A method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate and its application

Abstract

The present invention relates to the technical field of wastewater treatment, and in particular, to a method and application for recovering phosphorus in phosphorus-containing wastewater containing iron phosphate. The method for recovering phosphorus in phosphorus-containing wastewater containing iron phosphate comprises the following steps: (a) mixing salt-containing wastewater and filtrate to obtain a mixed water sample A; (b) adding an oxidant to the mixed water sample A to obtain a mixed solution B; (c) adding ferrous sulfate to the mixed solution B to obtain a reaction slurry C; (d) performing a first solid-liquid separation on the reaction slurry C to obtain a filter cake D; (e) adjusting the pH of the slurry containing the filter cake D to 1.4 to 1.8, and then performing a stirring reaction, a second solid-liquid separation, drying and calcining to obtain iron phosphate. The method for recovering phosphorus in phosphorus-containing wastewater containing iron phosphate has a high phosphorus recovery rate, and the obtained iron phosphate is of good quality and high purity, and can be used as a precursor of lithium battery positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and application of recovering phosphorus in phosphorus-containing iron phosphate wastewater. Background Art

[0002] Lithium iron phosphate is an important component of lithium battery positive electrode materials, and the production of its precursor iron phosphate has exploded in recent years. The preparation of iron phosphate by ferrous sulfate is one of the most important processes, and different types of wastewater will be produced during the reaction. Among them, phosphorus sources often exist in these wastewaters in the form of soluble salts, and the cost of phosphorus sources in the preparation of iron phosphate accounts for a large proportion. If this part of the phosphorus source is not recycled, it will cause great losses.

[0003] Phosphorus recovery methods include chemical precipitation, enhanced biological phosphorus removal, crystallization, adsorption / desorption, etc. Chemical precipitation is more suitable for large chemical plants, but it has the problems of high cost, complicated process and low phosphorus recovery rate.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present invention is to provide a method and application for recovering phosphorus in phosphorus-containing wastewater of iron phosphate. The method for recovering phosphorus in phosphorus-containing wastewater of iron phosphate has the advantages of high phosphorus recovery rate, good quality and high purity of the produced iron phosphate, etc.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0007] One aspect of the present invention relates to a method for recovering phosphorus from phosphorus-containing iron phosphate wastewater, comprising the following steps:

[0008] (a) mixing the saline wastewater and the filtrate to obtain a mixed water sample A;

[0009] (b) adding an oxidant to the mixed water sample A to obtain a mixed solution B;

[0010] (c) adding ferrous sulfate to the mixed solution B to obtain a reaction slurry C;

[0011] (d) performing a first solid-liquid separation on the reaction slurry C to obtain a filter cake D;

[0012] (e) adjusting the pH of the slurry containing the filter cake D to 1.4 to 1.8, and then performing stirring reaction, second solid-liquid separation, drying and calcination to obtain iron phosphate.

[0013] The method for recovering phosphorus from phosphorus-containing wastewater of iron phosphate has a high phosphorus recovery rate, and the prepared iron phosphate has good quality and high purity, and can be used as a precursor of lithium battery positive electrode material.

[0014] Preferably, the pH of the saline wastewater is 6-8.

[0015] Preferably, the pH of the filtrate is 1.5-2.

[0016] Preferably, the pH of the mixed water sample A is 2.1-2.4.

[0017] Preferably, the volume ratio of the saline wastewater to the filtrate is 0.6 to 0.8.

[0018] Preferably, the molar ratio of phosphorus, ferrous sulfate and the oxidant in the mixed water sample A is 1:1-1.5:0.75-1.125.

[0019] Preferably, the calcination temperature is 550-600°C.

[0020] Preferably, the calcination time is 1.5 to 2 hours.

[0021] Preferably, the stirring reaction temperature is 85-90°C.

[0022] Preferably, the stirring reaction time is 0.5 to 1 h.

[0023] Preferably, the method for recovering phosphorus from phosphorus-containing iron phosphate wastewater further comprises:

[0024] The filter cake obtained by the second solid-liquid separation is washed with desalted water.

[0025] Preferably, the conductivity of the washing water is less than 1000 μS / cm.

[0026] Another aspect of the present invention also relates to a method for treating ferric phosphate wastewater, including the method for recovering phosphorus from ferric phosphate phosphorus-containing wastewater.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate provided by the present invention uses the salt-containing wastewater and filtrate generated in the process of preparing iron phosphate as phosphorus recovery raw materials, and simultaneously recycles and regenerates two different types of phosphorus-containing wastewater. The salt-containing wastewater itself has a higher pH value and can be used as an alkali agent, without the need to add additional alkali agents, thereby saving reagent costs.

[0029] (2) Compared with the existing phosphorus recovery methods for phosphorus-containing wastewater, which require the addition of various expensive chemical agents, the method provided by the present invention does not require concerns about the increased cost due to the addition of these agents, nor does it require consideration of post-treatment issues if excessive amounts are added. The method is highly consistent with the preparation process of iron phosphate, which is conducive to practical application in factories that adopt similar preparation processes for iron phosphate.

[0030] (3) The method for recovering phosphorus from phosphorus-containing wastewater of iron phosphate provided by the present invention has a high phosphorus recovery rate, and the obtained iron phosphate is of good quality and high purity, and can be used as a precursor of lithium battery positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The XRD spectrum of FePO4 provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] One aspect of the present invention relates to a method for recovering phosphorus from phosphorus-containing iron phosphate wastewater, comprising the following steps:

[0035] (a) mixing the saline wastewater and the filtrate to obtain a mixed water sample A;

[0036] (b) adding an oxidant to the mixed water sample A to obtain a mixed solution B;

[0037] (c) adding ferrous sulfate to the mixed solution B to obtain a reaction slurry C;

[0038] (d) performing a first solid-liquid separation on the reaction slurry C to obtain a filter cake D;

[0039] (e) adjusting the pH of the slurry containing the filter cake D to 1.4-1.8 (for example, it can be but not limited to any one of 1.4, 1.5, 1.6, 1.7 or 1.8 or a range between any two of them), and then stirring the reaction, performing a second solid-liquid separation, drying and calcining to obtain iron phosphate.

[0040] The method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate uses the salt-containing wastewater and filtrate generated in the process of preparing iron phosphate as phosphorus recovery raw materials, and simultaneously recycles and regenerates two different types of phosphorus-containing wastewater. The salt-containing wastewater itself has a higher pH and can be used as an alkali agent, without the need to add an additional alkali agent, thereby saving reagent costs.

[0041] Compared with the existing phosphorus recovery method for phosphorus-containing wastewater, which requires the addition of various expensive chemical agents, the method of recovering phosphorus from phosphorus-containing wastewater does not need to worry about the increased cost due to the addition of these agents, and if excessive amounts are added, there is no need to consider post-treatment and other issues; the method is highly consistent with the preparation process of iron phosphate, which is conducive to practical application in factories that adopt similar iron phosphate preparation processes.

[0042] The method for recovering phosphorus from phosphorus-containing wastewater of iron phosphate has a high phosphorus recovery rate, and the prepared iron phosphate has good quality and high purity, and can be used as a precursor of lithium battery positive electrode material.

[0043] The pH of the slurry containing the filter cake D is adjusted to 1.4-1.8 because amorphous ferric phosphate dihydrate is converted into crystalline ferric phosphate dihydrate within this pH range. When the pH is higher than this range, the crystal transformation is affected and the slurry will not turn white. When the pH is lower than this range, the crystal transformation will occur prematurely, the material will turn white prematurely, and the grain size will be smaller.

[0044] Furthermore, the pH of the saline wastewater is 6 to 8, including but not limited to any point value of 6, 6.5, 7, 7.5 or 8 or a range value between any two of them.

[0045] Furthermore, the salt-containing wastewater comes from the concentrated water obtained by the filtrate obtained from the first solid-liquid separation after removing impurity elements such as Mg, Fe, and Mn through a chemical reaction and then concentrating and separating through a high-pressure reverse osmosis device.

[0046] Furthermore, the pH of the filtrate is 1.5-2, including but not limited to any point value of 1.5, 1.6, 1.7, 1.8, 1.9 or 2 or a range of values ​​between any two of them.

[0047] Furthermore, the filtrate is a filtrate obtained by solid-liquid separation of reaction slurry during the preparation of ferric phosphate by the ferrous process.

