Method for removing titanium impurities from phosphoric acid solutions

Abstract

The application discloses a method for removing titanium impurities in phosphoric acid solution, which comprises the following steps: extracting the phosphoric acid solution containing titanium impurities by using an organic solvent, and collecting the organic phase; mixing the organic phase with the phosphoric acid solution, adding an oxidant and hydrofluoric acid, and mixing uniformly to obtain a mixed solution; adding an ammonium fluoride solution dropwise into the mixed solution to react, and obtaining a reaction solution; washing, clarifying and separating the phases of the reaction solution, and back-extracting the organic phase to obtain the phosphoric acid solution from which the titanium impurities are removed; the removal method is characterized in that: firstly, trace H2O2 is used to convert titanium into active peroxotitanium species; secondly, the initiation effect of NH4F is used to activate the activity of fluoride ions; finally, HF is used as a main fluorine source to form a stable fluorotitanium complex and migrate to the acid phase, and low-titanium purified phosphoric acid is obtained after separation, so that the removal of titanium impurities is realized.

Description

Technical Field

[0001] This invention relates to the field of impurity removal technology in phosphoric acid solutions, and specifically to a method for removing titanium impurities from phosphoric acid solutions. Background Technology

[0002] Wet-process phosphoric acid (WPA) is an industrial-grade phosphoric acid produced by reacting fluorine-containing phosphate rock with sulfuric acid, followed by extraction or clarification steps. It is an important raw material for food-grade, electronic-grade, and high-purity phosphoric acid. Due to the complex source of the raw ore, its production process often involves metallic impurities such as Ti, Fe, Al, Mg, V, Na, and K. In particular, titanium (Ti) impurities, due to their unique chemical properties, exhibit high polymerization, strong complexation, and difficulty in washing in the wet-process phosphoric acid system, making it the most challenging impurity in the current production of high-purity wet-process phosphoric acid.

[0003] Currently, the industry widely uses the MIBK-n-butanol mixed solvent extraction method. The mechanism is that MIBK has selective extractability for phosphoric acid, allowing metal impurities to accumulate in the acid phase. However, in reality, titanium ions readily exist in the forms of Ti–O–Ti chain polymers, Ti–O–PO3H network structures, insoluble titanium oxyphosphate complexes, and some micro-colloidal titanium oxyhydroxide species. These forms result in a significant "trapping effect" of Ti, making it difficult to wash out in the extraction organic solvent along with residual phosphoric acid.

[0004] Countercurrent washing can use clean phosphoric acid to wash impurities back to the acid phase, but its elution effect on Ti is extremely poor. Even with a high washing-to-acid ratio, titanium is still significantly retained after multi-stage countercurrent washing. It is generally believed in the industry that Ti is a major challenge in wet phosphoric acid extraction and refining.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for removing titanium impurities from phosphoric acid solution. The method first converts titanium into active peroxytitanium species with a trace amount of H2O2, then activates the activity of fluoride ions through the initiation effect of NH4F, and finally forms a stable fluorine-titanium complex with HF as the main fluorine source, which migrates to the acid phase. After separation, low-titanium purified phosphoric acid is obtained, thus achieving the removal of titanium impurities.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of this invention provides a method for removing titanium impurities from a phosphoric acid solution, the method comprising the following steps: (a) Extracting a phosphoric acid solution containing titanium impurities with an organic solvent and collecting the organic phase; (b) The organic phase is mixed with the phosphoric acid solution, and then an oxidant and hydrofluoric acid are added and mixed well to obtain a mixture; (c) Add ammonium fluoride solution dropwise to the mixture to carry out the reaction, and obtain the reaction solution; (d) The reaction solution is washed, clarified and separated into phases, and the organic phase is back-extracted to obtain a phosphoric acid solution with titanium impurities removed.

[0008] Preferably, in step (a), the organic solvent is selected from at least one of methyl isobutyl ketone (MIBK), n-butanol, isooctyl alcohol, nonanol, TBP and dimethylheptyl methylphosphonate; the volume ratio of the organic solvent to the phosphoric acid solution containing titanium impurities is (3~5):1.

[0009] Preferably, the organic solvent is a mixture of methyl isobutyl ketone and dimethylheptyl methylphosphonate in a mass ratio of (3.2~3.8):1.

[0010] Preferably, in step (a), the extraction is a multi-stage countercurrent extraction, and the extraction temperature is less than 50°C.

[0011] