Composite seed crystal for treating high-calcium low-magnesium wastewater, preparation method and nucleation granulation process

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a composite seed crystal for treating high-calcium and low-magnesium wastewater, a preparation method and a nucleation granulation process, the composite seed crystal takes zinc-based MOF as a base material, and through organic modification, namely grafting of sodium alginate, the synchronous induction enrichment effect on calcium and magnesium ions is effectively enhanced, and the high-calcium and low-magnesium wastewater is obtained. Therefore, efficient and synchronous removal of calcium and magnesium ions in high-calcium and low-magnesium type wastewater is realized, and the wastewater recycling efficiency is improved; the preparation method of the composite seed crystal is simple in process and mild in reaction condition, and the obtained composite seed crystal is high in purity and does not need to be further purified.

Description

Technical Field

[0001] The present disclosure relates to the technical field of wastewater treatment, and in particular to a composite crystal seed, a preparation method and a core crystal granulation process for treating high-calcium and low-magnesium type wastewater. Background Art

[0002] The amount of circulating cooling water accounts for about 80%-90% of the total industrial water consumption. Recycling can directly improve water utilization and save water resources. However, as the number of times industrial circulating cooling water is reused increases, the salts in the water are concentrated. The higher the concentration, the higher the concentration of hardness ions such as calcium and magnesium in the water, which leads to the formation of scale and enrichment in the pipeline, especially on the heat exchange surface. The enrichment of scale reduces the flow area of ​​the heat exchange space, resulting in a sharp increase in the pressure drop in the equipment, while affecting the normal heat transfer, reducing the heat exchange efficiency of the equipment and wasting energy; in addition, corrosion is prone to occur under the scale layer, eventually leading to damage to the pipeline. Commonly used water treatment technologies such as chemical precipitation add precipitants to water containing calcium and magnesium ions to turn them into insoluble compounds that precipitate from the water; this method is easy to operate and has wide adaptability, but the operating cost is high when the water volume is large; in addition, this method will form a large amount of loose sludge with high water content, which needs to be coupled with the subsequent plate and frame filter press process, which also greatly increases the floor space.

[0003] In view of the limitations of traditional technology, nuclear crystal granulation technology came into being. This technology adds seeds and precipitants to the nuclear crystal granulation reactor, and under the control of hydrodynamic and hydrochemical parameters, strengthens the contact and mass transfer between seeds and scaling ions, and induces them to attach and precipitate on the surface of seeds. However, due to the simultaneous presence of calcium and magnesium ions in circulating cooling water, the existing commercial seeds are not sufficient to induce calcium and magnesium to precipitate simultaneously. When this technology is used, it often causes residual magnesium ions in the water or excessive increase in effluent turbidity. Therefore, in view of the above problems, how to provide a special seed suitable for treating high-calcium and low-magnesium circulating cooling water to achieve the simultaneous enhanced removal of calcium and magnesium in the water has become an urgent problem to be solved. Summary of the invention

[0004] In order to solve the above technical problems, the present disclosure provides a composite crystal seed, a preparation method and a nuclear crystal granulation process for treating high-calcium and low-magnesium wastewater. The composite crystal seed uses a zinc-based MOF as a matrix material and is organically modified, i.e., grafted with sodium alginate, to effectively enhance the synchronous induced enrichment of calcium and magnesium ions, thereby achieving efficient synchronous removal of calcium and magnesium ions in high-calcium and low-magnesium wastewater and improving the wastewater reuse efficiency.

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

[0006] The present invention uses zinc-based MOF as a matrix material, and obtains a special composite seed for treating high-calcium and low-magnesium wastewater by grafting sodium alginate on the surface. On the one hand, in the obtained special composite seed, the crystal structure of the zinc-based MOF matrix material is similar to the magnesium hydroxide nucleus, which can effectively reduce the nucleation barrier of magnesium hydroxide on the surface of the composite seed; at the same time, the active sites on the surface of the composite seed strengthen 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 the calcium ions in the bonded water body, enrich them on the surface of the composite seed, and form calcium carbonate attached to the surface of the composite seed under the action of the precipitant to form a dense granulation body. The composite seed described in the present invention realizes the simultaneous and efficient removal of calcium and magnesium in high-calcium and low-magnesium wastewater through the above-mentioned improvements, which is conducive to industrial application.

