A method for producing iron phosphate

Abstract

This invention discloses a method for preparing ferric phosphate, comprising the following steps: pretreating wastewater from the ferric phosphate production process; concentrating the pretreated filtrate through adsorption with a phosphorus removal resin to obtain a regenerated solution; concentrating the regenerated solution through nanofiltration for salt separation to obtain a concentrated solution; and mixing the concentrated solution with a phosphate salt solution from ferric phosphate production to prepare a phosphate salt mixed solution for use in ferric phosphate production. This invention utilizes chemical precipitation, filtration, reverse osmosis combined with MVR to recover pure water, and then employs phosphorus removal resin adsorption regeneration and NF membrane salt separation to concentrate the phosphate salt. This results in a high phosphate salt concentration, low impurities, and reuse of the relatively scarce phosphorus source, reducing raw material costs and maintenance costs for ferric phosphate production enterprises by 8.0%–20.0%, improving production efficiency, and making it a suitable measure for enterprises to reduce costs, increase efficiency, and improve product performance.

Description

Technical Field

[0001] This invention relates to a method for preparing ferric phosphate, and more particularly to a low-cost method for preparing ferric phosphate based on phosphorus source recovery technology. Background Technology

[0002] Ferric phosphate, also known as high-ferric phosphate or orthophosphate, is mainly used in the manufacture of ferric phosphate precursor materials. Meanwhile, the development of phosphorus resources, especially inorganic phosphates, phosphate fertilizers, organic phosphates, and electronic-grade phosphorus-based chemicals, is an important way to maximize the economic benefits of phosphorus resources. Currently, phosphorus source development enterprises are generally small in scale, with low recovery rates; poor ore beneficiation, high beneficiation costs; low beneficiation efficiency, and insufficient comprehensive utilization; the phenomenon of "high-quality but underutilized" phosphate ore processing is prominent; high-end products are scarce, and high-value, high-efficiency utilization is very low.

[0003] However, in the production of ferric phosphate, due to the large-scale use of phosphorus sources—such as some companies using phosphoric acid to remove impurities from ferrous sulfate, the amount of phosphorus source used in preparing the reaction solution often exceeding the theoretical Fe / P ratio, and the addition of phosphoric acid during the washing process to adjust the pulping rate—a large amount of filtrate and washing wastewater is often generated during the preparation process. In this case, the phosphorus content in the wastewater is typically 10%–20% of the normal production volume. Currently, some ferric phosphate wastewater treatment processes and equipment recover ammonia nitrogen and phosphorus resources. These mainly involve recovering a portion of phosphate salts through chemical precipitation, followed by phosphate salt concentration via reverse osmosis combined with MVR evaporation and crystallization. For example, adding a magnesium source to adjust the pH value can generate magnesium ammonium phosphate precipitate. The recovered magnesium ammonium phosphate and low-concentration ammonium phosphate are mostly agricultural byproducts. Both byproducts have relatively low phosphorus content, low economic value, and significant resource waste. They also pose a significant risk of scaling in the system. Furthermore, the magnesium ammonium phosphate precipitation method consumes a large amount of chemical reagents, making the treatment cost relatively expensive. Traditional biological treatment processes are simple to operate, but have low phosphorus removal efficiency. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a low-cost method for preparing iron phosphate.

[0005] Technical solution: The method for preparing ferric phosphate according to the present invention includes the following steps: pretreating the wastewater in the ferric phosphate production process, concentrating the pretreated filtrate by adsorption with a phosphorus removal resin to obtain a regenerated liquid, concentrating the regenerated liquid by nanofiltration and salt separation to obtain a concentrated liquid, and mixing the concentrated liquid with the phosphate salt solution in the ferric phosphate production to prepare a phosphate salt mixed solution for use in the ferric phosphate production to obtain ferric phosphate.

[0006] Preferably, the raw material of the present invention is wastewater from the production process of ferric phosphate enterprises, and the solution temperature in the process is 20-40°C.

[0007] Preferably, the concentrations of iron, calcium, magnesium, and manganese in the pretreated filtrate are less than 0.1 ppm, and the sludge pollution index (SDI) is less than 3.

[0008] More preferably, the TP concentration in the pretreated filtrate is 100–3000 mg / L, and the sludge density index (SDI) is less than 2.

