A method for preparing ferric phosphate using waste acid of titanium dioxide produced by chlorination process and its application

Abstract

The present invention relates to the technical field of waste acid recycling, and more specifically, to a method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process, and its application. The method comprises: adding an alkaline slurry to the waste acid from the chloride process to carry out an aluminum-chromium removal reaction; after the aluminum-chromium removal reaction reaches a pH of 3.8 to 4.5, performing solid-liquid separation to obtain a filtrate; mixing the filtrate with an oxidant and conducting an oxidation reaction; then adding an alkaline slurry to the waste acid to carry out a precipitation reaction; after the precipitation reaction reaches a pH of 2.5 to 4.0, performing solid-liquid separation to obtain a main filter cake; adding a phosphoric acid solution to the filter cake, adjusting the pH of the mixture to 3.0 to 3.5, performing an ferric phosphate synthesis reaction, and after the ferric phosphate synthesis reaction is complete, performing solid-liquid separation to obtain ferric phosphate. This method not only provides qualified raw materials for ferric phosphate production, but also achieves the reuse of waste acid from titanium dioxide produced by the chloride process.

Description

Technical Field

[0001] The present invention relates to the technical field of waste acid recycling, and in particular to a method for preparing ferric phosphate by utilizing waste acid of titanium dioxide produced by a chloride process and an application thereof. Background Art

[0002] The chloride process for titanium dioxide production generates a large amount of acidic metal chlorides, including ferrous, aluminum, manganese, magnesium, hydrogen, and aluminum ions. Currently, these acidic metal chlorides are treated by neutralization before discharge. This neutralization process produces a large amount of solid matter, which is typically disposed of by stacking. This method not only occupies land but also wastes the iron resources contained in the solid matter.

[0003] In addition, the iron source currently used in the production of ferric phosphate is ferrous sulfate, which is relatively expensive.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first objective of the present invention is to provide a method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process. This method prevents the iron in the acidic metal chlorides (i.e., waste acid from the chloride process) generated during the production of titanium dioxide from being lost during storage, thus avoiding waste of iron resources. Furthermore, the recovered iron is used as an iron source to prepare ferric phosphate, reducing the production cost of ferric phosphate.

[0006] The second object of the present invention is to provide the use of the iron phosphate prepared by the method of preparing iron phosphate using waste acid of titanium dioxide by the chloride process in the preparation of lithium iron phosphate batteries.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0008] The present invention provides a method for preparing ferric phosphate using waste acid of titanium dioxide produced by a chloride process, comprising the following steps:

[0009] Adding alkaline slurry to the waste acid of titanium dioxide produced by the chloride process to carry out aluminum and chromium removal reaction, and after the aluminum and chromium removal reaction reaches the pH value of the mixture of 3.8 to 4.5, performing solid-liquid separation to obtain a filtrate;

[0010] The filtrate is mixed with an oxidant and subjected to an oxidation reaction to oxidize the ferrous ions in the filtrate into ferric ions; the alkaline slurry is then added thereto to carry out a precipitation reaction, and after the precipitation reaction reaches a pH of 2.5 to 4.0, the solid-liquid separation is performed to obtain a filter cake whose main component is ferric hydroxide;

[0011] adding a phosphoric acid solution to the filter cake, adjusting the pH of the mixture to 3.0-3.5, performing an iron phosphate synthesis reaction, and performing solid-liquid separation after the iron phosphate synthesis reaction is completed to obtain iron phosphate;

[0012] Wherein, the waste acid of titanium dioxide produced by the chloride process includes ferrous ions, aluminum ions, chromium ions, manganese ions and magnesium ions;

[0013] The alkaline slurry is a mixture containing an alkaline substance and water, and the alkaline substance includes at least one of sodium hydroxide, calcium hydroxide, quicklime and calcium carbide sludge.

[0014] Preferably, the mass ratio of the alkaline substance to the water in the alkaline slurry is 1:1-5.

[0015] Preferably, the oxidant comprises hydrogen peroxide.

[0016] Preferably, the molar ratio of the iron element in the filtrate to the H2O2 in the hydrogen peroxide is 1-3:1-2.

[0017] Preferably, the reaction time of the oxidation reaction is 2 to 5 hours.

