A liquid ferric chloride or polyferric chloride product and a continuous oxygen oxidation process for its preparation

Abstract

The present application belongs to the field of inorganic iron salt water treatment agent, and provides a ferric chloride liquid product or a polyferric chloride liquid product and a continuous oxygen oxidation preparation method thereof. The present application introduces a self-derived iron-based core-shell active seed containing oxygen-based ferric chloride core and chlorine-rich hydroxy ferric chloride shell into the ferric chloride liquid product or the polyferric chloride liquid product, controls oxygen supply, circulation, acidity and back-feeding conditions in the continuous oxygen oxidation system, forms a stable and recyclable iron-based oxidation and coagulation active system, realizes ferrous residue reduction, controlled water insoluble substance, stable seed dispersion and coagulation application performance, solves the problem that oxidation efficiency, dispersion stability, structural integrity and coagulation performance are difficult to unify, and is suitable for raw water, municipal sewage and industrial wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of inorganic ferric salt water treatment agents and continuous oxidation preparation technology, specifically to a ferric chloride liquid product or a polyferric chloride liquid product and its continuous oxygen oxidation preparation method. Background Technology

[0002] Ferric chloride and polyferric chloride, as iron-based inorganic coagulants, are widely used in applications such as raw water purification, municipal wastewater treatment, phosphorus removal from industrial wastewater, and turbidity removal in low-temperature, low-turbidity water bodies. The practical application of these products requires not only stable iron content, low ferrous residue, and minimal water-insoluble matter, but also good dispersion and reactivity during storage, transportation, and continuous dosing. For continuous production, the oxidation efficiency of ferrous chloride to ferric chloride directly affects equipment load, energy consumption, and batch-to-batch stability. For water treatment applications, the particle size, shell structure, basicity, and acidity of the iron-based active species affect floc formation, settling velocity, phosphorus removal capacity, and turbidity removal capacity. Therefore, developing ferric chloride or polyferric chloride liquid products that balance continuous oxidation efficiency, liquid product stability, core-shell seed structure integrity, and coagulation performance is crucial for improving the industrial continuous production level and adaptability to complex water qualities of iron-based water treatment agents.

[0003] Existing technologies have proposed methods for preparing ferric chloride or polyferric chloride through the oxidation of ferrous chloride. For example, Chinese patent CN101514034A discloses a method for rapidly oxidizing ferrous chloride to prepare ferric chloride; Chinese patent CN101891258A discloses a process for preparing polyferric chloride using sodium nitrite catalytic oxidation, and points out that direct oxidation, catalytic oxidation, hydrogen peroxide oxidation, and chlorine gas introduction methods have shortcomings in terms of cost, safety, or exhaust gas treatment. While these methods can promote the conversion of ferrous chloride to ferric iron, most still focus on the oxidant, catalyst, or gas-liquid contact method itself, paying insufficient attention to the in-situ structure of iron-based active seeds in continuous systems, the acid-chlorine environment, the core-shell interface, and the stability of refeeding. This easily leads to problems such as the mutual constraint between improved oxidation efficiency and seed aggregation and sedimentation, and the mutual restraint between enhanced coagulation activity and the maintenance of core-shell structural integrity. Summary of the Invention

[0004] The purpose of this invention is to provide a ferric chloride liquid product or a polyferric chloride liquid product and its continuous oxygen oxidation preparation method, so as to solve the problem that it is difficult to balance the efficiency of continuous oxygen oxidation with the dispersion stability of iron-based seeds, the integrity of the core-shell structure and the coagulation performance.

[0005] This invention constructs a self-derived iron-based core-shell active seed by using an oxy-ferric chloride core and a chlorine-enriched ferric chloride shell. Under acidic oxygen supply cycles and refeeding conditions, the seed maintains its activity and dispersion state, thus coordinating the interfacial activity that promotes ferrous oxidation and the structural stability required for coagulation. This reduces the adverse effects of simply enhancing oxidation or simply increasing coagulation activity.

[0006] In this invention, the self-derived iron-based core-shell active seed refers to an iron-based core-shell particle prepared from an iron salt system homologous to the main oxidation system, and composed of an oxy-ferric chloride core and a chlorine-enriched ferric chloride shell layer located outside the oxy-ferric chloride core; when the self-derived iron-based core-shell active seed is added to the main oxidation reactor in slurry form, its content is calculated based on the dry basis mass of the iron-based core-shell particle.

[0007] In this invention, the chlorine-enriched ferric chloride shell refers to a low-crystallinity or amorphous ferric chloride outer layer located outside the ferric chloride core and containing iron, oxygen, and chlorine elements. The chlorine enrichment state is measured by the radial or planar distribution of Cl elements recorded by energy dispersive X-ray spectroscopy as quality control data, and the shell thickness is measured by transmission electron microscopy image statistics as quality control data.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A ferric chloride liquid product or polyferric chloride liquid product, based on the total mass of the final product, wherein the total iron content of the liquid product, calculated by total elemental iron, is 10.0–30.0 wt%, the liquid product comprises an iron salt main component, a self-derived iron-based core-shell active seed, and the balance being water and free hydrochloric acid; the dry basis content of the self-derived iron-based core-shell active seed is 0.001–0.100 wt%; the self-derived iron-based core-shell active seed comprises an oxyferric chloride core and a chlorine-enriched ferric chloride shell coating the oxyferric chloride core; the liquid product contains, based on elemental iron, Fe 2+ The mass ratio of iron to total iron is ≤0.020.

[0009] Furthermore, the average particle size of the oxy-ferric chloride core, measured by dynamic light scattering, is 80–300 nm, and the thickness of the chlorine-enriched oxy-ferric chloride shell, measured by transmission electron microscopy images, is 5–20 nm; when the liquid product is a ferric chloride liquid product, the content of free hydrochloric acid, based on the total mass of the final product, is 0.10–1.00 wt%; when the liquid product is a polyferric chloride liquid product, the basicity is 5.0–15.0%.

[0010] Furthermore, the oxyferric chloride core is prepared by the following steps: A1, dissolve one or both of anhydrous ferric chloride and ferric chloride hexahydrate in deionized water or tap water to obtain a precursor solution with a mass fraction of 25.0–45.0 wt% based on ferric chloride; A2, the precursor solution is dehydrated at 180–230℃ and an absolute pressure of 0.005–0.030 MPa for 10–60 min to obtain the oxyferric chloride nucleus precursor; A3, the oxy-ferric chloride precursor is added to an aqueous solution containing 0.10–1.00 wt% hydrochloric acid and dispersed for 10–30 min; A4 yields an oxygen-containing ferric chloride core dispersion with a solid content of 0.50–5.00 wt% and an average particle size of 80–300 nm.

[0011] Furthermore, the chlorine-enriched ferric chloride shell is prepared through the following steps: B1, add one or both of anhydrous ferric chloride and ferric chloride hexahydrate, along with hydrochloric acid, to the ferric chloride core dispersion obtained in step A4 to adjust the ferric chloride core and Fe... 3+ The mass ratio is 1:0.5–10, and the free hydrochloric acid content is 0.10–2.00 wt%. B2, under conditions of 60–85℃, introduce oxygen or oxygen-enriched gas for 10–60 min, and simultaneously add deionized water, so that the amount of water added is 2.0–15.0 wt% of the mass of the oxygen-containing ferric chloride core dispersion; B3, continue aging at 60–85℃ for 10–40 min; B4 yielded a self-derived iron-based core-shell active seed slurry with a chlorine-enriched ferric chloride shell thickness of 5–20 nm and a mass ratio of oxy-ferric chloride core to chlorine-enriched ferric chloride shell of 1:0.10–1.00.

[0012] Furthermore, the self-derived iron-based core-shell active seed slurry is not washed with water after preparation. Instead, it is directly adjusted to a solid content of 0.50–5.00 wt% with an aqueous solution containing 0.10–1.00 wt% hydrochloric acid. The slurry is then continuously fed back into the main oxidation reaction system used to prepare the liquid product at a dry basis dosage of 0.001–0.100 wt% of the iron-based core-shell particles based on the total mass of the final product. When the liquid product is a ferric chloride liquid product, the water-insoluble matter is ≤0.20 wt%.

[0013] As a concept of this invention, the present invention employs a self-derived iron-based core-shell active seed design consisting of an oxy-containing ferric chloride core and a chlorine-enriched ferric chloride shell. This design primarily aims to achieve a synergistic balance between dispersion stability and oxidation efficiency. In existing technologies, to improve the continuous oxygen oxidation efficiency of ferrous chloride, methods typically involve enhancing gas-liquid contact, increasing oxygen supply intensity, or introducing more reactive iron-based species. However, these measures easily cause iron-based particles to aggregate, settle, or form more water-insoluble substances in acidic, high-ferric environments. Furthermore, maintaining seed dispersion stability often requires reducing the content of active species or weakening the interfacial reaction intensity, which in turn limits the conversion of ferrous to ferric iron. This invention, through its core-shell structure, chlorine-enriched shell, acidity matching, and content control, achieves mutual correction between the interfacial activity required for oxidation and the stable state of the liquid product, thereby balancing the stability requirements of both the continuous oxidation process and storage / application processes.

[0014] This invention also discloses a continuous oxygen oxidation method for ferric chloride liquid products or polyferric chloride liquid products, comprising the following steps: S1, ferrous chloride tetrahydrate and anhydrous ferrous chloride are prepared into a ferrous chloride feed solution with a total iron concentration of 80–180 g / L based on elemental iron and a free hydrochloric acid content of 0.5–8.0 wt% based on the total mass of the ferrous chloride feed solution; S2, providing a self-derived iron-based core-shell active seed slurry containing the self-derived iron-based core-shell active seeds, and continuously adding the self-derived iron-based core-shell active seed slurry to the main oxidation reactor at a dry basis dosage of 0.001–0.100 wt% of iron-based core-shell particles based on the total mass of the final product; S3, under conditions of 65–95℃ and a reactor internal gauge pressure of 0.02–0.15 MPa, oxygen or oxygen-enriched gas is continuously introduced into the main oxidation reactor, such that the oxygen supply is such that the Fe in the ferrous chloride feed liquid is reduced. 2+ Oxidized to Fe 3+ The required amount of oxygen is 1.05–1.50 times the theoretical amount, and the average residence time of the liquid phase in the main oxidation reactor is controlled to be 15–120 min to obtain ferric chloride oxidizing liquid; S4, the ferric chloride oxidation liquid with water-insoluble matter ≤0.20wt% is directly discharged as ferric chloride liquid product continuously; or the ferric chloride oxidation liquid is aged at 50–70℃ for 30–120 min, and the amount of water added is controlled to be 3.0–15.0wt% of the mass of the ferric chloride oxidation liquid to obtain polyferric chloride liquid product.

