A method for purifying and recycling phosphate mother liquor wastewater

Abstract

The application discloses a method for purifying and recycling phosphate mother liquor wastewater, and belongs to the field of industrial wastewater treatment. The method uses hydroxyapatite, zeolite and bentonite as base materials, and obtains modified adsorption materials through hydroxyaluminum-titanium bimetallic bonding, modified chitosan functionalization and polyethyleneimine crosslinking. The adsorption materials are used to realize deep removal of fluorine ions, silicon-containing substances, lead, arsenic and other heavy metals in the phosphate mother liquor wastewater, and ensure that NH4 + , PO4 3‑ core resources are efficiently recycled. The method for purifying and recycling phosphate mother liquor wastewater is simple, has strong adaptability, can realize green closed-loop recycling of the phosphate mother liquor wastewater, and has remarkable economic and environmental protection benefits.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment, specifically to a method for purifying and reusing phosphate mother liquor wastewater. Background Technology

[0002] Phosphate is a key raw material in chemical, agricultural, food, and pharmaceutical fields. Its production typically follows a process of "acid-base neutralization → cooling crystallization → centrifugal separation → drying," which generates a large amount of mother liquor during the centrifugal separation stage. This mother liquor contains a high concentration of target salt ions (such as NH4+). + PO4 3- (etc.), while also carrying impurities introduced by the raw materials (such as fluoride ions, silicon-containing substances, heavy metal Pb). 2+ As 3+ If these substances are directly discharged, they will not only waste resources but also cause serious environmental pollution problems; if they are directly reused, impurities will accumulate in the production system, leading to a series of problems such as decreased product purity, equipment corrosion and scaling, and unstable production processes.

[0003] Existing phosphate mother liquor treatment technologies mainly include chemical precipitation, membrane separation, evaporation crystallization, and single adsorption. Chemical precipitation removes fluoride, silicon, and heavy metals by adding calcium and magnesium salts, requiring large amounts of reagents and generating significant amounts of solid waste such as gypsum and calcium phosphate, resulting in high solid waste disposal costs. Furthermore, impurity removal is incomplete, failing to meet the stringent impurity concentration requirements for mother liquor reuse. While membrane separation methods (such as ceramic membrane ultrafiltration, reverse osmosis, and electrodialysis) can achieve water-salt separation, trace amounts of colloids and heavy metal complexes in the mother liquor easily cause membrane pore blockage. Membrane fouling cycles are only 3-6 months, requiring frequent cleaning and resulting in short membrane lifespans. Additionally, high-pressure operation leads to energy consumption issues. High energy consumption and high investment costs make them unsuitable for the actual needs of small and medium-sized phosphate production enterprises. Evaporation crystallization can recover salt resources, but it has poor tolerance to impurities. Fluorine, silicon, and heavy metals can cause scaling in the crystallizer and substandard product purity, requiring complex pretreatment processes, making the process cumbersome. Existing adsorbent materials are mostly single-function modifications or use high-cost substrates such as graphene, which have problems such as insufficient targeting, low adsorption capacity, weak anti-fouling ability, and high cost. They are also difficult to adapt to the high salt and specific pH conditions of phosphate mother liquor, and are prone to problems such as functional group detachment and core resource adsorption loss, failing to achieve a balance between deep impurity removal and efficient resource retention. In addition, existing combined processes generally have problems such as complex processes and poor adaptability, making it difficult to deeply integrate with existing phosphate production processes and limiting their industrial application.

[0004] Therefore, there is an urgent need to develop a method for purifying and reusing phosphate mother liquor wastewater to achieve simultaneous and deep removal of impurities such as fluoride, silicon, and heavy metals, while maximizing the retention of NH4. + PO4 3-By utilizing core resources such as these, a green closed-loop cycle for phosphate production can be achieved, which has significant economic and environmental value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for purifying and reusing phosphate mother liquor wastewater, comprising the following steps:

[0006] S1: The collected mother liquor is fed into a filter press and filtered through a filter cloth to obtain pretreated mother liquor;

[0007] S2: Pass the pretreated mother liquor into an adsorption tower filled with modified adsorption material and perform adsorption treatment at room temperature.

