Method for directly preparing iron phosphate from high-iron phosphorus fine powder

Abstract

The invention relates to a method for directly preparing iron phosphate from high-iron-phosphorus fine powder, which comprises the following steps of: reacting the high-iron-phosphorus fine powder or high-iron-phosphorus fine powder slurry with iron salt and corresponding acid for more than 1.5 hours under the conditions of normal temperature, micro negative pressure and stirring to obtain decomposed slurry M; carrying out filter pressing and washing to obtain filtrate A; oxidizing the filtrate A with an oxidizing agent until no ferrous ions exist, adjusting the pH value to 1.5-2.5, reacting for 0.5-2 hours at 40-50 DEG C while stirring, carrying out filter pressing, and washing to obtain a filtrate B and a crude iron phosphate filter cake B; carrying out secondary acidolysis on the filter cake B, reducing the filter cake B until the filter cake B is free of ferric ions, adjusting the pH value to 2.5-3.0, carrying out filter pressing, washing to obtain a sold filter cake and a filter washing solution, and repeating the operations of the steps 3) and 4) on the filter washing solution to obtain a filter cake C and a filter washing solution C; the filter cake C meets the industrial standard of battery-grade iron phosphate and can be used as a precursor of lithium iron phosphate to enter the market or be directly used for preparing lithium iron phosphate; and performing post-treatment on the filtrate B and the filtrate C to obtain agricultural ammonium chloride for sale. The method solves the problem that the utilization rate of phosphorus in existing phosphorite is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphorus chemical industry, and particularly relates to a method for directly processing phosphate or high-grade ferric phosphate by using phosphate rock, that is, a method for directly preparing ferric phosphate by using high-iron phosphorus concentrate. Background Art

[0002] Technological advances in lithium batteries have driven the rapid development of related industries. In particular, lithium iron phosphate batteries have surged in popularity in recent years, surpassing ternary lithium batteries. However, as the cathode material for power and energy storage batteries, lithium iron phosphate (LIFP) has stringent requirements for its impurity content. Consequently, companies producing LFP and LFP also have very high requirements for their phosphorus sources, typically using refined phosphoric acid or industrial-grade monoammonium phosphate (MAP).

[0003] The wet process currently dominates the production of lithium iron phosphate (LIFP) precursor ferric phosphate. These processes are divided into two categories: the sodium process and the ammonium process. The phosphorus sources used are refined phosphoric acid and industrial-grade monoammonium phosphate, respectively. These two phosphorus raw materials are the only ones that can easily achieve acceptable impurity levels. Because both raw materials are relatively pure, the phosphorus utilization rate in phosphate rock is often kept low to achieve high quality, sometimes as low as less than 50%.

[0004] The reason for the low phosphorus utilization rate is that during the wet process of producing phosphoric acid from phosphate rock and the subsequent purification process, nearly half of the phosphorus is eliminated along with the heavy metals, transition metals and other cations in the phosphate rock, and the phosphate ions are also removed.

[0005] In particular, the iron content in the raw phosphoric acid produced from high-iron phosphate rock is very high. Originally, iron and phosphorus are the two major elements used by downstream companies to prepare iron phosphate. However, the current purification process will inevitably remove iron and phosphorus together when removing impurity cations.

[0006] To date, there are no reports of any phosphorus chemical company or production line retaining this iron and phosphorus in refined phosphoric acid or industrial monoammonium phosphate during the purification process, allowing it to be directly converted into finished iron phosphate or lithium iron phosphate by downstream iron phosphate companies. Producers of refined phosphoric acid or industrial-grade monoammonium phosphate typically use a simplistic, one-size-fits-all approach, removing the iron and other impurity cations along with the phosphorus. This is the primary reason for the low phosphorus utilization rate in phosphate rock.

