Polyferric sulfate and preparation method thereof

Abstract

The invention relates to the technical field of water treatment agent preparation and environmental governance material processing, in particular to polymeric ferric sulfate and a preparation method thereof.The preparation method comprises the steps that steam condensation recycled water of a thermal power plant of an aluminum factory is mixed with ferrous sulfate and concentrated sulfuric acid to form a reaction solution, oxygen is introduced for an oxidative polymerization reaction, and a liquid intermediate is generated; gradient cooling is carried out on the liquid intermediate to control the molar ratio of ferric ions to hydroxyl, and a porous solid precursor is formed through concentration and closed aging; crushing the precursor, performing graded drying by adopting a rotary kiln and flash drying, and synchronously spraying a hydrophobic modifier to reduce the surface hydroxyl activity; the powdery product is secondarily dried in a nitrogen inert environment, and moisture absorption and agglomeration are inhibited. The invention solves the problems of mixed crystal forms, delayed release of effective components and secondary pollution in the traditional process. The obtained product is uniform in crystal form, concentrated in particle size distribution, remarkably improved in dissolution rate and storage stability, and suitable for black and odorous water body treatment and industrial sewage treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment agent preparation and environmental management material processing, in particular to polyferric sulfate and a preparation method thereof. Background Art

[0002] Polyferric sulfate is an inorganic polymer coagulant, typically present as a reddish-brown viscous liquid or a pale yellow solid. This compound is prepared by the polymerization of ferrous sulfate under strong oxidizing conditions. The presence of hydroxyl bridges in its molecular structure forms a multinuclear complex, giving it a higher charge density and larger molecular weight than traditional ferric sulfate.

[0003] Polyferric sulfate, as a water treatment agent, faces application challenges in the treatment of aquaculture wastewater and black and odorous water bodies. This is primarily due to the difficulty in simultaneously controlling product morphology, dissolution rate, and environmental compatibility with existing preparation processes. The technical root of this problem lies in the insufficient precision in controlling the degree of hydroxyl bridging and Fe³⁺ ratio during the ferrous sulfate oxidation polymerization process, leading to problems such as mixed crystal forms and discrete particle size distribution in the solid product. For example, the irregular solids formed by conventional hot air drying tend to form a coating upon contact with water due to excessive condensation of surface hydroxyl groups, which delays the release of the active ingredient. Furthermore, powdered products that do not incorporate a directional crystallization process are prone to moisture absorption and aggregation during storage, resulting in dosage deviations. For example, in river and lake management, powders agglomerate upon contact with moisture and then disperse unevenly, resulting in excessive iron ion concentrations in localized areas and causing secondary chromatic contamination of the water. This problem is closely related to the instability of the pH gradient control of the reaction system and the lack of surface modification in the post-treatment process. Summary of the Invention

[0004] In response to the deficiencies in the prior art, the present invention provides a polyferric sulfate and a preparation method thereof. The present invention solves the problems in the existing polyferric sulfate preparation process, such as insufficient precision in controlling the hydroxyl bridging degree and the ratio of trivalent iron ions, which leads to mixed product crystal forms and discrete particle size distribution, as well as excessive condensation of surface hydroxyl groups caused by hot air drying, which delays the release of active ingredients, and moisture absorption and agglomeration of powdered products during storage, which causes dosage deviation and secondary chromatic contamination.

[0005] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows: The present invention provides a polyferric sulfate and a preparation method thereof, wherein the polyferric sulfate is prepared by a method comprising the following steps: mixing condensed water, ferrous sulfate and concentrated sulfuric acid to form a reaction solution, and introducing oxygen into the reaction solution to perform an oxidative polymerization reaction to generate a liquid intermediate; The liquid intermediate is subjected to buffer cooling, concentration treatment and aging reaction in sequence to form a solid precursor; Crushing and drying the solid precursor in a graded manner to obtain granular or powdery polyferric sulfate; The graded drying process includes sequentially performing rotary kiln drying and flash drying on the crushed material.

[0006] Furthermore, the polyferric sulfate and preparation method of the present invention include the following steps: Condensed water, ferrous sulfate and concentrated sulfuric acid are mixed to form a reaction solution, and oxygen is introduced simultaneously during the mixing process to cause the ferrous sulfate in the reaction solution to undergo a hydroxyl bridging reaction under oxidative conditions to generate liquid polyferric sulfate; The liquid polyferric sulfate is introduced into a buffer cooling device to be cooled to 40-60° C., and then transferred to a concentration device to remove free water by steam heating to obtain a concentrated slurry; The concentrated slurry is placed in a sealed environment for aging reaction, and the aging temperature is controlled to be in the range of 50 to 80° C., so that the concentrated slurry is solidified into a solid precursor with a porous structure; The solid precursor is crushed by a crusher, and then subjected to rotary kiln drying and flash drying treatments in sequence, wherein the rotary kiln drying temperature is 100-150° C. and the flash drying pressure is 0.1-0.5 MPa to obtain a mixture of granules and powdered polyferric sulfate; The mixture is sieved to separate granular polyferric sulfate and powdery polyferric sulfate.

[0007] Furthermore, in the polyferric sulfate and preparation method of the present invention, the condensed water is steam condensation recovered from the aluminum plant thermal power plant, and the amount introduced is 20-40% of the total mass of the reaction liquid.

