Preparation method of phosphoric acid

Abstract

The invention provides a preparation method of phosphoric acid, and belongs to the technical field of wet-process phosphoric acid.The preparation method comprises the steps that ground phosphate rock and lithium iron tailing powder are mixed, and a composite phosphorus source is obtained; mixing the composite phosphorus source and sulfuric acid, heating and stirring to obtain reaction slurry; and carrying out solid-liquid separation on the reaction slurry to obtain phosphoric acid and a calcium sulfate filter cake. The invention aims to solve the technical problem of high production cost caused by excessive dependence on phosphorite in the existing phosphoric acid preparation process.

Description

Technical Field

[0001] This application belongs to the field of wet-process phosphoric acid technology, and particularly relates to a method for preparing phosphoric acid. Background Technology

[0002] Wet-process phosphoric acid typically uses inorganic acids and phosphate rock as reactants, obtained through an acidolysis reaction. Taking concentrated sulfuric acid as an example, the reaction for wet-process phosphoric acid is as follows: Ca5(PO4)3F+5H2SO4+10H2O→3H3PO4+5CaSO4·2H2O+HF.

[0003] This method is highly dependent on high-quality natural phosphate rock, and the demand is relatively large.

[0004] However, as phosphate rock mining increases and phosphate rock becomes increasingly scarce, the production cost of phosphoric acid may gradually increase. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method for preparing phosphoric acid, which aims to solve the technical problem of high production costs caused by the over-reliance on phosphate rock in the existing phosphoric acid preparation process.

[0006] This application provides a method for preparing phosphoric acid, comprising the following steps: A composite phosphorus source is obtained by mixing phosphate rock powder and lithium iron ore tailings powder. The composite phosphorus source and sulfuric acid are mixed, heated and stirred to obtain a reaction slurry; The reaction slurry was separated into solid and liquid components to obtain phosphoric acid and calcium sulfate filter cake.

[0007] In the technical solution of this application embodiment, by blending lithium iron phosphate tailings powder with phosphate rock powder as a composite phosphorus source and then acid-hydrolyzing it, on the one hand, the amount of phosphate rock used in the phosphorus source can be reduced, thereby reducing the over-reliance on natural phosphate rock in phosphoric acid production. On the other hand, lithium iron phosphate tailings are rich in phosphorus, and this process can achieve efficient recovery of phosphorus from the lithium iron phosphate tailings (in some embodiments, the phosphorus recovery rate can reach over 95%), thus helping to solve the resource waste and environmental pollution problems caused by the accumulation of lithium iron phosphate tailings, turning waste into treasure, improving resource utilization, and reducing overall raw material procurement costs and solid waste treatment costs. In addition, this process is seamlessly integrated with existing wet-process phosphoric acid production processes, requiring no major equipment modifications and exhibiting high applicability.

[0008] In some embodiments, before the step of mixing phosphate rock powder and lithium iron ore tailings powder to obtain a composite phosphorus source, the method further includes: After drying the phosphate rock to a moisture content of less than or equal to 2%, grind it and pass it through an 80-100 mesh sieve to obtain phosphate rock powder. After drying the lithium iron ore tailings to a moisture content of less than or equal to 2%, grind them and pass them through an 80-100 mesh sieve to obtain lithium iron ore tailings powder.

[0009] In this embodiment, phosphate rock and lithium iron ore tailings are first dried and ground to reduce their moisture content and control the particle size within a suitable range. This helps to improve the reaction activity when the two are mixed as a composite phosphorus source to participate in the acid hydrolysis reaction.

[0010] In some embodiments, the phosphate rock is dried at a temperature of 80-110°C.

[0011] In this embodiment, drying under the above-mentioned temperature conditions can improve drying efficiency and effectiveness while avoiding high-temperature damage to the phosphate rock.

[0012] In some embodiments, the lithium iron phosphate tailings are dried at a temperature of 80-110°C.

[0013] In this embodiment, drying under the above-mentioned temperature conditions can improve drying efficiency and effectiveness while avoiding high-temperature damage to the components in the lithium iron phosphate tailings.

[0014] In some embodiments, the mass percentage of the lithium iron phosphate tailings in the composite phosphorus source, on a dry basis, is 10-40%, preferably 10-30%.

