Inferior brine refining preparation method based on oxidation adsorption coupling

Abstract

The invention relates to the technical field of brine sewage treatment, and discloses an inferior brine refining preparation method based on oxidation-adsorption coupling, which comprises the following steps: adding an efficient CuO / Al2O3 catalyst according to 0.5-1.5% of the volume of brine under the accurate control of the pH value of 2.5-3.0, and adding sodium chlorite according to the molar ratio of 3: 1-5: 1 to realize the specific deep oxidation of I <->; and carrying out targeted enrichment on the generated I2 by using a high-capacity adsorbent. According to the combined process, the iodine concentration of effluent is stably lower than 0.1 mg / L, and the catalyst can be recycled for more than or equal to 50 times. Comparison data proves that the iodine residue is up to 0.85 mg / L when no catalyst exists, and iodine removal is not thorough due to the fact that the oxidizing agent is insufficient. According to the efficient iodine removal method, the deposition of iodine in the ionic membrane electrolytic bath is fundamentally avoided, the expensive ionic membrane is effectively protected, the service life of the ionic membrane is prolonged by more than 30%, the energy consumption of the system is reduced by about 15%, and the brine recycling efficiency and the economic benefit are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of brine wastewater treatment technology, and in particular to a method for refining and preparing inferior brine based on oxidation-adsorption coupling. Background Technology

[0002] Low-quality saline wastewater refers to industrial wastewater or by-product salt solutions produced by industries such as chemical and coking, containing high levels of salt, iodine, and other impurities. In addition to high concentrations of sodium chloride, this type of wastewater is typically rich in harmful impurities such as iodide ions, calcium, magnesium, and sulfate, as well as organic matter and heavy metals. Its complex composition poses a serious obstacle to subsequent treatment and resource recovery, placing it within the category of difficult-to-treat high-salinity industrial wastewater.

[0003] Existing technologies typically employ a multi-stage processing flow: first, inferior salt is dissolved, and calcium and magnesium ions are removed by chemical precipitation using alkali (NaOH) and sodium carbonate (Na2CO3); then, suspended impurities are separated using a membrane filter; subsequently, residual heavy metals are deeply purified using ion exchange resin; some processes also use oxidants combined with activated carbon adsorption to remove organic matter and some iodine, ultimately obtaining refined brine that can be used for ion membrane electrolysis.

[0004] Two problems exist with existing technology: Existing treatment methods are not very effective against iodide ions. Residual iodine is prone to deposit during electrolysis, which can clog the ion exchange membrane, leading to increased energy consumption, shortened membrane life, and seriously affecting the efficiency of resource recovery and reuse after wastewater treatment.

[0005] Existing processes are unable to efficiently separate mixed salts (such as sodium chloride and sodium sulfate) in wastewater, resulting in low purity and limited recovery value of the crystallized products. This not only wastes resources but also increases the cost and environmental burden of subsequent wastewater treatment. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the existing technology has the disadvantages of incomplete iodine removal and difficulty in separating and recycling miscellaneous salts. To this end, we propose a method for refining and preparing inferior brine based on oxidation-adsorption coupling.

[0007] To achieve the above objectives, this application adopts the following technical solution: a method for purifying and preparing inferior brine based on oxidation-adsorption coupling, comprising the following steps: S1: Dissolve inferior raw salt at 55-65℃ to obtain homogeneous brine with a concentration of 280-310g / L. Add excess liquid alkali and sodium carbonate solution successively, and react at 50℃ to remove magnesium and calcium ions. After the reaction, the brine is filtered through a membrane to achieve solid-liquid separation and obtain refined brine. S2: Adjust the pH of the refined brine to 2.5-3.0, add a heterogeneous catalyst, add an oxidant at a redox potential of 200-300mV, and react at 40-50℃ to oxidize iodide ions. After oxidation, the effluent is fed into an adsorption tower for targeted adsorption and enrichment. After adsorption saturation, it is regenerated with sodium hydroxide solution. S3: Continuously inject seed slurry at a rate of 0.5-1.0% of the feed flow rate into the concentrate side of the nanofiltration system, and perform separation under an operating pressure of 2.5-3.0 MPa. The nanofiltration permeate is a sodium chloride solution, and the nanofiltration concentrate enters the crystallizer for programmed cooling and crystallization to obtain high-purity sodium sulfate product. S4: The nanofiltration permeate is deeply purified by an integrated resin tower, and the pH is adjusted to 9-11 to obtain ultrapure brine that meets the requirements of ion-exchange membrane electrolysis.

