A composite seed for treating high-calcium low-magnesium wastewater, a preparation method and a core seed granulation process

Abstract

The present disclosure relates to the technical field of wastewater treatment, in particular to a composite seed for treating high-calcium and low-magnesium wastewater, a preparation method and a core crystal granulation process. The composite seed takes a zinc-based MOF as a matrix material and is organically modified by branch-connection sodium alginate, effectively strengthening the synchronous induction and enrichment of calcium and magnesium ions, thereby realizing efficient synchronous removal of calcium and magnesium ions in high-calcium and low-magnesium wastewater and improving the wastewater reuse efficiency. The preparation method of the composite seed is simple in process and mild in reaction conditions, and the obtained composite seed has high purity and does not need further purification.

Description

Technical Field

[0001] This disclosure relates to the field of wastewater treatment technology, and in particular to a composite seed crystal for treating high-calcium and low-magnesium wastewater, its preparation method, and its nucleation granulation process. Background Technology

[0002] Circulating cooling water accounts for approximately 80%-90% of total industrial water consumption. Recycling directly improves water utilization and saves water resources. However, with the increasing number of times industrial circulating cooling water is reused, salts in the water become concentrated. The higher the concentration, the higher the concentration of hardness ions such as calcium and magnesium, leading to scale formation and accumulation in pipes, especially on heat exchange surfaces. Scale accumulation reduces the flow area of ​​the heat exchange space, causing a sharp increase in pressure drop within the equipment and affecting normal heat transfer, resulting in decreased heat exchange efficiency and wasted energy. Furthermore, corrosion easily occurs under the scale layer, ultimately leading to pipe damage. Common water treatment technologies, such as chemical precipitation, involve adding a precipitant to water containing calcium and magnesium ions, causing them to become insoluble compounds that precipitate out of the water. This method is convenient and widely adaptable, but its operating cost is high when dealing with large volumes of water. In addition, this method generates a large amount of loose, high-moisture sludge, requiring subsequent plate and frame filtration processes, which significantly increases the floor space required.

[0003] To address the limitations of traditional technologies, nucleogranulation technology has emerged. This technology involves adding seed crystals and a precipitant to the nucleogranulation reactor. Under the control of hydrodynamic and hydrochemical parameters, it enhances the contact mass transfer between the seed crystals and scale-forming ions, inducing them to adhere and precipitate on the seed crystal surface. However, since calcium and magnesium ions coexist in circulating cooling water, existing commercially available seed crystals are insufficient to simultaneously induce calcium and magnesium precipitation. When using this technology, magnesium ion residues in the water or excessively high turbidity in the effluent often result. Therefore, to address these issues, providing a specialized seed crystal suitable for treating high-calcium, low-magnesium circulating cooling water, and achieving simultaneous and enhanced removal of calcium and magnesium from the water, has become an urgent problem to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this disclosure provides a composite seed crystal for treating high-calcium, low-magnesium wastewater, its preparation method, and a nucleation granulation process. The composite seed crystal uses zinc-based MOF as the matrix material and undergoes organic modification, specifically grafting sodium alginate, to effectively enhance the simultaneous induction and enrichment of calcium and magnesium ions. This achieves efficient and simultaneous removal of calcium and magnesium ions from high-calcium, low-magnesium wastewater, thereby improving wastewater reuse efficiency.

[0005] In a first aspect, this disclosure provides a composite seed crystal for treating high-calcium, low-magnesium wastewater, the composite seed crystal comprising a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

[0006] This disclosure uses zinc-based MOF as the matrix material and obtains a special composite seed for treating high-calcium, low-magnesium wastewater by surface grafting sodium alginate. On one hand, the crystal structure of the zinc-based MOF matrix material in the obtained composite seed is similar to that of magnesium hydroxide nuclei, effectively reducing the nucleation energy barrier of magnesium hydroxide on the composite seed surface. Simultaneously, the active sites on the composite seed surface enhance the induced enrichment of low-concentration magnesium ions, thereby strengthening the nucleation and growth of magnesium hydroxide. On the other hand, the surface of the obtained composite seed is rich in hydroxyl and carboxyl groups, which can efficiently induce bonding of calcium ions in the water, causing them to accumulate on the composite seed surface. Under the action of a precipitant, calcium carbonate is formed and adheres to the composite seed surface, forming dense granules. Through the above improvements, the composite seed described in this disclosure achieves simultaneous and efficient removal of calcium and magnesium from high-calcium, low-magnesium wastewater, which is beneficial for industrial application.

