Method for directly preparing iron phosphate from phosphorite by hydrochloric acid hydrolysis

Abstract

The present application belongs to the technical field of phosphorite wet decomposition, phosphoric acid extraction purification and ferric phosphate preparation, and discloses a method for directly preparing ferric phosphate from phosphorite hydrochloric acid solution. The method directly extracts phosphoric acid from the phosphorite hydrochloric acid solution without evaporation and concentration, and the organic phase loaded with phosphoric acid is reacted with ferrous sulfate and an oxidizing agent to generate ferric phosphate precipitate, and the organic phase after the reaction is recycled by ammonia regeneration. The present application avoids the energy consumption of the acid solution concentration, selectively separates impurities, realizes efficient coupling utilization of the hydrochloric acid phosphorus resources and ferrous sulfate, and can be used for preparing battery-grade ferric phosphate.

Description

Technical Field

[0001] This invention belongs to the technical field of wet decomposition of phosphate rock, phosphoric acid extraction and purification, and preparation of iron phosphate, specifically relating to a method for directly preparing iron phosphate from phosphate rock by hydrochloric acid hydrolysis. Background Technology

[0002] Lithium iron phosphate (LiFePO4) cathode materials have become one of the mainstream cathode materials for lithium-ion batteries due to their advantages such as high safety, long cycle life, environmental friendliness, and relatively low raw material costs. As a core precursor for the preparation of lithium iron phosphate, the purity, impurity content, and morphology control of battery-grade iron phosphate (FePO4) directly determine the electrochemical performance of the cathode material. With the rapid development of new energy vehicles and energy storage industries, the demand for lithium iron phosphate has surged, driving the continued prosperity of the "phosphate rock-phosphoric acid-iron phosphate" industry chain. How to utilize low-cost phosphorus sources, reduce phosphoric acid concentration and purification costs, and improve the utilization level of by-product resources has become an important direction for optimizing the iron phosphate production process.

[0003] Current ferric phosphate preparation technologies mainly employ the "iron method," which uses industrial phosphoric acid, purified wet-process phosphoric acid, or monoammonium phosphate as the phosphorus source and pure iron, iron blocks, or ferrous sulfate as the iron source. The process involves precipitation, oxidation, washing, drying, and calcination. For example, high-purity iron ingots and purified phosphoric acid are used as raw materials, followed by mixed acid dissolution, oxidation precipitation, and high-temperature calcination to prepare ferric phosphate; or ferrous sulfate (a byproduct of titanium dioxide production) and wet-process phosphoric acid are used as raw materials to synthesize the precursor via co-precipitation. These processes require high purity phosphoric acid sources, typically using thermal phosphoric acid or deeply purified wet-process phosphoric acid. However, the purification process of wet-process phosphoric acid suffers from significant phosphorus loss, difficulty in handling the byproduct phosphogypsum, and high energy consumption, resulting in high production costs for ferric phosphate.

[0004] Hydrochloric acid decomposition of phosphate rock is another important technical route for the utilization of phosphorus resources. Hydrochloric acid can decompose phosphate rock under relatively mild conditions, allowing phosphorus in the phosphate rock to enter the liquid phase in the form of phosphoric acid, forming an acid hydrolysis solution containing phosphoric acid, hydrochloric acid, calcium chloride, and impurities such as Fe, Al, Mg, and F. Existing technologies disclose processes for producing phosphoric acid or phosphate products by decomposing phosphate rock with hydrochloric acid. For example, Chinese patent application CN201910965188.6 discloses a method for preparing phosphoric acid by decomposing phosphate rock with hydrochloric acid. This method involves obtaining crude phosphoric acid through hydrochloric acid acid hydrolysis, filtration, two-stage nanofiltration membrane separation, and reverse osmosis membrane treatment, followed by evaporation concentration, impurity removal, decolorization, and arsenic removal to obtain the phosphoric acid product. For example, Chinese patent application CN200510019049 discloses a method for producing industrial phosphoric acid by hydrochloric acid decomposition of low-grade phosphate rock. This method first neutralizes the acid hydrolysis solution with lime slurry to generate precipitated dicalcium phosphate, then re-dissolves the precipitate with hydrochloric acid, followed by extraction with tributyl phosphate (TBP), washing, back-extraction, and concentration to obtain industrial phosphoric acid. As another example, Chinese patent application CN200810196844 discloses a method for producing phosphoric acid and ammonium phosphate salts by hydrochloric acid decomposition of phosphate rock and phosphorus-containing minerals. This method similarly employs a process of first neutralizing the precipitation, then re-dissolving with hydrochloric acid, extracting with organic solvents, and back-extracting with pure water to obtain phosphoric acid, which is then aminated to prepare ammonium phosphate salts.

[0005] However, the existing technologies for hydrochloric acid decomposition of phosphate rock all aim to obtain purified phosphoric acid, industrial phosphoric acid, or fertilizer-grade phosphate, and do not directly address the preparation of iron phosphate, a precursor for battery materials. If the hydrochloric acid hydrolysate is first evaporated, concentrated, or deeply purified before being used for iron phosphate preparation, it significantly increases evaporation energy consumption, equipment corrosion risk, and process complexity. Conversely, if the unpurified hydrochloric acid hydrolysate is directly reacted with the iron source, impurities such as calcium, magnesium, aluminum, fluorine, and chlorine in the hydrolysate can easily enter the iron phosphate product, affecting product purity and subsequent calcination performance, making it difficult to meet the stringent requirements for battery-grade iron phosphate.