[0008] Furthermore, in the polyferric sulfate and preparation method of the present invention, during the buffered cooling process, the liquid polyferric sulfate is cooled to the target temperature at a cooling rate of 1 to 5°C / min, and the molar ratio of trivalent iron ions to hydroxyl groups in the cooled liquid polyferric sulfate is controlled at 1:2.5 to 1:3.5.

[0009] Furthermore, in the polyferric sulfate and preparation method of the present invention, the particle size of the solid precursor after crushing by the crusher is 0.5-5 mm, and during the crushing process, a hydrophobic modifier accounting for 0.1-0.5% of the total mass of the material is sprayed onto the surface of the material.

[0010] Furthermore, in the polyferric sulfate and preparation method of the present invention, an intermediate screening process is provided between the rotary kiln drying and the flash drying treatment, the screened powdered material directly enters the flash drying, and the granular material returns to the rotary kiln for secondary drying.

[0011] Furthermore, in the polyferric sulfate and preparation method of the present invention, the powdered polyferric sulfate after flash drying is secondary dried in a drying oven, nitrogen is introduced into the drying oven to maintain an inert environment, the drying temperature is 60-90° C., and the drying time is 10-30 minutes.

[0012] Furthermore, the method also includes the step of collaboratively optimizing the process parameters using a genetic algorithm: taking the amount of condensed water introduced (20-40%), buffer cooling rate (1-5°C / min), aging temperature (50-80°C), rotary kiln drying temperature (100-150°C), flash drying pressure (0.1-0.5MPa) and hydrophobic modifier dosage (0.1-0.5%) as the parameters to be optimized, constructing a genetic algorithm including product crystal uniformity (characterized by X-ray diffraction peak width), dissolution rate (dissolution within 5 minutes), and the like. The method adopted a multi-objective fitness function with the following parameters: moisture absorption rate ≥95%) and storage moisture absorption rate (moisture absorption ≤0.8% under 30°C / 80%RH conditions for 72 hours). A genetic algorithm was used to iteratively optimize the above parameter combination and dynamically adjust the process conditions of each step to achieve a synergistic effect among the hydroxyl bridging reaction, gradient cooling, directional growth of aged crystals, graded drying, and surface modification. The result was polyferric sulfate with a more uniform crystal form (XRD characteristic peak half-width ≤0.3°), a dissolution rate 1.6-1.8 times that of the traditional process, and a moisture absorption agglomeration rate ≤2% after 6 months of storage.

[0013] Beneficial effects of the present invention: The present invention optimizes the chemical stability of the reaction system by recycling water from the steam condensation of the aluminum plant thermal power plant, combines gradient cooling with dynamic regulation of the molar ratio of trivalent iron ions to hydroxyl groups, suppresses hydroxyl condensation and disordered growth of crystal nuclei, and realizes regularization of the structure of the multi-nuclear complex; adopts rotary kiln and flash drying graded drying process, and synergizes by temperature gradient and pressure drop to reduce excessive condensation of surface hydroxyl groups and accelerate water desorption; introduces silane hydrophobic modifier and nitrogen inert environment secondary drying, blocks the particle surface moisture adsorption path and neutralizes the electrostatic effect, significantly reduces the powder moisture absorption and agglomeration tendency; intermediate screening process and closed-loop return system are adapted to the drying characteristics of materials of different particle sizes, and improves heat energy utilization efficiency. The above-mentioned technical means act synergistically, make the product crystal form uniform, particle size distribution concentrated, dissolution rate improves and storage stability enhances, effectively solves the problems of crystal form mixing, effective ingredient release delay and secondary chromaticity pollution in traditional technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on the drawings without paying any creative labor.

[0015] Figure 1 A flow chart of a polyferric sulfate and a preparation method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The technical solutions provided by each embodiment of the present invention are described in detail below in conjunction with the drawings. In order to better understand the purpose of the present invention, the present invention is further described in detail below.

[0017] See also Figure 1 The present invention provides a polyferric sulfate and a preparation method thereof, wherein the polyferric sulfate is prepared by a method comprising the following steps: Step 1: mixing condensed water, ferrous sulfate and concentrated sulfuric acid to form a reaction solution, and introducing oxygen into the reaction solution to perform an oxidative polymerization reaction to generate a liquid intermediate; Step 2, subjecting the liquid intermediate to buffer cooling, concentration treatment and aging reaction in sequence to form a solid precursor; Step 3, crushing and graded drying the solid precursor to obtain granular or powdery polyferric sulfate; The graded drying process includes sequentially performing rotary kiln drying and flash drying on the crushed material.

[0018] In the method for preparing polyferric sulfate provided by the present invention, when condensed water, ferrous sulfate, and concentrated sulfuric acid are mixed to form a reaction solution, condensed water is used as a solvent medium, and the mass ratio of condensed water to ferrous sulfate is adjusted to ensure that the reaction system has a suitable initial viscosity and ion concentration. During the mixing process, oxygen is introduced into the reaction solution at a controllable flow rate, promoting the hydroxyl bridging reaction of ferrous sulfate in an oxidizing environment to form a liquid intermediate with a multinuclear complex structure. The oxidative polymerization process of the reaction solution needs to be maintained within a specific temperature range to avoid the premature formation of an insoluble precipitate.