[0007] According to USGS data, my country held the world's second-largest phosphate rock reserves before 2021, behind Morocco. However, the USGS's "Mineral Community Summary 2023" forecasts global phosphate rock reserves of 72 billion tons in 2022 (a 1.4% year-on-year increase from 2021). Morocco and Western Sahara hold the largest reserves, reaching 50 billion tons, accounting for approximately 70%. China's phosphate rock reserves are 1.9 billion tons, representing a 2.6% share (up from 3.2 billion tons in 2021, or 4.51%), a significant gap compared to Morocco and Western Sahara. Morocco and Western Sahara possess the world's largest phosphate rock reserves, but their production in 2021 was only 40 million tons, representing approximately 47% of my country's and 18% of the world's total. Overall, my country accounts for 2.6% of global phosphate rock reserves but contributes 38.3% of global production. According to USGS forecast data, my country's reserves will decline rapidly for the first time in 2022. my country has dropped from the second largest phosphate reserve country to the fifth largest reserve country. my country's phosphate reserves (1.9 billion tons) are less than Morocco, Egypt, Tunisia and Algeria's 50 billion, 28 billion, 25 billion and 22 billion tons respectively.

[0008] In recent years, with the rising price of phosphate rock, the beneficiation industry has emerged. While the phosphate concentrate extracted from titanium tailings is of high grade (P2O5 content consistently exceeding 30%, sometimes reaching 38%), its iron content is also generally elevated, far exceeding that of ordinary phosphate rock. Whether processed dry or wet, the iron in this phosphate concentrate will transform into ferric phosphate during subsequent refining and purification. This iron, when removed as an impurity or mixed into phosphate fertilizers, becomes ineffective phosphorus, unusable by plants, thus losing its original value.

[0009] Therefore, in the context of shrinking domestic phosphorus resources, it is particularly important to improve the phosphorus yield of phosphate rock and make full use of all valuable elements in phosphate rock.

[0010] After our country designated non-renewable phosphate rock as a strategic resource in 2016, the goal of this application was to change the traditional phosphate rock processing model of the current wet-process phosphoric acid industry, without producing phosphogypsum as a by-product, without wasting phosphorus resources, and to directly convert the iron and phosphorus in the phosphate rock into the iron phosphate needed by the lithium iron phosphate battery industry, bypassing the intermediate steps. This allows for a low-cost and efficient production model of iron phosphate from phosphate rock, and to improve the utilization rate of phosphorus in phosphate rock, especially high-iron phosphate rock (for example, improving the utilization rate of phosphorus in high-iron "phosphorus concentrate" refloated from ilmenite tailings). Based on this, this application was developed. Summary of the Invention

[0011] The present invention aims to overcome the shortcomings of the prior art by providing a method for directly preparing ferric phosphate from high-iron phosphorus concentrate. This method allows the iron in the phosphate ore to be retained during the separation of other metallic impurities, preventing it from being removed along with the phosphorus as an impurity. This method thereby improves the phosphorus utilization rate in the phosphate ore while simultaneously reducing the iron source in subsequent processes, achieving a dual purpose and resolving the low phosphorus utilization rate in existing phosphate ore.

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] A method for directly preparing ferric phosphate from high-iron phosphorus concentrate comprises the following steps:

[0014] 1) Mixing high iron phosphorus concentrate or high iron phosphorus concentrate slurry with iron salt and corresponding acid at room temperature, slight negative pressure and stirring, and reacting for more than 1.5 hours to obtain decomposed slurry M;

[0015] 2) Filter-filtering and washing the slurry M to obtain filter cake A, filtrate A, and washing liquid A; filter cake A is an acid-insoluble residue used in the cement and construction industries; washing liquid A is used to dilute concentrated acid; and filtrate A is acidolysis liquid A;

[0016] 3) The acid hydrolyzed solution A is oxidized with an oxidant until there is no ferrous ion, the pH value is adjusted to 1.5-2.5, and the reaction is maintained at 40-50°C for 0.5-2 hours under stirring at 300-450 rpm, and then filtered and washed to obtain a filtrate and washing solution B and a crude ferric phosphate filter cake B;