[0006] Therefore, there is an urgent need in this field for a method that can selectively transfer and separate phosphoric acid before reacting it with ferrous sulfate to prepare iron phosphate without evaporation and concentration after filtration of hydrochloric acid hydrolysate, and simultaneously realize the recycling of organic phase and resource utilization of nitrogen-containing byproducts, so as to solve the process connection problem between hydrochloric acid hydrolysate phosphorus resources and battery-grade iron phosphate preparation. Summary of the Invention

[0007] To address the technical shortcomings of existing technologies, such as the high cost of ferric phosphate preparation due to reliance on high-purity phosphorus sources, the high energy consumption and equipment corrosion risk caused by the need for evaporation, concentration, or deep purification of the hydrochloric acid-derived phosphate rock solution before use, and the easy entry of impurities from the hydrochloric acid solution into the ferric phosphate product affecting battery-grade quality, this invention provides a method for directly preparing ferric phosphate from hydrochloric acid-derived phosphate rock. This method aims to solve the technical problems of easy entry of impurities into the product, high concentration cost of the hydrochloric acid solution, and difficulty in coordinating the utilization of ferrous sulfate and hydrochloric acid-derived phosphorus resources when directly preparing ferric phosphate from hydrochloric acid solution.

[0008] To solve the above technical problems, the present invention provides a method for directly preparing iron phosphate from phosphate rock by hydrochloric acid hydrolysis, comprising the following steps: S1: Phosphate rock is mixed with hydrochloric acid for acid hydrolysis. After acid hydrolysis, solid and liquid are separated to obtain a hydrochloric acid hydrolysis solution containing phosphoric acid. S2: Without evaporating and concentrating the hydrochloric acid hydrolysate obtained in S1, the hydrochloric acid hydrolysate is mixed with an organic phase containing an extractant and subjected to phosphoric acid extraction to obtain an organic phase loaded with phosphoric acid and a raffinate containing calcium chloride and metal impurities. S3: The organic phase loaded with phosphoric acid obtained in S2 is mixed with ferrous sulfate solution and oxidant to carry out a liquid-liquid-solid reaction, so that the phosphoric acid in the organic phase is transferred into the aqueous phase and reacts with iron ions to form ferric phosphate precipitate. Solid-liquid separation is performed to obtain ferric phosphate and the organic phase after the liquid-liquid-solid reaction. S4: The organic phase obtained from the liquid-liquid-solid reaction in S3 is mixed with ammonia or ammonia water for regeneration, so that the residual acidic components in the organic phase are transferred into the aqueous phase and form an aqueous phase containing ammonium sulfate. At the same time, the entrained or co-extracted metal impurities are precipitated, and the solid-liquid separation yields the regenerated organic phase. S5: Return the regenerated organic phase obtained in S4 to S2 for recycling.

[0009] According to a preferred embodiment of the method of the present invention, in step S1, the phosphate rock is one or more of apatite, collophane, medium- and low-grade phosphate rock, phosphate tailings, or phosphorus-containing minerals; the phosphorus content in the phosphate rock, calculated as P2O5, is 15-35 wt%.

[0010] According to a preferred embodiment of the method of the present invention, in step S1, the hydrochloric acid mass concentration is 10-31 wt%, the ratio of the theoretical acid consumption of HCl in the hydrochloric acid to the acid-consuming components in the phosphate rock calculated as CaO, MgO and P2O5 is 1.0-1.3:1, the acidolysis temperature is 60-90 ℃, and the acidolysis time is 0.5-4 h; the hydrochloric acid acidolysis solution obtained in step S1 is directly introduced into step S2 for phosphoric acid extraction after filtration, sedimentation or clarification, without evaporation and concentration; the phosphorus concentration in the hydrochloric acid acidolysis solution, calculated as P2O5, is 15-30 wt%.

[0011] According to a preferred embodiment of the method of the present invention, in step S2, the extractant is one or more of tributyl phosphate, amine extractant and alcohol extractant; the amine extractant is selected from one or more of trioctylamine, triisooctylamine, trialkylamine, N235, methyltrioctylammonium chloride, and trioctylmethylammonium chloride; the alcohol extractant is selected from one or more of n-octanol, isooctanol, sec-octanol, decanol, and isodecanol; the organic phase is composed of extractant and diluent, the diluent is selected from one or more of kerosene, sulfonated kerosene, n-alkanes, isoalkanes, and aromatic solvents; the volume fraction of the extractant in the organic phase is 20-70%; when the extractant is a mixed extractant composed of tributyl phosphate, amine extractant and alcohol extractant, the volume ratio of the three is (10-70):(5-60):(5-30).

[0012] According to a preferred embodiment of the method of the present invention, in step S2, the phosphoric acid extraction adopts a single-stage or multi-stage extraction, the extraction temperature is 20-60 °C, the volume ratio of organic phase to aqueous phase is 5:1-1:2, and the single-stage extraction time is 5-30 min.

[0013] According to a preferred embodiment of the method of the present invention, the raffinate containing calcium chloride and metal impurities obtained in step S2 is used to recover calcium chloride, prepare calcium salt products, return to the hydrochloric acid acidolysis system, or undergo neutralization treatment.

