Method for treating and recycling and utilizing wastewater of a magnetic powder plant

Abstract

The application discloses a kind of magnetic powder factory wastewater treatment and resource recycling and utilization method, steps are as follows: wastewater is passed into reaction sedimentation tank, aeration is carried out, and alkali liquor is added to adjust wastewater pH to neutral, and after precipitation reaction, upper clear liquid is discharged;Polybasic carboxylic acid and hydroxide are added in the bottom layer flocculus obtained by precipitation, then flocculating agent is added, and after stirring, further precipitation is carried out, to obtain blue solution A and flocculent precipitate;The flocculent precipitate obtained is pressure filtered, dried and crushed to obtain recovered iron red;The pH of blue solution A is adjusted to 9~10.5, white precipitate is precipitated and blue solution B is obtained;The pH of blue solution B is adjusted to 11~12, to obtain blue flocculent precipitate.The application can recover Cu, alkaline earth metal and other metal ions in wastewater, reduce impurities in recovered iron red, increase its ferrite content, so that it can be directly used for the preparation of bonded permanent magnet ferrite magnetic powder and sintered permanent magnet ferrite magnetic powder, to realize resource utilization.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource utilization technology, and in particular to a method for wastewater treatment, resource recovery and utilization in a magnetic powder plant. Background Technology

[0002] Magnetic powder manufacturing requires a large amount of water during production. Currently, with optimized processes, most water can be recycled within production, resulting in minimal external discharge. Furthermore, the primary goal of wastewater treatment is to meet discharge requirements and recycling targets; the separation and reuse of solid waste after treatment remains insufficient. Additionally, the wastewater contains a large amount of Fe before treatment. 3+ The Fe(OH)3 particles precipitated after adjusting the pH with alkali using conventional methods are too fine, resulting in low efficiency of pressure filtration.

[0003] In the prior art, CN112299630A discloses an apparatus and method for recovering sodium chloride from wastewater in the preparation of bonded permanent magnet ferrite powder. This invention utilizes the heat generated during the preparation of bonded permanent magnet ferrite powder to crystallize and concentrate the wastewater, and can separate salts from the wastewater. However, it does not mention a systematic wastewater treatment method for magnetic powder plants, nor does it propose a method for recovering metals such as Cu.

[0004] CN201410530017.8 discloses a method for treating wastewater from manganese-zinc ferrite production, comprising the following steps: after coarse filtration of the wastewater, the pH of the wastewater is adjusted to 6.5-7.5 in an equalization tank; then, a flocculant is added in a coagulation sedimentation tank with stirring; after mixing and sedimentation, the supernatant is the treated wastewater that meets the standards. This method is limited to ensuring wastewater discharge meets standards; it cannot recover other metals and does not mention the recovery and application of iron oxide (Fe3O4).

[0005] CN110395770A discloses a method for producing iron oxide red using sludge. Although the method mentions the resource utilization of iron oxide red, the impurity metal ions are not removed, and a high temperature of 95°C needs to be maintained, which consumes a lot of energy.

[0006] Other literature mentions methods for recovering iron oxide from wastewater for use in permanent magnet production. While these methods have some theoretical feasibility, the recovered ferrite is mixed in composition and has low purity, requiring a corresponding purification line, which increases costs and makes it unsuitable for production. This invention aims to further separate impurity metal ions from sludge, further improving the feasibility of recovering iron oxide for ferrite manufacturing. Simultaneously, while meeting wastewater discharge standards, it enriches and separates impurities such as Cu and Sr from the precipitate, enabling their recovery as raw materials for permanent magnet ferrite. Summary of the Invention

[0007] The present invention aims to overcome the aforementioned problems in the prior art and provides a method for wastewater treatment, resource recovery and utilization in magnetic powder plants. This method can recover metal ions such as Cu and alkaline earth metals from wastewater, reduce impurities in the recovered iron oxide, and increase its ferrite content, making it directly usable in the preparation of bonded permanent magnet ferrite powder and sintered permanent magnet ferrite powder, thereby achieving resource utilization.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for treating and recycling wastewater from a magnetic powder plant, comprising the following steps:

[0010] (1) Pass the wastewater into the reaction sedimentation tank, aerate it, and add alkaline solution to adjust the pH of the wastewater to neutral. After the reaction sedimentation, discharge the supernatant.