[0008] Furthermore, S1 specifically includes the following steps: S11: Inferior raw salt is put into a salt dissolving tank at 55-65℃ and circulated by mechanical stirring at a speed of 60-80rpm to accelerate the dissolution of salt blocks and maintain the brine concentration at 280-310g / L to form a homogeneous raw material solution. S12: Add industrial-grade 32% liquid alkali at an excess of 0.2-0.6 g / L to the front baffle tank, and react with Mg. 2+ The reaction instantly produces magnesium hydroxide flocs. Industrial-grade sodium carbonate solution is added to the coarse brine tank at an excess of 0.3-0.6 g / L, and the reaction is continuously stirred at 50°C for no less than 30 minutes. S13: After the reaction, the brine flows by gravity into the Kai membrane filter, where solid-liquid separation is carried out under the condition that the inlet pressure difference is less than 0.05MPa. The refined brine enters the subsequent process, while the filter residue is automatically backflushed into the salt mud treatment system for pressure filtration and resource utilization.

[0009] Furthermore, S2 specifically includes the following steps: S21: The clear liquid is introduced into a fixed-bed corrosion-resistant catalytic reactor, and the pH value of the system is precisely controlled within the optimal weakly acidic range of 2.5-3.0 by adding hydrochloric acid; S22: Under the above pH conditions, a heterogeneous catalyst was added, and real-time monitoring was performed using an ORP meter. The catalyst was added at a sodium chlorite to iodine molar ratio of 3-5:1, and the reaction was carried out at 40-50℃ for 25-40 minutes. I was then converted through specific oxidation. - Deep oxidation to I2; S23: After oxidation, the effluent flows into the packed adsorption tower, and the empty tower flow rate is controlled at 2-4 BV / h. The iodine is targeted for adsorption using the modification material.

[0010] Furthermore, in step S21, sodium chlorite is added at a molar ratio of 4:1 to the initial iodine.

[0011] Furthermore, S2 also includes: S24: In-situ regeneration using a 5-8% warm sodium hydroxide solution restores the adsorbent's activity and enables its recycling.

[0012] Furthermore, a heterogeneous catalyst is added to S22 at 0.5%–1.5% of the brine volume.

[0013] Furthermore, S3 specifically includes the following steps: S31: First, prepare seed crystals. Using a nanofiltration membrane system, continuously inject seed crystal slurry into the concentrate side through a precision metering pump at 0.5-1.0% of the nanofiltration feed flow rate. S32: Nanofiltration separation is carried out under operating pressure of 2.5-3.0 MPa and temperature of 25-30℃, combined with particle pretreatment; S33: The nanofiltration concentrate rich in seed crystals enters the Oslo-type crystallization tank. A heat pump system is added to recover waste heat for preheating the brine pool. The temperature is programmed to decrease to 5℃ at a rate of 0.5℃ / h, while maintaining a stirring speed of 40rpm.

[0014] Furthermore, in step S32, seed slurry is continuously injected at 1% of the nanofiltration feed flow rate.

[0015] Furthermore, in step S31, the preparation of seed crystals specifically involves preparing anhydrous sodium sulfate or calcium sulfate microcrystals with a particle size distribution of 10-30 μm in a seed crystal preparation tank by controlling the cooling rate, and preparing a seed crystal slurry with a solid content of 5-10% for later use.

[0016] Furthermore, S4 specifically includes the following steps: S41: Heat the post-membrane brine to 60°C and pass it through the integrated resin tower in a fixed-bed mode to reduce Ca2+. 2+ Mg 2+ content; S42: The regeneration process is carried out by acid washing and alkali washing in sequence with 5% hydrochloric acid solution and 4% sodium hydroxide solution. The amount of regenerator is 2-3 times the theoretical amount. The generated acidic and alkaline regeneration wastewater is collected and sent to the neutralization tank for treatment, and then returned to the salt tank for reuse. S43: The pH of the purified secondary brine is adjusted to 9-11, and its redox potential is detected to finally produce ultrapure brine that meets the requirements of ion-exchange membrane electrolysis.

