A continuous crystallization process of high-purity nickel nitrate hexahydrate

Abstract

The present application relates to the technical field of crystallization process, and particularly relates to a continuous crystallization process of high-purity nickel nitrate hexahydrate, which takes the reaction of metal nickel and nitric acid as a starting point to generate a nickel nitrate solution, and obtains a purified solution through filtration; the purified solution is concentrated through falling film evaporation under negative pressure to obtain a high-concentration nickel solution; the concentrated solution enters a crystallizer to precipitate crystals to form a crystal slurry and a mother liquor; the crystal slurry is separated and dried to obtain the final product, nickel nitrate hexahydrate; the separated mother liquor enters a fixed bed adsorption column provided with a specific adsorption medium to deeply remove iron ions; and the purified mother liquor is returned to the evaporation and concentration step to be mixed with fresh feed liquid, so that the material is recycled and continuously produced.

Description

Technical Field

[0001] This invention relates to the field of crystallization technology, and in particular to a continuous crystallization process for high-purity nickel nitrate hexahydrate. Background Technology

[0002] High-purity nickel nitrate hexahydrate is an important inorganic functional material with significant applications in precision electroplating, nickel-based catalyst synthesis, precursors for cathode materials in new energy batteries, and special functional ceramics. Currently, the industrial production of nickel nitrate hexahydrate primarily employs a batch crystallization process, where all operations—solution concentration, cooling nucleation, crystal growth, and separation—are sequentially completed within the same reactor. While this traditional production method offers advantages such as lower equipment investment and greater operational flexibility, it often faces numerous challenges in large-scale, high-quality product preparation due to the unsteady characteristics of thermodynamics and mass transfer behavior. For example, fluctuations in operating parameters between batches make it difficult to maintain consistent product purity, and localized supercooling-induced explosive nucleation can lead to a broadened crystal particle size distribution, thus affecting solid-liquid separation efficiency and product bulk density.

[0003] Continuous crystallization technology decomposes the crystallization process into multiple series of steady-state operating units, allowing crystal nucleation and growth to occur independently in a precisely controlled kinetic environment. This enables more precise control over crystal grain size distribution, crystal morphology, and product purity. Studies have shown that continuous crystallization effectively maintains constant supersaturation within the crystallizer, avoiding explosive nucleation phenomena caused by local concentration fluctuations in intermittent operation. This is of great significance for preparing high-purity, high-packing-density nickel nitrate hexahydrate crystals.

[0004] However, in continuous production, the mother liquor is usually recycled. Over time, trace impurities (such as iron ions) introduced from the raw nitric acid or nickel plates will continuously concentrate and accumulate in the mother liquor. Because nickel nitrate hexahydrate requires extremely high purity, these accumulated iron ions will eventually reach supersaturation, causing co-precipitation or physical adsorption on the surface of the product crystals, leading to a batch-by-batch decrease in product purity. Traditional processes either lack effective online impurity removal methods or can only maintain balance by discharging large amounts of mother liquor, resulting in yield losses. Furthermore, traditional processes typically use chemical precipitation for impurity removal in the upstream raw liquor preparation stage. However, if the mother liquor is recycled, impurities will re-accumulate in the system. Attempting to use chemical precipitation (e.g., adjusting pH with alkali) again in the mother liquor recycling path presents a series of technical challenges: firstly, new chemical reagents (e.g., alkali) need to be introduced into the mother liquor, potentially introducing new cation contamination; secondly, the precipitation process generates ferric hydroxide colloids, which are fine-grained, difficult to filter, and easily clog pipes and equipment; simultaneously, the precipitation reaction consumes nitric acid in the mother liquor, altering the chemical balance between nickel ions and nitrate ions, disrupting the stability of the crystallization system, and affecting crystal growth quality. Furthermore, the mother liquor of nickel nitrate hexahydrate typically exhibits high salt content, weak acidity, and high nickel ion concentration, making conventional adsorption materials unsuitable. If ordinary ion exchange resins are used, the high concentration of nickel ions competes with iron ions for exchange sites on the resin, causing the resin to quickly become saturated with nickel ions, resulting in extremely low adsorption capacity and poor selectivity for iron ions; simultaneously, the high-salt environment significantly reduces the resin's activity, drastically decreasing its exchange efficiency. If ordinary activated carbon is used, its adsorption capacity for inorganic metal ions is very limited, making it almost impossible to effectively remove iron ions. If silica gel or molecular sieve adsorbents are used, the hydrothermal stability of silicon-based materials is poor in a high-humidity, acidic mother liquor environment. The framework is prone to hydrolysis, collapse, and even dissolution of silicon elements, causing secondary pollution. Summary of the Invention

[0005] To address the problems mentioned in the background section, the present invention provides a continuous crystallization process for high-purity nickel nitrate hexahydrate.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A continuous crystallization process for high-purity nickel nitrate hexahydrate includes the following steps:

[0008] S1. React metallic nickel with nitric acid to obtain nickel nitrate solution. After filtration, a purified solution is obtained. The metallic nickel is electrolytic nickel plate with a purity ≥99.95% and a particle size of 5-10 mm. The filtration membrane has a pore size of 0.22-0.45 μm, the filtration pressure is controlled at 0.1-0.3 MPa, and the filtration temperature is 45-55℃.