[0011] (2) Add polycarboxylic acid and hydroxide to the bottom flocculent obtained in step (1), then add flocculant, stir and precipitate further to obtain blue solution A and flocculent precipitate; filter, dry and crush the obtained flocculent precipitate to obtain recovered iron red;

[0012] (3) Adjust the pH of blue solution A to 9-10.5 to precipitate a white precipitate and obtain blue solution B; filter the white precipitate to obtain alkaline earth metal salt;

[0013] (4) Adjust the pH of blue solution B to 11-12 to obtain blue flocculent precipitate. After filtration, the remaining liquid is discharged into the reaction sedimentation tank described in step (1) and mixed with wastewater.

[0014] In step (1) of this invention, the wastewater is first aerated and an alkaline solution is added to adjust the pH of the wastewater to neutral. The main purpose of aeration is to reduce the COD caused by ferrous iron and to have a stirring effect. After adjusting the pH to neutral, Fe... 3+ Cu 2+ Alkaline earth metal ions can form hydroxide precipitates, and the supernatant meets the Class III standard requirements of the Integrated Wastewater Discharge Standard GB 8978-1996. The wastewater from the magnetic powder plant may contain Cr. 6+ These are the main environmentally hazardous ions monitored, due to the presence of Cr in the magnetic powder production process. 6+ It has been placed under close monitoring, and the wastewater itself contains Fe. 2+ It can convert Cr 6+ Reduced to Cr 3+ Furthermore, the Fe(OH)3 colloids generated during pH adjustment have adsorption properties, and most major metal ions are adsorbed. The Cr content in the supernatant is reduced. 6+ The concentration meets emission standards. The trace metal ions in the discharged supernatant are mainly sodium. +K + Light metals can be recycled in production, mainly used as cooling water for products, where a large amount of water is consumed during evaporation.

[0015] After the upper clear liquid is discharged, the bottom flocculent is too fine for pressure filtration due to the excessively fine Fe(OH)3, resulting in the inability to achieve rapid dehydration through pressure filtration and other methods. Therefore, further flocculation is required. In step (2) of this invention, before adding the flocculant, polycarboxylic acid and hydroxide are added first, which can play a role in coagulation, reduce the amount of PAM, and dissolve the copper ions and alkaline earth metal ions in the precipitate. Then, the flocculant is added for flocculation, resulting in a blue solution A containing copper ions and alkaline earth metal ions and a flocculent precipitate with Fe(OH)3 as the main component. After the flocculent precipitate is pressure filtered, dried, and pulverized, the recovered iron oxide has a high iron content, which can reach more than 98%, and the content of Cu, alkaline earth metal and other metal ion impurities is low. It can be directly used in the preparation of low-end bonded permanent magnet ferrite powder and sintered permanent magnet ferrite powder (in low-end products, the iron oxide content is more than 98.5%). Since the raw materials contain Cu when preparing ferrite, 2+ The content is extremely low (<0.05%), therefore, existing technologies for recovering iron oxide from magnetic particle plant wastewater do not focus on Cu. 2+ The separation of Fe(OH)3 into Fe2O3. This invention found that before the addition of polycarboxylic acids and hydroxides, Cu is enriched in the flocculant, with a content approaching 10 wt%. Failure to separate it would significantly affect the subsequent resource utilization of recovered iron oxide. In step (1), the supernatant is first discharged, which reduces the amount of water treated in subsequent work, prevents excessive dilution of PAM, reduces sedimentation time, and increases the metal ion concentration of the blue solution A. In step (2), the drying process includes decomposing Fe(OH)3 into Fe2O3.

[0016] After recovering the Fe(OH)3 precipitate, the pH of the blue solution A is adjusted to 9–10.5 to recover alkaline earth metal salts, mainly strontium salts and trace amounts of barium or calcium salts. Then, the pH of the obtained blue solution B is adjusted to 11–12 to precipitate and recover copper ions. The final residue can be mixed with wastewater in a reaction sedimentation tank for further treatment. The pH adjustment in step (3) is crucial because it overlaps with the precipitation pH in step (4). If the precipitation pH in step (3) exceeds 10.5, copper ions will co-precipitate with alkaline earth metal citrates, making separate recovery for subsequent use impossible.

[0017] Preferably, after the upper clear liquid is discharged in step (1), the solid content of the bottom flocculent is 3.5wt% to 10wt%.

[0018] Preferably, the polycarboxylic acid in step (2) is selected from one or more of citric acid, oxalic acid, malic acid, tartaric acid, and succinic acid; and the hydroxide is selected from one or two of sodium hydroxide and potassium hydroxide.

[0019] Preferably, the mass ratio of polycarboxylic acid to hydroxide added in step (2) is 1.5 to 5:1; the concentration of the added polycarboxylic acid in the bottom flocculent is 0.1 to 4 g / L. If the ratio of polycarboxylic acid to hydroxide is too small, the pH of the water will be too high after addition, and the salt generated by the reaction of polycarboxylic acid and impurity metal ions will precipitate prematurely, resulting in a decrease in the purity of the ferric hydroxide filter cake and affecting the subsequent utilization of the recovered iron oxide.

