Method for promoting crystallization of high-salt solution based on seed crystal method

Abstract

The invention belongs to the technical field of industrial high-salinity wastewater treatment, and discloses a method for promoting crystallization of a high-salinity solution based on a seed crystal method. The method comprises the following steps: pre-treating high-salinity wastewater to remove suspended solids and colloidal impurities; putting a photo-thermal response type composite seed crystal into a crystallizer; starting a thermal control and stirring device to maintain a preset temperature; forming a local supersaturated environment through photo-thermal conversion; and refluxing and reusing the fine seed crystal through regeneration treatment. The photo-thermal response type composite seed crystal is of a core-shell-functional layer structure, an inner core is high-purity single crystal particles, a middle shell layer is a porous salt-tolerant screening layer, and a surface functional layer is a photo-thermal-temperature-sensitive double-response composite coating. The method provided by the invention can realize directional quality-divided crystallization of the target salt of the multi-component high-salt system, the product reaches industrial-grade purity, the seed crystal cycle stability is excellent, and the method is suitable for multi-industry high-salt wastewater treatment and has both resource recovery and environmental benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of industrial high-salinity wastewater treatment, and relates to a method for promoting crystallization of high-salinity solution based on a seed method. BACKGROUND

[0002] In the industrial production process, coal chemical industry, petroleum chemical industry, pharmaceutical industry and other industries will produce a large amount of high-salinity wastewater. Such wastewater usually contains a high concentration of various salt substances, and the total dissolved solids (TDS) often exceeds 10,000 mg / L. If directly discharged, it will not only cause serious environmental pollution, but also lead to waste of salt resources. Therefore, effective treatment of high-salinity solution and recovery and utilization of salt resources have become an important issue in the field of industrial wastewater treatment.

[0003] At present, the crystallization technology is the core means to realize the separation and recovery of salt in high-salinity solution. The seed method is widely used in the crystallization treatment of high-salinity solution because it can guide the directional growth of crystals and reduce the problem of uneven crystal size caused by spontaneous nucleation. The existing seed method mostly uses single-structure seeds. By introducing seeds with the same crystal form as the target salt in the supersaturated solution, a core is provided for the growth of target salt crystals, and the target salt is precipitated on the surface of the seeds.

[0004] However, in the actual application process, the existing seed method for treating high-salinity solution still has many deficiencies: first, for multi-component high-salinity systems containing various salts, the traditional single-structure seeds lack the ability to selectively recognize and screen target ions, making it difficult to achieve directional separation and crystallization of different salts. The resulting crystalline product has a high impurity content and low purity, often failing to meet the utilization standards of industrial-grade salt products, limiting the recovery value of salt resources; second, the seeds are easily wrapped by impurity ions in the wastewater or passivated due to the adsorption of too many impurities on the surface, leading to rapid decay of seed activity. New seeds need to be frequently added to maintain the crystallization effect, which not only increases the operating cost of the process, but also may affect the stability of the crystallization process due to improper control of the amount of added seeds; third, the recycling mechanism of the existing seeds is not perfect, and the regeneration method for inactive or small seeds is single, with limited regeneration effect. It is difficult to achieve long-term stable reuse of seeds, further increasing the operation burden and resource consumption of the process, which is not conducive to the popularization and application of the technology in the industrial large-scale treatment of high-salinity wastewater.

[0005] To solve the above-mentioned problems in the existing technology, such as low separation precision of multi-component salt, rapid decay of seed activity, and poor recycling effect of seeds, a new seed method crystallization technology is needed, which can realize directional separation and crystallization of multi-component salt, improve the stability of seed activity, and efficiently recycle seeds, to meet the actual needs of industrial high-salinity wastewater treatment and salt resource recovery. SUMMARY

[0006] In view of the problems of low separation precision of multi-component salt, rapid attenuation of seed activity and poor recycling effect of seed in the existing seed method for treating high-salt solution, the present application realizes low-energy consumption fractional crystallization and salt resource recovery of high-salt wastewater by designing a photo-thermal response type composite seed and a crystallization method. Specifically, the present application provides the following technical scheme.

[0007] Firstly, the present application provides a method for promoting crystallization of high-salt solution based on seed method, comprising the following steps: 1) pretreating high-salt wastewater to remove suspended solids and colloidal impurities; 2) putting photo-thermal response type composite seeds corresponding to target salt into the crystallizer, wherein the photo-thermal response type composite seeds are of a core-shell-function layer three-layer structure, the inner core is a high-purity single crystal particle of the same crystal type as the target salt, the intermediate shell layer is a porous salt-tolerant screening layer, and the surface functional layer is a photo-thermal-temperature sensitive dual-response composite coating; 3) starting the heat control device and the stirring device to maintain a preset temperature in the crystallizer, forming a local supersaturation environment through photo-thermal conversion, and the target ions grow directionally in the seed inner core after being screened by the intermediate shell layer; 4) separating the generated crystals from the mother liquor; 5) returning the separated fine seed particles to the crystallizer for recycling after being treated in a regeneration module.

[0008] Further, in the above method, polyaluminum chloride is used as a flocculant during pretreatment, and the addition amount is 80-120 mg / L.

[0009] Further, in the above method, the amount of the photo-thermal response type composite seeds added is 2-5% of the mass of the solution.

[0010] Further, in the above method, the preset temperature is 25-35℃.

[0011] Further, in the above method, the stirring device is a pulse flow field stirrer, and the frequency is 1-3 Hz.

[0012] Further, in the above method, the treatment process of the regeneration module includes acid washing, ultrasonic dispersion and photo-thermal activation, wherein the acid washing uses hydrochloric acid with a mass fraction of 1-2%, the ultrasonic dispersion has a frequency of 30-50 kHz, the treatment time is 5-10 min, and the photo-thermal activation time is 3-5 min; the fine seed particles treated by the regeneration module are returned to the crystallizer for recycling.

[0013] Secondly, the present application provides a photo-thermal response type composite seed, comprising an inner core, an intermediate shell layer and a surface functional layer. The inner core is a high-purity single crystal particle of the same crystal type as the target salt, and the particle size is 50-100 μm. The intermediate shell layer is a porous salt-resistant screening layer wrapped outside the core, with a thickness of 5-10 microns, using modified mesoporous SiO2 or MXenes nanomaterials, and a pore size of 0.2-0.5 nm. The surface functional layer is a photo-thermal and temperature-sensitive double-response composite coating grafted outside the intermediate shell layer, with a thickness of 2-3 microns, a critical solution temperature of 30-35 DEG C, and being composed of graphene oxide and poly-N-isopropyl acrylamide (PNIPAM).