[0015] In this embodiment, by controlling the amount of lithium iron phosphate tailings incorporated into the composite phosphorus source within the above-mentioned range, the optimal balance can be achieved between reducing the amount of phosphate rock used, increasing the total phosphorus yield, and reducing impurities, thus achieving high phosphorus yield and low iron impurities.

[0016] In some embodiments, the mass percentage of sulfate ions in the reaction slurry is controlled within the range of 35-47%.

[0017] In this embodiment, controlling the concentration of sulfate ions in the reaction system within the above-mentioned range can provide a suitable acid-base environment for the acidolysis reaction and promote the reaction.

[0018] In some embodiments, the mass ratio of the composite phosphorus source to the sulfuric acid is 1:(2~3); or, In the step of mixing the composite phosphorus source and sulfuric acid, heating and stirring to obtain a reaction slurry, a portion of the phosphoric acid is refluxed as a circulating mother liquor to be mixed with the composite phosphorus source and sulfuric acid, and the mass ratio of the composite phosphorus source, the sulfuric acid and the circulating mother liquor is 1:(1.95~2.8):(0.25~0.2).

[0019] In this embodiment, when a composite phosphorus source and sulfuric acid are used as reaction raw materials, the concentration of sulfate ions in the reaction slurry can be regulated by controlling the mass ratio of the composite phosphorus source and the sulfuric acid within the above-mentioned range, thereby promoting the reaction. When a composite phosphorus source, sulfuric acid, and circulating mother liquor are used as reaction raw materials, the introduction of circulating mother liquor helps to increase the concentration of phosphoric acid products. At the same time, controlling the mass ratio of the three within the above-mentioned range can regulate the concentration of sulfate ions in the reaction slurry, thereby promoting the reaction.

[0020] In some embodiments, the heating and stirring temperature is 80~95°C, and the heating and stirring time is 2~4 hours.

[0021] In this embodiment, controlling the heating and stirring temperature and time within the aforementioned range ensures that the reaction proceeds efficiently and stably. The method described in this application has a wide process window and is suitable for industrial production.

[0022] In some embodiments, the stirring speed during heating and stirring is 200~350 r / min.

[0023] In this embodiment, controlling the stirring speed within the above range can promote uniform mixing of the reactants, avoid excessively high local concentrations, help improve phosphorus yield, and reduce impurity generation.

[0024] In some embodiments, the mass concentration of the sulfuric acid is 70-98%.

[0025] In this embodiment, a high concentration of sulfuric acid is used in the reaction to ensure a sufficient acid-base environment to promote acidolysis.

[0026] In some embodiments, the phosphoric acid contains 5 to 12.6% P2O5 by mass.

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0029] Figure 1 This is a schematic flowchart of a method for preparing phosphoric acid according to an embodiment of this application. Detailed Implementation

[0030] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0032] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0033] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0035] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0036] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0037] In the description of the embodiments of this application, "ppm" means the mass of the tested element, molecule or ion in parts per million of the sample mass.

[0038] In the description of the embodiments of this application, unless otherwise specified, the solvent in the "solution" is selected from at least one of distilled water, deionized water, deionized water, pure water, and ultrapure water.

[0039] Traditional wet-process phosphoric acid production relies heavily on high-quality natural phosphate rock, resulting in substantial demand. However, as phosphate rock resources become increasingly scarce due to mining, the production cost of phosphoric acid may gradually rise. Therefore, this application proposes a method for preparing phosphoric acid that helps reduce dependence on phosphate rock and avoids increased phosphoric acid production costs due to rising phosphate rock costs.

[0040] Please see Figure 1 This application provides a method for preparing phosphoric acid, the method comprising the following steps: S10, a composite phosphorus source is obtained by mixing phosphate rock powder and lithium iron ore tailings powder; S20, the composite phosphorus source and sulfuric acid are mixed, heated and stirred to obtain a reaction slurry; S30, the reaction slurry is separated into solid and liquid components to obtain phosphoric acid and calcium sulfate filter cake.

