A method for preparing ferric phosphate from refined phosphoric acid

Abstract

The present invention provides a method for preparing iron phosphate from refined phosphoric acid, the method comprising the following steps: (1) mixing ferrous sulfate solution, an oxidant and refined phosphoric acid to obtain a pre-precipitation liquid; (2) heating the pre-precipitation liquid and keeping it warm to precipitate to obtain a slurry containing iron phosphate precipitate; (3) subjecting the slurry to solid-liquid separation to obtain iron phosphate. The method forms a method for preparing iron phosphate based on phosphoric acid rather than monoammonium phosphate, which can avoid the problem of a large amount of low-concentration ammonium sulfate wastewater in the traditional iron phosphate preparation process, opens up a new way for the preparation of iron phosphate, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of chemical metallurgy, and in particular to a method for preparing ferric phosphate from refined phosphoric acid. Background Art

[0002] Lithium iron phosphate batteries are gradually surpassing ternary batteries in terms of vehicle installation volume. The overtaking of lithium iron phosphate batteries is not only related to the price of raw materials for power batteries, but also closely related to the high safety of lithium iron phosphate batteries. It can be predicted that lithium iron phosphate batteries will also have a wide range of applications in the field of energy storage.

[0003] There are many preparation processes for lithium iron phosphate, among which the mainstream technologies include three, namely, the solid phase method based on iron phosphate, the solid phase method based on ferrous oxalate, and the liquid phase method based on ferric nitrate. As the core precursor of the first method, the development of low-cost preparation technology for iron phosphate is an important demand. The preparation process of iron phosphate generally includes two methods: one-step method and two-step method. Because the two-step method can improve the quality of iron phosphate better than the one-step method, it is the main method used in industrial production. The two-step method includes two synthesis modes. The first synthesis mode is to first adjust the pH value of ferrous source (such as FeSO4·7H2O) and phosphorus source (such as (NH4)2HPO4) to 4-5 with ammonia water and then precipitate to obtain ferrous phosphate octahydrate (Fe3(PO4)2·8H2O). After washing, the ferrous phosphate octahydrate is stirred and slurried with an aqueous solution, and phosphoric acid and hydrogen peroxide are added to the slurry, and the slurry is heated to below 100°C to obtain dihydrated iron phosphate crystals (FePO4·2H2O). The dihydrated iron phosphate crystals The first mode of synthesis is to first react a ferrous source (such as FeSO4·7H2O) and a phosphorus source (such as (NH4)2HPO4) in an aqueous solution environment in the presence of an oxidant (such as hydrogen peroxide) to generate an amorphous ferric phosphate precipitate, and then wash the obtained amorphous ferric phosphate precipitate, and then add the washed amorphous ferric phosphate precipitate to a phosphoric acid solution and crystallize at 85-100°C to obtain dihydrate ferric phosphate crystals, which will also be washed again to remove the entrained free ions.

[0004] In addition, CN112390237A discloses a method for preparing nanostructured iron phosphate, which specifically comprises pumping a mixture of hydrogen peroxide and phosphate or concentrated phosphoric acid into an acidic liquid (pH value 0.1-1.0) obtained by dissolving and filtering ferrous sulfate as a by-product of titanium dioxide, then introducing ammonia water to adjust the pH value to 1.0-3.0, stirring at below 100°C to obtain a white iron phosphate slurry, and after solid-liquid separation, dehydrating the solid to obtain anhydrous nanostructured iron phosphate.

[0005] CN104944400B and CN110482512A also use ferrous sulfate and phosphoric acid as the iron source and phosphorus source respectively to precipitate ferric phosphate, but do not adjust the pH value of the mixed solution by adding ammonia alkali or sodium alkali. Instead, they increase the pH value by adding water to dilute and help ferric phosphate precipitation. The precipitation temperature is below 100°C. This is a dilution hydrolysis precipitation method, which can avoid the generation of salt-containing wastewater such as ammonium sulfate, but the water circulation volume is large.

[0006] CN102491302B discloses a battery-grade anhydrous ferric phosphate and a preparation method thereof. The method uses ferrous sulfate or ferrous chloride as an iron source and phosphoric acid or phosphate as a phosphorus source, prepares a mixed solution of the iron source and the phosphorus source, and prepares an alkaline regulator based on ammonium radicals, pumps the mixed solution and the alkaline regulator into a stirred reactor, and inputs compressed air, controls the pH value to be 0.5-7.5 by adjusting the liquid material and air flow rate, generates NH4Fe2(OH)(PO4)2·2H2O solid, fully washes the solid and roasts it to obtain orthorhombic battery-grade anhydrous ferric phosphate.