[0009] S2. The purified liquid is concentrated by negative pressure evaporation to obtain a concentrated liquid;

[0010] S3. The concentrate is sent to a crystallizer for cooling and crystallization to obtain mother liquor and crystal slurry;

[0011] S4. The mother liquor is passed through a fixed-bed adsorption column containing adsorption medium for purification to remove iron ions. The purified mother liquor is then returned to step S2 and mixed with fresh purified liquid. The bed height of the fixed-bed adsorption column is 80-120 cm, the column diameter to bed height ratio is 1:(5-8), and the return ratio is 30-50% of the volume of fresh purified liquid.

[0012] S5. The crystal slurry is subjected to solid-liquid separation to obtain wet crystals. The obtained wet crystals are then dried to obtain high-purity nickel nitrate hexahydrate product. Solid-liquid separation is performed using a centrifuge at a speed of 3000-4000 rpm for 10-20 minutes. Drying is performed using a drying oven at a temperature of 50-60℃ and a vacuum degree of (-0.07)-(-0.09) MPa for 3-5 hours.

[0013] Further, in step S1, the reaction of metallic nickel with nitric acid is carried out with excess metallic nickel, a nickel to nitric acid mass ratio of 1:(2.68-3.01), and a nitric acid concentration of 20-30 wt%. The reaction temperature is controlled at 50-60℃, the pH value at the reaction endpoint is 4.0-5.0, the reaction is carried out in a stirred reactor with a stirring rate of 80-120 rpm, and the reaction time is 2-3 h. Nitric acid is added dropwise during the reaction with a dropping rate of 5-10 mL / min, and the reaction is kept at the temperature for 30-60 min after the addition is completed. The initial concentration of nickel ions in the solution after the reaction is 200-250 g / L.

[0014] Further, in step S2, the negative pressure evaporation and concentration are carried out in a falling film evaporator, with the vacuum degree controlled at (-0.06)-(-0.08) MPa, the evaporation temperature at 70-80℃, and the evaporation rate at 50-80 L / h, to obtain a concentrated solution with a nickel ion concentration of 400-450 g / L; after evaporation and concentration, the solution is filtered while hot using a ceramic filter membrane with a pore size of 0.1-0.2 μm and a filtration time of 20-30 min to remove insoluble matter.

[0015] Furthermore, in step S3, the crystallization temperature is 30-35℃, the residence time is 5-7h, and the stirring rate is 50-100rpm; the cooling adopts jacket cooling, the cooling medium is chilled water, the chilled water temperature is 10-15℃, and the cooling rate is 2-5℃ / h.

[0016] Furthermore, the adsorption medium in step S4 is prepared by the following steps:

[0017] A1. Dissolve zirconium oxychloride octahydrate and titanium chloride in water and prepare a mixed salt solution of 0.5-0.8 mol / L under ice bath conditions, denoted as solution A; dissolve furfuryl methacrylate and allyl aniline in N,N-dimethylformamide, add ferric chloride and an initiator, and prepare solution B; dilute phosphoric acid to prepare a phosphoric acid solution of 2-3 mol / L, denoted as solution C; wherein, the ice bath temperature is 0-5℃.

[0018] A2. Under nitrogen protection, solutions A and B are simultaneously added dropwise to solution C, controlling the pH of the reaction system to be 2-3. After the addition is complete, the reaction system is heated to 60-70℃ and stirred for 4-6 hours at a stirring rate of 100-150 rpm to obtain a mixture.

[0019] A3. Transfer the mixture to a reaction vessel and crystallize at 100-110℃ for 12-24 hours. After crystallization, perform solid-liquid separation. The obtained solid is washed, eluted with a template, and dried sequentially to obtain mesoporous material powder. The stirring rate of the reaction vessel is 50-70 rpm, and the pressure inside the vessel is maintained at 0.1-0.15 MPa during crystallization. Solid-liquid separation is performed by vacuum filtration at a pressure of -0.05 to (-0.07) MPa. Deionized water is used for washing, and the washing is performed 3-5 times. The amount of water used for each washing is 2-3 times the mass of the solid. The washing is continued until the pH of the washing solution is 6.5-7.5.

[0020] A4. Mix the mesoporous material powder with silica sol, granulate and shape it into spherical particles to obtain the adsorption medium; wherein the mass ratio of the mesoporous material powder to the silica sol is 1:(0.3-0.5), and the solid content of the silica sol is 30-40wt%; during the mixing process, add an appropriate amount of deionized water to adjust the moisture content of the material to 30-40%, stir evenly and then granulate.

[0021] Further, the operating conditions of the fixed-bed adsorption column in step S4 are as follows: adsorption temperature is 30-40℃, liquid hourly space velocity is 1-3 BV / h, flow direction is top inlet and bottom outlet, and the operating pressure of the adsorption column is 0.2-0.4 MPa; when the iron ion content in the mother liquor at the adsorption column outlet is >0.001 g / L, adsorption is stopped, and the adsorption medium is regenerated. The regenerator is 0.5-1.0 mol / L hydrochloric acid solution or 0.3-1.0 mol / L EDTA solution, the regeneration temperature is 40-50℃, the regeneration hourly space velocity is 0.5-1.0 BV / h, and the regeneration time is 2-3 h.