[0014] Further, for the above-mentioned photo-thermal response type composite seed, the photo-thermal conversion efficiency of the surface functional layer is greater than or equal to 85%.

[0015] Further, for the above-mentioned photo-thermal response type composite seed, the purity of the core is greater than or equal to 99.9%.

[0016] Further, for the above-mentioned photo-thermal response type composite seed, the specific surface area of the modified mesoporous SiO2 used in the intermediate shell layer is 800-1000 m 2 / g.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. Strong directional separation and crystallization ability of multi-component high-salt system For a complex high-salt system containing multiple salt components, by using photo-thermal response type composite seeds of target salts in stages, combined with the ion screening function of the intermediate shell layer of the seeds, different salts can be directionally identified and separated, effectively solving the mixed crystal problem caused by the inability of traditional single seeds to distinguish impurity ions, and realizing the separation and crystallization of multi-component salts; with the help of the photo-thermal response characteristics of the surface functional layer of the composite seed, a local supersaturation environment can be quickly formed, greatly shortening the induction period of crystal precipitation, and at the same time, the crystallization rate is improved, compared with the traditional non-seed or single seed system, the efficiency of high-salt solution crystallization treatment is significantly improved.

[0018] 2. High quality of crystallization product and high value of resource recovery The composite seed can guide the directional growth of target ions, reduce the mixing of impurity ions into the crystal lattice, and finally obtain a crystallization product with a purity meeting the utilization requirements of industrial-grade salt products, breaking through the limitations of low product purity and difficulty in resource recycling in traditional technologies; the composite seed can efficiently recover salt resources from high-salt wastewater, greatly reducing salt resource waste, converting the originally discharged high-salt wastewater into reusable industrial-grade salt products, and significantly improving the resource utilization value of high-salt wastewater.

[0019] 3. Stable seed circulation, reducing process operation cost Through the regeneration process composed of acid elution, ultrasonic dispersion and photo-thermal activation, the activity of fine or inactivated seeds can be effectively recovered. After multiple cycles of use, the seeds can still maintain good crystallization guiding performance with low activity attenuation. At the same time, the problems of seed being easily wrapped and passivated by impurities and the need for frequent addition of new seeds in traditional technology are avoided, reducing seed raw material consumption and the operation complexity caused by frequent addition of seeds. Long-term operation can significantly reduce process costs.

[0020] 4. Wide application scenarios, with environmental and industrial benefits The composite seeds can be used for high-salinity wastewater treatment needs in multiple industries such as pharmaceuticals, coal chemical industry, and petroleum chemical industry. The pretreatment stage can effectively remove suspended solids and colloidal impurities in wastewater, without the need for significant process adjustments for different industry wastewater, and has strong applicability. The composite seeds achieve resource recycling through salt resource recovery, creating industrial value, and reducing environmental pollution caused by direct discharge of high-salinity wastewater, meeting the requirements of green environmental protection and industrial sustainable development, and have a broad application prospect. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described below in conjunction with the embodiments, obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] The test methods in the following examples are conventional methods, unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained commercially.

[0023] Example 1 This embodiment describes the preparation and performance test of a photo-thermal responsive composite seed (taking NaCl as an example).

[0024] I. Purpose of the test By improving the preparation process and adjusting the material formula, the microstructure and performance of the photo-thermal responsive composite seed are optimized, the directional crystallization guiding ability of the seed to the target salt in high-salinity solution is improved, and the controllability and repeatability of the preparation process are ensured, providing a stable performance and accurate selection of seed material basis for subsequent high-salinity solution crystallization treatment.

[0025] II. Test method (1) Material preparation 1. Core material: Select high-purity NaCl single crystal particles with the same crystal form as the target salt (NaCl as an example) as the core, with a particle size of 50-100 pm, a purity of ≥99.9%, and a complete lattice structure without impurity phase interference. Use a laser particle size analyzer to verify the particle size distribution, control the D50 at 70-80 pm, and ensure the uniformity of the core particles to provide a stable base for subsequent shell coating and crystal directional growth.

[0026] 2. Intermediate shell material: Select modified mesoporous SiO2 nanomaterials (particle size 20-50 nm, specific surface area 800-1000 m 2 / g) as the porous salt-resistant screening layer raw material; surface modification is performed using silane coupling agent KH-550, with a modifier dosage of 5-8% of the mass of mesoporous SiO2 to improve its bonding force with the core and salt-resistant stability; prepare a modified mesoporous SiO2 sol with a mass fraction of 15-20%, using a mixture of ethanol and deionized water (volume ratio 3:1) as the solvent, and adding 0.5-1% polyvinyl alcohol (PVA, molecular weight 80000) as a dispersant to prevent mesoporous SiO2 agglomeration and ensure shell uniformity.

[0027] 3. Surface functional layer material: The photothermal component is graphene oxide (GO, with a sheet size of 1-5 pm and an oxidation degree of ≥30%), and the temperature-sensitive component is poly-N-isopropyl acrylamide (PNIPAM, with a number average molecular weight of 50000-80000 and a lower critical solution temperature LCST=32-34℃); mix GO and PNIPAM at a mass ratio of 1:4, add N,N-dimethylformamide (DMF) solvent to prepare a composite coating solution with a mass fraction of 8-10%; then add 1-2% azobisisobutyronitrile (AIBN) as an initiator and 1.5-2% ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent to ensure the formation of a stable three-dimensional network structure in the grafting reaction, combining the functions of light-heat conversion and temperature-sensitive response.

[0028] 4. Auxiliary reagents: Hydrochloric acid (mass fraction 37%), ammonia water (mass fraction 25%), anhydrous ethanol, deionized water, etc.

[0029] (II) Preparation process 1. Core pretreatment Place the screened high-purity NaCl single crystal particles in a 1-2% hydrochloric acid solution and ultrasonically clean (frequency 40 kHz, power 300 W) at 30-35℃ for 15-20 min to remove trace amounts of impurity ions (such as Ca 2+ , Mg 2 +); then repeatedly washed with deionized water until pH = 6.5-7.5, placed in a vacuum drying oven (temperature 60-70℃, vacuum degree 0.08-0.1 MPa) and dried for 2-3 h to obtain clean and dry core particles, ready for use.