[0008] S3: After adsorption treatment, the mother liquor first passes through the stainless steel screen at the bottom of the adsorption tower to filter the adsorbent material it carries, and then passes through the filter for secondary filtration to obtain purified mother liquor.

[0009] S4: The purified mother liquor is fed into the evaporator and heated using the residual heat from the production process to concentrate the mother liquor to a supersaturated state. Then it is fed into the cooling crystallizer for crystallization. Finally, it is separated by centrifugation and dried to obtain phosphate crystals.

[0010] S5: Phosphate crystals are transported to the drying process and mixed with fresh liquid to prepare the finished product; the condensate from the evaporation process is filtered and reused for phosphoric acid dilution or washing of production equipment;

[0011] S6: A mixed regenerant is fed into the adsorption tower in reverse to carry out the regeneration reaction. Then, the adsorption tower is rinsed with condensate. The trace adsorbent particles trapped by the filter in S3 are collected and recycled along with the adsorption tower regeneration process.

[0012] The modified adsorbent material is prepared by using hydroxyapatite, zeolite and bentonite as substrates, through hydroxyaluminum-titanium bimetallic bonding, modified chitosan functionalization and polyethyleneimine crosslinking.

[0013] Preferably, in step S1, the pore size of the filter cloth is 5-10 μm; in step S2, the flow rate of the pretreatment mother liquor is 1.5-2.0 BV / h, and the residence time is 35-40 min.

[0014] Preferably, in step S2, the preparation of the modified adsorbent material includes the following steps:

[0015] T1: Hydroxyapatite, zeolite and bentonite are sequentially immersed in a mixed solution containing AlCl3 and Ti(SO4)2. The pH of the system is adjusted to 5.5-6.0 with 10% dilute ammonia water. The reaction is carried out at 65℃ for 2-3 hours. Then, the mixture is washed with deionized water and dried at 95-100℃ for 1-2 hours to obtain the treated substrate.

[0016] T2: Dissolve chitosan in 2% dilute hydrochloric acid, add thiourea and formaldehyde, and react at 60-65℃ for 2-2.5h to obtain modified chitosan.

[0017] T3: Add the treated substrate to the modified chitosan, react at a constant temperature of 70-80℃ for 2-3 hours, and dry at 90-95℃ for 1-2 hours to obtain the functionalized substrate;

[0018] T4: Immerse the functionalized substrate in a 1.5% (w / w) polyethyleneimine solution and react at 55-60℃ for 1-2 hours. Add 0.4% (w / w) glutaraldehyde and continue the reaction for 30 minutes. After washing, dry at 80-90℃ for 1-2 hours to obtain the modified adsorbent material.

[0019] In this context, a modified adsorbent material is prepared using a hydroxyapatite-zeolite-bentonite composite substrate as a carrier, through hydroxyapatite-titanium bimetallic bonding, modified chitosan functionalization, and polyethyleneimine crosslinking. Specifically, the high-density Al-OH-Ti active sites are constructed on the substrate surface via hydroxyapatite-titanium bimetallic bonding, enabling the utilization of F... - With Al 3+ Ti 4+ The strong coordination between the two forms an Al-Ti-F ternary complex, which efficiently captures free F in the mother liquor. - and F released after the complexation of fluorosilicate complexes. - It can also undergo dehydration condensation reactions with monosilicic acid, oligosilicic acid, and silicon-containing components generated after complex breaking in the mother liquor to form stable Si-O-Al-Ti covalent bonds, achieving simultaneous deep removal of fluorine- and silicon-containing impurities; at the same time, it introduces amino (-NH2) and mercapto (-SH) bifunctional groups on the substrate surface, wherein the amino group interacts with Pb through lone pair electrons. 2+ Formation of coordination chelates, thiol group and As 3+ Nucleophilic reactions occur to form As-S covalent bonds, achieving the removal of heavy metal ions. Furthermore, the dense amine film formed by cross-linking polyethyleneimine blocks the adhesion of large molecular organic impurities through steric hindrance. Simultaneously, this amine film exhibits a weakly positive charge under the target operating conditions, preventing it from reacting with the core NH4+ in the mother liquor. + PO4 3- Static electricity is generated to ensure that core resources are not lost.

