Composite dephosphorizing agent based on sodium citrate as well as preparation method and application of composite dephosphorizing agent

Abstract

The invention discloses a sodium citrate-based composite dephosphorizing agent and a preparation method thereof, the sodium citrate-based composite dephosphorizing agent comprises a calcium chloride mother solution, a PAC mother solution, a sodium citrate mother solution and a diluent, and the mass ratio of the calcium chloride mother solution to the PAC mother solution to the sodium citrate mother solution is 9: (0.5-1.5): (0.5-1.5); compared with the prior art, the method has the advantages that the calcium chloride mother liquor is adopted to provide a core calcium source, rapid saturation of Ca < 2 + > in the solution is ensured by the ultrahigh solubility of the calcium chloride mother liquor, the PAC mother liquor is matched to serve as a flocculation enhancer to provide strong current neutralizing capacity, and a'precipitation-complexing-flocculation 'triple synergistic system is constructed according to the adding proportion of the calcium chloride mother liquor, the PAC mother liquor and the sodium citrate mother liquor; the pH application range of the dephosphorizing agent is widened, the phosphate removal efficiency is remarkably improved, the synergistic effect of precipitation and complexation is enhanced, and the calcium-phosphorus precipitation effect and the phosphate adsorption capacity are synchronously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of dephosphorizing agents, and particularly to a composite dephosphorizing agent based on sodium citrate, its preparation method and application. Background Art

[0002] In recent years, the pollution of phosphorus-containing wastewater has become one of the prominent problems in the field of industrial water treatment. As a key link in metal anti-corrosion treatment, the high-concentration phosphorus-containing wastewater generated by the phosphating process has the characteristics of complex pollutant components (including phosphates, heavy metal ions, suspended solids, etc.) and difficult treatment.

[0003] The treatment of phosphorus-containing wastewater generally uses dephosphorizing agents for dephosphorization treatment, but the existing dephosphorizing agents face certain limitations.

[0004] For example, CN110386645 A discloses a high-efficiency dephosphorizing agent and its preparation method. The dephosphorizing agent uses sodium sulfate, ferric sulfate and sodium hypochlorite as raw materials, and synthesizes a multi-core high-valence complex ion dephosphorizing agent through steps such as aging and filtration. After the dephosphorizing agent is applied to biochemical treatment, the phosphorus removal efficiency can reach more than 3 times that of traditional chemicals. However, this method mainly relies on chemical precipitation to remove phosphorus, and only shows good phosphorus removal performance in the treatment of low-phosphorus-concentration wastewater (TP < 1mg / L).

[0005] In the report on page 3 of the 42nd volume, issue 1 of the Journal of Materials Protection in 2009, a process for treating high-concentration phosphating wastewater using a composite of quicklime (CaO) and sodium fluoride (NaF) as a flocculant and supplemented with polyacrylamide (PAM) as a coagulant aid was reported. This method uses lime to adjust the pH of the reaction system to the range of 8.5 - 9.0, and through the synergistic reaction of Ca2 + , F - and phosphate ions, a stable and insoluble phosphate precipitate is formed. Combining with the adsorption bridging and net trapping effects of PAM, the formation and sedimentation rate of flocs are effectively accelerated, and the phosphorus removal rate exceeds 99%. However, this method has certain deficiencies in practical applications. To maintain the reaction system in the optimal pH range, a large amount of CaO needs to be added, resulting in high operating chemical consumption, and lime powder is prone to cause operational problems such as scaling and blockage of dosing equipment during use.

[0006] The patent technical problems raised for the above content mainly include the following points:

[0007] 1. Limited scope of phosphorus removal applicability:

[0008] The high-efficiency dephosphorizing agents in the prior art (such as those disclosed in CN110386645 A) mainly rely on chemical precipitation to remove phosphorus, and are only applicable to the treatment of low-phosphorus-concentration wastewater (TP < 1mg / L), and have poor treatment effects on high-concentration phosphorus-containing wastewater.

[0009] 2. High operating costs:

[0010] In the process of treating high-concentration phosphating wastewater by using a composite of quicklime (CaO) and sodium fluoride (NaF) as a flocculant, although the phosphorus removal rate exceeds 99%, a large amount of CaO needs to be added to maintain the reaction system within the optimal pH range (8.5 - 9.0), resulting in high operating chemical consumption.

