Method for circularly inducing crystallization, hardness removal and desalination of calcium carbonate

Abstract

The invention relates to the technical field of water treatment, and discloses a method for circularly inducing crystallization, hardness removal and desalination of calcium carbonate. Adding the seed crystal into high salt water; adding sodium hydroxide into the heavy salt water; adding sodium carbonate to generate a supersaturated solution; introducing the solution containing the calcium carbonate crystal nucleus into crystallization equipment; treating the reacted solution through solid-liquid separation equipment; further desalting the water body subjected to hardness removal by adopting a membrane separation mode; collecting and treating the formed calcium carbonate precipitate, and recovering the precipitate by adopting a separation technology; by adopting the synthesized vaterite type seed crystal, the hardness removal and desalination efficiency is remarkably improved in the cyclic induced crystallization process of calcium carbonate. Compared with the traditional non-synthetic seed crystal, the synthetic seed crystal has higher surface area and uniformity, so that the combination of calcium ions and carbonate ions can be more quickly induced to form a stable crystal nucleus, and the overall effect of the reaction is finally improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and specifically to a method for removing hardness and desalting by calcium carbonate cyclic induced crystallization. Background Technique

[0002] With the increasingly prominent problem of high-salt wastewater discharge in industries such as coal chemical industry, petrochemical industry, and iron and steel coking, the efficient removal of hardness ions has become a key link in the advanced treatment of wastewater. In the existing technology, the calcium carbonate precipitation method is widely used for removing hardness ions such as Ca 2+ and Mg 2+ due to its mild reaction conditions and simple operation. However, in specific engineering applications, this method has many bottlenecks.

[0003] First of all, the low efficiency of induced crystallization is a common problem. Traditional methods usually rely on natural nucleation or the addition of coarse crystal seeds. The primary growth of crystals is slow, and the reaction window is not easy to control. The crystal nucleus density is low, and the nucleation start lags, resulting in a longer reaction cycle, especially obvious under low calcium concentration conditions.

[0004] Furthermore, most systems do not achieve the recycling and reuse of crystal seeds. Fresh crystal seeds need to be synthesized or added again in each round of treatment, resulting in serious waste of resources. The activity of crystal nuclei cannot be continuously accumulated, and the overall stability of the system is poor. It is easy to cause fluctuations in the hardness removal effect due to changes in crystal seeds.

[0005] In addition, the low equipment integration and poor system coupling are also a shortcoming of the current process route. The precipitation system and the membrane module are often arranged in series, without fully considering the linkage relationship between the crystal formation path and the separation efficiency. As a result, the crystallization and separation efficiency are out of touch, the residual amount of hardness ions is high, and membrane fouling occurs frequently, making it difficult to meet the long-term treatment requirements of high-hardness water quality. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a method for removing hardness and desalting by calcium carbonate cyclic induced crystallization, which solves the problems of low efficiency of removing existing hardness ions, poor control of crystals, unstable system operation, and low resource utilization rate.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for removing hardness and desalting by calcium carbonate cyclic induced crystallization, including the following steps; Put crystal seeds into high-salt water, and the particle size of the crystal seeds is 10 - 30 μm to induce a crystallization reaction; Add sodium hydroxide to the high-salt water, and the sodium hydroxide and sodium carbonate are added in a molar ratio of 1:5 - 2:5; Generate a supersaturated solution by adding sodium carbonate, form insoluble calcium carbonate precipitates in the water, and promote the precipitation of calcium ions by controlling the supersaturation of the solution; Introduce the solution containing calcium carbonate crystal nuclei into the crystallization equipment, and control the reaction temperature, flow rate, and stirring rate to further promote the crystallization of calcium carbonate. The solution flow rate is controlled at 0.2 - 1.0 m / s; Treat the reaction solution with a solid-liquid separation equipment to separate the formed calcium carbonate precipitate and obtain the water body after hardness removal; Further desalt the water body after hardness removal by membrane separation to remove residual salts and improve the water quality purity; Collect and process the formed calcium carbonate precipitate, recycle the precipitate using separation technology, return calcium carbonate particles with a particle size less than 30 μm to the system as crystal seeds for continuous recycling, and extract and collect and process calcium carbonate precipitates with a particle size greater than 30 μm; Ensure that the treated water quality meets the reuse standard through water quality monitoring. The water quality standards include a total hardness between 100 - 150 mg / L, a calcium ion concentration between 30 - 50 mg / L, and a magnesium ion concentration between 20 - 30 mg / L.

