Method for preparing anhydrous iron phosphate from medium- and low-grade phosphate rock

Abstract

The present invention discloses a method for preparing anhydrous iron phosphate from medium and low grade phosphate rock, which comprises the following steps: Step 1: Provide medium and low grade phosphate rock; Step 2: Mix the phosphate rock with hydrochloric acid in a decomposition tank and fully react to obtain a first slurry; Step 3: Place the first filtrate into a sedimentation tank; Step 4: Add mixed acid to calcium dihydrogen chloride phosphate crystals, carry out pulping and filtration to obtain a second filtrate and a filter cake; Step 5: Finally, filter to obtain a gypsum product and a third filtrate; Step 6: The third filtrate in Step 5 is purified with saturated ferrous sulfate. The fourth filtrate obtained through a microfilter is continuously added with a saturated ferrous sulfate solution, then continuously added with 5-25% hydrogen peroxide, reacted for 5-35 minutes, then added with sodium hydroxide solution to adjust the pH value to 1.9-2.1, and kept warm and continuously reacted for 3-6 hours, and the iron phosphate obtained by filtration; Step 7: Dry the iron phosphate obtained in Step 6 at 150-170 °C to obtain anhydrous iron phosphate.

Description

Technical Field

[0001] The present invention relates to the technical field of iron phosphate preparation, and particularly relates to a method for preparing anhydrous iron phosphate from medium- and low-grade phosphate rock. Background Art

[0002] Medium- and low-grade phosphate rock refers to phosphate rock with relatively low phosphorus content, and its phosphorus pentoxide (P2O5) content is usually lower than a certain specific value, and the specific value may vary depending on regions and industry standards. Generally, phosphate rock with a phosphorus pentoxide content between 18% and 28% is called medium-grade phosphate rock, while that with a content lower than 18% is regarded as low-grade phosphate rock. Such ores dominate China's phosphate rock resources, and have the characteristics of rich reserves but low grade, high impurity content, and many difficult-to-concentrate ores.

[0003] The production methods of iron phosphate mainly include six processes: sodium method, ammonium method, iron method, fertilizer phosphoric acid, iron oxide red, and calcium hydrogen phosphate. In China, the production processes mostly adopt three production process routes: ammonium method, sodium method, and iron method. The ammonium method is that ferrous sulfate reacts with monoammonium phosphate, and after precipitation and filtration, ammonia water is used to neutralize the excessive acid to obtain iron phosphate, and the filtrate is ammonium sulfate solution; the sodium method is that ferrous sulfate is acidified with phosphoric acid and then reacts with hydrogen peroxide, and then the pH value is adjusted with sodium hydroxide solution to produce iron 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 large equipment investments, and even all have problems of environmental pollution. Summary of the Invention

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

[0006] According to the method for preparing anhydrous iron phosphate from medium- and low-grade phosphate rock provided by the present invention, the following steps are included:

[0007] Step 1: Provide medium- and low-grade phosphate rock with P2O5≥15wt%;

[0008] Step 2: Mix the phosphate rock with hydrochloric acid in a decomposition tank and fully react to obtain a first slurry. The first slurry is filtered to remove impurities such as silicon slag and a first filtrate, and at the same time, fluorine-containing gas is decomposed;

[0009] Step 3: The first filtrate is placed in a sedimentation tank, and calcium dihydrogen chloride phosphate crystals and mother liquor are precipitated and filtered at 15 - 38°C;

[0010] Step 4: Mixed acid is added to the calcium dihydrogen chloride phosphate crystals, and after pulping and filtering, a second filtrate and a filter cake are obtained;

[0011] Step Five: Add water and 40 - 70% sulfuric acid solution to the filter cake obtained in Step Four, then beat into pulp, fully react and then carry out crystal cultivation, and finally filter to obtain gypsum product and the third filtrate;

[0012] Step Six: Remove impurities from the third filtrate in Step Five with saturated ferrous sulfate. The fourth filtrate obtained through the microfilter is continuously added with saturated ferrous sulfate solution and then 5 - 25% hydrogen peroxide is added, react for 5 - 35 min, then add sodium hydroxide solution to adjust the pH value to 1.9 - 2.1, keep warm and continue to react for 3 - 6 h, and filter to obtain iron phosphate;

[0013] Step Seven: Dry the iron phosphate obtained in Step Six at 150 - 170 °C to obtain anhydrous iron phosphate.