[0018] Preferably, the molar ratio of the iron element in the filter cake to the phosphorus element in the phosphoric acid solution is 1:1 to 1.2.

[0019] Preferably, the reaction time of the ferric phosphate synthesis reaction is 2 to 5 hours.

[0020] Preferably, the purity of the ferric phosphate is ≥97.5%.

[0021] Preferably, in the ferric phosphate, the mass fraction of aluminum oxide is ≤0.38%, the mass fraction of chromium oxide is ≤0.29%, the mass fraction of magnesium oxide is ≤0.29%, and the mass fraction of manganese oxide is ≤0.26%.

[0022] The present invention also provides the use of the iron phosphate prepared by the above-mentioned method of preparing iron phosphate using waste acid of titanium dioxide by chloride process in the preparation of lithium iron phosphate batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention utilizes the pH differences of different ion precipitations to perform preliminary impurity removal (primarily removing aluminum and chromium). Furthermore, during the conversion of divalent iron ions into trivalent precipitates, the iron ions are separated from impurity ions such as aluminum, chromium, manganese, and magnesium. This provides qualified raw materials for ferric phosphate production while enabling the reuse of waste acid from titanium dioxide produced by the chloride process. This not only avoids the waste of iron resources but also reduces the production cost of ferric phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is the XRD pattern of the iron phosphate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0028] In a first aspect, the present invention provides a method for preparing ferric phosphate using waste acid from titanium dioxide produced by a chloride process, the method comprising the following steps:

[0029] An alkaline slurry is added to the waste acid of titanium dioxide produced by the chloride process to carry out an aluminum-chromium removal reaction (mainly to remove aluminum ions and chromium ions in the waste acid of titanium dioxide produced by the chloride process). After the aluminum-chromium removal reaction reaches a pH of 3.8 to 4.5 (including but not limited to any one of 3.9, 4.0, 4.1, 4.2, 4.3, and 4.4 or a range of values ​​between any two of them) (i.e., the amount of alkaline slurry added is: the pH added until the end point of the aluminum-chromium removal reaction is 3.8 to 4.5), solid-liquid separation is performed to obtain a filtrate.

[0030] The waste acid from the chloride process is generated during the production of titanium dioxide. The waste acid contains ferrous ions, aluminum ions, chromium ions, manganese ions, and magnesium ions. The iron in the waste acid is primarily present in the form of ferrous ions.

[0031] In some specific embodiments of the present invention, the waste acid of titanium dioxide produced by the chloride process further includes a large amount of hydrogen ions and chloride ions, that is, the pH of the waste acid of titanium dioxide produced by the chloride process is less than 0.

[0032] In some specific embodiments of the present invention, the waste acid of titanium dioxide produced by the chloride process includes the following components in terms of mass concentration: 60 to 120 g / l of iron (mainly ferrous ions), 8 to 12 g / l of aluminum, 4 to 8 g / l of manganese, 2 to 6 g / l of magnesium, 0.5 to 3 g / l of chromium, and 100 to 250 g / l of chlorine.

[0033] During the aluminum-chromium removal reaction, aluminum ions and chromium ions will precipitate at a low pH to form corresponding hydroxides, thereby achieving the purpose of aluminum and chromium removal.

[0034] The filtrate is mixed with an oxidant and subjected to an oxidation reaction to oxidize the ferrous ions in the filtrate into ferric ions.

[0035] Then, the alkaline slurry is added thereto for a precipitation reaction. After the precipitation reaction reaches a pH of the mixed material of 2.5 to 4.0 (including but not limited to any one of 2.6, 2.8, 3.0, 3.2, 3.4, 3.5, 3.8, 3.9 or a range of values ​​between any two of them) (i.e., the amount of alkaline slurry added is: the pH added until the end point of the precipitation reaction is 2.5 to 4.0), solid-liquid separation is performed to obtain a filter cake whose main component is ferric hydroxide.

[0036] The oxidant can oxidize the ferrous ions in the filtrate into ferric ions, and then an alkaline slurry is added thereto. The ferric ions can be precipitated at a low pH, thereby being separated from other impurities.