[0017] 4) Acid hydrolyzing filter cake B twice, then reducing it to a state free of trivalent iron ions, adjusting the pH to 2.5-3.0, filtering and washing to obtain a white fertilizer filter cake (for sale) and a filtrate and washing liquid, repeating steps 3) and 4) on the filtrate and washing liquid to obtain filter cake C, i.e., wet-base iron phosphate, and filtrate and washing liquid C; filter cake C meets industry standards for battery-grade iron phosphate and can be marketed as a precursor for lithium iron phosphate or used directly in the preparation of lithium iron phosphate;

[0018] 5) The pH of the filtrate and wash liquid B is adjusted to 6.5-7.0, excess carbon dioxide is introduced, and the reaction is carried out at room temperature for 0.5-1 hour. The resulting slurry N is filtered and washed to obtain a filter cake D and a filtrate and wash liquid D. The filter cake D is sold as wet-based industrial calcium carbonate or further processed to increase its value. The filtrate and wash liquid D is concentrated, cooled, crystallized, and centrifuged to obtain agricultural ammonium chloride D1. The remaining mother liquor is returned to the filtrate and wash liquid D concentration step;

[0019] 6) The pH of the filtrate and wash solution C is adjusted to 5.0-6.0, and the reaction is carried out at room temperature for 0.5-1 hour. The resulting reaction solution is concentrated, cooled, crystallized, and centrifuged to obtain another salt-containing byproduct, agricultural ammonium chloride D2, which is combined with D1 for blending and sale. The remaining mother liquor is returned to the reaction solution concentration step.

[0020] Specifically, in step 1), the high-iron phosphate concentrate or high-iron phosphate concentrate slurry is calculated as P2O5, and the iron salt is calculated as Fe2O3, and is added according to a molar ratio of P2O5 to Fe2O3 of 0.95 to 0.98:1; the iron salt is ferrous chloride tetrahydrate, ferric chloride, or ferric nitrate; and the corresponding acid is at least one of hydrochloric acid, nitric acid, etc., including but not limited to hydrochloric acid, nitric acid, a mixture of the two, and all other acids that can be used for acidolysis of various phosphates. The high-iron phosphate concentrate can also be replaced by phosphate rock, various types of agricultural monoammonium phosphate, agricultural diammonium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate, and byproducts such as low-grade monoammonium phosphate, which is a byproduct of the preparation of industrial monoammonium phosphate, or phosphorus-containing white fertilizer used to prepare iron phosphate from low-grade hypophosphoric acid.

[0021] Furthermore, in step 1), hydrochloric acid can be added at a rate of 101-105% of the theoretical amount of P and HCl in the high-iron phosphorus concentrate or high-iron phosphorus concentrate slurry (molar ratio of 1:3). Micro-negative pressure is a form of negative pressure, except that its negative pressure value is relatively small. Negative pressure itself refers to a gas pressure state lower than the existing atmospheric pressure, while micro-negative pressure emphasizes that this negative pressure state is very weak, generally referring to a pressure between 0 and -10Pa, such as -10Pa, -8Pa, -5Pa, -3Pa, etc.

[0022] Specifically, in step 3), the oxidant can be any one of air, oxygen, hydrogen peroxide, etc.

[0023] Specifically, in step 4), filter cake B can be acidified with hydrochloric acid and / or nitric acid, preferably hydrochloric acid, which is a low-cost industrial by-product, and then electrolytically reduced or reduced with a reducing agent to free of trivalent iron ions. The reducing agent can be a common reducing agent such as iron powder or ascorbic acid. The reduction method and reducing agent herein include but are not limited to the above-mentioned contents listed in the present invention.

[0024] Specifically, in step 5), the molar ratio of carbon dioxide to calcium ions contained in the filtrate and washing liquid B can be 1-1.05:1.

[0025] Furthermore, in step 5), the pH value can be adjusted to 6.5-7.0 with industrial ammonia water; and in step 6), the pH value can be adjusted to 5.0-6.0 with industrial ammonia water.