[0008] Preferably, the addition amount of the crystal seeds is 2% - 5% of the calcium ion concentration in water.

[0009] Preferably, the added crystal seeds are synthetic and vaterite-type crystal seeds modified with surfactants.

[0010] Preferably, the synthesis of vaterite-type crystal seeds specifically includes the following steps; React a calcium chloride solution with a concentration of 0.05 - 0.2 mol / L with a sodium carbonate solution of the same molar concentration at a temperature of 25 - 35 °C; Maintain the stirring rate at 200 - 500 rpm during the reaction, and slowly drip the sodium carbonate solution into the calcium chloride solution to form calcium carbonate precipitate; Control the reaction time to 10 - 30 min, and obtain vaterite-type crystal seeds with a particle size of 10 - 30 μm through washing, drying, and particle size screening.

[0011] Preferably, the high-salt water comes from the wastewater of coal chemical industry, petrochemical industry or steel industry.

[0012] Preferably, the total salt content of the wastewater is 0.6 - 2%, including total hardness (1000 - 2000 mg / L), chloride ions (800 - 3000 mg / L), sulfate ions (800 - 5000 mg / L), and a small amount of ammonia nitrogen.

[0013] Preferably, the reaction temperature of the crystallization equipment is controlled between 20 - 40 °C, and the stirring rate is controlled at 10 - 100 rpm to promote the uniform growth of crystal nuclei and prevent precipitate agglomeration.

[0014] Preferably, the calcium carbonate precipitate is recovered from the reacted solution through a filter with a pore size of 10 - 30 μm.

[0015] Preferably, the supersaturation of the supersaturated solution is controlled at 50 - 80 during the seeded crystallization reaction stage.

[0016] The device for calcium carbonate cyclic induced crystallization for hardness removal and desalination includes; A crystallization tank, the lower surface of the crystallization tank is fixedly connected with a filter, the outer wall of the filter is fixedly connected with a discharge pipe, the lower surface of the filter is fixedly connected with a conveying pipe, one end of the conveying pipe is fixedly connected with a feed pipe, one end of the feed pipe is fixedly connected with a circulation pump, the output end of the circulation pump is fixedly connected with a heat exchanger, the outer wall of the heat exchanger is fixedly connected with a cold water pipe, the outer wall of the heat exchanger is fixedly connected with a drain pipe, the outer wall of the heat exchanger is fixedly connected with a connecting pipe, and one end of the connecting pipe is fixedly connected to the outer wall of the crystallization tank.

[0017] The present invention provides a method for calcium carbonate cyclic induced crystallization for hardness removal and desalination. It has the following beneficial effects: 1. By using synthetic vaterite-type seeds, the present invention significantly improves the efficiency of hardness removal and desalination during the calcium carbonate cyclic induced crystallization process. Compared with traditional non-synthetic seeds, synthetic seeds have a higher surface area and uniformity, which can more quickly induce the combination of calcium ions and carbonate ions to form stable crystal nuclei, ultimately enhancing the overall effect of the reaction and providing a more efficient solution for wastewater treatment.

[0018] 2. By separating and processing the generated calcium carbonate precipitate, the part with an appropriate particle size can be used as seeds again, thereby maintaining the stability and reactivity of the system, significantly improving the utilization rate of resources, and reducing the operating cost.

[0019] 3. By controlling the supersaturation during the crystallization process, the present invention ensures the optimal balance between the combination rate of calcium ions and carbonate ions and the crystal nucleus growth rate. This precise supersaturation regulation not only improves the precipitation rate of calcium carbonate but also reduces the doping of impurities, ensuring the uniformity and stability of the generated precipitate, and ultimately improving the purity of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the process flow chart of the method of the present invention; Figure 2 is the three-dimensional view of the device of the present invention.

[0021] Among them, 1. Crystallization tank; 2. Filter; 3. Conveying pipe; 4. Feed pipe; 5. Discharge pipe; 6. Circulation pump; 7. Cold water pipe; 8. Heat exchanger; 9. Drain pipe; 10. Connecting pipe. Detailed implementation manners

[0022] Next, in conjunction with the accompanying drawings of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0023] Please refer to the attached Figure 1 , the embodiment of the present invention provides a method for removing hardness and desalting by calcium carbonate cycle-induced crystallization; Example 1: Prepare vaterite-type seeds with a particle size of 20 μm.

[0024] React 0.1 mol / L calcium chloride solution with 0.1 mol / L sodium carbonate solution at 25 °C.

[0025] The stirring rate during the reaction is 350 rpm, and the reaction time is 20 min.

[0026] Wash and dry, and screen to obtain seeds with particles of 20 μm.

[0027] Source of high-salt water: A certain petrochemical plant with a salt content of 1.2%.

[0028] The calcium ion concentration is 1350 mg / L, the chloride ion concentration is 2000 mg / L, and the sulfate ion concentration is 3000 mg / L.

[0029] Add 20-μm seeds to the high-salt water, and the seed addition amount is 4% of the calcium ion concentration in the water.

[0030] Add sodium hydroxide and add it according to the molar ratio of sodium hydroxide to sodium carbonate of 1:5 (the sodium hydroxide addition amount is 0.0432 mol / L, and the sodium carbonate addition amount is 0.216 mol / L).

[0031] Generate a supersaturated solution to promote the formation of insoluble calcium carbonate precipitates.

[0032] Supersaturation control: Measure the S value to be about 65 during the reaction stage.

[0033] Introduce the reacted solution into the crystallization equipment, control the reaction temperature at 30 °C, the stirring rate at 50 rpm, and the flow rate at 0.5 m / s.

[0034] After solid-liquid separation treatment, recover the precipitate by passing the solution after hardness removal through a filter with a pore size of 10-30 μm.

[0035] The recovered calcium carbonate precipitate is partially returned for recycling, and calcium carbonate particles with a particle size less than 30 μm are used as crystal seeds again.

[0036] The water quality monitoring results after treatment meet the standards, with a total hardness of 140 mg / L, a calcium ion concentration of 35 mg / L, and a magnesium ion concentration of 28 mg / L.

[0037] Example 2: Prepare vaterite-type crystal seeds with a particle size of 30 μm.

[0038] React a 0.2 mol / L calcium chloride solution with a 0.2 mol / L sodium carbonate solution at 35°C.

[0039] During the reaction, the stirring rate is 200 rpm and the reaction time is 10 min.

[0040] Wash and dry, and screen to obtain crystal seeds with a particle size of 30 μm.

[0041] Source of high-salt water: A coal chemical enterprise with a salt content of 2%.

[0042] The calcium ion concentration is 2000 mg / L, the chloride ion concentration is 3000 mg / L, and the sulfate ion concentration is 5000 mg / L.

[0043] Add 30-μm crystal seeds to the high-salt water, and the dosage of crystal seeds is 5% of the calcium ion concentration in the water.

[0044] Add sodium hydroxide, and add it according to the molar ratio of sodium hydroxide to sodium carbonate of 1:5 (the dosage of sodium hydroxide is 0.0432 mol / L, and the dosage of sodium carbonate is 0.216 mol / L).

[0045] Generate a supersaturated solution to promote the formation of insoluble calcium carbonate precipitate.

[0046] Supersaturation control: In the reaction stage, S≈80; Introduce the reacted solution into the crystallization equipment, control the reaction temperature at 40°C, the stirring rate at 100 rpm, and the flow rate at 1.0 m / s.

[0047] After solid-liquid separation treatment, recover the precipitate by passing the dehardened solution through a filter with a pore size of 10-30 μm.

[0048] The recovered calcium carbonate precipitate is partially returned for recycling, and calcium carbonate particles with a particle size less than 30 μm are used as crystal seeds again.

[0049] The water quality monitoring results after treatment meet the standards, with a total hardness of 100 mg / L, a calcium ion concentration of 30 mg / L, and a magnesium ion concentration of 20 mg / L.

[0050] Example 3: Lower Limit Scheme Prepare vaterite-type seeds with a particle size of 10 μm.

[0051] React a 0.05 mol / L calcium chloride solution with a 0.05 mol / L sodium carbonate solution at 25°C.

[0052] During the reaction, the stirring rate is 500 rpm and the reaction time is 30 min.

[0053] Wash, dry, and screen to obtain seeds with particles of 10 μm.

[0054] Source of high-salt water: A certain steel plant with a salt content of 0.6%.

[0055] Calcium ion concentration is 1000 mg / L, chloride ion concentration is 800 mg / L, and sulfate ion concentration is 800 mg / L.

[0056] Add 10-μm seeds to the high-salt water, and the seed addition amount is 2% of the calcium ion concentration in the water.