[0020] Preferably, in step (2), the polycarboxylic acid and hydroxide are added in the form of an aqueous solution; when adding, the polycarboxylic acid and hydroxide are first prepared into a mixed solution and then added to the bottom flocculent; or the polycarboxylic acid solution is added to the bottom flocculent first and then the hydroxide solution is added. The present invention has found that the amount of PAM used when the polycarboxylic acid is added first and then the hydroxide is added is less than that when the hydroxide is added first and then the polycarboxylic acid is added. Adding the polycarboxylic acid first can reduce the amount of PAM used by about 50 wt%.

[0021] Preferably, the flocculant in step (2) is PAM, and the concentration of the added flocculant in the bottom floc is 0.01 to 0.1 g / L.

[0022] Secondly, the present invention provides an application of the recovered iron oxide obtained by the above method in the preparation of bonded permanent magnet ferrite powder, comprising the following steps: the recovered iron oxide is mixed into iron oxide with a purity of 98.5% or higher at a mass ratio of 1% to 2%, and then BaCO3 is added to make the molar ratio of Fe to Ba 5.5 to 5.8 to obtain a mixture. Then the mixture is densified, pelletized, pre-calcined, crushed and pulverized to obtain bonded permanent magnet ferrite powder.

[0023] Preferably, the densification time is 0.5–1.5 h; the pre-firing temperature is 1180–1230 °C; the pre-firing time is 60–120 min; and the average particle size of the obtained bonded permanent magnet ferrite powder is 2.0–2.3 μm.

[0024] Thirdly, the present invention provides an application of the recovered iron oxide obtained by the above method in the preparation of sintered permanent magnet ferrite powder, comprising the following steps: the recovered iron oxide is added to iron oxide with a purity of 99% or higher at a mass ratio of 1% to 2%, and SrCO3 is added to make the molar ratio of Fe to Sr 5.3 to 6.0 to obtain a mixture. Then the mixture is densified, pelletized, pre-fired, crushed and pulverized to obtain sintered permanent magnet ferrite powder.

[0025] Preferably, the densification time is 0.5–1.5 h; the pre-firing temperature is 1240–1280 °C; the pre-firing time is 60–120 min; and the average particle size of the sintered permanent magnet ferrite powder is 3–6 μm.

[0026] The performance of permanent magnet ferrites is greatly affected by the composition of raw materials. Existing technologies recover iron oxide from wastewater in magnetic powder plants, which contains low ferrite content and high levels of metallic impurities. Using this untreated iron oxide directly in ferrite preparation easily leads to substandard products. The method described in this invention recovers iron oxide with a high ferrite content and low levels of metal ion impurities such as Cu. This iron oxide can be directly incorporated into iron oxide for preparing bonded or sintered permanent magnet ferrites without affecting the performance of the resulting ferrite.

[0027] Therefore, the present invention has the following beneficial effects:

[0028] (1) It can further optimize the utilization of wastewater resources in magnetic powder plants and reduce wastewater discharge;

[0029] (2) It can recover metal ions in the wastewater of magnetic powder plant, further improving the feasibility of iron red recovery for ferrite manufacturing; (3) It has high processing efficiency and the additives are environmentally friendly and have no environmental hazards. Attached Figure Description

[0030] Figure 1 This is a flowchart of the wastewater treatment and resource recovery process for a magnetic powder plant according to the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. The methods in the following embodiments are conventional methods in the field unless otherwise specified.

[0033] The wastewater from the magnetic powder plant used in this embodiment of the invention comes from the magnetic powder production wastewater of Zhejiang Ante Magnetic Materials Co., Ltd. The sampling point is the inlet of the wastewater treatment plant, and the obtained wastewater is untreated.

[0034] Example 1:

[0035] A method for wastewater treatment and resource recovery in a magnetic powder plant, the process is as follows: Figure 1 The steps shown are as follows:

[0036] (1) Wastewater was introduced into a reaction sedimentation tank, aerated, and sodium hydroxide solution was added to adjust the pH of the wastewater to 7. The water turned into an orange-yellow turbid liquid. After standing for 60 minutes, stratified wastewater was obtained; the Cr content of the upper clear liquid was measured. 6+The content meets the emission standards, the upper clear liquid is discharged, and the bottom flocculent is obtained; the solid content of the bottom flocculent is measured to be 3.8%, and the composition of the bottom flocculent is measured as shown in Table 1;