[0014] According to a preferred embodiment of the method of the present invention, in step S3, the ferrous sulfate solution is obtained by dissolving, filtering, or purifying ferrous sulfate heptahydrate, ferrous sulfate by-product of titanium dioxide, ferrous sulfate by-product of steel pickling, or other ferrous sulfate-containing materials; the ferrous sulfate solution contains Fe 2+ The concentration is 0.2-2.5 mol / L; the oxidant is one or more of hydrogen peroxide, air, oxygen, ozone, and persulfate; the amount of oxidant used is such that Fe 2+ Oxidized to Fe 3+ The required theoretical quantity is 1.0-1.3 times.

[0015] According to a preferred embodiment of the method of the present invention, in step S3, the molar ratio of iron to phosphorus in the supported phosphate is 1:(1.01-1.15), the liquid-liquid-solid reaction temperature is 30-60 °C, the reaction time is 5-30 min, and the pH of the reaction system is 1.0-2.5.

[0016] According to a preferred embodiment of the method of the present invention, the ferric phosphate obtained in step S3 is washed with water, dried and calcined to obtain anhydrous ferric phosphate; wherein the drying temperature is 90-130 ℃, the calcination temperature is 450-650 ℃, and the calcination time is 1-4 h.

[0017] According to a preferred embodiment of the method of the present invention, in step S4, the ammonia or ammonia water is gaseous ammonia, liquid ammonia or ammonia water; the regeneration temperature is 20-60 ℃, the regeneration time is 15-45 min, and the regeneration endpoint pH is 7.0-10.5; the aqueous phase containing ammonium sulfate obtained in S4 is recovered as a nitrogen fertilizer raw material; the aqueous phase containing ammonium sulfate is subjected to solid-liquid separation to remove metal impurities and then enters the ammonium sulfate utilization process.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention allows the acid hydrolysis solution obtained from hydrolyzing phosphate rock to be directly used for phosphoric acid extraction after filtration, eliminating the need for prior evaporation and concentration of the acid hydrolysis solution. This significantly reduces evaporation energy consumption and equipment corrosion risk, and simplifies the process flow.

[0019] 2. This invention selectively transfers phosphoric acid through an extraction system composed of tributyl phosphate, amine extractants, and / or alcohol extractants, so that most impurities such as calcium chloride, magnesium, aluminum, and fluorine in the acid hydrolysate remain in the raffinate, effectively reducing the risk of them entering the ferric phosphate. The content of impurities such as Ca, Mg, Al, Na, and K in the obtained ferric phosphate product can be controlled below 50 ppm, meeting the quality requirements of battery-grade ferric phosphate.

[0020] 3. This invention uses ferrous sulfate as the sole iron source and, in conjunction with an oxidant, performs a liquid-liquid-solid reaction to transfer phosphoric acid from the organic phase to the aqueous phase, and Fe... 2+ Oxidized to Fe 3+ The precipitation of ferric phosphate is completed in the same reaction section, reducing the steps of separate preparation of purified phosphoric acid and reprecipitation, and realizing the efficient coupling and utilization of hydrochloric acid acid hydrolysis phosphorus resources and ferrous sulfate iron source.

[0021] 4. In the process of organic phase regeneration, the present invention forms an aqueous phase containing ammonium sulfate, which can be recovered as nitrogen fertilizer raw material, thereby improving the utilization rate of sulfate and ammonia resources; the regenerated organic phase is returned to the extraction step for recycling, reducing the consumption of extractant and waste liquid discharge.

[0022] 5. This invention has broad requirements for phosphate rock grade and can be applied to medium and low grade phosphate rock and phosphate tailings with a phosphorus content of 15-35 wt%, which expands the range of phosphorus sources for iron phosphate preparation and helps to reduce raw material costs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0024] Figure 1This is a process flow diagram of a method for directly preparing iron phosphate from phosphate rock by hydrochloric acid acid hydrolysis according to the present invention. Detailed Implementation

[0025] The following description is based on specific embodiments.

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the present invention.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0028] like Figure 1 As shown, the present invention provides a method for directly preparing iron phosphate from phosphate rock by hydrochloric acid hydrolysis. The overall process route includes five sequentially connected and closed-loop steps: S1 hydrochloric acid hydrolysis, S2 direct extraction of phosphoric acid, S3 liquid-liquid-solid reaction, S4 organic phase regeneration, and S5 organic phase recycling.