[0007] The following are preferred technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.

[0008] As a preferred technical solution of this disclosure, in the composite seed crystal, the mass ratio of the zinc-based MOF matrix material to the sodium alginate is 1:(0.2-1), such as 1:0.2, 1:0.4, 1:0.6, 1:0.8 or 1:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0009] As a preferred technical solution of this disclosure, the composite seed crystal is in the form of granules, and the particle size of the composite seed crystal is 0.25-1mm, such as 0.25mm, 0.3mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0010] Secondly, this disclosure provides a method for preparing composite seed crystals as described in the first aspect, the method comprising the following steps:

[0011] (1) A composite solution was obtained by mixing zinc-based MOF matrix material with sodium alginate, alkaline compound and water;

[0012] (2) The composite solution obtained in step (1) is added dropwise to an ethanol aqueous solution to form small particles. The resulting small particles are the composite seed crystals used to treat high-calcium and low-magnesium wastewater.

[0013] The method for preparing the composite seed crystals described in this disclosure is simple, the reaction conditions are mild, and the resulting composite seed crystals have high purity and do not require further purification.

[0014] As a preferred technical solution of this disclosure, the preparation method of the zinc-based MOF matrix material in step (1) includes: mixing amide ligands, carboxylic acid ligands, zinc salts, alkaline catalysts and organic solvents and reacting them, and then performing solid-liquid separation to obtain the zinc-based MOF matrix material;

[0015] Preferably, the amide ligand comprises one or more of N,N-dimethylformamide, N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine or N,N'-bis(3-methyl-2-amino-benzoyl)1,3-propanediamine, such as a combination of N,N-dimethylformamide and N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine, or a combination of N,N-dimethylformamide and N,N'-bis(3-methyl-2-amino-benzoyl)1,3-propanediamine, etc.

[0016] Preferably, the carboxylic acid ligand includes one or more of phthalic acid, tartaric acid, or malonic acid, such as a combination of phthalic acid and tartaric acid, or a combination of phthalic acid, tartaric acid, and malonic acid.

[0017] Preferably, the zinc salt includes one or more of zinc acetate dihydrate, zinc chloride, or zinc nitrate hexahydrate, such as a combination of zinc acetate dihydrate and zinc chloride, or a combination of zinc chloride and zinc nitrate hexahydrate.

[0018] Preferably, the alkaline catalyst comprises one or more of triethylamine, tetrahydropyridine, or trimethylamine, such as a combination of triethylamine and tetrahydropyridine, or a combination of triethylamine and trimethylamine, etc.

[0019] Preferably, the organic solvent includes ethanol and / or propanol.

[0020] As a preferred technical solution of this disclosure, the mass ratio of the amide ligand, the carboxylic acid ligand, the zinc salt, and the alkaline catalyst is 1:(0.5-5):(0.5-5):(5-15), for example, 1:0.5:0.5:5, 1:1:1:8, 1:4:5:10, 1:2:5:15, or 1:5:5:15, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In this disclosure, a reasonable ratio of raw materials helps to improve the overall performance of zinc-based MOF matrix materials. Excessive or insufficient addition of any raw material will affect the ability of the composite seed crystals to enrich and capture calcium and magnesium ions in water, thereby further limiting the heterogeneous nucleation efficiency of calcium and magnesium ions on the surface of the composite seed crystals.

[0022] Preferably, the reaction is first stirred.