[0037] (2) Dissolve citric acid and sodium hydroxide in water at a mass ratio of 2.4:1 to obtain sodium citrate aqueous solution; take 100 mL of the bottom flocs obtained in step (1), add sodium citrate aqueous solution, and then add flocculant PAM until the flocs aggregate and precipitate clear liquid; in the added sodium citrate aqueous solution, the concentration of citric acid in the bottom flocs is 0.38 g / L, and the concentration of added PAM in the bottom flocs is 0.08 g / L; let stand for 5 min, at which time the pH is 7.8, and obtain blue solution A and flocculent precipitate; after the obtained flocculent precipitate is filtered, dried, and pulverized, 5.6 g of recovered iron red is obtained, and its composition is measured as shown in Table 2;

[0038] (3) Add sodium hydroxide solution to adjust the pH of blue solution A to 9, precipitate a white precipitate and obtain blue solution B; filter and dry the white precipitate to obtain 1.2g of alkaline earth metal citrate, and measure its composition as shown in Table 2;

[0039] (4) Add sodium hydroxide solution to adjust the pH of blue solution B to 11 to obtain blue flocculent precipitate. After filtration, the remaining liquid is discharged into the reaction sedimentation tank described in step (1) and mixed with wastewater. After drying the blue flocculent precipitate, 0.65g of blue filter residue is obtained. Its composition is measured as shown in Table 2.

[0040] Example 2:

[0041] The difference between Example 2 and Example 1 is that the concentration of citric acid added in step (2) in the bottom flocs is 1.92 g / L; the concentration of PAM added in the bottom flocs is 0.05 g / L; the rest are the same as in Example 1; the mass of recovered iron red is 5.5 g, alkaline earth metal citrate is 1.3 g, and blue filter residue is 0.66 g.

[0042] Example 3:

[0043] The difference between Example 3 and Example 1 is that the concentration of citric acid added in step (2) in the bottom flocs is 3.84 g / L, and the concentration of PAM added in the bottom flocs is 0.1 g / L; the rest are the same as in Example 1; the recovered iron red mass is 11 g, alkaline earth metal citrate is 2.74 g, and blue filter residue is 1.31 g.

[0044] Example 4:

[0045] The difference between Example 4 and Example 1 is that the concentration of PAM added in step (2) in the bottom flocculent is 0.09 g / L; the pH of blue solution A is adjusted to 10 in step (3), and the rest is the same as in Example 1; the recovered iron red mass is 5.6 g, alkaline earth metal citrate is 1.5 g, and blue filter residue is 0.63 g.

[0046] Example 5:

[0047] The difference between Example 5 and Example 1 is that in step (4), the pH of the blue solution B is adjusted to 12, and the rest is the same as in Example 1; the recovered iron red mass is 5.53g, alkaline earth metal citrate is 1.32g, and blue filter residue is 0.67g.

[0048] Example 6:

[0049] The difference between Example 6 and Example 1 is that in step (2), citric acid aqueous solution is added to the bottom floc first, then sodium hydroxide aqueous solution is added, and finally PAM is added. The concentration of citric acid in the bottom floc is 0.19 g / L, the concentration of sodium hydroxide in the bottom floc is 0.04 g / L, and the concentration of PAM in the bottom floc is 0.07 g / L. After standing, the pH is 5.8, and the precipitate is blue-green. The rest is the same as in Example 1. The recovered iron oxide red mass is 5.38 g, alkaline earth metal citrate is 1.61 g, and blue filter residue is 0.64 g.

[0050] Example 7:

[0051] The difference between Example 7 and Example 1 is that in step (2), citric acid aqueous solution is added to the bottom flocculent first, then sodium hydroxide aqueous solution is added, and finally PAM is added. The concentration of citric acid in the bottom flocculent is 0.19 g / L, the concentration of sodium hydroxide in the bottom flocculent is 0.08 g / L, and the concentration of PAM in the bottom flocculent is 0.05 g / L. After standing, the pH is 6.4, and the precipitate is blue-green. The rest is the same as in Example 1. The recovered iron oxide red mass is 5.42 g, alkaline earth metal citrate is 1.55 g, and blue filter residue is 0.62 g.

[0052] Example 8:

[0053] The difference between Example 8 and Example 1 is that in step (2), sodium hydroxide aqueous solution is added to the bottom floc first, then citric acid aqueous solution is added, and finally PAM is added. The concentration of citric acid in the bottom floc is 0.19 g / L, the concentration of sodium hydroxide in the bottom floc is 0.04 g / L, and the concentration of PAM in the bottom floc is 0.09 g / L. After standing, the pH is 5.8. The rest is the same as in Example 1. The recovered iron red mass is 5.38 g, alkaline earth metal citrate is 1.61 g, and blue filter residue is 0.64 g.