[0030] 2. Intermediate shell coating (sol-gel method) Take 50 g of pretreated NaCl core particles and add them to 200 mL of modified mesoporous SiO2 sol, and magnetically stir (speed 300-400 r / min) at 35-40℃ for 30-40 min to uniformly disperse the core particles in the sol; Add ammonia water drop by drop to adjust the pH of the system to 8.5-9.0, start the sol-gel reaction, and incubate and stir at 50-55℃ for 2-3 h, during which the modified mesoporous SiO2 nanoparticles gradually aggregate and crosslink on the surface of the core to form a gel layer; After the reaction is completed, use suction filtration (filter membrane pore size 0.22 μm) to separate the coated intermediate, wash it with anhydrous ethanol 3-4 times to remove unreacted sol components; place the intermediate in a forced air drying oven (temperature 70-80℃) and dry for 4-5 h, then transfer it to a muffle furnace and calcine at 300-320℃ for 1.5-2 h to convert the gel layer to a dense porous SiO2 shell layer; Observe the shell thickness by scanning electron microscopy (SEM) and control it to be 5-10 μm (if the thickness does not meet the requirements, repeat the coating step 1-2 times); use high-resolution transmission electron microscopy (HRTEM) to determine the shell pore size and ensure that the pore size distribution is 0.2-0.5 nm to meet the target ion screening requirements, and obtain the "core-shell" intermediate.

[0031] 3. Surface functional layer grafting Add 30 g of "core-shell" intermediate to 150 mL of graphene oxide-poly N-isopropyl acrylamide composite coating solution, heat to 60-65℃ under nitrogen protection (flow rate 50-100 mL / min), magnetically stir (speed 250-300 r / min) and incubate for 4-5 h, AIBN initiates PNIPAM polymerization, and at the same time, grafting reaction occurs with the hydroxyl groups on the surface of GO, making the composite coating tightly adhere to the surface of the intermediate shell; After the reaction is completed, cool the product to room temperature, wash it with a mixture of DMF and anhydrous ethanol (volume ratio 1:1) 2-3 times to remove ungrafted free GO and PNIPAM, and then place the washed product in a vacuum drying oven and dry it at 60℃ and 0.09 MPa for 4 h; Use atomic force microscopy (AFM) to detect the thickness of the functional layer and control it to be 2-4 μm to obtain a complete "core-shell-functional layer" structure of the photo-thermal response type composite seed.

[0032] 4. Seed post-processing The prepared composite seed is sieved through a 200-mesh screen to remove agglomerated particles, and the finished composite seed is obtained, with a pass rate of 98%.

[0033] (III) Performance test 1. Photothermal and temperature-sensitive response performance test The composite seed is dispersed in 100 g of deionized water (5% by mass), and placed under simulated sunlight irradiation (power 1000 W / m 2 ). The temperature data within 0-30 min are monitored and recorded, and the photothermal conversion efficiency η is calculated according to the formula η = (m × c × ΔT) / (P × t), where m is the mass of the solution, c is the specific heat capacity of water, ΔT is the temperature change value, P is the light power, and t is the light time. At the same time, the temperature response near 32-34℃ (LCST of PNIPAM) is monitored to ensure that the functional layer can quickly shrink when the temperature reaches LCST, exposing the screening channels of the intermediate shell layer.

[0034] 2. Ion screening performance test A simulated high-salt solution A containing NaCl (20 g / L), Na2SO4 (10 g / L), and CaCl2 (5 g / L) is prepared, and 5% of the composite seed is added. After stirring at 30℃ for 2 h (at a speed of 200 r / min), the ion concentrations in the solution are measured (using an ion chromatograph), and the adsorption rate of the target ions (Cl - , Na + ) and the rejection rate of the impurity ions (SO4 2- , Ca 2+ ) are calculated to verify the screening effect of the intermediate shell layer.

[0035] 3. Crystallization promotion ability test 100 mL of the above-mentioned simulated high-salt solution is taken, and 5 g of the composite seed is added. The crystallization experiment is carried out at 30℃ with a stirring speed of 200 r / min. The laser particle size analyzer is used to monitor the change in crystal particle size every 10 min, and the particle size growth rate within 60 min is recorded. After the experiment, the crystals are separated and analyzed by XRD to detect the crystal purity and whether impurity crystals are generated.

[0036] 4. Stability test After the experiment, the fine seed particles obtained by separation are treated by acid elution (spraying with 1.5% hydrochloric acid), ultrasonic dispersion (40 kHz, 8 min), and photothermal activation (simulated sunlight irradiation for 4 min), and then re-injected into the same crystallization test (repeated 3 times). The photothermal conversion efficiency, target ion adsorption rate, and crystal growth rate are measured, and the performance stability of the seed is evaluated according to the changes in the measured results.

[0037] III. Test Results (I) Microstructure The composite seeds were observed by SEM to have a regular spherical structure, with the inner core (NaCl single crystal) coated with a uniform intermediate shell (modified mesoporous SiO2), and the shell had no obvious cracks or shedding. The shell thickness was 6-8 μm. HRTEM measurement showed that the intermediate shell had a uniform pore size distribution, with a pore size of 0.3-0.4 nm, which met the requirements of ion screening. AFM detection showed that the surface functional layer (GO-PNIPAM) had a dense network structure, uniformly covering the surface of the shell, with a thickness of 2.2-2.5 μm, and the three-layer structure was clearly distinguishable, which was completely consistent with the designed "core-shell-functional layer" structure.

[0038] (II) Performance data 1. Photothermal and temperature-sensitive response performance The light absorption rate of the composite seeds in the wavelength range of 300-1200 nm was 85-90%, and the light absorption rate in the near-infrared region (700-1200 nm) was more than 88%. Under simulated sunlight irradiation, the preset temperature was maintained at 30°C by the thermal control device, and a local supersaturation environment was formed on the surface of the seeds through photothermal conversion, and the local temperature rose to 40-44°C (without affecting the overall solution constant temperature). After 20 min, the local temperature stabilized at 42°C, and the calculated value of the photothermal conversion efficiency η was 86.5%, which met the design requirement of ≥85%. When the temperature rose to 33°C (the LCST of PNIPAM), the functional layer rapidly contracted within 30 s, and through dynamic light scattering (DLS) detection, the hydration particle size of the seeds decreased from 500 nm to 380 nm, which proved that the temperature-sensitive response function was effective and could timely expose the screening channels of the intermediate shell.