[0017] The technical effects and advantages of this invention are as follows: In this invention, under precise pH control of 2.5-3.0, a highly efficient CuO / Al2O3 catalyst is added at 0.5-1.5% of the brine volume, and sodium chlorite is added at a molar ratio of 3:1 to 5:1 to achieve the desired effect on I... -The process involves specific deep oxidation followed by targeted enrichment of the generated I₂ using a high-capacity adsorbent. This combined process ensures a stable iodine concentration in the effluent below 0.1 mg / L, and the catalyst can be recycled ≥50 times. Comparative data shows that without a catalyst, iodine residue reaches as high as 0.85 mg / L, while insufficient oxidant leads to incomplete iodine removal. This highly efficient iodine removal fundamentally avoids iodine deposition in the ion-exchange membrane electrolyzer, effectively protecting the expensive ion-exchange membrane and extending its lifespan by more than 30%. It also reduces system energy consumption by approximately 15%, significantly improving brine reuse efficiency and economic benefits.

[0018] In this invention, specially formulated sodium sulfate microcrystalline seed crystals are continuously injected into the concentrate side of the nanofiltration system at a rate of 0.5-1.0% of the feed flow. These seed crystals preferentially induce the precipitation of supersaturated salts such as calcium sulfate and sodium sulfate on the membrane surface, rather than causing scaling. This reduces the nanofiltration membrane fouling rate by more than 40% and extends the system's stable operating cycle to 168 hours, more than four times that of seedless systems. During subsequent crystallization, the seed crystals continue to exert an inducing effect, increasing the sodium sulfate crystallization efficiency to over 90% and yielding high-quality sodium sulfate product with a purity ≥99.2%. This transforms traditionally considered waste salt residue into a commercially valuable byproduct, achieving clean separation and resource utilization of sodium chloride and sodium sulfate. It reduces solid waste generation and disposal costs at the source, turning waste into treasure, resulting in significant environmental and economic benefits. Attached Figure Description

[0019] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a flowchart of the overall method of the present invention. Detailed Implementation

[0020] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0021] Reference Figure 1 As shown, the present invention provides a technical solution: a method for purifying and preparing inferior brine based on oxidation-adsorption coupling, comprising the following steps: Step 1: Pretreatment and Chemical Purification Thermal enhanced dissolution: Inferior raw salt is put into a salt dissolution tank at 55-65℃ and circulated by mechanical stirring at a speed of 60-80 rpm to accelerate the dissolution of salt blocks and maintain the brine concentration at 280-310 g / L, forming a homogeneous raw material solution.

[0022] Two-stage precision sedimentation: Industrial-grade 32% liquid alkali is added to the pre-baffle tank at an excess of 0.2-0.6 g / L, along with Mg... 2+ The reaction instantly produces magnesium hydroxide flocs; industrial-grade sodium carbonate solution is added to the coarse brine tank at an excess of 0.3-0.6 g / L, and the reaction is continuously stirred at 50±5℃ for no less than 30 minutes to ensure complete precipitation of calcium carbonate.

[0023] Precision membrane filtration: After the reaction, the brine flows into the Kai membrane filter by gravity. Solid-liquid separation is carried out under the condition that the inlet pressure difference is less than 0.05MPa. The refined brine enters the subsequent process, while the filter residue is automatically backwashed into the salt mud treatment system for pressure filtration and resource utilization. The main components of the filter residue are magnesium hydroxide, calcium carbonate and insoluble matter.

[0024] Step 2: Catalytic oxidation and targeted adsorption for iodine removal Catalytic environment setup: The clarified liquid is introduced into a fixed-bed corrosion-resistant catalytic reactor, and the pH value of the system is precisely controlled within the optimal weakly acidic range of 2.5-3.0 by adding hydrochloric acid. During this process, real-time monitoring and feedback control are performed using an online pH meter.

