Method for preparing calcium sulfate dihydrate from iron phosphate production waste liquid and calcium sulfate dihydrate

Abstract

The invention discloses a method for preparing calcium sulfate dihydrate from iron phosphate production waste liquid and calcium sulfate dihydrate. The method comprises the following steps: S1, adding an oxidizing agent into the iron phosphate production waste liquid, adding phosphate or phosphoric acid to generate FePO4. 2H2O precipitate, and carrying out solid-liquid separation to obtain filtrate; s2, purifying the filtrate through chelating resin to obtain effluent; s3, Ca (OH) 2 is added into the effluent until the pH value is 11.0-12.0; then slowly dropwise adding sulfuric acid to adjust the pH value to 10.0-11.0 to generate calcium sulfate precipitate until no precipitate is generated, and carrying out solid-liquid separation to obtain a calcium sulfate crude product; and S4, washing and drying the calcium sulfate crude product to obtain a calcium sulfate dihydrate finished product. According to the method for preparing the calcium sulfate dihydrate from the iron phosphate production waste liquid and the calcium sulfate dihydrate, the calcium sulfate dihydrate has high whiteness and high purity, the requirement for high quality is met, and the preparation cost is low.

Description

Technical Field

[0001] The present application relates to the intersection of industrial waste liquid resource utilization and inorganic material preparation, and specifically to a method for preparing calcium sulfate dihydrate from iron phosphate production waste liquid and calcium sulfate dihydrate. Background Art

[0002] As the core raw material of medical gypsum, food additives and special building materials, calcium sulfate dihydrate has extremely high requirements for whiteness (≥95%) and purity (≥99%). Currently, industrial production of calcium sulfate dihydrate can be prepared from natural gypsum ore or recycled from waste liquid of iron phosphate production.

[0003] The existing method of preparing calcium sulfate from natural gypsum ore has insufficient whiteness due to the impurities such as Fe2O3 (mass percentage content of 0.2%-1.5%) and organic matter (mass percentage content of 0.3%-0.8%) in natural gypsum ore, and the whiteness can only reach 87%-92%. Therefore, natural gypsum ore needs to be processed through multiple steps of flotation-calcination-bleaching to prepare calcium sulfate dihydrate that meets the requirements of whiteness (≥95%) and purity (≥99%). These processing steps will increase the cost by 400-600 yuan / ton; The existing method for preparing calcium sulfate dihydrate from waste liquid is generally to prepare calcium sulfate dihydrate from waste liquid of iron phosphate production. The waste liquid of iron phosphate production mainly comes from the production process of iron phosphate, including washing water, filter press water, etc. The cations contained in the waste liquid include: ① ammonium ion (NH4 + ) or sodium ion (Na + ② Heavy metal ions: including calcium (Ca 2+ ), magnesium (Mg 2+ ), iron (Fe 2+ / Fe 3+ ), manganese (Mn 2+ ); Anions contained in the wastewater include: ① Phosphate ions (PO4 3- ): In the process of iron phosphate production, unreacted phosphate will enter the waste liquid; ② High concentration of sulfate ions (SO4 2- ): It comes from the acidic reaction system. If ferrous sulfate is used as the raw material, a large amount of sulfate will remain. The existing methods for preparing calcium sulfate dihydrate from ferrous phosphate production wastewater are generally direct precipitation method, crystallization method and comprehensive process combined with pretreatment. The direct precipitation method is to remove the calcium ions (Ca 2+ ) and sulfate ions (SO4 2- ) directly react to form calcium sulfate dihydrate precipitate, but the impurity ions in the waste liquid (such as Fe 2+ / Fe 3+ , Mn 2+The crystallization method is to slowly crystallize calcium sulfate dihydrate by controlling the reaction conditions (such as temperature and pH value). However, during the crystallization process, impurity ions may be encapsulated in the crystals, resulting in a decrease in purity; at the same time, the presence of iron ions and manganese ions will make the product appear yellow or brown, reducing the whiteness. There are also production methods that use a pretreatment step in the prior art, but because of incomplete impurity removal, improper control of reaction conditions or poor control of the crystallization process, it will still affect the whiteness and purity of the finished calcium sulfate dihydrate, resulting in low whiteness of calcium sulfate dihydrate, excessive impurities and poor quality.