[0007] However, the above documents still have the problem of large water circulation volume or generation of ammonia-containing wastewater. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for preparing ferric phosphate from refined phosphoric acid. The method is based on the idea of ​​combining with phosphorus chemical enterprises to develop a method for preparing ferric phosphate using phosphoric acid instead of monoammonium phosphate, so as to avoid the problem of a large amount of low-concentration ammonium sulfate wastewater existing in the traditional method for preparing ferric phosphate.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for preparing ferric phosphate from refined phosphoric acid, the method comprising the following steps:

[0011] (1) mixing a ferrous sulfate solution, an oxidant, and refined phosphoric acid to obtain a pre-precipitation solution;

[0012] (2) the pre-precipitation liquid is heated and kept warm for precipitation to obtain a slurry containing iron phosphate precipitation;

[0013] (3) The slurry is subjected to solid-liquid separation to obtain iron phosphate.

[0014] The method for preparing ferric phosphate from refined phosphoric acid provided by the present invention can be applied to a ferrous sulfate solution containing impurities, and the characteristics of ferric phosphate being lower in an inorganic acidic environment or a mixed solvent acidic environment, being able to preferentially crystallize and inhibiting the substitution of impurities at the iron lattice site in the ferric phosphate lattice are utilized, so that a ferric phosphate product with high purity can still be obtained subsequently. At the same time, by directly heating and heat-insulating the pre-precipitation liquid for precipitation, the generation of a large amount of circulating water and ammonia-containing wastewater is avoided, thereby realizing the green production of ferric phosphate.

[0015] The present invention has no special restrictions on the mixing steps of the ferrous sulfate solution, the oxidant and the refined phosphoric acid, and the ferrous sulfate solution, the oxidant and the refined phosphoric acid can be mixed in any order, for example, the hydrogen peroxide and the refined phosphoric acid are first mixed evenly and then mixed into the ferrous sulfate solution, or the ferrous sulfate solution and the refined phosphoric acid are first mixed evenly and then ferrous ions are oxidized with hydrogen peroxide to obtain the ferrous sulfate solution, or the ferrous sulfate solution is first oxidized with hydrogen peroxide and then mixed with refined phosphoric acid to obtain the ferrous sulfate solution. Alternatively, the three can be directly added into a container at the same time for mixing.

[0016] Preferably, the preparation of the ferrous sulfate solution in step (1) comprises: mixing a ferrous sulfate raw material and a solvent, mixing iron powder and a sulfuric acid solution, or mixing a ferrous sulfate raw material, iron powder and a solvent, and dissolving and refining the mixed mixture to obtain a ferrous sulfate solution.

[0017] Preferably, the ferrous sulfate raw material includes any one or a combination of at least two of high-purity ferrous sulfate, industrial-grade ferrous sulfate or ferrous sulfate produced as a byproduct of acid-process titanium dioxide, wherein a typical but non-limiting combination is: a combination of high-purity ferrous sulfate and industrial-grade ferrous sulfate, a combination of high-purity ferrous sulfate and ferrous sulfate produced as a byproduct of acid-process titanium dioxide, a combination of industrial-grade ferrous sulfate and ferrous sulfate produced as a byproduct of acid-process titanium dioxide, and a combination of high-purity ferrous sulfate, industrial-grade ferrous sulfate and ferrous sulfate produced as a byproduct of acid-process titanium dioxide. In the method of the present invention, the raw material source of ferrous sulfate is wide, the cost is low, and even if the raw material contains some impurities, the purity of ferric phosphate in the final product is not affected.

[0018] Preferably, the iron powder comprises any one of pig iron powder, reduced iron powder, electrolytic iron powder, hydroxyl iron powder or atomized iron powder, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of pig iron powder and reduced iron powder, a combination of pig iron powder and electrolytic iron powder, a combination of electrolytic iron powder and reduced iron powder, a combination of hydroxyl iron powder and reduced iron powder, and a combination of pig iron powder and atomized iron powder.

[0019] Preferably, the impurities include any one of titanium, magnesium, aluminum, calcium, vanadium, chromium, manganese, nickel, cobalt, zinc, lead, sodium, potassium, silicon or copper ions, or a combination of at least two thereof. For example, titanium, magnesium, aluminum and calcium may be contained at the same time.

[0020] Preferably, the refined phosphoric acid contains any one or at least two of the impurities of iron, aluminum, magnesium, manganese, titanium, zinc, calcium, sodium, chromium or vanadium, but the concentration of iron, aluminum, magnesium and manganese is lower than 0.85 g / L, and the concentration of titanium, zinc, calcium, sodium, chromium and vanadium does not exceed 0.35 g / L.

[0021] Preferably, the solvent comprises water and / or sulfuric acid solution.

[0022] Preferably, the total iron ion concentration in the ferrous sulfate solution is 0.1-2 mol / L, for example, it can be 0.1 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, but is not limited to the listed values, and other unlisted values ​​within the range are equally applicable.