[0025] Heterogeneous catalytic oxidation: Under the above pH conditions, a heterogeneous catalyst (calculated as CuO, with the loading increased to 8% wt Al2O3 supported type) was added at 0.5-1.5% of the brine volume, and the ORP value was maintained at 200-300 mV by real-time monitoring with an ORP meter. Sodium chlorite (NaClO2) was added at a molar ratio of 3-5:1 to the initial iodine. The reaction was carried out at 40-50℃ for 25-40 minutes, and I was oxidized through specific oxidation. - Deep oxidation to I2, catalyst can be recycled ≥50 times.

[0026] Targeted adsorption and enrichment: After oxidation, the effluent flows into the packed adsorption tower. The empty tower flow rate is controlled at 2-4 BV / h. Iodine is targeted for adsorption by utilizing the specific interaction of the modified materials. The iodine adsorption capacity can reach 150-200 mg / g, and the breakthrough point is significantly delayed.

[0027] In-situ regeneration of adsorbent: When adsorption is saturated, in-situ desorption and regeneration are performed using a 5-8% warm sodium hydroxide solution to restore the adsorbent activity and realize the recycling of the adsorbent. The adsorption capacity decay rate after regeneration is ≤5% / cycle.

[0028] Step 3: Membrane-coupled nucleation and salt decomposition resource utilization Seed slurry preparation: In the seed preparation tank, anhydrous sodium sulfate (Na2SO4) or calcium sulfate (CaSO4) microcrystals with a particle size distribution of 10-30μm are prepared in advance by controlling the cooling rate, and a seed slurry with a solid content of 5-10% is prepared for later use.

[0029] Film-side seed implantation: using SO4 2- For nanofiltration membrane systems with a rejection rate of ≥98%, the above-mentioned seed slurry is continuously injected into the concentrate side via a precision metering pump at 0.5-1.0% of the nanofiltration feed flow rate to ensure thorough mixing of the seed crystals and concentrate.

[0030] Anti-fouling nanofiltration concentration: Nanofiltration separation is performed under operating pressure of 2.5-3.0 MPa and temperature of 25-30℃, combined with particle pretreatment. The presence of seed crystals effectively induces the precipitation of salts such as calcium sulfate and sodium sulfate in the solution and on the seed crystal surface, effectively preventing fouling on the membrane surface, reducing the membrane fouling rate by more than 40%, and extending the stable operation cycle of the system to 1.5-2 times the original length. Nanofiltration permeate (mainly containing NaCl) is sent to subsequent processes.

[0031] Enhanced freeze crystallization: Nanofiltration concentrate rich in seed crystals enters an Oslo-type crystallization tank. A heat pump system is added to recover waste heat for preheating the salt bath, and the temperature is programmed to decrease to 5±1℃ at a rate of 0.5℃ / h, while maintaining a stirring speed of 40 rpm. Due to the inductive effect of the seed crystals, the sodium sulfate crystallization efficiency is increased to over 90%, and the obtained Glauber's salt product has a purity of ≥99.2%, with large and uniform crystal particle size. After crystallization, part of the mother liquor is recycled to the nanofiltration feed end to further improve the system recovery rate.

[0032] Step 4: Ion exchange polishing Resin bed refining: The post-membrane brine is heated to 60±5℃ and passed through an integrated resin column in a fixed-bed mode. Utilizing the resin's high selectivity for multivalent ions, Ca2+ is purified. 2+ Mg 2+ The concentration was reduced to below 20 ppb. The effluent water quality was monitored using an online trace ion analyzer.

[0033] Programmed regeneration: After the resin is saturated with adsorption, it is regenerated by sequentially acid washing with 5% hydrochloric acid solution and 4% sodium hydroxide solution, with the amount of regenerant used being 2-3 times the theoretical amount, to ensure that the resin is completely converted to the Na form. The generated acidic and alkaline regeneration wastewater is collected and sent to a neutralization tank for treatment, and then returned to the brine tank for reuse.

[0034] Final quality control: The pH of the purified secondary brine is adjusted to 9-11, and its redox potential (ORP) is monitored to ensure it is below -50mV. Heavy metals (such as Cu) are added. 2+ The system detects indicators such as free chlorine and ultimately produces ultrapure brine that meets the requirements of ion-exchange membrane electrolysis.