[0009] Preferably, the pretreated filtrate is passed through a phosphorus removal resin Prr, and the pH of the original resin solution is adjusted to 4.0-7.0.

[0010] Preferably, the Prr phosphorus removal resin tower stock solution is diluted to 50 wt% using a concentrated sulfuric acid diluent, and the pH is adjusted with dilute sulfuric acid. Anionic B... - The principle of ion exchange resin is: RN(CH3)3OH + B - →R-(CH3)3B+OH - .

[0011] Preferably, the Prr resin mainly uses American Dusheng resin. A-107 is a type I quaternary ammonium functional group strong basic anion exchange resin; it is also supplemented with... The T-42UPS mixed bed Prr employs a mixed bed forward adsorption and countercurrent regeneration process for deep phosphorus removal. The high bed volume increases the volume of treated water and reduces the phosphate concentration in the system effluent, with the best effect being approximately 10–20 BV. The flow rate of the filtrate through the resin is generally 1–2 BV / h. The phosphorus removal resin has a large exchange capacity, with a minimum of 1.25 meq / ml, and a saturated adsorption capacity of 45 g / L for orthophosphate.

[0012] Preferably, the resin Prr particle size is 0.4–1.6 mm (d90). This controllable particle size reduces pressure under high-flow-rate operation. When the system pressure exceeds 0.2 bar, the pressure rises or the flow rate decreases, requiring the vent valve to be opened to remove air from the tower. Adjust the resin operating parameters so that the filtrate TP content is less than 1 ppm.

[0013] More preferably, the pH of the raw solution in the resin tower is 5.5, the water temperature is between 25℃ and 35℃, the bed volume of the resin tower is 15 BV, and the flow rate of the filtrate passing through the resin is 2 BV / h.

[0014] More preferably, during the resin adsorption of TP, adsorption saturation can be determined when the concentration of the effluent is about 1 / 10 of the initial sample concentration.

[0015] Preferably, the pretreated filtrate is passed through a phosphorus removal resin. After the phosphorus removal resin is saturated, it is backwashed to remove impurities and then regenerated using ammonia as a resin regenerator, controlling the pH of the regenerated solution to be 9.0–12.0; the TP recovery rate is 95–99%; the Prr resin can remove phosphorus of all valence states from the wastewater, while removing most of the other impurities in the original solution, resulting in a higher TP concentration in the regenerated solution; the resin adopts a countercurrent regeneration and cocurrent filtration process, and the phosphate content in the wastewater after resin adsorption and filtration is less than 1 ppm; after the Prr resin is saturated, it is backwashed with pure water; the phosphate anions adsorbed by the resin will be released in a solution with a higher pH value, and alkaline washing is performed at a backwash flow rate of 2–4 BV / h; the resin regenerator is 27 wt% ammonia, and the rate of phosphate desorption is proportional to the pH value of the regenerated solution.

[0016] More preferably, the pH of the resin regeneration solution is 10-11, and the resin is alkali washed for 1 hour at a flow rate of 3 BV / h.

[0017] Preferably, the nanofiltration salt concentration step comprises: filtering the regenerated solution through an NF membrane, wherein the NF membrane employs a two-stage membrane concentration process, the NF membrane retaining divalent and higher-valent ion salts, Mg 2+ S04 2- NH4 + SO4 2- The retention rate is 80-99%, and the phosphate permeability is 95-98%.

[0018] Preferably, the NF membrane is an amide-based multilayer spiral wound membrane with an aromatic structure, primarily used to remove SO4 from the regenerated solution. 2- The main chemical reaction between PO4 and high-valence cation molecules is: PO4 3- +NH4 + +H2SO4→NH4H2PO4+(NH4)2SO4.

[0019] Preferably, the NF membrane is selected as NP010 or NP030.

[0020] Preferably, the pH of the regenerated solution is adjusted to 2.0–6.0 before nanofiltration salt concentration.

[0021] More preferably, before nanofiltration salt concentration, the pH of the regenerated solution is adjusted to 4.0–6.0.

[0022] Preferably, the pH of the regenerated solution is adjusted using 50 wt% dilute sulfuric acid.