[0023] Preferably, the refining in step (1) includes: adjusting the pH value of the dissolved solution to 2 to 10 and solid-liquid separation, for example, it can be 2.0, 2.2, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 8.0, 9.0 or 10.0, etc., but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable. The present invention further improves the purity of the final ferric phosphate by further refining and then performing a subsequent precipitation process.

[0024] Preferably, the substance for adjusting the pH value of the dissolved solution includes an alkaline substance.

[0025] Preferably, the alkaline substance comprises any one of sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, lime, limestone, slaked lime, metallic calcium, magnesium hydroxide, magnesium oxide, magnesium powder, magnesium chips, ferric hydroxide, ferric oxide, iron carbonate, iron powder or iron chips, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of sodium carbonate and sodium hydroxide, a combination of potassium carbonate and sodium hydroxide, a combination of potassium hydroxide and sodium hydroxide, a combination of sodium carbonate and lime, a combination of slaked lime and magnesium hydroxide, a combination of metallic calcium and sodium hydroxide, a combination of magnesium powder and sodium hydroxide, a combination of magnesium powder and ferric hydroxide, a combination of magnesium powder and magnesium chips, and a combination of ferric carbonate and ferric oxide.

[0026] Preferably, the oxidant in step (1) comprises hydrogen peroxide.

[0027] Preferably, the amount of hydrogen peroxide is 0.5 to 2 times the total molar amount of ferrous ions in the ferrous sulfate solution, for example, 0.5 times, 1.0 times, 1.5 times or 2.0 times, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable. The present invention further preferably controls the amount of hydrogen peroxide within the above range, which is more conducive to ensuring the state of iron in the solution before precipitation.

[0028] Preferably, the amount of the refined phosphoric acid added is based on a molar ratio of iron to phosphorus in the pre-precipitation solution of 0.8 to 1.1:1, for example, 0.8:1, 0.9:1, 1.0:1 or 1.1:1, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0029] Preferably, the concentration of the refined phosphoric acid is 5 to 85wt% P2O5, for example, it can be 5wt% P2O5, 10wt% P2O5, 15wt% P2O5, 20wt% P2O5, 25wt% P2O5, 30wt% P2O5, 35wt% P2O5, 40wt% P2O5, 45wt% P2O5, 50wt% P2O5, 55wt% P2O5, 60wt% P2O5, 65wt% P2O5, 70wt% P2O5, 75wt% P2O5, 80wt% P2O5 or 85wt% P2O5, but is not limited to the listed values, and other values ​​not listed within the range are equally applicable.

[0030] Preferably, the temperature of the heat preservation precipitation is 60 to 150°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are equally applicable. The present invention further preferably has a temperature of heat preservation precipitation of 60 to 150°C, which can be matched with the hydrogen ion concentration, alcohol solvent or nucleation promoter in the pre-precipitation liquid to better achieve the precipitation of iron phosphate under strong acid, and can avoid the entrainment of impurities.

[0031] Preferably, the heat preservation precipitation is carried out under stirring conditions.

[0032] Preferably, before heating in step (2), the pre-precipitation solution and the sulfuric acid solution are mixed until H + The concentration is 1 to 5 mol / L, for example, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 4.0 mol / L or 5.0 mol / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable. The present invention further adjusts the hydrogen ion concentration in the system before heating and heat preservation precipitation to ensure that the system is in a strongly acidic environment, thereby facilitating the subsequent separation of iron phosphate from impurities and further improving the purity of iron phosphate.

[0033] Preferably, before the temperature is raised in step (2), the pre-precipitation liquid and the alcohol solvent are mixed. In the present invention, an alcohol solvent is further preferably added to further enhance the precipitation of the iron phosphate precipitate in the strongly acidic system.

[0034] Preferably, the alcohol solvent comprises any one of methanol, ethanol, propanol or isopropanol, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of methanol and ethanol, a combination of methanol and propanol, a combination of ethanol and propanol, a combination of methanol and isopropanol, a combination of methanol, ethanol and propanol, etc.

[0035] Preferably, the amount of the alcohol solvent added is 5 to 100% of the liquid volume fraction before precipitation, for example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%, etc., but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0036] Preferably, before the temperature is raised in step (2), the pre-precipitation liquid and the nucleation promoter are mixed. In the present invention, the nucleation promoter is further preferably added to further enhance the precipitation of the iron phosphate precipitate in the strongly acidic system.

[0037] Preferably, the nucleation promoter includes any one of isobarbital iron phosphate, monoclinic iron phosphate, orthorhombic iron phosphate, α-quartz iron phosphate, monoclinic iron phosphate dihydrate or orthorhombic iron phosphate dihydrate, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of isobarbital iron phosphate and monoclinic iron phosphate, a combination of orthorhombic iron phosphate and monoclinic iron phosphate, a combination of isobarbital iron phosphate and α-quartz iron phosphate, a combination of monoclinic iron phosphate dihydrate and monoclinic iron phosphate, and a combination of isobarbital iron phosphate and orthorhombic iron phosphate dihydrate.