[0037] In some specific embodiments of the present invention, after obtaining the filter cake mainly composed of ferric hydroxide, the filter cake mainly composed of ferric hydroxide is further washed with water. Preferably, the amount of water used for washing is 1 to 3 times the wet basis of the filter cake, and may be 2 times.

[0038] A phosphoric acid solution is added to the filter cake, and the pH of the mixture is adjusted to 3.0 to 3.5 (including but not limited to any one of 3.1, 3.2, 3.3, and 3.4 or a range of values ​​between any two), and a ferric phosphate synthesis reaction is performed. After the ferric phosphate synthesis reaction is completed, solid-liquid separation is performed to obtain ferric phosphate. In some specific embodiments of the present invention, adjusting the pH of the mixture to 3.0 to 3.5 is achieved by adding ammonia water and / or sodium hydroxide solution.

[0039] The alkaline slurry is a mixture containing an alkaline substance and water, and the alkaline substance includes at least one of sodium hydroxide, calcium hydroxide, quicklime and calcium carbide sludge.

[0040] The calcium carbide sludge is waste residue after producing acetylene gas, and has calcium hydroxide as its main component.

[0041] In some specific embodiments of the present invention, the solid-liquid separation method can be any conventional method for separating solids and liquids, such as, but not limited to, atmospheric filtration, vacuum filtration, centrifugal filtration, etc. The filtration device can be, for example, a disc filter or a belt filter, etc., but not limited to these.

[0042] The present invention utilizes the different pH values ​​of different ion precipitations to perform preliminary impurity removal (mainly removing aluminum and chromium), and separates impurity ions such as aluminum ions, chromium ions, manganese ions and magnesium ions from the process of converting divalent iron ions into trivalent precipitates, thereby providing qualified raw materials for ferric phosphate production and realizing the reuse of waste acid from titanium dioxide produced by the chloride process.

[0043] This method prevents the iron in the waste acid produced during the chloride process from being dumped and lost, thus avoiding the waste of iron resources. Furthermore, the recovered iron is used as an iron source to prepare ferric phosphate, reducing the production cost of ferric phosphate.

[0044] In addition, the method for preparing ferric phosphate using waste acid of titanium dioxide produced by the chloride process provided by the present invention also has the advantages of simple operation, short process flow, and suitability for mass production.

[0045] Preferably, the mass ratio of the alkaline substance to the water in the alkaline slurry is 1:1-5, including but not limited to any one of 1:1, 1:2, 1:3, 1:4 or a range between any two of them.

[0046] Preferably, the oxidant comprises hydrogen peroxide.

[0047] In some specific embodiments of the present invention, the concentration of the hydrogen peroxide solution can be any concentration.

[0048] Using hydrogen peroxide as an oxidant can avoid the introduction of other impurities, thereby not easily affecting the purity of the final ferric phosphate and not increasing the difficulty of water washing.

[0049] Preferably, the molar ratio of the iron element in the filtrate to the H2O2 in the hydrogen peroxide is 1-3:1-2, including but not limited to any one of 1:1, 1:1.5, 1:2, 2:1, 2:1.5, 3:1, 3:2 or a range between any two of them.

[0050] Preferably, the reaction time of the oxidation reaction is 2 to 5 hours, including but not limited to any one of 2.5 hours, 3 hours, 3.5 hours, 4 hours, and 4.5 hours, or a range between any two of them.

[0051] Preferably, the molar ratio of the iron element in the filter cake to the phosphorus element in the phosphoric acid solution is 1:1-1.2, including but not limited to any one of 1:1.05, 1:1.1, 1:1.15 or a range between any two of them.

[0052] Preferably, the reaction time of the ferric phosphate synthesis reaction is 2 to 5 hours, including but not limited to any one of 2.5 hours, 3 hours, 3.5 hours, 4 hours, and 4.5 hours, or a range between any two of them.

[0053] In some specific embodiments of the present invention, during the aluminum-chromium removal reaction, the temperature of the mixed material is 10-55°C, including but not limited to any one of 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range between any two of them.

[0054] During the oxidation reaction, the temperature of the mixed material is 10-55°C, including but not limited to any one of 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range between any two of them.

[0055] During the precipitation reaction, the temperature of the mixed material is 10-55°C, including but not limited to any one of 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range between any two of them.