[0004] In addition, in the existing method of preparing calcium sulfate dihydrate from the waste liquid of iron phosphate production, resin adsorption is used for pretreatment of the waste liquid. Conventional cationic resins (such as 001×7 type) have a high affinity for Fe 3+ -PO4 3- The adsorption capacity of the complex is only 0.15mmol / mL, and 10% HCl solution is required for regeneration, which will produce high-salt wastewater (Cl - >8000ppm), increasing the cost of wastewater treatment.

[0005] The method for generating calcium sulfate in the prior art has at least the following defects: (1) The prior art of preparing calcium sulfate dihydrate from natural gypsum ore has the disadvantage of high cost; (2) The purity and whiteness of calcium sulfate dihydrate prepared from ferric phosphate production wastewater in the prior art do not meet the high quality requirements, cannot meet market demand, and will increase the cost of wastewater treatment. Summary of the invention

[0006] The purpose of the present application is to provide a method for preparing calcium sulfate dihydrate from waste liquid of iron phosphate production and calcium sulfate dihydrate, so as to solve the technical problem that the purity and whiteness of calcium sulfate dihydrate prepared from waste liquid of iron phosphate production in the prior art do not meet the requirements of high quality, cannot meet market demand, and increase the cost of wastewater treatment. The preferred technical scheme among the many technical schemes provided in the present application can produce many technical effects as described below.

[0007] To achieve the above objectives, this application provides the following technical solutions: In a first aspect, the present application provides a method for preparing calcium sulfate from ferric phosphate production waste liquid, comprising the following steps: S1. Add an oxidant to the waste liquid from the production of iron phosphate, and add phosphate or phosphoric acid; generate FePO4·2H2O precipitation, separate the solid and liquid, and obtain FePO4·2H2O and a filtrate; S2, purifying the filtrate obtained in step S1 by a chelating resin to obtain an effluent; S3, adding Ca(OH)2 to the effluent obtained in step S2 until the pH is 11.0-12.0; then slowly adding sulfuric acid to adjust the pH to 10.0-11.0 to generate calcium sulfate precipitate until no more precipitation is produced, and solid-liquid separation is performed to obtain crude calcium sulfate; S4, washing and drying the calcium sulfate primary product obtained in step S4 to obtain a finished calcium sulfate dihydrate product.

[0008] Further, in step S1, the oxidant includes any one of ozone and hydrogen peroxide; And / or, in step S1, the phosphate includes any one of monoammonium phosphate and sodium dihydrogen phosphate; And / or, in step S1, the solid-liquid separation adopts plate and frame filter pressing; And / or, in step S1, before adding the oxidant, the pH is adjusted to 3.0-3.5; And / or, in step S1, the stirring rate is 100-300 rpm.

[0009] Furthermore, in step S1, when the added oxidant is ozone, the added ozone reacts with Fe 2+ The molar ratio is 1-1.2:2; And / or, in step S1, when the added oxidant is hydrogen peroxide, the added hydrogen peroxide reacts with Fe 2+ The molar ratio is 1-1.2:2; And / or, in step S1, the phosphate or phosphoric acid added is based on the Fe 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding phosphate or phosphoric acid, Fe 3+ With PO4 3- The molar ratio is 1:0.9-0.95; And / or, in step S1, the pH regulator includes any one of ammonia water and sodium hydroxide; And / or, in step S1, the stirring rate is 150 rpm-250 rpm.

[0010] Further, in step S2, the chelating resin includes any one of an aminocarboxylic acid chelating resin and an iminodiacetic acid chelating resin; And / or, in step S2, during purification by chelating resin, the flow rate is controlled to be 1BV / h-5BV / h; And / or, in the step S2, after purification by chelating resin, the Fe 3+ <15ppm, Mn 2+<5ppm.

[0011] Furthermore, in step S2, during purification with chelating resin, the flow rate is controlled to be 3BV / h-4BV / h.

[0012] Furthermore, in step S3, the Ca(OH)2 added is a Ca(OH)2 emulsion, and the concentration of the Ca(OH)2 emulsion is 8%-12%; And / or, in step S3, slowly adding sulfuric acid is to convert SO4 2- The release rate is controlled at 0.3mol / (L·h)-0.8mol / (L·h); And / or, in step S3, after the addition of sulfuric acid is completed, the reaction is continued for 1h-2h; And / or, in step S3, the stirring rate is 100 rpm-300 rpm; And / or, in step S3, the sulfuric acid is 98% sulfuric acid; And / or, in step S3, the solid-liquid separation is performed by plate and frame filter pressing.

