A continuous preparation method and system of nano-barium sulfate based on waste acid resource utilization and internal circulation

Abstract

This application discloses a continuous preparation method and system for nano-barium sulfate based on waste acid resource utilization and internal circulation. It belongs to the interdisciplinary technical field of industrial waste resource utilization and advanced inorganic nanomaterial preparation. It aims to solve the technical bottlenecks of traditional processes for preparing barium sulfate, such as wide particle size distribution, low purity, pollution caused by the formation of soluble barium nitrate from nitrate ions, and low resource utilization. The method uses industrial waste acid containing sulfuric acid and nitric acid and a barium source as raw materials. The two are fed into a dual-channel centrifugal atomizer for atomization, mixing and reaction. The molar ratio of sulfate ions to barium ions is controlled. After separation and washing of the reaction products, most of the acidic washing liquid is recycled for slurry preparation, a small part is bypassed for purification, and CO2 is recovered and recycled. Finally, the product is dried to obtain nano-barium sulfate powder.

Description

Technical Field

[0001] This application belongs to the field of nano-barium sulfate preparation technology, specifically relating to a continuous preparation method and system for nano-barium sulfate based on waste acid resource utilization and internal recycling. Background Technology

[0002] Nano-barium sulfate, due to its excellent chemical stability, superior optical properties (high whiteness, high refractive index), good dispersibility in polymer matrices, and mechanical reinforcing effect, has become an indispensable functional filler in high-end coatings, engineering plastics, specialty rubbers, radiation shielding materials, and cosmetics. With the upgrading of downstream industries, the market demand for high-purity, fine-particle-size, and narrow-distribution nano-barium sulfate is becoming increasingly urgent.

[0003] Currently, large-scale industrial production of barium sulfate still primarily utilizes the traditional sodium sulfate-barium chloride metathesis process. While this process is mature, it suffers from several inherent drawbacks: First, raw material costs remain high, and approximately 0.7 tons of sodium chloride are produced as a byproduct for every ton of barium sulfate produced. This byproduct has low economic value, and improper handling can easily lead to soil salinization and water pollution, creating significant environmental pressure. Second, to control the size and morphology of barium sulfate particles, various organic dispersants or crystal form regulators are typically added during the reaction process. This not only increases raw material costs and process complexity but also makes subsequent product purification difficult. Third, traditional batch-type sedimentation reactions are limited by macroscopic mixing efficiency, making it difficult to achieve instantaneous uniform dispersion of reactants. Crystal nucleation and growth processes are not easily controlled precisely, resulting in a wide particle size distribution and poor batch stability, failing to meet the specifications of nanoscale products. Finally, this linear production model of resource-product-waste exhibits low resource utilization and ineffective integration of byproducts, severely deviating from the development concepts of circular economy and green manufacturing.

[0004] On the other hand, the chemical process of producing nitrate esters (such as isooctyl nitrate and nitrocellulose) through nitration reactions generates a large amount of complex waste acid, mainly composed of sulfuric acid, nitric acid, water, and trace organic impurities. This type of waste acid is highly acidic and corrosive, and is classified as hazardous waste. Current treatment methods primarily rely on neutralization with alkalis (such as lime and sodium hydroxide), which not only consumes large amounts of alkali and incurs high treatment costs, but more importantly, it converts the available sulfur resources (sulfate ions) in the waste acid into worthless gypsum slag or sodium sulfate solution, resulting in serious resource waste. Direct discharge would pose a significant threat to the ecological environment.

[0005] To address these issues, researchers have attempted to utilize such waste acid to produce barium sulfate, aiming to treat waste and turn it into a valuable resource. However, existing technologies are mostly based on traditional batch stirred tank reactor processes. When processing mixed acids containing nitric acid, this process reveals two fatal weaknesses: First, the mixing intensity in a batch reactor is limited, resulting in uneven micro-mixing and easily leading to excessive local supersaturation, causing explosive nucleation and rapid particle aggregation, making it difficult to control the product particle size; second, and most critically, the nitrate ions (NO3) in the waste acid... - It will react with barium ions (Ba 2+ This reacts to form soluble barium nitrate. During conventional filtration and washing processes, barium nitrate easily penetrates the filter layer or becomes trapped between barium sulfate particles, leading to decreased product purity (manifested as low whiteness and poor thermal stability). Furthermore, the washing process generates massive amounts of wastewater containing high concentrations of nitrates and barium salts, resulting in high treatment costs and secondary pollution. How to achieve high-value utilization of waste acid while ensuring high purity of the final product and achieving near-zero emissions in the production process remains a significant and long-standing technical challenge in this field. Summary of the Invention

[0006] To achieve the aforementioned objectives, this application provides a continuous preparation method and system for nano-barium sulfate based on waste acid resource utilization and internal circulation. This application changes the traditional approach to single-use materials, providing a closed-loop production system that includes instantaneous reaction, efficient separation, directional circulation, and equilibrium purification stages. By combining rapid mixing reaction under high-speed centrifugal atomization with material recycling, a continuous preparation process for nano-barium sulfate can be achieved.

[0007] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for the continuous preparation of nano-barium sulfate based on waste acid resource utilization and internal recycling, comprising the following steps: An industrial waste acid containing sulfuric acid, nitric acid and trace amounts of organic nitrate esters, and a barium source, wherein the barium source is barium carbonate, barium oxide or barium hydroxide; a slurry is prepared by mixing the industrial waste acid and the barium source; The slurry prepared by the industrial waste acid and barium source is introduced into different atomizing discs of a dual-channel centrifugal atomizer through independent conveying pipelines. It is atomized and instantaneously mixed in the atomizer, and then reacted and preliminarily dried in a hot air environment to obtain a mixture containing barium sulfate solid and soluble components. The resulting mixture was separated into solid and liquid components to obtain a solid wet material and a primary mother liquor. The solid wet material was then washed with a washing solution, and the washing endpoint was controlled to obtain a nano-barium sulfate wet material and an acidic washing solution. A portion of the acidic washing liquid is used as industrial waste acid and recycled for the preparation of the slurry. The carbon dioxide-containing gas generated during the reaction and drying process is recovered and purified, and at least a portion is recycled for hot air supply in the hot air environment. The remaining portion of the acidic washing liquid is bypassed and purified to control the concentration of impurity ions in the reaction system. The wet nano-barium sulfate material is dried to obtain nano-barium sulfate powder product.