[0035] The key indicators of the ultrapure purified brine produced by this method are as follows: iodide ions (I... - The concentration of ions was below 0.1 mg / L, the total calcium and magnesium ions were below 50 ppb, and the sulfate (SO4) concentration was below 0.1 mg / L. 2- The concentration is less than 2.5 g / L, which fully meets the stringent requirements of "Refined Brine for Ion-Exchange Membrane Electrolysis".

[0036] Example 1: Step 1: Add the inferior raw salt to a 60℃ salt dissolving tank and circulate it at 70 rpm using mechanical stirring to accelerate the dissolution of the salt blocks and maintain the brine concentration at 290 g / L, forming a homogeneous raw material solution. In the pre-baffle tank, add an excess of 0.4 g / L of industrial-grade 32% liquid alkali, along with Mg... 2+ The reaction instantly generates magnesium hydroxide flocs. Industrial-grade sodium carbonate solution is added to the coarse brine tank at an excess of 0.45 g / L. The reaction is carried out under continuous stirring at 50°C for no less than 30 minutes. After the reaction, the brine flows by gravity into the KEM filter. Solid-liquid separation is carried out under the condition that the inlet pressure difference is less than 0.05 MPa. The refined brine enters the subsequent process, while the filter residue is automatically backflushed into the salt mud treatment system for pressure filtration and resource utilization.

[0037] Step 2: The clarified liquid is introduced into a fixed-bed corrosion-resistant catalytic reactor. The pH value of the system is precisely controlled to the optimal weakly acidic range of 2.75 by adding hydrochloric acid. Heterogeneous catalyst is added at 1% of the brine volume and monitored in real time by an ORP meter. Sodium chlorite is added at a molar ratio of 4:1 to the initial iodine. The reaction is carried out at 45°C for 33 minutes. After oxidation, the effluent flows into the packed adsorption tower. The empty tower flow rate is controlled at 2-4 BV / h. When the adsorption is saturated, in-situ regeneration is performed using a 6.5% warm sodium hydroxide solution.

[0038] Step 3: In the seed crystal preparation tank, anhydrous sodium sulfate or calcium sulfate microcrystals with a particle size distribution of 20 μm are pre-prepared by controlling the cooling rate, and a seed crystal slurry with a solid content of 7.5% is prepared for later use. SO42- is then used as the catalyst. 2- For nanofiltration membrane systems with a rejection rate of ≥98%, the above-mentioned seed slurry is continuously injected into the concentrate side via a precision metering pump at 0.75% of the nanofiltration feed flow rate. Nanofiltration separation is carried out under operating conditions of 2.75 MPa and 27.5℃. Combined with particle pretreatment, the seed-rich nanofiltration concentrate enters the Oslo-type crystallization tank. A heat pump system is added to recover waste heat for preheating the brine pool, and the temperature is programmed to decrease to 5℃ at a rate of 0.5℃ / h while maintaining a stirring speed of 40 rpm.

[0039] Step 4: Heat the post-membrane brine to 60°C and pass it through the integrated resin tower in a fixed-bed mode. After the resin adsorption is saturated, it is regenerated by acid washing with 5% hydrochloric acid solution and 4% sodium hydroxide solution in sequence. The pH of the purified secondary brine is adjusted to 10, and its redox potential is monitored to ensure that it is below -50mV. Finally, ultrapure brine that meets the requirements of ion-exchange membrane electrolysis is produced.

[0040] Example 2: Unlike Example 1, sodium chlorite was added in a 3:1 molar ratio to the initial iodine, while all other contents remained unchanged.

[0041] Example 3: Unlike Example 1, sodium chlorite was added in a molar ratio of 5:1 to the initial iodine, while all other contents remained unchanged.

[0042] Comparative Example 1: Unlike Example 1, sodium chlorite was added at a molar ratio of 2.9:1 to the initial iodine, while all other aspects remained unchanged.

[0043] Comparative Example 2: Unlike Example 1, sodium chlorite was added at a molar ratio of 5.1:1 to the initial iodine, while all other aspects remained unchanged.

[0044] Blank Example 1: Unlike Example 1, Example 2, or Example 3, no heterogeneous catalyst loaded with copper oxide was added at 1% of the brine volume; all other contents remained unchanged.