[0013] Further, in step S3, the concentration of the Ca(OH)2 emulsion is 9%-11%; And / or, in step S3, slowly adding concentrated sulfuric acid is to convert SO4 2- The release rate is controlled at 0.5mol / (L·h)-0.6mol / (L·h); And / or, in step S3, after the addition of sulfuric acid is completed, the reaction is continued for 1.2h-1.8h; And / or, in step S3, the stirring rate is 150 rpm-250 rpm.

[0014] Furthermore, in step S4, the washing is performed by washing with pure water until the conductivity of the washing water is less than 100 μS / cm and then the washing is stopped; And / or, in step S4, the drying is performed at a temperature of 70° C.-90° C. for 10 h-14 h.

[0015] Furthermore, in step S4, the washing is performed by countercurrent washing with pure water at 50°C-80°C; And / or, in step S4, the drying is performed at a temperature of 75° C.-85° C. for 11 h-13 h.

[0016] In a second aspect, the present application provides calcium sulfate dihydrate prepared by the above method.

[0017] The oxidant used in this application is ozone or hydrogen peroxide, which converts Fe 2+ Oxidized to Fe3+ , Fe 3+ With PO4 3- The reaction generates FePO4 iron phosphate precipitate, and the iron and PO4 in the waste liquid can be removed by filtration. 3- , the iron removal principle can be expressed by the following reaction formulas (Ⅰ), (Ⅱ) and (Ⅲ): (I); (II); (III).

[0018] Based on the above technical solution, the embodiments of the present application can at least produce the following technical effects: The method for preparing calcium sulfate dihydrate from waste liquid of iron phosphate production provided in the present application is to prepare high-purity and high-whiteness calcium sulfate by multi-stage impurity removal and crystal directional growth control. The method in the present application is particularly suitable for treating Fe-containing 2+ / Fe 3+ PO4 3- , Mn 2+ The acidic ammonium sulfate waste liquid with complex impurities such as phosphate sulfate can solve the technical problems of low whiteness and excessive impurities in the dihydrate calcium sulfate prepared from the waste liquid of iron phosphate production in the prior art. It is a low-cost waste liquid high-value conversion technology. The dihydrate calcium sulfate prepared in this application can achieve high purity and high whiteness, and has low preparation cost. Specifically: (1) High quality. This application adds an oxidant to the wastewater from the production of iron phosphate and adds PO4 3- Phosphate or phosphoric acid can remove Fe in the wastewater from iron phosphate production. 2+ and PO4 3- Converted to FePO4·2H2O, achieving the removal of Fe 2+ and PO4 3- For the purpose of 3- Residue, avoid the formation of calcium phosphate, can reduce the impurity content in the subsequent calcium sulfate dihydrate, and avoid PO4 3- The effect of residual calcium phosphate on the whiteness of calcium sulfate dihydrate. The FePO4·2H2O obtained can also be used for production; the chelating resin purification step can deeply remove the remaining Fe in the wastewater of iron phosphate production. 3+ , Mn 2+ and magnesium (Mg 2+), reduce the heavy metal impurity content of the final calcium sulfate and avoid the influence of impurities on the whiteness of calcium sulfate dihydrate; after removing impurities in the waste liquid, crystallization is carried out. During crystallization, sulfuric acid is slowly added to adjust the pH for crystallization. The pH fluctuation is small. The crystallization speed is controlled by pH buffering to avoid crystallization too fast or too slow. The uniform growth of crystals is controlled to achieve regular crystals, which can reduce impurity adsorption and improve the whiteness of the finished calcium sulfate dihydrate product; finally, the ammonium ions (NH4 + ) or sodium ion (Na + This application removes iron (and removes PO4 3- ), resin adsorption, staged pH-controlled crystallization and pure water washing have a synergistic effect, which improves the whiteness and purity of calcium sulfate dihydrate, so that the obtained calcium sulfate dihydrate meets the standards of high whiteness and high purity.