[0008] As a further improvement of this application, the mass ratio of sulfuric acid, nitric acid and water in the industrial waste acid is (80~82):(6~8):(12~14), and the content of trace organic nitrate esters is ≤300ppm; Preferably, the mass fraction of barium carbonate in the slurry is 20% to 50%.

[0009] As a further improvement of this application, when the barium source is barium oxide or barium hydroxide, the barium oxide or barium hydroxide is reacted with water and recycled carbon dioxide gas in a preparation tank to completely convert it into barium carbonate before it is used to prepare the slurry. Preferably, in the mixture containing barium sulfate solid and soluble components, the ratio R of the total molar number of sulfate ions to barium ions in the reaction system is controlled to be (1.01~1.10):1.

[0010] As a further improvement of this application, the dual-channel centrifugal atomizer is a coaxial non-coaxial two-stage high-speed centrifugal atomizer, including a central atomizing disk and a coaxial annular atomizing disk sleeved outside it; wherein, the diameter of the annular atomizing disk is larger than the diameter of the central atomizing disk, the waste acid is introduced into the central atomizing disk, and the slurry is introduced into the annular atomizing disk.

[0011] As a further improvement of this application, the ratio of the diameter D1 of the central atomizing disk to the diameter D2 of the annular atomizing disk is 1.3:1 to 1.8:1.

[0012] As a further improvement of this application, the rotation speed of the central atomizing disk and the annular atomizing disk is synchronized, and the rotation speed is from 15,000 rpm to 40,000 rpm; and / or, the inlet temperature of the hot air environment is from 180°C to 300°C.

[0013] As a further improvement of this application, in the dual-channel centrifugal spray reaction tower, the effective reaction zone length-to-diameter ratio (L / D) of the reaction tower is 4:1 to 8:1; Preferably, the hot air enters the reaction tower in a tangential or swirling manner, and its average flow velocity across the cross-section of the reaction tower is 15 m / s to 35 m / s. Preferably, the ratio R is from 1.03:1 to 1.06:1.

[0014] As a further improvement of this application, the control of the washing endpoint refers to: monitoring the pH value of the final stage washing effluent, and stopping washing when the pH value reaches the range of 5.5 to 7.0; Preferably, the mass ratio of the acidic washing liquid to the solid wet material is 0.5:1 to 1.5:1; Preferably, 80%-95% of the acidic washing liquid is used as industrial waste acid and recycled for the preparation of the slurry, and 5%-20% of the acidic washing liquid is subjected to bypass purification treatment.

[0015] As a further improvement of this application, the bypass purification treatment includes at least one of ion exchange, electrodialysis or evaporation crystallization to remove alkali metal ions and trace organic nitrate ester decomposition products from the circulating liquid. Preferably, the drying temperature is 100°C to 200°C.

[0016] Secondly, this application provides a continuous preparation system for nano-barium sulfate based on waste acid resource utilization and internal recycling, for implementing the method of the first aspect, including: The raw material preparation and slurry preparation unit is used to store waste acid and prepare and store barium source slurry. A dual-channel centrifugal spray reaction unit is provided with a dual-channel centrifugal atomizer and a reaction tower. The two feed inlets of the atomizer are respectively connected to the waste acid outlet and the slurry outlet of the raw material preparation and slurry preparation unit. The separation and washing unit has its inlet connected to the solid outlet of the reaction unit for washing and solid-liquid separation of the solid product, and is provided with a washing liquid outlet and a wet material outlet. The gas processing and circulation unit has its inlet connected to the tail gas outlet of the reaction unit for recovering carbon dioxide gas, and is provided with at least two carbon dioxide recycling outlets. The material circulation and balancing unit includes: A liquid circulation pipeline connects the washing liquid outlet of the separation and washing unit to the liquid inlet of the slurry preparation tank of the raw material preparation and slurry preparation unit. A bypass purification branch is connected to the liquid circulation pipeline to divert and purify a portion of the circulating washing liquid; The gas circulation pipeline is connected to the carbon dioxide recovery outlet of the gas treatment and circulation unit to the hot air system of the raw material preparation and slurry preparation unit and the dual-channel centrifugal spray reaction unit, respectively. Preferably, the liquid circulation pipeline is equipped with an online analyzer for real-time monitoring of the ion concentration of the circulating liquid and a control valve group for controlling the diversion ratio.

[0017] Compared with existing technologies, the technical solution provided in this application has significant technological progress and comprehensive benefits, specifically reflected in: This application aims to solve the technical challenges of traditional batch reactor processes in the preparation of barium sulfate, such as wide particle size distribution, low purity, high salinity wastewater pollution caused by the combination of nitrate and barium ions to form soluble barium nitrate, and low resource utilization. It also addresses the problems of high treatment costs and severe resource waste from the sulfuric and nitric acid-containing industrial waste acids generated during nitrate ester production. The goal is to achieve high-value utilization of waste acid, clean and continuous preparation of nano-barium sulfate, and closed-loop material recycling, thus achieving a balance between economic and environmental benefits. The process realizes the high-value resource utilization of industrial waste acid, converting hazardous waste acid containing sulfuric and nitric acid generated during nitrate ester production into high-value-added nano-barium sulfate products. Sulfur in the waste acid can be converted into the main product with a near 100% conversion rate, while nitrogen serves as an internal recycling medium with a recycling rate exceeding 85%, significantly reducing the consumption of fresh raw materials. Instantaneous micro-mixing of waste acid and barium source slurry is achieved through a dual-channel centrifugal atomizer. Combined with a feed ratio control strategy of slightly excess sulfate ions, barium ions are thermodynamically driven to preferentially convert to barium sulfate, effectively inhibiting the formation of soluble barium nitrate. The prepared nano-barium sulfate product has a stable and controllable particle size. This application constructs a closed-loop material system of nitrate recycling + carbon dioxide recycling. Most of the acidic washing liquid is recycled for slurry preparation, and the carbon dioxide generated in the reaction is also recycled after purification. Only a small portion of the washing liquid undergoes bypass purification treatment. The entire process has no high-salt or high-nitrogen wastewater discharge, reducing wastewater volume by more than 95% and achieving near-zero emissions of waste gas. It truly realizes the harmless and resource-based treatment of hazardous waste, with outstanding environmental benefits. At the same time, this application adopts a continuous production mode, integrating raw material preparation, spray reaction, separation and washing, material circulation, and product drying into one unit. The process flow is compact and efficient, the equipment occupies a small area, and the degree of automation is high. It can adapt to large-scale stable production of tens of thousands of tons per year, solving the bottleneck problem of similar laboratory technologies being difficult to scale up industrially.

[0018] Furthermore, this application employs a coaxial, non-uniform diameter, two-stage high-speed centrifugal atomizer as the core for achieving instantaneous micro-mixing. This atomizer consists of a central small-diameter atomizing disk (D1) and a coaxially fitted large-diameter annular atomizing disk (D2), with the diameter ratio D2 / D1 optimized within the range of 1.3 to 1.8. This design is based on the differences in the characteristics of the materials being processed: the large-diameter disk provides a longer centrifugal acceleration path for high-viscosity, high-solids-content slurries, ensuring they are fully sheared and atomized into suitable droplets; the small-diameter disk allows low-viscosity waste acid to form slightly larger droplets that are less prone to premature evaporation. In a reaction tower with a specific length-to-diameter ratio (L / D = 4~8), the two work synergistically with high-speed tangential hot air (15~35 m / s) to form a stable, strong swirling mixing field below the atomizing disks, achieving uniform molecular-scale contact and reaction within milliseconds. Thanks to the millisecond-level micro-mixing spray reaction, the number of crystal nuclei is enormous and uniform, and the primary particle size of the product can be stably controlled within the range of 20-80nm with a narrow distribution (D90 / D10<3). By controlling the feed ratio of slightly excess sulfate ions (R=1.01~1.10) and combining it with a deep washing process with intelligent endpoint control, the product purity (based on BaSO4) can be stably maintained at over 99.5%, and the whiteness (ISO standard) ≥98.5%, fully meeting the requirements of high-end applications.

[0019] Furthermore, the sulfur (sulfate) in the waste acid is converted into the main product with a near 100% conversion rate; the nitrogen (nitrate) in the waste acid serves as the internal circulation medium of the system, with a recycling rate exceeding 85%, significantly reducing the consumption of fresh nitric acid or barium salts. The carbon dioxide produced as a byproduct of the reaction is also fully recycled. Overall raw material costs can be reduced by 30%-50% compared to traditional methods, resulting in a significant improvement in resource utilization and economic benefits.

[0020] Furthermore, the process generates no high-salt or high-nitrogen wastewater, producing only a small amount of concentrated waste liquid that requires outsourcing for treatment, resulting in a wastewater reduction of over 95%. Exhaust gas emissions are near zero. This truly achieves a green transformation, completely converting hazardous waste (waste acid) into a safe product (barium sulfate).

[0021] Furthermore, by integrating traditionally dispersed multiple processes into a continuous closed-loop system, the equipment boasts a small footprint, low energy consumption, high automation, and significantly improved labor productivity. It is ideally suited for large-scale (tens of thousands of tons per year) continuous and stable production, overcoming the industrial bottleneck that hinders the scaling up of similar laboratory technologies. This results in a compact, efficient process flow that is easily industrialized.

[0022] Furthermore, the integrated reaction-separation-circulation-equilibrium technology system constructed in this application forms a multi-level technological integration advantage. The system's dynamic equilibrium design gives it a certain degree of resistance to raw material fluctuations, enabling long-term stable operation with relatively low maintenance costs.

[0023] Furthermore, taking into account the differences in physical properties between waste acid and barium slurry, an innovative coaxial non-uniform diameter atomizer design, combined with an optimized reaction tower structure, achieves optimal atomization, mixing, and reaction of the two materials with different properties. This solves the engineering problem of uneven mixing when traditional single atomizing discs process multi-component materials with different properties, resulting in more stable and reliable equipment operation.

[0024] Furthermore, by combining high-temperature reaction decomposition, deep exhaust gas purification, and side-stream purification of washing liquid, not only is the balance of inorganic ions achieved, but also the trace organic impurities introduced by the raw materials are effectively controlled, preventing their accumulation in the closed-loop system and ensuring the ultra-high purity of the product and the long-term operational stability of the system. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the continuous preparation system for nano-barium sulfate and its material circulation as described in this application; Figure 2 The image shows the Malvern laser particle size analyzer results of the nano-barium sulfate product obtained in Example 1. Figure 3 The image shows the Malvern laser particle size analyzer results of the nano-barium sulfate product obtained in Example 2. Figure 4 The image shows the Malvern laser particle size analyzer results for the nano-barium sulfate product obtained in Example 3. Figure 5 Comparison of X-ray diffraction (XRD) patterns of the product obtained in Example 3; Figure 6 This is a structural appearance drawing of the coaxial non-uniform diameter two-stage high-speed centrifugal atomizer of this application; Figure 7 This is a side view of the coaxial non-uniform diameter two-stage high-speed centrifugal atomizer structure of this application; Figure 8 This is a top sectional view of the coaxial, non-uniform diameter, two-stage high-speed centrifugal atomizer structure of this application. Detailed Implementation

[0026] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0028] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0029] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0030] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0031] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0032] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0033] This application belongs to the interdisciplinary technical field of industrial waste resource utilization and advanced inorganic nanomaterial preparation, specifically involving a continuous and clean production method and its dedicated integrated system for converting industrial waste acid containing nitric acid and sulfuric acid into high-value-added nano-barium sulfate. More specifically, this application simultaneously solves three major technical challenges—waste acid resource utilization, product nano-scale production, and impurity detoxification—through innovative reaction engineering design and a closed-loop material recycling strategy.