[0057] Add sodium hydroxide and add it according to the molar ratio of sodium hydroxide to sodium carbonate of 2:5 (sodium hydroxide addition amount is 0.0432 mol / L, and sodium carbonate addition amount is 0.108 mol / L).

[0058] Generate a supersaturated solution to promote the formation of insoluble calcium carbonate precipitate.

[0059] Supersaturation control: Maintain S≈60.

[0060] Introduce the reacted solution into the crystallization equipment, control the reaction temperature at 20°C, the stirring rate at 10 rpm, and the flow rate at 0.2 m / s.

[0061] After solid-liquid separation treatment, recover the precipitate by passing the dehardened solution through a filter with a pore size of 10-30 μm.

[0062] Part of the recovered calcium carbonate precipitate is returned for recycling, and calcium carbonate particles with a particle size less than 30 μm are used as seeds again.

[0063] The water quality monitoring results after treatment meet the standards, with a total hardness of 150 mg / L, a calcium ion concentration of 50 mg / L, and a magnesium ion concentration of 30 mg / L.

[0064] Comparative Example 1: Compared with Example 1, the difference is that ordinary non-synthetic seeds, rather than synthetic vaterite-type seeds, are used, and the rest are the same.

[0065] Comparative Example 2: Compared with Example 1, the difference is that the molar ratio of sodium hydroxide to sodium carbonate is 1:1, and the rest are the same.

[0066] Comparative Example 3: Compared with Example 1, the difference lies in that the supersaturation was not controlled during the crystallization process, and the rest were the same.

[0067] Experiment 1: Comparative experiment on calcium carbonate crystallization efficiency Experiment description Purpose: To compare the differences in calcium carbonate crystallization efficiency between Example 1 and Comparative Example 1.

[0068] Test object: Example 1: Using synthetic vaterite-type seeds Comparative Example 1: Using ordinary non-synthetic seeds Experimental procedure: Prepare high-salt water: Using high-salt water from the same source to ensure the same chemical composition of the samples, with a salt concentration of 1.2%.

[0069] Add seeds: Add the corresponding seeds to the two groups of high-salt water respectively: Example 1: Add 20-μm vaterite-type seeds, with a quantity of 4% of the calcium ion concentration in the water.

[0070] Comparative Example 1: Add ordinary seeds, with a quantity of 1% of the calcium ion concentration in the water.

[0071] Add reactants: Add sodium hydroxide and sodium carbonate to the two reaction systems, and the specific molar ratios are as follows: Example 1: 1:5 Comparative Example 1: 1:1 Reaction condition setting: Place the two groups of samples in a constant-temperature incubator, keep the reaction temperature at 30 °C, and stir evenly at a rate of 50 rpm.

[0072] Record the time from the start to the end of the reaction, and continue the reaction for 3 hours.

[0073] Solid-liquid separation: After the reaction, use a 30-μm filter for solid-liquid separation, and collect the precipitate and supernatant.

[0074] Weigh the separated precipitate and record the results of three repeated experiments.

[0075] Data collection and analysis: Calculate the mass of each group of precipitates, and calculate the crystallization efficiency based on the known calcium ion concentration.

[0076] Collect the results and organize them into a table.

[0077] Table 1: Comparison of experimental data on calcium carbonate crystallization efficiency

[0078] Summary; In this experiment, the comparison results between Example 1 and Comparative Example 1 showed that the use of synthesized vaterite-type seeds could significantly improve the crystallization efficiency of calcium carbonate. The core of this mechanism lies in the uniformity and specific physicochemical properties of the synthesized seeds, which enable them to effectively induce calcium ions and carbonate ions to form stable crystal nuclei in the reaction liquid. These seeds have appropriate particle sizes and large specific surface areas, which help to improve the contact efficiency of the reaction, thereby encouraging more Ca 2+ and CO3 2- to combine and form crystals, promoting the entire crystallization process.

[0079] The use of synthesized vaterite-type seeds not only optimizes the crystal nucleus formation process but also effectively improves the precipitation rate and crystallization purity of calcium carbonate. Compared with ordinary non-synthesized seeds, the synthesized seeds show better stability and adaptability under reaction conditions and can promote the crystallization reaction within a wider supersaturation range. Research shows that controlling the dosing ratio of sodium hydroxide and sodium carbonate and the reaction conditions can effectively regulate the supersaturation of the solution, further promoting the crystallization process and ensuring that the generated precipitate particles are uniform and have a stable morphology.