[0029] Reference Figure 1 In the S1 hydrochloric acid acidolysis process, phosphate rock powder and hydrochloric acid are reacted in an acid-resistant reactor. After acidolysis, solid-liquid separation is performed to obtain a hydrochloric acid acidolysis solution containing phosphoric acid and an acid-insoluble residue. This acidolysis solution is directly introduced into the S2 direct phosphoric acid extraction process without evaporation and concentration. In S2, the hydrochloric acid acidolysis solution containing phosphoric acid is contacted with an organic phase containing an extractant in an extraction device. Through multi-stage countercurrent extraction, phosphoric acid is selectively transferred to the organic phase, resulting in a phosphoric acid-loaded organic phase and a raffinate containing calcium chloride and metal impurities. The raffinate can be further used to recover calcium chloride, prepare calcium salt products, return to the hydrochloric acid acidolysis system, or undergo neutralization treatment. The phosphoric acid-loaded organic phase enters the S3 liquid-liquid-solid reaction process, where it is mixed with ferrous sulfate solution and an oxidant in a reactor, causing the phosphoric acid in the organic phase to be released into the aqueous phase and react with Fe. 3+The reaction produces ferric phosphate precipitate. After solid-liquid separation, the ferric phosphate is washed with water, dried, and calcined to obtain anhydrous ferric phosphate product. The organic phase after the liquid-liquid-solid reaction enters the S4 organic phase regeneration process. In S4, the organic phase is mixed with ammonia or ammonia water for regeneration, causing the residual acidic components to transfer to the aqueous phase and form an aqueous phase containing ammonium sulfate, while entrained or co-extracted metal impurities precipitate. After solid-liquid separation, the regenerated organic phase is returned to S2 for recycling through S5, and the aqueous phase containing ammonium sulfate is further separated to remove the metal impurity precipitate before being recovered as a nitrogen fertilizer raw material.

[0030] In the above general implementation, S1 uses an acid-resistant reactor with a stirring device, and the stirring rate is controlled at 100-300 r / min; S2 can be carried out by multi-stage countercurrent extraction using a mixing and clarification tank or a centrifugal extractor, with a single-stage mixing time of 5-30 min and a settling time of 10-60 min; S3 is carried out in an acid-resistant reactor with a stirring device, with a stirring rate of 200-400 r / min, and the reaction endpoint is controlled by online pH monitoring during the reaction; S4 is carried out in an acid-resistant regeneration reactor with a stirring device, with a stirring rate of 150-300 r / min, and the regeneration endpoint is controlled by adding ammonia dropwise and monitoring the pH.

[0031] Example 1

[0032] Raw material preparation: Medium- to low-grade phosphate rock powder was selected as raw material, and crushed and ground to below 200 mesh. This phosphate rock was used as feed for the S1 hydrochloric acid acidolysis process. Testing revealed that the phosphate rock contained 18 wt% phosphorus (P2O5), and the main impurities included CaO (approximately 40 wt%), MgO (approximately 3 wt%), Fe2O3 (approximately 1.5 wt%), Al2O3 (approximately 1 wt%), and a small amount of fluoride.

[0033] S1 Hydrochloric Acid Acid Hydrolysis: The above-mentioned phosphate rock powder and 20 wt% industrial hydrochloric acid were added to an acid-resistant reactor equipped with mechanical stirring at a solid-liquid ratio of 1:3 (mass ratio). The stirring speed was set to 200 r / min. The theoretical acid consumption ratio of HCl in the hydrochloric acid to the acid-consuming components in the phosphate rock, calculated as CaO, MgO, and P2O5, was controlled at 1.10:1. The heating device was turned on, and the reactants were heated to 60 ℃ and maintained at a constant temperature for 2 h for acid hydrolysis. During the acid hydrolysis process, the phosphates in the phosphate rock reacted with hydrochloric acid to produce phosphoric acid, calcium chloride, and a small amount of soluble salts such as magnesium chloride and ferric chloride. A small amount of hydrogen fluoride gas was released at the same time. A condenser reflux and tail gas absorption device was connected to the top of the reactor to recover the acidic gas.

[0034] After acidolysis, the reactants are filtered while hot (using acid-resistant filter cloth as the filter medium, at an operating temperature of approximately 60 °C) to obtain an acid-insoluble residue (mainly silica and unreacted minerals) and a hydrochloric acid hydrolysate containing phosphoric acid. Analysis revealed that the hydrochloric acid hydrolysate contained 18 wt% phosphorus (P₂O₅), approximately 28 wt% calcium chloride, approximately 2.5 wt% magnesium chloride, and less than 1 wt% total concentration of metallic impurities such as iron and aluminum. This hydrolysate was not evaporated or concentrated and was directly used as feed for the S2 direct extraction of phosphoric acid process.

[0035] S2 Direct Extraction of Phosphoric Acid: Tributyl phosphate (TBP), trioctylamine and isooctyl alcohol are mixed in a preparation tank at a volume ratio of 50:30:20 and stirred thoroughly to obtain an extractant; the extractant is then mixed with sulfonated kerosene at a volume ratio of 60:40 to prepare an organic phase containing the extractant, wherein the volume fraction of the extractant is 60%.

[0036] The hydrochloric acid hydrolysate and the organic phase were preheated to 40 °C and then pumped into a two-stage countercurrent extraction mixing and clarification tank. The phosphoric acid-containing hydrochloric acid hydrolysate and the organic phase containing the extractant were contacted in the extraction equipment, with phosphoric acid selectively entering the organic phase. The volume ratio of the organic phase to the aqueous phase was controlled at 3:1, the mixing speed per stage was 250 r / min, the mixing time was 15 min, and the settling time was 30 min. During the extraction process, phosphoric acid in the hydrochloric acid medium was selectively extracted into the organic phase mainly in the form of H3PO4·HCl or H3PO4 by the TBP-amine-alcohol synergistic extraction system, while calcium chloride, magnesium chloride, and most metal impurities remained in the aqueous phase due to their low partition coefficients. After the two-stage countercurrent extraction, a phosphoric acid-loaded organic phase and a raffinate containing calcium chloride and metal impurities were obtained. The P2O5 concentration in the raffinate was reduced to approximately 1.5 wt%, and the phosphoric acid extraction rate was approximately 91.7%. The raffinate can be used to recover calcium chloride, prepare calcium salt products, return to the hydrochloric acid hydrolysate system, or undergo neutralization treatment.