[0015] Furthermore, in step S3, when oxygen-enriched gas is introduced, the oxygen content of the oxygen-enriched gas is 60.0–99.5 vol.

[0016] Furthermore, the main oxidation reactor is one of a bubbling circulation reactor, a static mixing circulation reactor, or a gas-liquid circulation tower, with a liquid circulation ratio of 1:1–20:1.

[0017] Further, a side stream liquid for preparing the self-derived iron-based core-shell active seed slurry is extracted from the circulating liquid in the main oxidation reactor. The extraction amount of the side stream liquid is 1.0–10.0% of the flow rate of the circulating liquid in the main oxidation reactor. When the ferric chloride oxidation liquid is directly and continuously discharged as a ferric chloride liquid product, the water-insoluble matter in the ferric chloride oxidation liquid obtained in step S3 is ≤0.20wt%. When the ferric chloride oxidation liquid is aged to obtain a polyferric chloride liquid product, the water-insoluble matter in the ferric chloride oxidation liquid obtained in step S3 is ≤0.30wt%.

[0018] Furthermore, the main oxidation reactor and the preparation unit for preparing the self-derived iron-based core-shell active seed slurry are respectively adopted as one of glass-lined equipment, polytetrafluoroethylene-lined equipment, nickel-based corrosion-resistant alloy equipment, or titanium alloy equipment.

[0019] As another aspect of this invention, the preparation method employs continuous oxygen oxidation, primarily to achieve, stabilize, or amplify the aforementioned synergistic effects. While existing technologies, by simply increasing the oxygen supply or extending the oxidation residence time, help reduce ferrous residue, they easily amplify the risks of hydrolysis, aggregation, and sedimentation of iron-based particles. Similarly, simply strengthening dispersion control may lead to insufficient oxidation reaction interface. This invention, through controlling the concentration of ferrous chloride feed liquid and the content of free hydrochloric acid, continuously adding self-derived iron-based core-shell active seed slurry, matching the temperature, pressure, and oxygen supply of the main oxidation reactor, and coordinating liquid circulation and side-stream refeeding, ensures that the seed structure remains in a state capable of participating in oxidation and coagulation during continuous operation. The ferric chloride oxidation liquid is then directly discharged or aged to convert into polyferric chloride products, thereby simultaneously maintaining oxidation efficiency, structural stability, and application performance in the continuous process.

[0020] The oxy-based ferric chloride core primarily provides iron-based interfacial activity and a solid-phase core that can participate in continuous oxygen oxidation, thus contributing to the improvement of Fe... 2+ To Fe 3+ The reaction contact efficiency of the conversion is high, but when it exists alone or its particle size is too small, it is prone to aggregation in acidic ferric salt liquids, increasing water-insoluble matter; the chlorine-enriched ferric chloride shell mainly regulates the acid-chlorine microenvironment outside the core and the coagulation active interface, which helps to improve floc formation and phosphorus and turbidity removal performance in water treatment applications, but if the shell is too thick or discontinuous, it may reduce the oxidation participation capacity of the core and weaken the dispersion stability. This invention constructs a core-shell relationship by matching the ratio of ferric chloride core to trivalent ferric salt hydrochloric acid system, oxygen or oxygen-enriched gas treatment, simultaneous water addition and aging, so that the core provides activity while the shell restricts agglomeration and participates in coagulation, thus taking into account the naturally contradictory performance.

[0021] Furthermore, the use of the ferric chloride liquid product or polyferric chloride liquid product in the coagulation treatment of raw water, municipal sewage or industrial wastewater.

[0022] Furthermore, the coagulation treatment is at least one of low-temperature, low-turbidity raw water turbidity removal or phosphorus removal from phosphorus-containing wastewater.

[0023] Furthermore, the total iron content is calculated based on the total mass of iron in the liquid product. After sampling the liquid product, the sample is acidified to convert the iron species into detectable iron ion forms, and then the total iron mass concentration in the sample is measured. This is then converted to the total iron content based on the total mass of the final product, combined with the sample mass or density. The Fe... 2+ The mass ratio of Fe to total iron was determined using the same sample as the test object. 2+ The content and total iron content were calculated afterward.

[0024] Furthermore, the dehydration step of the oxyferric chloride nucleus precursor is carried out in a vacuum dehydration device, which is selected from one of a vacuum evaporator, a thin film evaporator, and a vacuum dryer. After the precursor liquid enters the vacuum dehydration device, it is dehydrated at 180–230°C and an absolute pressure of 0.005–0.030 MPa. The dehydrated water vapor leaves the dehydration zone through the exhaust channel and enters the condensation unit for condensation. The solid or slurry obtained after dehydration is used as the oxyferric chloride nucleus precursor in the subsequent dispersion step.

[0025] Furthermore, in the preparation of the oxy-ferric chloride core dispersion, the oxy-ferric chloride core precursor is added to an aqueous solution containing 0.10–1.00 wt% hydrochloric acid, and then treated by a dispersion method selected from mechanical stirring, cyclic shearing, and ultrasonic dispersion for 10–30 min. After the material is dispersed and its average particle size measured by dynamic light scattering is confirmed to be between 80–300 nm by particle size detection, it is used as the oxy-ferric chloride core dispersion to enter the chlorine enrichment ferric chloride shell preparation step.

[0026] Further, in the preparation of the chlorine-enriched ferric chloride shell, one or both of anhydrous ferric chloride and ferric chloride hexahydrate, along with hydrochloric acid, are added to the ferric chloride core dispersion. The system temperature is controlled at 60–85°C. Deionized water is added simultaneously with the introduction of oxygen or oxygen-enriched gas. The total amount of deionized water added is 2.0–15.0 wt% of the mass of the ferric chloride core dispersion. After the water addition is complete, the system is aged at 60–85°C for 10–40 minutes. The resulting slurry is used as the self-derived iron-based core-shell active seed slurry. When introducing oxygen or oxygen-enriched gas, the type of gas, oxygen content, introduction time, and the ratio of ferric chloride core to Fe are considered. 3+ Mass ratio, water addition amount, and obtained shell thickness were used as process control data for the preparation of chlorine-enriched ferric chloride shells.

[0027] Furthermore, the chlorine-enriched ferric chloride shell is formed from a reaction system consisting of an ferric chloride core dispersion, ferric salt, and hydrochloric acid. The chlorine-containing ferric chloride shell is formed by treating the core with oxygen or oxygen-enriched gas and simultaneously adding water. The solid sample obtained from the derived iron-based core-shell active seed slurry is observed by transmission electron microscopy and elemental distribution is tested. The thickness of the outer shell of the ferric chloride core, the distribution of iron, and the distribution of chlorine are recorded. The shell thickness and the distribution of chlorine relative to the outer region of the core are used as quality control data for the shell structure.

[0028] Furthermore, the average particle size of the oxyferric chloride core is detected using the oxyferric chloride core dispersion as the test sample. Before detection, the oxyferric chloride core dispersion is diluted to the dispersion state required for particle size detection, and the particle size intensity distribution data is recorded, with the average particle size used as the release data. The thickness of the chlorine-enriched oxyferric chloride shell is detected using the solid sample in the self-derived iron-based core-shell active seed slurry as the test sample, and is determined by the thickness data of the continuous shell region outside the oxyferric chloride core in the microscopic image.

[0029] Furthermore, in the preparation of the ferrous chloride feed solution, one or both of ferrous chloride tetrahydrate and anhydrous ferrous chloride are dissolved in an aqueous medium containing hydrochloric acid to adjust the total iron concentration in the resulting ferrous chloride feed solution, calculated as iron element, to 80–180 g / L, and the free hydrochloric acid content is adjusted to 0.5–8.0 wt% based on the total mass of the ferrous chloride feed solution; the ferrous chloride feed solution is sampled and tested before entering the main oxidation reactor, and the test data includes the total iron concentration and the free hydrochloric acid content.

[0030] Furthermore, in the continuous oxygen oxidation process, Fe in the ferrous chloride feed solution... 2+ The calculation of Fe content and continuous feed flow rate will be used to determine the Fe content. 2+ Oxidized to Fe 3+ The required theoretical oxygen quantity, wherein the theoretical oxygen quantity is calculated according to 4Fe 2+ +O2+4H + →4Fe 3+ The stoichiometric relationship of +2H2O is determined, and the actual oxygen supply in the oxygen or oxygen-enriched gas is controlled to be 1.05–1.50 times the theoretical oxygen amount. When oxygen-enriched gas is used, the oxygen content and inlet flow rate of the oxygen-enriched gas are recorded and used as the oxygen supply control data of the main oxidation reactor.

[0031] Furthermore, the liquid circulation ratio is the ratio of the circulating liquid flow rate in the main oxidation reactor to the ferrous chloride feed liquid flow rate. During operation of the main oxidation reactor, the liquid circulation ratio is controlled to be 1:1–20:1. Side-stream liquid is extracted from the circulating liquid in the main oxidation reactor for the preparation of self-derived iron-based core-shell active seed slurry. The extraction amount of the side-stream liquid is 1.0–10.0% of the circulating liquid flow rate in the main oxidation reactor.