[0019] The liquid intermediate is then transferred to a buffer cooling unit, where the temperature is adjusted to the target range through gradient cooling, reducing the intensity of molecular thermal motion within the system and stabilizing the hydroxyl-bridged structure. The cooled liquid intermediate enters a concentration unit, where steam heating removes free water to form a concentrated slurry with a high solids content. During the concentration process, the steam heat input rate matches the slurry's fluidity to prevent local overheating that could damage the hydroxyl structure. The concentrated slurry undergoes an aging reaction in a closed environment, where temperature regulation induces molecular alignment to form a porous solid precursor. This structure facilitates the uniform escape of water during the subsequent drying process.

[0020] After the solid precursor is mechanically crushed, the particle size distribution is controlled by sieve classification. During the crushing process, surface modification treatment is simultaneously applied to reduce the activity of hydroxyl groups on the particle surface. The crushed material enters the graded drying stage. First, a rotary kiln drying process is adopted to gradually remove internal bound water through hot air circulation to maintain the integrity of the particle skeleton; then flash drying is used to achieve instantaneous dehydration, and the sudden drop in pressure is used to cause the residual water to evaporate rapidly. The combined process of rotary kiln and flash drying effectively avoids the excessive surface condensation caused by traditional hot air drying, while shortening the drying cycle. The final product is separated by screening into two forms: granular and powdered, meeting the dosing requirements of different application scenarios. The material transfer between each step is completed through sealed pipes or closed conveying equipment to prevent environmental humidity interference and secondary contamination.

[0021] Specifically, the polyferric sulfate and preparation method of the present invention include the following steps: Condensed water, ferrous sulfate and concentrated sulfuric acid are mixed to form a reaction solution, and oxygen is introduced simultaneously during the mixing process to cause the ferrous sulfate in the reaction solution to undergo a hydroxyl bridging reaction under oxidative conditions to generate liquid polyferric sulfate; The liquid polyferric sulfate is introduced into a buffer cooling device to be cooled to 40-60° C., and then transferred to a concentration device to remove free water by steam heating to obtain a concentrated slurry; The concentrated slurry is placed in a sealed environment for aging reaction, and the aging temperature is controlled to be in the range of 50 to 80° C., so that the concentrated slurry is solidified into a solid precursor with a porous structure; The solid precursor is crushed by a crusher, and then subjected to rotary kiln drying and flash drying treatments in sequence, wherein the rotary kiln drying temperature is 100-150° C. and the flash drying pressure is 0.1-0.5 MPa to obtain a mixture of granules and powdered polyferric sulfate; The mixture is sieved to separate granular polyferric sulfate and powdery polyferric sulfate.

[0022] In the method for preparing polyferric sulfate provided by the present invention, when condensed water, ferrous sulfate, and concentrated sulfuric acid are mixed to form a reaction solution, condensed water is used as a solvent medium, and the mass ratio of condensed water to ferrous sulfate is adjusted to provide the reaction system with a suitable initial viscosity and ion concentration. During the mixing process, oxygen is introduced into the reaction solution at a controllable flow rate, promoting the hydroxyl bridging reaction of ferrous sulfate in an oxidizing environment to form liquid polyferric sulfate having a multinuclear complex structure. The oxidative polymerization process of the reaction solution needs to be maintained within a specific temperature range to avoid the premature formation of an insoluble precipitate.

[0023] The liquid polyferric sulfate is then transferred to a buffer cooling unit, where the temperature is adjusted to the target range through gradient cooling, reducing the intensity of molecular thermal motion within the system and stabilizing the hydroxyl bridge structure. The cooled liquid intermediate enters a concentration device, where free water is removed through steam heating to form a concentrated slurry with a high solids content. During the concentration process, the steam heat input rate is matched to the slurry's fluidity to prevent local overheating that could damage the hydroxyl structure. The concentrated slurry undergoes an aging reaction in a closed environment, where temperature regulation induces directional molecular alignment to form a solid precursor with a porous structure that facilitates the uniform escape of water during the subsequent drying process.

[0024] After the solid precursor is mechanically crushed, the particle size distribution is controlled by sieve classification. During the crushing process, surface modification treatment is simultaneously applied to reduce the activity of hydroxyl groups on the particle surface. The crushed material enters the graded drying stage. First, a rotary kiln drying process is adopted to gradually remove internal bound water through hot air circulation to maintain the integrity of the particle skeleton; then flash drying is used to achieve instantaneous dehydration, and the sudden drop in pressure is used to cause the residual water to evaporate rapidly. The combined process of rotary kiln and flash drying effectively avoids the excessive surface condensation caused by traditional hot air drying, while shortening the drying cycle. The final product is separated by screening into two forms: granular and powdered, meeting the dosing requirements of different application scenarios. The material transfer between each step is completed through sealed pipes or closed conveying equipment to prevent environmental humidity interference and secondary contamination.