[0039] 2. Ion screening performance After the simulated high-salt solution was treated by the composite seeds, the concentration of Na + in the solution decreased from the initial 11.1 g / L to 2.1 g / L, the concentration of Cl - decreased from the initial 15.36 g / L to 3.3 g / L, and the target ion adsorption rates were 81.1% and 78.5%, respectively; the concentration of SO4 2- decreased from the initial 4.8 g / L to 3.8 g / L, and the concentration of Ca 2+ decreased from the initial 2.0 g / L to 1.5 g / L, and the impurity ion rejection rates were 79.2% and 75.0%, respectively. The ion screening effect of the intermediate shell was significant, and it could effectively enrich the target ions and reject the impurity ions.

[0040] 3. Crystallization promotion ability In the crystallization experiment, the crystal size increased from 0.1 μm to 0.9 μm in 0-60 min, with an average growth rate of 0.8 μm / h; XRD analysis showed that the characteristic diffraction peaks of the crystallization product completely matched the NaCl standard card, no impurity peaks appeared, and the crystal purity was 99.6%, which proved that the composite seed could efficiently promote the directional crystallization of the target salt, and no impurity ions were mixed in.

[0041] 4. Stability The photo-thermal conversion efficiency of the composite seed decreased from 86.5% to 84.2%, the target ion adsorption rate decreased from 81.7% to 79.5%, and the crystal growth rate decreased from 0.8 μm / h to 0.78 μm / h, indicating that the seed had good stability.

[0042] Four, test conclusion In this embodiment, NaCl was used as an example to successfully prepare a photo-thermal response type composite seed with a "core-shell-functional layer" three-layer structure. The microstructure of the seed was clear, the three-layer materials were combined tightly, and the seed had good photo-thermal conversion efficiency, target ion adsorption capacity and crystallization promotion capacity, and good stability.

[0043] Example 2 This embodiment describes the optimization of the heat control parameters in the method of promoting the crystallization of high salt solution based on the seed method.

[0044] I. Test purpose Verify the synergistic effect of different heat control parameters (preset temperature, stirring frequency) and photo-thermal response type composite seeds in a single crystallizer, determine the appropriate heat control conditions to improve the crystallization rate and product purity of the target salt in high salt solution, and provide experimental support for the selection of heat control devices, preset temperature and stirring parameters.

[0045] II. Test method (1) Test materials and equipment 1. Preparation of high salt solution Prepare simulated high salt solution B, mainly containing NaCl 25 g / L, Na2SO4 15 g / L, pH 7.1; adjust the concentration by adding a small amount of deionized water or concentrating to ensure that the components of each batch of solution are uniform and consistent for subsequent crystallization tests.

[0046] 2. Seed material NaCl type composite seed: photo-thermal conversion efficiency 86.5%, prepared by the method of Example 1.

[0047] Na2SO4 type composite seed: The core is a high-purity Na2SO4 single crystal particle (particle size 70~90μm, purity ≥99.9%) with the same crystal form as Na2SO4; the middle shell is MXenes nanomaterial (thickness 7~9μm, pore size 0.4~0.5nm); the functional layer is the same as NaCl type composite seed, with a photothermal conversion efficiency of 86.2%, and is prepared using the method of Example 1.

[0048] 3. Test equipment Pretreatment equipment: coagulation reaction tank (effective volume 50L); Single crystallizer: effective volume 10L, made of 316L stainless steel, with good salt corrosion resistance, and a built-in temperature sensor (accuracy ±0.5℃) in the vessel wall to monitor the temperature of the solution in the chamber in real time; Thermal control device: Used with crystallizer, including electric heating module and temperature control system, can achieve constant temperature control within the range of 25~40℃, with temperature fluctuation range of ±0.5℃; Stirring device: pulse flow field stirrer, the stirring frequency can be adjusted in the range of 1~3Hz, the stirring paddle is a three-blade propulsion type, to ensure that the solution is mixed evenly and without damaging the seed crystal structure; Detection equipment: Ion chromatograph, used to determine the ion concentration in solution; laser particle size analyzer, used to measure the crystal particle size distribution and average particle size; X-ray diffractometer, used to analyze the crystal form purity; electronic balance, used to weigh seed crystals and crystal mass.

[0049] (II) Test Procedure 1. Pretreatment of high-salt solutions Take 40L of simulated high-salt solution and add 100mg / L of polyaluminum chloride (PAC) as a flocculant. Stir at 200r / min for 10min to fully mix the flocculant with the solution and adsorb trace suspended solids and colloidal impurities in the water. Then let it stand for 30min until the flocs have completely settled. Filter the solution using a 0.45μm pore size membrane to remove residual flocs and impurities, and obtain the pretreated high-salt solution for later use.

[0050] 2. Experimental grouping and parameter settings The pretreated high-salt solution was divided into four groups (10 L each), and each group was added to one of four identical single crystallizers for crystallization experiments of NaCl and Na2SO4. The heat control and stirring parameters for each group were set as follows: Group 1 (Low Temperature and Low Frequency Group): Photothermal responsive composite seed crystals are added at a rate of 3% of the solution mass (i.e., 300g); the thermal control device is set to a preset temperature of 25~30℃ to maintain a constant temperature inside the cavity; the pulse flow field stirrer is set to a frequency of 1~2Hz, with each stirring session lasting 30s and followed by a 30s resting period.

[0051] Group 2 (Medium-temperature high-frequency group): Add photothermal responsive composite seed crystals, the amount is the same as Group 1 (300g); the heat control device is set to a preset temperature of 30~35℃ to maintain a constant temperature inside the cavity; the pulse flow field stirrer is set to a frequency of 2~3Hz, and the stirring mode is the same as Group 1.

[0052] Group 3 (no seed control group): No seed crystals were added; the temperature of the heat control device was set to 30~35℃ (same as Group 2); the frequency of the pulse flow stirrer was set to 2~3Hz (same as Group 2), to compare the effect of seed crystals on the crystallization process; Group 4 (Single Seed Control Group): Traditional single seed crystal, dosage same as Group 1 (300g); the heat control device is set to a preset temperature of 30~35℃ to maintain a constant temperature inside the cavity; the pulse flow field stirrer is set to a frequency of 2~3Hz, and the stirring mode is the same as Group 1.

[0053] 3. Monitoring and control of the crystallization process Simultaneously, the heat control and stirring devices of four crystallizers were activated to begin the crystallization experiment, with a total crystallization time of 8 hours. During the experiment, samples were taken every hour (50 mL per sample per group), and the Na content in the samples was determined using an ion chromatograph. + Cl - SO4 2- The concentration of the target salt (NaCl, Na2SO4) was calculated, and the crystallization rate was derived. The average particle size of the crystals was determined by a laser particle size analyzer. The time of first crystal precipitation in each group of solutions was observed and recorded.