[0020] Preferably, in step S3, the filter element material includes any one of silicon carbide ceramic, polytetrafluoroethylene, and polypropylene.

[0021] In this situation, silicon carbide ceramics, polytetrafluoroethylene, and polypropylene all withstand the high salt and weakly alkaline environment of the mother liquor and do not react with NH4. + PO4 3-Alternatively, the regenerator may react, trapping trace amounts of adsorbent particles and ensuring the purity of the purified mother liquor.

[0022] Preferably, in step S4, the mass concentration of the supersaturated state is 35%-40%; the crystallization temperature is 10-15℃; the drying temperature is 100-105℃, and the drying time is 1-2 hours.

[0023] Preferably, in step S6, the mixed regenerator is a mixture of 10% by mass dilute ammonia and 5% by mass dilute hydrochloric acid in a volume ratio of 1:1; the flow rate of the mixed regenerator is 1.0-1.5 BV / h; the temperature of the regeneration reaction is 85-90℃, and the time is 2-3h.

[0024] In this case, a mixed solution of 10% dilute ammonia and 5% dilute hydrochloric acid will react under acidic conditions. + With F - Competition Al 3+ Ti 4+ Coordination sites disrupt the Al-Ti-F complex; OH under alkaline conditions - With Pb 2+ As 3+ It forms hydroxide precipitates, which detach from the adsorption sites, resulting in a regeneration efficiency superior to that of single acids and bases.

[0025] Preferably, in T1, the mass ratio of hydroxyapatite, zeolite, bentonite and the mixed solution is (3-4):(5-6):(2-3):(100-150).

[0026] Preferably, in T1, the mass fraction of AlCl3 in the mixed solution containing AlCl3 and Ti(SO4)2 is 4-5%, and the mass fraction of Ti(SO4)2 is 1-2%.

[0027] Preferably, in T2, the mass ratio of chitosan, 2% dilute hydrochloric acid, thiourea, and formaldehyde is 1:(23-26):(0.03-0.05):(0.01-0.03).

[0028] Preferably, in T3, the mass ratio of the treated substrate to the modified chitosan is 1:(13-15); in T4, the mass ratio of the functionalized substrate, polyethyleneimine solution, and glutaraldehyde is 1:(10-11):(0.04-0.06).

[0029] Beneficial technical effects:

[0030] This application uses a hydroxyapatite-zeolite-bentonite composite substrate as a carrier to prepare a modified adsorbent material through hydroxyaluminum-titanium bimetallic bonding, modified chitosan functionalization, and polyethyleneimine crosslinking. Specifically, a high-density Al-OH-Ti active sites are constructed on the substrate surface through hydroxyaluminum-titanium bimetallic bonding, enabling the utilization of F... - With Al 3+ Ti 4+ The strong coordination between the two forms an Al-Ti-F ternary complex, which efficiently captures free F in the mother liquor. - and F released after the complexation of fluorosilicate complexes. - It can also undergo dehydration condensation reactions with monosilicic acid, oligosilicic acid, and silicon-containing components generated after complex breaking in the mother liquor to form stable Si-O-Al-Ti covalent bonds, achieving simultaneous deep removal of fluorine- and silicon-containing impurities; at the same time, it introduces amino (-NH2) and mercapto (-SH) bifunctional groups on the substrate surface, wherein the amino group interacts with Pb through lone pair electrons. 2+ Formation of coordination chelates, thiol group and As 3+ Nucleophilic reactions occur to form As-S covalent bonds, achieving the removal of heavy metal ions. Furthermore, the dense amine film formed by cross-linking polyethyleneimine blocks the adhesion of large molecular organic impurities through steric hindrance. Simultaneously, this amine film exhibits a weakly positive charge under the target operating conditions, preventing it from reacting with the core NH4+ in the mother liquor. + PO4 3- Electrostatic interaction ensures that core resources are not lost. While adapting to high-salt conditions of mother liquor, it achieves deep removal of impurities from mother liquor and efficient recovery of core resources, thus realizing a green closed-loop cycle for phosphate production. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for purifying and reusing phosphate mother liquor wastewater according to this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0033] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0034] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. The invention will be further described below with reference to embodiments, but is not limited thereto.