[0056] During the ferric phosphate synthesis reaction, the temperature of the mixed material is 10-55°C, including but not limited to any one of 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range between any two of them.

[0057] Preferably, the purity of the ferric phosphate is ≥97.5%, including but not limited to any one of 97.8%, 98.0%, 98.5%, 98.8%, 99.0%, 99.5%, 99.8%, 99.9% or any range between two of them.

[0058] Preferably, in the ferric phosphate, the mass fraction of aluminum oxide is ≤0.38% (i.e., the mass fraction of aluminum element calculated as aluminum oxide is ≤0.38%), the mass fraction of chromium oxide is ≤0.29% (i.e., the mass fraction of chromium element calculated as chromium oxide is ≤0.38%), the mass fraction of magnesium oxide is ≤0.29% (i.e., the mass fraction of magnesium element calculated as magnesium oxide is ≤0.38%), and the mass fraction of manganese oxide is ≤0.26% (i.e., the mass fraction of manganese element calculated as manganese oxide is ≤0.38%).

[0059] In a second aspect, the present invention provides the use of iron phosphate prepared by the method for preparing iron phosphate using waste acid from titanium dioxide by the chloride process as described above in the preparation of lithium iron phosphate batteries.

[0060] The lithium iron phosphate battery can be prepared by using the iron phosphate prepared by the method for preparing iron phosphate using waste acid of titanium dioxide by the chloride process provided by the present invention, thereby reducing production costs.

[0061] In some specific embodiments of the present invention, the ferric phosphate is further washed and calcined before use.

[0062] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0063] Example 1

[0064] The method for preparing ferric phosphate using waste acid of titanium dioxide produced by the chloride process provided in this embodiment comprises the following steps:

[0065] (1) Adding alkaline slurry to waste acid of titanium dioxide produced by the chloride process (wherein the hydrogen ion concentration is 1.6 mol / l) to carry out aluminum and chromium removal reaction, controlling the pH at the end point of the reaction to be 3.9, and then filtering to obtain a filtrate. The alkaline slurry is prepared by uniformly mixing calcium carbide sludge and deionized water in a mass ratio of 1:2 (hereinafter referred to as "calcium carbide sludge slurry").

[0066] The main chemical components of the above-mentioned titanium dioxide waste acid produced by the chloride process and the above-mentioned filtrate are shown in Table 1 below.

[0067] Table 1 Chemical composition of spent acid and filtrate of titanium dioxide produced by chloride process

[0068] Element content Iron Aluminum Chromium Manganese magnesium Chlorine Chlorination process titanium dioxide waste acid 85g / l 9.8g / l 2.6g / l 4.6g / l 3.7g / l 165g / l filtrate 60g / l 20mg / l 1.5mg / l 3.2g / l 2.5g / l 118g / l

[0069] (2) The filtrate obtained in step (1) is mixed with hydrogen peroxide at a molar ratio of iron in the filtrate to H2O2 in the hydrogen peroxide of 2.2:1, and an oxidation reaction is carried out (reaction for 3 hours). Then, calcium carbide slurry is added thereto, and a precipitation reaction is carried out. The pH at the end of the reaction is controlled to be 2.8, and then the mixture is filtered to obtain a filter cake whose main component is ferric hydroxide.

[0070] The filter cake was washed with water at a rate of 2.0 times the wet basis. The elemental content of the filter cake after washing was analyzed as shown in Table 2:

[0071] Table 2 Elemental analysis of filter cake after washing (unit: wt.%)

[0072] Na Mg Si S Cl K Ca Ti 0.470 0.734 0.645 0.051 13.5 0.015 2.429 0.017 Mn Fe Co Ni Zn Sr Y Ce 2.526 52.500 0.065 0.062 0.028 0.006 0.033 0.058

[0073] (3) adding a phosphoric acid solution to the filter cake obtained in step (2), wherein the molar ratio of the iron element in the filter cake to the phosphorus element in the phosphoric acid solution is 1:1.2, and adding a sodium hydroxide solution thereto to adjust the pH of the mixture to 3.3, performing an iron phosphate synthesis reaction (reaction for 3 hours), and then filtering to obtain iron phosphate.