[0041] Among them, lithium iron phosphate tailings powder refers to solid waste generated during the production process of lithium iron phosphate battery cathode material (lithium iron phosphate, LiFePO4). For example, it may include, but is not limited to, unqualified powder, furnace adhering material, dust removal ash and other waste generated during the sintering process and screening and crushing process when preparing lithium iron phosphate by solid phase method, or reaction vessel residue, filter residue, washing waste residue, unqualified products and other waste generated when preparing lithium iron phosphate by liquid phase method.

[0042] In the technical solution of this application embodiment, by blending lithium iron phosphate tailings powder with phosphate rock powder as a composite phosphorus source and then acid-hydrolyzing it, on the one hand, the amount of phosphate rock used in the phosphorus source can be reduced, thereby reducing the over-reliance on natural phosphate rock in phosphoric acid production. On the other hand, lithium iron phosphate tailings are rich in phosphorus, and this process can achieve efficient recovery of phosphorus from the lithium iron phosphate tailings (in some embodiments, the phosphorus recovery rate can reach over 94%), thus helping to solve the resource waste and environmental pollution problems caused by the accumulation of lithium iron phosphate tailings, turning waste into treasure, improving resource utilization, and reducing overall raw material procurement costs and solid waste treatment costs. In addition, this process is seamlessly integrated with existing wet-process phosphoric acid production processes, requiring no major equipment modifications and exhibiting high applicability.

[0043] Furthermore, in some embodiments, the following steps may be included before step S10: S1. After drying the phosphate rock to a moisture content of less than or equal to 2%, grind it and pass it through an 80-100 mesh sieve to obtain phosphate rock powder.

[0044] S2. After drying the lithium iron ore tailings to a moisture content of less than or equal to 2%, grind them and pass them through an 80-100 mesh sieve to obtain lithium iron ore tailings powder.

[0045] The specifications of the screen can be referenced in GB / T 5330-2003: "Industrial Metal Wire Woven Square Hole Screen".

[0046] In this embodiment, phosphate rock and lithium iron ore tailings are first dried and ground to reduce their moisture content and control the particle size within a suitable range. This helps to improve the reaction activity when the two are mixed as a composite phosphorus source to participate in the acid hydrolysis reaction.

[0047] Furthermore, in some embodiments, the phosphate rock is dried at a temperature of 80-110°C. The drying temperature can be 80°C, 90°C, 100°C, 110°C, or any value between two of the above.

[0048] In this embodiment, drying under the above-mentioned temperature conditions can improve drying efficiency and effectiveness while avoiding high-temperature damage to the phosphate rock.

[0049] Furthermore, in some embodiments, the lithium iron phosphate tailings are dried at a temperature of 80-110°C. The drying temperature can be 80°C, 90°C, 100°C, 110°C, or any value between two of the above.

[0050] In this embodiment, drying under the above-mentioned temperature conditions can improve drying efficiency and effectiveness while avoiding high-temperature damage to the components in the lithium iron phosphate tailings.

[0051] Further, in some embodiments, in step S10, the mass percentage of the lithium iron phosphate tailings in the composite phosphorus source, on a dry basis, is 10-40 wt%; for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any value between any two of the above. More preferably, the mass percentage of the lithium iron phosphate tailings is 10-20 wt%.

[0052] In this embodiment, by controlling the amount of lithium iron phosphate tailings incorporated into the composite phosphorus source within the above-mentioned range, the optimal balance can be achieved between reducing the amount of phosphate rock used, increasing the total phosphorus yield, and reducing impurities, thus achieving high phosphorus yield and low iron impurities.

[0053] Furthermore, in some embodiments, in step S20, the mass percentage content of sulfate ions in the reaction slurry is controlled within the range of 35-47%, for example, it can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, or any value between any two of the above. More preferably, the mass percentage content of sulfate ions is 40-47 wt%.

[0054] In this embodiment, controlling the concentration of sulfate ions in the reaction system within the aforementioned range provides a suitable acid-base environment for the acidolysis reaction, promoting its progress. In actual operation, the concentration of sulfate ions in the reaction system can be precisely controlled by adjusting the feed ratio and adding water.

[0055] Furthermore, in some embodiments, in step S20, the mass ratio of the composite phosphorus source to the sulfuric acid is 1:(2~3); for example, it can be 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, and any two of the above values.