[0080] In addition, precise setting of the reaction temperature and stirring rate during the reaction process also plays an important role. The optimization of these parameters not only affects the formation and growth of crystal nuclei but also helps to reduce the agglomeration of precipitates, improving the yield and quality of the precipitate. At the same time, it can effectively remove excess calcium ions in water, achieving a good hardness removal effect and creating favorable conditions for the subsequent improvement of water quality.

[0081] Experiment 2: Comparative Experiment on Water Quality Index Monitoring Objective: To compare the water quality indexes after treatment in Example 1 and Comparative Example 2, including total hardness, calcium ion concentration, and magnesium ion concentration.

[0082] Test Objects: Example 1: The molar ratio of sodium hydroxide to sodium carbonate is 1:5.

[0083] Comparative Example 2: The same high-salt water is used, but the molar ratio of sodium hydroxide to sodium carbonate is 1:1.

[0084] Experimental Procedures: Prepare High-Salt Water: Prepare two groups of high-salt water from the same source, with consistent chemical components and concentrations, to ensure the comparability of the experiment.

[0085] Add Reactants: Add the required sodium hydroxide and sodium carbonate to their respective high-salt waters according to the ratio: Example 1: The volume ratio of sodium hydroxide to sodium carbonate is 1:5. After thorough mixing, it is left to stand for 5 minutes.

[0086] Comparative Example 2: The volume ratio of sodium hydroxide to sodium carbonate is 1:1. After thorough mixing, it is left to stand for 5 minutes.

[0087] Induced crystallization reaction: Synthetic vaterite-type seeds and ordinary non-synthetic seeds are added to the two groups of solutions, ensuring that the total amount of seeds is 4% (Example 1) or 1% (Comparative Example 2) of the calcium ion concentration.

[0088] The reaction temperature is maintained at 30 °C. The stirring rate is set at 50 rpm using a stirrer, and the reaction time is 3 hours.

[0089] Post-reaction treatment: After the reaction, the precipitate and supernatant are obtained by solid-liquid separation, and a filter is used for separation to ensure minimal loss of the precipitate.

[0090] Water quality monitoring index test: Supernatant samples are collected, and standardized reagents are used for water quality detection to measure the total hardness, calcium ion concentration, and magnesium ion concentration.

[0091] The measurement of each index is repeated three times, and the average value is taken to record the results.

[0092] Data collation: The data obtained from the experiment is collated into a table for analysis and comparison. Table 2: Comparison of experimental data on water quality index monitoring

[0093] Summary; In this experiment, the water quality monitoring results of Example 1 and Comparative Example 2 showed significant differences. The mechanism of this phenomenon is mainly related to the concentration relationship of calcium ions and carbonate ions in the reaction system, the type of seeds used, and the molar ratio. In Example 1, by using synthetic vaterite-type seeds and a higher molar ratio of sodium hydroxide to sodium carbonate (1:5), the supersaturation of the solution was increased, promoting the crystallization reaction of calcium carbonate. The higher crystallization efficiency significantly reduced the calcium ion and magnesium ion concentrations in the water, resulting in a significant decrease in water hardness and thus improving the compliance of the effluent water quality.

[0094] On the other hand, in Comparative Example 2, due to the decrease in the molar ratio (1:1) and the use of ordinary seeds, the efficiency of the combination of calcium ions and carbonate ions decreased, and the crystallization reaction rate slowed down. This reduced reaction efficiency failed to effectively reduce the calcium ion concentration in the water, thus increasing the total hardness of the treated water. The experimental results showed that reducing the seed dosage and the reactant molar ratio would result in more free calcium ions remaining in the water, affecting the effluent quality, and this phenomenon was fully reflected in the experimental data.

[0095] In addition, optimized reaction conditions such as temperature and stirring rate all play an important auxiliary role in improving water quality. By maintaining an appropriate temperature and effective stirring, the collision opportunities between calcium ions and carbonate ions increase, thereby promoting crystal formation and increasing their precipitation, and further improving the overall treatment effect of water quality.

[0096] Experiment 3: Analysis Experiment on the Purity of Calcium Carbonate Crystals Purpose: To compare the purity differences of the calcium carbonate precipitates generated after the treatment of Example 1 and Comparative Example 3.

[0097] Test objects: Example 1: Using synthetic vaterite-type seeds and controlling supersaturation Comparative Example 3: Without controlling supersaturation Sample preparation: Take 5 portions of the precipitates of Example 1 and Comparative Example 3 respectively, each portion being 10 g, and grind them into powder form.