[0048] The saline wastewater obtained in the process of preparing ferric phosphate has a higher pH. After mixing with the filtrate obtained in the process of preparing ferric phosphate, the pH of the mixed water sample A is controlled within a certain range without the need to add additional alkali, thereby reducing the consumption of reagents and the cost of phosphorus recovery.

[0049] Furthermore, the pH of the mixed water sample A is 2.1 to 2.4, including but not limited to any point value of 2.1, 2.2, 2.3 or 2.4 or the range value between any two of them. Since the reaction pH should be controlled at 1.9 to 2.1 after adding iron salt and hydrogen peroxide according to n(Fe):n(P); n(H2O2)=1:1:0.75, and since the iron salt used is obtained after removing impurities from the by-product ferrous sulfate of titanium dioxide, it still contains a small amount of metal elements. If the pH is higher than this value, the manganese content in the obtained iron phosphate will exceed the standard; if the pH is too high, basic iron phosphate will be generated, which will greatly reduce the electrochemical performance of the product. If the reaction pH is too low, the composite phosphate cannot be converted into a precipitate, and the sulfur content will also increase, causing the subsequent product sulfur index to be unqualified.

[0050] Furthermore, the volume ratio of the saline wastewater to the filtrate is 0.6 to 0.8, including but not limited to any point value of 0.6, 0.7 or 0.8 or any range value between the two. By limiting the addition ratio of the saline wastewater and the filtrate to a certain range, the pH and phosphorus content of the mixed water sample A can be controlled within a reasonable range, which is conducive to the subsequent reaction, reduces the occurrence of side reactions, and improves the recovery rate of phosphorus.

[0051] The salt-containing wastewater and filtrate used in the present invention are both from the process of preparing ferric phosphate by the ferrous sulfate method, and the water samples both contain soluble phosphorus.

[0052] Furthermore, the temperature of the reaction system in steps (a) to (c) is 40 to 50° C., including but not limited to any point value of 40° C., 42° C., 44° C., 46° C., 48° C. or 50° C. or any range value between two thereof. Limiting the temperature of the reaction system to a certain range is conducive to accelerating the reaction rate.

[0053] Furthermore, the molar ratio of phosphorus in the mixed water sample A, the ferrous sulfate and the oxidant is 1:1-1.5:0.75-1.125, including but not limited to 1:1:1.125, 1:1.2:1.05, 1:1.4:0.95 or 1:1.5:0.75. The amount of ferrous sulfate and the oxidant is further determined according to the soluble phosphorus content in the mixed water sample A, so that the phosphorus in the mixed water sample A can be recovered to the greatest extent, and excessive addition of ferrous sulfate and the oxidant can be avoided, resulting in waste of reagents or reducing the probability of side reactions.

[0054] The present invention does not specifically limit the specific type of oxidant, and any conventional oxidant in the art can be used to implement the technical solution of the present invention. In some specific embodiments, the oxidant includes but is not limited to: H2O2 and / or sodium hypochlorite.

[0055] Furthermore, the method for recovering phosphorus from phosphorus-containing iron phosphate wastewater also includes:

[0056] The filter cake obtained by the second solid-liquid separation is washed with desalted water. Washing the filter cake obtained by the second solid-liquid separation can improve the quality of the prepared iron phosphate, reduce the content of impurities, and improve the purity of the iron phosphate.

[0057] Furthermore, the desalted water includes: water with an electrical conductivity lower than 10 μS / cm.

[0058] Further, the conductivity of the washing water is less than 1000 μS / cm, including but not limited to any point value of 500 μS / cm, 550 μS / cm, 600 μS / cm, 650 μS / cm, 700 μS / cm, 750 μS / cm, 800 μS / cm, 850 μS / cm, 900 μS / cm, 950 μS / cm or 1000 μS / cm or any range value between two of them. Free impurity ions remaining in the filter cake are removed by washing.

[0059] Furthermore, the calcination temperature is 550-600°C, including but not limited to any one of 550°C, 560°C, 570°C, 580°C, 590°C or 600°C or a range between any two of them.

[0060] Furthermore, the calcination time is 1.5 to 2 hours, including but not limited to any one of 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2 hours or a range between any two of them.

[0061] Calcination at this temperature and time can improve the purity of iron phosphate, make the structure of iron phosphate more stable, the particles more uniform, and increase the specific surface area.