[0011] 3. Operational problems:

[0012] During the use of lime powder, operational problems such as scaling and clogging of the dosing equipment are likely to occur, increasing the maintenance difficulty and cost of the equipment and affecting the stability and reliability of the process.

[0013] 4. Lack of a phosphorus remover with a wide pH application range:

[0014] Existing phosphorus removers often have relatively strict requirements for the pH value, and there is a lack of a phosphorus remover that can maintain high phosphorus removal performance within a wide pH range, which limits the application of phosphorus removers under different water quality conditions.

[0015] In summary, the patent technical problems mainly focus on aspects such as the limited phosphorus removal application range of existing phosphorus removers, high operating costs, operational problems, and the lack of a phosphorus remover with a wide pH application range. Summary of the Invention

[0016] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a composite phosphorus remover based on sodium citrate, its preparation method and application, so as to solve the problems in the prior art, such as the limited phosphorus removal application range of existing phosphorus removers, high operating costs, operational problems, and the lack of a phosphorus remover with a wide pH application range.

[0017] To achieve the above purpose, the following technical solution is adopted in the first aspect of the present invention: A composite phosphorus remover based on sodium citrate is composed of a calcium chloride mother liquor, a PAC mother liquor, a sodium citrate mother liquor and deionized water. Among them, the mass ratio of the calcium chloride mother liquor, the PAC mother liquor and the sodium citrate mother liquor is 9:0.5 - 1.5:0.5 - 1.5.

[0018] Furthermore, its mass concentration is 20% - 25%.

[0019] Furthermore, the mass concentration of the calcium chloride mother liquor is 30% - 50% and it includes anhydrous calcium chloride and deionized water.

[0020] Furthermore, the mass concentration of the PAC mother liquor is 10% - 30% and it includes polyaluminum chloride and deionized water.

[0021] Further, the mass concentration of the sodium citrate mother liquor is 10% - 30% and it includes sodium citrate and deionized water.

[0022] The second aspect of the present invention adopts the following technical solution: A preparation method of the sodium citrate-based composite dephosphorizer described in the first aspect of the present invention, comprising the following steps:

[0023] Prepare calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor respectively;

[0024] Take the calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor in proportion, and then mix and stir for 10 - 30 min;

[0025] Then add deionized water to dilute to the target concentration.

[0026] Further, the preparation process of the calcium chloride mother liquor is as follows:

[0027] Dissolve anhydrous calcium chloride in deionized water and stir until completely dissolved.

[0028] Further, the preparation process of the PAC mother liquor is as follows:

[0029] Dissolve polyaluminum chloride in deionized water and stir until completely dissolved.

[0030] Further, the preparation process of the sodium citrate mother liquor is as follows:

[0031] Dissolve sodium citrate in deionized water and stir until completely dissolved.

[0032] The third aspect of the present invention adopts the following technical solution: An application, using the sodium citrate-based composite dephosphorizer described in the first aspect of the present invention to carry out dephosphorization treatment on phosphorus-containing wastewater under the condition of pH 8 - 10.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The preparation method of the present invention uses calcium chloride mother liquor to provide the core calcium source, ensuring the rapid saturation of Ca in the solution with its ultra-high solubility, 2+ cooperating with PAC mother liquor as a flocculation enhancer to provide strong electro-neutralization ability, and constructing a "precipitation - complexation - flocculation" triple synergistic system through the addition ratios of calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor; broadening the pH application range of the dephosphorizer, significantly improving the removal efficiency of phosphate, enhancing the synergistic effect of precipitation and complexation, and realizing the synchronous improvement of calcium-phosphorus precipitation effect and phosphate adsorption capacity;

[0035] 2. The preparation method of the present invention has simple process, low cost, easy operation and control of conditions, and is conducive to large-scale preparation and industrial application;

[0036] 3. For wastewater with an initial phosphorus concentration of 200 mg / L, after phosphorus removal by the composite phosphorus removal agent of the present invention, under the condition of pH = 8, the phosphorus removal rate reaches more than 88%; under the condition of pH = 10, the phosphorus removal rate reaches more than 91%.