[0022] Further, in step A1, the mass ratio of zirconium oxychloride octahydrate to titanium chloride is 1.70:1, the mass ratio of furfuryl methacrylate to allyl aniline is (3.5-4.0):1, the amount of ferric chloride added is 28-33% of the total mass of furfuryl methacrylate and allyl aniline, the initiator is selected from benzoyl peroxide, azobisisobutyronitrile, or dilauryl peroxide, and its addition amount is 1.2-2.5% of the total mass of furfuryl methacrylate and allyl aniline, and the amount of N,N-dimethylformamide is 2-3 times the total mass of furfuryl methacrylate and allyl aniline. When azobisisobutyronitrile is used as the initiator, it needs to be dissolved in N,N-dimethylformamide at 40-50℃ for 20-30 minutes.

[0023] Furthermore, in step A3, template elution involves soaking the template in a 0.1-0.5 mol / L ethylenediaminetetraacetic acid solution for 2-6 hours, repeating this process until Fe is undetectable in the eluent. 3+ To remove ions, the temperature of the ethylenediaminetetraacetic acid solution was 40-50℃, and the solution was stirred once every 1 hour for 10-15 minutes each time during the soaking process; Fe 3+ The detection limit for ions is 0.0001 g / L.

[0024] Furthermore, in step A4, the granulation is carried out into spherical particles with a particle size of 0.5-1.0 mm. After molding, the particles are calcined at 180-220℃ for 1-3 hours and then naturally cooled to room temperature after calcination.

[0025] The beneficial effects of this invention are:

[0026] 1. In the technical solution of this invention, through iron ion template-guided polymerization and organic-inorganic hybrid framework construction, specific recognition sites that are highly matched with the spatial size and functional group coordination environment of iron ions are formed. In a weakly acidic mother liquor system with high concentration of nickel ions, trace iron ions can be efficiently and selectively adsorbed, significantly inhibiting the adsorption of nickel ions in the target product. This effectively solves the problem of removing specific impurities under high background ion intensity, greatly improves the purity of nickel nitrate hexahydrate products, and ensures that product quality meets standards.

[0027] 2. This process uses a continuous mother liquor circulation purification system. After the crystallization mother liquor is purified by fixed bed adsorption, it is returned to the evaporation and concentration process and mixed with fresh purified liquid for reuse. This effectively blocks the enrichment path of impurity ions in the system, ensuring long-term stability of product purity, and also achieves near-complete recycling of nickel resources, reducing the consumption of metallic nickel raw materials and increasing the total metal recovery rate.

[0028] 3. The continuous process framework, combined with precise unit operation control such as negative pressure evaporation, programmed cooling crystallization, and fine crystal elimination, keeps the crystallization process in a steady-state supersaturated environment, effectively suppressing explosive nucleation and promoting uniform nucleation and growth of crystals. This results in concentrated particle size distribution and regular morphology of nickel nitrate hexahydrate crystals, which not only improves the physical properties of the product but also reduces the operational difficulty of subsequent solid-liquid separation and drying processes, thereby increasing production efficiency. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, metallic nickel reacts with nitric acid in a reactor and is then filtered to obtain a purified liquid (S1). The purified liquid enters a falling film evaporator for negative pressure evaporation and concentration to obtain a high-concentration concentrate (S2). The concentrate is then sent to a crystallizer for cooling and crystallization to form a mixture of crystal slurry and mother liquor (S3). After solid-liquid separation, the crystal slurry enters a drying process to finally obtain a high-purity nickel nitrate hexahydrate product (S5); the separated mother liquor enters a fixed-bed adsorption column to remove iron ions through a special adsorption medium (S4). The purified mother liquor is returned to the evaporation and concentration step (S2), mixed with fresh purified liquid, and reintroduced into the system to achieve mother liquor recycling. For clarity, detailed explanations are provided below through the following preparation examples, embodiments, and comparative examples.

[0032] Preparation Example 1

[0033] The adsorption medium is prepared by the following steps:

[0034] A1. Dissolve 8.5g of zirconium oxychloride octahydrate and 5.0g of titanium chloride in water, stir for 30min under 0℃ ice bath conditions, and prepare a 0.5mol / L mixed salt solution, denoted as solution A; Dissolve 7.0g of furfuryl methacrylate and 2.0g of allyl aniline in 18.0g of N,N-dimethylformamide, add 2.52g of ferric chloride and 0.108g of benzoyl peroxide initiator, stir and dissolve for 20min, and prepare solution B; Dilute phosphoric acid to prepare a 2mol / L phosphoric acid solution, denoted as solution C;

[0035] A2. Under nitrogen protection, solutions A and B are simultaneously added dropwise to solution C at a rate of 10 mL / min. The pH of the reaction system is controlled to be 2. After the addition is complete, the reaction system is heated to 60℃ and stirred at a rate of 100 rpm for 4 hours to obtain a mixture.

[0036] A3. Transfer the mixture to a reaction vessel, adjust the stirring speed to 50 rpm, maintain the pressure inside the vessel at 0.1 MPa, and crystallize at 100℃ for 12 h. After crystallization, perform vacuum filtration at a pressure of -0.07 MPa. Wash the obtained solid three times with deionized water until the pH of the washing solution is 7.0. Then soak it in 0.1 mol / L ethylenediaminetetraacetic acid solution at 40℃ for 2 h, stirring once every 1 h for 10 min each time. Repeat the soaking operation until Fe is undetectable in the eluent. 3+ The ions were then dried at 55°C and a vacuum of -0.08 MPa for 4 hours to obtain mesoporous material powder.