[0054] 4. Crystal separation and purity testing After the crystallization experiment, the heat control and stirring devices were turned off. The crystal-mother liquor mixture in the crystallizer was transferred to a Buchner funnel, and solid-liquid separation was achieved by vacuum filtration (0.08 MPa) to obtain wet crystals and mother liquor. The wet crystals were washed three times with a small amount of deionized water (at the same temperature as the crystallization temperature to avoid dissolving the crystals) to remove the mother liquor and impurities adhering to the surface. The washed crystals were then placed in a vacuum drying oven (60℃, 0.09 MPa) and dried for 4 hours until the crystal mass was constant. The dried crystals were analyzed using X-ray diffraction to determine the purity of NaCl and Na2SO4. The total mass of the crystals was weighed using an electronic balance, and the recovery rate of the target salt was calculated.

[0055] 5. Stability of seed crystal properties After the experiment, the fine seed crystals separated in group 2 were collected, and after being treated with acid washing (1.5% hydrochloric acid spray), ultrasonic dispersion (40kHz, 8min), and photothermal activation (simulated sunlight irradiation for 4min), they were put back into the crystallization experiment under the same conditions (repeated 3 times). The crystallization rate was measured, and the stability of the seed crystals was evaluated based on the change in the crystallization rate.

[0056] III. Test Results (a) Crystallization rate and particle size variation The statistical results of the crystallization rate and average crystal size of the target salt in the four groups of experiments are shown in Table 1 below: Table 1. Crystallization rate and average particle size

[0057] As shown in the table above, in terms of crystallization rate, the NaCl crystallization rate of group 2 is significantly higher than that of other groups, followed by groups 1, 4, and 3. Although the crystallization rate of group 4 is higher than that of group 3, it is significantly lower than that of group 2. This proves that the core-shell-functional layer structure of the photothermal responsive composite seed crystal of the present invention can greatly improve the crystallization kinetic efficiency, while the crystallization rate of traditional single seed crystals is significantly limited due to the lack of ion screening and temperature-sensitive dual response capabilities.

[0058] Regarding the average crystal size: after 8 hours of crystallization, the average crystal size of NaCl and Na2SO4 in Group 2 was the largest, while the average crystal size of Group 4 (single seed control group) was only 70~80μm and 65~75μm, respectively. The crystal size of Group 3 was the smallest, further verifying the guiding effect of the composite seed on the directional growth of crystals in this invention.

[0059] Regarding crystal precipitation time: Group 2 showed obvious crystal precipitation within 30 minutes after the start of the experiment, which was 64.7% shorter than Group 4 (85 min), 50% shorter than Group 1 (60 min), and 75% shorter than Group 3 (120 min). This proves that the composite seed crystal can quickly form a local supersaturated environment through the photothermal conversion of the surface functional layer, which greatly shortens the induced crystallization time. In contrast, traditional single seed crystals rely on the overall supersaturation of the solution, which significantly prolongs the induction period.

[0060] (ii) Crystal purity and recovery rate The purity of the crystallized product and the recovery rate of the target salt are shown in Table 2 below: Table 2. Crystal Purity and Recovery Rate

[0061] As shown in the table above, Group 2 has the highest crystal purity and recovery rate. Although the crystal purity of Group 4 is higher than that of Group 3, it is lower than that of Group 2. Furthermore, traditional single-seed crystals cannot screen for impurity ions (such as SO42-). 2- Ca 2+The purity of Group 4 is low because some impurities are embedded in the crystal lattice. The recovery rate of Group 4 is only 79.5-80.2% of that of Group 2, mainly because traditional seed crystals are easily encapsulated and deactivated by impurities, and cannot continuously guide crystal growth. The crystal purity and recovery rate of Group 1 are slightly lower than those of Group 2, mainly because the preset temperature (25-30℃) is lower than the critical dissolution temperature of the surface functional layer (32-34℃), resulting in insufficient shrinkage of the functional layer and incomplete exposure of the intermediate screening channels, leading to the incorporation of some impurities. However, it is still higher than that of Group 3, proving that even under non-optimal thermal control conditions, the composite seed crystal of this invention is still superior to the seedless system. The crystal purity of Group 3 is the lowest because the lack of seed guidance makes it easy for impurity ions to be incorporated into the crystal lattice during spontaneous nucleation, and the recovery rate is only about 70% of that of Group 2.

[0062] (III) Seed stability After three regeneration cycles, the NaCl crystallization rate of group 2 decreased from 0.88 μm / h to 0.79 μm / h, a decrease of 10.2%; the Na2SO4 crystallization rate decreased from 0.78 μm / h to 0.71 μm / h, a decrease of 8.9%, with relatively small performance degradation.

[0063] IV. Experimental Conclusions The synergistic effect of photothermal responsive composite seed crystals with thermal control and stirring parameters can significantly improve the crystallization performance of target salts in high-salt solutions: compared with the blank control group without seed crystals (group 3), the groups with added seed crystals showed improvements in crystallization rate, average crystal particle size, product purity and recovery rate, with group 2 showing the best effect.

[0064] Determine the optimal thermal control and stirring parameters: When the preset temperature is 30~35℃, the functional layer on the surface of the seed crystal can quickly reach the critical dissolution temperature and shrink, exposing the screening channels of the intermediate shell layer. At the same time, a local supersaturated environment is formed through photothermal conversion, which accelerates the directional growth of target ions in the seed crystal core. The stirring frequency of 2~3Hz can ensure that ions in the solution diffuse evenly to the surface of the seed crystal, promoting crystallization.

[0065] Verification of the stability and practicality of the composite seed crystals: After recycling, they still maintain good crystallization guidance ability and can achieve efficient directional crystallization in a single crystallizer, which can be used for large-scale treatment of industrial high-salt wastewater.

[0066] Example 3 This embodiment describes the practical application of the method of the present invention in the recovery of salt resources from pharmaceutical wastewater.

[0067] I. Experimental Objective The study aims to verify the practical application effect of the composite seed crystals in the recovery of salt resources from pharmaceutical wastewater (mainly containing NH4Cl and Na2CO3), clarify the applicability of this method to wastewater in specific industries, and verify the ability of photothermal responsive composite seed crystals to guide the directional crystallization of NH4Cl and Na2CO3.