[0025] Condensate recycled from the aluminum smelter's thermal power plant is preferred, as its low impurity content helps improve the purity of the reaction liquid. Oxygen is introduced through a bottom aeration device, with a gas distributor ensuring uniform dispersion and enhancing oxidation efficiency. The buffer cooling phase utilizes a multi-stage heat exchanger for phased gradient cooling, ensuring a uniform temperature drop in the liquid intermediate. The concentration equipment utilizes a thin-film evaporator, increasing the heat transfer area to enhance water removal efficiency. During the aging reaction, a constant temperature control system is implemented within the enclosed environment, optimizing molecular density through a staged temperature increase strategy. The crusher utilizes a combination of jaw and roller crushing, coupled with a vibrating screening device for precise particle size control. Surface modifiers are evenly applied through atomizing nozzles to form a hydrophobic protective layer. The rotary kiln drying utilizes countercurrent hot air circulation, while the flash drying utilizes a pressure regulating valve to control the instantaneous pressure relief rate. These two methods work together to prevent particle agglomeration and powder agglomeration. The screening process utilizes a multi-layer vibrating screen to separate different product forms based on particle size thresholds, which are then sorted and stored via a pneumatic conveying system.

[0026] Specifically, in the polyferric sulfate and preparation method of the present invention, the condensed water is steam condensation recovered from the aluminum plant thermal power plant, and the amount introduced is 20-40% of the total mass of the reaction liquid.

[0027] In the present invention, the condensed water is recycled steam condensate from the aluminum plant's thermal power plant, as its low impurity content helps maintain the chemical stability of the reaction system. The steam condensed water from the aluminum plant's thermal power plant undergoes multi-stage purification, and the concentrations of heavy metal ions and suspended solids are significantly lower than those in conventional industrial water, which can prevent impurities from interfering with the hydroxyl bridging reaction process. The amount of condensed water introduced is controlled within the range of 20-40% of the total mass of the reaction solution. The balance between the viscosity of the reaction solution and the ion concentration is achieved through proportional adjustment. Excessive introduction will dilute the ferrous sulfate concentration, resulting in a decrease in polymerization efficiency, while insufficient introduction will increase the viscosity of the system and hinder oxygen diffusion.

[0028] During the reaction liquid preparation stage, the condensate from the aluminum plant is accurately delivered to the mixing container through a metering pump and added simultaneously with ferrous sulfate and concentrated sulfuric acid in a preset ratio. During the mixing process, the condensate acts as a solvent medium to dissolve the ferrous sulfate crystals. At the same time, its weak acidic characteristics assist the concentrated sulfuric acid in adjusting the initial pH value of the reaction system, providing a suitable environment for subsequent oxidative polymerization. The temperature of the condensate is controlled at 25-35°C to avoid incomplete dissolution of ferrous sulfate due to low temperature or pre-reaction caused by high temperature. The ion concentration of the mixed reaction liquid is fed back in real time by the online conductivity monitoring device, and the addition rate of condensate and ferrous sulfate is dynamically adjusted to stabilize the solid content of the reaction liquid within the target range.

[0029] The recycling of aluminum smelter condensate and steam recovery from the concentration process form a closed-loop resource system. Secondary steam generated during the concentration stage is condensed and reused in the reaction solution, reducing fresh water consumption. Optimizing the amount of condensate introduced synergistically with the oxygen infusion rate maintains a dynamic balance between the Fe³⁺ formation rate and the formation of multinuclear complexes during the hydroxyl bridging reaction, preventing localized overoxidation and disordered nuclei growth. This ratio range, verified through preliminary orthogonal experiments, achieves the optimal balance between reaction activity and product morphology, providing a structurally uniform liquid intermediate for subsequent cooling, concentration, and aging processes.

[0030] Specifically, in the polymerized ferric sulfate and preparation method of the present invention, during the buffered cooling process, the liquid polymerized ferric sulfate is cooled to the target temperature at a cooling rate of 1 to 5°C / min, and the molar ratio of trivalent iron ions to hydroxyl groups in the cooled liquid polymerized ferric sulfate is controlled at 1:2.5 to 1:3.5.

[0031] During the buffer cooling phase, the liquid polyferric sulfate is cooled in stages through a multi-stage heat exchanger. The cooling medium is circulating cooling water or a low-temperature ethylene glycol solution. Temperature sensors are installed within the heat exchanger to monitor the temperature changes of the liquid intermediate in real time. The cooling rate is controlled within a range of 1-5°C / min by adjusting the cooling medium flow rate to avoid sudden temperature drops that could cause the hydroxyl bridge structure to break or localized supersaturation and precipitation of trivalent iron ions. During the cooling process, the viscosity of the liquid intermediate gradually increases as the temperature drops. A stirring device is used to maintain the fluidity of the system to prevent a decrease in heat transfer efficiency due to excessive viscosity.

[0032] The molar ratio of ferric iron to hydroxyl groups is regulated through online pH monitoring and the addition of a hydroxyl source. A sampling port is installed at the cooling device outlet, and the Fe⁺ and hydroxyl content is periodically monitored using ion chromatography or UV spectroscopy. The amount of condensed water or dilute sulfuric acid added is dynamically adjusted to maintain a stable molar ratio between 1:2.5 and 1:3.5. This ratio range prevents excessive hydroxyl condensation and Fe⁺ aggregation, ensuring the structural regularity of the multinuclear complex and providing a molecularly ordered basis for subsequent concentration and aging.

[0033] The buffer cooling system utilizes a series combination of a shell-and-tube heat exchanger and a plate heat exchanger. The front-end shell-and-tube heat exchanger achieves rapid cooling across a large temperature gradient, while the rear-end plate heat exchanger utilizes a multi-channel design to finely adjust the cooling rate. The cooled liquid intermediate is temporarily stored in a buffer tank, where a nitrogen blanket isolates oxygen to prevent secondary oxidation of residual Fe²⁺ components, disrupting the molar ratio balance. The synergistic effect of cooling rate and molar ratio control effectively reduces the risk of disordered crystal nucleus growth and avoids the occurrence of mixed crystal forms or discrete particle size distribution in the solid precursor.

[0034] Cooling process parameters are linked to the steam heating intensity of the concentration step. When the molar ratio is detected approaching a lower threshold, the steam supply during the concentration stage is automatically increased. This accelerates free water removal, shortens the aging reaction time, and compensates for process delays caused by cooling rate adjustments. This linkage logic, integrated through a central control system, dynamically matches process parameters across the cooling, concentration, and aging stages, ensuring consistent morphology and controllable dissolution rates in the final product.

[0035] Specifically, in the polyferric sulfate and preparation method of the present invention, the particle size of the solid precursor after crushing by the crusher is 0.5-5 mm, and during the crushing process, a hydrophobic modifier accounting for 0.1-0.5% of the total mass of the material is sprayed onto the surface of the material.

[0036] In this method, the solid precursor is crushed using a combination of a jaw crusher and a roller crusher. A screening baffle is installed within the crushing chamber, and the discharge particle size is controlled within a range of 0.5 to 5 mm by adjusting the gap between the crushing rollers and the vibration frequency. During the crushing process, the material undergoes primary crushing and then enters a secondary roller crushing and refinement process. A screening device separates excess particles in real time and returns them to the crushing chamber, achieving precise control of the particle size distribution. The crusher discharge is connected to a pneumatic conveying system, which transports the crushed material to the surface treatment section via negative pressure airflow, preventing dust emission caused by mechanical transportation.

[0037] A hydrophobic modifier is evenly sprayed onto the surface of the crushed material through an atomizing nozzle, with the spray amount accounting for 0.1-0.5% of the total material mass. The modifier is a silane or fatty acid compound. The hydrophobic groups in its molecular chain chemically bond with the hydroxyl groups on the particle surface, forming a dense coating. The spray system is equipped with a flow meter and pressure sensor to dynamically adjust the modifier atomization rate based on the instantaneous material flow rate. This ensures that the modifier coverage is negatively correlated with the particle size distribution. This means that the amount of modifier attached to the surface of larger particles is relatively reduced, preventing localized excess that affects subsequent drying efficiency.

[0038] The synergistic crushing and modification processes are linked via a timed controller. After the crusher starts, the spraying device is triggered 2-5 seconds later, allowing the material to be initially dispersed before contact with the modifier droplets, improving coating uniformity. The modified material is then transferred to a temporary storage bin via a screw conveyor, where a relative humidity of 30-50% is maintained to prevent the modified layer from swelling and failing due to excessive humidity. The synergistic effect of particle size control and surface modification effectively reduces the particle surface energy, blocking moisture adsorption pathways and thus inhibiting hygroscopic agglomeration during storage.

[0039] The introduction of a hydrophobic modifier forms a complementary mechanism with the subsequent rotary kiln drying process. The modified layer undergoes thermal stability testing and screening at the initial stage of drying to prevent decomposition at high temperatures and the production of volatile substances. The hot air temperature gradient in the rotary kiln matches the thermal decomposition temperature of the modifier, allowing the modified layer to gradually solidify during the drying process. At the same time, the internal bound water escapes through the capillary pores, maintaining the integrity of the particle skeleton structure. The lower limit of the crushed particle size is associated with the flash drying pressure parameter. Smaller particle size materials are subjected to a higher pressure difference during the flash stage, prompting the instantaneous desorption of residual moisture, while the surface hydrophobic layer prevents the particles from breaking or pulverizing due to instantaneous pressure release.

[0040] An electrostatic eliminator is installed at the exit of the temporary storage bin, neutralizing particle surface charges with ionized air to prevent clumping of modified materials due to electrostatic attraction. Particle size classification data and drying process parameters interact with each other through a central control system. When the particle size distribution deviates from the set range, the crusher roller gap or spray system pressure is automatically adjusted to achieve closed-loop process control. This collaborative design ensures the fluidity and dosing accuracy of the final product, eliminating secondary contamination caused by agglomeration of powdered products when exposed to moisture.

[0041] Specifically, in the polyferric sulfate and preparation method of the present invention, an intermediate screening process is set between the rotary kiln drying and the flash drying treatment, the screened powdered material directly enters the flash drying, and the granular material returns to the rotary kiln for secondary drying.

[0042] An intermediate screening process is implemented between the rotary kiln drying and flash drying processes, utilizing either a vibrating screen or a drum screening device. The screen aperture is set between 100 and 500 mesh, depending on the target particle size range. The material, dried in the rotary kiln, is conveyed through the discharge port to the feed end of the screening machine. The screening machine incorporates multiple layers of screens, which adjust the amplitude and inclination to achieve graded separation of powdered and granular materials. Screening efficiency is controlled by matching the material flow rate with the screen vibration frequency, ensuring a minimum of 90% of powdered material is screened off. Granular materials are then collected by a guide plate and directed to the return port.