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

[0008] As a preferred technical solution of the present 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), for example, 1:0.2, 1:0.4, 1:0.6, 1:0.8 or 1:1, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0009] As a preferred technical solution of the present invention, the composite crystal seeds are in granular form, and the particle size of the composite crystal seeds is 0.25-1mm, for example, 0.25mm, 0.3mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1mm, etc., but are not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0010] In a second aspect, the present disclosure provides a method for preparing the composite seed crystal according to the first aspect, the preparation method comprising the following steps:

[0011] (1) mixing a zinc-based MOF matrix material with sodium alginate, an alkaline compound and water to obtain a composite solution;

[0012] (2) adding the composite solution obtained in step (1) dropwise into an ethanol aqueous solution to form granular balls, wherein the granular balls obtained are the composite crystal seeds for treating high-calcium and low-magnesium wastewater.

[0013] The preparation method of the composite crystal seeds disclosed in the present invention has a simple process, mild reaction conditions, and the obtained composite crystal seeds have high purity and do not require further purification.

[0014] As a preferred technical solution of the present disclosure, the preparation method of the zinc-based MOF matrix material in step (1) comprises: mixing and reacting an amide-type ligand, a carboxylic acid-type ligand, a zinc salt, an alkaline catalyst and an organic solvent, and performing solid-liquid separation after the reaction to obtain a zinc-based MOF matrix material;

[0015] Preferably, the amide-type ligand includes 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-propylenediamine, for example, a combination of N,N-dimethylformamide and N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine, a combination of N,N-dimethylformamide and N,N'-bis(3-methyl-2-amino-benzoyl)1,3-propylenediamine, and the like.

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

[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, a combination of zinc chloride and zinc nitrate hexahydrate, and the like.

[0018] Preferably, the basic catalyst includes one or more of triethylamine, tetrahydropyridine or trimethylamine, such as a combination of triethylamine and tetrahydropyridine, a combination of triethylamine and trimethylamine, and the like.

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

[0020] As a preferred technical solution of the present invention, 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, and other unlisted values ​​within the range are also applicable.

[0021] In the present disclosure, a reasonable raw material ratio helps to improve the comprehensive performance of the zinc-based MOF matrix material. Excessive or insufficient addition of any raw material will affect the ability of the composite seed 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.

[0022] Preferably, a first stirring is performed during the reaction.

[0023] Preferably, the first stirring rotation speed is 500-1000 r / min, for example 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, and other unlisted values ​​within the range are also applicable.

[0024] In the present disclosure, an appropriate stirring speed is conducive to sufficient contact reaction and mass transfer between the raw materials; if the stirring speed is too low, it will cause the raw materials to aggregate, thereby reducing the utilization rate of the raw materials; if it is too high, the formed products will be broken up, affecting their induced enrichment of calcium and magnesium ions.

[0025] Preferably, the reaction time is 6-12 h, for example 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] In the present 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 crystal structure of the formed product will be unstable, and the enrichment ability of calcium and magnesium ions will be weakened; if the reaction time is too long, a large amount of by-products will be generated, resulting in a decrease in the purity of the target product.

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

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

[0029] Preferably, the first washing uses the amide-type ligand as a detergent.

[0030] Preferably, the second washing uses the organic solvent as a washing agent.

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

[0032] Preferably, in step (1), the mass ratio of the sodium alginate, the zinc-based MOF matrix material, the alkaline compound and the water 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, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0033] As a preferred technical solution of the present invention, in the ethanol-water solution of step (2), the mass ratio of ethanol to water is 1:(5-10), for example 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the dripping speed in step (2) is (5-10) mL / min, for example 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min or 10 mL / min, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0035] Preferably, a second stirring is performed during the dropwise adding in step (2).

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

[0037] In a third aspect, the present disclosure provides a nuclear crystal granulation process for treating high-calcium and low-magnesium type wastewater, wherein the nuclear crystal granulation process is carried out using the composite crystal seeds as described in the first aspect or the composite crystal seeds prepared by the preparation method as described in the second aspect;

[0038] The core crystal granulation process comprises the following steps:

[0039] (1) filling the composite seed crystal into a nuclear crystal granulation reactor;

[0040] (2) introducing high-calcium and low-magnesium wastewater and a precipitant from the lower part of the nuclear crystal granulation reactor to fluidize the composite seed crystals and cause a reaction, wherein the regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor;

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

[0042] Preferably, the filling height of the composite seed crystals in step (1) is 10%-30% of the height of the nuclear crystal granulation reactor, for example 10%, 15%, 20%, 25% or 30%, etc., but is not limited to the listed values, and 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 comprises sodium carbonate and sodium hydroxide.