[0068] II. Test Methods (I) Wastewater Sources and Water Quality Analysis The pharmaceutical wastewater used in the experiment was taken from the equalization tank of the wastewater treatment plant of an antibiotic manufacturing company. This wastewater originates from processes such as acid-base neutralization and solvent recovery during drug synthesis, and mainly contains NH4Cl, Na2CO3, and a small amount of residual drug intermediates (organic matter). The water quality indicators of this pharmaceutical wastewater were as follows: NH4Cl content 16.8 g / L, Na2CO3 content 8.6 g / L, chemical oxygen demand (COD) 610 mg / L, pH 8.0~8.5.

[0069] (II) Test Materials and Equipment 1. Seed materials Including two types, NH4Cl and Na2CO3, the preparation method is the same as in Example 1, both of which have a three-layer structure of "core-shell-functional layer": NH4Cl type composite seed crystals: The core consists of high-purity NH4Cl single crystal particles (particle size 70~90μm, purity ≥99.9%) isomorphous with NH4Cl; the middle shell is modified mesoporous SiO2 (thickness 7~9μm, pore size 0.3~0.4nm), used for screening NH4. + Cl - It also blocks organic matter and impurity ions; the surface functional layer is a graphene oxide-polyN-isopropylacrylamide composite coating (thickness 2~3μm, photothermal conversion efficiency 87.2%).

[0070] Na2CO3 type composite seed crystal: The core is a high-purity Na2CO3 single crystal particle with the same crystal form as Na2CO3 (particle size 80~100μm, purity ≥99.9%); the middle shell is MXenes nanomaterial (thickness 8~10μm, pore size 0.4~0.5nm); the surface functional layer is the same as NH4Cl type seed crystal (thickness 2~3μm, photothermal conversion efficiency 86.8%).

[0071] 2. Test equipment Pretreatment equipment: Same as in Example 2; Crystallization equipment: 2 single crystallizers of the same specifications (effective volume 10L, material 316L stainless steel). Heat control device and stirring device: same as in Example 2; Separation and detection equipment: centrifuge, vacuum drying oven, ion chromatograph, X-ray diffractometer.

[0072] (III) Test Procedure 1. Pharmaceutical wastewater pretreatment 50L of pharmaceutical wastewater was injected into a coagulation reaction tank, and filtered through a 0.45μm filter membrane using PAC coagulation sedimentation to obtain pretreated pharmaceutical wastewater. The specific method is described in Example 2.

[0073] 2. Seed crystal placement and staged crystallization First stage (NH4Cl crystallization): 20L of pretreated wastewater was injected into the first single crystallizer, and NH4Cl photothermal responsive composite seed crystals were added at a rate of 3.5% of the wastewater mass (i.e., 700g). The thermal control device was activated, and the preset temperature was set to 33℃ (matching the critical dissolution temperature of the functional layer on the seed crystal surface), maintaining a constant temperature inside the crystallizer. The pulse flow field stirrer was activated, with a frequency of 2~3Hz, alternating between 30s of stirring and 30s of settling to ensure a homogeneous solution and sufficient contact between the seed crystals and ions. Crystallization continued for 8 hours, with samples taken every hour during this period to monitor the NH4 content of the wastewater using an ion chromatograph. + Cl - Record the crystallization rate of NH4Cl by varying the concentration.

[0074] Second stage (Na2CO3 crystallization): After the first stage of crystallization is completed, the mother liquor (mainly containing Na2CO3) in the first crystallizer is transferred to the second single crystallizer. Na2CO3-type photothermal responsive composite seed crystals are added to the second crystallizer at a rate of 3% (600g) of the mother liquor mass. The thermal control device is activated, and the preset temperature is set to 32-34℃. The frequency of the pulse flow stirrer is adjusted to 2-3Hz, and crystallization continues for 8 hours. Samples are taken every hour during this period, and the Na2CO3 content is monitored using an ion chromatograph. + CO3 2- Record the concentration changes and the crystallization rate of Na2CO3.

[0075] 3. Crystal separation, washing and drying Solid-liquid separation: After the crystallization of each stage is completed, the heat control device and the stirrer are turned off, and the crystal-mother liquor mixture in the crystallizer is transferred to a centrifuge and centrifuged at 4500 r / min for 10 min to separate the crystals from the mother liquor. The wet NH4Cl crystals, wet Na2CO3 crystals and the final mother liquor are collected separately.

[0076] Crystal washing: Wash NH4Cl wet crystals and Na2CO3 wet crystals three times with a small amount of deionized water (at the same temperature as the corresponding crystallization temperature to avoid crystal dissolution) to remove the mother liquor and trace impurities adhering to the crystal surface.

[0077] Drying and Detection: The washed NH4Cl crystals and Na2CO3 crystals were placed in a vacuum drying oven for vacuum drying under the same conditions as in Example 2. The crystal purity of the dried crystals was detected using an X-ray diffractometer, the mass of the crystals was weighed using an electronic balance, and the recovery rates of NH4Cl and Na2CO3 were calculated.

[0078] 4. Seed stability After crystallization, the fine seed crystals separated from the first and second crystallizers were collected, and after acid washing to remove impurities, ultrasonic dispersion, and photothermal activation, they were put back into the same pharmaceutical wastewater crystallization test under the same conditions (repeated 3 times). The stability of the seed crystals was evaluated by the change in crystallization rate.

[0079] III. Test Results (a) Crystallization rate and stability The initial crystallization rate of NH4Cl was 0.7 μm / h, and after 3 cycles, the crystallization rate was 0.6 μm / h, which is 85.7% of the initial value; the initial crystallization rate of Na2CO3 was 0.8 μm / h, and after 3 cycles, the crystallization rate was 0.7 μm / h, which is 87.5% of the initial value. This demonstrates that the photothermal responsive composite seed crystals have good cycle stability in pharmaceutical wastewater treatment.

[0080] (ii) Crystal purity X-ray diffraction analysis showed that the characteristic diffraction peaks of the recovered NH4Cl crystals completely matched the NH4Cl standard card, with no impurity peaks and a purity of 98.6%; the characteristic diffraction peaks of the Na2CO3 crystals were consistent with the Na2CO3 standard card, and the purity was 98.8%.

[0081] (iii) Recovery rate The weighing results showed that 306g of NH4Cl crystals were recovered from 20L of pretreated wastewater. Based on the initial NH4Cl content of the wastewater (336g), the NH4Cl recovery rate was 91.07%. 155g of Na2CO3 crystals were recovered (initial content 172g), with a recovery rate of 90.11%, achieving efficient recovery of the main salt resources in pharmaceutical wastewater.