[0032] Furthermore, the water-insoluble matter in the ferric chloride oxidation liquid is tested using the ferric chloride oxidation liquid obtained in step S3 as the test sample. During testing, the test sample is filtered, washed, and the filtration residue is dried. The water-insoluble matter content is calculated based on the ratio of the mass of the filtration residue to the mass of the test sample. When the ferric chloride oxidation liquid is directly used as a continuous discharge of ferric chloride liquid product, the water-insoluble matter in the continuously discharged sample is tested, and the test result is used as a quality control indicator for the ferric chloride liquid product. The water-insoluble matter in the continuously discharged sample is controlled to be ≤0.20wt%. When the ferric chloride oxidation liquid is aged to prepare polyferric chloride liquid product, the water-insoluble matter in the ferric chloride oxidation liquid obtained in step S3 is tested, and ≤0.30wt% is used as a process control indicator for entering the aging step.

[0033] Furthermore, when preparing the polyferric chloride liquid product, the ferric chloride oxidizing liquid obtained in step S3 is aged at 50–70°C for 30–120 min, and water is added at 3.0–15.0 wt% of the mass of the ferric chloride oxidizing liquid. After aging, the basicity of the obtained polyferric chloride liquid product is tested. The basicity is calculated based on the ratio of the amount of hydroxide to the amount of ferric iron, and the basicity of 5.0–15.0% is taken as the quality control range of the polyferric chloride liquid product.

[0034] 1. By constructing a self-derived iron-based core-shell active seed by using an oxy-containing ferric chloride core and a chlorine-enriched ferric chloride shell, the product maintains the activity of the iron-based interface while reducing the tendency of direct aggregation of core particles. This achieves a coordinated relationship between the reaction contact efficiency in continuous oxygen oxidation and the dispersion stability of the liquid product, which is beneficial for reducing ferrous residues and controlling water-insoluble matter.

[0035] 2. By controlling total iron content, free hydrochloric acid content, basicity, seed content, and Fe... 2+ Compared to the total iron mass ratio, both ferric chloride liquid products and polyferric chloride liquid products can achieve a relatively stable quality window between acidity, iron content and polymerization state, which is beneficial to improving batch-to-batch consistency during continuous discharge, storage and transportation and coagulation dosing.

[0036] 3. By continuously adding self-derived iron-based core-shell active seed slurry to the main oxidation reactor and matching the oxygen supply, liquid circulation ratio, temperature and pressure, the oxidation reaction can achieve a relatively complete ferrous conversion without relying on strong oxidants or chlorination, which helps to reduce the risk of side reactions and improve the controllability of continuous production.

[0037] 4. By analyzing shell thickness, core size, chlorine distribution, total iron, and Fe... 2+ Using water-insoluble matter and basicity as quality control data, this invention can correlate structural state, process conditions and application performance, making it easier to establish repeatable evaluation criteria in scenarios such as turbidity removal of low-temperature and low-turbidity raw water and phosphorus removal of phosphorus-containing wastewater. Attached Figure Description

[0038] Figure 1 The effect of dry basis content of self-derived iron-based core-shell active seeds on Fe 2+ / Influence of total iron mass ratio and turbidity removal rate of low-temperature, low-turbidity raw water.

[0039] Figure 2 The average particle size of the ferric chloride nucleus is related to the Fe 2+ / Influence of total iron mass ratio and 30-day settlement rate.

[0040] Figure 3 The main oxidation temperature affects Fe 2+ / Diagram showing the effect of total iron mass ratio and oxygen utilization rate.

[0041] Figure 4 For oxygen supply to Fe 2+ / Diagram showing the effect of total iron mass ratio and oxygen utilization rate.

[0042] Figure 5 The DLS differential particle size distribution diagrams are for Example 1, Comparative Example 3, and Comparative Example 9.

[0043] Figure 6 The cumulative particle size distribution of DLS in Example 1, Comparative Example 3, and Comparative Example 9 is shown.

[0044] Figure 7 EDS radial line scans of iron element in Examples 1, 9, and 10 are shown.

[0045] Figure 8 The images show EDS radial line scans of chlorine in Examples 1, 9, and 10.

[0046] Figure 9 The continuous oxidation process of Fe in Examples 1, 6, and 7 2+ / Total iron over time curve.

[0047] Figure 10The graph shows the oxygen utilization rate over time during the continuous oxidation process of Example 1, Comparative Example 6, and Comparative Example 7.

[0048] Figure 11 The time series plots show the storage settling rates of Example 1, Comparative Example 8, and Comparative Example 11.

[0049] Figure 12 The scatter plot of the turbidity removal rate of low-temperature, low-turbidity raw water for Examples 1, 8, 9 and 11 is shown as mean ± SD.

[0050] Figure 13 The graph shows the scatter plot and mean ± SD of the phosphorus removal rate of phosphorus-containing wastewater for Examples 1, 8, 9 and 11.

[0051] Figure 14 The XRD broad peak background spectra of Example 1, Comparative Example 9, and Comparative Example 10 are shown.

[0052] Figure 15 Scatter plots showing the correlation between water-insoluble matter and 30-day sedimentation rate for Examples 1, 8, 9, and 11.

[0053] Figure 16 The images show a comparison of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 9; where a is a macroscopic optical photograph of the final product of Example 1 and b is a macroscopic optical photograph of the final product of Comparative Example 9.

[0054] Figure 17 The images show a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 9; where a is a low-magnification SEM image of the final product of Example 1; b is a low-magnification SEM image of the final product of Comparative Example 9; c is a medium-magnification SEM image of the final product of Example 1; d is a medium-magnification SEM image of the final product of Comparative Example 9; e is a high-magnification SEM image of the final product of Example 1; and f is a high-magnification SEM image of the final product of Comparative Example 9.

[0055] Figure 18 The images show a comparison of the TEM structures of the final product of Example 1 and the final product of Comparative Example 9; where a is the HRTEM image of the final product of Example 1; b is the HRTEM image of the final product of Comparative Example 9; c is the EDS surface scan of the final product of Example 1; and d is the EDS surface scan of the final product of Comparative Example 9.

[0056] Figure 19 The images shown are macroscopic optical photographs of the evolution from S1 to the final product in Example 1; where a is a macroscopic optical photograph of the S1 oxyferric chloride core dispersion; b is a macroscopic optical photograph of the S2 self-derived iron-based core-shell active seed slurry; c is a macroscopic optical photograph of the S3 ferric chloride oxidized solution; and d is a macroscopic optical photograph of the final product. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0058] Example 1 In this embodiment, 1000 kg of ferric chloride liquid product was prepared. The product was a reddish-brown acidic liquid with a total iron content of 10.0 wt% based on elemental iron, an iron-based core-shell particle dry basis content of 0.001 wt% based on the total mass of the final product, a free hydrochloric acid content of 0.10 wt%, and Fe... 2+ The mass ratio of total iron to water is 0.018, and the water-insoluble matter is 0.14 wt%. The raw materials in this embodiment include anhydrous ferric chloride, ferric chloride hexahydrate, ferrous chloride tetrahydrate, hydrochloric acid, deionized water, and oxygen. All raw materials are commercially available industrial grade or analytical grade. The purity of anhydrous ferric chloride is ≥98.0%, the purity of ferric chloride hexahydrate is ≥98.0%, the purity of ferrous chloride tetrahydrate is ≥98.0%, the hydrochloric acid is analytical grade or industrial water treatment grade, and the oxygen purity is ≥99.0%.

[0059] S1: Preparation of ferric chloride oxycarbonate nuclei. Anhydrous ferric chloride was dissolved in deionized water to prepare a precursor solution of 50 kg with a ferric chloride mass fraction of 25.0 wt%. The precursor solution was added to a glass-lined vacuum evaporator and dehydrated for 10 min at 180 °C and 0.005 MPa absolute pressure. The dehydrated water vapor was condensed in a condensation unit through the exhaust channel. The resulting light brown solid or slurry was used as the ferric chloride oxycarbonate nuclei precursor. The ferric chloride oxycarbonate nuclei precursor was added to an aqueous solution containing 0.10 wt% hydrochloric acid and dispersed for 10 min at 25 °C, atmospheric pressure, and 300 rpm using mechanical stirring to obtain a ferric chloride oxycarbonate nuclei dispersion with a solid content of 0.50 wt% and an average particle size of 80 nm. The particle size was obtained by dynamic light scattering test of the diluted dispersion and verification by microscopic image analysis.

[0060] S2: Preparation of a chlorine-enriched ferric chloride shell. Anhydrous ferric chloride and hydrochloric acid are added to the ferric chloride core dispersion to adjust the relationship between the ferric chloride core and Fe. 3+ The mass ratio of the two components was 1:0.5, and the free hydrochloric acid content in the system was 0.10 wt%. The system was heated to 60 °C, and oxygen was introduced at 50 L / min for 10 min under normal pressure, while deionized water was added simultaneously, with the amount of water added being 2.0 wt% of the mass of the oxy-ferric chloride core dispersion. After the water addition was complete, the system was aged at 60 °C for another 10 min to obtain a self-derived iron-based core-shell active seed slurry with a shell thickness of 5 nm and a mass ratio of oxy-ferric chloride core to chlorine-enriched hydroxyferric chloride shell of 1:0.10. The seed slurry was not washed with water and was directly adjusted to a solid content of 0.50 wt% with an aqueous solution containing 0.10 wt% hydrochloric acid.

[0061] S3: Continuous oxygen oxidation to prepare ferric chloride oxidant. Ferrous chloride tetrahydrate is dissolved in an aqueous medium containing hydrochloric acid to prepare a ferrous chloride feed solution with a total iron concentration of 80 g / L and a free hydrochloric acid content of 0.5 wt%. The main oxidation reactor is a bubbling circulation reactor made of glass-lined material, with a liquid circulation ratio of 1:1. Self-derived iron-based core-shell active seed slurry is continuously added to the main oxidation reactor, with the dry basis addition of iron-based core-shell particles being 0.001 wt% based on the total mass of the final product. The main oxidation reactor is controlled at a temperature of 65℃ and an internal pressure of 0.02 MPa, with continuous oxygen supply. The oxygen supply rate is equal to the amount of Fe in the feed solution. 2+ Oxidized to Fe 3+ The required amount of oxygen is 1.05 times the theoretical amount, and the oxidation is carried out continuously for 15 minutes to obtain ferric chloride oxidized solution.