[0023] Preferably, the salt content of the influent to the NF membrane system is less than 35 wt%, the concentration ratio of the first-stage NF is 3 to 6 times, and the concentration ratio of the second-stage NF is 2 to 4 times; the TP content of the concentrate is 25.0 to 45.0 g / L, and the concentration of metal ions such as Fe, Ca, Mn, and Mg is less than 0.1 ppm; the concentrate can be transported to the phosphate salt preparation system for ferric phosphate production as part of the phosphate salt for the production of ferric phosphate.

[0024] More preferably, the TP concentration of the concentrated solution is 30–40 g / L; SO4 2- The retention rate is 80-93%.

[0025] Preferably, the phosphate salt solution is obtained after dissolving and filtering phosphate salts in the production of ferric phosphate; more preferably, the TP content is 32-36 g / L. The phosphate salt mixed solution is prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 6-20:1. The phosphate salt mixed solution is used in the normal process production of ferric phosphate, and the low-cost preparation of ferric phosphate reduces the amount of phosphate salt used in the production of ferric phosphate by 8.0%-20.0%.

[0026] Preferably, the TP concentration of the phosphate salt mixed solution is 30-38 g / L.

[0027] More preferably, the TP concentration of the phosphate salt mixed solution is 32–36 g / L.

[0028] Preferably, the wastewater from the iron phosphate production process is treated with a combination of chemical precipitation, solid-liquid separation, and manganese sand contact oxidation to remove impurities from the solution. The impurities include metallic impurities, suspended solids, and colloids, and the metallic impurities include iron, calcium, magnesium, and manganese.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention reuses the relatively scarce phosphorus source, reducing the raw material costs of iron phosphate production enterprises by 8.0% to 20.0%, with high maintenance costs, high reuse rate, and high production efficiency. By combining chemical precipitation, filtration, reverse osmosis with MVR to recover pure water, and then using phosphorus removal resin adsorption regeneration and NF membrane salt separation process to concentrate phosphate salts, the phosphate salt concentration is high and the impurities are low, resulting in high reuse value for iron phosphate production. It is a suitable measure for enterprises to reduce costs, increase efficiency, and improve product performance. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation process of the present invention.

[0031] Figure 2 This is a SEM image of the previously prepared ferric orthophosphate.

[0032] Figure 3 This is a SEM image of the iron phosphate prepared in Example 2 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1:

[0035] After pretreatment of the ferric phosphate wastewater at a temperature of 25℃, a 4m³ sample was taken. 3 The filtrate was transferred to a filtrate tank. The TP content of the filtrate was measured to be 410 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.06 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.09 ppm. The sludge density index (SDI) was measured to be 2.0. The pH of the filtrate was adjusted to 5.5 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 15 BV at a flow rate of 2 BV / h. After 45.0 h of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH 10.5) was used to regenerate the resin for 1 h at a resin volume of 3 BV / h. The TP concentration of the regenerated solution was measured to be 12 g / L, m / V(Ca) = 0.4 ppm, m / V(Mg) = 0.6 ppm, and m / V(Fe / Mn) < 0.1 ppm. The adsorption capacity of the saturated resin was 36.0 g / L, and the recovery rate of phosphate salts from the resin was 97.56%. The pH of the regenerated solution was adjusted to 4.5 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 3571 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 21 g / L, and the salt content was 27.5 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution 5 times, and the second-stage NF membrane concentrated it 2 times. The TP concentration in the concentrate was 34 g / L. The phosphate recovery rate of the NF membrane system was 95.21%, and SO4 content was [not specified]. 2- The rejection rate was 92.21%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate salt mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 10:1. Ferrous solution and the phosphate salt mixed solution were added according to a Fe / P mass ratio of 56:32 in the reaction solution, and the calculated volume of ferrous solution added was 163.5 L. The pH of the reaction solution was then adjusted to 1.88 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate production. The phosphate salt recovery rate of the new system was 92.89% (based on TP). The amount of phosphate salt used was reduced by 8.44%.

