Method for preparing anhydrous iron phosphate from medium-low-grade phosphorite

Abstract

The invention discloses a method for preparing anhydrous iron phosphate from medium-low-grade phosphorite. The method comprises the following steps: step 1, providing medium-low-grade phosphorite; 2, mixing phosphorite and hydrochloric acid in a decomposition tank, and fully reacting to obtain first slurry; 3, putting the first filtrate into a settling tank; 4, adding mixed acid into the chlorinated calcium dihydrogen phosphate crystal, pulping, and filtering to obtain second filtrate and a filter cake; 5, finally filtering to obtain a gypsum product and a third filtrate; step 6, removing impurities from the third filtrate in the step 5 by using saturated ferrous sulfate, continuously adding a saturated ferrous sulfate solution into a fourth filtrate obtained by the micro-filter, continuously adding 5-25% hydrogen peroxide, reacting for 5-35 minutes, adding a sodium hydroxide solution to adjust the pH value to 1.9-2.1, keeping the temperature, continuously reacting for 3-6 hours, and filtering to obtain iron phosphate; and 7, drying the iron phosphate obtained in the step 6 at 150-170 DEG C to obtain the anhydrous iron phosphate.

Description

Technical Field

[0001] The invention relates to the technical field of ferric phosphate preparation, and in particular to a method for preparing anhydrous ferric phosphate from medium- and low-grade phosphate ore. Background Art

[0002] Medium- and low-grade phosphate ore refers to phosphate ore with relatively low phosphorus content, and its phosphorus pentoxide (P2O5) content is usually lower than a certain value, which may vary depending on regional and industry standards. Generally speaking, phosphate ore with a phosphorus pentoxide content between 18% and 28% is called medium-grade phosphate ore, while phosphate ore with a content below 18% is considered low-grade phosphate ore. This type of ore occupies a dominant position in my country's phosphate resources, with rich reserves but low grade, high impurity content, and difficult to beneficiate.

[0003] There are six main production methods for ferric phosphate: sodium method, ammonium method, iron method, fertilizer phosphoric acid, red iron oxide, and calcium hydrogen phosphate. In my country, the production process mostly adopts three production process routes: ammonium method, sodium method, and iron method. The ammonium method is the reaction of ferrous sulfate and monoammonium phosphate, and then the excess acid is neutralized with ammonia water after precipitation and filtration to obtain ferric phosphate, and the filtrate is ammonium sulfate solution; the sodium method is the acidification of ferrous sulfate with phosphoric acid and then the reaction with hydrogen peroxide, and then the pH value is adjusted with sodium hydroxide solution to produce ferric phosphate, and the filtrate is sodium sulfate solution; the iron method is a process route using phosphoric acid to react with iron powder.

[0004] The above methods either have high production costs or too much equipment investment, and even have the problem of environmental pollution. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing anhydrous ferric phosphate from medium and low grade phosphate ore, which not only utilizes the medium and low grade phosphate ore, but also reduces the production cost of ferric phosphate, and the by-product is calcium sulfate, which can be directly used as a commodity exchange.

[0006] According to the present invention, a method for preparing anhydrous ferric phosphate from medium- and low-grade phosphate ore comprises the following steps: Step 1: Provide low- to medium-grade phosphate ore, with a phosphate ore content of P2O5 ≥ 15wt%; Step 2: mixing phosphate rock and hydrochloric acid in a decomposition tank and reacting them fully to obtain a first slurry, filtering out impurities such as silicon slag and a first filtrate from the first slurry, and decomposing fluorine-containing gas at the same time; Step 3: The first filtrate is placed in a sedimentation tank, precipitated at 15-38°C and filtered to obtain chlorinated calcium dihydrogen phosphate crystals and mother liquor; Step 4: adding mixed acid to the chlorinated calcium dihydrogen phosphate crystals, beating the mixture, and filtering to obtain a second filtrate and a filter cake; Step 5: adding water and 40-70% sulfuric acid solution to the filter cake in step 4, followed by pulping for sufficient reaction and then crystallization, and finally filtering to obtain a gypsum product and a third filtrate; Step 6: The third filtrate in step 5 is impurity-removed with saturated ferrous sulfate, and the fourth filtrate obtained through the microfilter is further added with saturated ferrous sulfate solution and then 5-25% hydrogen peroxide, reacted for 5-35 minutes, and then sodium hydroxide solution is added to adjust the pH value to 1.9-2.1, and the reaction is continued for 3-6 hours at a temperature, and the obtained iron phosphate is filtered; Step 7: Dry the iron phosphate obtained in step 6 at 150-170° C. to obtain anhydrous iron phosphate.