[0062] S4: Continuous Discharge and Quality Control. Ferric chloride oxidation liquid is directly discharged as a continuous ferric chloride liquid product. Side-stream liquid is extracted from the circulating liquid in the main oxidation reactor for the preparation of self-derived iron-based core-shell active seed slurry; the side-stream liquid extraction rate is 1.0% of the circulating liquid flow rate in the main oxidation reactor. The total iron content of the discharged samples is determined after acidification. Fe content is measured using the same sample. 2+ And total iron and calculate Fe 2+ The mass ratio of iron to total iron; the water-insoluble matter was calculated by weighing the residue after filtration, washing, and drying. The test was repeated three times, and the total iron content of the product was 10.0 wt%, Fe... 2+ The mass ratio of total iron to total iron was 0.018±0.002, the water-insoluble matter was 0.14±0.02wt%, the average particle size of the oxy-ferric chloride core was 80±5nm, and the shell thickness was 5±1nm.

[0063] Features and application scenarios of this embodiment. This embodiment adopts a relatively conservative low-ratio scheme and mild oxidation conditions. The iron content, dry basis content of iron-based core-shell particles, core particle size, shell thickness, oxygen supply intensity, and liquid circulation intensity of the product are all in a low range. It is suitable for the continuous preparation of low-concentration ferric chloride liquid products and raw water pretreatment scenarios with high requirements for controlling water-insoluble matter.

[0064] Example 2 Raw materials and proportions The preparation was carried out on a scale of 3000 kg of polyferric chloride liquid product. The product form was a reddish-brown polyferric salt liquid with a total iron content of 30.0 wt% (based on elemental iron), an iron-based core-shell particle dry basis content of 0.100 wt% (based on the total mass of the final product), and a basicity of 15.0%. (Fe...) 2+The mass ratio of iron to total iron is 0.010. The raw materials include ferric chloride hexahydrate, anhydrous ferric chloride, anhydrous ferrous chloride, hydrochloric acid, deionized water, and oxygen-enriched gas. All raw materials are commercially available industrial grade or analytical grade raw materials; the purity of anhydrous ferrous chloride is ≥97.0%, the purity of ferric chloride hexahydrate is ≥98.0%, and the oxygen content of the oxygen-enriched gas is 99.5 vol.

[0065] Preparation process of oxyferric chloride core Anhydrous ferric chloride and ferric chloride hexahydrate were dissolved in deionized water at a mass ratio of 1:1 (based on ferric chloride) to obtain 120 kg of a precursor solution with a mass fraction of 45.0 wt% (based on ferric chloride). The precursor solution was fed into a polytetrafluoroethylene-lined thin-film evaporator and dehydrated for 60 min at 230 °C and 0.030 MPa absolute pressure. The dehydrated water vapor was collected by a condenser unit, and the dehydrated product yielded an oxyferric chloride core precursor. The oxyferric chloride core precursor was added to an aqueous solution containing 1.00 wt% hydrochloric acid and dispersed using a cyclic shearing method at 30 °C, atmospheric pressure, and a shear rate of 2500 rpm for 30 min to obtain an oxyferric chloride core dispersion with a solid content of 5.00 wt% and an average particle size of 300 nm.

[0066] Chlorine enrichment ferric chloride shell construction process Ferric chloride hexahydrate and hydrochloric acid were added to the oxygen-based ferric chloride core dispersion to adjust the relationship between the oxygen-based ferric chloride core and Fe. 3+ The mass ratio was 1:10, and the free hydrochloric acid content was 2.00 wt%. The system was controlled at 85℃, and oxygen-enriched gas with an oxygen content of 99.5 vol% was introduced at atmospheric pressure for 60 min, while deionized water was added simultaneously, with the water volume being 15.0 wt% of the mass of the oxy-ferric chloride core dispersion. After the water addition was completed, the system was aged at 85℃ for another 40 min to obtain a self-derived iron-based core-shell active seed slurry with a chlorine-enriched ferric chloride shell thickness of 20 nm and a mass ratio of oxy-ferric chloride core to chlorine-enriched ferric chloride shell of 1:1.00. The obtained slurry was not washed with water, but was adjusted to a solid content of 5.00 wt% using an aqueous solution containing 1.00 wt% hydrochloric acid.

[0067] Continuous oxygen oxidation and aging of polyferric chloride Anhydrous ferrous chloride was dissolved in an aqueous medium containing hydrochloric acid to prepare a ferrous chloride feed solution with a total iron concentration of 180 g / L and a free hydrochloric acid content of 8.0 wt%. The main oxidation reactor employed a gas-liquid circulation tower with a PTFE-lined structure and a liquid-to-hydrochloric acid ratio of 20:1. Self-derived iron-based core-shell active seed slurry was continuously added to the main oxidation reactor, with the dry basis dosage of the iron-based core-shell particles being 0.100 wt% based on the total mass of the final product. The main oxidation reactor temperature was 95℃, the internal pressure was 0.15 MPa, and the oxygen-enriched gas supply was increased by increasing the Fe content in the feed solution. 2+ Oxidized to Fe 3+The required amount of oxygen is 1.50 times the theoretical amount, and continuous oxidation is carried out for 120 minutes to obtain ferric chloride oxidizing solution. The ferric chloride oxidizing solution is aged at 70℃ for 120 minutes, and deionized water is added at 15.0 wt% of the ferric chloride oxidizing solution mass to obtain polyferric chloride liquid product. The side stream liquid extraction rate is 10.0% of the circulating liquid flow rate in the main oxidation reactor.

[0068] Quality testing methods and results Total iron content was determined after acidification and conversion and then converted according to product quality. 2+ The mass ratio of Fe to total iron was determined separately from the same sample. 2+ The basicity was calculated after adding total iron, using the ratio of hydroxide ions to ferric ions. Water-insoluble matter was weighed after filtration, washing, and drying. The test was repeated three times, and the total iron content of the product was 30.0 wt%, Fe... 2+ The mass ratio of iron to total iron is 0.010±0.001, the basicity is 15.0±0.4%, the water-insoluble matter is 0.24±0.03wt%, the average particle size of the oxyferric chloride core is 300±12nm, and the shell thickness is 20±2nm.

[0069] Features of the solution in this embodiment This embodiment adopts an optimized scheme with a relatively high load. The iron content, core particle size, shell thickness, dry basis addition of iron-based core-shell particles, oxygen content of oxygen-enriched gas, liquid circulation ratio, and aging conditions are all in a relatively high range. It is suitable for the preparation of high iron content polyferric chloride liquid products and for scenarios with high treatment requirements for phosphorus-containing wastewater.

[0070] Example 3 The key parameters of this embodiment are as follows: 1500 kg of ferric chloride liquid product is prepared, the final product has a total iron content of 20.0 wt%, an iron-based core-shell particle dry basis content of 0.050 wt%, a free hydrochloric acid content of 1.00 wt% in the ferric chloride liquid, and Fe... 2+ The mass ratio of total iron is 0.006, and the water-insoluble matter is 0.20 wt%; the average particle size of the oxy-containing ferric chloride core is 150 nm, and the thickness of the chlorine-enriched ferric chloride shell is 12 nm; the main oxidation reactor adopts a static mixed circulation reactor, the equipment material is nickel-based corrosion-resistant alloy equipment, and the oxygen content of the oxygen-enriched gas is 60.0 vol.

[0071] In preparing the ferric chloride oxycarbonate nucleus, ferric chloride hexahydrate was dissolved in tap water to obtain 80 kg of a precursor solution with a mass fraction of 35.0 wt% (based on ferric chloride). The precursor solution was added to a vacuum dryer and dehydrated for 35 min at 205 °C and 0.015 MPa absolute pressure. The resulting solid was used as the ferric chloride oxycarbonate nucleus precursor. The ferric chloride oxycarbonate nucleus precursor was added to an aqueous solution containing 0.50 wt% hydrochloric acid and ultrasonically dispersed for 20 min at 25 °C, atmospheric pressure, and 800 W power to obtain a ferric chloride oxycarbonate nucleus dispersion with a solid content of 2.50 wt% and an average particle size of 150 nm.

[0072] When constructing the chlorine-enriched ferric chloride shell, anhydrous ferric chloride and hydrochloric acid are added to the ferric chloride core dispersion to adjust the ferric chloride core and Fe. 3+ The mass ratio of the oxy-ferric chloride core to the chlorinated hydroxychloride core was 1:5, and the free hydrochloric acid content was 1.00 wt%. The system temperature was controlled at 72℃, and oxygen-enriched gas with an oxygen content of 60.0 vol% was introduced for 35 min, while deionized water was added simultaneously, with the amount of water added being 8.5 wt% of the mass of the oxy-ferric chloride core dispersion. After the water addition was completed, the mixture was aged at 72℃ for another 25 min to obtain a self-derived iron-based core-shell active seed slurry with a shell thickness of 12 nm and a mass ratio of oxy-ferric chloride core to chlorinated hydroxychloride shell of 1:0.55. The obtained slurry was not washed with water, but was adjusted to a solid content of 2.50 wt% using an aqueous solution containing 0.60 wt% hydrochloric acid.

[0073] During continuous oxygen oxidation, ferrous chloride tetrahydrate and anhydrous ferrous chloride are added to an aqueous medium containing hydrochloric acid at an iron element mass ratio of 7:3 to prepare a ferrous chloride feed solution with a total iron concentration of 130 g / L and a free hydrochloric acid content of 4.0 wt%. The liquid circulation ratio in the static mixed circulation reactor is 10:1, the temperature in the main oxidation reactor is 80℃, the gauge pressure in the reactor is 0.08 MPa, and the oxygen enrichment gas supply is increased by increasing the Fe content in the feed solution. 2+ Oxidized to Fe 3+ The required oxygen quantity is 1.25 times the theoretical oxygen quantity, with continuous oxidation for 60 minutes. The continuous addition amount of the self-derived iron-based core-shell active seed slurry, based on the dry weight of the iron-based core-shell particles, is 0.050 wt% of the total final product mass. The side-stream liquid extraction rate is 5.0% of the circulating liquid flow rate in the main oxidation reactor.