[0035] Example 1

[0036] like Figure 1 As shown in the figure, this embodiment provides a method for purifying and reusing phosphate mother liquor wastewater, including the following steps:

[0037] S1: Pass the collected mother liquor into a filter press and filter it with a 5μm filter cloth to obtain pretreated mother liquor;

[0038] S2: The pretreated mother liquor is fed into an adsorption tower filled with modified adsorption material at a flow rate of 1.5 BV / h and held at room temperature for 35 min for adsorption.

[0039] S3: After adsorption, the mother liquor is filtered through the stainless steel screen at the bottom of the adsorption tower to remove the adsorption material, and then filtered a second time through a silicon carbide ceramic filter to obtain purified mother liquor.

[0040] S4: The purified mother liquor is passed into the evaporator and heated using the residual heat from the production process. It is then concentrated to a supersaturated state with a mass concentration of 35%. The mother liquor is then passed into a cooling crystallizer and crystallized at 10°C. After centrifugation and drying at 100°C for 2 hours, phosphate crystals are obtained.

[0041] S5: Phosphate crystals are transported to the drying process and mixed with fresh liquid to prepare the finished product; the condensate from the evaporation process is filtered and reused for phosphoric acid dilution or washing of production equipment;

[0042] S6: Mix 10% dilute ammonia water and 5% dilute hydrochloric acid at a volume ratio of 1:1 to obtain a mixed regenerant. Backwash the adsorption tower with the mixed regenerant at a flow rate of 1.0 BV / h, regenerate at 85℃ for 3 hours, and then rinse the adsorption tower with condensate until the effluent pH=7.5. The adsorption material can then be reused. The trace adsorption material particles trapped by the filter in S3 are collected and recovered along with the regeneration process.

[0043] The preparation of the modified adsorbent material described in S2 includes the following steps:

[0044] T1: Hydroxyapatite, zeolite, and bentonite are immersed in a mixed solution containing AlCl3 and Ti(SO4)2, the pH is adjusted to 5.5 with 10% dilute ammonia, the reaction is carried out at 65℃ for 2 hours, washed with deionized water and dried at 100℃ for 2 hours to obtain the treated substrate.

[0045] T2: Chitosan, 2% dilute hydrochloric acid, thiourea and formaldehyde are mixed in a mass ratio of 1:23:0.03:0.01 and reacted at 60℃ for 2.5h to obtain modified chitosan;

[0046] T3: Add the treated substrate to the modified chitosan at a mass ratio of 1:13, react at 80℃ for 3 hours, and dry at 90℃ for 2 hours to obtain the functionalized substrate.

[0047] T4: Weigh the functionalized substrate, 1.5% polyethyleneimine solution, and 0.4% glutaraldehyde in a mass ratio of 1:10:0.04. Immerse the functionalized substrate in the 1.5% polyethyleneimine solution and react at 55°C for 2 hours. Then add 0.4% glutaraldehyde and continue the reaction for 30 minutes. After washing, dry at 80°C for 2 hours to obtain the modified adsorbent material.

[0048] The mass fraction of AlCl3 in the mixed solution containing AlCl3 and Ti(SO4)2 is 4%; the mass fraction of Ti(SO4)2 is 1%; and the mass ratio of hydroxyapatite, zeolite, bentonite and the mixed solution is 3:5:2:100.

[0049] Example 2

[0050] like Figure 1 As shown in the figure, this embodiment provides a method for purifying and reusing phosphate mother liquor wastewater, including the following steps:

[0051] S1: Pass the collected mother liquor into a filter press and filter it with a 10μm filter cloth to obtain pretreated mother liquor;

[0052] S2: The pretreated mother liquor is fed into an adsorption tower filled with modified adsorption material at a flow rate of 1.5 BV / h and held at room temperature for 35 min for adsorption.

[0053] S3: After adsorption, the mother liquor is filtered through the stainless steel screen at the bottom of the adsorption tower to remove the adsorption material, and then filtered a second time through a polytetrafluoroethylene filter cartridge to obtain purified mother liquor.