[0036] Example 2:

[0037] After pretreatment of the ferric phosphate wastewater at a temperature of 30℃, a 4m³ sample was taken. 3The filtrate was transferred to a filtrate tank. The TP content of the filtrate was measured to be 2470 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.04 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.07 ppm. The sludge density index (SDI) was measured to be 1.8. The pH of the filtrate was adjusted to 5.5 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 20 BV at a flow rate of 1 BV / h. After 15.87 h of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH 10.8) was used to regenerate the resin for 1 h at a resin volume of 3 BV / h. The TP concentration of the regenerated solution was measured to be 12.8 g / L, m / V(Ca) = 0.3 ppm, m / V(Mg) = 0.5 ppm, and m / V(Fe / Mn) < 0.01 ppm. The adsorption capacity of the saturated resin was 38.4 g / L, and the recovery rate of phosphate salts from the resin was 97.96%. The pH of the regenerated solution was adjusted to 5.0 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 5465 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 28.6 g / L, and the salt content was 29.6 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution 4 times, and the second-stage NF membrane concentrated it 2 times. The TP content of the concentrate was 42.0 g / L. The phosphate recovery rate of the NF membrane system was 96.08%, and SO4 content was [not specified]. 2- The rejection rate was 81.55%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate salt mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 6:1. Ferrous solution and the phosphate salt mixed solution were added according to a Fe / P mass ratio of 56:32 in the reaction solution, and the calculated volume of the added ferrous solution was 170.8 L. The pH of the reaction solution was then adjusted to 1.76 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate production. The phosphate salt recovery rate of the new system was 94.12% (based on TP). The amount of phosphate salt used was reduced by 13.45%.

[0038] Example 3:

[0039] After pretreatment of the ferric phosphate wastewater at a temperature of 25℃, a 4m³ sample was taken. 3The filtrate was transferred to a filtrate tank. The TP content of the filtrate was measured to be 290 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.04 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.05 ppm. The sludge density index (SDI) was measured to be 2. The pH of the filtrate was adjusted to 5.5 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 15 BV at a flow rate of 2 BV / h. After 50 hours of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH = 11) was used to regenerate the resin for 1 hour with a resin volume of 3 BV / h. The TP concentration of the regenerated solution was measured to be 11 g / L, m / V(Ca) = 0.2 ppm, m / V(Mg) = 0.4 ppm, and m / V(Fe / Mn) < 0.01 ppm. The adsorption capacity of the saturated resin was 30 g / L, and the recovery rate of phosphate salts from the resin was 96.55%. The pH of the regenerated solution was adjusted to 4.5 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 2975 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 23 g / L, and the salt content was 27.9 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution 4 times, and the second-stage NF membrane concentrated it 3 times. The TP content in the concentrate was 35.2 g / L. The phosphate recovery rate of the NF membrane system was 98.60%, and SO4 content was [not specified]. 2- The rejection rate was 84.65%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 9:1. Ferrous solution and the phosphate mixed solution were added according to a Fe / P mass ratio of 56:35, and the calculated volume of ferrous solution added was 149.7 L. The pH of the reaction solution was then adjusted to 1.85 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate production. The phosphate recovery rate of the new system was 95.20% (based on TP). The amount of phosphate used was reduced by 9.52%.

[0040] Example 4:

[0041] After pretreatment of the ferric phosphate wastewater at a temperature of 25℃, a 4m³ sample was taken. 3The filtrate was transferred to a filtrate tank. The TP content of the filtrate was determined to be 1100 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.07 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.09 ppm. The sludge density index (SDI) was determined to be 2. The pH of the filtrate was adjusted to 5.5 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 15 BV at a flow rate of 2 BV / h. After 17 hours of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH 10.8) was used to regenerate the resin for 1 hour at a resin volume of 3 BV / h. The TP concentration of the regenerated solution was determined to be 12.5 g / L, m / V(Ca) = 0.4 ppm, m / V(Mg) = 0.8 ppm, and m / V(Fe / Mn) < 0.01 ppm. The adsorption capacity of the saturated resin was 37.5 g / L, and the recovery rate of phosphate salts from the resin was 95.65%. The pH of the regenerated solution was adjusted to 5 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 4280 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 27.5 g / L, and the salt content was 29.6 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution by 3 times, and the second-stage NF membrane concentrated it by 3 times. The phosphorus content in the concentrate was 37.89 g / L. The phosphate recovery rate of the NF membrane system was 98.36%, and SO4 content was [not specified]. 2- The rejection rate was 83.9%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate salt mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 8:1. Ferrous solution and the phosphate salt mixed solution were added according to a Fe / P mass ratio of 56:35 in the reaction solution, and the calculated volume of the added ferrous solution was 166.3 L. The pH of the reaction solution was then adjusted to 1.78 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate production. The phosphate salt recovery rate of the new system was 95.20% (based on TP). The amount of phosphate salt used was reduced by 10.58%.