[0062] Furthermore, the solid content of the slurry containing the filter cake D is 10wt% to 15wt%, including but not limited to any point value of 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt% or a range value between any two of them.

[0063] Further, the stirring reaction temperature is 85-90° C., including but not limited to any point value of 85° C., 86° C., 87° C., 88° C., 89° C. or 90° C. or any range value between two of them. This temperature is mainly to provide energy for the conversion of amorphous ferric phosphate dihydrate into crystalline ferric phosphate dihydrate. If the temperature is lower than this range, the slurry whitening time, i.e., the crystal transformation time, will be prolonged.

[0064] Furthermore, the stirring reaction time is 0.5 to 1 h, including but not limited to any one of 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h or a range between any two of them.

[0065] Another aspect of the present invention also relates to a method for treating ferric phosphate wastewater, including the method for recovering phosphorus from ferric phosphate phosphorus-containing wastewater.

[0066] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0067] The specific composition information of the saline wastewater and filtrate used in the following examples is shown in Table 1 and Table 2.

[0068] Table 1 Composition of saline wastewater

[0069] Components Phosphorus content (ppm) Salty wastewater 400-800

[0070] Table 2 Composition of filtrate

[0071] Components Phosphorus content (ppm) filtrate 600-1000

[0072] Example 1

[0073] The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided in this embodiment comprises the following steps:

[0074] Step S1: stirring and mixing the saline wastewater with a pH of 6 and the filtrate with a pH of 1.5 to obtain a mixed water sample A, wherein the pH of the mixed water sample A is 2.2;

[0075] Step S2: adding hydrogen peroxide to the mixed water sample A to obtain a mixed solution B;

[0076] Step S3: continue to add ferrous sulfate solution to the mixed solution B to obtain reaction slurry C; the molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1:0.75;

[0077] Step S4: performing solid-liquid separation on the reaction slurry C by vacuum filtration to obtain a filter cake D and a filtrate;

[0078] Step S5: slurry the filter cake D at a solid content of 10% to 15%, then add H3PO4 to adjust the pH value of the reaction solution to 1.4, and after the reaction slurry turns white, heat the system to 85°C and stir at a constant temperature for 0.5h to obtain reaction slurry E;

[0079] Step S6: performing solid-liquid separation on the slurry E to obtain a wet filter cake, washing the wet filter cake until the conductivity of the washing water is less than 1000 μS / cm, and drying the washed wet filter cake to obtain a dry cake F;

[0080] Step S7: calcining the dry cake F at a high temperature to obtain iron phosphate. The calcination temperature is 550° C. and the calcination time is 1.5 h.

[0081] Example 2

[0082] The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided in this embodiment comprises the following steps:

[0083] Step S1: stirring and mixing saline wastewater with a pH of 8 and filtrate with a pH of 2, wherein the volume ratio of saline wastewater to filtrate is 0.8, to obtain a mixed water sample A, wherein the pH of the mixed water sample A is 2.1;

[0084] Step S2: adding hydrogen peroxide to the mixed water sample A to obtain a mixed solution B;

[0085] Step S3: continue to add ferrous sulfate solution to the mixed solution B to obtain reaction slurry C; the molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1.5:1.125;

[0086] Step S4: performing solid-liquid separation on the reaction slurry C by vacuum filtration to obtain a filter cake D and a filtrate;

[0087] Step S5: slurry the filter cake D at a solid content of 10% to 15%, then add H3PO4 to adjust the pH value of the reaction solution to 1.8, and after the reaction slurry turns white, heat the system to 90°C and stir at a constant temperature for 1 hour to obtain reaction slurry E;

[0088] Step S6: performing solid-liquid separation on the slurry E to obtain a wet filter cake, washing the wet filter cake until the conductivity of the washing water is less than 1000 μS / cm, and drying the washed wet filter cake to obtain a dry cake F;

[0089] Step S7: calcining the dry cake F at a high temperature to obtain iron phosphate. The calcination temperature is 600° C. and the calcination time is 2 h.