[0074] After testing, the purity of the ferric phosphate prepared in this embodiment is 99.92%. The other element analysis is shown in Table 3 below:

[0075] Table 3 Analysis of other elements in iron phosphate (unit: ppm)

[0076] Al Ca Co Cu Mg Mn Na Ni Pb Zn S 36.529 36.429 88.133 8.000 33.600 79.789 19.874 76.027 7.426 34.506 73.200

[0077] According to calculation, the recovery rate of iron in this embodiment is 99.8%.

[0078] The XRD pattern of the iron phosphate prepared in this example is shown in Figure 1 .

[0079] Example 2

[0080] The method for preparing ferric phosphate using waste acid of titanium dioxide produced by the chloride process provided in this embodiment comprises the following steps:

[0081] (1) Adding alkaline slurry to waste acid of titanium dioxide produced by the chloride process (wherein the hydrogen ion concentration is 1.3 mol / l) to carry out aluminum and chromium removal reaction, controlling the pH at the end point of the reaction to be 3.8, and then filtering to obtain a filtrate. The alkaline slurry is prepared by uniformly mixing calcium carbide sludge and deionized water in a mass ratio of 1:2 (hereinafter referred to as "calcium carbide sludge slurry").

[0082] Among them, the main chemical components of the above-mentioned chloride process titanium dioxide waste acid and the above-mentioned filtrate in this embodiment are shown in Table 4 below.

[0083] Table 4 Chemical composition of spent acid and filtrate of titanium dioxide produced by chloride process

[0084] Element content Iron Aluminum Chromium Manganese magnesium Chlorine Chlorination process titanium dioxide waste acid 89g / l 9.3g / l 2.3g / l 5.7g / l 3.5g / l 159g / l filtrate 61g / l 21.8mg / l 1.5mg / l 3.8g / l 2.4g / l 110g / l

[0085] (2) The filtrate obtained in step (1) is mixed with hydrogen peroxide at a molar ratio of iron in the filtrate to H2O2 in the hydrogen peroxide of 2.5:1, and an oxidation reaction is carried out (reaction for 2 hours). Then, calcium carbide slurry is added thereto, and a precipitation reaction is carried out. The pH at the end of the reaction is controlled to be 3.5, and then the mixture is filtered to obtain a filter cake whose main component is ferric hydroxide.

[0086] The filter cake was washed with water at 1.5 times the wet basis water. After testing, the filter cake after washing had a mass fraction of ferric hydroxide of 52%, a mass fraction of chlorine of 6.7%, and a mass fraction of calcium of 3.9%.

[0087] (3) adding a phosphoric acid solution to the filter cake obtained in step (2), wherein the molar ratio of the iron element in the filter cake to the phosphorus element in the phosphoric acid solution is 1:1.2, and adding a sodium hydroxide solution thereto to adjust the pH of the mixture to 3.2, performing an iron phosphate synthesis reaction (reaction for 4 hours), and then filtering to obtain iron phosphate.

[0088] After testing, the purity of the ferric phosphate prepared in this embodiment is 99.91%. The analysis of other elements is shown in Table 5 below:

[0089] Table 5 Analysis of other elements in iron phosphate (unit: ppm)

[0090] Al Ca Co Cu Mg Mn Na Ni Pb Zn S 43.412 46.429 53.614 7.200 35.400 75.141 30.146 73.676 4.641 42.531 73.200

[0091] According to calculation, the recovery rate of iron in this embodiment is 99.7%.

[0092] Example 3

[0093] The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process provided in this embodiment is substantially the same as that in Example 1, except that the alkaline slurry used in steps (1) and (2) is prepared by uniformly mixing sodium hydroxide and deionized water in a mass ratio of 1:5; and the pH at the end point of the aluminum-chromium removal reaction in step (1) is controlled to be 4.3. The waste acid from titanium dioxide produced by the chloride process used in this embodiment is from the same batch as that used in Example 1 and has the same chemical composition.

[0094] The main chemical components of the filtrate obtained in step (1) of this example are shown in Table 6 below.