[0037] A4. Mix 10.0g of mesoporous material powder with 3.0g of silica sol (solid content 30wt%), add deionized water to adjust the moisture content of the material to 30%, stir evenly and granulate to make spherical particles with a particle size of 0.5mm; after molding, calcine at 180℃ for 1h, and after calcine, naturally cool to room temperature to obtain the adsorption medium.

[0038] Preparation Example 2

[0039] The adsorption medium is prepared by the following steps:

[0040] A1. Dissolve 10.2g of zirconium oxychloride octahydrate and 6.0g of titanium chloride in water, stir for 45min in an ice bath at 3℃ to prepare a 0.65mol / L mixed salt solution, denoted as solution A; Dissolve 9.5g of furfuryl methacrylate and 2.5g of allyl aniline in 30.0g of N,N-dimethylformamide, add 3.66g of ferric chloride and 0.216g of initiator azobisisobutyronitrile at 45℃, stir for 30min to prepare solution B; Dilute phosphoric acid to prepare a 2.5mol / L phosphoric acid solution, denoted as solution C;

[0041] A2. Under nitrogen protection, solutions A and B are simultaneously added dropwise to solution C at a rate of 12 mL / min. The pH of the reaction system is controlled at 2.5. After the addition is complete, the reaction system is heated to 65℃ and stirred at a rate of 125 rpm for 5 hours to obtain a mixture.

[0042] A3. Transfer the mixture to a reaction vessel, adjust the stirring speed to 60 rpm, maintain the pressure inside the vessel at 0.12 MPa, and crystallize at 105℃ for 18 h. After crystallization, filter under vacuum at a pressure of -0.06 MPa. Wash the obtained solid four times with deionized water until the pH of the washing solution is 7.0. Then soak it in 0.3 mol / L ethylenediaminetetraacetic acid solution at 45℃ for 4 h, stirring once every 1 h for 12 min each time. Repeat the soaking operation until Fe is undetectable in the eluent. 3+ The ions were then dried at 55°C and a vacuum of -0.08 MPa for 4 hours to obtain mesoporous material powder.

[0043] A4. Mix 10.0g of mesoporous material powder with 4.0g of silica sol (solid content 35wt%), add deionized water to adjust the moisture content of the material to 35%, stir evenly and granulate to make spherical particles with a particle size of 0.75mm; after molding, calcine at 200℃ for 2h, and after calcine, naturally cool to room temperature to obtain the adsorption medium.

[0044] Preparation Example 3

[0045] The adsorption medium is prepared by the following steps:

[0046] A1. Dissolve 13.6g of zirconium oxychloride octahydrate and 8.0g of titanium chloride in water, stir for 60min in an ice bath at 5℃, and prepare a 0.8mol / L mixed salt solution, denoted as solution A; Dissolve 12.0g of furfuryl methacrylate and 3.0g of allyl aniline in 45.0g of N,N-dimethylformamide, add 4.95g of ferric chloride and 0.375g of initiator dilauryl peroxide, stir and dissolve for 30min, and prepare solution B; Dilute phosphoric acid to prepare a 3mol / L phosphoric acid solution, denoted as solution C;

[0047] A2. Under nitrogen protection, solutions A and B are simultaneously added dropwise to solution C at a rate of 15 mL / min. The pH of the reaction system is controlled to be 3. After the addition is complete, the reaction system is heated to 70℃ and stirred at a rate of 150 rpm for 6 hours to obtain a mixture.

[0048] A3. Transfer the mixture to a reaction vessel, adjust the stirring speed to 70 rpm, maintain the pressure inside the vessel at 0.15 MPa, and crystallize at 110℃ for 24 h. After crystallization, filter under vacuum at a pressure of -0.05 MPa. Wash the obtained solid five times with deionized water until the pH of the washing solution is 7.0. Then soak it in 0.5 mol / L ethylenediaminetetraacetic acid solution at 50℃ for 6 h, stirring once every 1 h for 15 min each time. Repeat the soaking operation until Fe is undetectable in the eluent. 3+The ions were then dried at 55°C and a vacuum of -0.08 MPa for 4 hours to obtain mesoporous material powder.

[0049] A4. Mix 10.0g of mesoporous material powder with 5.0g of silica sol (solid content 40wt%), add an appropriate amount of deionized water to adjust the moisture content of the material to 40%, stir evenly and granulate to make spherical particles with a particle size of 1.0mm; after molding, calcine at 220℃ for 3h, and after calcine, naturally cool to room temperature to obtain the adsorption medium.

[0050] Example 1

[0051] A continuous crystallization process for high-purity nickel nitrate hexahydrate includes the following steps:

[0052] S1. 1000g of metallic nickel was reacted with 2680g of 20wt% nitric acid in a stirred reactor at a stirring rate of 80rpm. The reaction temperature was controlled at 50℃ for 2h. Nitric acid was added dropwise at a rate of 5mL / min. After the addition was complete, the reaction was kept at the temperature for 30min. The pH at the end of the reaction was 4.0, and the initial concentration of nickel ions in the solution after the reaction was 200g / L. After the reaction, the solution was filtered with a 0.22μm filter membrane at a pressure of 0.1MPa and a temperature of 45℃ to obtain a purified solution.