[0056] In this embodiment, a composite phosphorus source and sulfuric acid are used as reaction raw materials. By controlling the mass ratio of the composite phosphorus source and the sulfuric acid within the aforementioned range, the concentration of sulfate ions in the reaction slurry can be regulated, thus promoting the reaction. Furthermore, to more precisely control the concentration of sulfate ions, an appropriate amount of water can be added during step S20.

[0057] Furthermore, in some other embodiments, in step S20, a portion of the phosphoric acid is recycled as a mother liquor to be mixed with the composite phosphorus source and sulfuric acid, and the mass ratio of the composite phosphorus source, the sulfuric acid, and the mother liquor is 1:(1.95~2.8):(0.2~0.25); for example, it can be 1:1.95:0.2, 1:2:0.2, 1:2.4:0.2, 1:2.5:0.2, 1:2.8:0.2, 1:2.5:0.22, 1:2.5:0.25, 1:2.7:0.225, 1:2.8:0.225, 1:2.8:0.23, 1:1.95:0.25, 1:1.96:0.25, etc.

[0058] In this embodiment, a composite phosphorus source, sulfuric acid, and circulating mother liquor are used as reaction raw materials. The introduction of circulating mother liquor helps to increase the concentration of phosphoric acid product. At the same time, controlling the mass ratio of the three within the above-mentioned range can regulate the concentration of sulfate ions in the reaction slurry and promote the reaction. Furthermore, in order to more precisely control the concentration of sulfate ions, an appropriate amount of water can be added during step S20.

[0059] Furthermore, in some embodiments, the heating and stirring temperature is 80~95℃, for example, it can be 80℃, 82℃, 85℃, 87℃, 89℃, 90℃, 93℃, 95℃ and any two of the above values, preferably 85~90℃; the heating and stirring time is 2~4h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h and any two of the above values.

[0060] In this embodiment, controlling the heating and stirring temperature and time within the aforementioned range ensures that the reaction proceeds efficiently and stably. The method described in this application has a wide process window and is suitable for industrial production.

[0061] Furthermore, in some embodiments, the stirring speed during heating and stirring is 200~350 r / min; for example, it can be 200 r / min, 230 r / min, 250 r / min, 280 r / min, 300 r / min, 330 r / min, 350 r / min, and any value between any two of the above.

[0062] In this embodiment, controlling the stirring speed within the above range can promote uniform mixing of the reactants, avoid excessively high local concentrations, and help improve phosphorus yield.

[0063] Furthermore, in some embodiments, the mass concentration of the sulfuric acid is 70~98wt%; for example, it can be 70%, 75%, 80%, 85%, 90%, 95%, 98%, or any value between any two of the above.

[0064] In this embodiment, a high concentration of sulfuric acid is used in the reaction to ensure a sufficient acid-base environment to promote acidolysis.

[0065] Furthermore, in some embodiments, the solid-liquid separation in step S30 can be implemented in various ways, such as vacuum filtration, centrifugation, etc., and this application is not limited to these methods. To improve the separation effect and efficiency, the reaction slurry can be subjected to solid-liquid separation while it is hot.

[0066] Furthermore, in some embodiments, the mass percentage of P2O5 in the phosphoric acid is 5-10 wt%; for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, or any value between any two of the above.

[0067] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0068] I. Preparation Method In the following examples, the composition of the phosphate rock used is shown in Table 1-1, and the composition of the lithium iron phosphate tailings is shown in Table 1-2.

[0069] Table 1-1 Composition of Phosphate Concentrate

[0070] Table 1-2 Composition of Lithium Iron Oxide Tailings

[0071] Example 1 (1) Take phosphate concentrate, dry it at 100℃ to a moisture content of 1.0%, then grind it and pass it through a 90-mesh sieve to obtain phosphate powder. Take lithium iron ore tailings, dry them at 100℃ to a moisture content of 1.0%, then grind them and pass them through a 90-mesh sieve to obtain lithium iron ore tailings powder.