[0014] Further, the mixed acid includes 2 - 8% by mass of H3PO4 and 1 - 4% by mass of HCI.

[0015] Further, in Step Two, 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.

[0016] Further, for the filtration of the first slurry in Step Two, the belt filtration method is selected, and the acid water at 40 - 60 °C in the system is used, and then multi - stage cross - flow washing is carried out in combination with tap water at 40 - 60 °C.

[0017] Further, the mixed acid is selected to be 0.5 - 3 mol / L, and the molar ratio of H3PO4 to HCl is (0.2 - 3.2):1.

[0018] Further, the molar ratio of H3PO4 to ferrous sulfate in the fourth filtrate in Step Six is (20 - 80):1.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. By using medium - and low - grade phosphate rock to prepare anhydrous iron phosphate, the production cost is greatly reduced;

[0021] 2. 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 for commodity exchange. Description of the Drawings

[0022] Figure 1 It is a flow chart of the method for preparing anhydrous iron phosphate from medium - and low - grade phosphate rock according to the embodiment of the present invention. Detailed Embodiments

[0023] To enable those skilled in the art to better understand the solution of this application, the following will clearly and completely describe the technical solution in the embodiments of this application in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0024] The invention provides a method for preparing anhydrous ferric phosphate from medium and low grade phosphate rock, which comprises the following steps:

[0025] Step 1: Provide medium and low grade phosphate rock with P2O5 ≥ 15wt%.

[0026] Step 2: Mix the phosphate rock with hydrochloric acid in a decomposition tank and fully react to obtain a first slurry. Filter out impurities such as silica slag and a first filtrate from the first slurry, and decompose fluorine-containing gas at the same time.

[0027] Step 3: Place the first filtrate in a sedimentation tank, precipitate and filter at 15 - 38°C to obtain calcium dihydrogen phosphate chloride crystals and mother liquor.

[0028] Step 4: Add mixed acid to the calcium dihydrogen phosphate chloride crystals, carry out pulping and filtering to obtain a second filtrate and a filter cake.

[0029] Step 5: Add water and 40 - 70% sulfuric acid solution to the filter cake in Step 4, then carry out pulping and fully react, followed by crystal cultivation, and finally filter to obtain gypsum products and a third filtrate.

[0030] Step 6: Remove impurities from the third filtrate in Step 5 with saturated ferrous sulfate. The fourth filtrate obtained through a microfilter is continuously added with saturated ferrous sulfate solution, then continuously added with 5 - 25% hydrogen peroxide, react for 5 - 35 minutes, then add sodium hydroxide solution to adjust the pH value to 1.9 - 2.1, keep warm and continuously react for 3 - 6 hours, and filter to obtain ferric phosphate.

[0031] Step 7: Dry the ferric phosphate obtained in Step 6 at 150 - 170°C to obtain anhydrous ferric phosphate.

[0032] The whole process uses medium and low grade phosphate rock to prepare anhydrous ferric phosphate, greatly reducing the production cost. By decomposing medium and low grade phosphate rock with hydrochloric acid, high-quality anhydrous ferric phosphate is directly produced, and the by-product is gypsum, which can be directly used for commodity exchange.

[0033] The mixed acid includes H3PO4 with a mass fraction of 2 - 8% and HCI with a mass fraction of 1 - 4%.

[0034] In Step 2, the phosphate rock and hydrochloric acid are mixed and fully reacted in a decomposition tank at a reaction temperature of 70 - 100°C and a reaction time of 10 - 30 minutes.

[0035] In step 2, for the filtration of the first slurry, the belt filtration method is selected, and the acid water at 40 - 60 °C in the system is used, and it is combined with tap water at 40 - 60 °C for multi-stage cross-flow washing.

[0036] The mixed acid is selected to be 0.5 - 3 mol / L, and the molar ratio of H3PO4 to HCl is (0.2 - 3.2):1.