[0038] Preferably, before mixing the nucleation promoter and the pre-precipitation solution, the nucleation promoter is firstly ground. The present invention further firstly grinds the nucleation promoter, so as to facilitate the regulation of the particle size and morphology of the iron phosphate.

[0039] Preferably, the molar amount of the nucleation promoter added is 0.01 to 10 times the total molar amount of iron in the liquid before precipitation, for example, it can be 0.01 times, 0.02 times, 0.05 times, 0.1 times, 0.2 times, 0.5 times, 1.0 times, 2.0 times, 3.0 times, 5.0 times, 7.5 times, 9.0 times or 10.0 times, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] The acid solution, alcohol solvent and nucleation promoter supplemented in the present invention can be added simultaneously, or one or at least two can be added selectively, preferably all three are added simultaneously, which has a better regulating effect.

[0041] Preferably, the solid phase after the solid-liquid separation in step (3) is washed.

[0042] Preferably, the washing comprises washing with water.

[0043] Preferably, after the washing in step (3), the solid phase is further calcined.

[0044] Preferably, the calcination is preceded by grinding.

[0045] Preferably, the grinding method comprises any one of ball milling, stirred milling or sand milling, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of ball milling and stirred milling, a combination of stirred milling and sand milling, and a combination of ball milling and sand milling.

[0046] Preferably, the particle size of the ground particles is below 20 μm, for example, 20 μm, 19 μm, 18 μm, 16 μm, 15 μm, 12 μm, 10 μm or 8 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the calcination temperature in step (3) is 400-900°C, for example, 400°C, 500°C, 600°C, 700°C, 800°C or 900°C, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0048] Preferably, the calcination time is 0.5 to 12 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or 12 h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0049] The present invention has no special restrictions on solid-liquid separation, and any method known to those skilled in the art for solid-liquid separation may be used, and may also be adjusted according to the actual process, such as centrifugal separation, filtration separation, or sedimentation separation.

[0050] As a preferred technical solution of the present invention, the method comprises the following steps:

[0051] (1) mixing a ferrous sulfate raw material and a solvent, mixing iron powder and a sulfuric acid solution, or mixing a ferrous sulfate raw material, iron powder and a solvent, dissolving the mixed solution, adjusting the pH value of the dissolved solution to 2 to 10, and performing solid-liquid separation to obtain a ferrous sulfate solution having a total iron ion concentration of 0.1 to 2 mol / L;

[0052] Mixing the ferrous sulfate solution, hydrogen peroxide and refined phosphoric acid with a concentration of 5 to 85 wt% P2O5, wherein the amount of hydrogen peroxide is 0.5 to 2 times the total molar amount of ferrous ions in the ferrous sulfate solution, and the amount of refined phosphoric acid is added according to a molar ratio of iron to phosphorus in the pre-precipitation solution of 0.8 to 1.1:1, to obtain a pre-precipitation solution;

[0053] (2) adding any one or a combination of at least two of an acidic solution, an alcohol solvent or a nucleation promoter to the pre-precipitation liquid, heating the liquid to 60 to 150° C. and maintaining the temperature under stirring conditions to obtain a slurry containing iron phosphate precipitate;

[0054] When the acid solution is added, it is mixed into the system.+ The concentration is 1 to 5 mol / L; when an alcohol solvent is added, the amount of the alcohol solvent added is 5 to 100% of the liquid volume fraction before precipitation; when a nucleation promoter is added, the molar amount of the nucleation promoter added is 0.01 to 10 times the total molar amount of iron in the liquid before precipitation;

[0055] (3) The solid phase of the slurry is separated into solid and liquid and then washed to obtain iron phosphate.

[0056] Further preferably, the liquid phase obtained by solid-liquid separation of the slurry is distilled to recover alcohol solvent and acid solution, and the alcohol solvent can be circulated to the heat preservation precipitation step; the acid solution is circulated to the wet phosphoric acid system for decomposition of phosphate rock.

[0057] Further preferably, the solid phase obtained by solid-liquid separation of the slurry can be washed and then ground to a particle size of less than 20 μm, and then calcined at 400-900° C. for 0.5-12 h to obtain iron phosphate. The particle size and product purity of the final iron phosphate can be further preferably controlled.