[0037] 4. Compared with traditional conventional phosphorus removal agents, when pH = 8 or 10, the total phosphorus removal rate of the composite phosphorus removal agent of the present invention is increased by at least more than 10% and more than 5% respectively.

[0038] 5. The composite phosphorus removal agent based on sodium citrate of the present invention, under the same conditions, the total phosphorus removal efficiency is significantly better than other compounded phosphorus removal agents, and has the value of popularization and application in the field of wastewater treatment technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a performance comparison diagram of the phosphorus removal agents prepared in Example 1, Example 2 and Example 3;

[0040] Figure 2 It is a performance comparison diagram of the phosphorus removal agents prepared in Example 1, Control Example 1, Control Example 2, Control Example 3 and Control Example 4;

[0041] Figure 3 It is a performance comparison diagram of Example 1, Control Example 5, Control Example 6 and Control Example 7;

[0042] Figure 4 It is a performance comparison diagram of the phosphating wastewater of Example 1 and Control Example 1 at different pH values;

[0043] Figure 5 It is a comparison diagram of the suspended solid removal rates of the phosphating wastewater of Example 1 and Control Example 1 at different pH values;

[0044] Figure 6 It is the sludge XRD diagram of Example 1 and Control Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention will be further described in detail below through specific embodiments:

[0046] Example 1

[0047] The preparation process of a composite phosphorus removal agent based on sodium citrate is as follows:

[0048] S1. Dissolve 44.3 parts of anhydrous calcium chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a calcium chloride mother liquor;

[0049] S2. Dissolve 20 parts of polyaluminum chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a PAC mother liquor;

[0050] S3. Dissolve 20 parts of sodium citrate in 100 parts of deionized water, and stir until completely dissolved to obtain a sodium citrate mother liquor;

[0051] S4. Take the calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor and mix them according to a mass ratio of 9:1:1, stir for 10 - 30 min, and then add deionized water to dilute to 22% (wt%), thus obtaining the composite dephosphorization agent.

[0052] Example 2

[0053] The preparation process of a composite dephosphorization agent based on sodium citrate is as follows:

[0054] S1. Dissolve 30 parts of anhydrous calcium chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a calcium chloride mother liquor;

[0055] S2. Dissolve 10 parts of polyaluminum chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a PAC mother liquor;

[0056] S3. Dissolve 10 parts of sodium citrate in 100 parts of deionized water, and stir until completely dissolved to obtain a sodium citrate mother liquor;

[0057] S4. Take the calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor and mix them according to a mass ratio of 9:0.5:0.5, stir for 10 - 30 min, and then add deionized water to dilute to 20% (wt%), thus obtaining the composite dephosphorization agent.

[0058] Example 3

[0059] The preparation process of a composite dephosphorization agent based on sodium citrate is as follows:

[0060] S1. Dissolve 50 parts of anhydrous calcium chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a calcium chloride mother liquor;

[0061] S2. Dissolve 30 parts of polyaluminum chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a PAC mother liquor;

[0062] S3. Dissolve 30 parts of sodium citrate in 100 parts of deionized water, and stir until completely dissolved to obtain a sodium citrate mother liquor;

[0063] S4. Take the calcium chloride mother liquor, PAC mother liquor and sodium citrate mother liquor and mix them according to a mass ratio of 9:1.5:1.5, stir for 10 - 30 min, and then add deionized water to dilute to 25% (wt%), thus obtaining the composite dephosphorization agent.

[0064] Control Example 1

[0065] The preparation process of a traditional and conventional dephosphorizer is as follows:

[0066] S1. Dissolve 44.3 parts of anhydrous calcium chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a calcium chloride mother liquor;

[0067] S2. Dissolve 20 parts of polyaluminum chloride in 100 parts of deionized water, and stir until completely dissolved to obtain a PAC mother liquor;

[0068] S3. Take the calcium chloride mother liquor and the PAC mother liquor and mix them according to a mass ratio of 9:1. After stirring for 10 - 30 min, add deionized water to dilute to 22% (wt%), and then the dephosphorizer is obtained.