[0053] S2. The purified liquid is fed into a falling film evaporator for negative pressure evaporation and concentration. The vacuum degree is controlled at -0.08MPa, the evaporation temperature is 70℃, and the evaporation rate is 50L / h to obtain a concentrated liquid with a nickel ion concentration of 400g / L. After evaporation and concentration, it is filtered while hot using a ceramic filter membrane with a pore size of 0.1μm and a filtration time of 20min to remove insoluble matter.

[0054] S3. The concentrate is fed into a crystallizer for cooling and crystallization. The cooling is a jacketed cooling system with chilled water as the cooling medium. The chilled water temperature is 10℃, the cooling rate is 2℃ / h, the crystallization temperature is 30℃, the residence time is 5h, and the stirring rate is 50rpm to obtain mother liquor and crystal slurry.

[0055] S4. The mother liquor is passed through a fixed-bed adsorption column containing the adsorption medium prepared in Preparation Example 1 for purification. The bed height of the fixed-bed adsorption column is 80 cm, the column diameter to bed height ratio is 1:5, the operating conditions are: adsorption temperature is 30℃, liquid hourly space velocity is 1 BV / h, the flow direction is top in and bottom out, and the operating pressure of the adsorption column is 0.2 MPa. After purification, the mother liquor is returned to step S2 and mixed with fresh purified liquid. The return ratio is 30% of the volume of fresh purified liquid.

[0056] S5. The crystal slurry is subjected to solid-liquid separation using a centrifuge at a speed of 3000 rpm for 10 min to obtain wet crystals. The wet crystals are then dried in a drying oven at a temperature of 50℃ and a vacuum of -0.09 MPa for 3 h to obtain high-purity nickel nitrate hexahydrate.

[0057] Example 2

[0058] A continuous crystallization process for high-purity nickel nitrate hexahydrate includes the following steps:

[0059] S1. 1200g of metallic nickel was reacted with 3414g of 25wt% nitric acid in a stirred reactor at a stirring rate of 100rpm. The reaction temperature was controlled at 55℃, and the reaction time was 2.5h. Nitric acid was added dropwise at a rate of 7.5mL / min. After the addition was complete, the reaction was kept at the temperature for 45min. The pH value at the end of the reaction was 4.5, and the initial concentration of nickel ions in the solution after the reaction was 225g / L. After the reaction, the solution was filtered with a filter membrane pore size of 0.33μm at a filtration pressure of 0.2MPa and a filtration temperature of 50℃ to obtain a purified solution.

[0060] S2. The purified liquid is fed into a falling film evaporator for negative pressure evaporation and concentration. The vacuum degree is controlled at -0.07MPa, the evaporation temperature is 75℃, and the evaporation rate is 65L / h to obtain a concentrated liquid with a nickel ion concentration of 425g / L. After evaporation and concentration, it is filtered while hot using a ceramic filter membrane with a pore size of 0.15μm and a filtration time of 25min to remove insoluble matter.

[0061] S3. The concentrate is fed into a crystallizer for cooling and crystallization. The cooling is a jacketed cooling system with chilled water as the cooling medium. The chilled water temperature is 12.5℃, the cooling rate is 3.5℃ / h, the crystallization temperature is 32.5℃, the residence time is 6h, and the stirring speed is 75rpm to obtain mother liquor and crystal slurry.

[0062] S4. The mother liquor is passed through a fixed-bed adsorption column containing the adsorption medium prepared in Preparation Example 2 for purification. The bed height of the fixed-bed adsorption column is 100 cm, the column diameter to bed height ratio is 1:6.5, and the operating conditions are: adsorption temperature is 35℃, liquid hourly space velocity is 2 BV / h, flow direction is top in and bottom out, and the operating pressure of the adsorption column is 0.3 MPa. After purification, the mother liquor is returned to step S2 and mixed with fresh purified liquid. The return ratio is 40% of the volume of fresh purified liquid.

[0063] S5. The crystal slurry is subjected to solid-liquid separation using a centrifuge at a speed of 3500 rpm for 15 min to obtain wet crystals. The wet crystals are then dried in a drying oven at a temperature of 55℃ and a vacuum of -0.08 MPa for 4 h to obtain high-purity nickel nitrate hexahydrate.

[0064] Example 3

[0065] A continuous crystallization process for high-purity nickel nitrate hexahydrate includes the following steps:

[0066] S1. 1500g of metallic nickel was reacted with 4515g of 30wt% nitric acid in a stirred reactor at a stirring rate of 120rpm. The reaction temperature was controlled at 60℃ for 3h. Nitric acid was added dropwise at a rate of 10mL / min. After the addition was complete, the reaction was maintained at the temperature for 60min. The pH at the end of the reaction was 5.0, and the initial concentration of nickel ions in the solution after the reaction was 250g / L. After the reaction, the solution was filtered with a 0.45μm filter membrane at a pressure of 0.3MPa and a temperature of 55℃ to obtain a purified solution.

[0067] S2. The purified liquid is fed into a falling film evaporator for negative pressure evaporation and concentration. The vacuum degree is controlled at -0.06MPa, the evaporation temperature is 80℃, and the evaporation rate is 80L / h to obtain a concentrated liquid with a nickel ion concentration of 450g / L. After evaporation and concentration, it is filtered while hot using a ceramic filter membrane with a pore size of 0.2μm and a filtration time of 30min to remove insoluble matter.