[0058] Compared with the prior art, the present invention has at least the following beneficial effects:

[0059] (1) The method for preparing ferric phosphate from refined phosphoric acid provided by the present invention can be applied to ferrous sulfate and iron powder from a wide range of sources, wherein the purity of ferrous sulfate in the ferrous sulfate raw material can be as low as 82wt%, and the purity of iron powder can be as low as 95wt%. The purity requirements for raw materials such as ferrous sulfate and iron powder themselves are relatively low, and the method can be combined with phosphorus chemical industry, with simple operation and low process cost, thereby reducing production costs. Even if raw materials containing impurities are used, an ferric phosphate product with a purity of more than 99.7%, preferably more than 99.9%, can be obtained. Under optimal conditions, the recovery rate of ferrous phosphate can reach more than 90%, and the iron-phosphorus ratio is more than 0.9.

[0060] (2) The method for preparing ferric phosphate from refined phosphoric acid provided by the present invention directly precipitates ferric phosphate under strong acid conditions, thereby avoiding the generation of a large amount of circulating water or ammonia-containing wastewater, thereby achieving low-cost green production of ferric phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The present invention provides a flow chart of a method for preparing ferric phosphate from refined phosphoric acid. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0063] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0064] As a specific embodiment of the present invention, a method for preparing ferric phosphate from refined phosphoric acid is provided, such as Figure 1 As shown, the method comprises the following steps:

[0065] (1) mixing a ferrous sulfate raw material and a solvent or mixing iron powder and a sulfuric acid solution, dissolving the mixture, adjusting the pH value of the dissolved solution to 2 to 10, and performing solid-liquid separation to obtain a ferrous sulfate solution having a total iron ion concentration of 0.1 to 2 mol / L;

[0066] Mixing the ferrous sulfate solution, hydrogen peroxide and refined phosphoric acid with a concentration of 5 to 85 wt% P2O5, wherein the amount of hydrogen peroxide is 0.5 to 2 times the total molar amount of ferrous ions in the ferrous sulfate solution, and the amount of refined phosphoric acid is added according to a molar ratio of iron to phosphorus in the pre-precipitation solution of 0.8 to 1.1:1, to obtain a pre-precipitation solution;

[0067] (2) After adding any one or a combination of at least two of an acidic solution, an alcohol solvent or a nucleation promoter to the pre-precipitation solution ( Figure 1 The dotted line indicates that any one or a combination of at least two or more of them can be added), the temperature is raised to 60-150° C. and kept warm under stirring conditions to obtain a slurry containing iron phosphate precipitation;

[0068] When the acid solution is added, it is mixed into the system. + The concentration is 1 to 5 mol / L; when an alcohol solvent is added, the amount of the alcohol solvent added is 5 to 100% of the liquid volume fraction before precipitation; when a nucleation promoter is added, the molar amount of the nucleation promoter added is 0.01 to 10 times the total molar amount of iron in the liquid before precipitation;

[0069] (3) The solid phase of the slurry is separated into solid and liquid and then washed to obtain iron phosphate.

[0070] Further preferably, in the above specific implementation manner, Figure 1 As shown, the liquid phase obtained by solid-liquid separation of the slurry is distilled to recover alcohol solvent and acid solution, and the alcohol solvent can be circulated to the heat preservation precipitation step; the acid solution is circulated to the wet phosphoric acid system for decomposition of phosphate rock.

[0071] Further preferably, in the above specific implementation manner, Figure 1 As shown, the solid phase obtained by solid-liquid separation of the slurry can be washed and then ground to a particle size of less than 20 μm, and then calcined at 400-900° C. for 0.5-12 h to obtain iron phosphate. The particle size and product purity of the final iron phosphate can be further preferably controlled.

[0072] Example 1

[0073] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid, the method comprising the following steps:

[0074] (1) mixing a ferrous sulfate raw material (ferrous sulfate produced as a byproduct of acid-process titanium dioxide, with a ferrous sulfate content of 87 wt%, containing 0.40 wt% of magnesium, 0.10 wt% of aluminum, 0.17 wt% of silicon, 0.02 wt% of potassium, 0.03 wt% of calcium, 5.4 wt% of titanium, 0.03 wt% of vanadium, 0.12 wt% of manganese, 0.02 wt% of nickel, 0.07 wt% of zinc and free water), dissolving the mixture, adding ferric hydroxide to adjust the pH value of the dissolved solution to 8, filtering the mixture, and obtaining a ferrous sulfate solution having a total iron ion concentration of 0.5 mol / L;

[0075] The ferrous sulfate solution, hydrogen peroxide and refined phosphoric acid with a concentration of 50wt% P2O5 (wherein the concentrations of iron, aluminum, magnesium and manganese are less than 0.5g / L, and the concentrations of titanium, zinc, calcium, sodium, chromium and vanadium do not exceed 0.2g / L) are mixed, wherein the amount of hydrogen peroxide is 0.8 times the total molar amount of ferrous ions in the ferrous sulfate solution, and the amount of refined phosphoric acid is added according to the molar ratio of iron to phosphorus in the pre-precipitation solution of 1.0:1, to obtain a pre-precipitation solution;