[0098] Acid dissolution test: Add each sample to excessive dilute hydrochloric acid (concentration 1 mol / L), and stir well until completely dissolved.

[0099] Record the volume of the gas generated (CO2) during the reaction process to preliminarily judge the calcium carbonate content.

[0100] Detection of unreacted raw materials: Use the EDTA titration method to determine the residual calcium ion concentration in the solution.

[0101] Determine the contents of unreacted sodium hydroxide and sodium carbonate (using phenolphthalein as an indicator) by acid-base titration.

[0102] Data recording: Each group of experiments is repeated 3 times, and the average value is taken and the deviation range is recorded.

[0103] Table 3: Experimental Data of the Analysis of the Purity of Calcium Carbonate Precipitates

[0104] Summary; In this experiment, the purity difference between Example 1 and Comparative Example 3 indicates that by controlling the supersaturation, the crystallization purity of calcium carbonate can be significantly improved. The precise regulation of supersaturation (50 - 80) ensures the balance between the binding rate of calcium ions and carbonate ions in the solution and the crystal nucleation growth rate, avoiding the phenomena of impurity encapsulation or disordered crystallization caused by excessive local supersaturation. This control enables the calcium carbonate crystals to grow orderly on the seed crystal surface, reducing the residue of unreacted raw materials (such as sodium hydroxide and sodium carbonate), thereby improving the chemical homogeneity of the product.

[0105] The use of synthesized vaterite-type seed crystals further optimizes the crystallization process. The active sites on the seed crystal surface can preferentially adsorb calcium ions and carbonate ions to form stable crystal nuclei, inhibiting the formation of stray crystals. In Comparative Example 3, the lack of control of supersaturation led to an imbalance between the crystal nucleation rate and the growth rate in the solution, and excessive supersaturation in some regions triggered secondary nucleation, making it easier for impurity ions (such as magnesium ions) to mix into the crystal lattice, reducing the purity of the product.

[0106] In addition, the stability of reaction conditions is also crucial for purity. In Example 1, through constant monitoring of temperature, stirring rate, and supersaturation, the continuity of crystal growth was ensured, reducing crystal defects caused by environmental fluctuations.

[0107] The equipment for calcium carbonate cyclic-induced crystallization for hardness removal and desalination includes: A crystallization tank 1, the lower surface of the crystallization tank 1 is fixedly connected with a filter 2, the outer wall of the filter 2 is fixedly connected with a discharge pipe 5, the lower surface of the filter 2 is fixedly connected with a conveying pipe 3, one end of the conveying pipe 3 is fixedly connected with a feed pipe 4, one end of the feed pipe 4 is fixedly connected with a circulation pump 6, the output end of the circulation pump 6 is fixedly connected with a heat exchanger 8, the outer wall of the heat exchanger 8 is fixedly connected with a cold water pipe 7, the outer wall of the heat exchanger 8 is fixedly connected with a drain pipe 9, the outer wall of the heat exchanger 8 is fixedly connected with a connecting pipe 10, and one end of the connecting pipe 10 is fixedly connected to the outer wall of the crystallization tank 1; Specifically, the solution of calcium carbonate crystal nuclei is poured into the feed pipe 4, and the solution is transported to the heat exchanger 8 by starting the circulation pump 6 and then transported to the inside of the crystallization tank 1 through the connecting pipe 10. Thus, the solution inside the crystallization tank 1 is crystallized, and after crystallization, it is transported to the inside of the filter 2. Then, the crystallization is separated by the filter 2, and the crystallization is discharged through the discharge pipe 5. The solution is transported to the inside of the feed pipe 4 through the conveying pipe 3, thereby achieving the effect of circulating the solution. Cold water enters the heat exchanger 8 through the cold water pipe 7 and exchanges heat with the solution inside, and then the hot water is discharged through the drain pipe 9, thereby achieving the effect of heat exchange.