[0026] The method of this invention solves the existing problems of low phosphorus utilization, long process times, and high costs in phosphate rock. It also avoids the industry's persistent byproduct, phosphogypsum, and innovatively utilizes the iron in the phosphate rock as a raw material. This method significantly differs from the current phosphorus chemical process of producing acid and salt followed by ferric phosphate, opening up an alternative channel for phosphate rock processing or the production of ferric phosphate or phosphates.

[0027] In the method of the present invention, the reaction principles involved are as follows:

[0028] ①Ca5F(PO4)3+10HCl→5CaCl2+H3PO4+HF

[0029] ②4HF+SiO2→2H2O+SiF4↑

[0030] ③2HF+SiF4→H2SiF6

[0031] ④H2SiF6+2NaCI→Na2SiF6↓+2HCl

[0032] ⑤2Fe 3+ +Fe→3Fe 2+

[0033] ⑥2H3PO4+2FeCI2+H2O2→2FePO4·2H2O↓+4HCI

[0034] ⑦H3PO4+FeCI3+2H2O→3HCl+FePO4·2H2O↓

[0035] ⑧HCl+NaOH→H2O+NaCl

[0036] ⑨HCl+NH4OH→NH4Cl+H2O

[0037] ⑩CaCl2+CO2+H2O→CaCO3↓+2HCl

[0038] The present invention utilizes wet-process phosphoric acid technology, but differs from conventional wet-process phosphoric acid production. Instead of using a single acid or mixed acid to acidize phosphate ore, particularly high-iron (Fe2O3 content greater than 5%) phosphate concentrate, the process employs a mixed solution of an iron salt and a corresponding acid. This process differs significantly from other wet-process phosphoric acid production methods in that the acid-insoluble matter separated after acid hydrolysis is not primarily a byproduct composed of phosphogypsum, but rather contains only trace amounts of phosphogypsum, with over 90% being silicon dioxide. Under certain conditions, the resulting acid hydrolysis solution forms an iron phosphate precipitate, which is then separated from a solution of soluble calcium, magnesium, and other hydrochloric acid salts. The resulting crude iron phosphate is then purified to obtain high-grade iron phosphate. The remaining mother liquor is then pH-adjusted and carbon dioxide is introduced to produce a harmless carbonate byproduct. The secondary mother liquor is then recovered to produce sodium chloride or ammonium chloride. Through this process, a low-cost, high-value utilization of phosphate ore resources is achieved by using a mixed acid hydrolysis solution of a low-cost acid and its corresponding iron salt.

[0039] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows:

[0040] The method of directly preparing ferric phosphate using high-iron phosphorus concentrate of the present invention allows the iron in the phosphate ore to be retained when separating other metal impurities, and is not removed together with the phosphorus as an impurity, thereby achieving the purpose of improving the phosphorus utilization rate in the phosphate ore and simultaneously reducing the iron source in the subsequent process, achieving a two-pronged effect and solving the problem of low phosphorus utilization rate in existing phosphate ore. DETAILED DESCRIPTION

[0041] To make the purpose, technical methods and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the implementation cases described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Normal temperature refers to 25±5℃.

[0043] Example 1

[0044] This embodiment provides a novel method for directly preparing ferric phosphate using high-iron phosphorus concentrate, comprising the following steps:

[0045] 1) Phosphorus concentrate powder from a place in Sichuan. The test results are shown in Table 1.

[0046] Table 1 Statistics of the test results of phosphorus concentrate in a certain place in Sichuan

[0047]

[0048] 2) According to the ratio of P2O5 / Fe2O3 molar ratio = 0.96, ferrous chloride tetrahydrate is added and dissolved in 20% hydrochloric acid to obtain a mixed solution. The hydrochloric acid in the mixed solution is measured according to 103% of the theoretical amount of P and HCl in the phosphorus concentrate (P:HCl molar ratio = 1:3) (or rust removal waste hydrochloric acid of corresponding concentration and mass). The above-mentioned phosphorus concentrate is added while stirring at room temperature and slightly negative pressure (-10Pa). This phosphorus concentrate is 387 kg and 20% hydrochloric acid is 1000 kg. After 1.5 hours of reaction, acid hydrolysis and defluorination are carried out to obtain a decomposed slurry M.