[0076] (2) The pre-precipitation liquid is placed in a precipitator, and sulfuric acid solution is added to the system. + The concentration is 1 mol / L, and methanol is added, the amount of methanol added is 50% of the liquid volume fraction before precipitation, the temperature is raised to 120°C and the temperature is kept under stirring to precipitate, and a slurry containing iron phosphate precipitation is obtained;

[0077] (3) The liquid phase obtained by filtering the slurry is distilled to recover the alcohol solvent and the acid solution, and the alcohol solvent can be circulated to the heat preservation precipitation step; the acid solution is circulated to the wet phosphoric acid system for the decomposition of phosphate rock; the solid phase obtained by filtering the slurry can be washed and first ground to a particle size of less than 20 μm, and then calcined at 500° C. for 10 hours to obtain iron phosphate.

[0078] Example 2

[0079] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid, the method comprising the following steps:

[0080] (1) mixing a ferrous sulfate raw material (industrial grade ferrous sulfate, ferrous sulfate content of 91wt%, containing 0.33wt% magnesium, 0.09wt% aluminum, 0.30wt% silicon, 0.20wt% potassium, and 0.24wt% calcium) and a sulfuric acid solution, dissolving, adding iron filings (iron content of 97wt%, containing 0.67wt% magnesium, 0.10wt% aluminum, 1.05wt% silicon, and 0.12wt% calcium), adjusting the pH value of the dissolved solution to 2 and filtering, to obtain a ferrous sulfate solution with a total iron ion concentration of 0.1mol / L;

[0081] The ferrous sulfate solution, hydrogen peroxide and refined phosphoric acid with a concentration of 85wt% P2O5 (wherein the concentrations of iron, aluminum, magnesium and manganese are less than 0.85g / L, and the concentrations of titanium, zinc, calcium, sodium, chromium and vanadium do not exceed 0.35g / L) are mixed, the amount of hydrogen peroxide is twice the total molar amount of ferrous ions in the ferrous sulfate solution, and the amount of refined phosphoric acid is added according to the molar ratio of iron to phosphorus in the pre-precipitation solution of 1.1:1, to obtain a pre-precipitation solution;

[0082] (2) the pre-precipitation liquid is placed in a precipitator, and monoclinic ferric phosphate dihydrate is added as a nucleation promoter, the molar amount of the nucleation promoter added is 10 times the total molar amount of iron in the pre-precipitation liquid, and methanol is added, the amount of methanol added is 5% of the volume fraction of the pre-precipitation liquid, the temperature is raised to 60° C. and the temperature is kept under stirring to precipitate, to obtain a slurry containing ferric phosphate precipitate;

[0083] (3) The liquid phase obtained by filtering the slurry is distilled to recover the alcohol solvent and the acid solution, and the alcohol solvent can be circulated to the heat preservation precipitation step; the acid solution is circulated to the wet phosphoric acid system for the decomposition of phosphate rock; the solid phase obtained by filtering the slurry can be washed and first ground to a particle size of less than 20 μm, and then calcined at 400° C. for 12 hours to obtain iron phosphate.

[0084] Example 3

[0085] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid, the method comprising the following steps:

[0086] (1) mixing iron powder (iron content of 99 wt%), ferrous sulfate raw material (high-purity ferrous sulfate, ferrous sulfate content of 99 wt%) and sulfuric acid solution, dissolving, adding ferric hydroxide to adjust the pH value of the dissolved solution to 10 and filtering to obtain a ferrous sulfate solution with a total iron ion concentration of 2 mol / L;

[0087] The ferrous sulfate solution, hydrogen peroxide and refined phosphoric acid with a concentration of 5wt% P2O5 (wherein the concentrations of iron, aluminum, magnesium and manganese are less than 0.05g / L, and the concentrations of titanium, zinc, calcium, sodium, chromium and vanadium do not exceed 0.02g / L) are mixed, the amount of hydrogen peroxide is 0.5 times the total molar amount of ferrous ions in the ferrous sulfate solution, and the amount of refined phosphoric acid is added according to the iron-phosphorus molar ratio in the pre-precipitation solution of 0.8:1, to obtain a pre-precipitation solution;

[0088] (2) The pre-precipitation liquid is placed in a precipitator, and sulfuric acid solution is added to the system. + The concentration is 5 mol / L, and monoclinic iron phosphate is added as a nucleation promoter, the molar amount of the nucleation promoter added is twice the total molar amount of iron in the solution before precipitation, the temperature is raised to 150° C. and the precipitation is carried out under stirring to obtain a slurry containing iron phosphate precipitation;

[0089] (3) The liquid phase obtained by filtering the slurry is distilled to recover the alcohol solvent and the acid solution, and the alcohol solvent can be circulated to the heat preservation precipitation step; the acid solution is circulated to the wet phosphoric acid system for the decomposition of phosphate rock; the solid phase obtained by filtering the slurry can be washed and first ground to a particle size of less than 18 μm, and then calcined at 900° C. for 0.5 h to obtain iron phosphate.