[0023] Preferably, the rotation speed of the first stirring is 500-1000 r / min, such as 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min or 1000 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] In this disclosure, an appropriate stirring speed helps the raw materials to fully contact and react, and to transfer mass. If the stirring speed is too low, the raw materials will agglomerate, reducing the utilization rate of the raw materials. If the stirring speed is too high, the formed product will be broken up, affecting its ability to induce the enrichment of calcium and magnesium ions.

[0025] Preferably, the reaction time is 6-12 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] In this disclosure, controlling a reasonable reaction time helps to ensure the quality of the obtained composite seed crystals. If the reaction time is too short, the reaction will be incomplete, the resulting product crystal structure will be unstable, and the enrichment ability of calcium and magnesium ions will be weakened; if the reaction time is too long, a large number of by-products will be generated, leading to a decrease in the purity of the target product.

[0027] As a preferred technical solution of this disclosure, the preparation method of the zinc-based MOF matrix material in step (1) further includes: washing and drying the obtained zinc-based MOF matrix material in sequence.

[0028] Preferably, the washing includes a first wash and a second wash performed sequentially.

[0029] Preferably, the amide ligand in the first wash is used as a detergent.

[0030] Preferably, the organic solvent used in the second washing process is a detergent.

[0031] As a preferred technical solution of this disclosure, the alkaline compound in step (1) includes sodium hydroxide.

[0032] Preferably, the mass ratio of sodium alginate, zinc-based MOF matrix material, alkaline compound and water in step (1) is 1:(1-5):(4-8):(100-200), for example 1:1:4:100, 1:3:7:150, 1:2:4:120, 1:5:8:200, 1:4:6:140 or 1:3:6:150, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] As a preferred technical solution of this disclosure, in the ethanol-water solution described in step (2), the mass ratio of ethanol to water is 1:(5-10), such as 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the dripping rate in step (2) is (5-10) mL / min, such as 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min or 10 mL / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, a second stirring is performed during the dripping process described in step (2).

[0036] Preferably, the second stirring speed is 200-600 r / min, such as 200 r / min, 300 r / min, 400 r / min, 500 r / min or 600 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Thirdly, this disclosure provides a nucleus crystal granulation process for treating high-calcium and low-magnesium wastewater, wherein the nucleus crystal granulation process uses composite seed crystals as described in the first aspect or composite seed crystals prepared by the preparation method described in the second aspect.

[0038] The nucleus crystal granulation process includes the following steps:

[0039] (1) Fill the composite seed crystals into the nucleation granulation reactor;

[0040] (2) High-calcium and low-magnesium wastewater and precipitant are introduced into the lower part of the nuclear crystal granulation reactor to make the composite seed crystals fluidized and react. The regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granules obtained after the reaction are discharged from the bottom of the nuclear crystal granulation reactor.

[0041] In the high-calcium, low-magnesium wastewater, the concentration of calcium ions is not less than 1000 mg / L, such as 1000 mg / L, 1500 mg / L, 2000 mg / L, 3000 mg / L, or 4000 mg / L; the concentration of magnesium ions does not exceed 100 mg / L, such as 10 mg / L, 20 mg / L, 50 mg / L, 60 mg / L, 80 mg / L, or 100 mg / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0042] Preferably, the filling height of the composite seed crystal in step (1) is 10%-30% of the height of the nucleus granulation reactor, such as 10%, 15%, 20%, 25% or 30%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the precipitant in step (2) is introduced in the form of a solution, and the precipitant includes sodium carbonate and sodium hydroxide.

[0044] Preferably, the mass ratio of sodium carbonate to sodium hydroxide is (2-9):1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this disclosure, the specific amount of high-calcium, low-magnesium wastewater and precipitant introduced can be determined and adjusted by those skilled in the art based on the concentration of the wastewater to be treated, the concentration of the precipitant, the hydraulic conditions, and the water chemical conditions.

[0046] The technical solution provided in this disclosure has the following advantages compared with the prior art:

[0047] (1) The composite seed crystal described in this disclosure uses zinc-based MOF as the matrix material and is modified organically, namely by grafting sodium alginate, which effectively enhances the synchronous induction and enrichment of calcium and magnesium ions, thereby achieving efficient synchronous removal of calcium and magnesium ions from high-calcium and low-magnesium wastewater and improving the wastewater reuse efficiency.