[0019] (2) The preparation cost of calcium sulfate dihydrate in the present application is low. Specifically, the production cost is reduced from the following three aspects: ①Save raw material costs: Compared with traditional methods, expensive precipitants or complexing agents are required to remove Fe 3+ In comparison, the present application not only achieves efficient iron removal but also reduces the use of chemicals through the combined treatment of phosphate precipitation and chelating resin.

[0020] ② Reduce energy consumption: Compared with the traditional natural gypsum ore preparation of calcium sulfate dihydrate, which requires high-temperature treatment such as calcination and bleaching, this application adopts room temperature oxidation and low-temperature drying (70℃-90℃), avoiding high-temperature energy consumption and reducing energy consumption; ③Reduce wastewater treatment costs: Compared with the traditional HCl regeneration resin adsorption method, it will lead to Cl - Compared with >8000ppm, this application adopts low-salt resin adsorption to avoid the problem of high Cl⁻ content wastewater treatment. At the same time, the FePO4·2H2O recovered in the production process can be reused, which not only reduces the cost of solid waste treatment, but also improves the resource utilization rate of waste liquid.

[0021] (3) High resource utilization. The FePO4·2H2O prepared in this application can be used for production. The purity of the produced calcium sulfate dihydrate can reach more than 98.6%, and the whiteness can reach more than 95.2%. It has high whiteness and high purity, meeting the high quality requirements. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other implementation methods obtained by ordinary technicians in the field without creative work belong to the scope of protection of the present application.

[0023] The wastewater from the production of iron phosphate used in the following examples has a pH of 2.1 and Fe 2+ The mass fraction of Fe is 0.12%, 3+ 165pm, PO4 3- 354ppm, Mn 2+ 68ppm, Mg 2+ It is 83ppm. 2. Embodiment Example 1

[0024] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 200rpm; adjust the pH to 3.2 with 10% ammonia water; introduce ozone into the waste liquid, and the added ozone reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio is 1:2, the concentration of ozone is 120 mg / L, and the ventilation rate of ozone is 4 L / min; Add monoammonium phosphate solution to the waste liquid; the amount of monoammonium phosphate solution added is based on the Fe content of the waste liquid. 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding monoammonium phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.95; After the ozone was introduced, the reaction was continued for 30 minutes, and a dense FePO4·2H2O precipitate (particle size D50 = 8-12μm) was generated in the waste liquid; FePO4·2H2O and filtrate were obtained by plate and frame filter pressing; S2, the filtrate obtained in step S1 was passed through a D401 resin column (column height 1.2m, diameter 0.4m) at a flow rate of 3BV / h, and the resin column adsorbed Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent was stirred continuously at a stirring rate of 200 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH was 11.5, and the concentration of Ca(OH)2 emulsion was 10%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH to 10.5, and SO4 2-The release rate was controlled at 0.5 mol / (L·h), and calcium sulfate precipitate was generated. After the addition of concentrated sulfuric acid was completed, the reaction was continued for 1.5 hours, and no more precipitation was precipitated. Plate and frame filter pressing was performed to obtain the primary calcium sulfate product. S4. The calcium sulfate product obtained in step S4 is washed three times with 60° C. pure water in countercurrent, and the conductivity of the washing water is <100 μS / cm. The washing is stopped, and then dried at 80° C. for 12 h to obtain a finished calcium sulfate dihydrate product. Example 2

[0025] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 100rpm; adjust the pH to 3.5 with 10% ammonia water, and pass ozone into the waste liquid. The added ozone reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio of ozone is 1.1:2, the concentration of ozone is 80 mg / L, and the ventilation rate of ozone is 5 L / min; and monoammonium phosphate solution is added to the waste liquid. The amount of monoammonium phosphate solution added is based on the Fe content in the waste liquid. 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding monoammonium phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.93; After the ozone was introduced, the reaction was continued for 60 minutes, and a dense FePO4·2H2O precipitate (particle size D50 = 8-12μm) was generated in the waste liquid; FePO4·2H2O and filtrate were obtained by plate and frame filter pressing; S2, the filtrate obtained in step S1 was passed through a D401 resin column (column height 1.2m, diameter 0.4m) at a flow rate of 5BV / h, and the resin column adsorbed Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent obtained in step S2 was stirred continuously at a stirring rate of 100 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH value was 11.0, and the concentration of the Ca(OH)2 emulsion was 8%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH value to 10.0, and SO4 2- The release rate is controlled at 0.3 mol / (L·h), and calcium sulfate precipitates are generated. After the addition of concentrated sulfuric acid is completed, the reaction is continued for 1 hour until no more precipitates are precipitated, and plate and frame filter pressing is performed to obtain the primary calcium sulfate product; S4. The calcium sulfate product obtained in step S4 is washed three times with 60° C. pure water in countercurrent, and the conductivity of the washing water is <100 μS / cm. The washing is stopped, and then dried at 70° C. for 14 h to obtain a finished calcium sulfate dihydrate product. Example 3