[0074] Quality testing methods and results: The total iron content (Fe) of continuously discharged samples was determined after acidification and conversion. 2+ The same sample was used for determination and the total iron content was converted. Water-insoluble matter was determined by filtration, washing, drying, and weighing of the retained residue. Particle size was measured using dynamic light scattering and verified by statistical analysis of microscopic images. Shell thickness was statistically analyzed using transmission electron microscopy images. The test was repeated three times. The total iron content of the product was 20.0 wt%, the free hydrochloric acid content was 1.00 ± 0.03 wt%, and the Fe content was...2+ The mass ratio of iron to total iron is 0.006±0.001, the water-insoluble matter is 0.20±0.02wt%, the average particle size of oxyferric chloride core is 150±8nm, and the shell thickness is 12±1nm.

[0075] The applicable scenarios for this embodiment are as follows: This embodiment uses a ferric chloride liquid solution with medium iron content and high acidity, and the oxygen content of the oxygen-enriched gas is biased towards the low value range. Combined with a static mixing and circulating reactor, it forms a stable gas-liquid contact process, which is suitable for industrial wastewater pretreatment scenarios that require high free acid stability, low ferrous residue, and continuous and stable discharge.

[0076] Example 4 I. Preparation Object and Product Form: Using 2000 kg of polyferric chloride liquid as the preparation object, the resulting product is a reddish-brown liquid with a total iron content of 15.0 wt% (based on elemental iron), an iron-based core-shell particle dry basis content of 0.020 wt%, a basicity of 5.0%, and Fe... 2+ The mass ratio of iron to total iron is 0.012, and the product contains 0.18 wt% water-insoluble matter. The raw materials include anhydrous ferric chloride, ferric chloride hexahydrate, ferrous chloride tetrahydrate, hydrochloric acid, deionized water, and oxygen-enriched gas, all of which are commercially available industrial grade or analytical grade raw materials, with an oxygen content of 80.0 vol.

[0077] II. Preparation of ferric chloride core dispersion: Anhydrous ferric chloride and ferric chloride hexahydrate were dissolved in deionized water at a mass ratio of 3:7 (based on ferric chloride) to obtain 70 kg of precursor solution with a mass fraction of 30.0 wt% (based on ferric chloride). The precursor solution was fed into a vacuum evaporator and dehydrated for 20 min at 190 °C and 0.010 MPa absolute pressure. The water vapor entered the condensation unit through the exhaust channel. The resulting slurry after dehydration was used as the ferric chloride core precursor. The ferric chloride core precursor was added to an aqueous solution containing 0.30 wt% hydrochloric acid and treated for 18 min using a combination of mechanical stirring and cyclic shearing. The mechanical stirring speed was 500 rpm and the cyclic shearing linear velocity was 12 m / s, resulting in a ferric chloride core dispersion with a solid content of 1.50 wt% and an average particle size of 200 nm.

[0078] III. Preparation of self-derived iron-based core-shell active seed pulp: Ferric chloride hexahydrate and hydrochloric acid were added to the ferric chloride core dispersion to adjust the interaction between the ferric chloride core and Fe. 3+The mass ratio of the two components was 1:2, and the free hydrochloric acid content was 0.50 wt%. The system temperature was controlled at 65℃, and oxygen-enriched gas with an oxygen content of 80.0 vol% was introduced for 20 min. Deionized water was added simultaneously, with the amount of water added being 3.0 wt% of the mass of the oxy-ferric chloride core dispersion. After the water addition was completed, the mixture was aged at 65℃ for another 15 min to obtain a self-derived iron-based core-shell active seed slurry with a shell thickness of 8 nm and a mass ratio of oxy-ferric chloride core to chlorine-enriched hydroxyferric chloride shell of 1:0.25. This slurry was not washed with water and was adjusted to a solid content of 1.00 wt% using an aqueous solution containing 0.20 wt% hydrochloric acid.

[0079] IV. Continuous Oxidation and Polyferric Chloride Conversion: Ferrous chloride tetrahydrate is dissolved in an aqueous medium containing hydrochloric acid to prepare a ferrous chloride feed solution with a total iron concentration of 100 g / L and a free hydrochloric acid content of 1.5 wt%. The main oxidation reactor is a bubbling circulation reactor. Both the main oxidation reactor and the preparation unit are made of titanium alloy equipment, with a liquid circulation ratio of 5:1. Self-derived iron-based core-shell active seed slurry is continuously added to the main oxidation reactor. The dry basis addition of iron-based core-shell particles is 0.020 wt% based on the total mass of the final product. The temperature of the main oxidation reactor is 70℃, the internal pressure is 0.05 MPa, and the oxygen-enriched gas supply is increased by the amount of Fe in the feed solution. 2+ Oxidized to Fe 3+ The required amount of oxygen is 1.20 times the theoretical amount, and continuous oxidation is carried out for 45 minutes to obtain ferric chloride oxidizing solution. The ferric chloride oxidizing solution is aged at 50℃ for 30 minutes, and deionized water is added at 3.0 wt% of the ferric chloride oxidizing solution mass to obtain polyferric chloride liquid product. The side stream liquid extraction rate is 2.0% of the circulating liquid flow rate in the main oxidation reactor.

[0080] V. Testing and Quality Control: Total Iron, Fe 2+ The total iron content, basicity, and water-insoluble matter were determined according to their respective detection methods. Before particle size testing, the oxy-ferric chloride core dispersion was diluted to a suitable dispersion state. The shell thickness was determined statistically by analyzing the continuous shell region outside the nucleus in transmission electron microscopy images. The test was repeated three times. The total iron content of the product was 15.0 wt%, the basicity was 5.0 ± 0.3%, and the Fe content was... 2+ The mass ratio of iron to total iron is 0.012±0.001, the water-insoluble matter is 0.18±0.02wt%, the average particle size of oxyferric chloride core is 200±10nm, and the shell thickness is 8±1nm.

[0081] VI. Process characteristics and application directions of this embodiment: This embodiment adopts polyferric chloride aging conditions with a preference for low-value regions and a product scheme with a lower basicity. Combined with a medium-sized core and a thinner shell structure, it is suitable for water treatment scenarios that require a mild degree of polymerization and have requirements for storage stability and turbidity removal from low-temperature and low-turbidity raw water.

[0082] Comparative Example 1: Basically the same as Example 1, except that the dry basis content of iron-based core-shell particles in the final product was adjusted to 0.0002 wt%. The change occurred in the addition control stage of S3, where the self-derived iron-based core-shell active seed slurry was continuously added. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-oxidized ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in the feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of the reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side stream liquid extraction volume 1.0%.

[0083] Comparative Example 2: Basically the same as Example 1, except that the dry basis content of iron-based core-shell particles in the final product was adjusted to 0.150 wt%. The change occurred in the addition control stage of S3, where the self-derived iron-based core-shell active seed slurry was continuously added. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-oxidized ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in the feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of the reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side stream liquid extraction volume 1.0%.

[0084] Comparative Example 3: Basically the same as Example 1, except that the average particle size of the oxy-ferric chloride core was adjusted to 50 nm. The change occurred in the preparation and particle size release stages of the S1 oxy-ferric chloride core dispersion. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, chlorine-enriched oxy-ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of the reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side liquid extraction volume 1.0%.

[0085] Comparative Example 4: Basically the same as Example 1, except that the thickness of the chlorine-enriched ferric chloride shell was adjusted to 30 nm. The change occurred during the addition of ferric salt and aging control in the preparation of the S2 shell. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of ferric chloride core 80 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side liquid extraction volume 1.0%.

[0086] Comparative Example 5: Basically the same as Example 1, except that Fe was added after continuous oxidation. 2+ The mass ratio of iron to total iron was controlled at 0.050. The change occurred during the S3 oxidation endpoint control stage, specifically by maintaining the oxygen supply at 1.05 times the standard but shortening the continuous oxidation time to 6 minutes. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-containing ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, main oxidation temperature 65℃, internal pressure of reactor 0.02 MPa, liquid circulation ratio 1:1, and side stream extraction rate 1.0%.

[0087] Comparative Example 6: Basically the same as Example 1, except that the main oxidation temperature was adjusted to 55°C. The change occurred during the temperature control stage of the S3 main oxidation reactor. Other conditions were maintained as follows: total iron content of product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-containing ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, internal pressure of reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side stream liquid extraction volume 1.0%.

[0088] Comparative Example 7: Basically the same as Example 1, except that the oxygen supply was adjusted to 0.95 times the theoretical oxygen supply. The change occurred in the S3 oxygen flow control stage. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-containing ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of reactor 0.02 MPa, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side stream liquid extraction volume 1.0%.

[0089] Comparative Example 8: Basically the same as Example 1, except that the side-stream liquid extraction rate was adjusted to 0.20% of the circulating liquid flow rate in the main oxidation reactor. The change occurred in the S4 side-stream liquid extraction and preparation of the self-derived iron-based core-shell active seed slurry stage. Other conditions were maintained as follows: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-oxidized ferric chloride core 80 nm, chlorine-enriched ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in feed liquid 0.5 wt%, main oxidation temperature 65 °C, internal pressure of reactor 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, and liquid circulation ratio 1:1.