[0095] Table 6 Chemical composition of the filtrate

[0096] Element content Iron Aluminum Chromium Manganese magnesium Chlorine filtrate 55g / l 13.6mg / l 2.3mg / l 3.5g / l 2.2g / l 98.3g / l

[0097] After testing, the purity of the ferric phosphate prepared in this embodiment is 99.91%. The analysis of other elements is shown in Table 7 below:

[0098] Table 7 Analysis of other elements in iron phosphate (unit: ppm)

[0099] Al Ca Co Cu Mg Mn Na Ni Pb Zn S 52.941 42.143 71.241 6.400 56.400 92.183 21.214 97.189 4.641 36.111 53.200

[0100] According to calculation, the recovery rate of iron in this embodiment is 99.9%.

[0101] Example 4

[0102] The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process provided in this example is substantially the same as that in Example 1, except that, in step (2), the pH at the endpoint of the precipitation reaction is controlled to be 3.8. The waste acid from titanium dioxide produced by the chloride process used in this example is from the same batch as that used in Example 1 and has the same chemical composition.

[0103] The main chemical components of the filtrate obtained in step (1) of this example are shown in Table 8 below.

[0104] Table 8 Chemical composition of the filtrate

[0105] Element content Iron Aluminum Chromium Manganese magnesium Chlorine filtrate 60g / l 20mg / l 1.5mg / l 3.2g / l 2.5g / l 118g / l

[0106] After testing, the purity of the ferric phosphate prepared in this embodiment is 99.90%. The analysis of other elements is shown in Table 9 below:

[0107] Table 9 Analysis of other elements in iron phosphate (unit: ppm)

[0108] Al Ca Co Cu Mg Mn Na Ni Pb Zn S 69.353 67.857 89.602 8.000 56.400 68.169 25.456 73.676 7.426 34.506 73.200

[0109] According to calculation, the recovery rate of iron in this embodiment is 99.8%.

[0110] Comparative Example 1

[0111] To the same batch and chemical composition of the chloride process titanium dioxide waste acid in Example 1 (wherein the hydrogen ion concentration is 1.6 mol / l) was added an alkaline slurry (the composition of the alkaline slurry was also the same as in Example 1), and the pH at the reaction end point was controlled to 6.0 (at this pH, part of the ferrous ions were precipitated, and the aluminum ions and chromium ions impurity ions were also precipitated), followed by filter pressing, and the obtained filter cake was washed with water, and the washing water volume was 1.5 times the wet basis. After washing, the mass fraction of ferric hydroxide in the filter cake was 33.1%, the mass fraction of chlorine was 6.8%, the mass fraction of calcium was 3.9%, the mass fraction of aluminum was 5.8%, the mass fraction of manganese was 1.6%, the mass fraction of magnesium was 0.33%, and the mass fraction of chromium was 1.03%.

[0112] Due to the high impurity content in the filter cake, it cannot be completely removed after the subsequent reaction with phosphoric acid and cannot be used for the preparation of iron phosphate.

[0113] Comparative Example 2

[0114] To the same batch and chemical composition of the chloride process titanium dioxide waste acid in Example 1 (wherein the hydrogen ion concentration is 1.6 mol / l), an alkaline slurry was added (the composition of the alkaline slurry was also the same as in Example 1), and the pH at the reaction end point was controlled to 10.0 (at this pH, ferrous ions and impurity metal ions were basically precipitated), and then the mixture was filtered, and the obtained filter cake was washed with water, and the amount of washing water was 1.5 times the wet basis. After washing, the mass fraction of ferric hydroxide in the filter cake was 28.5%, the mass fraction of chlorine was 19.4%, the mass fraction of calcium was 10.9%, the mass fraction of aluminum was 2.4%, the mass fraction of manganese was 4.1%, the mass fraction of magnesium was 1.4%, and the mass fraction of chromium was 0.3%.

[0115] Due to the high impurity content in the filter cake, it cannot be completely removed after the subsequent reaction with phosphoric acid and cannot be used for the preparation of iron phosphate.