[0082] IV. Experimental Conclusions The method of this invention is applicable to the recovery of salt resources from pharmaceutical wastewater (containing NH4Cl and Na2CO3): by introducing NH4Cl and Na2CO3 photothermal responsive composite crystals in stages, and with appropriate heat control and stirring parameters, the two salts can be separated by directional crystallization, and the recovered salt has high purity, which solves the problems of incomplete salt separation and low product purity in traditional methods.

[0083] Example 4 This embodiment describes the application of the method of the present invention in the crystallization treatment of high-salt wastewater (containing NaCl, Na2SO4, and CaSO4) from coal chemical industry.

[0084] I. Experimental Objective The study aims to verify the practical application effect of the composite seed crystals in the fractional crystallization of high-salt wastewater (mainly containing NaCl, Na2SO4, and CaSO4) from coal chemical industry, clarify the applicability of this method to multi-component high-salt wastewater containing trace amounts of organic matter, and verify the ability of different types of photothermal responsive composite seed crystals to guide the directional crystallization of corresponding target salts.

[0085] II. Test Methods (I) Wastewater Sources and Water Quality Analysis The high-salt wastewater from the coal chemical industry used in the experiment was taken from the wastewater pond before evaporation and crystallization of a coal-to-methanol enterprise. This wastewater originates from the coal gasification, methanol synthesis, and advanced wastewater treatment processes, and mainly contains NaCl, Na₂SO₄, and CaSO₄, as well as small amounts of phenolic organic matter and suspended impurities. The water quality indicators of this wastewater were as follows: NaCl concentration 21 g / L, Na₂SO₄ concentration 11 g / L, CaSO₄ concentration 3 g / L, pH 7.3.

[0086] (II) Test Materials and Equipment 1. Seed materials Customized photothermal responsive composite seed crystals are used, categorized into three types: NaCl, Na2SO4, and CaSO4, all of which have a three-layer structure of "core-shell-functional layer". NaCl type composite seed crystals: prepared using the method in Example 1.

[0087] Na2SO4 type composite seed crystals: prepared using the method in Example 1, with basic parameters shown in Example 2.

[0088] CaSO4 type composite seed crystal: The core is a high-purity CaSO4 single crystal particle (particle size 50~70μm, purity ≥99.9%) with the same crystal form as CaSO4; the middle shell is modified mesoporous SiO2 (thickness 5~7μm, pore size 0.2~0.3nm); the surface functional layer is the same as that of NaCl type seed crystal, and it is prepared by the method of Example 1, with a photothermal conversion efficiency of 85.8%.

[0089] 2. Test equipment The pretreatment equipment, crystallization equipment, separation and detection equipment are the same as those in the previous embodiments; the ultrafiltration device (the membrane material is polyvinylidene fluoride, and the membrane pore size is 0.05μm).

[0090] (III) Test Procedure 1. Pretreatment of high-salinity wastewater from coal chemical industry Pre-sedimentation and coagulation: 50L of high-salt coal chemical wastewater is injected into a coagulation reactor. First, 0.15~0.2g / L of CaSO4 seed crystals are added. Stirring is then started (100~150r / min) for 30 minutes to promote the partial precipitation of Ca in the wastewater. 2+Pre-precipitate as CaSO4; then add 100 mg / L polyaluminum chloride (PAC), adjust the stirring speed to 200 r / min and stir for 5 min, then add 5 mg / L anionic polyacrylamide (PAM, molecular weight 800~1200 million), stir slowly at 100 r / min for 3 min to promote the growth of suspended solids, colloids and phenolic organic matter flocs; turn off the stirring and let stand for 35~45 min to allow the precipitate and flocs to settle fully.

[0091] Filtration: A plate and frame filter press is used to filter the coagulated wastewater, removing settled CaSO4 precipitates and flocs to obtain primary filtrate. This primary filtrate is then passed through an ultrafiltration unit (pressure 0.1~0.15MPa) to further remove residual fine particles and large organic molecules, ensuring that the pretreated wastewater has SS ≤ 10mg / L, COD ≤ 100mg / L, and CaSO4 ≤ 10mg / L. 2+ The concentration was reduced to 40-50 mg / L to avoid impurities interfering with the subsequent fractional crystallization process; the pretreated wastewater was collected for later use.

[0092] 2. Seed crystal placement and staged, fractional crystallization First stage (NaCl crystallization): 30L of pretreated wastewater was injected into the first single crystallizer, and NaCl-type photothermal responsive composite seed crystals were added at a rate of 4% (1200g) of the wastewater mass. The thermal control device was activated, and the preset temperature was set to 33℃ to maintain a constant temperature within the crystallizer. The pulse flow stirrer was activated, with a frequency of 2-3Hz, alternating between 30s of stirring and 30s of settling to ensure a homogeneous solution and sufficient contact between the seed crystals and ions. Crystallization continued for 8 hours, with samples taken every hour during this period to monitor the NaCl content in the wastewater using an ion chromatograph. + Cl - Record the NaCl crystallization rate by observing the concentration changes.

[0093] Second stage (Na2SO4 crystallization): After the first stage of crystallization is completed, the mother liquor (mainly containing Na2SO4 and a small amount of CaSO4) in the first crystallizer is transferred to the second single crystallizer. Na2SO4 photothermal responsive composite seed crystals are added to the second crystallizer at a rate of 3% (900g) of the mother liquor mass. The thermal control device is activated, and the preset temperature is set to 31℃. The frequency of the pulse flow stirrer is adjusted to 2~3Hz, and crystallization continues for 8 hours. Samples are taken every hour during this period, and the Na2SO4 content is monitored using an ion chromatograph. + SO4 2- Record the Na2SO4 crystallization rate by measuring the concentration changes.

[0094] The third stage (CaSO4 crystallization): After the second stage of crystallization is completed, the mother liquor (mainly containing CaSO4) in the second crystallizer is transferred to the third single crystallizer. CaSO4-type photothermal responsive composite seed crystals are added to this third crystallizer at a rate of 3% of the mother liquor mass (approximately 900g). The thermal control device is activated, and the preset temperature is set to 30℃. The frequency of the pulse flow stirrer is adjusted to 2-3Hz, and crystallization continues for 8 hours. Samples are taken every hour during this period, and the CaSO4 content is monitored using an ion chromatograph. 2+ SO4 2- Record the concentration changes and the crystallization rate of CaSO4.