[0037] S3 Liquid-Liquid-Solid Reaction: Ferrous sulfate heptahydrate (FeSO4·7H2O, analytical grade) is dissolved in deionized water to prepare Fe... 2+ A 0.8 mol / L ferrous sulfate solution was filtered to remove insoluble matter. The organic phase loaded with phosphoric acid and the ferrous sulfate solution were added to an acid-resistant reactor equipped with a stirrer at a molar ratio of iron to phosphorus in the loaded phosphoric acid of 1:1.05. Stirring was started (300 r / min), and a 30% (w / w) hydrogen peroxide solution was slowly added dropwise as an oxidant. The amount of oxidant used was Fe. 2+ Completely oxidized to Fe 3+ The required amount is 1.05 times the theoretical amount. The reaction temperature is controlled at 45 ℃, and the reaction time is 30 min. During the reaction, phosphoric acid in the organic phase is gradually released into the aqueous phase under the action of ferrous sulfate in the aqueous phase, while Fe...2+ Oxidized to Fe 3+ Fe 3+ It reacts with phosphate ions in the pH range of 1.0-2.5 to form a pale yellow ferric phosphate precipitate. During the reaction, the pH of the reaction system was maintained at around 1.6 by monitoring with an online pH meter and adding a small amount of circulating mother liquor as needed.

[0038] After the reaction, the material was pumped into a centrifuge for solid-liquid separation, yielding a ferric phosphate filter cake and the organic phase resulting from the liquid-liquid-solid reaction. The filter cake was washed three times with deionized water (each wash using five times the mass of the filter cake) to remove soluble impurities such as chloride ions and sulfate ions adsorbed on the surface. Analysis showed that the Cl- content in the washed filter cake was... - Content less than 100 ppm, SO4 2- The content is less than 200 ppm. The ferric phosphate filter cake then proceeds to the washing, drying and calcination processes.

[0039] S4 Organic Phase Regeneration: The organic phase after the liquid-liquid-solid reaction is transferred to an acid-resistant regeneration vessel equipped with a stirrer. Stirring is started (speed 200 r / min), and 25% (w / w) ammonia solution is slowly introduced while monitoring the system pH. The regeneration temperature is controlled at 40℃, and the regeneration time is 30 min. Ammonia addition is stopped when the system pH reaches 8.5. During the regeneration process, residual acidic components such as sulfuric acid and hydrochloric acid in the organic phase react with ammonia solution to generate ammonium sulfate and ammonium chloride, which are then transferred to the aqueous phase. Simultaneously, a small amount of Fe entrained or co-extracted in the organic phase... 3+ Al 3+ Mg 2+ Metallic impurities precipitate as hydroxides or phosphates under alkaline conditions. After regeneration, the material is allowed to stand for 30 minutes to separate into a regenerated organic phase and an aqueous phase containing ammonium sulfate.

[0040] The regenerated organic phase, after its acidity is restored to the initial level, is returned to the S2 direct phosphoric acid extraction process via S5 for recycling. The aqueous phase containing ammonium sulfate, after being filtered by plate and frame filters to remove metal impurities, enters the ammonium sulfate crystallization or concentration process for recovery as a nitrogen fertilizer feedstock.

[0041] Post-processing: The ferric phosphate filter cake was placed in a forced-air drying oven and dried at 105 °C for 4 h to obtain ferric phosphate dihydrate. The dried material was then transferred to a muffle furnace and heated to 550 °C at a heating rate of 5 °C / min, calcined at a constant temperature for 3 h, and then naturally cooled to room temperature to obtain anhydrous ferric phosphate product.

[0042] Product Testing: A full analysis of the final anhydrous ferric phosphate product showed the following results: P / Fe molar ratio of 1.002, Ca content of 32 ppm, Mg content of 18 ppm, Al content of 15 ppm, Na content of 22 ppm, K content of 8 ppm, and the content of each impurity not exceeding 50 ppm; laser particle size analysis showed a D50 of 3.5 μm; and a BET specific surface area of ​​7.2 m². 2 / g; The X-ray diffraction (XRD) pattern is in perfect agreement with the FePO4 standard card (PDF#29-0715), and no impurities are observed.

[0043] Example 2

[0044] Raw material preparation: Phosphate rock powder is selected as the raw material and crushed and ground to below 200 mesh. This phosphate rock then enters the S1 hydrochloric acid acid hydrolysis process. The phosphorus content (P2O5) in this phosphate rock is 25 wt%.

[0045] S1 Hydrochloric Acid Acid Hydrolysis: Phosphate rock powder and 25 wt% industrial hydrochloric acid were added to an acid-resistant reactor at a solid-liquid ratio of 1:2.5, with a stirring rate of 220 r / min. The ratio of HCl to theoretical acid consumption was controlled at 1.15:1, and the temperature was raised to 70 ℃ for acid hydrolysis for 1.5 h. After acid hydrolysis, the mixture was filtered to obtain an acid-insoluble residue and a hydrochloric acid hydrolysis solution containing phosphoric acid. The phosphorus concentration in the hydrolysis solution, calculated as P2O5, was found to be 22 wt%. This hydrolysis solution was not evaporated or concentrated and was directly introduced into the S2 direct extraction process for phosphoric acid.