[0090] Example 3

[0091] The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided in this embodiment comprises the following steps:

[0092] Step S1: stirring and mixing the saline wastewater with a pH of 6.5 and the filtrate with a pH of 1.6 to obtain a mixed water sample A, wherein the pH of the mixed water sample A is 2.15;

[0093] Step S2: adding hydrogen peroxide to the mixed water sample A to obtain a mixed solution B;

[0094] Step S3: continue to add ferrous sulfate solution to the mixed solution B to obtain reaction slurry C; the molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1.2:0.95;

[0095] Step S4: performing solid-liquid separation on the reaction slurry C by vacuum filtration to obtain a filter cake D and a filtrate;

[0096] Step S5: slurry the filter cake D at a solid content of 10% to 15%, then add H3PO4 to adjust the pH value of the reaction solution to 1.5, and after the reaction slurry turns white, heat the system to 86°C and stir at a constant temperature for 0.6h to obtain reaction slurry E;

[0097] Step S6: performing solid-liquid separation on the slurry E to obtain a wet filter cake, washing the wet filter cake until the conductivity of the washing water is less than 1000 μS / cm, and drying the washed wet filter cake to obtain a dry cake F;

[0098] Step S7: calcining the dry cake F at a high temperature to obtain iron phosphate. The calcination temperature is 560° C. and the calcination time is 1.6 h.

[0099] Example 4

[0100] The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided in this embodiment comprises the following steps:

[0101] Step S1: stirring and mixing the saline wastewater with a pH value of 7.5 and the filtrate with a pH value of 1.9 to obtain a mixed water sample A, wherein the pH value of the mixed water sample A is 2.3;

[0102] Step S2: adding hydrogen peroxide to the mixed water sample A to obtain a mixed solution B;

[0103] Step S3: continue to add ferrous sulfate solution to the mixed solution B to obtain reaction slurry C; the molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1.4:1.025;

[0104] Step S4: performing solid-liquid separation on the reaction slurry C by vacuum filtration to obtain a filter cake D and a filtrate;

[0105] Step S5: slurry the filter cake D at a solid content of 10% to 15%, then add H3PO4 to adjust the pH value of the reaction solution to 1.7, and after the reaction slurry turns white, heat the system to 89° C. and stir at a constant temperature for 0.9 h to obtain reaction slurry E;

[0106] Step S6: performing solid-liquid separation on the slurry E to obtain a wet filter cake, washing the wet filter cake until the conductivity of the washing water is less than 1000 μS / cm, and drying the washed wet filter cake to obtain a dry cake F;

[0107] Step S7: calcining the dry cake F at a high temperature to obtain iron phosphate. The calcination temperature is 590° C. and the calcination time is 1.9 h.

[0108] Example 5

[0109] The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided in this embodiment comprises the following steps:

[0110] Step S1: stirring and mixing the saline wastewater with a pH of 7 and the filtrate with a pH of 1.8 to obtain a mixed water sample A, wherein the pH of the mixed water sample A is 2.4;

[0111] Step S2: adding hydrogen peroxide to the mixed water sample A to obtain a mixed solution B;

[0112] Step S3: continue to add ferrous sulfate solution to the mixed solution B to obtain reaction slurry C; the molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1.3:0.95;

[0113] Step S4: performing solid-liquid separation on the reaction slurry C by vacuum filtration to obtain a filter cake D and a filtrate;

[0114] Step S5: slurry the filter cake D at a solid content of 10% to 15%, then add H3PO4 to adjust the pH value of the reaction solution to 1.6, and after the reaction slurry turns white, heat the system to 88°C and stir at a constant temperature for 0.8h to obtain reaction slurry E;

[0115] Step S6: performing solid-liquid separation on the slurry E to obtain a wet filter cake, washing the wet filter cake until the conductivity of the washing water is less than 1000 μS / cm, and drying the washed wet filter cake to obtain a dry cake F;

[0116] Step S7: calcining the dry cake F at a high temperature to obtain iron phosphate. The calcination temperature is 580° C. and the calcination time is 1.8 h.

[0117] The XRD pattern of the iron phosphate prepared in this example is as follows: Figure 1 As shown by Figure 1It can be seen that the peaks of the iron phosphate prepared in this example correspond to the standard spectrum of FePO4, and no diffraction peaks of impurity phase appear, which indicates that the prepared product is pure.

[0118] Comparative Example 1

[0119] The only difference between this comparative example and Example 5 is that the pH of the mixed water sample A is 1.9.

[0120] Comparative Example 2

[0121] The only difference between this comparative example and Example 5 is that the calcination temperature is 650°C.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 5 is that the stirring reaction temperature is 80°C.