[0069] Control Example 2

[0070] The difference from Example 1 is only that: sodium citrate is replaced by ferric poly chloride.

[0071] Control Example 3

[0072] The difference from Example 1 is only that: sodium citrate is replaced by ferric aluminum chloride.

[0073] Control Example 4

[0074] The difference from Example 1 is only that: sodium citrate is replaced by sodium fluoride.

[0075] Control Example 5, Control Example 6, and Control Example 7 are respectively commercially available dephosphorizers purchased, namely, phosphorus removal agent, polyferric sulfate high - efficiency phosphorus removal agent, and Puni'ao composite phosphorus removal agent.

[0076] I. Detection and Analysis

[0077] 1) Performance evaluation method of the dephosphorizer

[0078] The specific operation steps are as follows:

[0079] a. Adjust the pH value of the special phosphating wastewater sample to 10:

[0080] Pretreatment: Take a special phosphating wastewater sample from a chemical plant in Chongqing with a phosphorus concentration of 200 mg / L, and adjust its pH value to 10 to promote the precipitation of Fe ions in the wastewater;

[0081] Sub - sampling: Take 10 parts of the pretreated special phosphating wastewater sample, each part being 100 mL;

[0082] Mixing: Add 0.374 mL of the dephosphorizer prepared in Examples 1 - 3 and Control Examples 1 to 7 to each of the 10 parts of the special phosphating wastewater sample respectively. Stir rapidly at a speed of 950 rpm for 5 min and then let it stand for 30 min, and observe the formation of flocs;

[0083] Sampling and detection: Then, 2 mL of the supernatant of the treated water sample was taken respectively, filtered, and the total phosphorus content was measured to evaluate the treatment effects of each phosphorus removal agent.

[0084] b. Adjust the pH value of the special phosphating wastewater sample to 8:

[0085] Pretreatment: Take a special phosphating wastewater sample from a chemical plant in Chongqing with a phosphorus concentration of 200 mg / L, and adjust its pH value to 8 to promote the precipitation of Fe ions in the wastewater.

[0086] Sub-sampling: Take 2 portions of the pretreated special phosphating wastewater sample, 100 mL for each portion.

[0087] Mixing: Add 0.374 mL of the phosphorus removal agents prepared in Example 1 and Comparative Example 1 respectively to the 2 portions of the special phosphating wastewater sample, stir rapidly at a speed of 950 rpm for 5 min, and then let it stand for 30 min to observe the formation of flocs.

[0088] Sampling and detection: Then, 2 mL of the supernatant of the treated water sample was taken respectively, filtered, and the total phosphorus content was measured to evaluate the treatment effects of each phosphorus removal agent.

[0089] 1.1. The total phosphorus removal efficiency obtained by the phosphorus removal agents prepared in Example 1, Example 2, and Example 3 under the condition of pH = 10 is as Figure 1 shown.

[0090] From Figure 1 it can be seen that under the condition of pH = 10, the composite phosphorus removal agents with three formulations show gradient phosphorus removal performance: the total phosphorus removal rate of Example 1 can reach 91.35%, the total phosphorus removal rate of Example 2 can reach 88.53%, and the total phosphorus removal rate of Example 3 can reach 97.52%. Among them, Example 3 shows the most excellent phosphorus removal performance, which is mainly due to the strong supersaturated system formed by its higher calcium ion concentration, combined with the optimized flocculation-complexation synergistic effect, significantly promoting the precipitation of hydroxyapatite; Example 1 achieves the best balance between technical performance and economy with a removal rate of 91.35%, and its unit treatment cost is about 40% lower than that of Example 3, while maintaining excellent floc sedimentation, verifying that this formulation has significant technical advantages while ensuring economy; the removal rate of Example 2 drops to 88.53%, which reveals that when the concentration of key components is insufficient, the synergistic effect of the system will be significantly weakened, which is mainly reflected in insufficient calcium ion supersaturation and decreased flocculation electro-neutralization ability.