[0007] Furthermore, the mixed acid comprises 2-8% by mass of H3PO4 and 1-4% by mass of HCl.

[0008] Furthermore, in step 2, the phosphate rock and hydrochloric acid are mixed and fully reacted in a decomposition tank, the reaction temperature is 70-100° C., and the reaction time is 10-30 minutes.

[0009] Furthermore, in step 2, the first slurry is filtered by belt filtration, using acid water at 40-60°C in the system and tap water at 40-60°C for multi-stage washing.

[0010] Furthermore, the mixed acid is selected to be 0.5-3 mol / L, wherein the molar ratio of H3PO4 to HCl is (0.2-3.2):1.

[0011] Furthermore, in step six, the molar ratio of H3PO4 to ferrous sulfate in the fourth filtrate is (20-80):1.

[0012] The beneficial effects of the present invention are: 1. By using medium and low-grade phosphate rock to prepare anhydrous iron phosphate, the production cost is greatly reduced; 2. By decomposing low- and medium-grade phosphate ore with hydrochloric acid, high-quality anhydrous iron phosphate can be directly produced, and the by-product is gypsum, which can be directly used as a commodity exchange. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a flowchart of a method for preparing anhydrous ferric phosphate from medium- and low-grade phosphate ore according to an embodiment of the present invention. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0015] The invention provides a method for preparing anhydrous ferric phosphate from medium- and low-grade phosphate ore, comprising the following steps: Step 1: Provide low- to medium-grade phosphate ore, with a phosphate ore content of P2O5 ≥ 15wt%; Step 2: mixing phosphate rock and hydrochloric acid in a decomposition tank and reacting them fully to obtain a first slurry, filtering out impurities such as silicon slag and a first filtrate from the first slurry, and decomposing fluorine-containing gas at the same time; Step 3: The first filtrate is placed in a sedimentation tank, precipitated at 15-38°C and filtered to obtain chlorinated calcium dihydrogen phosphate crystals and mother liquor; Step 4: adding mixed acid to the chlorinated calcium dihydrogen phosphate crystals, beating the mixture, and filtering to obtain a second filtrate and a filter cake; Step 5: adding water and 40-70% sulfuric acid solution to the filter cake in step 4, followed by pulping for sufficient reaction and then crystallization, and finally filtering to obtain a gypsum product and a third filtrate; Step 6: The third filtrate in step 5 is impurity-removed with saturated ferrous sulfate, and the fourth filtrate obtained through the microfilter is further added with saturated ferrous sulfate solution and then 5-25% hydrogen peroxide, reacted for 5-35 minutes, and then sodium hydroxide solution is added to adjust the pH value to 1.9-2.1, and the reaction is continued for 3-6 hours at a temperature, and the obtained iron phosphate is filtered; Step 7: Dry the iron phosphate obtained in step 6 at 150-170° C. to obtain anhydrous iron phosphate.

[0016] The entire process utilizes medium and low-grade phosphate rock to prepare anhydrous iron phosphate, greatly reducing production costs. By decomposing medium and low-grade phosphate rock with hydrochloric acid, high-quality anhydrous iron phosphate is directly produced, and the by-product is gypsum, which can be directly used as a commodity exchange.

[0017] The mixed acid includes 2-8% by mass of H3PO4 and 1-4% by mass of HCl.

[0018] In step 2, the phosphate rock and hydrochloric acid are mixed in a decomposition tank and fully reacted, the reaction temperature is 70-100° C., and the reaction time is 10-30 minutes.

[0019] In step 2, the first slurry is filtered by belt filtration, using acid water at 40-60°C in the system and tap water at 40-60°C for multi-stage washing.

[0020] The mixed acid is selected to be 0.5-3 mol / L, wherein the molar ratio of H3PO4 to HCl is (0.2-3.2):1.

[0021] The molar ratio of H3PO4 to ferrous sulfate in the fourth filtrate in step six is ​​(20-80):1.