[0044] Preferably, the mass ratio of the sodium carbonate to the 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, and other unlisted values ​​within the range are also applicable.

[0045] In the present disclosure, those skilled in the art can determine and adjust the specific introduction amount of high-calcium, low-magnesium wastewater and precipitant according to the concentration of the wastewater to be treated, the concentration of the precipitant, hydraulic conditions, and water chemical conditions.

[0046] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

[0047] (1) The composite crystal seeds disclosed in the present invention use zinc-based MOF as the matrix material and are organically modified, i.e., grafted with sodium alginate, to effectively enhance the simultaneous induced enrichment of calcium and magnesium ions, thereby achieving efficient simultaneous removal of calcium and magnesium ions in high-calcium and low-magnesium wastewater, and improving the wastewater reuse efficiency.

[0048] (2) The preparation method of the composite seed crystals disclosed in the present invention has a simple process, mild reaction conditions, and the obtained composite seed crystals are of high purity without the need for further purification. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0051] Figure 1 This is an infrared spectrum of the composite crystal seed for treating high-calcium and low-magnesium wastewater described in Example 1 of the present disclosure.

[0052] Figure 2 This is the XRD diagram of the composite crystal seed for treating high-calcium and low-magnesium wastewater described in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0053] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0054] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0055] Example 1

[0056] The present embodiment provides a composite crystal seed, a preparation method and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The composite crystal seed 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 crystal seeds are in granular form, and the particle size of the composite crystal seeds is 1 mm.

[0059] The preparation method comprises the following steps:

[0060] (1) Dissolving N,N-dimethylformamide, phthalic acid dihydrate zinc acetate and triethylamine in ethanol at a mass ratio of 1:0.5:0.5:5, controlling the stirring speed to 500 r / min, reacting for 6 hours, and then centrifuging at a speed of 5000 r / min in a centrifuge, washing the obtained solid with N,N-dimethylformamide and ethanol in turn, and then drying to obtain a zinc-based MOF matrix material;

[0061] (2) mixing sodium alginate, the zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water 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 granular balls with a particle size of 0.5 mm. The obtained granular balls are the composite crystal seeds for treating high-calcium and low-magnesium wastewater.

[0063] The infrared spectrum of the obtained composite seed is as follows: Figure 1 Its XRD pattern is shown in Figure 2 As shown. Figure 1It can be seen that at about 1010cm -1 , 1430cm -1 , 1605cm -1 and 3350cm -1 There are peaks at , which correspond to the stretching vibration peaks of CO (carbon-oxygen bond), -COO- (ester group), C=O (carbonyl group) and -OH (hydroxyl group) respectively; Figure 2 It can be seen that there are peaks at 19.1°, 32.4°, and 45.3°, corresponding to different crystal planes of Zn-MOF. Figure 1 and Figure 2 Both mean that the composite seed crystals are successfully synthesized.

[0064] The core crystal granulation process includes:

[0065] (1) filling the composite seed crystals into a nuclear crystal granulation reactor, the filling height being 15% of the height of the nuclear crystal granulation reactor;

[0066] (2) 70 L / h of high-calcium and 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 (wherein the sodium carbonate concentration is 1500 mg / L and the sodium hydroxide concentration is 600 mg / L) are introduced from the lower end of the side wall of the nuclear crystal granulation reactor to make the composite crystal seeds fluidized and react. The regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0067] Example 2

[0068] The present embodiment provides a composite crystal seed, a preparation method and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The composite crystal seed 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 crystal seeds are in granular form, and the particle size of the composite crystal seeds is 1 mm.

[0071] The preparation method comprises the following steps:

[0072] (1) Dissolving N,N-dimethylformamide, zinc acetate dihydrate of phthalic acid and triethylamine in ethanol at a mass ratio of 1:3:3:10, controlling the stirring speed to 500 r / min, reacting for 8 h, and then centrifuging at a speed of 8000 r / min in a centrifuge. The obtained solid is washed with N,N-dimethylformamide and ethanol in turn, and then dried to obtain a zinc-based MOF matrix material;

[0073] (2) mixing sodium alginate, the zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water 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 granular balls with a particle size of 0.3 mm. The obtained granular balls are the composite crystal seeds for treating high-calcium and low-magnesium wastewater.

[0075] The core crystal granulation process includes:

[0076] (1) filling the composite seed crystals into a nuclear crystal granulation reactor, the filling height being 20% ​​of the height of the nuclear crystal granulation reactor;

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

[0078] Example 3

[0079] The present embodiment provides a composite crystal seed, a preparation method and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The composite crystal seed 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 crystal seeds are in granular form, and the particle size of the composite crystal seeds is 1 mm.

[0082] The preparation method comprises the following steps:

[0083] (1) Dissolving N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine, malonic acid, zinc nitrate hexahydrate and trimethylamine in ethanol at a mass ratio of 1:5:5:15, controlling the stirring speed to 500 r / min, reacting for 12 h, and then centrifuging at a speed of 10000 r / min in a centrifuge. The obtained solid was washed with N,N'-bis(3-methyl-2-amino-benzoyl)ethylenediamine and ethanol in turn, and then dried to obtain a zinc-based MOF matrix material;

[0084] (2) mixing sodium alginate, the zinc-based MOF matrix material obtained in step (1), sodium hydroxide and water 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 granular beads with a particle size of 0.25 mm. The obtained granular beads are the composite crystal seeds for treating high-calcium and low-magnesium wastewater.

[0086] The core crystal granulation process includes:

[0087] (1) filling the composite seed crystals into a nuclear crystal granulation reactor, the filling height being 30% of the height of the nuclear crystal granulation reactor;

[0088] (2) 70 L / h of high-calcium and 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 (wherein the sodium carbonate concentration is 3000 mg / L and the sodium hydroxide concentration is 350 mg / L) are introduced from the lower end of the side wall of the nuclear crystal granulation reactor to make the composite crystal seeds fluidized and react. The regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0089] Example 4

[0090] This embodiment provides a method for preparing a composite crystal seed and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The preparation method refers to the preparation method in Example 3, with the only difference being that in step (1), the mass ratio of N,N-dimethylformamide, phthalic acid dihydrate zinc acetate and triethylamine is 5:5:5:15.

[0091] The core crystal granulation process refers to the core crystal granulation process in Example 3, with the only difference being that the composite crystal seeds prepared in this example are used instead of the composite crystal seeds described in Example 3.

[0092] Example 5

[0093] This embodiment provides a method for preparing a composite crystal seed and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The preparation method refers to the preparation method in Example 3, with the only difference being that in step (1), the mass ratio of N,N-dimethylformamide, phthalic acid dihydrate zinc acetate and triethylamine is 1:10:5:15.

[0094] The core crystal granulation process refers to the core crystal granulation process in Example 3, with the only difference being that the composite crystal seeds prepared in this example are used instead of the composite crystal seeds described in Example 3.

[0095] Example 6

[0096] This embodiment provides a method for preparing a composite crystal seed and a core crystal granulation process for treating high-calcium and low-magnesium wastewater. The preparation method refers to the preparation method in Example 3, with the only difference being that in step (1), the mass ratio of N,N-dimethylformamide, phthalic acid dihydrate zinc acetate and triethylamine is 1:5:10:15.

[0097] The core crystal granulation process refers to the core crystal granulation process in Example 3, with the only difference being that the composite crystal seeds prepared in this example are used instead of the composite crystal seeds described in Example 3.

[0098] Comparative Example 1

[0099] This comparative example provides a commercial seed crystal and core crystal granulation process, wherein the commercial seed crystal is calcium feldspar.

[0100] The core crystal granulation process is similar to the core crystal granulation process in Example 1, with the only difference being 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 core crystal granulation process, wherein the seed crystal is the zinc-based MOF matrix material prepared in Example 1.

[0103] The core crystal granulation process refers to the core crystal granulation process in Example 1, with the only difference being that the composite crystal seeds described in Example 1 are replaced by the crystal seeds of this comparative example.

[0104] The concentrations of calcium ions 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 use of the composite crystal seeds described in the present disclosure in the nuclear crystal granulation process in Examples 1-6 can achieve efficient treatment of high-calcium and low-magnesium wastewater. In the reclaimed water obtained after treatment, the calcium ion removal rate is more than 93.9%; the magnesium ion removal rate is more than 85.3%; the present disclosure also further improves the effect of the composite crystal seeds by controlling the raw material ratio for preparing the zinc-based MOF matrix material, so that in the reclaimed water obtained after treatment, the calcium ion removal rate is more than 98.4%; the magnesium ion removal rate is more than 92%.