[0049] 3) The slurry M is filtered, washed, and separated to obtain a filter cake A which is an acid-insoluble residue, the main components of which are silicon dioxide, cryolite, etc., which can be used in cement, construction and other industries.

[0050] 4) Filtrate A and washing solution A will be obtained at the same time in the previous step.

[0051] 5) The filtrate A obtained by pressure filtration separation is the original acid hydrolysis solution, and the washing solution A is used as the diluted concentrated hydrochloric acid for the next reaction.

[0052] 6) The original acid hydrolyzate A was oxidized with oxygen until ferrous ions were eliminated (oxygen flow rate was 120 ml / min, and samples were taken every 10 minutes for testing using the potassium ferrocyanide method until no blue precipitate was produced). The pH was then slowly adjusted to 1.5 with 32% liquid caustic soda. The reaction was continued at 45°C with stirring at 300 rpm for 1.0 hour, followed by filter pressing, washing, and separation to obtain filtrate and wash solution B and crude ferric phosphate filter cake B.

[0053] 7) Filter cake B was again acidified with 1000 kg of 20% hydrochloric acid at room temperature for 90 minutes to obtain a secondary acid solution, which was then electrolytically reduced to free of trivalent iron ions (tested by potassium thiocyanate method until no color change. The electrolytic reduction of trivalent iron ions can be performed using conventional techniques in the art, which is not the innovation of the present application and will not be described in detail here). The pH was then adjusted to 2.8 with dilute alkali, filtered, and washed with ultrapure water to obtain a white fertilizer filter cake (for sale) and a filtrate and wash solution. The filtrate and wash solution was then subjected to the "6) and 7)" steps to obtain filter cake C and filtrate and wash solution C.

[0054] 8) The analysis results of filter cake C are shown in Table 2. It meets the industry standards for battery-grade iron phosphate and can be used as a precursor for lithium iron phosphate to enter the market or be used to directly prepare lithium iron phosphate.

[0055] Table 2 Analysis results of filter cake C

[0056]

[0057]

[0058] 9) The pH of the filtrate and wash liquid B is adjusted to 6.8 with industrial ammonia water, and industrial carbon dioxide is introduced in an amount equimolar to the calcium ions contained in the filtrate and wash liquid B. After reacting at room temperature for 1 hour, the resulting slurry N is filtered and washed to obtain a filter cake D and a filtrate and wash liquid D. The filter cake D is sold as wet-based industrial calcium carbonate or further processed to increase its value. The filtrate and wash liquid D is concentrated, cooled, crystallized, and centrifuged to obtain agricultural ammonium chloride D1. The remaining mother liquor is returned to the filtrate and wash liquid D concentration step.

[0059] 10) The pH of the filtrate and wash solution C is adjusted to 5.5 with industrial ammonia water. After reacting at room temperature for 1 hour, the resulting reaction solution is concentrated, cooled, crystallized, and centrifuged to obtain another salt-containing byproduct, agricultural ammonium chloride D2, which is combined with D1 for sale. The remaining mother liquor is returned to the reaction solution concentration step.

[0060] Example 2

[0061] This embodiment provides a novel method for directly preparing ferric phosphate using high-iron phosphorus concentrate, comprising the following steps:

[0062] 1) Phosphorus concentrate powder from a place in Hebei Province. The test results are shown in Table 3.

[0063] Table 3 Statistics of the test results of phosphorus concentrate in a certain place in Hebei

[0064]

[0065] 2) According to the molar ratio of P2O5 / Fe2O3 = 0.97, ferric nitrate is supplemented and dissolved in 20% nitric acid to obtain a mixed solution. The nitric acid in the mixed solution is measured according to 103% of the theoretical amount of P and HNO3 in the phosphorus concentrate (P:HNO3 = 1:3). The above-mentioned phosphorus concentrate is added while stirring at room temperature and slightly negative pressure (-8 Pa). This phosphorus concentrate is 224 kg and 1000 kg of 20% nitric acid. After 1.5 hours of reaction, acid hydrolysis and defluorination are carried out to obtain the decomposed slurry M.