[0048] (2) The preparation method of the composite seed crystal described in this disclosure is simple, the reaction conditions are mild, and the obtained composite seed crystal has high purity and does not require further purification. Attached Figure Description

[0049] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0050] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 The infrared spectrum of the composite seed crystals used for treating high-calcium and low-magnesium wastewater as described in Embodiment 1 of this disclosure.

[0052] Figure 2 The image shows the XRD pattern of the composite seed crystals for treating high-calcium, low-magnesium wastewater as described in Embodiment 1 of this disclosure. Detailed Implementation

[0053] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0054] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0055] Example 1

[0056] This embodiment provides a composite seed crystal for treating high-calcium and low-magnesium wastewater, a preparation method, and a nucleation granulation process. The composite seed crystal includes a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

[0057] Furthermore, in the composite seed crystal, the mass ratio of the zinc-based MOF matrix material to the sodium alginate is 1:1.

[0058] Furthermore, the composite seed crystal is in the form of granules, and the particle size of the composite seed crystal is 1 mm.

[0059] The preparation method includes the following steps:

[0060] (1) N,N-dimethylformamide, zinc acetate dihydrate and triethylamine were dissolved in ethanol at a mass ratio of 1:0.5:0.5:5. The stirring speed was controlled at 500 r / min and the reaction was carried out for 6 h. Then the mixture was centrifuged at 5000 r / min. The resulting solid was washed with N,N-dimethylformamide and ethanol in sequence and then dried to obtain zinc-based MOF matrix material.

[0061] (2) Sodium alginate, zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water are mixed in a mass ratio of 1:1:4:200 to obtain a composite solution;

[0062] (3) The composite solution obtained in step (2) is added dropwise to an ethanol aqueous solution (the mass ratio of ethanol to water is 1:5) at a rate of 5 mL / min to form small particles with a particle size of 0.5 mm. The obtained small particles are the composite seed crystals used to treat high-calcium and low-magnesium wastewater.

[0063] The infrared spectrum of the obtained composite seed crystal is as follows: Figure 1 As shown, its XRD pattern is as follows: Figure 2 As shown. From Figure 1It can be seen that at approximately 1010cm -1 1430cm -1 1605cm -1 And 3350cm -1 Peaks appear at these locations, corresponding to the stretching vibration peaks of CO (carbon-oxygen bond), -COO- (ester group), C=O (carbonyl group), and -OH (hydroxyl group), respectively; from Figure 2 It can be seen that peaks are present at 19.1°, 32.4°, and 45.3°, corresponding to different crystal planes of Zn-MOF, respectively. Figure 1 and Figure 2 All of these indicate that the synthesis of the composite seed crystal was successful.

[0064] The nucleus crystal granulation process includes:

[0065] (1) The composite seed crystals are filled into the nucleation granulation reactor, and the filling height is 15% of the height of the nucleation granulation reactor;

[0066] (2) 70 L / h of high-calcium, low-magnesium wastewater (calcium ion concentration of 500 mg / L, magnesium ion concentration of 60 mg / L, pH = 7.2) and 5 L / h of precipitant solution (sodium carbonate concentration of 1500 mg / L and sodium hydroxide concentration of 600 mg / L) are introduced from the lower end of the side wall of the nucleus crystal granulation reactor to make the composite seed crystals fluidized and react. The regenerated water obtained after the reaction is discharged from the top of the nucleus crystal granulation reactor, and the granules obtained after the reaction are discharged from the bottom of the nucleus crystal granulation reactor.

[0067] Example 2

[0068] This embodiment provides a composite seed crystal for treating high-calcium and low-magnesium wastewater, a preparation method, and a nucleation granulation process. The composite seed crystal includes a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

[0069] Furthermore, in the composite seed crystal, the mass ratio of the zinc-based MOF matrix material to the sodium alginate is 1:0.33.