[0072] (2) Weigh out phosphate rock powder (about 108g dry product) and lithium iron ore tailings powder (about 12g dry product) according to the ratio of phosphate rock powder dry product to lithium iron ore tailings powder dry product of 9:1 (i.e., the mass percentage of lithium iron ore tailings is 10wt%), mix them evenly, and obtain a composite phosphorus source.

[0073] (3) The composite phosphorus source, sulfuric acid, and circulating mother liquor were added to the reactor at a mass ratio of 1:2.7:0.225. 329g of 70wt% sulfuric acid, 27g of circulating mother liquor (P2O5 mass percentage of 12.6wt%), and 148g of water were also added. The reaction temperature was controlled at 90℃, the stirring rate at 220 r / min, and the reaction time at 3h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system was approximately 45.7wt%.

[0074] (4) After the reaction is completed, the reaction slurry is vacuum filtered while it is hot to separate crude phosphoric acid and calcium sulfate filter cake. A portion of the crude phosphoric acid is recycled back to step (3) as mother liquor.

[0075] Example 2 (1) Take phosphate concentrate, dry it at 80°C to a moisture content of 0.8%, then grind it and pass it through an 80-mesh sieve to obtain phosphate powder. Take lithium iron ore tailings, dry them at 80°C to a moisture content of 0.9%, then grind them and pass them through an 80-mesh sieve to obtain lithium iron ore tailings powder.

[0076] (2) Weigh out phosphate rock powder (about 108g dry product) and lithium iron ore tailings powder (about 12g dry product) according to the ratio of phosphate rock powder dry product to lithium iron ore tailings powder dry product of 9:1 (i.e., the mass percentage of lithium iron ore tailings is 10wt%), mix them evenly, and obtain a composite phosphorus source.

[0077] (3) The composite phosphorus source, sulfuric acid, and circulating mother liquor were added to the reactor at a mass ratio of 1:2.4:0.2. 288g of 80wt% sulfuric acid, 24g of circulating mother liquor (P2O5 mass percentage of 9.2wt%), and 189g of water were also added. The reaction temperature was controlled at 90℃, the stirring rate at 200 r / min, and the reaction time at 4h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system was approximately 45.9wt%.

[0078] (4) After the reaction is completed, the reaction slurry is vacuum filtered while it is hot to separate crude phosphoric acid and calcium sulfate filter cake. A portion of the crude phosphoric acid is recycled back to step (3) as mother liquor.

[0079] Example 3 (1) Take phosphate concentrate, dry it at 110℃ to a moisture content of 0.6%, then grind it and pass it through a 100-mesh sieve to obtain phosphate powder. Take lithium iron ore tailings, dry them at 110℃ to a moisture content of 0.7%, then grind them and pass them through a 100-mesh sieve to obtain lithium iron ore tailings powder.

[0080] (2) Weigh out phosphate rock powder (about 108g dry product) and lithium iron ore tailings powder (about 12g dry product) according to the ratio of phosphate rock powder dry product to lithium iron ore tailings powder dry product of 9:1 (i.e., the mass percentage of lithium iron ore tailings is 10wt%), mix them evenly, and obtain a composite phosphorus source.

[0081] (3) The composite phosphorus source, sulfuric acid, and circulating mother liquor were added to the reactor at a mass ratio of 1:1.96:0.25. 235g of 98wt% sulfuric acid, 30g of circulating mother liquor (P2O5 mass percentage of 12.5wt%), and 242g of water were also added. The reaction temperature was controlled at 90℃, the stirring rate at 350 r / min, and the reaction time at 2h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system was approximately 45.5wt%.

[0082] (4) After the reaction is completed, the reaction slurry is vacuum filtered while it is hot to separate crude phosphoric acid and calcium sulfate filter cake. A portion of the crude phosphoric acid is recycled back to step (3) as mother liquor.

[0083] Example 4 The scheme in this embodiment is basically the same as that in embodiment 1, except that the total mass of the mixed phosphorus source remains unchanged, but the mass percentage of lithium iron phosphate tailings is changed to 9%. Accordingly, in step (3), the concentration of sulfate in the system is 46.1 wt%.

[0084] Example 5 The scheme in this embodiment is basically the same as that in embodiment 1, except that the total mass of the mixed phosphorus source remains unchanged, but the mass percentage of lithium iron phosphate tailings is changed to 20%. Accordingly, in step (3), the concentration of sulfate in the system is 46.9 wt%.