[0054] S4: The purified mother liquor is passed into the evaporator and heated using the residual heat from the production process. It is then concentrated to a supersaturated state with a mass concentration of 40%. The mother liquor is then passed into a cooling crystallizer and crystallized at 15°C. After centrifugation and drying at 105°C for 1 hour, phosphate crystals are obtained.

[0055] S5: Phosphate crystals are transported to the drying process and mixed with fresh liquid to prepare the finished product; the condensate from the evaporation process is filtered and reused for phosphoric acid dilution or washing of production equipment;

[0056] S6: Mix 10% dilute ammonia water and 5% dilute hydrochloric acid at a volume ratio of 1:1 to obtain a mixed regenerant. Backwash the adsorption tower with the mixed regenerant at a flow rate of 1.5 BV / h, regenerate at 90℃ for 2 hours, and then rinse the adsorption tower with condensate until the effluent pH=8.2. The adsorption material can then be reused. The trace adsorption material particles trapped by the filter in S3 are collected and recovered along with the regeneration process.

[0057] The preparation of the modified adsorbent material described in S2 includes the following steps:

[0058] T1: Hydroxyapatite, zeolite, and bentonite are immersed in a mixed solution containing AlCl3 and Ti(SO4)2, the pH is adjusted to 6.0 with 10% dilute ammonia, the reaction is carried out at 65℃ for 2 hours, washed with deionized water and dried at 100℃ for 2 hours to obtain the treated substrate.

[0059] T2: Chitosan, 2% dilute hydrochloric acid, thiourea and formaldehyde are mixed in a mass ratio of 1:26:0.05:0.03 and reacted at 60℃ for 2.5h to obtain modified chitosan;

[0060] T3: Add the treated substrate to the modified chitosan at a mass ratio of 1:15, react at 60℃ for 3 hours, and dry at 90℃ for 2 hours to obtain the functionalized substrate.

[0061] T4: Weigh the functionalized substrate, 1.5% polyethyleneimine solution, and 0.4% glutaraldehyde in a mass ratio of 1:11:0.06. Immerse the functionalized substrate in the 1.5% polyethyleneimine solution and react at 60°C for 1 hour. Then add 0.4% glutaraldehyde and continue the reaction for 30 minutes. After washing, dry at 90°C for 1 hour to obtain the modified adsorbent material.

[0062] The mass fraction of AlCl3 in the mixed solution containing AlCl3 and Ti(SO4)2 is 4%; the mass fraction of Ti(SO4)2 is 1%; and the mass ratio of hydroxyapatite, zeolite, bentonite and the mixed solution is 4:6:3:150.

[0063] Example 3

[0064] like Figure 1 As shown in the figure, this embodiment provides a method for purifying and reusing phosphate mother liquor wastewater, including the following steps:

[0065] S1: Pass the collected mother liquor into a filter press and filter it using an 8μm filter cloth to obtain pretreated mother liquor;

[0066] S2: The pretreated mother liquor is fed into an adsorption tower filled with modified adsorption material at a flow rate of 1.8 BV / h and held at room temperature for 35 min for adsorption.

[0067] S3: After adsorption, the mother liquor is filtered through the stainless steel screen at the bottom of the adsorption tower to remove the adsorption material, and then filtered a second time through a polytetrafluoroethylene filter cartridge to obtain purified mother liquor.

[0068] S4: The purified mother liquor is passed into the evaporator and heated using the residual heat from the production process. It is then concentrated to a supersaturated state with a mass concentration of 37%. The mother liquor is then passed into a cooling crystallizer and crystallized at 12°C. After centrifugation and drying at 105°C for 1 hour, phosphate crystals are obtained.

[0069] S5: Phosphate crystals are transported to the drying process and mixed with fresh liquid to prepare the finished product; the condensate from the evaporation process is filtered and reused for phosphoric acid dilution or washing of production equipment;

[0070] S6: Mix 10% dilute ammonia water and 5% dilute hydrochloric acid at a volume ratio of 1:1 to obtain a mixed regenerant. Backwash the adsorption tower with the mixed regenerant at a flow rate of 1.2 BV / h, regenerate at 90℃ for 2 hours, and then rinse the adsorption tower with condensate until the effluent pH is 7.8. The adsorption material can then be reused. The trace adsorption material particles trapped by the filter in S3 are collected and recovered along with the regeneration process.