[0070] Furthermore, the composite seed crystal is in the form of granules, and the particle size of the composite seed crystal is 1 mm.

[0071] The preparation method includes the following steps:

[0072] (1) N,N-dimethylformamide, zinc acetate dihydrate and triethylamine were dissolved in ethanol at a mass ratio of 1:3:3:10. The stirring speed was controlled at 500 r / min and the reaction was carried out for 8 h. Then the mixture was centrifuged at 8000 r / min. The resulting solid was washed with N,N-dimethylformamide and ethanol in sequence and then dried to obtain zinc-based MOF matrix material.

[0073] (2) Sodium alginate, zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water are mixed in a mass ratio of 1:3:6:200 to obtain a composite solution;

[0074] (3) The composite solution obtained in step (2) is added dropwise to an ethanol aqueous solution (the mass ratio of ethanol to water is 1:8) at a rate of 8 mL / min to form small particles with a particle size of 0.3 mm. The obtained small particles are the composite seed crystals used to treat high-calcium and low-magnesium wastewater.

[0075] The nucleus crystal granulation process includes:

[0076] (1) The composite seed crystals are filled into the nucleus crystal granulation reactor, and the filling height is 20% of the height of the nucleus crystal granulation reactor;

[0077] (2) 70 L / h of high-calcium, low-magnesium wastewater (calcium ion concentration of 800 mg / L, magnesium ion concentration of 80 mg / L, pH = 7.2) and 3 L / h of precipitant solution (sodium carbonate concentration of 2500 mg / L and sodium hydroxide concentration of 1000 mg / L) are introduced from the lower end of the side wall of the nucleus crystal granulation reactor to make the composite seed crystals fluidized and react. The regenerated water obtained after the reaction is discharged from the top of the nucleus crystal granulation reactor, and the granules obtained after the reaction are discharged from the bottom of the nucleus crystal granulation reactor.

[0078] Example 3

[0079] This embodiment provides a composite seed crystal for treating high-calcium and low-magnesium wastewater, a preparation method, and a nucleation granulation process. The composite seed crystal includes a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

[0080] Furthermore, in the composite seed crystal, the mass ratio of the zinc-based MOF matrix material to the sodium alginate is 1:0.2.

[0081] Furthermore, the composite seed crystal is in the form of granules, and the particle size of the composite seed crystal is 1 mm.

[0082] The preparation method includes the following steps:

[0083] (1) N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine, malonic acid, zinc nitrate hexahydrate and trimethylamine were dissolved in ethanol at a mass ratio of 1:5:5:15. The stirring speed was controlled at 500 r / min and the reaction was carried out for 12 h. Then the mixture was centrifuged at 10000 r / min. The resulting solid was washed with N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine and ethanol in sequence, and then dried to obtain zinc-based MOF matrix material.

[0084] (2) Sodium alginate, zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water are mixed in a mass ratio of 1:5:8:200 to obtain a composite solution;

[0085] (3) The composite solution obtained in step (2) is added dropwise to an ethanol aqueous solution (the mass ratio of ethanol to water is 1:10) at a rate of 10 mL / min to form small particles with a particle size of 0.25 mm. The obtained small particles are the composite seed crystals used to treat high-calcium and low-magnesium wastewater.

[0086] The nucleus crystal granulation process includes:

[0087] (1) The composite seed crystals are filled into the nucleus crystal granulation reactor, and the filling height is 30% of the height of the nucleus crystal granulation reactor;

[0088] (2) 70 L / h of high-calcium, low-magnesium wastewater (calcium ion concentration of 1000 mg / L, magnesium ion concentration of 100 mg / L, pH = 7.2) and 2.5 L / h of precipitant solution (sodium carbonate concentration of 3000 mg / L and sodium hydroxide concentration of 350 mg / L) are introduced from the lower end of the side wall of the nucleus crystal granulation reactor to make the composite seed crystals fluidized and react. The regenerated water obtained after the reaction is discharged from the top of the nucleus crystal granulation reactor, and the granules obtained after the reaction are discharged from the bottom of the nucleus crystal granulation reactor.