[0042] Example 5:

[0043] After pretreatment of the ferric phosphate wastewater at a temperature of 25℃, a 4m³ sample was taken. 3The filtrate was transferred to a filtrate tank. The TP content of the filtrate was measured to be 1480 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.08 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.09 ppm. The sludge density index (SDI) was measured to be 2. The pH of the filtrate was adjusted to 5.5 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 15 BV at a flow rate of 2 BV / h. After 13.8 h of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH 10.6) was used to regenerate the resin for 1 h at a resin volume of 3 BV / h. The TP concentration of the regenerated solution was measured to be 13.1 g / L, m / V(Ca) = 0.5 ppm, m / V(Mg) = 0.7 ppm, and m / V(Fe / Mn) < 0.01 ppm. The adsorption capacity of the saturated resin was 37.5 g / L, and the recovery rate of phosphate salts from the resin was 95.94%. The pH of the regenerated solution was adjusted to 4.8 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 4640 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 28.8 g / L, and the salt content was 29.9 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution 4 times, and the second-stage NF membrane concentrated it 2 times. The TP content in the concentrate was 36.16 g / L. The phosphate recovery rate of the NF membrane system was 97.41%, and SO42- was [not specified]. 2- The rejection rate was 82.4%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate salt mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 7:1. Ferrous solution and the phosphate salt mixed solution were added according to a Fe / P mass ratio of 56:34 in the reaction solution, and the calculated volume of ferrous solution added was 181.0 L. The pH of the reaction solution was then adjusted to 1.78 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate preparation. The phosphate salt recovery rate of the new system was 93.46% (based on TP). The amount of phosphate salt used was reduced by 11.68%.

[0044] Example 6:

[0045] After pretreatment of the ferric phosphate wastewater at a temperature of 25℃, a 4m³ sample was taken. 3The filtrate was transferred to a filtrate tank. The TP content of the filtrate was measured to be 880 mg / L, Fe concentration 0.01 ppm, Ca concentration 0.05 ppm, Mn concentration 0.01 ppm, and Mg concentration 0.07 ppm. The sludge density index (SDI) was measured to be 2. The pH of the filtrate was adjusted to 5.0 with dilute sulfuric acid, and 1 L of resin was used in the Prr resin tower. The filtrate was passed through a resin bed volume of 15 BV at a flow rate of 2 BV / h. After 31.6 h of resin adsorption, the resin became saturated. The resulting filtrate was returned to the post-treatment stage of water treatment, backwashed with pure water, and then the resin tower was emptied. The saturated resin regenerated solution (pH 11.0) was used to regenerate the resin for 1 h at a resin volume of 3 BV / h. The TP concentration of the regenerated solution was measured to be 11.8 g / L, m / V(Ca) = 0.3 ppm, m / V(Mg) = 0.5 ppm, and m / V(Fe / Mn) < 0.01 ppm. The adsorption capacity of the saturated resin was 37.5 g / L, and the recovery rate of phosphate salts from the resin was 97.73%. The pH of the regenerated solution was adjusted to 4.8 with dilute sulfuric acid. The TP concentration of the regenerated concentrate was determined to be 3890 mg / L, m / V (SO4). 2- The phosphorus concentration (TP) was 24.6 g / L, and the salt content was 27.7 wt%. The regenerated solution was pumped to the NF membrane system. The first-stage NF membrane concentrated the solution 5 times, and the second-stage NF membrane concentrated it 2 times. The TP concentration in the concentrate was 38.30 g / L. The phosphate recovery rate of the NF membrane system was 98.46%, and SO4 content was [not specified]. 2- The rejection rate was 86.8%, and the concentrations of metal ions such as Fe, Ca, Mn, and Mg in the concentrated solution were less than 0.1 ppm. The TP concentration of the ammonium phosphate solution after dissolving and filtering ammonium phosphate during the ferric phosphate production process was measured to be 30 g / L, and the Fe concentration after impurity removal and filtration was measured to be 65 g / L. A 200.0 L phosphate salt mixed solution was prepared by mixing the phosphate salt solution and the concentrated solution at a total TP ratio of 9:1. Ferrous solution and the phosphate salt mixed solution were added according to a Fe / P mass ratio of 56:33 in the reaction solution, and the calculated volume of the added ferrous solution was 161.0 L. The pH of the reaction solution was then adjusted to 1.82 using concentrated sulfuric acid. Finally, the reaction solution was sent to the ferric phosphate pilot line for ferric phosphate production. The phosphate salt recovery rate of the new system was 96.22% (based on TP). The amount of phosphate salt used was reduced by 9.62%.