[0054] Comparative Example 1:

[0055] The difference between Comparative Example 1 and Example 1 is that sodium citrate solution is not added in step (2), the concentration of added PAM in the bottom flocculent is 0.2 g / L, the pH is 7 after standing, and the precipitate is a colorless and transparent solution; the rest is the same as in Example 1; the mass of recovered iron red is 7.3 g, and there is basically no precipitation when adjusting the pH of the colorless and transparent solution in steps (3) and (4).

[0056] Comparative Example 2:

[0057] The difference between Comparative Example 2 and Example 1 is that only citric acid solution was added in step (2), and sodium hydroxide solution was not added; the concentration of added citric acid in the bottom flocculent was 0.19 g / L, the concentration of added PAM in the bottom flocculent was 0.21 g / L, the pH after standing was 4.8, the precipitate was pale yellow and turbid, and after filtration, a colorless and transparent solution was obtained; the rest was the same as in Example 1; the mass of recovered iron red was 7.3 g, and only yellow substances precipitated when the pH of the colorless and transparent solution was adjusted in steps (3) and (4).

[0058] Comparative Example 3:

[0059] The difference between Comparative Example 3 and Example 1 is that only sodium hydroxide solution was added in step (2), and no citric acid solution was added; the concentration of sodium hydroxide in the bottom flocculent was 0.04 g / L, the concentration of PAM in the bottom flocculent was 0.18 g / L, the pH after standing was 8.2, and the precipitate was a colorless and transparent solution; the rest were the same as in Example 1; the mass of recovered iron oxide red was 7.5 g, and there was basically no precipitation when adjusting the pH of the colorless and transparent solution in steps (3) and (4).

[0060] Comparative Example 4:

[0061] The difference between Comparative Example 4 and Example 1 is that in step (2), acetic acid solution is used instead of sodium citrate aqueous solution in Example 1, and the concentration of acetic acid added in the bottom flocculent is 0.12 g / L; the rest are the same as in Example 1.

[0062] Comparative Example 5:

[0063] The difference between Comparative Example 5 and Example 1 is that sodium acetate solution was used instead of sodium citrate aqueous solution in Example 1 in step (2), and the concentration of sodium acetate added in the bottom flocculent was 0.16 g / L; the rest were the same as in Example 1.

[0064] Comparative Example 6:

[0065] The difference between Comparative Example 6 and Example 1 is that the concentration of citric acid added in step (2) in the bottom flocculent is 0.19 g / L; the rest are the same as in Example 1; the mass of recovered iron red is 6.63 g, alkaline earth metal citrate is 1.03 g, and blue filter residue is 0.45 g.

[0066] Comparative Example 7:

[0067] The difference between Comparative Example 7 and Example 1 is that in step (3), the pH of the blue solution A is adjusted to 10.8, while the rest is the same as in Example 1.

[0068] Table 1: Mass percentage of metal elements in the bottom flocculent material.

[0069]

[0070] Table 2: Component measurement results of the recovered products.

[0071]

[0072] Among them, whether the discharged supernatant meets the standard refers to whether it meets the Class III standard requirements of the "Integrated Wastewater Discharge Standard" GB 8978-1996.

[0073] As shown in Table 2, the method of this invention used in Examples 1-8 can effectively separate Cu ions, Sr, and other alkaline earth metal ions from the precipitate, obtaining recovered iron red with a high Fe content. Furthermore, the order of addition of citric acid and sodium hydroxide has a certain impact on the recovery effect: in Examples 1-5, adding citric acid and sodium hydroxide to prepare a sodium citrate aqueous solution can achieve better flocculation effects with a lower PAM addition amount; in Examples 6 and 7, adding citric acid first and then sodium hydroxide, compared to adding sodium hydroxide first and then citric acid in Example 8, can reduce the amount of PAM used and lower the processing cost; however, adding acid first results in a blue-green precipitate, possibly because the added acid reacts with ferric hydroxide, leading to the introduction of a small amount of Fe. 3+ .