[0090] Comparative Example 9: Essentially the same as Example 1, except that a chlorine-enriched ferric chloride shell was not formed. Instead, an oxy-ferric chloride core dispersion with an average particle size of 80 nm was directly added as a seed slurry to the main oxidation reactor. This change occurred during the S2 shell preparation stage. Other conditions remained the same: total iron content of the product 10.0 wt%, dry basis addition of oxy-ferric chloride core seeds 0.001 wt%, free hydrochloric acid content 0.10 wt%, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in the feed liquid 0.5 wt%, main oxidation temperature 65℃, reactor internal pressure 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side-stream liquid extraction rate 1.0%. This comparative example was used to investigate the synergistic relationship between the oxy-ferric chloride core and the chlorine-enriched ferric chloride shell.

[0091] Comparative Example 10: Essentially the same as Example 1, except that the simultaneous oxygen and water introduction steps were omitted during shell preparation. Ferric chloride and hydrochloric acid were added only at 60°C, followed by a 20-minute settling period. This change occurred during the S2 chlorine-enriched ferric chloride shell construction stage. Other conditions remained the same: total iron content of the product 10.0 wt%, seed dry basis dosage 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of ferric chloride core 80 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in the feed liquid 0.5 wt%, main oxidation temperature 65°C, reactor internal gauge pressure 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 minutes, liquid circulation ratio 1:1, and side-stream liquid extraction rate 1.0%. This comparative example was used to investigate the synergistic relationship between simultaneous oxygen and water supply in shell construction and core-shell structure formation.

[0092] Comparative Example 11: Essentially the same as Example 1, except that after preparation of the self-derived iron-based core-shell active seed slurry, it was washed with deionized water until the pH of the washing solution reached 4.0, and then adjusted with deionized water to a solid content of 0.50 wt% before being added to the main oxidation reactor. The changes occurred in the S2 seed slurry post-treatment and S3 continuous addition stages. Other conditions remained the same: total iron content of the product 10.0 wt%, dry basis content of iron-based core-shell particles 0.001 wt%, free hydrochloric acid content 0.10 wt%, average particle size of oxy-ferric chloride core 80 nm, chlorine-enriched hydroxy-ferric chloride shell thickness 5 nm, total iron concentration of ferrous chloride feed liquid 80 g / L, free hydrochloric acid in the feed liquid 0.5 wt%, main oxidation temperature 65 °C, reactor internal pressure 0.02 MPa, oxygen supply 1.05 times, continuous oxidation for 15 min, liquid circulation ratio 1:1, and side-stream liquid extraction rate 1.0%. This comparative example was used to investigate the synergistic relationship between the retention of acid and chlorine environment without water washing and the continuous oxidation system.

[0093] Characterization tests: Using ferric chloride liquid products and polyferric chloride liquid products as test objects, the total iron and Fe content were evaluated. 2+ The purpose of measuring the total iron mass ratio, free hydrochloric acid, and basicity is to confirm the degree of iron species transformation and product quality after continuous oxidation. Ferric chloride products were tested for total iron, ferrous iron, insoluble matter, and free acid according to the applicable test methods in GB / T 4482-2018 "Ferric Chloride for Water Treatment Agents". Polyferric chloride products were tested for basicity according to the applicable test methods in HG / T 4672-2022 "Polyferric Chloride for Water Treatment Agents" combined with acid-induced depolymerization and titration methods. Each sample was repeated three times, and the mean total iron, standard deviation of total iron, and Fe were recorded. 2+ / Mean total iron, mean free hydrochloric acid, and mean basicity.

[0094] Using ferric chloride oxyhydroxide core dispersion and self-derived iron-based core-shell active seed slurry as test objects, the average particle size of the ferric chloride oxyhydroxide core, the apparent particle size distribution of the core-shell particles, and the thickness of the chlorine-enriched ferric chloride shell were evaluated to confirm whether the core-shell structure dimensions corresponded to the process parameters. The ferric chloride oxyhydroxide core dispersion or the self-derived iron-based core-shell active seed slurry was diluted with an aqueous phase containing the same mass fraction of hydrochloric acid to a suitable dispersion state. The average particle size and distribution width were recorded using dynamic light scattering. Separately, solid samples were dried and observed using transmission electron microscopy. At least 100 particles and 50 shell regions were counted, and the average particle size of the ferric chloride oxyhydroxide core, the apparent particle size of the core-shell particles, the shell thickness, the iron element distribution, and the chlorine element distribution were recorded. This experimental data was included in the data table and used as a core field of the characterization scheme.

[0095] Using the feed liquid, circulating liquid, and effluent liquid of a continuous main oxidation reactor as test objects, this study evaluates the continuous oxygen oxidation efficiency and oxygen utilization. The aim is to illustrate the effects of seed reintroduction, oxygen supply rate, liquid circulation ratio, and temperature and pressure on Fe. 2+ The effect of conversion. Feed and effluent samples were collected at set time points, and Fe was measured separately. 2+ Total iron; Simultaneously record oxygen content, intake flow rate, and exhaust oxygen content of oxygen or oxygen-enriched gas, with Fe as the metric. 2+ Oxygen utilization rate is calculated based on the reduction in oxygen consumption and the amount of oxygen consumed. The data field is Fe. 2 + / Total iron mean, oxygen utilization mean, oxygen utilization standard deviation and target Fe 2+ The required dwell time for the proportion.

[0096] Using ferric chloride oxidizing liquid, ferric chloride liquid products, and polyferric chloride liquid products as test objects, the water-insoluble matter, 30-day sedimentation rate, and Fe after storage were evaluated. 2+ The purpose of this study was to confirm the stability of the core-shell active seeds in the liquid iron salt product. After sampling, the samples were filtered, washed, and dried at 105°C to constant weight. The water-insoluble matter was calculated based on the ratio of the mass of the retained product to the mass of the sample. The samples were then left to stand in a sealed container at 25°C for 30 days, and the volume fraction of the sedimentation layer and the Fe content were recorded. 2+ / Total iron variation. Data fields include mean water-insoluble matter, standard deviation of water-insoluble matter, mean 30-day sedimentation rate, and Fe after storage. 2+ / Total iron mean.

[0097] Using the products obtained in the examples and comparative examples as coagulants, the turbidity removal capacity of low-temperature, low-turbidity raw water and the phosphorus removal capacity of phosphorus-containing wastewater were evaluated to correspond to actual water treatment application scenarios. A simulated low-temperature, low-turbidity water sample at 4°C and a turbidity of 20 NTU was taken, and a test water sample with a total phosphorus concentration of 5 mg / L was prepared. The same iron dosage (calculated as elemental iron) was applied, and the samples were subjected to rapid stirring, slow stirring, and static sedimentation. The turbidity and total phosphorus of the supernatant were measured. The data fields are the mean turbidity removal rate, the mean phosphorus removal rate, and the corresponding standard deviation of the low-temperature, low-turbidity raw water. Higher values ​​indicate better coagulation performance.

[0098] Using self-derived iron-based core-shell active seed slurry and its circulating liquid after entering the main oxidation reactor as test objects, this study evaluated seed dispersion stability and refeedability, aiming to confirm the effects of side-stream pulping, no water washing, acid conditioning, and liquid circulation on seed state. Samples were allowed to stand at 25℃ for 24 hours, and the supernatant height, settling layer volume, and redispersion time were recorded. Simultaneously, the apparent average particle size of the core-shell particles in the circulating liquid was measured. Data fields included the average 24-hour settling rate, average redispersion time, average apparent average particle size of the core-shell particles in the circulating liquid, and particle size change rate. These values ​​were combined with the stability direction for assessment.

[0099] Figures 1 to 4 This study aims to illustrate the synergistic effects of the dry basis dosage, core particle size, primary oxidation temperature, and oxygen supply of self-derived iron-based core-shell active seeds on the continuous oxygen oxidation process. Figure 1 The effect of dry basis content of self-derived iron-based core-shell active seeds on Fe 2 + The graph shows the effect of total iron mass ratio on the turbidity removal rate of low-temperature, low-turbidity raw water. Based on the continuous oxidation process of Example 1, only the dry content of the self-derived iron-based core-shell active seed was changed. The results show that when the dry seed content is too low, there are insufficient interfacial active sites available in the system, resulting in weak ferrous oxidation induction and Fe... 2+ The residual content is too high, and the generated iron-based active structure is insufficient to fully exert the turbidity removal effect on low-temperature, low-turbidity raw water; when the seed dry basis content is in the range of 0.001–0.100 wt%, Fe 2 + The decrease in the total iron mass ratio and the increase in the turbidity removal rate of low-temperature, low-turbidity raw water indicate that core-shell active seeds within the above range can simultaneously promote oxidation reactions and subsequent coagulation. Figure 2 The average particle size of the ferric chloride nucleus is related to the Fe 2+ The graph shows the effect of total iron mass ratio and 30-day sedimentation rate, using Example 1 as a baseline, with only the average particle size of the ferric chloride core being varied. The results show that when the core particle size is too small, the particle surface energy is high, making secondary aggregation more likely and leading to an increased 30-day sedimentation rate; when the core particle size is too large, the effective interface area per unit mass of particles decreases, affecting the Fe... 2+The oxidation-promoting effect is weakened; when the core particle size is controlled within the range of 80–300 nm, it can maintain high interfacial activity and reduce the risk of long-term sedimentation. Figure 3 The main oxidation temperature affects Fe 2+ The graph showing the effect of total iron mass ratio and oxygen utilization rate, based on the oxidation system of Example 1, only changes the main oxidation temperature. The results show that at lower temperatures, the oxidation kinetics are insufficient, and Fe... 2+ The total iron content is relatively high; although the local reaction rate can be increased when the temperature is too high, it is easy to cause ineffective oxygen loss or enhanced side reactions, resulting in a decrease in oxygen utilization; the temperature range of 65–95℃ can balance the reaction rate and effective oxygen utilization. Figure 4 For oxygen supply to Fe 2+ The graph showing the effect of total iron mass ratio and oxygen utilization rate, using theoretical oxygen quantity as a reference and only changing the actual oxygen supply ratio, indicates that when oxygen supply is insufficient, Fe... 2+ Incomplete oxidation leads to decreased oxygen utilization and increased system disturbances when oxygen supply is excessive; an oxygen supply range of 1.05–1.50 times can reduce Fe... 2+ While maintaining a high oxygen utilization rate, the residual oxygen is also maintained. Therefore, this scheme does not simply enhance oxidation by increasing seed quantity, raising temperature, or increasing oxygen supply, but rather achieves a balance between continuous oxygen oxidation efficiency and dispersion stability through the matching of seed dry weight content, particle size, temperature, and oxygen supply.

