitation process is combined with intelligent process control to stably produce high-quality products with ultra-low heavy metal content.

[0021] From a chemical perspective, the formation of polyferric sulfate is essentially a hydrolysis-polymerization process of ferric ions in an acidic medium. When iron-containing raw materials are oxidized to ferric ions in a sulfuric acid medium, these ions do not exist in a simple free state but immediately undergo hydrolysis with water molecules to generate a series of hydroxyl iron complexes. These complexes further polymerize through hydroxyl bridging, forming hydroxyl polyferric ions with polynuclear structures. These polynuclear complexes are not only the effective components of polyferric sulfate but also provide a specific chemical environment for subsequent heavy metal complexation and impurity removal. Studies have shown that under strongly acidic conditions with a pH below 2.5, ferric ions mainly exist in a low-polymerization state, while the high-polymerization state gradually increases with increasing pH and reaction progress. This characteristic is crucial for gradient complexation precipitation impurity removal because it determines the relative advantage of ferric ions and heavy metal ions in the competitive complexation reaction.

[0022] The removal of heavy metal impurities is based on a different set of chemical principles. The precipitant precursor used in this invention can release active complexing groups under specific conditions. These groups have a high selective affinity for heavy metal ions. Taking the dithiocarbamate group as an example, its molecular structure contains sulfur atoms. The lone pair electrons of the sulfur atom can form coordinate bonds with the empty orbitals of heavy metal ions, generating stable five- or six-membered ring chelates. This selectivity of chelation stems from the differences in electronic configuration, ionic radius, and coordination field stability energy between heavy metal ions and iron ions. Heavy metal ions such as lead, cadmium, and mercury are soft acids or boundary acids, and tend to coordinate with soft bases containing sulfur and nitrogen; while iron ions are hard acids, and tend to bind with oxygen-containing coordination groups. Utilizing this principle, within an appropriate pH range, selective capture of heavy metal ions can be achieved, avoiding competitive reactions with iron ions.

[0023] To further enhance the selective capture capability of heavy metal ions, this invention introduces chelate-type directional capture agents into the precipitant precursor. These chelate-type directional capture agents are organic ligands containing coordinating atoms such as nitrogen, oxygen, and sulfur, capable of forming stable five- or six-membered cyclic chelates with heavy metal ions under acidic conditions. The design of these capture agents is based on the hard and soft acid-base theory in coordination chemistry. By selecting coordinating atoms and ligand structures that match the heavy metal ions, the directional capture capability of target heavy metal ions such as lead, cadmium, mercury, and arsenic is significantly enhanced. Compared with traditional sulfide and phosphate precipitants, chelate-type directional capture agents maintain stable coordination activity under strongly acidic conditions (pH 1.5-2.5) and within a certain temperature range (30-70℃) during the polyferric sulfate reaction, avoiding the problem of easy decomposition or inactivation of traditional precipitants under acidic conditions. Simultaneously, the chelate precipitates formed have complete crystal structures, high density, and are easy to separate from liquids, effectively solving the process problem of difficult separation of colloidal precipitates generated by traditional precipitation methods.

[0024] Guided by the aforementioned chemical principles, the specific implementation process of this invention is as follows. First, the iron-containing raw materials used need to be analyzed. Before or simultaneously with the input of the iron-containing raw materials into the production system, an online heavy metal analyzer or a rapid digestion-detection device is used to obtain precise composition and content data of heavy metal impurities in the raw materials. This data includes, but is not limited to, the types and concentrations of elements such as lead, cadmium, chromium, and arsenic. This data is transmitted in real time to the intelligent control system as the basis for subsequent dynamic optimization of process parameters.

[0025] The intelligent control system incorporates an optimized algorithm model trained on extensive experimental data and validated against process mechanisms. Based on the received heavy metal fingerprint data of the raw materials and the quality requirements of the target product, the system automatically calculates the optimal process parameters required for the current batch of raw materials and adjusts the operating conditions of subsequent production units accordingly. The core decision-making logic of the intelligent control system is based on the thermodynamic and kinetic parameters of the complexation reaction between heavy metals and active groups. Different heavy metal ions have different stability constants with specific complexing groups, requiring different reaction pH values, temperatures, and times. For example, the optimal removal pH for arsenic ions is typically between 6 and 7, while cadmium ions require pH 8-9 to achieve a removal rate of over 90%. The intelligent control system calculates the optimal combination of process parameters based on this fundamental chemical data and the actual composition of the raw materials.

[0026] Based on this, the core impurity removal step of the present invention is carried out by gradient complexation precipitation, and two optional implementation routes are provided, namely the raw material pre-impurity removal route and the intermediate impurity removal route, which production units can flexibly choose according to the actual raw material characteristics and equipment conditions.