[0068] S3. The concentrate is fed into a crystallizer for cooling and crystallization. The cooling is a jacketed cooling system with chilled water as the cooling medium. The chilled water temperature is 15℃, the cooling rate is 5℃ / h, the crystallization temperature is 35℃, the residence time is 7h, and the stirring speed is 100rpm to obtain mother liquor and crystal slurry.

[0069] S4. The mother liquor is passed through a fixed-bed adsorption column containing the adsorption medium prepared in Preparation Example 3 for purification. The bed height of the fixed-bed adsorption column is 120 cm, the column diameter to bed height ratio is 1:8, and the operating conditions are: adsorption temperature is 40 °C, liquid hourly space velocity is 3 BV / h, flow direction is top in and bottom out, and the operating pressure of the adsorption column is 0.4 MPa. After purification, the mother liquor is returned to step S2 and mixed with fresh purified liquid. The return ratio is 50% of the volume of fresh purified liquid.

[0070] S5. The crystal slurry is subjected to solid-liquid separation using a centrifuge at a speed of 4000 rpm for 20 min to obtain wet crystals. The wet crystals are then dried in a drying oven at a temperature of 60℃ and a vacuum of -0.07 MPa for 5 h to obtain high-purity nickel nitrate hexahydrate.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Preparation Example 1 is that zirconium oxychloride octahydrate is not added; the remaining steps are the same as in Preparation Example 1.

[0073] Comparative Example 2

[0074] The difference between this comparative example and preparation example 2 is that titanium chloride is not added; the remaining steps are the same as in preparation example 2.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Preparation Example 3 is that no furfuryl methacrylate was added; the remaining steps are the same as in Preparation Example 3.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Preparation Example 1 is that allyl aniline is not added; the remaining steps are the same as in Preparation Example 1.

[0079] Comparative Example 5

[0080] The difference between this comparative example and preparation example 2 is that ferric chloride is not added; the remaining steps are the same as in preparation example 2.

[0081] Comparative Example 6

[0082] The difference between this comparative example and Example 1 is that the medium prepared in Comparative Example 1 is used instead of the medium prepared in Example 1, while the remaining steps are the same as in Example 1.

[0083] Comparative Example 7

[0084] The difference between this comparative example and Example 2 is that the medium prepared in Comparative Example 2 is used instead of the medium prepared in Example 2, while the remaining steps are the same as in Example 2.

[0085] Comparative Example 8

[0086] The difference between this comparative example and Example 3 is that the medium prepared in Comparative Example 3 is used instead of the medium prepared in Example 3, while the remaining steps are the same as in Example 3.

[0087] Comparative Example 9

[0088] The difference between this comparative example and Example 1 is that the medium prepared in Comparative Example 4 is used instead of the medium prepared in Example 1, while the remaining steps are the same as in Example 1.

[0089] Comparative Example 10

[0090] The difference between this comparative example and Example 2 is that the medium obtained in Comparative Example 5 is used instead of the medium in Preparation Example 2, while the remaining steps are the same as in Example 2.

[0091] Comparative Example 11

[0092] The difference between this comparative example and Example 3 is that step S4 is omitted, while the remaining steps are the same as in Example 3.

[0093] Weigh 18.61 g of disodium EDTA, dissolve it in deionized water, and dilute to 1000 mL. After shaking well, standardize to obtain a 0.05 mol / L EDTA standard solution for later use. Weigh 54 g of ammonium chloride, dissolve it in water, add 350 mL of concentrated ammonia, and dilute to 1000 mL to obtain an ammonia-ammonium chloride buffer solution (pH≈10) for later use. Weigh 0.2 g of ammonium purpurate and grind it with 100 g of sodium chloride to obtain an ammonium purpurate indicator for later use.

[0094] Weigh 1.0 g of nickel nitrate hexahydrate from each sample of Examples 1-3 and Comparative Examples 6-11, place them in an Erlenmeyer flask, and dissolve them in 50 mL of deionized water. Add 10 mL of ammonia-ammonium chloride buffer solution and shake well. Add 0.10 g of ammonium purpurate indicator; the solution turns yellow. Titrate with 0.05 mol / L EDTA standard solution until the solution changes from yellow to purple-red, which is the endpoint. Record the volume of EDTA consumed, V (mL). Each batch of samples was measured in triplicate, and the average value was taken. Calculate the purity P of nickel ion mass (molar mass of nickel is taken as 58.69 g / mol) and nickel nitrate hexahydrate (molar mass of nickel is taken as 290.81 g / mol) using the following formula:

[0095]

[0096]

[0097] The results are shown in Table 1:

[0098] Table 1. Nickel content results of different examples and comparative examples

[0099]

[0100] Weigh 0.5 g of each of the nickel nitrate hexahydrate samples from Examples 1-3 and Comparative Examples 6-11, place them in a 100 mL quartz beaker, add 5 mL of pure nitric acid, cover with a watch glass, and heat on a hot plate at 120 °C until the sample is completely dissolved and evaporated to near dryness, taking care to prevent splashing. Remove and cool slightly, rinse the inner wall of the beaker with 2% nitric acid solution, transfer to a 50 mL volumetric flask, dilute to volume and shake well, ready for analysis. Simultaneously prepare a blank solution. Determine the elements Fe, Zr, and Ti by mass spectrometry. Construct a standard curve using a series of standard solutions, and sequentially determine the blank solution and sample solutions, calculating the concentration of each element (μg / L). The results are shown in Table 2:

[0101] Table 2. Results of impurity content determination in different examples and comparative examples

[0102]

[0103] Weigh 10.0 g of the fresh adsorption medium used in Examples 1-3, soak it in deionized water, and then wet-pack it into the adsorption column to a bed height of approximately 20 cm. Seal both ends of the column with glass wool to prevent medium loss. Use a constant flow pump to pass the simulated mother liquor through the adsorption column from top to bottom at a speed of 2 BV / h (space velocity), maintaining a temperature of 30°C. Collect the effluent every 0.5 BV and determine the Fe content. 3+ Concentration, until the Fe in the effluent 3+ Once the concentration reaches 90% of the feed concentration (i.e., the breakthrough point), record the breakthrough volume and saturated adsorption capacity. Calculate the saturated adsorption capacity Q0 (mg Fe / g) of the fresh medium.

[0104] After adsorption saturation, the column bed was first washed with deionized water at 5 BV / h for 30 min to remove residual mother liquor. Desorption was then performed counter-currently (from bottom to top) with 0.5 mol / L hydrochloric acid solution at a flow rate of 1 BV / h, and the eluent was collected. Fe was measured every 0.5 BV. 3+ Concentration, until the Fe in the effluent 3+ The concentration is below 1 mg / L. After desorption, the column bed is flushed with deionized water at 5 BV / h until the effluent pH ≈ 7, and then set aside. Five regeneration cycles are performed. The adsorption capacity Qn and desorption rate Rn (%) are recorded for each cycle, and the regeneration efficiency ηn (%) is calculated using the following formula:

[0105]

[0106]

[0107] The results are shown in Table 3-4:

[0108] Table 3. Adsorption performance results of fresh medium

[0109]

[0110] Table 4. Regeneration Cycle Performance Results

[0111]

[0112] As shown in Table 1-2, the purity of nickel nitrate hexahydrate in Examples 1-3 is all higher than 99.6%, Fe 3+ The residue was less than 0.5 ppm, and the content of metal ions such as Zr and Ti was extremely low (<0.15 ppm). This indicates that the adsorption medium prepared by iron ion template-directed polymerization can efficiently and selectively adsorb trace iron ions in a high-concentration nickel ion mother liquor, and has almost no adsorption on the target product nickel ions.

[0113] The purity of the products in Comparative Examples 6 and 7 decreased to 98.33% and 97.86%, respectively, Fe 3+ The contents increased to 3.84 ppm and 5.26 ppm, respectively, while high concentrations of Ti (1.24 ppm) and Zr (1.19 ppm) were also detected. Zirconium and titanium are key elements constituting the inorganic phosphate framework; the absence of either component will lead to structural defects in the framework, a decrease in mesoporous surface area, and negatively impact Fe. 3+ The number of recognition sites is reduced; at the same time, the incomplete skeleton may partially dissolve or fall off in the mother liquor, resulting in the release of another metal element into the product, causing cross-contamination.

[0114] The purities of Comparative Example 8 and Comparative Example 9 were 98.64% and 98.48%, respectively, Fe 3+ The contents were 2.47 ppm and 3.12 ppm, respectively, and the residual Zr and Ti were also significantly higher than in the examples. Furfuryl methacrylate and allyl aniline provide furfuryl and aniline groups, respectively, during the polymerization process. These functional groups can react with Fe... 3+ It forms coordination sites and works in conjunction with the inorganic framework to construct specific cavities. The absence of any organic component disrupts the coordination environment of the template site, leading to the loss of Fe... 3+ The selectivity decreases, and the adsorption capacity of impurity ions weakens, causing them to remain in the mother liquor and eventually enter the product.

[0115] Comparative Example 10's product purity was only 97.54%, Fe 3+ The content was as high as 6.83 ppm, with significant Zr and Ti residues. Without a template, the polymer-inorganic hybrid framework still possessed a porous structure, but lacked specific recognition sites for Fe. 3+ The adsorption capacity is greatly reduced, and the adsorption selectivity for other metal ions is poor, resulting in a general increase in product impurities.

[0116] Comparative Example 11 had the lowest product purity (95.83%), Fe 3+The content was as high as 15.57 ppm, indicating that the impurities in the mother liquor were returned to the system directly without purification, resulting in the enrichment of iron ions and serious contamination of the product.

[0117] Table 3 shows that the fresh media in Examples 1-3 have a positive effect on Fe. 3+ The saturated adsorption capacities were 12.3, 14.6, and 16.9 mg / g, respectively, and the breakthrough volumes also increased (18.5, 21.2, and 24.8 BV). This is closely related to its preparation conditions: with the optimization of parameters such as reaction temperature, time, and crystallization pressure, the order, specific surface area, and pore volume of the mesoporous material increased, and the template site density improved, thereby enhancing the adsorption capacity for Fe. 3+ The adsorption capacity and kinetic performance were as follows. Example 3, due to the use of the highest crystallization temperature (110°C) and pressure (0.15 MPa), has a more stable framework, more regular pores, and optimal adsorption performance.