[0066] 3) The slurry M is filtered, washed, and separated to obtain a filter cake A which is an acid-insoluble residue, the main components of which are silicon dioxide, cryolite, etc., which can be used in cement, construction and other industries.

[0067] 4) Filtrate A and washing solution A will be obtained at the same time in the previous step.

[0068] 5) The filtrate A obtained by pressure filtration separation is the acid hydrolysis solution, and the washing solution A is used as the diluted concentrated nitric acid for the next reaction.

[0069] 6) The acid hydrolyzed solution A was oxidized with air until ferrous ions were eliminated (air flow rate was 120 ml / min, and samples were taken every 10 minutes for testing using the potassium ferricyanide method until no blue precipitate was produced). The pH was then slowly adjusted to 2.0 with 32% liquid caustic soda. The solution was stirred at 450 rpm and maintained at 45°C for 1.0 hour. The solution was then filtered, washed, and separated to obtain a filtrate and wash solution B and a crude ferric phosphate filter cake B.

[0070] 7) Filter cake B was again acid-hydrolyzed with 1000 kg of 20% dilute nitric acid at room temperature for 80 minutes to obtain a secondary acid hydrolysis solution, which was then reduced with ascorbic acid to free of trivalent iron ions (tested by the potassium thiocyanate method until no color change occurred). The pH was then adjusted to 2.7 with dilute alkali, filtered, and washed with ultrapure water to obtain a white fertilizer filter cake (for sale) and a filtrate and washing solution. The filtrate and washing solution was then subjected to the same steps as in steps 6) and 7) to obtain filter cake C and filtrate and washing solution C.

[0071] 8) The analysis results of filter cake C are shown in Table 4. It meets the industry standards for battery-grade iron phosphate and can be used as a precursor for lithium iron phosphate to enter the market or be used to directly prepare lithium iron phosphate.

[0072] Table 4 Analysis results of filter cake C

[0073]

[0074] 9) The pH of the filtrate and wash liquid B is adjusted to 6.5 with industrial ammonia water. An amount of industrial carbon dioxide equivalent to the calcium ions contained in the filtrate and wash liquid B is introduced. After reacting at room temperature for 1 hour, the resulting slurry N is filter-pressed and washed to produce a filter cake D and filtrate and wash liquid D. The filter cake D can be sold as industrial-grade calcium carbonate or further processed to further enhance its value. The filtrate and wash liquid D is concentrated, cooled, crystallized, and centrifuged to obtain another byproduct, D1, agricultural ammonium nitrate. The remaining mother liquor is returned to the filtrate and wash liquid D concentration process.

[0075] 10) The pH of the filtrate and wash solution C is adjusted to 5.2 with industrial ammonia water. After reacting at room temperature for 1 hour, the resulting reaction solution is concentrated, cooled, crystallized, and centrifuged to obtain another salt-containing byproduct D2, agricultural ammonium nitrate, which is combined with D1 for blending and sale. The remaining mother liquor is returned to the reaction solution concentration step.

[0076] Example 3

[0077] This embodiment provides a novel method for directly preparing ferric phosphate using high-iron phosphorus concentrate, comprising the following steps:

[0078] 1) Phosphorus concentrate powder from a place in Liaoning Province. The test results are shown in Table 5.

[0079] Table 5 Statistics of the test results of phosphate concentrate in a certain place in Liaoning

[0080]

[0081] 2) According to the molar ratio of P2O5 / Fe2O3 = 0.98, add ferrous chloride tetrahydrate and dissolve it in a mixed acid solution of 20% hydrochloric acid and nitric acid, and adjust the amount of P in the phosphorus concentrate and the hydrogen ion in the mixed acid (P:H + =1:3) is used, and the above-mentioned phosphorus concentrate is added while stirring at room temperature and slightly negative pressure (-10Pa). This phosphorus concentrate is 395 kg, and a mixed acid of 20% hydrochloric acid and nitric acid is 1363 kg. After 1.5 hours of reaction, acid hydrolysis and defluorination are carried out to obtain a decomposed slurry M.