[0034] In a first aspect, this application provides a continuous method for preparing nano-barium sulfate based on waste acid resource utilization and internal recycling, comprising the following sequentially connected steps: (1) Refined pretreatment of raw materials and activation of barium source: The industrial waste acid containing sulfuric acid and nitric acid is pretreated to obtain purified waste acid with stable composition; the solid barium source is converted into a highly reactive slurry.

[0035] Preferably, the barium source is barium carbonate (BaCO3), but barium oxide (BaO) or barium hydroxide (Ba(OH)2) can also be used. When using BaO or Ba(OH)2, it needs to be fully reacted with water and recycled carbon dioxide gas in the preparation tank to completely convert it into a slurry. This process not only activates the barium source but also completes the initial fixation of carbon dioxide.

[0036] (2) High-speed centrifugal spray forced reaction and instantaneous drying: The purified waste acid and the slurry are transported to the special atomizer at the top of the dual-channel centrifugal spray reaction tower by two high-precision metering pumps.

[0037] Preferably, under the strong centrifugal force field generated by the atomizing disc (e.g., a rotation speed of 15,000-40,000 rpm), the two liquid streams are simultaneously torn into droplets of tens of micrometers, which then cross, collide, and mix instantaneously.

[0038] This micro-mixing process is completed within milliseconds, resulting in highly uniform reactant concentrations at the molecular scale. Subsequently, the droplets fall into a directional hot gas stream at a temperature of 180-300°C, undergoing flash evaporation of the solvent (water) and homogeneous precipitation of barium sulfate. This high-temperature environment simultaneously causes the vast majority of trace organic nitrate esters in the waste acid to undergo thermal decomposition and vaporization, which are then discharged with the exhaust gas.

[0039] The most critical control parameter in this step is the molar ratio of sulfate to total barium ions (denoted as R). This ratio must be precisely stabilized within the range of 1.01:1 to 1.10:1, preferably 1.03:1 to 1.06:1, through an online monitoring and feedback control system. This aims to utilize the extremely low solubility of barium sulfate to create and maintain a slight excess environment of sulfate ions, thermodynamically driving all barium ions to preferentially and completely convert into barium sulfate precipitate, thereby maximally suppressing the formation of soluble barium nitrate at the reaction source.

[0040] (3) Deep washing and precise solid-liquid separation: The gas-solid mixture obtained from the bottom of the reaction tower is separated by a high-efficiency cyclone separator, and the solid part enters a multi-stage countercurrent washing system. Deionized water is used for washing at a controllable temperature (40-60℃) and with moderate stirring. The washing process has clear endpoint control indicators: by monitoring the conductivity and pH value of the final stage washing effluent, its pH is controlled between 5.5 and 7.0, and its conductivity is below a certain threshold (e.g., 100 μS / cm). This design aims to ensure that soluble ions (such as NO3-) are separated. - K + And trace amounts of Ba that may be generated due to the local consumption of sulfate ions. 2+ The residue is completely removed, while avoiding the formation of secondary barium sulfate precipitate in subsequent processes due to residual acid and trace amounts of barium ions in the washing solution caused by insufficient washing, which would affect the cleanliness of the system. After washing, solid-liquid separation (such as pressure filtration and centrifugation) yields a high-purity nano-barium sulfate wet filter cake and an acidic washing solution.

[0041] (4) Internal circulation of multi-component materials and dynamic balance of the system.

[0042] (4.1) Nitrate closed-loop circulation: Approximately 80%-95% of the volume of the acidic washing liquid (mainly containing HNO3, trace amounts of dissolved Ba(NO3)2, and other impurity ions) generated in step (3) is directly pumped back to the slurry preparation tank in step (1). The nitric acid in this liquid reacts with the freshly added barium carbonate: 2HNO3 + BaCO3 → Ba(NO3)2 + CO2↑ + H2O, and the generated barium nitrate then enters the next round of spray reaction. Thus, nitrate is no longer discharged as a pollutant, but is instead circulated within the system via the path of nitric acid → barium nitrate → entering the reaction system. Its chemical essence is the reuse of nitrate in waste acid as a barium ion carrier and reaction medium.

[0043] (4.2) Full-path recycling of carbon dioxide: The carbon dioxide-rich tail gas generated in step (2) spray reaction and step (5) drying process is subjected to dust removal, cooling, deep dehydration and purification to obtain high-purity CO2 gas. This purification process also removes nitrogen oxides (NOx) from the tail gas. x The gas contains trace amounts of organic decomposition products. It is used in three ways: a) returned to the slurry preparation tank of step (1) for carbonation of barium oxide / barium hydroxide or to adjust the slurry pH; b) supplemented to the hot air generation system of the spray reactor as part of the inert carrier gas to reduce oxygen partial pressure and prevent local overheating or oxidation; c) used in small quantities for pressure balancing during system startup or balancing. This constitutes a complete carbon cycle.