[0026] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 300rpm; adjust the pH to 3.0 with 10% ammonia water, and introduce ozone into the waste liquid. The added ozone reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio of ozone is 1.2:2, the concentration of ozone is 150 mg / L, the ventilation rate of ozone is 1 L / min, and monoammonium phosphate solution is added to the waste liquid. The amount of monoammonium phosphate solution added is based on the Fe content in the waste liquid. 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding monoammonium phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.92; After the ozone is introduced, the reaction is continued for 25-60 minutes, and a dense FePO4·2H2O precipitate (particle size D50=8-12μm) is generated in the waste liquid; plate and frame filter press is used to obtain FePO4·2H2O and filtrate; S2, the filtrate obtained in step S1 was passed through a D401 resin column (column height 1.2m, diameter 0.4m) at a flow rate of 2BV / h, and the resin column adsorbed Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent was stirred continuously at a stirring rate of 300 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH was 12.0, and the concentration of the Ca(OH)2 emulsion was 12%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH to 11.0, and SO4 2- The release rate is controlled at 0.8 mol / (L·h) to generate calcium sulfate precipitate. After the addition of concentrated sulfuric acid is completed, the reaction is continued for 2 hours until no more precipitate is precipitated, and plate and frame filter pressing is performed to obtain the primary calcium sulfate product. S4. The calcium sulfate product obtained in step S4 is washed three times with 80° C. pure water in countercurrent, and the conductivity of the washing water is less than 100 μS / cm. The washing is stopped, and then dried at 90° C. for 10 hours to obtain a finished calcium sulfate dihydrate product. Example 4

[0027] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 150rpm; adjust the pH to 3.4 with 10% ammonia water, add 30% hydrogen peroxide to the waste liquid, and the added hydrogen peroxide reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio of Fe in the waste liquid is 1:2, and sodium dihydrogen phosphate solution is added to the waste liquid; the amount of sodium dihydrogen phosphate solution added is based on the Fe content in the waste liquid. 2+Oxidized to Fe 3+ After that, the total Fe 3+ After adding sodium dihydrogen phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.9; After hydrogen peroxide was added, the reaction continued for 50 minutes, and dense FePO4·2H2O precipitate (particle size D50=8-12μm) was generated in the waste liquid; plate and frame filter press was used to obtain FePO4·2H2O and filtrate; S2, the filtrate obtained in step S1 was passed through an aminocarboxylic acid chelating resin column (column height 1.2m, diameter 0.4m) at a flow rate of 4BV / h, and the Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent was stirred at a stirring rate of 150 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH was 11.8, and the concentration of the Ca(OH)2 emulsion was 11%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH to 10.8, and SO4 2- The release rate was controlled at 0.6 mol / (L·h), and calcium sulfate precipitate was generated. After the addition of concentrated sulfuric acid was completed, the reaction was continued for 1.8 hours, and no more precipitation was precipitated. Plate and frame filter pressing was performed to obtain the primary calcium sulfate product. S4. The calcium sulfate product obtained in step S4 is washed three times with 75° C. pure water in countercurrent, and the conductivity of the washing water is <100 μS / cm. The washing is stopped, and then dried at 75° C. for 13 h to obtain a finished calcium sulfate dihydrate product. Example 5