[0071] The preparation of the modified adsorbent material described in S2 includes the following steps:

[0072] T1: Hydroxyapatite, zeolite, and bentonite are immersed in a mixed solution containing AlCl3 and Ti(SO4)2, the pH is adjusted to 5.8 with 10% dilute ammonia, the reaction is carried out at 65℃ for 2 hours, washed with deionized water and dried at 100℃ for 2 hours to obtain the treated substrate.

[0073] T2: Chitosan, 2% dilute hydrochloric acid, thiourea and formaldehyde are mixed in a mass ratio of 1:24:0.04:0.02 and reacted at 60℃ for 2.5h to obtain modified chitosan;

[0074] T3: Add the treated substrate to the modified chitosan, mix at a mass ratio of 1:14, react at 60℃ for 3 hours, and dry at 90℃ for 2 hours to obtain the functionalized substrate.

[0075] T4: Weigh the functionalized substrate, 1.5% polyethyleneimine solution, and 0.4% glutaraldehyde according to a mass ratio of 1:10.5:0.05. Immerse the functionalized substrate in the 1.5% polyethyleneimine solution and react at 58°C for 1.5 hours. Then add 0.4% glutaraldehyde and continue the reaction for 30 minutes. After washing, dry at 85°C for 1.5 hours to obtain the modified adsorbent material.

[0076] The mass fraction of AlCl3 in the mixed solution containing AlCl3 and Ti(SO4)2 is 4.5%; the mass fraction of Ti(SO4)2 is 1.5%; and the mass ratio of hydroxyapatite, zeolite, bentonite and the mixed solution is 3.5:5.5:2.5:120.

[0077] Comparative Example 1

[0078] This comparative example provides a method for purifying and reusing phosphate mother liquor wastewater. The difference from Example 1 is that the T1 hydroxyaluminum-titanium bimetallic grafting step is omitted, and the mixed substrate of hydroxyapatite, zeolite, and bentonite is directly subjected to subsequent T2-T4 functionalization treatment. Other process steps S1-S5 are the same as in Example 1.

[0079] Comparative Example 2

[0080] This comparative example provides a method for purifying and reusing phosphate mother liquor wastewater. The difference from Example 1 is that the thiourea functionalization step T2-T3 is omitted in the preparation of the modified adsorbent material, and the bimetallic grafted substrate obtained in T1 is directly subjected to the polyethyleneimine crosslinking treatment in T4. Other process steps S1-S5 are the same as in Example 1.

[0081] Comparative Example 3

[0082] This comparative example provides a method for purifying and reusing phosphate mother liquor wastewater. The difference from Example 1 is that the T1 prepared by the modified adsorbent material replaces the mixed solution containing AlCl3 and Ti(SO4)2 with a single AlCl3 solution. Other process parameters and operating steps are the same as in Example 1.

[0083] The PO4 content of a method for purifying and reusing phosphate mother liquor wastewater according to Examples 1-3 and Comparative Examples 1-3 of this application was tested. 3- Recovery rate, NH4 + The results of the tests on retention rate, product purity, and regeneration efficiency of adsorbent material are shown in Table 1.

[0084] Test method:

[0085] PO4 3- Recovery rate: The gravimetric method of quinoline phosphomolybdate was used. Equal volumes of initial mother liquor and recovered crystals were taken, acidified, and then quinoline molybdate reagent was added to generate a precipitate. The initial and recovered PO4 were weighed and calculated. 3- Quality, recovery rate = (recovered quality / initial quality) × 100%.

[0086] NH4 + Retention rate: NH4+ in the initial mother liquor and the purified mother liquor were determined by Nessler's reagent spectrophotometry. + Concentration, retention rate = (concentration after purification / initial concentration) × 100%.

[0087] Product purity: Verified using HPLC combined with gravimetric method; HPLC calculates the purity of the main peak by peak area normalization, and gravimetric method measures the total mass of impurities. Purity = (total sample mass - impurity mass) / total sample mass × 100%.