[0100] Based on the determination of the above-mentioned process window Figure 5 and Figure 6 The dispersion uniformity of the iron-based particles obtained in Example 1 is further explained from the perspective of particle size distribution. Figure 5 The following are DLS differential particle size distribution diagrams for Example 1, Comparative Example 3, and Comparative Example 9. Figure 6 The DLS cumulative particle size distribution diagrams for Examples 1, 3, and 9 are shown. The differential particle size distribution results show that the particle size peaks in Example 1 are more concentrated and the distribution width is narrower, indicating that its particle population has better consistency in the aqueous dispersion system. The cumulative particle size distribution results further show that the cumulative curve of Example 1 has a narrower rising range and a smaller particle size span, while Comparative Examples 3 and 9 show particle size distribution shifts or widening. These results indicate that in Example 1, the formation of the oxy-ferric chloride core and the chlorine-enriched hydroxy-ferric chloride shell can inhibit disordered particle growth and uneven aggregation, maintaining a relatively stable nano-dispersion state of the core-shell active seeds during continuous oxidation and storage, thus providing a structural basis for subsequent oxidation efficiency and coagulation performance.

[0101] Figure 7 and Figure 8 Further verification of the spatial distribution characteristics of the iron-based matrix and chlorine-enriched shell in Example 1. Figure 7The EDS radial line scans of iron in Examples 1, 9, and 10 show that the normalized intensity of Fe in Example 1 is relatively smooth along the radial direction of the particles, and the signal in the central region is stable, indicating that its oxy-ferric chloride core structure is relatively complete and the particle nucleation and growth process is relatively uniform. The comparative sample, on the other hand, shows different degrees of signal fluctuation, indicating that the uniformity of the particle body formation process is insufficient. Figure 8 The EDS radial line scans of chlorine in Examples 1, 9, and 10 are shown. The results indicate that Example 1 exhibits a relatively obvious and symmetrical enhancement of the Cl signal at the particle edge region, consistent with the structural characteristic of chlorine being relatively enriched in the outer layer of the particles. Comparative Example 9, lacking a chlorine-enriched ferric chloride shell, shows indistinct Cl edge enrichment, while Comparative Example 10 exhibits uneven Cl distribution. The radial distribution results of Fe and Cl show that Example 1 forms a core-shell structure with an iron-based core and a relatively chlorine-rich outer layer. This structure is beneficial for maintaining the stability of the bulk while providing interfacial reactivity.

[0102] Figure 9 and Figure 10 Used to evaluate the actual reaction effect of core-shell active seeds participating in a continuous oxidation process. Figure 9 The continuous oxidation process of Fe in Examples 1, 6, and 7 2+ The total iron time curve shows that, in Example 1, Fe... 2+ The total iron mass ratio decreased rapidly and remained at a low level during subsequent oxidation, indicating a high degree of completion of the continuous oxidation reaction; Fe in Comparative Examples 6 and 7 2+ A slow decrease in the total iron mass ratio or a high residual iron content indicates that the oxidation process is difficult to carry out fully when there is a lack of appropriate acidity, oxygen supply circulation, or refeeding control. Figure 10 The graphs show the oxygen utilization rate over time during the continuous oxidation process of Example 1, Comparative Example 6, and Comparative Example 7. The results show that the oxygen utilization rate of Example 1 increases rapidly and remains at a high level, while the oxygen utilization rate of the comparative examples is relatively low. Combined with... Figure 9 and Figure 10 It can be shown that Example 1 can effectively couple the interface promotion effect of oxygen supply, ferrous oxidation and core-shell active seeds, achieving more complete oxidation in a shorter continuous residence time, and avoiding the ineffective loss of oxygen caused by simply increasing the oxygen supply.

[0103] Figures 11 to 13 The combined effect of the above-mentioned structural and process control was verified from two aspects: product storage stability and actual water treatment performance. Figure 11The time series plots of storage sedimentation rates for Example 1, Comparative Example 8, and Comparative Example 11 show that during the storage period from 0 to 30 days, the sedimentation rate of Example 1 increased slowly over time, and the sedimentation rate was low after 30 days, indicating that its iron-based seeds and water-insoluble matter maintained good dispersion stability in the acidic ferric chloride liquid system. The sedimentation rates of Comparative Example 8 and Comparative Example 11 increased more rapidly, indicating that the particles were more likely to settle when the acidity, shell layer, or refeeding conditions were unsuitable. Figure 12 The scatter plots and mean ± SD plots of the turbidity removal rates of low-temperature, low-turbidity raw water for Examples 1, 8, 9, and 11 show that Example 1 has a higher mean turbidity removal rate under low-temperature, low-turbidity raw water conditions and smaller fluctuations in parallel samples, indicating that it still has a stable treatment effect under unfavorable coagulation conditions. Figure 13 The scatter plots and mean ± SD of phosphorus removal rates from phosphorus-containing wastewater in Examples 1, 8, 9, and 11 are shown. The results indicate that Example 1 has a higher phosphorus removal rate and better repeatability, suggesting that its iron-based active structure can provide effective phosphate binding sites. Therefore, the product obtained by this method not only has a high degree of oxidation but also maintains good dispersibility and coagulation activity during storage and application, achieving a balance between preparation efficiency and performance.

[0104] Figure 14 and Figure 15 This is used to further illustrate the impact of product structure and composition and impurity control on stability. Figure 14 The XRD broad peak background spectra of Example 1, Comparative Example 9, and Comparative Example 10 show that Example 1 exhibits obvious broad peaks and background characteristics, indicating the presence of low crystallinity or some amorphous iron-based components in the sample. This result can be used as an auxiliary characterization basis for the iron-based solid phase state. The peaks of Comparative Example 9 and Comparative Example 10 are weaker or more dispersed, indicating that their effective active phase formation is insufficient or their structural uniformity is poor. Figure 15 The scatter plots showing the correlation between water-insoluble matter content and 30-day sedimentation rate for Examples 1, 8, 9, and 11 are presented. The results indicate that Example 1 exhibits both lower water-insoluble matter content and a lower 30-day sedimentation rate, while the comparative examples show an overall increase in both water-insoluble matter content and sedimentation rate. These results demonstrate that by controlling core-shell structure formation, acidity, and continuous oxidation conditions, the formation of unstable water-insoluble matter can be reduced, further lowering the risk of long-term sedimentation. This results in better homogeneity and storage reliability for ferric chloride liquid products or polyferric chloride liquid products.

[0105] Figures 16 to 18 Example 1 and Comparative Example 9 were compared at three levels: macroscopic appearance, SEM morphology, and TEM fine structure, to demonstrate the role of the chlorine-enriched ferric chloride shell in product uniformity and core-shell structure integrity. Figure 16 This is a comparison image of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 9, in which... Figure 16Example 1 shown in Figure a has a final product of 1000 kg of reddish-brown acidic ferric chloride liquid, with a total iron content of 10.0 wt%, a free hydrochloric acid content of 0.10 wt%, an iron-based core-shell particle dry basis content of 0.001 wt%, an average particle size of oxy-containing ferric chloride core of 80 ± 5 nm, and a chlorine-enriched hydroxy ferric chloride shell thickness of 5 ± 1 nm. This indicates that a liquid product with uniform appearance and stable composition can still be obtained under conditions of low seed dry basis content. Figure 16 Comparative Example 9 (shown in b) is a liquid ferric chloride product without a chlorine-enriched ferric chloride shell. Its seed is an oxyferric chloride nucleus with an average particle size of 80 nm, and the shell thickness is 0 nm. The difference between the two products under the same total iron content, acidity, and oxidation conditions indicates that the shell structure is an important factor in improving the macroscopic homogeneity of the liquid product.

[0106] Figure 17 The images show a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 9. Figure 17 a and Figure 17 b are low-magnification SEM images of Example 1 and Comparative Example 9, used to compare the wide-range distribution of seeds and water-insoluble residues after separation or drying; the residues in Example 1 are more uniformly distributed, indicating that the core-shell active seeds containing an 80±5nm oxyferric chloride core and a 5±1nm chlorine-enriched ferric chloride shell help reduce local enrichment of particles. Figure 17 c and Figure 17 d represents the medium magnification SEM images of the two examples. In Example 1, the local accumulation of particles was more controlled, while in Comparative Example 9, the oxygen-containing ferric chloride nuclei without a shell were more likely to exhibit local aggregation. Figure 17 e and Figure 17 f are high-magnification SEM images of the two examples. Example 1 maintains the 80nm particle outline and small aggregate details, while Comparative Example 9 shows insufficient surface control ability of the shell-less particles. The above low- to high-magnification morphology results indicate that chlorine enrichment of the ferric chloride shell can improve the interaction between particles, allowing the active seeds to still exhibit a relatively controllable aggregation morphology in the dry residual state.

[0107] Figure 18 The images show a comparison of the TEM structures of the final product of Example 1 and the final product of Comparative Example 9. Figure 18 a is the HRTEM image of the final product of Example 1, which shows the oxy-ferric chloride core, shell region and local lattice stripe features, indicating that a structural coupling is formed between the 5±1nm chlorine-enriched oxy-ferric chloride shell and the oxy-ferric chloride core. Figure 18 b is the HRTEM image of the final product of Comparative Example 9, which lacks the corresponding shell interface on its surface. Figure 18 c is the EDS surface scan of the final product of Example 1, showing that Fe, O and Cl elements have corresponding spatial distributions in the core-shell seed region, with Cl element matching the outer layer region; Figure 18Image d is the EDS surface scan of the final product of Comparative Example 9. Its shell-less oxyferric chloride core lacks the chlorine-rich shell distribution characteristics present in Example 1. TEM and elemental distribution results further confirm that in Example 1, the oxyferric chloride core and the chlorine-rich oxyferric chloride shell form a core-shell active seed with interfacial synergistic effects.