[0095] 3. Crystal separation, washing and drying Solid-liquid separation: After the crystallization of each stage is completed, the heat control device and the stirrer are turned off, and the crystal-mother liquor mixture in the crystallizer is transferred to a centrifuge and centrifuged at 4500 r / min for 10 min to separate the crystals from the mother liquor. The wet NaCl crystals, wet Na2SO4 crystals, wet CaSO4 crystals and the final mother liquor are collected respectively.

[0096] Crystal washing: Wash the three types of wet crystals separately with a small amount of deionized water (at the same temperature as the corresponding crystallization temperature to avoid dissolving the crystals). The volume ratio of washing solution to crystals is 2:1. Stir gently for 15-20 minutes and then centrifuge again. Repeat the washing process 3 times to remove the mother liquor and trace impurities attached to the crystal surface.

[0097] Drying and testing: The three types of crystals after washing were placed in a vacuum drying oven and dried at 60℃ and 0.09MPa for 4 hours until the crystal mass was constant. The purity of the dried crystals was detected by X-ray diffraction, the crystal mass was weighed by electronic balance, and the recovery rates of NaCl, Na2SO4 and CaSO4 were calculated.

[0098] 4. Seed stability test After crystallization, the fine seed crystals separated from the three crystallizers were collected, and after acid washing to remove impurities, ultrasonic dispersion, and photothermal activation treatment, they were put back into the crystallization test of coal chemical wastewater under the same conditions (repeated 3 times). The stability of the seed crystals was evaluated by the change in crystallization rate.

[0099] III. Test Results (a) Crystallization rate and stability The crystallization rates of NaCl, Na₂SO₄, and CaSO₄ were 0.7 μm / h, 0.73 μm / h, and 0.81 μm / h, respectively. After three cycles of seed crystal recycling, the crystallization rates of NaCl, Na₂SO₄, and CaSO₄ were 0.61 μm / h (87.1% of the initial values), NaCl, Na₂SO₄, and CaSO₄, respectively (82.2% of the initial values), and CaSO₄, respectively (82.7% of the initial values). This demonstrates that the composite seed crystals exhibit excellent cyclic stability in multi-component high-salt environments.

[0100] (ii) Crystal purity X-ray diffraction analysis showed that the characteristic diffraction peaks of the recovered NaCl crystals completely matched the NaCl standard card, with no impurity peaks and a purity of 99.7%; the characteristic diffraction peaks of the Na2SO4 crystals were consistent with the Na2SO4 standard card, with a purity of 99.4%; and the characteristic diffraction peaks of the CaSO4 crystals were consistent with the CaSO4 standard card, with a purity of 99.6%.

[0101] (iii) Recovery rate The weighing results showed that 592g of NaCl crystals (total content 630g) were recovered from 30L of pretreated wastewater, with a NaCl recovery rate of 93.9% based on the initial NaCl content of the wastewater; 311g of Na2SO4 crystals (total content 330g) were recovered, with a Na2SO4 recovery rate of 94.2%; and 86g of CaSO4 crystals (total content 90g) were recovered, with a CaSO4 recovery rate of 95.5%. This achieved efficient fractional recovery of the three main salt resources in coal chemical wastewater.

[0102] IV. Experimental Conclusions The method of this invention is applicable to the fractional crystallization treatment of high-salt wastewater (containing NaCl, Na2SO4, and CaSO4) from coal chemical industry: by introducing three types of suitable photothermal responsive composite crystal seeds in stages, and matching the thermal control parameters and stirring frequency with the critical dissolution temperature of the crystal seeds, the directional separation of multi-component salts can be achieved, solving the problems of mixed crystals and low purity of multi-component salts in traditional methods.

[0103] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for promoting crystallization of high-salt solutions based on seed crystal method, characterized in that, Includes the following steps: 1) Pre-treat high-salinity wastewater to remove suspended solids and colloidal impurities; 2) Add photothermal responsive composite seed crystals corresponding to the target salt into the crystallizer. The photothermal responsive composite seed crystals have a three-layer structure of core-shell-functional layer. The core is a high-purity single crystal particle with the same crystal form as the target salt. The middle shell layer is a porous salt-resistant screening layer. The surface functional layer is a photothermal-thermal dual-response composite coating. 3) Start the thermal control device and stirring device to maintain the preset temperature in the crystallizer. A local supersaturated environment is formed through photothermal conversion, and the target ions are directionally grown in the seed core after being screened by the intermediate shell. 4) Separate the generated crystals from the mother liquor; 5) The separated fine seed crystals are sent to the regeneration module for processing and then returned to the crystallizer for recycling.

2. The method according to claim 1, characterized in that, During pretreatment, polyaluminum chloride is used as a flocculant, with an addition amount of 80~120 mg / L.

3. The method according to claim 1, characterized in that, The amount of photothermal responsive composite seed crystals added is 2-5% of the solution mass.

4. The method according to claim 1, characterized in that, The preset temperature is 25~35℃.

5. The method according to claim 1, characterized in that, The stirring device is a pulse flow field stirrer with a frequency of 1~3Hz.

6. The method according to claim 1, characterized in that, The regeneration module's processing includes: acid rinsing to remove impurities, ultrasonic dispersion, and photothermal activation. The acid rinsing to remove impurities uses hydrochloric acid with a mass fraction of 1-2%, the ultrasonic dispersion frequency is 30-50kHz, the processing time is 5-10 minutes, and the photothermal activation time is 3-5 minutes. The fine seed crystals processed by the regeneration module are returned to the crystallizer for recycling.

7. A photothermal responsive composite seed crystal, characterized in that, It includes a kernel, an intermediate shell, and a surface functional layer; The core is a high-purity single-crystal particle with the same crystal structure as the target salt and a particle size of 50~100μm; The intermediate shell is a porous salt-resistant screening layer covering the core, with a thickness of 5~10μm, and is made of modified mesoporous SiO2 or MXenes nanomaterials with a pore size of 0.2~0.5nm. The surface functional layer is a photothermal-thermal dual-response composite coating grafted onto the outer layer of the intermediate shell, with a thickness of 2~3μm and a critical dissolution temperature of 30~35℃, and is composed of graphene oxide and poly(N-isopropylacrylamide).

8. The photothermal responsive composite seed crystal according to claim 7, characterized in that, The photothermal conversion efficiency of the surface functional layer is ≥85%.

9. The photothermal responsive composite seed crystal according to claim 7, characterized in that, The purity of the kernel is ≥99.9%.

10. The photothermal responsive composite seed crystal according to claim 7, characterized in that, The intermediate shell layer uses modified mesoporous SiO2 with a specific surface area of ​​800~1000 m². 2 / g.

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