[0088] Adsorption material regeneration efficiency: Static adsorption capacity comparison method, the adsorption capacity of fresh and regenerated adsorption materials are measured respectively, and the regeneration efficiency = (adsorption capacity after regeneration / adsorption capacity after freshness) × 100%.

[0089] Table 1. Test results of a method for purifying and reusing phosphate mother liquor wastewater in the examples and comparative examples.

[0090]

[0091] Examples 1-3 of this invention disclose a method for purifying and reusing phosphate mother liquor wastewater. Using a hydroxyapatite-zeolite-bentonite composite substrate as a carrier, a modified adsorbent material is prepared through hydroxyaluminum-titanium bimetallic bonding, modified chitosan functionalization, and polyethyleneimine crosslinking. Specifically, high-density Al-OH-Ti active sites are constructed on the substrate surface through hydroxyaluminum-titanium bimetallic bonding, enabling the utilization of F... - With Al 3+ Ti 4+ The strong coordination between the two forms an Al-Ti-F ternary complex, which efficiently captures free F in the mother liquor. - and F released after the complexation of fluorosilicate complexes. - It can also undergo dehydration condensation reactions with monosilicic acid, oligosilicic acid, and silicon-containing components generated after complex breaking in the mother liquor to form stable Si-O-Al-Ti covalent bonds, achieving simultaneous deep removal of fluorine- and silicon-containing impurities; at the same time, it introduces amino (-NH2) and mercapto (-SH) bifunctional groups on the substrate surface, wherein the amino group interacts with Pb through lone pair electrons. 2+ Formation of coordination chelates, thiol group and As 3+ Nucleophilic reactions occur to form As-S covalent bonds, achieving the removal of heavy metal ions. Furthermore, the dense amine film formed by cross-linking polyethyleneimine blocks the adhesion of large molecular organic impurities through steric hindrance. Simultaneously, this amine film exhibits a weakly positive charge under the target operating conditions, preventing it from reacting with the core NH4+ in the mother liquor. + PO4 3- Electrostatic interaction ensures that core resources are not lost. While adapting to high-salt conditions of mother liquor, it achieves deep removal of impurities from mother liquor and efficient recovery of core resources, thus realizing a green closed-loop cycle for phosphate production.

[0092] In Comparative Example 1, the adsorbent material lacked hydroxyl aluminum-titanium bimetallic grafting, preventing the formation of Al-OH-Ti active sites on the substrate surface, thus hindering the effective capture of fluoride ions and silicon-containing substances. Furthermore, the absence of stabilizing bimetallic sites led to the easy detachment of functionalized groups, reducing adsorbent regeneration efficiency. In Comparative Example 2, the lack of amino and thiol groups resulted in lower Pb content in the mother liquor. 2+ As 3+ It cannot be selectively removed; at the same time, the lack of functional groups to regulate the surface charge of the substrate results in the loss of core resources and a decrease in product purity; in Comparative Example 3, the single Al site cannot form a high-density Al-OH-Ti active site, and the ability to capture fluoride ions and silicon-containing substances is significantly reduced, with a product purity of only 90.5% and a serious loss of core resources.

[0093] It should be understood that the above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for purifying and reusing phosphate mother liquor wastewater, characterized in that, Includes the following steps: S1: The collected mother liquor is fed into a filter press and filtered through a filter cloth to obtain pretreated mother liquor; S2: Pass the pretreated mother liquor into an adsorption tower filled with modified adsorption material and perform adsorption treatment at room temperature. S3: After adsorption treatment, the mother liquor first passes through the stainless steel screen at the bottom of the adsorption tower to filter the adsorbent material it carries, and then passes through the filter for secondary filtration to obtain purified mother liquor. S4: The purified mother liquor is fed into the evaporator and heated using the residual heat from the production process to concentrate the purified mother liquor to a supersaturated state. Then it is fed into the cooling crystallizer for crystallization. Finally, it is separated by centrifugation and dried to obtain phosphate crystals. S5: Phosphate crystals are transported to the drying process and mixed with fresh liquid to prepare the finished product; the condensate from the evaporation process is filtered and reused for phosphoric acid dilution or washing of production equipment; S6: A mixed regenerant is fed into the adsorption tower in reverse to carry out the regeneration reaction. Then, the adsorption tower is rinsed with condensate. The trace adsorbent particles trapped by the filter in S3 are collected and recycled along with the adsorption tower regeneration process. The modified adsorbent material is prepared by using hydroxyapatite, zeolite and bentonite as substrates, through hydroxyaluminum-titanium bimetallic bonding, modified chitosan functionalization and polyethyleneimine crosslinking.