[0089] Example 4

[0090] This embodiment provides a method for preparing composite seed crystals for treating high-calcium and low-magnesium wastewater and a nucleation granulation process. The preparation method is the same as that in Example 3, except that the mass ratio of N,N-dimethylformamide, zinc acetate dihydrate phthalate and triethylamine in step (1) is 5:5:5:15.

[0091] The nucleus crystal granulation process is the same as that in Example 3, except that the composite seed crystal prepared in this example is used instead of the composite seed crystal in Example 3.

[0092] Example 5

[0093] This embodiment provides a method for preparing composite seed crystals for treating high-calcium and low-magnesium wastewater and a nucleation granulation process. The preparation method is the same as that in Example 3, except that the mass ratio of N,N-dimethylformamide, zinc acetate dihydrate and triethylamine in step (1) is 1:10:5:15.

[0094] The nucleus crystal granulation process is the same as that in Example 3, except that the composite seed crystal prepared in this example is used instead of the composite seed crystal in Example 3.

[0095] Example 6

[0096] This embodiment provides a method for preparing composite seed crystals for treating high-calcium and low-magnesium wastewater and a nucleation granulation process. The preparation method is the same as that in Example 3, except that the mass ratio of N,N-dimethylformamide, zinc acetate dihydrate phthalate and triethylamine in step (1) is 1:5:10:15.

[0097] The nucleus crystal granulation process is the same as that in Example 3, except that the composite seed crystal prepared in this example is used instead of the composite seed crystal in Example 3.

[0098] Comparative Example 1

[0099] This comparative example provides a commercial seed crystal and a nucleus crystal granulation process, wherein the commercial seed crystal is anorthite.

[0100] The nucleus crystal granulation process is the same as that in Example 1, except that commercial seed crystals are used instead of the composite seed crystals described in Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a seed crystal and a nucleus crystal granulation process, wherein the seed crystal is the zinc-based MOF matrix material prepared in Example 1.

[0103] The nucleus crystal granulation process is the same as that in Example 1, except that the seed crystals of this comparative example are used instead of the composite seed crystals in Example 1.

[0104] The concentrations of calcium and magnesium ions in the reclaimed water obtained in Examples 1-6 and Comparative Examples 1-2 were measured, and the removal rates were calculated. The results are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As can be seen from Table 1, the composite seed crystals described in this disclosure can achieve efficient treatment of high-calcium and low-magnesium wastewater in the nucleus crystal granulation process in Examples 1-6. The calcium ion removal rate in the reclaimed water after treatment is over 93.9%, and the magnesium ion removal rate is over 85.3%. This disclosure further improves the effect of the composite seed crystals by controlling the raw material ratio for preparing the zinc-based MOF matrix material, so that the calcium ion removal rate in the reclaimed water after treatment is over 98.4%, and the magnesium ion removal rate is over 92%.

[0109] Comparative Example 1 uses existing commercially available seed crystals, which have poor removal effects on calcium and magnesium ions.

[0110] In Comparative Example 2, only zinc-based MOF matrix material was used as seed crystal without surface modification, which also failed to efficiently and simultaneously remove calcium and magnesium ions from the water.

[0111] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0112] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing composite seed crystals for treating high-calcium, low-magnesium wastewater, characterized in that, The preparation method includes the following steps: (1) A composite solution was obtained by mixing the zinc-based MOF matrix material with sodium alginate, an alkaline compound and water; (2) The composite solution obtained in step (1) is added dropwise to an ethanol aqueous solution to form small granules. The resulting small granules are the composite seed crystals used to treat high-calcium and low-magnesium wastewater. The preparation method of the zinc-based MOF matrix material includes: mixing and reacting an amide ligand, a carboxylic acid ligand, a zinc salt, an alkaline catalyst, and an organic solvent; and performing solid-liquid separation after the reaction to obtain the zinc-based MOF matrix material; wherein the mass ratio of the amide ligand, the carboxylic acid ligand, the zinc salt, and the alkaline catalyst is 1:(0.5-5):(0.5-5):(5-15); In the high-calcium, low-magnesium wastewater, the concentration of calcium ions is not less than 1000 mg / L, and the concentration of magnesium ions is not more than 100 mg / L.