[0074] In Comparative Example 1, without the addition of citric acid and sodium hydroxide for coagulation aid, a relatively large amount of PAM was required to effectively flocculate and precipitate ferric hydroxide. Furthermore, Cu ions and alkaline earth metal ions could not be separated from the ferric hydroxide precipitate, resulting in a high amount of metallic impurities in the recovered iron oxide, affecting its subsequent utilization. Comparative Example 2, with only citric acid and no sodium hydroxide, and Comparative Example 3, with only sodium hydroxide and no citric acid, both required high amounts of PAM and still failed to separate Cu ions and alkaline earth metal ions from the ferric hydroxide precipitate. In Comparative Examples 4 and 5, acetic acid or sodium acetate were used instead of citric acid and sodium hydroxide as coagulation aids, but these failed to provide any coagulation aid effect. At the same PAM dosage, ferric hydroxide could not be flocculated and precipitated; nor could Cu ions and alkaline earth metal ions be separated from the ferric hydroxide precipitate. In Comparative Example 6, the addition of too little citric acid resulted in poor dissolution performance for Cu ions and alkaline earth metal ions, leading to a high amount of impurities in the recovered iron oxide. In Comparative Example 7, the pH of the blue solution A was adjusted too high, causing copper ions to precipitate together with alkaline earth metal ions, making it impossible to separate the two and affecting the subsequent utilization of the recovered product.

[0075] Application Example 1:

[0076] An application of the recovered iron oxide obtained by the above method in the preparation of sintered permanent magnet ferrite powder includes the following steps: the recovered iron oxide obtained in Example 1 is added to iron oxide with a purity of more than 99% at a mass ratio of 1%, and SrCO3 is added to make the molar ratio of Fe to Sr 5.9 to obtain a mixture. Then, the mixture is densified, pelletized, pre-fired, crushed and pulverized to obtain sintered permanent magnet ferrite powder with an average particle size of 4.21 μm. The densification time is 1.0 h, the pre-fired temperature is 1240 °C and the pre-fired time is 90 min.

[0077] Application Example 2:

[0078] An application of the recovered iron oxide obtained by the above method in the preparation of sintered permanent magnet ferrite powder includes the following steps: the recovered iron oxide obtained in Example 1 is added to iron oxide with a purity of more than 99% at a mass ratio of 2%, and SrCO3 is added to make the molar ratio of Fe to Sr 5.9 to obtain a mixture. Then, the mixture is subjected to densification, pelletizing, pre-firing, crushing and pulverizing to obtain sintered permanent magnet ferrite powder with an average particle size of 4.50 μm. The densification time is 1.0 h, the pre-firing temperature is 1240 °C and the pre-firing time is 90 min.

[0079] Comparative application example 1:

[0080] A method for preparing sintered permanent magnet ferrite powder includes the following steps: adding SrCO3 to iron oxide red with a purity of 99% or higher, so that the molar ratio of Fe to Sr is 5.9 to obtain a mixture, and then passing the mixture through densification, pelletizing, pre-firing, crushing and pulverizing to obtain sintered permanent magnet ferrite powder with an average particle size of 4.43 μm; the densification time is 1.0 h, the pre-firing temperature is 1240 °C, and the pre-firing time is 90 min.

[0081] Compare with application example 2:

[0082] The recovered iron oxide obtained in Comparative Example 1 was added to iron oxide with a purity of over 99% at a mass ratio of 1%. SrCO3 was added to make the molar ratio of Fe to Sr 5.9 to obtain a mixture. The mixture was then subjected to densification, pelletizing, pre-firing, crushing, and pulverizing to obtain sintered permanent magnet ferrite powder with an average particle size of 4.26 μm. The densification time was 1.0 h, the pre-firing temperature was 1240 °C, and the pre-firing time was 90 min.

[0083] Compare with example 3:

[0084] The recycled iron oxide obtained in Example 1 was added to iron oxide with a purity of over 99% at a mass ratio of 3%. SrCO3 was added to make the molar ratio of Fe to Sr 5.9 to obtain a mixture. The mixture was then subjected to densification, pelletizing, pre-firing, crushing, and pulverizing to obtain sintered permanent magnet ferrite powder with an average particle size of 4.34 μm. The densification time was 1.0 h, the pre-firing temperature was 1240 °C, and the pre-firing time was 90 min.

[0085] The performance of the sintered permanent magnet ferrite powders prepared in corresponding application examples 1-2 and comparative application examples 1-3 was tested, and the results are shown in Table 3. The test method was as follows: 1.2 wt% CaCO3, 0.15 wt% HBO3 and 0.25 wt% SiO2 were added to the sintered permanent magnet ferrite powders obtained in each application example and comparative application example, and then ball-milled for 10 h to obtain a slurry. The average particle size of the slurry magnetic powder was 0.85 μm. The slurry was pressed into shape under a magnetic field of 8000 Oe and sintered at 1260℃ for 1.5 h. The magnetic properties were then tested in a magnetic analyzer.

[0086] Table 3: Performance test results of sintered permanent magnet ferrite.