[0028] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 250rpm; adjust the pH to 3.4 with 10% ammonia water, and introduce ozone into the waste liquid. The added ozone reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio is 1:2; and monoammonium phosphate solution is added to the waste liquid. The amount of monoammonium phosphate solution added is based on the Fe content in the waste liquid. 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding monoammonium phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.94; After the ozone was introduced, the reaction was continued for 40 minutes, and a dense FePO4·2H2O precipitate (particle size D50 = 8-12μm) was generated in the waste liquid; FePO4·2H2O and filtrate were obtained by plate and frame filter pressing; S2, the filtrate obtained in step S1 was passed through a D401 resin column (column height 1.2m, diameter 0.4m) at a flow rate of 4.5BV / h, and the Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent obtained in step S2 was stirred continuously at a stirring rate of 250 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH value was 11.2, and the concentration of the Ca(OH)2 emulsion was 9%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH value to 10.2, and SO4 2- The release rate was controlled at 0.4 mol / (L·h) to generate calcium sulfate precipitate. After the addition of concentrated sulfuric acid was completed, the reaction was continued for 1.2 h until no more precipitate was precipitated, and plate and frame filter pressing was performed to obtain the primary calcium sulfate product. S4. The calcium sulfate product obtained in step S4 is washed three times with 65° C. pure water in countercurrent, and the conductivity of the washing water is <100 μS / cm. The washing is stopped, and then the product is dried at 85° C. for 11 h to obtain a finished calcium sulfate dihydrate product. Example 6

[0029] S1. Take 10L of ferric phosphate production waste liquid, start stirring, and continue stirring at a stirring rate of 200rpm; adjust the pH to 3.3 with 10% sodium hydroxide, and pass ozone into the waste liquid. The added ozone reacts with Fe in the ferric phosphate production waste liquid. 2+ The molar ratio is 1:2, the concentration of ozone is 120 mg / L, and the ventilation rate of ozone is 2 L / min; and monoammonium phosphate solution is added to the waste liquid. The amount of monoammonium phosphate solution added is based on the Fe content in the waste liquid. 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding monoammonium phosphate solution, Fe 3+ :PO4 3- The molar ratio is 1:0.91; After the ozone was introduced, the reaction was continued for 40 minutes, and a dense FePO4·2H2O precipitate (particle size D50 = 8-12μm) was generated in the waste liquid; FePO4·2H2O and filtrate were obtained by plate and frame filter pressing; S2, the filtrate obtained in step S1 was passed through a D401 resin column (column height 1.2m, diameter 0.4m) at a flow rate of 3BV / h, and the resin column adsorbed Fe 3+ , Mn 2+ Mg 2+ , the effluent is obtained; S3, the effluent was stirred at a stirring rate of 200 rpm, and Ca(OH)2 emulsion was added to the effluent until the pH was 11.5, and the concentration of the Ca(OH)2 emulsion was 10%; then 98% concentrated sulfuric acid was slowly added dropwise to adjust the pH to 10.5, and SO4 2- The release rate was controlled at 0.6 mol / (L·h) to generate calcium sulfate precipitate. After the addition of concentrated sulfuric acid was completed, the reaction was continued for 1.5 h until no more precipitate was precipitated, and plate and frame filter pressing was performed to obtain the primary calcium sulfate product. S4. The calcium sulfate product obtained in step S4 is washed three times with 75° C. pure water in countercurrent, and the conductivity of the washing water is <100 μS / cm. The washing is stopped, and then dried at 90° C. for 10 hours to obtain a finished calcium sulfate dihydrate product.

[0030] 1. Detection of Fe in the filtrate of step S1 3+ PO4 3- The content of Fe in the effluent of step S2 3+ , Mn 2+ Mg 2+ and detecting the whiteness and purity of the calcium sulfate dihydrate obtained in Examples 1-6.

[0031] 1.1 Testing standards (1) Whiteness is tested using a WSB-2 whiteness meter; (2) The purity of CaSO4·2H2O is quantitatively detected by XRD; (3) Fe 2+ , Fe 3+ , Mn 2+ Mg 2+ PO4 3- The content was detected by ICP-MS

[0032] 1.2 The test results are shown in Table 1 below: Table 1 Quality of calcium sulfate dihydrate prepared in Examples 1-6

[0033] As can be seen from Table 1, the purity of the calcium sulfate dihydrate prepared in Examples 1-6 of the present application can reach more than 98.6%, and the whiteness can reach more than 95.2%. It has high whiteness and high purity, and meets the high quality requirements.

[0034] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application.