[0082] 3) The slurry M is filtered, washed, and separated to obtain a filter cake A which is an acid-insoluble residue, the main components of which are silicon dioxide, cryolite, etc., which can be used in cement, construction and other industries.

[0083] 4) Filtrate A and washing solution A will be obtained at the same time in the previous step.

[0084] 5) The filtrate A obtained by pressure filtration separation is the acid solution, and the washing solution A is used as the dilution concentrated hydrochloric acid and concentrated nitric acid for the next reaction.

[0085] 6) The acid hydrolyzed solution A was oxidized with 27% hydrogen peroxide until ferrous ions were eliminated (samples were taken every ten minutes and tested using the potassium ferrocyanide method until no blue precipitate was produced). The pH was slowly adjusted to 2.2 with 32% liquid caustic soda. The solution was stirred at 400 rpm and maintained at 45°C for 1.0 hour. The solution was then filtered, washed, and separated to obtain a filtrate and wash solution B and a crude ferric phosphate filter cake B.

[0086] 7) Filter cake B was acidified again with 1363 kg of a mixture of 20% hydrochloric acid and nitric acid at room temperature for 100 minutes to obtain a secondary acid hydrolysis solution, which was then reduced with iron powder as a reducing agent to free of trivalent iron ions (tested by the potassium thiocyanate method until no color change occurred). The pH was adjusted to 2.7 with dilute alkali, filtered, and washed with ultrapure water to obtain a white fertilizer filter cake (for sale) and a filtrate and washing liquid. The filtrate and washing liquid were subjected to the same procedures as in steps 6) and 7) to obtain filter cake C and filtrate and washing liquid C.

[0087] 8) The analysis results of filter cake C are shown in Table 6. It meets the industry standards for battery-grade iron phosphate and can be used as a precursor for lithium iron phosphate to enter the market or be used to directly prepare lithium iron phosphate.

[0088] Table 6 Analysis results of filter cake C

[0089]

[0090] 9) The pH of the filtrate and washing liquid B is adjusted to 6.6 with industrial ammonia water, and industrial carbon dioxide is introduced in an amount corresponding to the calcium ions and other substances contained in the filtrate and washing liquid B. After reacting at room temperature for 1 hour, the resulting slurry N is filtered and washed to obtain a filter cake D and a filtrate and washing liquid D. The filter cake D is sold as wet-based industrial calcium carbonate or further processed to increase its value. The filtrate and washing liquid D is concentrated, cooled, crystallized, and centrifuged to obtain an agricultural ammonium chloride and ammonium nitrate mixed nitrogen fertilizer D1. The remaining mother liquor is returned to the filtrate and washing liquid D concentration step.

[0091] 10) The pH of the filtrate and wash solution C is adjusted to 5.8 with industrial ammonia water. After reacting at room temperature for 1 hour, the resulting reaction solution is concentrated, cooled, crystallized, and centrifuged to obtain another salt-containing byproduct D2, an agricultural nitrogen fertilizer, which is combined with D1 and sold. The remaining mother liquor is returned to the reaction solution concentration step.