[0022] It is worth noting that the components of the first filtrate are mainly: Phosphoric acid (H3PO4): One of the main products of the reaction between phosphate rock and hydrochloric acid is phosphoric acid. Calcium fluorophosphate (Ca5F(PO4)3) in phosphate rock is decomposed by hydrochloric acid to produce phosphoric acid, which is one of the main components. Its concentration depends on the quality of the phosphate rock, the amount of hydrochloric acid used and the reaction conditions.

[0023] Calcium chloride (CaCl2): Phosphate rock reacts with hydrochloric acid to produce calcium chloride. Chloride ions (Cl⁻) in hydrochloric acid combine with calcium ions (Ca²⁺) in phosphate rock to form calcium chloride, which is also an important component in the filtrate. Its concentration is closely related to the amount of hydrochloric acid used and the reaction conditions.

[0024] Other impurities: In addition to phosphoric acid and calcium chloride, it may also contain a small amount of phosphates with impurities such as iron and aluminum. These impurities may come from the phosphate rock itself or be introduced during the reaction process. The impurity content depends on the purity of the phosphate rock, the purity of the hydrochloric acid and the reaction conditions.

[0025] Likewise, the major components of the second filtrate may include: It mainly includes hydrochloric acid that failed to react with phosphate rock or failed to precipitate, and other soluble impurities. The specific components may include residual hydrochloric acid, unreacted phosphates, chlorides and other metal ions or anions dissolved in the solution.

[0026] The third filtrate mainly contains sulfuric acid that failed to react with the filter cake or failed to precipitate, and other soluble impurities. Specific components may include remaining sulfuric acid, unreacted phosphates, sulfates, and other metal ions or anions dissolved in the solution.

[0027] The composition of the fourth filtrate is relatively complex, but it should mainly contain the remaining sulfuric acid after the reaction, unreacted phosphates, possible sulfates, and other metal ions or anions dissolved in the solution. However, due to the oxidation of hydrogen peroxide, impurities such as iron ions may have been converted into insoluble precipitates and filtered out, so the impurity content in the fourth filtrate should be reduced.

[0028] The mixed acid includes 2-8% by mass of H3PO4 and 1-4% by mass of HCl.

[0029] In step six, sodium hydroxide solution is added to adjust the pH to 1.9-2.1.

[0030] In step 2, the reaction temperature is 70-100° C. and the reaction time is 10-30 minutes.

[0031] It is worth noting that the second filtrate in the present invention can be collected and returned to step 2 to be mixed in the decomposition tank for reuse.

[0032] It should be noted that the components of the mother liquor include: Unreacted hydrochloric acid: If there is an excess of hydrochloric acid, some of it may not participate in the reaction and remain in the mother liquor; Chloride ions: from hydrochloric acid and the resulting chlorinated calcium dihydrogen phosphate, and possibly other chloride by-products; Phosphate ions and other phosphates: incompletely reacted phosphates or phosphate impurities generated by the reaction; Calcium ions: Calcium from phosphate rock, which may exist in the form of calcium chloride or other calcium salts; Other impurity ions: such as magnesium ions, iron ions, etc., depending on the impurity content of the phosphate ore and the reaction conditions; Water: As a reaction medium and one of the products, the mother liquor contains a large amount of water.

[0033] Therefore, it is worth noting that after the chlorinated calcium dihydrogen phosphate crystals and mother liquor are precipitated in step three, the mother liquor can be collected and added to a neutralization tank, and the pH value is adjusted to 5-6 by adding lime milk for neutralization, and the filtered precipitated calcium dihydrogen phosphate is returned to the decomposition tank in step two, thereby achieving effective reuse of materials; Next, continue to add lime milk to neutralize to PH = 9, filter, add hydrochloric acid to adjust the filtrate to PH = 6-7, concentrate the adjusted liquid and spray granulate to produce anhydrous calcium chloride by-product to achieve full utilization of the material.

[0034] It should be explained that the decomposition tank, filter, microfilter, neutralization tank and other devices used in the present invention are all prior art.