[0091] 1.2. The total phosphorus removal efficiency obtained by the phosphorus removal agents prepared in Example 1 and Comparative Examples 1 to 4 under the condition of pH = 10 is as Figure 2 shown.

[0092] From Figure 2 It can be seen that under the condition of pH 10, the total phosphorus removal rate of Example 1 can reach 91.02%, the total phosphorus removal rate of Control Example 1 is 76.83%, the total phosphorus removal rate of Control Example 2 can reach 89.73%, the total phosphorus removal rate of Control Example 3 can reach 79.49%, and the total phosphorus removal rate of Control Example 4 can reach 76.7%. It is significantly better than the traditional formulations in Control Examples 1 to 4, indicating that the composite phosphorus removal agent of the present invention has excellent phosphorus removal performance. In addition, compared with Control Example 1, the present invention introduces sodium citrate as an organic complexing aid, which can form a stable complex with phosphate ions and cooperate with Ca 2+ to achieve efficient precipitation, significantly improve the phosphorus removal effect, and the removal rate is increased by about 14% or more.

[0093] 1.3. The total phosphorus removal efficiency obtained by using the commercially available phosphorus removal agents purchased in Example 1 and Control Examples 5 to 8 under the condition of pH 10 is as Figure 3 shown.

[0094] From Figure 3 It can be seen that under the same phosphating wastewater conditions, the total phosphorus removal rate of the phosphorus removal agent of the present invention is as high as 91.02%, which is significantly better than 44.22%, 28.42% and 28.03% of the commercially available Control Examples 5 to 7. Its removal efficiency is 46.8% higher than that of the best commercially available Control Example 5 and 62.99% higher than that of the worst commercially available Control Example 7, indicating that the phosphorus removal agent of the present invention has excellent phosphorus removal performance. Thus, it can be seen that the sodium citrate introduced in Example 1 can form a dual complexation and precipitation effect with phosphate ions and Ca 2+ to enhance the reaction kinetics, enabling phosphorus to flocculate and settle quickly and fully in a short time; the ternary ratio of CaCl2, PAC and sodium citrate realizes more efficient flocculation and sedimentation under alkaline conditions, overcoming the problem of insufficient efficiency in the treatment of high-concentration phosphorus wastewater by commercially available single or traditional formulations; compared with the single coagulation / adsorption mechanism of commercially available products, the phosphorus removal agent of the present invention has both organic complexation and inorganic precipitation dual mechanisms, is applicable to different water quality conditions, and has stronger robustness and stability. Thus, it can be seen that the phosphorus removal agent of Example 1 of the present invention not only exhibits excellent phosphorus removal ability under laboratory conditions, but also is significantly better than multiple commercially available products, having significant technological progress and application value.

[0095] 1.4. The total phosphorus removal efficiency obtained by using the phosphorus removal agents prepared in Example 1 and Control Example 1 under the conditions of pH 8 or 10 is as Figure 4 shown.

[0096] From Figure 4Analysis shows that in Comparative Example 1, the total phosphorus removal rates were 55.82% and 76.83% at pH 8 and 10 respectively; while the total phosphorus removal rates of Example 1 under the same conditions were 86.07% and 91.02% respectively. Thus, it can be seen that Example 1 exhibits more excellent phosphorus removal performance under different pH conditions. Especially in a slightly alkaline environment (pH = 8), its removal efficiency is increased by 30.25% compared with Comparative Example 1, indicating that it has stronger adaptability and stability to pH changes. Thus, it can be seen that the phosphorus remover described in the present invention significantly broadens the applicable pH range while maintaining a high phosphorus removal efficiency. This advantage is mainly due to the introduction of sodium citrate, which has good complexing ability and buffering effect, and can stabilize the reaction behavior of calcium ions and phosphate ions under different pH conditions, promote the precipitation and flocculation of phosphorus, thereby achieving efficient phosphorus removal in a wide pH range and solving the problem of the decline in phosphorus removal efficiency of traditional inorganic coagulants under high pH conditions.

[0097] 1.5. The suspended solid removal efficiencies of the phosphorus removers prepared in Example 1 and Comparative Example 1 under the condition of pH 8 or 10 are as Figure 5 shown.