2. The preparation method according to claim 1, characterized in that, The amide ligands include one or more of N,N-dimethylformamide, N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine or N,N'-bis(3-methyl-2-amino-benzoyl)1,3-propanediamine; The carboxylic acid ligands include one or more of phthalic acid, tartaric acid, or malonic acid. The zinc salt includes one or more of zinc acetate dihydrate, zinc chloride, or zinc nitrate hexahydrate; The alkaline catalyst includes one or more of triethylamine, tetrahydropyridine, or trimethylamine; The organic solvents include ethanol and / or propanol.

3. The preparation method according to claim 1, characterized in that, During the preparation of the zinc-based MOF matrix material, a first stirring is performed during the reaction process; The first stirring speed is 500-1000 r / min; The reaction time is 6-12 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The method for preparing the zinc-based MOF matrix material further includes washing and drying the obtained zinc-based MOF matrix material sequentially.

5. The preparation method according to claim 4, characterized in that, The washing process includes a first wash and a second wash performed sequentially. The first wash uses the amide ligand as a detergent; The second washing process uses the organic solvent as the detergent.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The alkaline compound in step (1) includes sodium hydroxide.

7. The preparation method according to any one of claims 1 to 3, characterized in that, In step (1), the mass ratio of sodium alginate, zinc-based MOF matrix material, alkaline compound and water is 1:(1-5):(4-8):(100-200).

8. The preparation method according to any one of claims 1 to 3, characterized in that, In step (2), the mass ratio of ethanol to water in the ethanol-water solution is 1:(5-10).

9. The preparation method according to any one of claims 1 to 3, characterized in that, The dripping rate in step (2) is (5-10) mL / min.

10. The preparation method according to any one of claims 1 to 3, characterized in that, During the dripping process described in step (2), a second stirring is performed; the speed of the second stirring is 200-600 r / min.

11. A composite seed crystal for treating high-calcium, low-magnesium wastewater, prepared by the method according to any one of claims 1 to 10, characterized in that, The composite seed crystals include a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

12. The composite seed crystal according to claim 11, characterized in that, In the composite seed crystal, the mass ratio of the zinc-based MOF matrix material to the sodium alginate is 1:(0.2-1).

13. The composite seed crystal according to claim 11, characterized in that, The composite seed crystals are granular, and the particle size of the composite seed crystals is 0.25-1 mm.

14. A nucleus crystal granulation process for treating high-calcium, low-magnesium wastewater, characterized in that, The nucleus crystal granulation process is carried out using the composite seed crystals prepared by the preparation method as described in any one of claims 1 to 10 or the composite seed crystals as described in any one of claims 11 to 13; The nucleus crystal granulation process includes the following steps: (1) The composite seed crystals are filled into the nucleus crystal granulation reactor; (2) High-calcium and low-magnesium wastewater and precipitant are introduced into the lower part of the nuclear crystal granulation reactor to make the composite seed crystals fluidized and react. The regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granules obtained after the reaction are discharged from the bottom of the nuclear crystal granulation reactor. In the high-calcium, low-magnesium wastewater, the concentration of calcium ions is not less than 1000 mg / L and the concentration of magnesium ions is not more than 100 mg / L.

15. The nucleus crystal granulation process according to claim 14, characterized in that, The filling height of the composite seed crystal in step (1) is 10%-30% of the height of the nucleus granulation reactor.

16. The nucleus crystal granulation process according to claim 14, characterized in that, In step (2), the precipitant is introduced in the form of a solution, and the precipitant includes sodium carbonate and sodium hydroxide.

17. The nucleus crystal granulation process according to claim 16, characterized in that, The mass ratio of sodium carbonate to sodium hydroxide is (2-9):1.

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