[0045] Table 1: Verification Data of Key Process Effects in the Refining of Inferior Brine

[0046] Data Interpretation: A comparison of data from Examples 2 (3:1), 1 (4:1), and 3 (5:1) shows that when the molar ratio is within the range of 3:1 to 5:1, the iodine concentration in the effluent from Step 2 consistently remains below the stringent requirement of 0.1 mg / L, achieving deep iodine removal. Simultaneously, the nanofiltration membrane fouling rate in the subsequent Step 3 is the lowest (relative value 0.6-1.0), and the purity of the Glauber's salt product is the highest (≥99.3%). This demonstrates that this molar ratio range is an effective operating window to ensure complete iodine oxidation and removal without affecting subsequent processes.

[0047] A sharp comparison between Comparative Example 1 (2.9:1) and Example 2 (3:1) reveals that even a slight deviation from the effective lower limit of oxidant dosage resulted in an excessive iodine concentration in the effluent (0.25 mg / L), leading to significant membrane fouling (relative value 1.8) and a decrease in product purity (98.5%). This clearly demonstrates that 3:1 is a critical process threshold that must be strictly maintained above.

[0048] A comparison between Comparative Example 2 (5.1:1) and Example 3 (5:1) shows that excessive oxidant is also detrimental to stable system operation. Although the iodine removal effect meets the standard, excessive oxidant may lead to side reactions and cause potential oxidative damage to the membrane material, manifested as an increase in the membrane fouling rate (relative value 1.5) compared to the example within the effective range.

[0049] A stark contrast between Blank Example 1 (without catalyst) and Example 1 (with catalyst) reveals that, at the same 4:1 molar ratio, the absence of catalyst resulted in extremely low oxidation efficiency, with iodine concentration in the effluent (0.85 mg / L) far exceeding the standard. This led to severe fouling of the subsequent membrane system (relative fouling rate 2.5) and significant deterioration in the quality of the crystallized product (purity 97.5%). This irrefutably demonstrates that the heterogeneous catalyst is the core of this highly efficient iodine removal process, playing a decisive role in the reaction rate and depth.

[0050] The correlation between effluent iodine concentration, nanofiltration membrane fouling rate, and Glauber's salt product purity across all groups demonstrates that iodine removal efficiency directly and significantly impacts operational performance and product quality. Incomplete iodine removal in the preceding stages (e.g., Control Example 1 and Blank Example 1) exacerbates nanofiltration membrane fouling and may affect the sodium sulfate crystallization process, leading to a decrease in the final Glauber's salt product purity. This reveals the crucial supporting role of preceding units in the process flow for subsequent units; deep iodine removal is a necessary prerequisite for ensuring efficient salt separation and resource utilization.

[0051] Conclusion: In the catalytic oxidation iodine removal process of inferior brine purification, precisely controlling the molar ratio of sodium chlorite to iodine within the range of 3:1 to 5:1, and adding 1% heterogeneous catalyst, is a necessary and sufficient condition for achieving deep and efficient removal of iodide ions. This optimized operation not only ensures that the effluent iodine content meets the standards, but also provides crucial protection for the stable operation of the entire process chain and the recovery of high-value products by reducing fouling of subsequent membranes and interference with the crystallization process. Any operation deviating from these core parameters will directly lead to a deterioration in iodine removal efficiency and a reduction in subsequent resource recovery efficiency.

[0052] Example 4: Unlike Example 1, the above seed slurry was continuously injected at 0.5% of the nanofiltration feed flow rate, while other contents remained unchanged.

[0053] Example 5: Unlike Example 1, the above seed slurry was continuously injected at 1% of the nanofiltration feed flow rate, while other contents remained unchanged.

[0054] Comparative Example 3: Unlike Example 1, the above seed slurry was continuously injected at 0.49% of the nanofiltration feed flow rate, while other contents remained unchanged.

[0055] Comparative Example 4: Unlike Example 1, the above seed slurry was continuously injected at 0.11% of the nanofiltration feed flow rate, while other contents remained unchanged.

[0056] Blank Example 2: Unlike Example 1, step 3 involves directly nanofiltration of the liquid obtained in step 2.