[0098] From Figure 5 it can be seen that under the conditions of pH 8 and 10, the removal efficiencies of the phosphorus remover prepared in Example 1 for suspended solids reached 77.39% and 83.45% respectively, which were significantly higher than 57.82% and 62.76% of Comparative Example 1 under the same conditions. Thus, it can be seen that the organic complexing auxiliary sodium citrate can form a multi-point bridging effect with Ca 2+ and suspended particles in the wastewater, promoting the rapid generation and sedimentation of large-size and high-density flocs; at the same time, the buffering effect of sodium citrate effectively maintains the optimal flocculation pH range of the system, further improving the removal efficiency of suspended solids.

[0099] 2) XRD analysis

[0100] The XRD of the precipitate obtained by the phosphorus removers prepared in Example 1 and Comparative Example 1 under the condition of pH 10 is as Figure 6 shown.

[0101] From Figure 6Analysis shows that there are obvious differences between Example 1 and Comparative Example 1 in terms of the crystallization state and phase composition of the precipitate, reflecting significant changes in the structure of the material after the dephosphorization treatment. In Comparative Example 1, obvious diffraction peaks are shown, indicating that its precipitate has a high crystallinity, which may correspond to phosphate or other inorganic crystal phases. In Example 1, however, these sharp peaks are significantly weakened or disappear, and the overall spectrum shows broad and gentle diffuse peaks, indicating that it is mainly composed of amorphous structures or substances with low crystallinity. This change shows that in the process of dephosphorization in Example 1, the introduction of sodium citrate may have promoted the amorphous precipitation of phosphorus, thus improving the embedding or fixation efficiency of phosphorus. In addition, amorphous precipitates usually have a higher specific surface area and reactivity, which is beneficial for subsequent treatment or resource recovery.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A composite dephosphorizer based on sodium citrate, characterized in that, It is composed of a calcium chloride mother liquor, a PAC mother liquor, a sodium citrate mother liquor and deionized water. Among them, the mass ratio of the calcium chloride mother liquor, the PAC mother liquor and the sodium citrate mother liquor is 9:0.5-1.5:0.5-1.

5.

2. The composite dephosphorizer based on sodium citrate according to claim 1, characterized in that, Its mass concentration is 20%-25%.

3. The sodium citrate-based composite dephosphorizer according to claim 1 or 2, characterized in that, The mass concentration of the calcium chloride mother liquor is 30%-50% and it includes anhydrous calcium chloride and deionized water.

4. The sodium citrate-based composite dephosphorizer according to claim 1 or 2, characterized in that The mass concentration of the PAC mother liquor is 10%-30% and it includes polyaluminum chloride and deionized water.

5. The composite dephosphorizing agent based on sodium citrate according to claim 1 or 2, characterized in that The mass concentration of the sodium citrate mother liquor is 10%-30% and it includes sodium citrate and deionized water.

6. A preparation method of the sodium citrate-based composite dephosphorizer according to any one of claims 1-5, characterized in that, It includes the following steps: Prepare the calcium chloride mother liquor, the PAC mother liquor and the sodium citrate mother liquor respectively; Take the calcium chloride mother liquor, the PAC mother liquor and the sodium citrate mother liquor in proportion, and then mix and stir for 10-30 minutes; Then add deionized water to dilute to the target concentration.

7. The preparation method of the composite dephosphorizer based on sodium citrate according to claim 6, wherein The preparation process of the calcium chloride mother liquor is as follows: Dissolve anhydrous calcium chloride in deionized water and stir until completely dissolved.

8. The preparation method of the sodium citrate-based composite dephosphorizer according to claim 6, wherein, The preparation process of the PAC mother liquor is as follows: Dissolve polyaluminum chloride in deionized water and stir until completely dissolved.

9. The preparation method of the sodium citrate-based composite dephosphorizer according to claim 7, characterized in that, The preparation process of the sodium citrate mother liquor is as follows: Dissolve sodium citrate in deionized water and stir until completely dissolved.

10. An application, characterized in that, Use the sodium citrate-based composite dephosphorizing agent described in any one of claims 1-5 to perform dephosphorization treatment on phosphorus-containing wastewater under the condition that the pH is 8-10.

Images