[0085] Example 6 The scheme in this embodiment is basically the same as that in embodiment 1, except that the total mass of the mixed phosphorus source remains unchanged, but the mass percentage of lithium iron phosphate tailings is changed to 30%. Accordingly, in step (3), the concentration of sulfate in the system is 45.7 wt%.

[0086] Example 7 The scheme in this embodiment is basically the same as that in embodiment 1, except that the total mass of the mixed phosphorus source remains unchanged, but the mass percentage of lithium iron phosphate tailings is changed to 40%. Accordingly, in step (3), the concentration of sulfate in the system is 46.6 wt%.

[0087] Example 8 The scheme in this embodiment is basically the same as that in embodiment 1, except that the total mass of the mixed phosphorus source remains unchanged, but the mass percentage of lithium iron phosphate tailings is changed to 41%. Accordingly, in step (3), the concentration of sulfate in the system is 46.5 wt%.

[0088] Example 9 The scheme in this embodiment is basically the same as that in embodiment 1, except that the reaction temperature in step (3) of this embodiment is 85°C.

[0089] Example 10 The scheme in this embodiment is basically the same as that in embodiment 1, except that the reaction temperature is 95°C in step (3) of this embodiment.

[0090] Example 11 The scheme in this embodiment is basically the same as that in Embodiment 1, except that this embodiment is a scale-up experiment in a reaction vessel, and the following adjustments are made accordingly: In step (2), according to the ratio of the dry mass of phosphate rock powder to the dry mass of lithium iron ore tailings powder of 7:3 (i.e., the mass percentage of lithium iron ore tailings is 30wt%), phosphate rock powder (about 3612g dry product) and lithium iron ore tailings powder (about 1697.3g dry product) are weighed and mixed evenly to obtain a composite phosphorus source.

[0091] In step (3), the composite phosphorus source, sulfuric acid, and circulating mother liquor were added to a 30L reactor at a mass ratio of 1:2.8:0.23. 14800g of 70wt% sulfuric acid, 1200g of circulating mother liquor (P2O5 mass percentage of 11.2 wt%), and 6660g of water were also added. The reaction temperature was controlled at 85℃, the stirring rate at 350 r / min, and the reaction time at 3h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system was approximately 46.8wt%.

[0092] Example 12 The scheme in this embodiment is basically the same as that in embodiment 1, except that the circulating mother liquor is not added in step (3) of this embodiment. Accordingly, step (3) is changed to: (3) The composite phosphorus source and sulfuric acid were added to the reactor at a mass ratio of 1:2.7. 329g of sulfuric acid with a concentration of 70wt% and 175g of water were added. The reaction temperature was controlled at 90℃, the stirring rate at 220 r / min and the reaction time at 3h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system was about 46.9wt%.

[0093] Comparative Example 1 This comparative example is basically the same as Example 1, except that only phosphate concentrate is used as the raw material in this comparative example. The preparation method is as follows: (1) Take phosphate concentrate, dry it at 100℃ until the moisture content is 1.6%, then grind it and pass it through a 90-mesh sieve to obtain phosphate powder.

[0094] (2) Weigh out phosphate rock powder (approximately 120 g dry product), add it to the reactor, along with 329 g of 70 wt% sulfuric acid, 27 g of circulating mother liquor (8 wt% P2O5), and 148 g of water. Control the reaction temperature at 85℃, the stirring rate at 200 r / min, and the reaction time at 3 h to obtain the reaction slurry. The mass concentration of sulfate in the reaction system is approximately 46.8 wt%.

[0095] (4) After the reaction is completed, the reaction slurry is vacuum filtered while it is hot to separate crude phosphoric acid and calcium sulfate filter cake. A portion of the crude phosphoric acid is recycled back to step (3) as mother liquor.

[0096] II. Testing Methods Elemental composition: determined using inductively coupled plasma optical emission spectrometer (ICP). The content of each element in the iron phosphate material was tested by OES, and the results are shown in Tables 2 and 3.