Claims

1. A method for directly preparing ferric phosphate from high-iron phosphorus concentrate, characterized in that: The steps include: 1) Mixing high iron phosphorus concentrate or high iron phosphorus concentrate slurry with iron salt and corresponding acid at room temperature, slight negative pressure and stirring, and reacting for more than 1.5 hours to obtain decomposed slurry M; 2) Filter-filtering and washing the slurry M to obtain filter cake A, filtrate A, and washing liquid A; filter cake A is an acid-insoluble residue used in the cement and construction industries; washing liquid A is used to dilute concentrated hydrochloric acid; and filtrate A is acidolysis liquid A. 3) Oxidizing the acid hydrolyzed solution A with an oxidizing agent until ferrous ions are eliminated, adjusting the pH to 1.5-2.5, maintaining the reaction at 40-50°C with stirring for 0.5-2 hours, filtering and washing to obtain a filtrate and washing solution B and a crude ferric phosphate filter cake B; 4) acid hydrolyzing filter cake B twice, then reducing it to a state free of trivalent iron ions, adjusting the pH to 2.5-3.0, filtering and washing to obtain a filter cake and a filtrate and washing liquid for sale, and repeating steps 3) and 4) on the filtrate and washing liquid to obtain filter cake C (i.e., wet-base ferric phosphate) and filtrate and washing liquid C; 5) The pH of the filtrate and wash liquid B is adjusted to 6.5-7.0, excess carbon dioxide is introduced, and the reaction is carried out at room temperature for 0.5-1 hour. The resulting slurry N is filtered and washed to obtain filter cake D and filtrate and wash liquid D. The filter cake D is sold as wet-based industrial calcium carbonate or further processed to increase its value. The filtrate and wash liquid D is concentrated, cooled, crystallized, and centrifuged to obtain agricultural ammonium chloride D1. The remaining mother liquor is returned to the filtrate and wash liquid D concentration process; 6) Adjust the pH of the filtrate and wash solution C to 5.0-6.0, react at room temperature for 0.5-1 hour, and concentrate, cool, crystallize, and centrifuge the resulting reaction solution to obtain another salt-containing byproduct, agricultural ammonium chloride D2, which is combined with D1 for sale. The remaining mother liquor is returned to the reaction solution concentration step.

2. The method for directly preparing ferric phosphate from high iron phosphorus concentrate according to claim 1, characterized in that: In step 1), the high-iron phosphorus concentrate or high-iron phosphorus concentrate slurry is calculated as P2O5, and the iron salt is calculated as Fe2O3, and is added according to a molar ratio of P2O5 to Fe2O3 of 0.95 to 0.98:1; the iron salt is ferrous chloride tetrahydrate, ferric chloride or ferric nitrate; the corresponding acid is at least one of hydrochloric acid and nitric acid; the high-iron phosphorus concentrate can also be replaced by phosphate rock, various types of agricultural monoammonium phosphate, agricultural diammonium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate, as well as low-grade monoammonium phosphate, a by-product of the preparation of industrial monoammonium phosphate, or phosphorus-containing white fertilizer used to prepare iron phosphate from low-grade hypophosphoric acid, and other by-products.

3. The method for directly preparing ferric phosphate from high iron phosphorus concentrate according to claim 1, characterized in that: In step 1), hydrochloric acid is added in an amount of 101-105% of the theoretical amount of P and HCl (molar ratio 1:3) in the high iron phosphorus concentrate or high iron phosphorus concentrate slurry.

4. The method for directly preparing ferric phosphate from high-iron phosphorus concentrate according to claim 1, characterized in that: In step 3), the oxidant is any one of air, oxygen, and hydrogen peroxide.

5. The method for directly preparing ferric phosphate from high iron phosphorus concentrate according to claim 1, characterized in that: In step 4), the filter cake B is acidified with hydrochloric acid and / or nitric acid, and then electrolytically reduced or reduced with a reducing agent until there is no trivalent iron ion. The reducing agent is a common reducing agent such as iron powder or ascorbic acid.

6. The method for directly preparing ferric phosphate from high iron phosphorus concentrate according to claim 1, characterized in that: In step 5), the molar ratio of carbon dioxide to calcium ions contained in the filtrate and washing solution B is 1-1.05:

1.

7. The method for directly preparing ferric phosphate from high iron phosphorus concentrate according to claim 1, characterized in that: In step 5), the pH value is adjusted to 6.5-7.0 with industrial ammonia water; in step 6), the pH value is adjusted to 5.0-6.0 with industrial ammonia water.

Images