[0090] Example 4

[0091] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid. The method is different from that of Embodiment 1 only in that the amount of refined phosphoric acid used in step (1) is added according to a molar ratio of iron to phosphorus in the pre-precipitation solution of 0.7:1.

[0092] Example 5

[0093] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid. The method is different from that of Embodiment 1 only in that the amount of refined phosphoric acid added in step (1) is such that the molar ratio of iron to phosphorus in the pre-precipitation solution is 1.3:1.

[0094] Example 6

[0095] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid. The method is different from that in Embodiment 1 only in that: in step (2), sulfuric acid solution is added to the system. + The concentration is 7mol / L.

[0096] Example 7

[0097] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid. The method is different from that in embodiment 1 only in that methanol is not added in step (2), and only sulfuric acid solution is added to the system. + The concentration is 1mol / L.

[0098] Example 8

[0099] This embodiment provides a method for preparing iron phosphate from refined phosphoric acid. The method is different from that of Embodiment 1 only in that monoclinic iron phosphate is also added as a nucleation promoter in step (2). The molar amount of the nucleation promoter added is 3 times the total molar amount of iron in the solution before precipitation.

[0100] Example 9

[0101] This embodiment provides a method for preparing ferric phosphate from refined phosphoric acid. The method is different from that of Embodiment 2 only in that methanol is not added in step (2), and only monoclinic ferric phosphate dihydrate is added.

[0102] Example 10

[0103] This embodiment provides a method for preparing iron phosphate from refined phosphoric acid. The method is different from that of Embodiment 1 only in that no calcination is performed in step (3).

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing ferric phosphate by hydrolysis, which is Example 1 in CN104944400B.

[0106] This comparative example adopts the hydrolysis method to prepare ferric phosphate, which requires water dilution to increase the pH value and help the precipitation of ferric phosphate. The water circulation volume is large, the precipitation efficiency of ferric phosphate is low, and this method is difficult to apply to raw materials with impurities.

[0107] Test method:

[0108] The purity of ferric phosphate was determined by dissolving the ferric phosphate with 6 mol / L hydrochloric acid, analyzing it by ICP-OES, and calculating the recovery rates of iron and phosphorus respectively as follows.

[0109] The molar ratio of phosphorus to iron in the ferric phosphate product is determined by ICP-OES analysis to obtain the mass content of iron and phosphorus in the ferric phosphate product, and then converted into an iron-phosphorus molar ratio.

[0110] The calculation formula of iron yield is: 1-(volume of liquid after precipitation×iron concentration in liquid after precipitation) / (volume of liquid before precipitation×iron concentration in liquid before precipitation).

[0111] The calculation formula of phosphorus yield is: 1-(volume of liquid after precipitation×phosphorus concentration in liquid after precipitation) / (volume of liquid before precipitation×phosphorus concentration in liquid before precipitation).

[0112] The test results of the above embodiments are shown in Table 1.

[0113] Table 1

[0114]

[0115] From Table 1, we can see the following points:

[0116] (1) Based on Examples 1 to 3, it can be seen that the method for preparing ferric phosphate from refined phosphoric acid provided by the present invention has high purity and high recovery rates of iron and phosphorus, wherein the purity of ferric phosphate is ≥99.9%, and the recovery rates of iron and phosphorus are ≥90%, and the method avoids the generation of a large amount of low-concentration ammonium sulfate wastewater;

[0117] (2) Combining Example 1 and Example 6, it can be seen that in Example 1, sulfuric acid solution is added to the system. + The concentration is 1 mol / L, compared to H in Example 6. +For example, when the concentration was 7 mol / L, the recovery rates of iron and phosphorus in Example 1 were 92%, while those in Example 6 were only 57%, indicating that the present invention preferably utilizes sulfuric acid solution to remove H + Controlling the concentration within a specific range can improve the recovery rate;

[0118] (3) It can be seen from Example 1 and Examples 7 to 8 that in Example 8, sulfuric acid solution, methanol and monoclinic ferric phosphate are added simultaneously as nucleation promoters. Compared with Example 1 in which no nucleation promoter is added and Example 7 in which only sulfuric acid solution is added, the recovery rate of iron and phosphorus in Example 8 is as high as 97%, while the recovery rate in Example 1 is only 92%, and the recovery rate in Example 7 is only 87%. Examples 2 and 9 have similar situations, which shows that the present invention further preferably adds sulfuric acid solution, methanol and monoclinic ferric phosphate as nucleation promoters simultaneously, which can better improve the recovery rate;

[0119] (4) It can be seen from Example 1 and Example 10 that a calcination step is performed in Example 1. Compared with Example 10 in which no calcination is performed, the purity of the iron phosphate in Example 1 is 99.9%, while the purity of the iron phosphate in Example 10 is only 99.7%. This indicates that the present invention further improves the purity of the iron phosphate by preferably adding a calcination step.