[0037] In step 6, the molar ratio of H3PO4 to ferrous sulfate in the fourth filtrate is (20 - 80):1.

[0038] It should be noted that the components of the above-mentioned first filtrate are mainly:

[0039] Phosphoric acid (H3PO4): One of the main products of the reaction between phosphate rock and hydrochloric acid is phosphoric acid. The fluorapatite (Ca5F(PO4)3) in the phosphate rock is decomposed by hydrochloric acid, generating phosphoric acid, which is one of the main components, and its concentration depends on the quality of the phosphate rock, the dosage of hydrochloric acid, and the reaction conditions.

[0040] Calcium chloride (CaCl2): The reaction between phosphate rock and hydrochloric acid also generates calcium chloride. The chloride ions (Cl⁻) in hydrochloric acid combine with the calcium ions (Ca²⁺) in the phosphate rock to form calcium chloride, which is also an important component in the filtrate, and its concentration is closely related to the dosage of hydrochloric acid and the reaction conditions.

[0041] Other impurities: In addition to phosphoric acid and calcium chloride, it may also contain a small amount of phosphates of 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 hydrochloric acid, and the reaction conditions.

[0042] Similarly, the main components of the second filtrate may include:

[0043] It mainly contains hydrochloric acid that has not reacted with the phosphate rock or has not precipitated, as well as other soluble impurities. The specific components may include the remaining hydrochloric acid, unreacted phosphates, chlorides, and other metal ions or anions dissolved in the solution.

[0044] The third filtrate mainly contains sulfuric acid that has not reacted with the filter cake or has not precipitated, as well as other soluble impurities. The specific components may include the remaining sulfuric acid, unreacted phosphates, sulfates, and other metal ions or anions dissolved in the solution.

[0045] The composition of the fourth filtrate is relatively complex, but it mainly should contain the remaining sulfuric acid after the reaction, unreacted phosphates, potentially formed 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.

[0046] The mixed acid includes H3PO4 with a mass fraction of 2 - 8% and HCI with a mass fraction of 1 - 4%.

[0047] In step six, sodium hydroxide solution is added to adjust the pH to 1.9 - 2.1.

[0048] In step two, the reaction temperature is 70 - 100 °C and the reaction time is 10 - 30 minutes.

[0049] It should be noted that in this invention, the second filtrate can be collected and returned to step two to be mixed in the decomposition tank for reuse.

[0050] It should be noted that the composition of the mother liquor includes:

[0051] Unreacted hydrochloric acid: If hydrochloric acid is in excess, some of it may not participate in the reaction and remain in the mother liquor.

[0052] Chloride ions: from hydrochloric acid and the generated calcium dihydrogen phosphate chloride, as well as possible other chloride by-products;

[0053] Phosphate ions and other phosphates: unreacted phosphates or phosphate impurities generated by the reaction;

[0054] Calcium ions: from the calcium element in the phosphate rock, and may exist in the form of calcium chloride or other calcium salts;

[0055] Other impurity ions: such as magnesium ions, iron ions, etc., depending on the impurity content of the phosphate rock and the reaction conditions;

[0056] Water: As one of the reaction media and products, the mother liquor contains a large amount of water.

[0057] Therefore, it should be noted that after the calcium dihydrogen phosphate chloride crystals and the mother liquor are precipitated in step three, the mother liquor can be collected and added to the neutralization tank, and lime milk is added to adjust the pH value to 5 - 6. The precipitated calcium hydrogen phosphate obtained by filtration is returned to the decomposition tank in step two, realizing the effective reuse of materials;

[0058] Immediately afterwards, continue to add lime milk to neutralize to pH = 9, filter, and the obtained filtrate is adjusted back to pH = 6 - 7 with hydrochloric acid. The adjusted liquid is concentrated and spray granulated to produce anhydrous calcium chloride by-product to achieve the comprehensive utilization of materials.

[0059] It should be noted that devices such as decomposition tanks, filters, microfilters, and neutralization tanks used in the present invention are all prior arts.