[0043] The screening machine outlet is connected to a sealed pneumatic conveying system, which transports the powdered material directly to the flash drying equipment's feed bin via a negative pressure pipe, preventing exposure to external moisture. The granular material is returned to the rotary kiln feed via a screw conveyor. During transport, the moisture content of the material is monitored, and the secondary drying temperature in the rotary kiln is dynamically adjusted to 120-180°C, with the dwell time extended to 15-30 minutes to fully remove the bound water within the granules. A metal detector is installed in the return path to intercept any metallic impurities that may have entered during the crushing process, preventing damage to the kiln lining during the secondary drying process.

[0044] The screening accuracy of the intermediate screening process forms a linkage mechanism with the parameters of the previous and subsequent processes. When it is detected that the moisture content of the powdered material exceeds the standard after flash drying, the vibration frequency of the screening machine is automatically increased, the return ratio of the granular material is increased, and the overall drying uniformity is improved by extending the secondary drying time. The material after secondary drying in the rotary kiln enters the screening process again, forming a closed-loop circulation process until the particle size of the granular material reaches the flash drying admission standard. A temperature buffer zone is set at the interface between the screening machine and the conveying equipment, and the material temperature is reduced to 50-70°C through the air cooling system to prevent screen deformation or powder agglomeration caused by high temperature.

[0045] The introduction of the screening process effectively distinguishes the drying characteristics of materials of different particle sizes. Due to its large specific surface area, powdered materials can be directly flash-dried to achieve instantaneous dehydration through a sudden drop in pressure. Granular materials have high internal water diffusion resistance and require secondary drying to enhance heat conduction efficiency. Compared with a single drying process, this graded treatment mode reduces ineffective heat energy loss by 20-30%, while also preventing surface hydroxyl condensation caused by excessive heating of small-particle materials in the rotary kiln. The dynamic adaptation of the return circulation system to the drying parameters ensures that the moisture content of the final product is controlled within ±0.5%, meeting the needs of high-precision dosing.

[0046] The screening machine's operating status is communicated with the central control system, collecting real-time data on parameters such as screen blockage rate and material distribution uniformity. When the effective pass rate of the screen falls below a threshold, an automatic cleaning process is triggered, and a high-pressure air pulse device reversely purges the screen surface to maintain stable screening efficiency. The return rate of particulate material is optimized using a mass flow meter and drying energy consumption data. A balance model is established between drying efficiency and energy costs, enabling adaptive adjustment of process parameters. This collaborative mechanism resolves the conflict between uneven drying and energy waste in traditional processes, improving the overall economic efficiency of the production line.

[0047] Specifically, the polyferric sulfate and preparation method of the present invention are as follows: the powdered polyferric sulfate after flash drying is secondary dried in a drying oven, nitrogen is introduced into the drying oven to maintain an inert environment, the drying temperature is 60-90°C, and the drying time is 10-30 minutes.

[0048] In the present invention, the powdered polyferric sulfate after flash drying is transferred to a drying oven via a closed conveying system. The cavity of the drying oven adopts a multi-layer porous tray structure, and the material is evenly spread on the tray surface with a thickness controlled to be 5 to 20 mm. Nitrogen is introduced into the bottom of the drying oven through an air inlet pipe. A gas distributor is set at the air inlet to allow the nitrogen to diffuse upward in a laminar flow, replacing the residual oxygen and moisture in the oven and maintaining an inert environment with an oxygen content of less than 0.5%. The nitrogen flow rate matches the volume of the drying oven, and the circulation rate is adjusted by a mass flow meter to form a dynamic gas exchange mechanism.

[0049] The drying temperature is controlled by the steam heating of the jacket outside the box and the internal electric heating elements. Temperature sensors are distributed in the tray area of each layer, and the temperature difference data is fed back to the temperature control system in real time to control the temperature gradient in the box within the range of ±2°C. The drying time is set to 10 to 30 minutes according to the initial moisture content of the material. The time control module is linked to the temperature parameters. When it is detected that the moisture content of the material has dropped to the target threshold, the discharge program is automatically triggered. During the drying process, the residual moisture in the powdered material is desorbed by the nitrogen carrier and discharged to the condensation recovery device through the exhaust pipe to prevent the re-condensation of water vapor from affecting the drying efficiency.

[0050] The drying oven outlet is connected to a nitrogen-sealed cabin, where the material is transferred to the ton bag packaging machine under an inert atmosphere. An electrostatic eliminator is installed at the packaging machine's feed end, using an ionizing fan to neutralize the powder's surface charge and prevent static adsorption and powder agglomeration. The dried powdered polyferric sulfate, as measured by an online moisture meter, maintains a stable moisture content below 0.5%. Its fluidity index is verified by an angle of repose test, meeting anti-caking storage requirements.

[0051] The synergistic effect of the nitrogen inert environment and drying temperature blocks the oxidation reaction pathway of hydroxyl groups on the powder surface, inhibiting moisture absorption and agglomeration during storage. The temperature zoning control strategy within the drying oven complements the flash drying pressure parameters. Lower temperatures (60-75°C) are suitable for powders with high specific surface areas to avoid excessive dehydration and particle breakage. Higher temperatures (76-90°C) are used to treat powders with high amounts of residual bound water during the flash evaporation stage, reducing thermal stress damage to the particle structure through a gradient temperature increase. Drying time and the rotary kiln secondary drying cycle are synchronously optimized through a central control system. When the returned particles enter the flash evaporation process again after secondary drying, the drying oven parameters are automatically adjusted to ensure continuous and stable operation of the production line.