[0108] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for removing hardness and desalination by circulating induced crystallization of calcium carbonate, characterized in that: The following steps are included: Adding seed crystals into the high brine, wherein the seed crystals have a particle size of 10-30 μm to induce a crystallization reaction; Adding sodium hydroxide to the high brine in a molar ratio of 1:5 to 2:5; By adding sodium carbonate, a supersaturated solution is generated, which causes insoluble calcium carbonate precipitation to form in the water, and the precipitation of calcium ions is promoted by controlling the supersaturation of the solution; The solution containing calcium carbonate crystal nuclei is introduced into the crystallization equipment, and the reaction temperature, flow rate and stirring rate are controlled to further promote the crystallization of calcium carbonate. The solution flow rate is controlled at 0.2-1.0m / s; The solution after the reaction is treated by a solid-liquid separation device to separate the formed calcium carbonate precipitate to obtain a de-hardened water body; The water after hardness removal is further desalinated by membrane separation to remove residual salt and improve water purity; The formed calcium carbonate precipitate is collected and processed, and the precipitate is recovered by separation technology. Calcium carbonate particles with a particle size of less than 30 μm are returned to the system as seeds for continued recycling, while calcium carbonate precipitates with a particle size of more than 30 μm are mined and collected for treatment; Water quality monitoring is used to ensure that the treated water meets the reuse standards, including a total hardness of 100-150 mg / L, a calcium ion concentration of 30-50 mg / L, and a magnesium ion concentration of 20-30 mg / L.

2. The method for removing hardness and desalination by calcium carbonate circulation-induced crystallization according to claim 1, characterized in that: The amount of the seed crystal added is 2%-5% of the calcium ion concentration in water.

3. The method for removing hardness and desalination by calcium carbonate circulation-induced crystallization according to claim 1, characterized in that: The added crystal seeds are synthetic vaterite type crystal seeds.

4. The method for removing hardness and desalination by calcium carbonate circulation-induced crystallization according to claim 3, characterized in that: The synthetic vaterite type crystal seed specifically comprises the following steps: React 0.05-0.2 mol / L calcium chloride solution with equimolar sodium carbonate solution at 25-35°C; During the reaction, the stirring rate was maintained at 200-500 rpm, and the sodium carbonate solution was slowly added dropwise to the calcium chloride solution to form a calcium carbonate precipitate; The reaction time is controlled to be 10-30 minutes, and vaterite-type crystal seeds with a particle size of 10-30 μm are obtained through washing, drying and particle size screening.

5. The method for removing hardness and desalination by calcium carbonate circulation-induced crystallization according to claim 1, characterized in that: The high-salt water comes from wastewater from coal chemical industry, petrochemical industry or steel industry.

6. The method for removing hardness and desalination by circulating induced crystallization of calcium carbonate according to claim 5, characterized in that: The total salt content of the wastewater is 0.6-2%, including total hardness (1000-2000 mg / L), chloride ions (800-3000 mg / L), sulfate ions (800-5000 mg / L) and a small amount of ammonia nitrogen.

7. The method for removing hardness and desalination by circulating induced crystallization of calcium carbonate according to claim 1, characterized in that: The reaction temperature of the crystallization equipment is controlled between 20-40° C., and the stirring rate is controlled between 10-100 rpm to promote uniform growth of crystal nuclei and prevent precipitation agglomeration.

8. The method for removing hardness and desalination by circulating induced crystallization of calcium carbonate according to claim 1, characterized in that: The solution after the reaction is passed through a filter to recover calcium carbonate precipitate, wherein the pore size of the filter is 10-30 μm.

9. The method for removing hardness and desalination by circulating induced crystallization of calcium carbonate according to claim 1, characterized in that: The supersaturation of the supersaturated solution is controlled at 50-80 during the seed crystal induced crystallization reaction stage.

10. A device for removing hardness and salt by circulating induced crystallization of calcium carbonate, according to the method for removing hardness and salt by circulating induced crystallization of calcium carbonate according to any one of claims 1 to 9, characterized in that: include; A crystallizer (1) is provided, wherein the lower surface of the crystallizer (1) is fixedly connected to a filter (2), the outer wall of the filter (2) is fixedly connected to a discharge pipe (5), the lower surface of the filter (2) is fixedly connected to a delivery pipe (3), one end of the delivery pipe (3) is fixedly connected to a feed pipe (4), one end of the feed pipe (4) is fixedly connected to a circulation pump (6), the output end of the circulation pump (6) is fixedly connected to a heat exchanger (8), the outer wall of the heat exchanger (8) is fixedly connected to a cold water pipe (7), the outer wall of the heat exchanger (8) is fixedly connected to a drain pipe (9), the outer wall of the heat exchanger (8) is fixedly connected to a connecting pipe (10), and one end of the connecting pipe (10) is fixedly connected to the outer wall of the crystallizer (1).

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