[0060] Specifically, taking Huji Mine as an example, 590 mL of the calcium dihydrogen chloride phosphate mother liquor and 1720 mL of hydrochloric acid (HCl = 30%) from the 6th cycle test of the Huji Mine sample were both put into a 5000 mL large beaker. The electric furnace was heated to above 60 °C, and then 1000 g of Huji Mine powder (all passing through 40 mesh) was slowly added. The reaction was carried out with stirring at nearly 90 °C. The generated foam was separated by a two-stage cyclone separator. The liquid phase was refluxed to the decomposition reaction, and the gas phase was absorbed by the sodium chloride solution generated in the system to obtain Na2SiF6. After the addition of the ore was completed, stirring was continued for 10 minutes, and then filtration was carried out while it was hot to obtain 2680 g of decomposition liquid. The wet silicon slag was dried to 268 g. The decomposition liquid was heat-treated to precipitate 809 g of calcium dihydrogen chloride phosphate (P2O5 = 20%) and 1020 g of mother liquor (P2O5 = 1.3%). The calcium dihydrogen chloride phosphate was washed with 90 g of mixed acid (P2O5 = 5%, Cl = 3%). The filtrate was returned to the decomposition tank. The filter cake was slurried with 90 g of water and mixed with 372 g of 60% sulfuric acid solution for full reaction, and then filtered to obtain wet calcium sulfate and a mixed filtrate containing phosphoric acid and trace hydrochloric acid. The calcium sulfate was washed to obtain high-quality calcium sulfate dihydrate, which was dried to 386.4 g. 25 g of 20% ferrous sulfate solution was added to the mixed filtrate and reacted for 30 min. After passing through the microfilter, 1730 g of 20% ferrous sulfate solution and 240 g of 25% hydrogen peroxide were added to the filtrate and reacted for 25 min. Then 282 g of 32% sodium hydroxide solution was added to adjust the pH to 1.9 - 2.1. After filtration, it was dried at 150 °C to obtain 324.1 g of anhydrous iron phosphate.

[0061] It is worth noting that one cycle means operating according to this process flow, from acid decomposition to the output of by-products and the partial recycle liquid in the subsequent process sections entering the next acid decomposition.

[0062] The above are only the preferred embodiments of the present application. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing anhydrous iron phosphate from medium and low grade phosphate rock, characterized in that, It includes the following steps: Step 1: Provide medium and low-grade phosphate rock with P2O5≥15wt%. Step 2: Mix the phosphate rock with hydrochloric acid in a decomposition tank and fully react to obtain a first slurry. Filter out impurities such as silica slag and a first filtrate from the first slurry, and decompose fluorine-containing gas at the same time. Step 3: Place the first filtrate in a settling tank, precipitate and filter at 15-38°C to obtain calcium dihydrogen chlorophosphate crystals and mother liquor. Step 4: Add mixed acid to the calcium dihydrogen chlorophosphate crystals, carry out pulping and filtering to obtain a second filtrate and filter cake. Step 5: Add water and 40-70% sulfuric acid solution to the filter cake in Step 4, then carry out pulping and fully react, followed by crystal cultivation, and finally filter to obtain gypsum products and a third filtrate. Step 6: Remove impurities from the third filtrate in Step 5 with saturated ferrous sulfate. The fourth filtrate obtained through a microfilter continues to add saturated ferrous sulfate solution, then add 5-25% hydrogen peroxide, react for 5-35 min, then add sodium hydroxide solution to adjust the pH value to 1.9-2.1, keep warm and continue to react for 3-6 h, and filter to obtain iron phosphate. Step 7: Dry the iron phosphate obtained in Step 6 at 150-170°C to obtain anhydrous iron phosphate. The mixed acid includes H3PO4 with a mass fraction of 2-8% and HCl with a mass fraction of 1-4%. The mixed acid is selected to be 0.5-3 mol / L, and the molar ratio of H3PO4 to HCl is (0.2-3.2):

1.

2. The method for preparing anhydrous iron phosphate from medium- and low-grade phosphate rock according to claim 1, characterized in that, 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.

3. The method for preparing anhydrous iron phosphate from medium and low-grade phosphate rock according to claim 1, characterized in that, For the filtration of the first slurry in Step 2, a belt filtration method is selected, and acid water at 40-60°C in the system is used, and multi-stage cross-flow washing is carried out in combination with tap water at 40-60°C.

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

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