[0108] Figure 19 This is used to illustrate the continuous transformation relationship from the initial core formation to the final product obtained in Example 1, and corresponds to the aforementioned structural and performance results. Figure 19 This is a macroscopic optical photographic evolution diagram of S1 to the final product in Example 1, wherein... Figure 19 a is a macroscopic optical photograph of the S1-oxyferric chloride core dispersion. This sample was formed by dehydrating the ferric chloride precursor solution at 180℃ and 0.005MPa for 10 min and then dispersing it in a 0.10wt% hydrochloric acid aqueous solution. The average particle size of the core is 80nm, indicating that the initial nanocore has been formed. Figure 19 b is a macroscopic optical photograph of the S2 self-derived iron-based core-shell active seed slurry. This sample was formed after simultaneous oxygenation, water addition and aging at 60℃. The average particle size of the oxy-ferric chloride core is 80±5nm, and the thickness of the chlorine-enriched hydroxy-ferric chloride shell is 5±1nm, indicating that the shell structure has achieved the transformation from oxy-ferric chloride core to core-shell active seed. Figure 19 c is a macroscopic optical photograph of the S3 ferric chloride oxidation solution. This sample was obtained by continuous oxidation of ferrous chloride feed solution at 65℃, 0.02MPa and 1.05 times the theoretical oxygen content for 15 min, indicating that the core-shell active seeds can enter the continuous oxidation system and participate in the regulation of the oxidation process. Figure 19 Image d is a macroscopic optical photograph of the final product. The sample contained 10.0 wt% total iron, 0.10 wt% free hydrochloric acid, and Fe. 2+ A reddish-brown acidic ferric chloride liquid product with a total iron mass ratio of 0.018±0.002 and water-insoluble matter of 0.14±0.02 wt%. This continuous evolution result indicates that the proposed method can sequentially complete the core formation, shell construction, continuous oxidation, and product stabilization processes, ultimately achieving a coordinated balance between oxidation efficiency, core-shell structure integrity, dispersion stability, and coagulation performance. This addresses the challenges in existing processes where continuous oxygen oxidation efficiency and iron-based seed stability are difficult to achieve simultaneously, and core-shell structure integrity and coagulation performance are difficult to improve concurrently.

[0109] Table 1 Performance summary of examples and comparative examples

[0110] As can be seen from the performance of the examples and comparative examples in Table 1, Examples 1–4 in Fe 2+The overall performance in terms of residue, oxygen utilization rate, low-temperature turbidity removal, phosphorus removal, and 30-day sedimentation rate showed a relatively balanced trend, indicating that the combined effects of core-shell active seeds, acid-chlorine shell, continuous oxygen supply, and refeeding control can achieve a good balance between oxidation efficiency and dispersion stability. In the conventional single-variable comparative example, low seed content, insufficient oxygen supply, or low temperature resulted in lower Fe content. 2+ Residual levels increase when particle size is too small, shell is too thick, or lateral lines are insufficient, leading to increased water-insoluble matter and sedimentation rate. In the synergistic comparison, the absence of the shell, disruption of simultaneous oxygen supply and water addition, or washing of seed pulp resulted in a reasonable decrease in coagulation-related indicators and stability, reflecting the inherent contradiction that performance depends on the core-shell structure and the matching of continuous processes.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A ferric chloride liquid product or a polyferric chloride liquid product, characterized in that, Based on the total mass of the final product, the liquid product contains 10.0–30.0 wt% total iron, comprising an iron salt main component, self-derived iron-based core-shell active seeds, and the remainder water and free hydrochloric acid. The self-derived iron-based core-shell active seeds have a dry basis content of 0.001–0.100 wt%. The self-derived iron-based core-shell active seeds comprise an oxyferric chloride core and a chlorine-enriched ferric chloride shell coating the oxyferric chloride core. The liquid product contains 10.0–30.0 wt% Fe, calculated as total iron. 2+ The mass ratio of iron to total iron is ≤0.

020.

2. The liquid product according to claim 1, characterized in that, The average particle size of the oxy-ferric chloride core, as measured by dynamic light scattering, is 80–300 nm; the thickness of the chlorine-enriched oxy-ferric chloride shell, as measured by transmission electron microscopy, is 5–20 nm; when the liquid product is a ferric chloride liquid product, the content of free hydrochloric acid, based on the total mass of the final product, is 0.10–1.00 wt%; when the liquid product is a polyferric chloride liquid product, the basicity is 5.0–15.0%.

3. The liquid product according to claim 2, characterized in that, The oxyferric chloride core is prepared by the following steps: A1, dissolve one or both of anhydrous ferric chloride and ferric chloride hexahydrate in deionized water or tap water to obtain a precursor solution with a mass fraction of 25.0–45.0 wt% based on ferric chloride; A2, the precursor solution is dehydrated at 180–230℃ and an absolute pressure of 0.005–0.030 MPa for 10–60 min to obtain the oxyferric chloride nucleus precursor; A3, the oxy-ferric chloride precursor is added to an aqueous solution containing 0.10–1.00 wt% hydrochloric acid and dispersed for 10–30 min; A4 yields an oxygen-containing ferric chloride core dispersion with a solid content of 0.50–5.00 wt% and an average particle size of 80–300 nm.

4. The liquid product according to claim 3, characterized in that, The chlorine-enriched ferric chloride shell is prepared by the following steps: B1, add one or both of anhydrous ferric chloride and ferric chloride hexahydrate, along with hydrochloric acid, to the ferric chloride core dispersion obtained in step A4 to adjust the ferric chloride core and Fe... 3+ The mass ratio is 1:0.5–10, and the free hydrochloric acid content is 0.10–2.00 wt%. B2, under conditions of 60–85℃, introduce oxygen or oxygen-enriched gas for 10–60 min, and simultaneously add deionized water, so that the amount of water added is 2.0–15.0 wt% of the mass of the oxygen-containing ferric chloride core dispersion; B3, continue aging at 60–85℃ for 10–40 min; B4 yielded a self-derived iron-based core-shell active seed slurry with a chlorine-enriched ferric chloride shell thickness of 5–20 nm and a mass ratio of ferric chloride core to chlorine-enriched ferric chloride shell of 1:0.10–1.

00.

5. The liquid product according to claim 4, characterized in that, The self-derived iron-based core-shell active seed slurry is prepared without water washing and is directly adjusted to a solid content of 0.50–5.00 wt% with an aqueous solution containing 0.10–1.00 wt% hydrochloric acid. It is then continuously fed back into the main oxidation reaction system used to prepare the liquid product at a dry basis dosage of 0.001–0.100 wt% of iron-based core-shell particles based on the total mass of the final product. When the liquid product is a ferric chloride liquid product, the water-insoluble matter is ≤0.20 wt%.

6. A continuous oxygen oxidation method for a liquid product as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1, ferrous chloride tetrahydrate and anhydrous ferrous chloride are prepared into a ferrous chloride feed solution with a total iron concentration of 80–180 g / L based on elemental iron and a free hydrochloric acid content of 0.5–8.0 wt% based on the total mass of the ferrous chloride feed solution; S2, providing a self-derived iron-based core-shell active seed slurry containing the self-derived iron-based core-shell active seeds, and continuously adding the self-derived iron-based core-shell active seed slurry to the main oxidation reactor at a dry basis dosage of 0.001–0.100 wt% of iron-based core-shell particles based on the total mass of the final product; S3, under conditions of 65–95℃ and a reactor internal gauge pressure of 0.02–0.15 MPa, oxygen or oxygen-enriched gas is continuously introduced into the main oxidation reactor, such that the oxygen supply is such that the Fe in the ferrous chloride feed liquid is reduced. 2+ Oxidized to Fe 3+ The required amount of oxygen is 1.05–1.50 times the theoretical amount, and the average residence time of the liquid phase in the main oxidation reactor is controlled to be 15–120 min to obtain ferric chloride oxidized liquid; S4, the ferric chloride oxidation liquid with water-insoluble matter ≤0.20wt% is directly discharged as ferric chloride liquid product continuously; or the ferric chloride oxidation liquid is aged at 50–70℃ for 30–120 min, and the amount of water added is controlled to be 3.0–15.0wt% of the mass of the ferric chloride oxidation liquid to obtain polyferric chloride liquid product.

7. The continuous oxygen oxidation method according to claim 6, characterized in that, In step S3, when oxygen-enriched gas is introduced, the oxygen content of the oxygen-enriched gas is 60.0–99.5 vol.

8. The continuous oxygen oxidation method according to claim 6, characterized in that, The main oxidation reactor is one of a bubbling circulation reactor, a static mixing circulation reactor, or a gas-liquid circulation tower, with a liquid circulation ratio of 1:1–20:

1.

9. The continuous oxygen oxidation method according to claim 6, characterized in that, Side stream liquid for preparing the self-derived iron-based core-shell active seed slurry is extracted from the circulating liquid in the main oxidation reactor. The extraction amount of the side stream liquid is 1.0–10.0% of the flow rate of the circulating liquid in the main oxidation reactor. When the ferric chloride oxidation liquid is directly discharged as a ferric chloride liquid product in step S4, the water-insoluble matter in the ferric chloride oxidation liquid obtained in step S3 is ≤0.20wt%. When the ferric chloride oxidation liquid is aged in step S4 to obtain a polyferric chloride liquid product, the water-insoluble matter in the ferric chloride oxidation liquid obtained in step S3 is ≤0.30wt%.

10. The continuous oxygen oxidation method according to claim 6, characterized in that, The main oxidation reactor and the preparation unit for preparing the self-derived iron-based core-shell active seed slurry are respectively made of glass-lined equipment, polytetrafluoroethylene-lined equipment, nickel-based corrosion-resistant alloy equipment, or titanium alloy equipment.

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