[0027] In the raw material pre-removal route, iron-containing raw materials, such as ferrous sulfate heptahydrate, iron powder, or ferrous sulfate by-products of titanium dioxide, are first dissolved or prepared into a slurry with an appropriate amount of water or dilute sulfuric acid to obtain a raw material solution. At this point, the heavy metal ions in the solution are not yet affected by the steric hindrance of the iron ion polymerization products and are in a relatively free ionic state, which is conducive to the full contact and reaction between the active complexing groups and the heavy metal ions. Subsequently, the raw material solution is sent to a gradient complexation precipitation reaction system and heated to a temperature range of 30 to 70 degrees Celsius under stirring. At this temperature, a precipitant precursor is added to the system through a precipitant precursor addition unit. The precipitant precursor is a substance that can release active complexing groups at a controlled rate under the temperature and acidity conditions of the reaction system, such as microencapsulated heavy metal traps, organophosphonic acid groups supported on porous silica or layered clay, or polymers with dithiocarbamate groups linked by hydrolyzable chemical bonds. These precursors can also be combined with chelate-type targeted capture agents, such as ethylenediaminetetraacetic acid (EDTA) derivatives, diethylenetriaminepentaacetic acid (DTPA) ligands, or sulfur-containing Schiff bases. These precursors release heavy metal ions under acidic conditions via sustained release or in-situ generation, achieving highly efficient targeted capture. The design of these precursors is based on the sustained-release principle: the microcapsule walls gradually swell and rupture at specific temperatures, and the active groups on the porous carrier are slowly released through diffusion, while hydrolyzable chemical bonds gradually break under acidic conditions. These mechanisms collectively achieve the controlled release of the active groups.

[0028] When these precursors are added to the reaction system, under continuous stirring, the active complexing groups encapsulated or bonded within them, such as dithiocarbamate groups, organophosphonate groups, or thio-functional groups, begin to be slowly released into the liquid phase. This slow release process creates a concentration field of active groups that varies from low to high, allowing heavy metal ions such as lead and cadmium in the raw material solution to preferentially combine with the small amount of active groups released earlier, forming initial precipitate nuclei. This stage follows the classical theory of crystal growth: low supersaturation conditions favor the orderly growth of crystal nuclei, forming structurally complete crystals; while high supersaturation easily leads to explosive nucleation, generating a large number of fine colloidal particles. This invention controls the release rate of active groups, maintaining the system within a suitable supersaturation range, allowing the precipitation reaction to proceed and grow orderly around the initial crystal nuclei, ultimately forming a heavy metal complex precipitate with uniform particle size, complete crystal structure, high density, and easy separation.

[0029] During the reaction, the pH of the system was controlled within the range of 1.5 to 2.2. This acidity range was chosen based on the following chemical principles: under these pH conditions, iron ions mainly exist as hydroxyl complexes, without forming a large amount of ferric hydroxide precipitate; simultaneously, active complexing groups such as dithiocarbamate maintain sufficient coordination activity at this acidity, enabling them to form stable chelates with heavy metal ions; furthermore, this pH range avoids the risk of protonation failure of chalcogenide coordination groups under strongly acidic conditions. By adjusting the physical morphology of the precipitant precursor, the dosing rate, or the dispersion state in the reactor, the release kinetics of the active groups can be precisely controlled to meet the removal requirements of different heavy metal impurities. After the reaction, the slurry containing the complexed precipitate was sent to a solid-liquid separation system and centrifuged or filtered under conditions of 40 to 65 degrees Celsius to obtain a purified raw material solution. The clear liquid is then transported to the raw material oxidation polymerization system, where a catalyst such as sodium nitrite or sodium chlorate is added to the sulfuric acid medium and heated to 70 to 90 degrees Celsius to carry out a catalytic oxidation reaction, which converts ferrous ions into ferric ions and causes preliminary hydrolysis polymerization to form a polymer liquid containing the effective component of polyferric sulfate.

[0030] In the intermediate purification route, the iron-containing raw material is first subjected to direct oxidative polymerization. The iron-containing raw material and sulfuric acid solution are added to a reactor in a specific ratio. A catalyst is added under stirring conditions, and the mixture is heated to 70-90 degrees Celsius to carry out catalytic oxidation and hydrolytic polymerization reactions, yielding an intermediate acidic polymerization solution with a pH value less than 2.5. This polymerization solution contains precursors for polyferric sulfate, such as various polyhydroxyferric polynuclear complexes, and also dissolves heavy metal impurities introduced from the raw material. In this polymerization system, some heavy metal ions may undergo preliminary complexation or adsorption with the polyferric species, increasing the difficulty of their removal. This intermediate polymerization solution is then transferred to a gradient complexation precipitation reaction system, heated to 50-70 degrees Celsius, and the aforementioned precipitant precursor is added through a precipitant precursor addition unit. Under stirring, the precursor releases active complexing groups at a controlled rate. These groups need to compete with the polyferric sulfate for the partially complexed heavy metal ions, thus requiring stronger coordination ability and more precise kinetic control. During the reaction, the pH value was controlled between 1.5 and 2.2, and the release rate was controlled by adjusting the precursor addition rate and morphology. The slurry after the reaction was also subjected to solid-liquid separation under a temperature of 40 to 65 degrees Celsius to obtain a clear polyferric sulfate solution.