Claims

1. A method for preparing calcium sulfate dihydrate from waste liquid from iron phosphate production, characterized in that: The steps include: S1. Add an oxidant to the waste liquid from the production of iron phosphate, and add phosphate or phosphoric acid; generate FePO4·2H2O precipitation, separate the solid and liquid, and obtain FePO4·2H2O and a filtrate; S2, purifying the filtrate obtained in step S1 by a chelating resin to obtain an effluent; S3, adding Ca(OH)2 to the effluent obtained in step S2 until the pH is 11.0-12.0; then slowly adding sulfuric acid to adjust the pH to 10.0-11.0 to generate calcium sulfate precipitate until no more precipitation is produced, and solid-liquid separation is performed to obtain crude calcium sulfate; S4, washing and drying the calcium sulfate primary product obtained in step S4 to obtain a finished calcium sulfate dihydrate product.

2. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 1, characterized in that: In the step S1, the oxidant includes any one of ozone and hydrogen peroxide; And / or, in step S1, the phosphate includes any one of monoammonium phosphate and sodium dihydrogen phosphate; And / or, in step S1, the solid-liquid separation adopts plate and frame filter pressing; And / or, in step S1, before adding the oxidant, the pH is adjusted to 3.0-3.5; And / or, in step S1, the stirring rate is 100-300 rpm.

3. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 2, characterized in that: In step S1, when the added oxidant is ozone, the added ozone reacts with Fe in the ferric phosphate production wastewater. 2+ The molar ratio is 1-1.2:2; And / or, in step S1, when the added oxidant is hydrogen peroxide, the added hydrogen peroxide reacts with Fe 2+ The molar ratio is 1-1.2:2; And / or, in step S1, the phosphate or phosphoric acid added is based on the Fe 2+ Oxidized to Fe 3+ After that, the total Fe 3+ After adding phosphate or phosphoric acid, Fe 3+ With PO4 3- The molar ratio is 1:0.9-0.95; And / or, in step S1, the pH regulator includes any one of ammonia water and sodium hydroxide; And / or, in step S1, the stirring rate is 150 rpm-250 rpm.

4. The method for preparing calcium sulfate from dihydrate in ferric phosphate production wastewater according to claim 1, characterized in that: In the step S2, the chelating resin comprises any one of an aminocarboxylic acid chelating resin and an iminodiacetic acid chelating resin; And / or, in step S2, during purification by chelating resin, the flow rate is controlled to be 1BV / h-5BV / h; And / or, in the step S2, after purification by chelating resin, the Fe 3+ <15ppm, Mn 2+ <5ppm.

5. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 4, characterized in that: In the step S2, during purification with the chelating resin, the flow rate is controlled to be 3BV / h-4BV / h.

6. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 1, characterized in that: In step S3, the added Ca(OH)2 is a Ca(OH)2 emulsion, and the concentration of the Ca(OH)2 emulsion is 8%-12%; And / or, in step S3, slowly adding sulfuric acid is to convert SO4 2- The release rate is controlled at 0.3mol / (L·h)-0.8mol / (L·h); And / or, in step S3, after the addition of sulfuric acid is completed, the reaction is continued for 1h-2h; And / or, in step S3, the stirring rate is 100 rpm-300 rpm; And / or, in step S3, the sulfuric acid is 98% sulfuric acid; And / or, in step S3, the solid-liquid separation is performed by plate and frame filter pressing.

7. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 6, characterized in that: In step S3, the concentration of the Ca(OH)2 emulsion is 9%-11%; And / or, in step S3, slowly adding concentrated sulfuric acid is to convert SO4 2- The release rate is controlled at 0.5mol / (L·h)-0.6mol / (L·h); And / or, in step S3, after the addition of sulfuric acid is completed, the reaction is continued for 1.2h-1.8h; And / or, in step S3, the stirring rate is 150 rpm-250 rpm.

8. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 1, characterized in that: In step S4, the washing is performed by washing with pure water until the conductivity of the washing water is less than 100 μS / cm and then the washing is stopped; And / or, in step S4, the drying is performed at a temperature of 70° C.-90° C. for 10 h-14 h.

9. The method for preparing calcium sulfate dihydrate from ferric phosphate production waste liquid according to claim 8, characterized in that: In step S4, the washing is performed by countercurrent washing with pure water at 50°C-80°C; And / or, in step S4, the drying is performed at a temperature of 75° C.-85° C. for 11 h-13 h.

10. Calcium sulfate dihydrate prepared by the method described in any one of claims 1 to 9.

Images