[0057] Table 2: Data on the Effect of Seed Slurry Injection Amount on Nanofiltration and Crystallization Processes

[0058] Data Interpretation: A comparison of the data from Examples 4 (0.5%), 1 (0.75%), and 5 (1.0%) shows that when the seed slurry injection volume is within the range of 0.5% to 1.0%, all key performance indicators of the system remain at excellent levels. The nanofiltration membrane fouling rate (relative value 0.6-0.8) is effectively suppressed, the system can operate stably for more than 150 hours, and the purity of the Glauber's salt product is higher than 99.3%, with a crystallization efficiency exceeding 88%. This proves that this range is the optimal window for ensuring efficient and stable operation of the process.

[0059] A stark contrast between Comparative Example 3 (0.49%) and Example 4 (0.5%) reveals that even with a difference of only 0.01% in the injection volume, system performance deteriorates significantly once the effective range of 0.5% is exceeded. The membrane fouling rate of Comparative Example 3 (1.5%) surged to nearly twice that of Example 4 (0.8), while operating time and product purity also declined substantially. This clearly demonstrates that 0.5% is a critical process threshold that must be strictly maintained above.

[0060] Data from Control Example 4 (0.11%) and Blank Example 2 (0%) show that when the seed crystal injection is severely insufficient or completely absent, the system essentially loses its ability to prevent scaling and induce crystallization. The membrane fouling rate increases dramatically (2.8 to 4.0), the operating cycle shortens to an unacceptable level (40-60 hours), the purity of the produced Glauber's salt is low (96.0-97.5%), and the resource value is significantly reduced. This, conversely, demonstrates the indispensability of seed crystal technology.

[0061] A comprehensive comparison of all examples, comparative examples, and blank example 2 reveals that the seed injection technology is the core of the high-efficiency operation of this process. It not only recovers sulfate impurities as high-purity sodium sulfate through an induced precipitation mechanism (crystallization efficiency > 88%, purity > 99.3%), but also significantly extends the stable operating cycle of the nanofiltration system from 40 hours in blank example 2 to 168 hours in optimal example 1 by preventing membrane fouling. This reduces equipment cleaning frequency and energy consumption, ensuring the feasibility of continuous production.

[0062] Conclusion: The injection rate of seed slurry is a critical operational parameter determining the success or failure of the membrane coupling nucleation and salt resource recovery steps. Precisely controlling the injection rate within the range of 0.5% to 1.0% of the nanofiltration feed flow rate is a necessary and sufficient condition for achieving long-term, anti-fouling, and stable operation of the membrane system and obtaining high-purity, high-recovery sodium sulfate byproducts. Any operation below this range will lead to increased membrane fouling and decreased product quality, thus failing to achieve the core objective of efficient resource recovery of mixed salts.

[0063] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for refining poor brine based on oxidation adsorption coupling, characterized in that, The method comprises the following steps: S1: dissolving the poor raw salt at 55-65℃ to obtain homogeneous brine with a concentration of 280-310g / L, adding excess liquid alkali and sodium carbonate solution in sequence, and removing magnesium and calcium ions by reaction at 50℃, and then performing solid-liquid separation on the reacted brine by membrane filtration to obtain refined brine; S2: adjusting the pH of the refined brine to 2.5-3.0, adding a heterogeneous catalyst, adding an oxidizing agent at an oxidation-reduction potential of 200-300mV, and oxidizing iodine ions at 40-50℃, and then passing the oxidized effluent into an adsorption tower for targeted adsorption and enrichment, and regenerating the saturated adsorbent with sodium hydroxide solution; S3: continuously injecting seed slurry accounting for 0.5-1.0% of the feed flow rate into the concentrated water side of a nanofiltration system, and performing separation under an operating pressure of 2.5-3.0MPa, wherein the nanofiltration product water is a sodium chloride solution, and the nanofiltration concentrated water enters a crystallizer for programmed cooling crystallization to obtain high-purity sodium sulfate product; S4: deeply purifying the nanofiltration product water through an integrated resin tower, adjusting the pH to 9-11, and obtaining ultrapure brine meeting the requirements of ion-exchange membrane electrolysis.