[0031] Regardless of the route used, the resulting polyferric sulfate solution is then introduced into a product maturation system, where it is continuously stirred at 60 to 80 degrees Celsius for 1 to 3 hours. This allows the ferric ions in the solution to further hydrolyze and polymerize, resulting in molecular chain growth, increased basicity, and ultimately, a stable liquid polyferric sulfate product. Depending on market demand, this product can also be further spray-dried into a solid powder.

[0032] Throughout the production process, the intelligent control system plays a central role. This system not only calculates parameters such as the total dosage of the precipitant precursor, the dosing rate, and reaction temperature and time based on the raw material heavy metal data, and adjusts the actuators in real time, but also continuously monitors sensor data at key nodes on the production line, such as trace heavy metal residue signals in the post-precipitation clear liquid. It compares actual feedback data with model predictions and continuously fine-tunes model parameters through machine learning algorithms, achieving self-evolution in process optimization capabilities. The intelligent control system's algorithm model incorporates fundamental chemical data such as the complexation stability constants, activation energies, and optimal pH ranges of various heavy metal ions with different active complexing groups, as well as numerous kinetic parameters obtained from experiments. When the raw material fingerprint indicates the coexistence of multiple heavy metals, the system calculates the optimal complexing group release curve and reaction conditions based on the complexation characteristics of each heavy metal ion and their mutual influence. For example, when lead and cadmium are present simultaneously, the system may select a group with good complexing ability for both and control the reaction conditions to achieve a balance in the removal rates of the two ions. In addition, the system can also make decisions based on the model, and fine-tune the redox potential of the system by adjusting the amount of oxidant introduced or the stirring intensity during the oxidative polymerization stage, so as to convert some heavy metal ions such as trivalent arsenic into pentavalent arsenic, making them easier to be captured by subsequent complexing groups, thereby further improving the impurity removal efficiency.

[0033] The apparatus for implementing the above method includes a raw material processing unit, a gradient complexation precipitation reaction system, a solid-liquid separation system, a product maturation system, and an intelligent control center. The raw material processing unit, used for dissolving, slurry preparation, or oxidative polymerization of iron-containing raw materials, can be a dissolving tank or an oxidative polymerization reactor. The gradient complexation precipitation reaction system is connected to the raw material processing unit and is equipped with a precipitant precursor storage tank and a metering and dosing unit, as well as precise temperature control and stirring components. The solid-liquid separation system, such as a centrifuge or filter press, is connected to the precipitation reaction system to separate the precipitate from the clarified liquid. The product maturation system, i.e., the maturation tank, is connected to the solid-liquid separation system. The intelligent control center consists of an industrial computer and a programmable logic controller (PLC), connected to the raw material component detection unit, the precipitant precursor dosing unit, and sensors and control valves in each system for temperature, pH, redox potential, flow rate, etc., to achieve closed-loop adaptive control of the entire process.

[0034] Through the above methods and apparatus, this invention can flexibly select pre-removal or intermediate removal routes based on the actual heavy metal impurities in the raw materials, and achieve dynamic optimization of process parameters through intelligent control. Its chemical basis lies in a deep understanding of the hydrolysis and polymerization mechanism of iron ions and the selective capture mechanism of heavy metal ions by active complexing groups, transforming these fundamental chemical principles into industrially applicable control strategies. Compared with traditional direct precipitation methods, the gradient complexation precipitation technology of this invention achieves kinetic regulation of the precipitation reaction by controlling the release rate of active groups, obtaining precipitates with complete crystal structures that are easy to separate. Compared with traditional fixed processes, the intelligent control system of this invention achieves adaptive optimization for different raw materials, thereby stably producing high-quality polyferric sulfate products with extremely low heavy metal content, effectively solving the problems of poor impurity removal selectivity, difficult precipitation separation, and insufficient process adaptability in existing technologies.

[0035] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation, characterized in that, Includes the following steps: S1. Obtain iron-containing raw materials, and obtain data on the composition and content of heavy metal impurities in the iron-containing raw materials before or at the same time as obtaining the iron-containing raw materials; S2. Based on the heavy metal impurity composition and content data, the process parameters of the complexation precipitation impurity removal treatment are dynamically optimized and controlled by an intelligent control system, and the complexation precipitation impurity removal treatment is carried out using one of the following two methods: Method A: First, the iron-containing raw material is subjected to complexation precipitation to remove impurities, and then the purified raw material is subjected to oxidative polymerization to obtain a polymerization liquid; Method B: First, the iron-containing raw material is subjected to oxidative polymerization to obtain an intermediate polymerization liquid. Then, the intermediate polymerization liquid is subjected to complexation precipitation to remove impurities, and the polymerization liquid is obtained. S3. Perform solid-liquid separation on the polymer solution obtained in step S2 to obtain a clear polyferric sulfate solution; S4. The polyferric sulfate solution is aged to obtain the polyferric sulfate product.