2. The method for purifying and reusing phosphate mother liquor wastewater according to claim 1, characterized in that, In step S1, the pore size of the filter cloth is 5-10 μm; in step S2, the flow rate of the pretreated mother liquor is 1.5-2.0 BV / h, and the residence time is 35-40 min.

3. The method for purifying and reusing phosphate mother liquor wastewater according to claim 1, characterized in that, In step S2, the preparation of the modified adsorbent material includes the following steps: T1: Hydroxyapatite, zeolite and bentonite are sequentially immersed in a mixed solution containing AlCl3 and Ti(SO4)2. The pH of the system is adjusted to 5.5-6.0 with 10% dilute ammonia water. The reaction is carried out at 65℃ for 2-3 hours. Then, the mixture is washed with deionized water and dried at 95-100℃ for 1-2 hours to obtain the treated substrate. T2: Dissolve chitosan in 2% dilute hydrochloric acid, add thiourea and formaldehyde, and react at 60-65℃ for 2-2.5h to obtain modified chitosan. T3: Add the treated substrate to the modified chitosan, react at a constant temperature of 70-80℃ for 2-3 hours, and dry at 90-95℃ for 1-2 hours to obtain the functionalized substrate; T4: Immerse the functionalized substrate in a 1.5% (w / w) polyethyleneimine solution and react at 55-60℃ for 1-2 hours. Add 0.4% (w / w) glutaraldehyde and continue the reaction for 30 minutes. After washing, dry at 80-90℃ for 1-2 hours to obtain the modified adsorbent material.

4. The method for purifying and reusing phosphate mother liquor wastewater according to claim 1, characterized in that, In S3, the filter element material includes any one of silicon carbide ceramic, polytetrafluoroethylene, and polypropylene.

5. The method for purifying and reusing phosphate mother liquor wastewater according to claim 1, characterized in that, In step S4, the mass concentration of the supersaturated purified mother liquor is 35%-40%; the crystallization temperature is 10-15℃; the drying temperature is 100-105℃, and the drying time is 1-2 hours.

6. The method for purifying and reusing phosphate mother liquor wastewater according to claim 1, characterized in that, In step S6, the mixed regenerator is a mixture of 10% by mass dilute ammonia and 5% by mass dilute hydrochloric acid in a volume ratio of 1:1; the flow rate of the mixed regenerator is 1.0-1.5 BV / h; the temperature of the regeneration reaction is 85-90℃, and the time is 2-3h.

7. The method for purifying and reusing phosphate mother liquor wastewater according to claim 3, characterized in that, In T1, the mass ratio of hydroxyapatite, zeolite, bentonite and mixed solution is (3-4):(5-6):(2-3):(100-150).

8. The method for purifying and reusing phosphate mother liquor wastewater according to claim 3, characterized in that, In T1, the mixed solution containing AlCl3 and Ti(SO4)2 has a mass fraction of 4-5% for AlCl3 and a mass fraction of 1-2% for Ti(SO4)2.

9. A method for purifying and reusing phosphate mother liquor wastewater according to claim 3, characterized in that, In T2, the mass ratio of chitosan, dilute hydrochloric acid, thiourea, and formaldehyde is 1:(23-26):(0.03-0.05):(0.01-0.03).

10. A method for purifying and reusing phosphate mother liquor wastewater according to claim 3, characterized in that, In T3, the mass ratio of the treated substrate to the modified chitosan is 1:(13-15); in T4, the mass ratio of the functionalized substrate, polyethyleneimine solution, and glutaraldehyde is 1:(10-11):(0.04-0.06).

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