[0052] A dust collector is installed in the drying oven exhaust duct to recover escaping powder and return it to the previous crushing process for reprocessing, forming a closed-loop material utilization system. The nitrogen circulation system is integrated with the aluminum smelter's thermal power plant gas supply network, utilizing nitrogen byproducts from the power plant's air separation unit to reduce inert gas production costs. This secondary drying process, in synergy with surface hydrophobic modification and graded screening, addresses the powder's moisture absorption challenge through both physical barriers and chemical modification. This ensures that the final product remains loose and fluid even in humid environments, avoiding dosage deviations and the risk of secondary color contamination.

[0053] Furthermore, the method also includes the step of collaboratively optimizing the process parameters using a genetic algorithm: taking the amount of condensed water introduced (20-40%), buffer cooling rate (1-5°C / min), aging temperature (50-80°C), rotary kiln drying temperature (100-150°C), flash drying pressure (0.1-0.5MPa) and hydrophobic modifier dosage (0.1-0.5%) as the parameters to be optimized, constructing a genetic algorithm including product crystal uniformity (characterized by X-ray diffraction peak width), dissolution rate (dissolution within 5 minutes), and the like. The method adopted a multi-objective fitness function with the following parameters: moisture absorption rate ≥95%) and storage moisture absorption rate (moisture absorption ≤0.8% under 30°C / 80%RH conditions for 72 hours). A genetic algorithm was used to iteratively optimize the above parameter combination and dynamically adjust the process conditions of each step to achieve a synergistic effect among the hydroxyl bridging reaction, gradient cooling, directional growth of aged crystals, graded drying, and surface modification. The result was polyferric sulfate with a more uniform crystal form (XRD characteristic peak half-width ≤0.3°), a dissolution rate 1.6-1.8 times that of the traditional process, and a moisture absorption agglomeration rate ≤2% after 6 months of storage.

[0054] The present invention addresses the shortcomings of existing processes through the following technical solutions: To control the ratio of hydroxyl bridging degree to ferric ion, the reaction medium uses steam condensate recovered from aluminum smelters and thermal power plants. Its low impurity content reduces interference from side reactions. Combined with a gradient cooling rate of 1 to 5°C / min during the buffer cooling phase, the molar ratio of ferric ions to hydroxyl groups is monitored online, and the amount of condensate replenished or dilute sulfuric acid added is dynamically adjusted to stabilize the molar ratio within a range of 1:2.5 to 1:3.5. This control mechanism inhibits excessive hydroxyl condensation and Fe⁺ aggregation, ensuring the structural regularity of the multinuclear complex and avoiding the mixed crystal forms and discrete particle size distribution caused by disordered nuclei growth.

[0055] To address the issue of excessive condensation of surface hydroxyl groups caused by hot air drying, a graded drying process combining rotary kiln and flash drying is employed. The rotary kiln uses countercurrent hot air circulation to gradually remove internal bound water, maintaining the integrity of the particle skeleton; flash drying utilizes a sudden drop in pressure to achieve instantaneous dehydration, reducing the exposure time of surface hydroxyl groups. The introduction of an intermediate screening step allows for graded processing of powdered and granular materials. The powdered material is directly flash dried to avoid secondary heating, while the granular material returns to the rotary kiln for enhanced drying. These two processes work together to block the hydroxyl condensation chain reaction caused by the continuous high temperatures of traditional hot air drying, thereby accelerating the release rate of the active ingredient.

[0056] To address the moisture absorption and agglomeration issues of powdered products, 0.1-0.5% of a hydrophobic modifier is sprayed simultaneously during the crushing stage. Silane or fatty acid compounds bond with the hydroxyl groups on the particle surface to form a hydrophobic layer, blocking the moisture adsorption path. After flash drying, the powdered material is secondary dried in a drying oven. Residual moisture is desorbed by increasing the temperature gradually from 60 to 90°C in a nitrogen inert environment. Combined with an electrostatic eliminator to neutralize surface charge, these dual actions inhibit powder agglomeration during storage. The nitrogen circulation system is integrated with the aluminum plant's thermal power plant gas supply network to further reduce ambient humidity interference, ensuring that the final product maintains loose fluidity even under humid conditions, eliminating the risk of dosage deviation and secondary color contamination.

[0057] In a specific embodiment of the present invention, water recovered from the condensation of steam from the thermal power plant of an aluminum plant is added to a mixing container via a metering pump at a ratio of 20 to 40% of the total mass of the reaction solution, and is mixed with ferrous sulfate and concentrated sulfuric acid to form a reaction solution. After multi-stage purification, the heavy metal ion concentration of the condensed water is lower than 0.1 ppm. Its weak acidic characteristics assist in adjusting the initial pH of the reaction system to 1.5 to 2.5, providing a stable environment for subsequent oxidative polymerization. Oxygen is introduced into the reaction solution at a flow rate of 0.5 to 2 L / min through a bottom aeration device. A gas distributor evenly disperses the oxygen, promoting the hydroxyl bridging reaction of ferrous sulfate to form a multinuclear complex. The reaction temperature is controlled at 50 to 70°C to avoid premature precipitation.