2. The method for preparing poor-quality brine according to claim 1, characterized in that: The S1 specifically comprises the following steps: S11: putting the poor raw salt into a salt dissolving tank at 55-65℃, and accelerating the dissolution of salt blocks and maintaining the salt water concentration at 280-310g / L by mechanical stirring at a rotation speed of 60-80rpm to form homogeneous raw material liquid; S12: In the front baffle, the standard industrial grade 32% liquid caustic soda is added with an excess of 0.2-0.6 g / L, and Mg 2+ The magnesium hydroxide flocculation body is generated by instantaneous reaction, and the industrial grade sodium carbonate solution is added with an excess of 0.3-0.6 g / L in the coarse salt water tank, and the reaction is continuously stirred at 50°C for not less than 30 minutes. S13: after reaction, the brine flows into a Kaimembrane filter for solid-liquid separation under the condition that the inlet pressure difference is less than 0.05MPa, the refined brine enters the subsequent process, and the filter residue is automatically back-flushed into a salt mud treatment system for pressure filtration and resource disposal.

3. The method for preparing poor-quality brine according to claim 1, characterized in that: The S2 specifically comprises the following steps: S21: introducing the clear liquid into a fixed-bed corrosion-resistant catalytic reactor, and accurately adjusting the pH value of the system to the optimal range of 2.5-3.0 weak acidity by adding hydrochloric acid; S22: Under the above pH conditions, the non-homogeneous catalyst is added and monitored in real time by ORP meter, and added in a molar ratio of sodium chlorite to initial iodine of 3-5:1, and reacted at 40-50°C for 25-40 minutes, and I - is oxidized to I2 by specific oxidation. S23: after oxidation, the effluent flows into the packed adsorption tower, the empty tower flow rate is controlled at 2-4BV / h, and the modified material is used for targeted adsorption of iodine.

4. The method for preparing poor-quality brine according to claim 3, characterized in that: In the S21, sodium chlorite and initial iodine are added in a molar ratio of 4:

1.

5. The method for preparing poor-quality brine according to claim 3, characterized in that: The S2 further comprises: S24: in-situ desorption regeneration with 5-8% warm sodium hydroxide solution to restore the activity of the adsorbent and realize the cyclic use of the adsorbent.

6. The method for preparing poor-quality brine according to claim 3, characterized in that: In the S22, the heterogeneous catalyst is added in an amount of 0.5-1.5% of the volume of the brine.

7. The method for preparing poor-quality brine according to claim 1, characterized in that: The S3 specifically comprises the following steps: S31: first preparing seed crystals, and continuously injecting seed slurry accounting for 0.5-1.0% of the nanofiltration feed flow rate into the concentrated water side of a nanofiltration membrane system through a precision metering pump; S32: performing nanofiltration separation under the conditions of an operating pressure of 2.5-3.0MPa and a temperature of 25-30℃, and combining with particle pretreatment; S33: the nanofiltration concentrated water rich in seed crystals enters an Oslo type crystallization tank, a heat pump system is additionally arranged to recover waste heat for preheating of the salt dissolving tank, the temperature is programmed to decrease to 5℃ at a rate of 0.5℃ / h, and the stirring rotation speed is maintained at 40rpm.

8. The method for preparing poor-quality brine according to claim 7, characterized in that: In the S32, seed slurry is continuously injected in an amount of 1% of the nanofiltration feed flow rate.

9. The method for preparing poor-quality brine according to claim 7, characterized in that: The seed crystal prepared in the S31 is specifically prepared in a seed crystal preparation tank by controlling the cooling rate, and a microcrystal of anhydrous sodium sulfate or calcium sulfate with a particle size distribution of 10-30 μm is prepared in advance and prepared into a seed crystal slurry with a solid content of 5-10% for standby.

10. The method for producing a poor-quality salt water according to claim 1, characterized by: The S4 specifically comprises the following steps: S41: The post membrane brine is warmed to 60°C and passed through the integrated resin tower in a fixed bed mode to reduce Ca 2+ , Mg 2+ content; S42: sequentially using 5% hydrochloric acid solution and 4% sodium hydroxide solution for acid pickling and alkali pickling regeneration, the amount of the regenerant is 2-3 times of the theoretical amount, the generated acidic and alkaline regeneration wastewater is collected and sent to a neutralization tank for treatment, and then returned to the salt dissolving tank for reuse; S43: adjusting the pH of the refined secondary brine to 9-11, and detecting the oxidation-reduction potential, finally producing ultra-pure brine meeting the requirements of ion-exchange membrane electrolysis.

Images