2. The method for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation according to claim 1, characterized in that, Step S2 adopts method A, wherein the complexation precipitation treatment of iron-containing raw materials includes: dissolving or slurrying the iron-containing raw materials, adding a precipitant precursor, and reacting under stirring conditions at 30-70℃. The precipitant precursor releases active complexing groups at a controlled rate, which undergo a gradient complexation reaction with heavy metal ions in the raw material solution to form heavy metal complex precipitates. Then, solid-liquid separation is performed to obtain purified raw material solution. The purified raw material solution is then catalytically oxidized in sulfuric acid medium to perform hydrolysis and polymerization to obtain a polymer solution.

3. The method for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation according to claim 1, characterized in that, In step S2, method B is adopted. The process of oxidizing and polymerizing the iron-containing raw material to obtain an intermediate polymer solution includes: catalytically oxidizing the iron-containing raw material in a sulfuric acid medium to perform preliminary hydrolysis and polymerization, thereby obtaining an intermediate acidic polymer solution with pH < 2.

5. The process of complexing and precipitating the intermediate polymer solution to remove impurities includes: adding a precipitant precursor to the intermediate acidic polymer solution and reacting it at 50-70°C with stirring. The precipitant precursor releases active complexing groups at a controlled rate, which undergo a gradient complexing reaction with heavy metal ions in the solution to form heavy metal complex precipitates.

4. The method according to claim 2 or 3, characterized in that, The precipitant precursor is a substance that can alleviate the release of dithiocarbamate groups, organophosphonate groups, or thio-functional groups under the temperature and acidity conditions of the reaction system. The precipitant precursor is selected from one or more of the following: microencapsulated heavy metal scavengers, heavy metal scavengers supported on porous or layered carriers, or polymers with active groups linked by hydrolyzable chemical bonds. It also includes chelate-type directional scavengers, which are organic ligands containing coordinating atoms such as nitrogen, oxygen, and sulfur. They can form stable five- or six-membered cyclic chelates with heavy metal ions under acidic conditions, enhancing the selective capture ability of heavy metal ions such as lead, cadmium, mercury, and arsenic, and adapting to the pH and temperature conditions of the polyferric sulfate reaction system.

5. The method according to claim 2 or 3, characterized in that, In step S2, the pH value of the reaction is controlled to be 1.5-2.

2.

6. The method according to claim 2 or 3, characterized in that, In step S2, the release rate of the active complexing group is controlled by adjusting the addition rate, physical form, or dispersion state of the precipitant precursor in the reaction system.

7. The method according to claim 1, characterized in that, The intelligent control system calculates and adjusts in real time the total dosage of the precipitant precursor, the addition rate, and the reaction temperature and time of step S2 based on the heavy metal impurity composition and content data and through a built-in process optimization model. The process optimization model also decides whether to adjust the redox potential of the oxidation stage in step S2 based on the types and proportions of different metal ions in the heavy metal impurity composition, so as to optimize the valence state of the heavy metal ions.

8. The method according to claim 1, characterized in that, The acquisition of heavy metal impurity composition and content data of iron-containing raw materials is accomplished by using an online heavy metal analyzer or a rapid digestion-detection device.

9. The method according to claim 1, characterized in that, In step S3, the solid-liquid separation is carried out under a heat preservation condition of 40-65℃.

10. An apparatus for implementing the method for preparing ultra-low heavy metal polyferric sulfate based on complexation precipitation as described in any one of claims 1-9, characterized in that, include: The raw material processing unit is used to perform operations such as dissolving, slurry preparation, or oxidative polymerization of iron-containing raw materials; A gradient complexation precipitation reaction system, connected to the raw material processing unit, is used to receive iron-containing raw material solution or intermediate polymer liquid and complete the gradient complexation precipitation reaction. It is equipped with a precipitant precursor addition unit. A solid-liquid separation system, connected to the gradient complexation precipitation reaction system, is used to separate heavy metal complex precipitates from polyferric sulfate solution; The product maturation system is connected to the solid-liquid separation system and is used to mature the polyferric sulfate solution into the final product. The intelligent control center is connected to the raw material component detection unit, the precipitant precursor addition unit, the raw material processing unit, and the key parameter detection and control unit in the gradient complexation precipitation reaction system. It is used to receive raw material heavy metal data and output control commands according to the preset model to dynamically optimize process parameters.

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