[0097] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 2 Product Characteristic Testing Table

[0098] Table 3 Phosphoric acid impurity content

[0099] As can be seen from the table above: All embodiments can produce phosphoric acid with high purity and maintain a high phosphorus yield. Although the impurity content in the product of some embodiments increased, the process flow can operate effectively in general, the quality of the phosphoric acid product is good, the burden of subsequent purification and concentration is small, and a large amount of lithium iron ore tailings can be consumed. This shows that the method of replacing part of the phosphate rock with lithium iron ore tailings is feasible. It can reduce raw material costs and develop a way to utilize lithium iron ore tailings waste while ensuring the purity and yield of the product. The overall process has good economic and environmental benefits.

[0100] Furthermore, the phosphoric acid obtained in Example 1 has high purity and low iron content, and its quality is not much different from that of the phosphoric acid obtained in Comparative Example 1. This shows that the method of replacing part of the phosphate rock with lithium iron ore tailings in this application can reduce raw material costs without sacrificing product quality.

[0101] Furthermore, comparing Examples 1, 4 to 8, it can be seen that Examples 1, 4 and 5 have the highest phosphorus yield, followed by Example 6, while Examples 7 and 8 have the lowest. Moreover, the impurity content in the products of Examples 7 and 8 is significantly higher. This indicates that controlling the amount of lithium iron ore added within the range of 10-40% can replace part of the phosphate rock while taking into account both phosphorus yield and product purity. Furthermore, when the amount added is controlled within the range of 10-30%, the optimal balance between high yield and low impurity content can be achieved.

[0102] Furthermore, comparing Example 1 and Example 11, Example 11 was able to produce high-purity phosphoric acid with a high phosphorus yield and a large amount of lithium iron phosphate tailings consumption, indicating that the method of this application remains stable and feasible in the scale-up device, proving the scalability and industrialization potential of the technology.

[0103] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing phosphoric acid, characterized in that, Includes the following steps: A composite phosphorus source is obtained by mixing phosphate rock powder and lithium iron ore tailings powder. The composite phosphorus source and sulfuric acid are mixed, heated and stirred to obtain a reaction slurry; The reaction slurry was separated into solid and liquid components to obtain phosphoric acid and calcium sulfate filter cake.

2. The preparation method according to claim 1, characterized in that, On a dry basis, the mass percentage of the lithium iron phosphate tailings in the composite phosphorus source is 10-40%.

3. The preparation method according to claim 1, characterized in that, On a dry basis, the mass percentage of the lithium iron phosphate tailings in the composite phosphorus source is 10-30%.

4. The preparation method according to claim 1, characterized in that, The mass percentage of sulfate ions in the reaction slurry is controlled within the range of 35-47%.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the composite phosphorus source to the sulfuric acid is 1:(2~3); or, In the step of mixing the composite phosphorus source and sulfuric acid, heating and stirring to obtain a reaction slurry, a portion of the phosphoric acid is refluxed as a circulating mother liquor to be mixed with the composite phosphorus source and sulfuric acid, and the mass ratio of the composite phosphorus source, the sulfuric acid and the circulating mother liquor is 1:(1.95~2.8):(0.2~0.25).

6. The preparation method according to claim 1, characterized in that, The heating and stirring temperature is 80~95℃, and the heating and stirring time is 2~4h.

7. The preparation method according to claim 1, characterized in that, The stirring speed during heating and stirring is 200~350 r / min.

8. The preparation method according to claim 1, characterized in that, The sulfuric acid has a mass concentration of 70-98%; and / or, The phosphoric acid contains 5-12.6% P2O5 by mass.

9. The preparation method according to claim 1, characterized in that, Before the step of mixing phosphate rock powder and lithium iron ore tailings powder to obtain a composite phosphorus source, the following steps are also included: After drying the phosphate rock to a moisture content of less than or equal to 2%, grind it and pass it through an 80-100 mesh sieve to obtain phosphate rock powder. After drying the lithium iron ore tailings to a moisture content of less than or equal to 2%, grind them and pass them through an 80-100 mesh sieve to obtain lithium iron ore tailings powder.

10. The preparation method according to claim 9, characterized in that, The phosphate rock is dried at a temperature of 80~110℃; and / or, The lithium iron phosphate tailings were dried at a temperature of 80~110℃.

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