[0044] (4.3) Impurity enrichment and side-stream purification: To ensure the long-term stable operation of the system (e.g., continuous operation for thousands of hours), it is necessary to control inert impurity ions (e.g., Na introduced from the raw materials). +K + This application addresses the accumulation of trace amounts of undecomposed organic nitrates or their decomposition products, etc., in the nitrate circulation pipeline. An online ion chromatograph or conductivity monitor is installed, connected to an adjustable split-ratio bypass purification unit (such as an ion exchange resin tower, electrodialysis, or evaporative crystallizer). When the concentration of impurity ions exceeds a preset upper limit, a portion of the circulating liquid (typically 5%-20%) is automatically diverted to the bypass for deep desalination and organic matter removal. The purified supernatant is returned to the system, while concentrated waste liquid or crystalline salt is outsourced for treatment. This main circulation + side-stream purification mode is crucial for maintaining the dynamic equilibrium of a complex component system.

[0045] (5) Low-temperature drying and packaging of products: The washed high-purity wet filter cake is dried by mild methods such as spray drying, vacuum belt drying or flash drying to finally obtain nano barium sulfate powder with a moisture content of less than 0.3% and good dispersibility, which is then packaged after grading.

[0046] Figure 1 This diagram fully illustrates the material and energy flow of this application. Solid arrows represent the main material flow: waste acid and barium source are pretreated separately, then converge and react in the core area of ​​a dual-channel centrifugal spray reactor. The products are separated and washed to obtain the final product, which terminates in drying and packaging. Dashed arrows outline two innovative cycles: loop 1 represents the nitrate cycle, where the majority of the washing liquid returns to the slurry preparation starting point; loop 2 represents the carbon dioxide cycle, where CO2 recovered from the exhaust gas by the purification unit is supplied to both the slurry preparation tank and the hot air system. This diagram visually reveals the essence of the green design of this application's self-closed dual-cycle material flow.

[0047] Secondly, this application provides a specific continuous preparation system for nano-barium sulfate based on waste acid resource utilization and internal circulation for implementing the above method. This system is a highly modular, automated, and closed-loop material flow continuous production device, mainly comprising: (a) Raw material preparation module. This includes a waste acid filtration buffer tank, a barium carbonate powder silo, a slurry preparation tank (with agitator, pH meter, and CO2 distributor), and a precision feed metering pump set.

[0048] (II) Core Reaction Module. The core equipment is a vertical dual-channel centrifugal spray reaction tower. It is equipped with a corrosion-resistant dual-channel centrifugal atomizer at the top, driven by a high-speed motor with adjustable speed; the upper part of the tower body is equipped with a tangential hot air inlet, the middle part is the reaction drying zone, and the lower part is the initial product collection cone; the side walls of the tower body can be equipped with observation windows and temperature measuring points as needed.

[0049] (iii) Separation and washing module. This includes a cyclone separator connected to the bottom of the reaction tower, a screw conveyor, a multi-stage series stirred washing tank (or a belt countercurrent washer), and a precision filter press or a horizontal centrifuge.

[0050] (iv) Circulation and Balancing Module. This system includes the following units: (1) Liquid circulation unit: It consists of a washing liquid buffer tank, a reuse transfer pump, an online mass spectrometer / ion chromatograph, automatic control valves, and pipelines connected to the slurry preparation tank. A branch of the pipeline leads to the bypass purification device.

[0051] (2) Gas circulation unit: consisting of exhaust gas collection hood, primary dust collector, condenser, gas purification tower (such as alkaline scrubbing, adsorption), used to remove nitrogen oxides (NOx). x It consists of a catalytic or adsorption device for organic matter, a carbon dioxide compressor, a gas storage buffer tank, and return gas pipelines leading to the slurry preparation tank and the hot air furnace, respectively.

[0052] (v) Product post-processing module: including dryer, air classifier, ton bag packaging machine and dust removal system.

[0053] (vi) Central Control System (DCS / PLC). Integrates all sensor signals and adjusts key parameters such as feed ratio (controlling R value), atomization speed, hot air temperature, washing water volume, and diversion valve opening in real time through preset algorithms to ensure fully automatic, safe, and stable operation of the system.

[0054] The present application will be further illustrated by the following examples, but the present application is not limited thereto.

[0055] Example 1: Standardized production operation using barium carbonate as raw material Reference Figure 1 The system shown is used to process waste acid from an isooctyl nitrate production line of a chemical company. Its typical composition, as determined by testing, is: sulfuric acid 81 wt%, nitric acid 7 wt%, water 13 wt%, and contains trace amounts of isooctyl nitrate (<0.3%).

[0056] Specifically, the steps include the following: (1) Pretreatment: Waste acid is allowed to stand and separate into layers and then adsorbed with acid-resistant resin to obtain clear and purified waste acid, which is then stored in a purified waste acid storage tank.

[0057] (2) Slurry preparation: Add 5 m to the slurry preparation tank. 3 Deionized water, 3.2 tons (approximately 16.2 kmol) of industrial-grade barium carbonate (purity ≥99.2%), and 4.2 m³ of acidic washing solution recycled from the previous cycle. 3 (Analysis showed approximately 0.6 mol / L of HNO3). Stirring was started, and a small amount of recycled CO2 (approximately 10 Nm³) was introduced. 3 To promote dispersion, the mixture is stirred for 1.5 hours to form a homogeneous slurry, which is then pumped into a barium salt mixed slurry storage tank. The slurry contains approximately 25% barium carbonate by mass.

[0058] (3) Spray reaction: The purified waste acid and slurry are respectively transported to the coaxial non-uniform diameter two-stage high-speed centrifugal atomizer at the top of the dual-channel centrifugal spray reaction tower by two diaphragm metering pumps at a flow rate of 9.8 L / min (waste acid) and 18.5 L / min (slurry).

[0059] like Figures 6 to 8 As shown, the dual-channel centrifugal atomizer 100 is a coaxial, non-uniform diameter, two-stage high-speed centrifugal atomizer, including a central atomizing disk 103 and a coaxial annular atomizing disk 104 sleeved outside it; wherein, the diameter of the annular atomizing disk 104 is larger than the diameter of the central atomizing disk 103, the waste acid is introduced into the central atomizing disk 103 from the waste acid inlet 101, and the slurry is introduced into the annular atomizing disk 104 from the slurry inlet 102.