[0058] The liquid polyferric sulfate is transferred to a buffer cooling unit consisting of a shell-and-tube and plate heat exchanger in series, where it is cooled at a gradient rate of 1-5°C / min to 40-60°C. During the cooling process, an online ion chromatograph monitors the molar ratio of Fe³⁺ to hydroxyl groups in real time. If the measured value deviates from the range of 1:2.5 to 1:3.5, dilute sulfuric acid or condensed water is automatically added for dynamic adjustment. The cooled liquid intermediate enters a thin-film evaporator for concentration. Steam heating is maintained at 80-100°C, and the free water removal rate is controlled at 60-80%, resulting in a concentrated slurry with a solids content of 45-55%. The concentrated slurry is heated in a sealed aging chamber at a rate of 0.5-2°C / min to 50-80°C and maintained at this temperature for 2-4 hours, inducing molecular alignment to form a porous solid precursor. The porosity, as measured by mercury intrusion porosimetry, is 30-50%.

[0059] The solid precursor is crushed to a particle size of 0.5-5 mm using a jaw crusher and roller crusher. A silane hydrophobic modifier (0.1-0.5%) is then sprayed onto the crushing chamber outlet using an atomizer nozzle at a pressure of 0.2-0.8 MPa. The modified material is then screened using a vibrating screen to a size range of 100-500 mesh. The powder then enters a flash dryer for instantaneous dehydration at a pressure of 0.1-0.5 MPa. The granular material then returns to a rotary kiln for a secondary drying process at 120-150°C for 15-30 minutes. The flash-evaporated powder is then transferred to a nitrogen drying oven and dried at a gradient temperature of 60-90°C for 10-30 minutes. The oxygen content within the oven is maintained below 0.5% by a nitrogen circulation system. The dried powder has a moisture content of ≤0.5% and an angle of repose of ≤35°. The granular and powdered products are classified and packaged through a pneumatic conveying system. When added to the black and odorous water treatment scene, the dissolution rate is increased by 40-60% compared with the traditional process, and the agglomeration rate is less than 3% after storage for 6 months, effectively solving the problems of secondary color pollution and measurement deviation.

Claims

1. A polyferric sulfate and a preparation method, characterized in that: The polyferric sulfate is prepared by a method comprising the following steps: mixing condensed water, ferrous sulfate and concentrated sulfuric acid to form a reaction solution, and introducing oxygen into the reaction solution to perform an oxidative polymerization reaction to generate a liquid intermediate; The liquid intermediate is subjected to buffer cooling, concentration treatment and aging reaction in sequence to form a solid precursor; Crushing and drying the solid precursor in a graded manner to obtain granular or powdery polyferric sulfate; The graded drying process includes sequentially performing rotary kiln drying and flash drying on the crushed material.

2. According to the polyferric sulfate and preparation method as claimed in claim 1, it is characterized in that, The following steps are involved: Condensed water, ferrous sulfate and concentrated sulfuric acid are mixed to form a reaction solution, and oxygen is introduced simultaneously during the mixing process to cause the ferrous sulfate in the reaction solution to undergo a hydroxyl bridging reaction under oxidative conditions to generate liquid polyferric sulfate; The liquid polyferric sulfate is introduced into a buffer cooling device to be cooled to 40-60° C., and then transferred to a concentration device to remove free water by steam heating to obtain a concentrated slurry; The concentrated slurry is placed in a sealed environment for aging reaction, and the aging temperature is controlled to be in the range of 50 to 80° C., so that the concentrated slurry is solidified into a solid precursor with a porous structure; The solid precursor is crushed by a crusher, and then subjected to rotary kiln drying and flash drying treatments in sequence, wherein the rotary kiln drying temperature is 100-150° C. and the flash drying pressure is 0.1-0.5 MPa to obtain a mixture of granules and powdered polyferric sulfate; The mixture is sieved to separate granular polyferric sulfate and powdery polyferric sulfate.

3. According to the polyferric sulfate and preparation method as claimed in claim 2, it is characterized in that, The condensed water is water recovered from the condensation of steam from the thermal power plant of the aluminum plant, and the amount of the condensed water introduced is 20-40% of the total mass of the reaction solution.

4. According to the polyferric sulfate and preparation method as claimed in claim 3, it is characterized in that: During the buffer cooling process, the liquid polyferric sulfate is cooled to the target temperature at a cooling rate of 1 to 5°C / min, and the molar ratio of trivalent iron ions to hydroxyl groups in the cooled liquid polyferric sulfate is controlled to be 1:2.5 to 1:3.

5.

5. According to the polyferric sulfate and preparation method as claimed in claim 2, it is characterized in that, The particle size of the solid precursor after being crushed by the crusher is 0.5-5 mm, and a hydrophobic modifier accounting for 0.1-0.5% of the total mass of the material is sprayed onto the surface of the material during the crushing process.

6. The polyferric sulfate and preparation method according to claim 2, characterized in that: An intermediate screening process is provided between the rotary kiln drying and the flash drying process, wherein the screened powdery material directly enters the flash drying process, and the granular material returns to the rotary kiln for secondary drying.

7. The polyferric sulfate and preparation method according to claim 2, characterized in that: The powdered polyferric sulfate after flash drying is dried for a second time in a drying oven, wherein nitrogen is introduced into the drying oven to maintain an inert environment, the drying temperature is 60-90° C., and the drying time is 10-30 minutes.

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