[0120] In summary, the method for preparing ferric phosphate from refined phosphoric acid provided by the present invention can be applied to refined phosphoric acid and iron powder containing impurities, the raw material sources are wide, and the obtained product has high purity and high recovery rate, which is suitable for industrial promotion.

[0121] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing ferric phosphate from refined phosphoric acid, characterized in that: The method comprises the following steps: (1) mixing a ferrous sulfate solution, an oxidant and refined phosphoric acid to obtain a pre-precipitation solution; wherein the refined phosphoric acid contains any one or at least two impurities of iron, aluminum, magnesium, manganese, titanium, zinc, calcium, sodium, chromium or vanadium; (2) The pre-precipitation liquid is heated and kept warm for precipitation to obtain a slurry containing iron phosphate precipitation; before the heating in step (2), the pre-precipitation liquid and the sulfuric acid solution are mixed to H + The concentration is 1 to 5 mol / L, and the pre-precipitation liquid, alcohol solvent and nucleation accelerator are mixed; (3) The slurry is subjected to solid-liquid separation, and the solid phase after the solid-liquid separation is washed to obtain iron phosphate; After the washing in step (3), the solid phase is further calcined; The calcination is preceded by grinding.

2. The method according to claim 1, characterized in that The preparation of the ferrous sulfate solution in step (1) comprises: mixing a ferrous sulfate raw material and a solvent, mixing iron powder and a sulfuric acid solution, or mixing a ferrous sulfate raw material, iron powder and a solvent, dissolving and refining the mixed materials to obtain a ferrous sulfate solution.

3. The method according to claim 2, characterized in that The ferrous sulfate raw material includes any one of high-purity ferrous sulfate, industrial-grade ferrous sulfate, or ferrous sulfate produced as a byproduct of acid-process titanium dioxide, or a combination of at least two thereof.

4. The method according to claim 2, characterized in that: The iron powder includes any one of pig iron powder, reduced iron powder, electrolytic iron powder, hydroxy iron powder or atomized iron powder, or a combination of at least two of them.

5. The method according to claim 2, characterized in that: The solvent includes water and / or sulfuric acid solution.

6. The method according to claim 2, characterized in that The total iron ion concentration in the ferrous sulfate solution is 0.1-2 mol / L.

7. The method according to claim 2, characterized in that The purification in step (1) includes: adjusting the pH value of the dissolved solution to 2-10 and performing solid-liquid separation.

8. The method according to claim 7, characterized in that The substance for adjusting the pH value of the dissolved solution includes an alkaline substance.

9. The method according to claim 1, characterized in that: The oxidant in step (1) includes hydrogen peroxide.

10. The method according to claim 9, characterized in that The dosage of the hydrogen peroxide is 0.5 to 2 times of the total molar amount of ferrous ions in the ferrous sulfate solution.

11. The method according to claim 1, characterized in that: The amount of the refined phosphoric acid added is based on the iron-phosphorus molar ratio of 0.8 to 1.1:1 in the solution before precipitation; The concentration of the refined phosphoric acid is 5 to 85 wt% P2O5.

12. The method according to claim 1, characterized in that The temperature of the heat preservation precipitation in step (2) is 60-150°C.

13. The method according to claim 12, characterized in that The heat preservation precipitation is carried out under stirring conditions.

14. The method according to claim 1, characterized in that The alcohol solvent includes any one of methanol, ethanol, propanol or isopropanol, or a combination of at least two of them.

15. The method according to claim 1, characterized in that The amount of the alcohol solvent added is 5 to 100% of the liquid volume fraction before precipitation.

16. The method according to claim 1, characterized in that The nucleation promoter includes any one of isophosphotyrite-type iron phosphate, monoclinic iron phosphate, orthorhombic iron phosphate, α-quartz crystal iron phosphate, monoclinic iron phosphate dihydrate or orthorhombic iron phosphate dihydrate, or a combination of at least two thereof.

17. The method according to claim 1, characterized in that The added molar amount of the nucleation promoter is 0.01 to 10 times the total molar amount of iron in the solution before precipitation.

18. The method according to claim 1, characterized in that The particle size of the ground particles is less than 20 μm.

19. The method according to claim 1, characterized in that The calcination temperature in step (3) is 400-900°C.

20. The method according to claim 1, characterized in that The calcination time is 0.5 to 12 hours.

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