[0060] Optionally, the ratio of the diameter D1 of the central atomizing disk 103 to the diameter D2 of the annular atomizing disk 104 is 1.3:1 to 1.8:1. The central atomizing disk 103 and the annular atomizing disk 104 rotate synchronously, with a rotation speed of 15,000 rpm to 40,000 rpm; and / or, the inlet temperature of the hot air environment is 180°C to 300°C. In the dual-channel centrifugal spray reaction tower, the effective reaction zone length-to-diameter ratio (L / D) of the reaction tower is 4:1 to 8:1; Preferably, the hot air enters the reaction tower in a tangential or swirling manner, and its average flow velocity across the cross-section of the reaction tower is 15 m / s to 35 m / s; more preferably, the ratio R is 1.03:1 to 1.06:1.

[0061] Low-viscosity waste acid enters the central atomizing disc (diameter D1 = 120 mm), while high-viscosity slurry enters the outer annular atomizing disc (diameter D2 = 180 mm, diameter ratio D2 / D1 = 1.5). The R value (SO4) is calculated and controlled in real time by the DCS system. 2- / Ba 2+ The value is 1.05. The spindle speed of the atomizing disc is set to 25,000 rpm to ensure synchronous rotation of the two discs. The hot air system provides 250°C hot air, which is delivered into the tower at a tangential velocity of 25 m / s, forming a strong swirling mixing zone below the atomizing disc. The effective reaction zone of the reaction tower has a height of 9.6 meters, a diameter of 1.6 meters, and a length-to-diameter ratio of L / D=6.

[0062] (4) Separation and Washing: After the reaction products are collected by a gas-solid separator, they are sent to a multi-stage countercurrent washing system by a screw conveyor. The flow rate and temperature of the washing water at each stage are precisely controlled by a PLC. Finally, the wet filter cake enters the drying unit and is pressed and separated by a plate and frame filter press. The pH of the final washing effluent is measured to be 6.8 and the conductivity is 85 μS / cm, reaching the set endpoint. Approximately 4.8 tons of nano-barium sulfate filter cake (wet product) with a wet content of about 45% is obtained.

[0063] (5) Circulation and Purification: All washing liquid and filter press mother liquor are collected in the washing liquid buffer monitoring tank. Online ion chromatography (IC) analysis shows Na + / K + The concentration is 850 ppm. DCS commands are executed as follows: 85% of the liquid is directly pumped back to the slurry preparation tank for recycling; 15% of the liquid is diverted to the purification bypass for further treatment. The bypass purification unit effectively traps and removes organic impurities, preventing their accumulation. Approximately 60% of the CO2 recovered from the dual-channel centrifugal spray reactor and subsequent drying exhaust gas is pressurized and reused in the slurry preparation tank and hot air system, with the remainder temporarily stored.

[0064] (6) Product drying: The wet filter cake is fed into the flash dryer via a screw feeder and dried at 140°C. Finally, the finished product is obtained by air classifier.

[0065] Results: The obtained nano-barium sulfate product was tested and found to be as follows: Figure 2 As shown, the average particle size (D50) is 46 nm (Malvin laser particle size analyzer). The product's chemical purity (BaSO4 dry basis) is 99.7%, and its whiteness (Hunter) is 99.3%. Single batch consumption: only 0.3 tons of fresh barium carbonate are needed for replenishment (mainly to compensate for system losses), and there is no process wastewater discharge.

[0066] Furthermore, based on a single batch production, material balance calculations show that by inputting approximately 6.0 tons of industrial waste acid composed of 81% H2SO4 and 7% HNO3, and supplementing with 0.3 tons of fresh barium carbonate (purity ≥99.2%), approximately 2.64 tons of nano-barium sulfate dry product can be prepared. At the same time, approximately 0.70 tons of carbon dioxide are recovered and most of it is recycled back into the system. The sulfur element in the waste acid is fixed in the form of barium sulfate with a conversion rate of over 99.5%. The recycling rate of nitrate ions in the system exceeds 85%. There is no wastewater discharge during the process, achieving efficient conversion of waste acid resources and closed-loop operation of materials.

[0067] Example 2: Process Operation and Validation Using Barium Oxide as Raw Material This embodiment aims to further verify the broad applicability of the method described in this application. By changing the type of barium source and fine-tuning some process parameters, it demonstrates that high-purity nano-barium sulfate products can still be stably synthesized within the process conditions protected by this patent. Based on the system and basic process flow described in Example 1, this embodiment mainly adjusts the following parameters: 1. Change of barium source: The raw material was changed from barium carbonate to industrial-grade barium oxide (BaO, purity ≥98.5%).

[0068] 2. Fine-tuning of waste acid composition: The waste acid composition used is: 80wt% sulfuric acid, 8wt% nitric acid, 12wt% water, containing trace amounts of organic nitrate esters (approximately 200ppm). This composition is still within the scope described in this application.

[0069] 3. Adjustment of core reaction parameters: (1) The molar ratio of sulfate to barium ions (R) is controlled at 1.04:1.

[0070] (2) Atomizer speed: set to 30,000 rpm (center disc and ring disc synchronized).

[0071] (3) Hot air inlet temperature: set to 220℃.

[0072] (4) The length-to-diameter ratio (L / D) of the effective zone of the reaction tower is 5:1.

[0073] 4. Slurry preparation: Barium oxide is carbonized in situ using recycled CO2 to form slurry.

[0074] Specifically, the steps include the following: (1) Raw material preparation: Provide the above-mentioned industrial waste acid, which is pretreated (filtered, adsorbed) to obtain purified waste acid. Provide industrial barium oxide powder.

[0075] (2) Slurry preparation and barium source activation: In the slurry preparation tank, add 4.8 m 3 The acidic wash solution recycled from the previous cycle (analyzed to contain approximately 0.65 mol / L HNO3) and 1.2 m 3 Deionized water. Start stirring and slowly add 2.8 tons (approximately 18.2 kmol) of barium oxide powder. Simultaneously introduce purified and recovered carbon dioxide gas (flow rate approximately 15 Nm³). 3 The reaction temperature was controlled below 50℃. The mixture was stirred for approximately 2 hours, and the pH and the amount of undissolved solids in the slurry were monitored to ensure complete conversion of barium oxide to barium carbonate, forming a homogeneous slurry. The resulting slurry contained approximately 28% barium carbonate (as BaCO3). It was then pumped into a storage tank for later use.

[0076] (3) Spray reaction and preliminary drying: The purified waste acid and the above slurry are respectively delivered to the atomizer at the top of the dual-channel centrifugal spray reaction tower via precision metering pumps at flow rates of 10.2 L / min (waste acid) and 17.8 L / min (slurry). The waste acid enters the central atomizing disc (D1=120 mm), and the slurry enters the annular atomizing disc (D2=192 mm, D2 / D1=1.6). The feed is precisely controlled by the DCS system to keep the R value stable at 1.04. The atomizer speed is set to 30,000 rpm. The hot air system provides 220°C hot air, which is delivered into the tower at a tangential velocity of 20 m / s. The effective zone size of the reaction tower is matched according to L / D=5.

[0077] (4) Separation and washing: The reaction products were subjected to gas-solid separation, and the solid was sent to a multi-stage countercurrent washing system. The washing water temperature was controlled at 50℃, and a plate and frame filter press was used for final solid-liquid separation. The pH of the final washing effluent was monitored to be 6.2, and the conductivity was 78 μS / cm, reaching the washing endpoint (pH 5.5-7.0). A wet filter cake of nano-barium sulfate with a moisture content of approximately 42% was obtained.

[0078] (5) Material circulation and system balance: After the washing liquid is collected, online analysis shows that Na + The concentration is 920 ppm. 85% of the washing liquid is directly recycled to the slurry preparation tank in step (2). 15% of the washing liquid is diverted to a bypass purification unit (an electrodialysis device is used in this example) for desalination. The concentrate is outsourced, and the desalinated liquid is returned to the system. CO2 in the reaction and drying exhaust gases is recovered and purified, and then recycled to the slurry preparation tank and hot air system as needed.

[0079] Step (6) Product drying: The wet filter cake is dried at 120°C using a vacuum belt dryer to obtain nano barium sulfate powder.

[0080] Results: The obtained nano-barium sulfate product was tested and found to be as follows: Figure 3 As shown, the average particle size (D50) is 44 nm (Malvin laser particle size analyzer). The chemical purity (dry basis BaSO4) is 99.6%, and the whiteness is 99.0%.

[0081] Furthermore, material balance analysis shows that this batch consumed approximately 6.1 tons of the aforementioned waste acid and 2.8 tons of barium oxide, producing approximately 2.71 tons of nano-barium sulfate. The sulfate conversion rate in the waste acid is >99.4%, the nitrate recycling rate is >87%, and there is no wastewater discharge during the process.

[0082] This embodiment successfully synthesized a nano-barium sulfate product with an average particle size of approximately 44 nm, a purity of 99.6%, and excellent whiteness by replacing the barium source with barium oxide and appropriately adjusting process parameters such as the composition of the waste acid, reaction temperature, rotation speed, and aspect ratio (all parameters are within the scope of protection of the claims in this application). This fully demonstrates that the green preparation method of nano-barium sulfate based on waste acid resource utilization and CO2 recycling provided in this application has clear process parameter boundaries and good operational flexibility. Within the conditions defined by its claims, it can stably and reliably achieve continuous and clean production of nano-barium sulfate, verifying the feasibility and universality of this patented technology.

[0083] Example 3: System Long-Term Operation Stability Test Based on Example 1, the process system of Example 1 was continuously run for 50 batches. Since the feedstock did not contain halide ions, the main accumulated impurity in the circulating liquid was Na.+ / K + (From raw material barium carbonate) and trace amounts of organic acids (decomposition products of nitrate esters). Samples of the circulating washing solution are taken every 5 batches to test total organic carbon (TOC) and sodium ion concentration. When TOC > 500 ppm or Na... + When the concentration exceeds 2000 ppm, the DCS system automatically directs 15% of the diverted solution to the bypass purification unit. This unit employs catalytic oxidation (removal of organic matter) + selective ion exchange (removal of sodium). + / K + The solution is processed using a combination of processes, and the treated clear liquid is returned to the system.

[0084] Take a mixed sample of 50 batches of the final product obtained in this example, and measure the average particle size (e.g., Figure 4 As shown in the figure, the average particle size (D50) is 47 nm (Malvin laser particle size analyzer). The chemical purity of the product (BaSO4 dry basis) is 99.7%, and the whiteness (Hunter) is 99.2%. The whiteness and purity indicators remain stable (standard deviation <2.5%), which proves that under the specific raw material conditions of this embodiment, the targeted main circulation + side-line catalytic oxidation / ion exchange purification mode can effectively maintain the long-term dynamic balance of the system. Figure 5 The XRD pattern of the mixed sample shows sharp and narrow diffraction peaks without obvious diffuse, dome-shaped peaks, indicating high crystallinity and large grain size. Multiple high-intensity diffraction peaks are present around 2θ ≈ 25.0°, 27.5°, and 30.0°, typical characteristics of barium sulfate. No characteristic peak of barium nitrate (23.5°) was detected; only pure barium sulfate crystal diffraction peaks were observed, without any impurity peaks, proving that barium nitrate is essentially absent. This directly proves that this process can successfully synthesize pure-phase barium sulfate, and the process effectively suppresses the formation and inclusion of the byproduct barium nitrate.

[0085] In summary, this application, through rigorous chemical engineering design and advanced system integration, has successfully constructed a new, technologically advanced, economically sound, and environmentally friendly pathway for the production of nano-barium sulfate, providing a highly valuable solution for the high-value utilization and circular economy of chemical byproducts. Those skilled in the art can make various modifications and variations within the spirit and essence of this application, and these equivalent forms also fall within the scope defined by the claims of this application.