[0087] project Br(Gs) Hcb(Oe) Hcj(Oe) HBmax(MGOe) Application Example 1 4216 2856 2882 4.24 Application Example 2 4196 2906 2956 4.24 Comparative Application Example 1 4220 2911 2821 4.24 Comparative Application Example 2 3938 2929 3041 4.23 Comparative Application Example 3 4085 2976 3015 4.24

[0088] As shown in Table 3, the remanence Br of the sintered permanent magnet ferrite obtained by adding the recovered iron oxide obtained in Example 1 of this invention in Application Examples 1 and 2 is not significantly different from that of the permanent magnet ferrite without the recovered iron oxide in Comparative Application Example 1, and has a slightly higher Hcj. However, the Br of the permanent magnet ferrite prepared using the recovered iron oxide obtained in Comparative Application Example 2 is significantly lower than that of Comparative Application Example 1. This is due to the presence of impurity elements. Although Comparative Application Example 2 has a higher Hcj, the requirements for Hcj are not as strict as for Br in practical applications. Therefore, adding the recovered iron oxide obtained in Comparative Example 1 may cause the product to be unqualified. As can be seen from Comparative Application Example 3, the addition of excessive amount of the recovered iron oxide obtained by this invention will also cause a decrease in remanence Br. In the product corresponding to this formula, the performance of Comparative Application Example 3 is already near the lower limit.

[0089] Application Example 3:

[0090] An application of the recovered iron oxide obtained by the above method in the preparation of bonded permanent magnet ferrite powder includes the following steps: the recovered iron oxide obtained in Example 1 is added to iron oxide with a purity of 98.5% or higher at a mass ratio of 1%, and BaCO3 is added to make the molar ratio of Fe to Ba 5.68 to obtain a mixture. Then, the mixture is subjected to densification, pelletizing, pre-firing, crushing and pulverizing to obtain bonded permanent magnet ferrite powder with an average particle size of 2.2 μm. The densification time is 1.0 h, the pre-firing temperature is 1200 °C, and the pre-firing time is 90 min.

[0091] Application Example 4:

[0092] An application of the recovered iron oxide obtained by the above method in the preparation of bonded permanent magnet ferrite powder includes the following steps: the recovered iron oxide obtained in Example 1 is added to iron oxide with a purity of 98.5% or higher at a mass ratio of 2%, and BaCO3 is added to make the molar ratio of Fe to Ba 5.68 to obtain a mixture. Then, the mixture is subjected to densification, pelletizing, pre-firing, crushing and pulverizing to obtain bonded permanent magnet ferrite powder with an average particle size of 2.15 μm. The densification time is 1.0 h, the pre-firing temperature is 1200 °C, and the pre-firing time is 90 min.

[0093] Compare with application example 4:

[0094] A method for preparing bonded permanent magnet ferrite powder includes the following steps: adding BaCO3 to iron oxide red with a purity of 98.5% or higher, so that the molar ratio of Fe to Ba is 5.68, to obtain a mixture; then, the mixture is subjected to densification, pelletizing, pre-firing, crushing, and pulverizing to obtain bonded permanent magnet ferrite powder with an average particle size of 2.20 μm; the densification time is 1.0 h, the pre-firing temperature is 1200 °C, and the pre-firing time is 90 min.

[0095] Compare with example 5:

[0096] The recovered iron oxide obtained in Comparative Example 1 was mixed into iron oxide with a purity of 98.5% or higher at a mass ratio of 1%. BaCO3 was added to make the molar ratio of Fe to Ba 5.68 to obtain a mixture. The mixture was then subjected to densification, pelletizing, pre-firing, crushing and pulverizing to obtain bonded permanent magnet ferrite powder with an average particle size of 2.19 μm. The densification time was 1.0 h, the pre-firing temperature was 1200 °C and the pre-firing time was 90 min.

[0097] Comparative application example 6:

[0098] The recycled iron oxide obtained in Example 1 was added to iron oxide with a purity of 98.5% or higher at a mass ratio of 3%. BaCO3 was added to make the molar ratio of Fe to Ba 5.68 to obtain a mixture. The mixture was then subjected to densification, pelletizing, pre-firing, crushing and pulverizing to obtain bonded permanent magnet ferrite powder with an average particle size of 2.16 μm. The densification time was 1.0 h, the pre-firing temperature was 1200 °C and the pre-firing time was 90 min.

[0099] The performance of the bonded permanent magnet ferrite powder prepared in corresponding use cases 3-4 and comparative application examples 4-6 was tested, and the results are shown in Table 4. The test method was as follows: 20g of magnetic powder was taken, 1.5g of water was added, and after mixing, the mixture was pressed into a cylindrical magnetic block with a diameter of Ф20mm under a hydraulic press with a pressure of 30MPa. The magnetic properties of the bonded magnet were then tested using a magnetometer.