[0035] Specifically, taking Huji Mine as an example, 590mL of monocalcium phosphate chloride mother liquor and 1720mL (HCl=30%) hydrochloric acid of the 6th cycle test of Huji Mine sample were put into a 5000mL beaker, and the electric furnace was heated to above 60°C. 1000g of Huji ore powder (all passed 40 mesh) was slowly added. The reaction was stirred at nearly 90°C. The foam produced was separated by a two-stage cyclone separator. During the liquid reflux decomposition reaction, the gas phase was absorbed by the sodium chloride solution produced by the system to obtain Na2SiF6. After the ore was added, it was stirred for 10 minutes and filtered while hot to obtain 2680g of decomposition liquid. The wet silicon slag was dried to 268g. The decomposition liquid was heat-treated to precipitate 809g of monocalcium phosphate chloride (P2O5=20%) and 1020g of mother liquor (P2O5= 1.3%), 90g of mixed acid (P2O5=5%, Cl=3%) was used to wash the chlorinated calcium dihydrogen phosphate, the filtrate was returned to the decomposition tank, the filter cake was slurried with 90g of water and mixed with 372g of 60% sulfuric acid solution for sufficient reaction, and wet calcium sulfate and a mixed filtrate containing phosphoric acid and trace hydrochloric acid were obtained by filtration. The calcium sulfate was washed to obtain high-quality calcium sulfate dihydrate, which was dried to obtain 386.4g. 20% ferrous sulfate solution 25g was added to the mixed filtrate, and the reaction was carried out for 30min. After passing through a microfilter, 1730g of 20% ferrous sulfate solution and 240g of 25% hydrogen peroxide were added to the filtrate, and the reaction was carried out for 25min. Then 282g of 32% sodium hydroxide solution was added to adjust the pH to 1.9-2.1, and 324.1g of anhydrous iron phosphate was obtained after filtration and drying at 150°C.

[0036] It is worth noting that one cycle refers to operating according to this process flow, from acid decomposition to the output of by-products and part of the circulating liquid in the subsequent sections entering the next acid decomposition.

[0037] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for preparing anhydrous ferric phosphate from medium and low-grade phosphate ore, characterized in that: The steps include: Step 1: Provide medium-low grade phosphate ore, with P2O5 ≥ 15wt%; Step 2: mixing phosphate rock and hydrochloric acid in a decomposition tank and reacting them fully to obtain a first slurry, filtering out impurities such as silicon slag and a first filtrate from the first slurry, and decomposing fluorine-containing gas at the same time; Step 3: The first filtrate is placed in a sedimentation tank, precipitated at 15-38°C and filtered to obtain chlorinated calcium dihydrogen phosphate crystals and mother liquor; Step 4: adding mixed acid to the chlorinated calcium dihydrogen phosphate crystals, beating the mixture, and filtering to obtain a second filtrate and a filter cake; Step 5: adding water and 40-70% sulfuric acid solution to the filter cake in step 4, followed by pulping for sufficient reaction and then crystallization, and finally filtering to obtain a gypsum product and a third filtrate; Step 6: The third filtrate in step 5 is impurity-removed with saturated ferrous sulfate, and the fourth filtrate obtained through the microfilter is further added with saturated ferrous sulfate solution and then 5-25% hydrogen peroxide, reacted for 5-35 minutes, and then sodium hydroxide solution is added to adjust the pH value to 1.9-2.1, and the reaction is continued for 3-6 hours at a temperature, and the obtained iron phosphate is filtered; Step 7: Dry the iron phosphate obtained in step 6 at 150-170° C. to obtain anhydrous iron phosphate.

2. The method for preparing anhydrous ferric phosphate from medium and low-grade phosphate ore according to claim 1, characterized in that: The mixed acid comprises 2-8% by mass of H3PO4 and 1-4% by mass of HCl.

3. The method for preparing anhydrous ferric phosphate from medium and low grade phosphate ore according to claim 1, characterized in that: In step 2, the phosphate rock and hydrochloric acid are mixed in a decomposition tank and fully reacted, the reaction temperature is 70-100° C., and the reaction time is 10-30 minutes.

4. The method for preparing anhydrous ferric phosphate from medium and low-grade phosphate ore according to claim 1, characterized in that: In step 2, the first slurry is filtered by belt filtration, using acid water at 40-60°C in the system and tap water at 40-60°C for multi-stage washing.

5. The method for preparing anhydrous ferric phosphate from medium and low grade phosphate ore according to claim 2, characterized in that: The mixed acid is selected to be 0.5-3 mol / L, wherein the molar ratio of H3PO4 to HCl is (0.2-3.2):

1.

6. The method for preparing anhydrous ferric phosphate from medium and low-grade phosphate ore according to claim 1, characterized in that: The molar ratio of H3PO4 to ferrous sulfate in the fourth filtrate in step six is ​​(20-80):1.

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