[0118] As shown in Table 4, after five adsorption-desorption cycles, the regeneration efficiencies of Examples 1-3 were 82.1%, 85.6%, and 87.6%, respectively, all remaining above 80%, indicating that the medium has good regeneration stability. The regeneration efficiency decreased slowly with increasing cycle number, possibly due to factors such as a small amount of Fe. 3+ Incomplete desorption occupies some sites; long-term use causes the pores to be blocked by trace amounts of organic matter or particles; mechanical stirring or acidic / alkaline environments cause slight collapse of the framework.

[0119] Example 3 exhibited the slowest decline in regeneration efficiency, thanks to its more robust organic-inorganic hybrid structure, which maintained high structural integrity even during multiple EDTA elutions and acid washes.

[0120] In summary, the technical solution of this invention, through a specific adsorption medium preparation method and a continuous crystallization process, can effectively improve the purity of nickel nitrate hexahydrate and reduce the impurity content. Furthermore, the adsorption medium has good adsorption and regeneration performance, and the various steps and components work together to achieve the preparation of high-purity nickel nitrate hexahydrate.

[0121] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0122] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A continuous crystallization process for high-purity nickel nitrate hexahydrate, characterized in that, Includes the following steps: S1. React metallic nickel with nitric acid to obtain a nickel nitrate solution, and then filter to obtain a purified solution; S2. The purified liquid is concentrated by negative pressure evaporation to obtain a concentrated liquid; S3. The concentrate is sent to a crystallizer for cooling and crystallization to obtain mother liquor and crystal slurry; S4. The mother liquor is passed through a fixed-bed adsorption column containing adsorption medium for purification to remove iron ions. The purified mother liquor is then returned to step S2 and mixed with fresh purified liquid. S5. The crystal slurry is subjected to solid-liquid separation to obtain wet crystals. The obtained wet crystals are dried to obtain high-purity nickel nitrate hexahydrate product.

2. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 1, characterized in that, In step S1, the reaction of metallic nickel with nitric acid is carried out with excess metallic nickel, the mass ratio of nickel to nitric acid being 1:(2.68-3.01), and the concentration of nitric acid being 20-30 wt%. The reaction temperature is controlled at 50-60℃, and the pH value at the reaction endpoint is 4.0-5.

0.

3. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 1, characterized in that, In step S2, negative pressure evaporation and concentration are carried out in a falling film evaporator, with the vacuum degree controlled at (-0.06)-(-0.08) MPa and the evaporation temperature at 70-80℃, to obtain a concentrated solution with a nickel ion concentration of 400-450 g / L; after evaporation and concentration, the solution is filtered while hot to remove insoluble matter.

4. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 1, characterized in that, In step S3, the crystallization temperature is 30-35℃, the residence time is 5-7h, and the stirring speed is 50-100rpm.

5. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 1, characterized in that, The adsorption medium in step S4 is prepared by the following steps: A1. Dissolve zirconium oxychloride octahydrate and titanium chloride in water and prepare a mixed salt solution of 0.5-0.8 mol / L under ice bath conditions, denoted as solution A; dissolve furfuryl methacrylate and allyl aniline in N,N-dimethylformamide, add ferric chloride and an initiator, and prepare solution B; dilute phosphoric acid to prepare a phosphoric acid solution of 2-3 mol / L, denoted as solution C; A2. Under nitrogen protection, solutions A and B are simultaneously added dropwise to solution C, controlling the pH of the reaction system to be 2-3; after the addition is complete, the reaction system is heated to 60-70℃ and stirred for 4-6 hours to obtain a mixture; A3. Transfer the mixture to a reaction vessel and crystallize it at 100-110℃ for 12-24 hours. After crystallization, perform solid-liquid separation, and wash, elute, and dry the obtained solid in sequence to obtain mesoporous material powder. A4. Mix mesoporous material powder with silica sol, granulate and shape it into spherical particles to obtain the adsorption medium.

6. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 1, characterized in that, The operating conditions for the fixed-bed adsorption column in step S4 are: adsorption temperature of 30-40℃, liquid hourly space velocity of 1-3 BV / h, and flow direction of top inlet and bottom outlet.

7. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 5, characterized in that, In step A1, the mass ratio of zirconium oxychloride octahydrate to titanium chloride is 1.70:1, the mass ratio of furfuryl methacrylate to allyl aniline is (3.5-4.0):1, the amount of ferric chloride added is 28-33% of the total mass of furfuryl methacrylate and allyl aniline, and the initiator is selected from one of benzoyl peroxide, azobisisobutyronitrile, or dilauryl peroxide, and its addition amount is 1.2-2.5% of the total mass of furfuryl methacrylate and allyl aniline.

8. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 5, characterized in that, In step A3, template elution involves soaking the sample in a 0.1-0.5 mol / L ethylenediaminetetraacetic acid solution for 2-6 hours, repeating this process until Fe is undetectable in the eluent. 3+ Until the ions are reached.

9. The continuous crystallization process for high-purity nickel nitrate hexahydrate according to claim 5, characterized in that, In step A4, the granulation produces spherical particles with a diameter of 0.5-1.0 mm, which are then calcined at 180-220℃ for 1-3 hours after molding.

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