[0100] Table 4: Test results of ferrite properties of bonded permanent magnets.

[0101] project Br(Gs) Hcb(Oe) Hcj(Oe) HBmax(MGOe) Application Example 3 1610 1501 2376 0.49 Application Example 4 1597 1569 2423 0.49 Comparative Application Example 4 1632 1456 2335 0.49 Comparative Application Example 5 1449 1586 2500 0.49 Comparative Application Example 6 1522 1623 2503 0.48

[0102] As can be seen from Table 4, when the recycled iron oxide obtained in the embodiments and comparative examples of the present invention is used for the preparation of bonded permanent magnet ferrite, it follows a similar pattern to that used for the preparation of sintered permanent magnet ferrite.

Claims

1. A method for wastewater treatment and resource recovery in a magnetic powder plant, characterized by the following steps: include: (1) Pass the wastewater into the reaction sedimentation tank, aerate it, and add alkaline solution to adjust the pH of the wastewater to neutral. After the reaction sedimentation, discharge the supernatant. (2) Add an aqueous solution of polycarboxylic acid and hydroxide to the bottom flocculent obtained in step (1), then add flocculant, stir and further precipitate to obtain blue solution A and flocculent precipitate; filter, dry and crush the obtained flocculent precipitate to obtain recovered iron red; the polycarboxylic acid is selected from one or more of citric acid, oxalic acid, malic acid, tartaric acid and succinic acid; the hydroxide is selected from NaOH and / or KOH; when adding, first prepare a mixed solution of polycarboxylic acid and hydroxide, and then add it to the bottom flocculent; or first add polycarboxylic acid solution to the bottom flocculent and then add hydroxide solution; (3) Adjust the pH of blue solution A to 9~10.5, precipitate a white precipitate and obtain blue solution B; filter the white precipitate to obtain alkaline earth metal salt, the main components of which are strontium salt and a very small amount of barium or calcium salt; (4) Adjust the pH of the blue solution B to 11~12, precipitate and recover the copper ions in it, and obtain a blue flocculent precipitate. After filtration, the remaining liquid is discharged into the reaction sedimentation tank of step (1) and mixed with the wastewater.

2. The method for wastewater treatment and resource recovery in a magnetic powder plant according to claim 1, characterized in that, After the upper clear liquid is discharged in step (1), the solid content of the bottom flocculent is 3.5wt%~10wt%.

3. The method for wastewater treatment and resource recovery in a magnetic powder plant according to claim 1, characterized in that, The polycarboxylic acid mentioned in step (2) is citric acid.

4. The method for wastewater treatment and resource recovery in a magnetic powder plant according to claim 1 or 3, characterized in that, The mass ratio of the polycarboxylic acid and hydroxide added in step (2) is 1.5~5:1; the concentration of the added polycarboxylic acid in the bottom flocculent is 0.1~4g / L.

5. The method for wastewater treatment and resource recovery in a magnetic powder plant according to claim 1, characterized in that, The flocculant mentioned in step (2) is PAM, and the concentration of the added flocculant in the bottom floc is 0.01~0.1g / L.

6. An application of the recovered iron oxide obtained by the method described in any one of claims 1 to 5 in the preparation of bonded permanent magnet ferrite powder, characterized in that, Includes the following steps: The recycled iron oxide is mixed into iron oxide with a purity of 98.5% or higher at a mass ratio of 1% to 2%, and then BaCO3 is added to make the molar ratio of Fe to Ba 5.5 to 5.8 to obtain a mixture. The mixture is then densified, pelletized, pre-fired, crushed and pulverized to obtain bonded permanent magnet ferrite powder.

7. The application according to claim 6, characterized in that, The densification time is 0.5~1.5h; the pre-firing temperature is 1180~1230℃ and the pre-firing time is 60~120min; the average particle size of the bonded permanent magnet ferrite powder is 2.0~2.3μm.

8. An application of the recovered iron oxide obtained by the method described in any one of claims 1 to 5 in the preparation of sintered permanent magnet ferrite powder, characterized in that, Includes the following steps: The recovered iron oxide is mixed into iron oxide with a purity of 99% or higher at a mass ratio of 1% to 2%, and then SrCO3 is added to make the molar ratio of Fe to Sr 5.3 to 6.0 to obtain a mixture. The mixture is then densified, pelletized, pre-fired, crushed and pulverized to obtain sintered permanent magnet ferrite powder.

9. The application according to claim 8, characterized in that, The densification time is 0.5~1.5h; the pre-firing temperature is 1240~1280℃, and the pre-firing time is 60~120min; the average particle size of the sintered permanent magnet ferrite powder is 3~6μm.

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