[0124] Comparative Example 4

[0125] The only difference between this comparative example and Example 5 is that the wet filter cake obtained in step 6 is not washed.

[0126] Experimental example

[0127] The ferrous phosphate prepared in each embodiment and comparative example was tested for component content and performance, and the results are shown in Table 3 and Table 4.

[0128] Table 3 Content of each element in iron phosphate

[0129]

[0130]

[0131]

[0132] Table 4 Performance test of iron phosphate

[0133] feature Water content% <![CDATA[Density g / cm 3 > <![CDATA[Specific surface area m 2 / g]]> Index requirements ≤0.5％ ≥0.6 3～16 Example 1 0.32 0.76 6.1575 Example 2 0.38 0.76 7.4117 Example 3 0.27 0.80 8.1266 Example 4 0.25 0.91 13.0359 Example 5 0.36 0.85 6.4333 Comparative Example 1 0.22 0.73 14.4918 Comparative Example 2 0.2 1.25 2.2337 Comparative Example 3 0.44 0.89 17.8885 Comparative Example 4 0.29 0.88 10.0337

[0134] It can be seen from Tables 3 and 4 that the method for recovering phosphorus from phosphorus-containing iron phosphate wastewater provided by the present invention, the iron phosphate finally obtained is of good quality, high purity, and excellent performance, and is a battery-grade iron phosphate that meets industry standards (HG / T 4701-2021).

[0135] The phosphorus recovery rates of the embodiments and comparative examples were statistically analyzed. The phosphorus recovery rates were calculated as follows: 1-(phosphorus content of the first solid-liquid separation filtrate*volume / (phosphorus content of mixed water sample A*volume of mixed water sample A)). The results are shown in Table 5.

[0136] Table 5 Phosphorus recovery

[0137]

[0138]

[0139] It can be seen from Table 5 that the method for recovering phosphorus in phosphorus-containing iron phosphate wastewater provided by the present invention has a high phosphorus recovery rate and can achieve the rational utilization of phosphorus resources in iron phosphate wastewater.

[0140] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate, characterized in that: The following steps are involved: (a) mixing the saline wastewater and the filtrate to obtain a mixed water sample A; (b) adding an oxidant to the mixed water sample A to obtain a mixed solution B; (c) adding ferrous sulfate to the mixed solution B to obtain a reaction slurry C; (d) performing a first solid-liquid separation on the reaction slurry C to obtain a filter cake D; (e) adjusting the pH of the slurry containing the filter cake D to 1.4 to 1.8, and then performing stirring reaction, second solid-liquid separation, drying and calcination to obtain iron phosphate.

2. The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater according to claim 1, characterized in that: The pH of the saline wastewater is 6-8.

3. The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater according to claim 1, characterized in that: The pH of the filtrate is 1.5-2.

4. The method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate according to claim 1, characterized in that: The pH of the mixed water sample A is 2.1-2.

4.

5. The method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate according to claim 1, characterized in that: The volume ratio of the saline wastewater to the filtrate is 0.6 to 0.

8.

6. The method for recovering phosphorus from phosphorus-containing iron phosphate wastewater according to claim 1, characterized in that: The molar ratio of phosphorus, ferrous sulfate and oxidant in the mixed water sample A is 1:1-1.5:0.75-1.

125.

7. The method for recovering phosphorus from phosphorus-containing wastewater containing ferric phosphate according to claim 1, characterized in that: The calcination temperature is 550-600°C; And / or, the calcination time is 1.5 to 2 hours.

8. The method for recovering phosphorus from phosphorus-containing wastewater containing ferric phosphate according to claim 1, characterized in that: The stirring reaction temperature is 85-90°C; And / or, the stirring reaction time is 0.5 to 1 h.

9. The method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate according to any one of claims 1 to 8, characterized in that: The method for recovering phosphorus in phosphorus-containing iron phosphate wastewater also includes: washing the filter cake obtained by the second solid-liquid separation with desalted water; Preferably, the conductivity of the washing water is less than 1000 μS / cm.

10. A method for treating iron phosphate wastewater, characterized in that: The invention comprises the method for recovering phosphorus from phosphorus-containing wastewater containing iron phosphate as described in any one of claims 1 to 9.

Images