[0046] S2 direct extraction of phosphoric acid: TBP and N235 (trialkylamine, the main component of which is C8-C) are used. 10 An extractant was prepared by mixing alkyl tertiary amines and n-octanol at a volume ratio of 60:25:15, and then mixed with kerosene at a volume ratio of 70:30 to prepare an organic phase containing the extractant, with a volume fraction of 70%. The acid hydrolysate and the organic phase were subjected to a three-stage countercurrent extraction at 45 °C, with an organic phase to aqueous phase volume ratio of 2:1. Each stage was mixed at a stirring rate of 280 r / min for 20 min, followed by a settling time of 40 min. This yielded an organic phase loaded with phosphoric acid and a raffinate containing calcium chloride and metal impurities. The phosphoric acid extraction rate was approximately 93.5%.

[0047] S3 Liquid-Liquid-Solid Reaction: Ferrous sulfate heptahydrate is dissolved to prepare Fe... 2+ A 1.2 mol / L ferrous sulfate solution was used. The organic phase loaded with phosphoric acid and the ferrous sulfate solution were added to the reactor at an iron-to-phosphorus molar ratio of 1:1.10, and the mixture was stirred at 350 r / min. Simultaneously, air was bubbled through the reactor (air flow rate 0.5 L / min), and a 30% hydrogen peroxide solution was added dropwise. The total amount of oxidant used was Fe. 2+The amount of ferric phosphate was 1.10 times the theoretical amount for complete oxidation. The reaction temperature was controlled at 50 °C, and the reaction time was 45 min. The pH of the reaction system was maintained at 1.8 by adding circulating mother liquor. After the reaction, the mixture was centrifuged to obtain ferric phosphate filter cake and the organic phase after the liquid-liquid-solid reaction. The filter cake was washed three times with deionized water.

[0048] S4 Organic Phase Regeneration: The organic phase after the liquid-liquid-solid reaction is transferred to a regeneration reactor. The reactor is stirred at 220 r / min, and 25% ammonia solution is added dropwise. The regeneration temperature is controlled at 45 ℃, and the regeneration time is 35 min, with a final pH of 9.0. After settling and separation, a regenerated organic phase and an ammonium sulfate-containing aqueous phase are obtained. The regenerated organic phase is returned to S2 via S5 for recycling, while the ammonium sulfate-containing aqueous phase is filtered to remove impurities and recovered as a nitrogen fertilizer feedstock.

[0049] Product post-processing: The ferric phosphate filter cake was dried at 110 ℃ for 3 h, and then calcined at 5 ℃ / min to 580 ℃ for 2.5 h to obtain anhydrous ferric phosphate.

[0050] Product testing: P / Fe molar ratio is 0.998; Ca content is 28 ppm; Mg content is 22 ppm; Al content is 12 ppm; Na content is 18 ppm; K content is 6 ppm; the content of each impurity does not exceed 40 ppm; D50 is 2.9 μm; BET specific surface area is 7.9 m². 2 / g; The XRD pattern matches the FePO4 standard card.

[0051] Example 3

[0052] Raw material preparation: Phosphate rock powder is selected as the raw material and crushed and ground to below 200 mesh. This phosphate rock then enters the S1 hydrochloric acid acid hydrolysis process. The phosphorus content (P2O5) in this phosphate rock is 15 wt%.

[0053] S1 Hydrochloric Acid Acid Hydrolysis: Phosphate rock powder and 18 wt% industrial hydrochloric acid were added to an acid-resistant reactor at a solid-liquid ratio of 1:3.5, with a stirring rate of 180 r / min. The ratio of HCl to theoretical acid consumption was controlled at 1.20:1, and the temperature was raised to 80 ℃ for acid hydrolysis for 3 h. After filtration, acid-insoluble residue and hydrochloric acid hydrolysis solution containing phosphoric acid were obtained. The phosphorus concentration in the hydrolysis solution, calculated as P2O5, was 15 wt%. This hydrolysis solution was not evaporated or concentrated and directly entered the S2 direct extraction of phosphoric acid process.

[0054] S2 Direct Extraction of Phosphoric Acid: TBP and isodecyl alcohol were mixed at a volume ratio of 80:20 to prepare the extractant, which was then mixed with isoparaffin (Isopar M) at a volume ratio of 80:20 to prepare an organic phase containing the extractant (80% by volume). The acid hydrolysate and the organic phase were subjected to a three-stage countercurrent extraction at 50 °C, with an organic phase to aqueous phase volume ratio of 4:1. Each stage was stirred at a stirring rate of 300 r / min for 20 min, followed by a settling time of 35 min. This yielded an organic phase loaded with phosphoric acid and a raffinate containing calcium chloride and metal impurities. The phosphoric acid extraction rate was approximately 89.2%.