Claims

1. A continuous preparation method of nano-barium sulfate based on waste acid resource utilization and internal circulation, characterized in that, Includes the following steps: An industrial waste acid containing sulfuric acid, nitric acid and trace amounts of organic nitrate esters, and a barium source, wherein the barium source is barium carbonate, barium oxide or barium hydroxide; a slurry is prepared by mixing the industrial waste acid and the barium source; The slurry prepared by the industrial waste acid and barium source is introduced into different atomizing discs of a dual-channel centrifugal atomizer through independent conveying pipelines. It is atomized and instantaneously mixed in the atomizer, and then reacted and preliminarily dried in a hot air environment to obtain a mixture containing barium sulfate solid and soluble components. The resulting mixture was separated into solid and liquid components to obtain a solid wet material and a primary mother liquor. The solid wet material was then washed with a washing solution, and the washing endpoint was controlled to obtain a nano-barium sulfate wet material and an acidic washing solution. A portion of the acidic washing liquid is used as industrial waste acid and recycled for the preparation of the slurry. The carbon dioxide-containing gas generated during the reaction and drying process is recovered and purified, and at least a portion is recycled for hot air supply in the hot air environment. Another portion of the acidic washing liquid is bypassed and purified to control the concentration of impurity ions in the reaction system. The wet nano-barium sulfate material is dried to obtain nano-barium sulfate powder product.

2. The method of claim 1, wherein, The mass ratio of sulfuric acid, nitric acid and water in the industrial waste acid is (80~82):(6~8):(12~14), and the content of trace organic nitrate esters is ≤300ppm; Preferably, the mass fraction of barium carbonate in the slurry is 20% to 50%.

3. The method of claim 1, wherein, When the barium source is barium oxide or barium hydroxide, the barium oxide or barium hydroxide is reacted with water and recycled carbon dioxide gas in a preparation tank to completely convert it into barium carbonate before it is used to prepare the slurry. Preferably, in the mixture containing barium sulfate solid and soluble components, the ratio R of the total molar number of sulfate ions to barium ions in the reaction system is controlled to be (1.01~1.10):

1.

4. The method of claim 1, wherein, The dual-channel centrifugal atomizer is a coaxial, non-uniform diameter, two-stage high-speed centrifugal atomizer, comprising a central atomizing disk and a coaxial annular atomizing disk sleeved outside it; wherein, the diameter of the annular atomizing disk is larger than the diameter of the central atomizing disk, the waste acid is fed into the central atomizing disk, and the slurry is fed into the annular atomizing disk.

5. The method of claim 4, wherein, The ratio of the diameter D1 of the central atomizing disc to the diameter D2 of the annular atomizing disc is 1.3:1 to 1.8:

1.

6. The method according to claim 4, characterized in that, The central atomizing disc and the annular atomizing disc rotate synchronously, with a rotation speed of 15,000 rpm to 40,000 rpm; and / or, the inlet temperature of the hot air environment is 180°C to 300°C.

7. The method according to claim 1, characterized in that, In a dual-channel centrifugal spray reaction tower, the effective reaction zone length-to-diameter ratio (L / D) of the reaction tower is 4:1 to 8:1; Preferably, the hot air enters the reaction tower in a tangential or swirling manner, and its average flow velocity across the cross-section of the reaction tower is 15 m / s to 35 m / s. Preferably, the ratio R is from 1.03:1 to 1.06:

1.

8. The method according to claim 1, characterized in that, The control of the washing endpoint refers to: monitoring the pH value of the final washing effluent, and stopping the washing process when the pH value reaches the range of 5.5 to 7.0; Preferably, the mass ratio of the acidic washing liquid to the solid wet material is 0.5:1 to 1.5:1; Preferably, 80%-95% of the acidic washing liquid is used as industrial waste acid and recycled for the preparation of the slurry, and 5%-20% of the acidic washing liquid is subjected to bypass purification treatment.

9. The method according to claim 1, characterized in that, The bypass purification process includes at least one of ion exchange, electrodialysis, or evaporative crystallization to remove alkali metal ions and trace organic nitrate decomposition products from the circulating liquid. Preferably, the drying temperature is 100°C to 200°C.

10. A continuous preparation system for nano-barium sulfate based on waste acid resource utilization and internal recycling, used to implement the method described in any one of claims 1 to 9, characterized in that, include: The raw material preparation and slurry preparation unit is used to store waste acid and prepare and store barium source slurry. A dual-channel centrifugal spray reaction unit is provided with a dual-channel centrifugal atomizer and a reaction tower. The two feed inlets of the atomizer are respectively connected to the waste acid outlet and the slurry outlet of the raw material preparation and slurry preparation unit. The separation and washing unit has its inlet connected to the solid outlet of the reaction unit for washing and solid-liquid separation of the solid product, and is provided with a washing liquid outlet and a wet material outlet. The gas processing and circulation unit has its inlet connected to the tail gas outlet of the reaction unit for recovering carbon dioxide gas, and is provided with at least two carbon dioxide recycling outlets. The material circulation and balancing unit includes: A liquid circulation pipeline connects the washing liquid outlet of the separation and washing unit to the liquid inlet of the slurry preparation tank of the raw material preparation and slurry preparation unit. A bypass purification branch is connected to the liquid circulation pipeline to divert and purify a portion of the circulating washing liquid; The gas circulation pipeline is connected to the carbon dioxide recovery outlet of the gas treatment and circulation unit to the hot air system of the raw material preparation and slurry preparation unit and the dual-channel centrifugal spray reaction unit, respectively. Preferably, the liquid circulation pipeline is equipped with an online analyzer for real-time monitoring of the ion concentration of the circulating liquid and a control valve group for controlling the diversion ratio.

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