[0109] In Comparative Example 1, existing commercial seed crystals were used, which had poor removal effects on calcium ions and magnesium ions.

[0110] In Comparative Example 2, only the zinc-based MOF matrix material was used as the seed crystal without surface modification, and the calcium and magnesium ions in the water body could not be removed efficiently and simultaneously.

[0111] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0112] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be 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 the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite seed for treating high-calcium and low-magnesium wastewater, characterized in that: The composite seed crystal comprises a zinc-based MOF matrix material and sodium alginate grafted onto the zinc-based MOF matrix material.

2. The composite seed crystal according to claim 1, 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).

3. The composite seed crystal according to claim 1 or 2, characterized in that: The composite crystal seeds are in granular form, and the particle size of the composite crystal seeds is 0.25-1 mm.

4. A method for preparing a composite crystal seed for treating high-calcium and low-magnesium wastewater according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) mixing a zinc-based MOF matrix material with sodium alginate, an alkaline compound and water to obtain a composite solution; (2) adding the composite solution obtained in step (1) dropwise into an ethanol aqueous solution to form granular balls, wherein the granular balls obtained are the composite crystal seeds for treating high-calcium and low-magnesium wastewater.

5. The preparation method according to claim 4, characterized in that: The preparation method of the zinc-based MOF matrix material in step (1) comprises: mixing and reacting an amide-type ligand, a carboxylic acid-type ligand, a zinc salt, an alkaline catalyst and an organic solvent, and performing solid-liquid separation after the reaction to obtain a zinc-based MOF matrix material; Preferably, the amide-type ligand includes 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-propylenediamine; Preferably, the carboxylic acid-type ligand comprises one or more of phthalic acid, tartaric acid or malonic acid; Preferably, the zinc salt comprises one or more of zinc acetate dihydrate, zinc chloride or zinc nitrate hexahydrate; Preferably, the basic catalyst comprises one or more of triethylamine, tetrahydropyridine or trimethylamine; Preferably, the organic solvent comprises ethanol and / or propanol.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the amide type ligand, the carboxylic acid type ligand, the zinc salt and the alkaline catalyst is 1:(0.5-5):(0.5-5):(5-15); Preferably, a first stirring is performed during the reaction; Preferably, the first stirring speed is 500-1000r / min; Preferably, the reaction time is 6-12 hours.

7. The preparation method according to claim 5 or 6, characterized in that: The method for preparing the zinc-based MOF matrix material in step (1) further comprises: washing and drying the obtained zinc-based MOF matrix material in sequence; Preferably, the washing comprises a first washing and a second washing performed sequentially; Preferably, the first washing uses the amide type ligand as a detergent; Preferably, the second washing uses the organic solvent as a washing agent.

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

9. The preparation method according to any one of claims 4 to 8, characterized in that: In the ethanol-water solution of step (2), the mass ratio of ethanol to water is 1:(5-10); Preferably, the dripping speed in step (2) is (5-10) mL / min; Preferably, a second stirring is performed during the dropwise addition in step (2); Preferably, the second stirring speed is 200-600 r / min.

10. A nuclear crystal granulation process for treating high calcium and low magnesium type wastewater, characterized in that: The nuclear crystal granulation process is carried out using the composite crystal seed according to any one of claims 1 to 3 or the composite crystal seed prepared by the preparation method according to any one of claims 4 to 9; The core crystal granulation process comprises the following steps: (1) filling the composite seed crystal into a nuclear crystal granulation reactor; (2) introducing high-calcium and low-magnesium wastewater and a precipitant from the lower part of the nuclear crystal granulation reactor respectively, so that the composite seed crystals are in a fluidized state and react, and the regenerated water obtained after the reaction is discharged from the upper part of the nuclear crystal granulation reactor, and the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor; Wherein, in the high-calcium and low-magnesium type 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; Preferably, the filling height of the composite seed crystals in step (1) is 10%-30% of the height of the nuclear crystal granulation reactor; Preferably, the precipitant in step (2) is introduced in the form of a solution, and the precipitant comprises sodium carbonate and sodium hydroxide; Preferably, the mass ratio of the sodium carbonate to the sodium hydroxide is (2-9):1.

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