[0046] The specific surface area, compacted density, iron-to-phosphorus ratio, and other impurities of the iron phosphate S220101 prepared in Example 2 were tested. The microstructure of the powder from Example 2 was also scanned. Figure 2 and Figure 3 The microstructure is regular and usable. Other key indicators are compared with those of the currently produced ferric phosphate A221001, as shown in the table below:

[0047] Product Model Particle size (D50) Specific surface area Iron-to-phosphorus ratio compaction density Trace elements A221001 8.6 4.003 0.971 0.72 S220101 7.9 5.181 0.972 0.74

[0048] The following table compares the theoretical data of phosphate recovery methods used by companies A and B in the production of ferric phosphate (ammonia process) with those of this invention, using methods for recovering magnesium ammonium phosphate and concentrated ammonium phosphate. The results in the table show that the low-cost ferric phosphate prepared using this patented method has significant advantages.

[0049]

Claims

1. A method for preparing ferric phosphate, characterized in that, Includes the following steps: Wastewater from the ferric phosphate production process is pretreated. The filtrate after pretreatment is concentrated by adsorption with a phosphorus removal resin to obtain a regenerated solution. The regenerated solution is then concentrated by nanofiltration to obtain a concentrated solution. The concentrated solution is mixed with the phosphate salt solution from the ferric phosphate production process to prepare a phosphate salt mixed solution for use in ferric phosphate production. The concentrations of iron, calcium, magnesium, and manganese in the pretreated filtrate were less than 0.1 ppm, and the sludge pollution index (SDI) was less than 3. The pretreated filtrate is passed through a phosphorus removal resin Prr, and the pH of the original resin solution is adjusted to 4.0~7.

0. The pretreated filtrate is passed through a phosphorus removal resin. After the phosphorus removal resin is saturated, it is backwashed to remove impurities and then regenerated using ammonia water as a resin regenerator. The pH of the regenerated solution is controlled at 9.0~12.

0. The nanofiltration salt concentration step is as follows: the regenerated liquid is filtered through an NF membrane, and the NF membrane adopts a two-stage membrane concentration, with the NF membrane retaining divalent and high-valent ion salts; The feed water of the NF membrane system has a salt content of less than 35 wt%, the first-stage NF concentration ratio is 3 to 6 times, and the second-stage NF concentration ratio is 2 to 4 times; the concentrate TP content is 25.0 to 45.0 g / L, and the concentration of Fe, Ca, Mn, and Mg metal ions is less than 0.1 ppm; The phosphate solution is obtained by dissolving and filtering phosphates during the production of iron phosphate, and the phosphate mixed solution is prepared by mixing the phosphate solution and the concentrate at a total TP ratio of 6 to 20:

1.

2. The method for preparing ferric phosphate according to claim 1, characterized in that, Before nanofiltration salt concentration, the pH of the regenerated solution is adjusted to 2.0~6.

0.

3. The method for preparing ferric phosphate according to claim 1, characterized in that, The TP concentration of the phosphate salt mixed solution is 30~38g / L.

4. The method for preparing ferric phosphate according to claim 1, characterized in that, The wastewater from the iron phosphate production process is treated with a combination of chemical precipitation, solid-liquid separation, and manganese sand contact oxidation to remove impurities from the solution, including metallic impurities, suspended solids, and colloids.

Images