[0055] S3 Liquid-Liquid-Solid Reaction: Ferrous sulfate, a byproduct of titanium dioxide production, is dissolved, filtered, and purified to prepare Fe... 2+ A 1.5 mol / L ferrous sulfate solution was used. The organic phase loaded with phosphoric acid was added to the reactor along with the ferrous sulfate solution at a ferric-phosphorus molar ratio of 1:1.15, and the mixture was stirred at 320 r / min. A 30% (w / w) hydrogen peroxide solution was added dropwise as an oxidant, at a volume 1.15 times the theoretical amount. The reaction temperature was controlled at 60 °C, and the reaction time at 60 min. The pH of the reaction system was maintained at 2.0 by replenishing the circulating mother liquor. After the reaction, the mixture was centrifuged to obtain a ferric phosphate filter cake and the organic phase resulting from the liquid-liquid-solid reaction. The filter cake was washed three times with deionized water.

[0056] S4 Organic Phase Regeneration: The organic phase after the liquid-liquid-solid reaction is transferred to a regeneration reactor. The reactor is stirred at 250 r / min, and 25% ammonia solution is added dropwise. The regeneration temperature is controlled at 50 ℃, and the regeneration time is 45 min, with a final pH of 9.5. After settling and separation, a regenerated organic phase and an ammonium sulfate-containing aqueous phase are obtained. The regenerated organic phase is returned to S2 via S5 for recycling, while the ammonium sulfate-containing aqueous phase is filtered to remove impurities and recovered as a nitrogen fertilizer feedstock.

[0057] Product post-processing: The ferric phosphate filter cake was dried at 120 °C for 2 h, and then calcined at 620 °C for 2 h at a rate of 5 °C / min to obtain anhydrous ferric phosphate.

[0058] Product testing: P / Fe molar ratio is 1.005; Ca content is 35 ppm; Mg content is 25 ppm; Al content is 20 ppm; Na content is 28 ppm; K content is 10 ppm; the content of each impurity does not exceed 55 ppm; D50 is 4.0 μm; BET specific surface area is 6.5 m². 2 / g; The XRD pattern matches the FePO4 standard card.

[0059] Example 4

[0060] To further illustrate the feasibility of variations of the technical solution of this invention, the following is combined with... Figure 1 Variant implementation examples are provided: Based on Example 1, the acidolysis temperature was adjusted to 75 °C, the acidolysis time was extended to 3 h, and the hydrochloric acid concentration was adjusted to 28 wt%, while other conditions remained unchanged. The P2O5 concentration in the acidolysis solution reached approximately 24 wt%. This acidolysis solution was directly introduced into S2 without evaporation and concentration. The subsequent extraction and iron phosphate preparation processes were the same as in Example 1, and the resulting product had comparable performance indicators to that of Example 1.

[0061] Based on Example 1, the volume ratio of TBP, trioctylamine, and isooctyl alcohol in the extractant was adjusted to 40:40:20, the diluent was changed to n-alkanes (n-dodecane), the volume fraction of the extractant in the organic phase was adjusted to 50%, the extraction stage was changed to four-stage countercurrent extraction, the extraction temperature was adjusted to 35 °C, and the volume ratio of the organic phase to the aqueous phase was adjusted to 4:1. The phosphoric acid extraction rate was approximately 90.3%. The subsequent S3 liquid-liquid-solid reaction and the iron phosphate preparation process were the same as in Example 1, and the properties of the obtained product were comparable to those of Example 1.

[0062] Based on Example 1, the ferrous sulfate solution was replaced with a purified solution of ferrous sulfate, a byproduct of steel pickling. 2+ The concentration was adjusted to 1.0 mol / L, and the oxidant was changed to bubbling oxygen (oxygen flow rate 0.3 L / min) with a small amount of sodium persulfate (dosage: Fe). 2+ The oxidation amount was 0.2 times the theoretical amount, and all other conditions were the same as in Example 1. The impurity content in the obtained iron phosphate product was comparable to that in Example 1, and the P / Fe molar ratio was 1.001.

[0063] Based on Example 1, the ammonia water used for regeneration was replaced with gaseous ammonia, the regeneration temperature was adjusted to 35 ℃, the regeneration time was adjusted to 20 min, and the endpoint pH was adjusted to 8.0, while other conditions remained unchanged. The acidity of the regenerated organic phase was well restored, and it was returned to S2 for recycling via S5. The concentration of ammonium sulfate in the ammonium sulfate-containing aqueous phase was slightly increased, which is beneficial for subsequent crystallization and recovery.

[0064] In the description of this invention, it should be understood that "-" and "~" represent a range between two values, and this range includes the endpoints. For example, "AB" represents a range greater than or equal to A and less than or equal to B. "A~B" represents a range greater than or equal to A and less than or equal to B.

[0065] In the description of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0066] In the description of the invention, the numerical values ​​of time, temperature, ratio, and mass involved can be based on actual measurements, standard equipment parameters, simplified rounding results, or within an acceptable error range, ensuring the practicality and repeatability of the invention.

[0067] In the description of this invention, the terms “about” or “approximately” are used to express approximate values ​​or ranges, allowing for a certain degree of error to ensure the flexibility and practicality of the description, while remaining within an acceptable range of error, with the maximum error not exceeding 10% of the corresponding value or range.