[0116] Comparative Example 3

[0117] To the same batch and chemical composition of the chloride process titanium dioxide waste acid in Example 1 (wherein the hydrogen ion concentration is 1.6 mol / l), hydrogen peroxide was added (the molar ratio of the iron element in the chloride process titanium dioxide waste acid to H2O2 in the hydrogen peroxide = 2.2: 1), and after reacting for 3 hours, an alkaline slurry was added thereto (the composition of the alkaline slurry was the same as in Example 1), and the pH at the end of the reaction was controlled to 3.8 (at this pH, trivalent iron ions, aluminum ions and chromium ions would precipitate), followed by filter pressing, and the obtained filter cake was washed with water, and the amount of washing water was 1.5 times the wet basis. After washing, the mass fraction of iron hydroxide in the filter cake was 37.2%, the mass fraction of chlorine was 12.6%, the mass fraction of calcium was 7.1%, the mass fraction of aluminum was 6.1%, and the mass fraction of chromium was 0.3%.

[0118] Due to the high impurity content in the filter cake, it cannot be completely removed after the subsequent reaction with phosphoric acid and cannot be used for the preparation of iron phosphate.

[0119] Comparative Example 4

[0120] The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process provided in this comparative example is essentially the same as that in Example 1, except that, in step (1), the pH at the end point of the aluminum-chromium removal reaction is controlled to be 5.0. The waste acid from titanium dioxide produced by the chloride process used in this comparative example is from the same batch as that used in Example 1 and has the same chemical composition.

[0121] After calculation, the recovery rate of iron in this comparative example is 75%.

[0122] By comparing the iron recovery rates in Example 1 and Comparative Example 4, it can be seen that the iron recovery rate in Comparative Example 4 is significantly lower than that in Example 1. This is because the pH at the end point of the aluminum-chromium removal reaction in Comparative Example 4 is relatively high, resulting in the precipitation of some ferrous ions.

[0123] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process, characterized in that: The steps include: Adding alkaline slurry to the waste acid of titanium dioxide produced by the chloride process to carry out aluminum and chromium removal reaction, and after the aluminum and chromium removal reaction reaches the pH value of the mixture of 3.8 to 4.5, performing solid-liquid separation to obtain a filtrate; The filtrate is mixed with an oxidant and subjected to an oxidation reaction to oxidize the ferrous ions in the filtrate into ferric ions; the alkaline slurry is then added thereto to carry out a precipitation reaction, and after the precipitation reaction reaches a pH of 2.5 to 4.0, the solid-liquid separation is performed to obtain a filter cake whose main component is ferric hydroxide; adding a phosphoric acid solution to the filter cake, adjusting the pH of the mixture to 3.0-3.5, performing an iron phosphate synthesis reaction, and performing solid-liquid separation after the iron phosphate synthesis reaction is completed to obtain iron phosphate; Wherein, the waste acid of titanium dioxide produced by the chloride process includes ferrous ions, aluminum ions, chromium ions, manganese ions and magnesium ions; The alkaline slurry is a mixture containing an alkaline substance and water, wherein the alkaline substance includes at least one of sodium hydroxide, calcium hydroxide, quicklime and calcium carbide sludge; In the ferric phosphate, the mass fraction of aluminum oxide is ≤0.38%, the mass fraction of chromium oxide is ≤0.29%, the mass fraction of magnesium oxide is ≤0.29%, and the mass fraction of manganese oxide is ≤0.26%.

2. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, wherein: The mass ratio of the alkaline substance to the water in the alkaline slurry is 1:1-5.

3. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, wherein: The oxidant includes hydrogen peroxide.

4. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 3, wherein: The molar ratio of the iron element in the filtrate to the H2O2 in the hydrogen peroxide is 1-3:1-2.

5. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, wherein: The reaction time of the oxidation reaction is 2 to 5 hours.

6. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, characterized in that: The molar ratio of the iron element in the filter cake to the phosphorus element in the phosphoric acid solution is 1:1 to 1.

2.

7. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, characterized in that: The reaction time of the ferric phosphate synthesis reaction is 2 to 5 hours.

8. The method for preparing ferric phosphate using waste acid from titanium dioxide produced by the chloride process according to claim 1, wherein: The purity of the ferric phosphate is ≥97.5%.

9. Use of the iron phosphate prepared by the method for preparing iron phosphate using waste acid from titanium dioxide produced by the chloride process as claimed in any one of claims 1 to 8 in the preparation of lithium iron phosphate batteries.

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