[0068] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for directly preparing ferric phosphate from phosphate rock by hydrochloric acid hydrolysis, characterized in that, Includes the following steps: S1: Phosphate rock is mixed with hydrochloric acid for acid hydrolysis. After acid hydrolysis, solid and liquid are separated to obtain a hydrochloric acid hydrolysis solution containing phosphoric acid. S2: Without evaporating and concentrating the hydrochloric acid hydrolysate obtained in S1, the hydrochloric acid hydrolysate is mixed with an organic phase containing an extractant and subjected to phosphoric acid extraction to obtain an organic phase loaded with phosphoric acid and a raffinate containing calcium chloride and metal impurities. S3: The organic phase loaded with phosphoric acid obtained in S2 is mixed with ferrous sulfate solution and oxidant to carry out a liquid-liquid-solid reaction, so that the phosphoric acid in the organic phase is transferred into the aqueous phase and reacts with iron ions to form ferric phosphate precipitate. Solid-liquid separation is performed to obtain ferric phosphate and the organic phase after the liquid-liquid-solid reaction. S4: The organic phase obtained from the liquid-liquid-solid reaction in S3 is mixed with ammonia or ammonia water for regeneration, so that the residual acidic components in the organic phase are transferred into the aqueous phase and form an aqueous phase containing ammonium sulfate. At the same time, the entrained or co-extracted metal impurities are precipitated, and the solid-liquid separation yields the regenerated organic phase. S5: Return the regenerated organic phase obtained in S4 to S2 for recycling.

2. The method according to claim 1, characterized in that, In step S1, the phosphate rock is one or more of the following: apatite, collophane, medium- and low-grade phosphate rock, phosphate tailings, or phosphorus-containing minerals; the phosphorus content in the phosphate rock, calculated as P2O5, is 15-35 wt%.

3. The method according to claim 1, characterized in that, In step S1, the hydrochloric acid concentration is 10-31 wt%, the theoretical acid consumption ratio of HCl in the hydrochloric acid to the acid-consuming components in the phosphate rock (calculated as CaO, MgO, and P2O5) is 1.0-1.3:1, the acidolysis temperature is 60-90 ℃, and the acidolysis time is 0.5-4 h. The hydrochloric acid hydrolysate obtained in step S1 is directly introduced into step S2 for phosphoric acid extraction after filtration, sedimentation, or clarification, without evaporation or concentration. The phosphorus concentration in the hydrochloric acid hydrolysate, calculated as P2O5, is 15-30 wt%.

4. The method according to claim 1, characterized in that, In step S2, the extractant is one or more of tributyl phosphate, amine extractant, and alcohol extractant; the amine extractant is selected from one or more of trioctylamine, triisooctylamine, trialkylamine, N235, methyltrioctylammonium chloride, and trioctylmethylammonium chloride; the alcohol extractant is selected from one or more of n-octanol, isooctanol, sec-octanol, decanol, and isodecanol; the organic phase is composed of extractant and diluent, the diluent is selected from one or more of kerosene, sulfonated kerosene, n-alkanes, isoalkanes, and aromatic solvents; the volume fraction of the extractant in the organic phase is 20-70%; when the extractant is a mixed extractant composed of tributyl phosphate, amine extractant, and alcohol extractant, the volume ratio of the three is (10-70):(5-60):(5-30).

5. The method according to claim 1, characterized in that, In step S2, phosphoric acid extraction is performed using one or more stages of extraction, with an extraction temperature of 20-60 ℃, a volume ratio of organic phase to aqueous phase of 5:1-1:2, and a single-stage extraction time of 5-30 min.

6. The method according to claim 1, characterized in that, The raffinate containing calcium chloride and metal impurities obtained in step S2 is used to recover calcium chloride, prepare calcium salt products, return to the hydrochloric acid acidolysis system, or undergo neutralization treatment.

7. The method according to claim 1, characterized in that, In step S3, the ferrous sulfate solution is obtained by dissolving, filtering, or purifying ferrous sulfate heptahydrate, ferrous sulfate by-products of titanium dioxide production, ferrous sulfate by-products of steel pickling, or other ferrous sulfate-containing materials; the ferrous sulfate solution contains Fe... 2+ The concentration is 0.2-2.5 mol / L; the oxidant is one or more of hydrogen peroxide, air, oxygen, ozone, and persulfate; the amount of oxidant used is such that Fe 2+ Oxidized to Fe 3+ The required theoretical quantity is 1.0-1.3 times.

8. The method according to claim 1, characterized in that, In step S3, the molar ratio of iron to phosphorus in the supported phosphate is 1:(1.01-1.15), the liquid-liquid-solid reaction temperature is 30-60 ℃, the reaction time is 5-30 min, and the pH of the reaction system is 1.0-2.

5.

9. The method according to claim 1, characterized in that, The ferric phosphate obtained in step S3 is washed with water, dried and calcined to obtain anhydrous ferric phosphate; wherein the drying temperature is 90-130 ℃, the calcination temperature is 450-650 ℃, and the calcination time is 1-4 h.

10. The method according to claim 1, characterized in that, In step S4, the ammonia or ammonia water is gaseous ammonia, liquid ammonia, or ammonia water; the regeneration temperature is 20-60 ℃, the regeneration time is 15-45 min, and the regeneration endpoint pH is 7.0-10.5; the aqueous phase containing ammonium sulfate obtained in S4 is recycled as nitrogen fertilizer raw material; the aqueous phase containing ammonium sulfate is subjected to solid-liquid separation to remove metal impurities and then enters the ammonium sulfate utilization process.

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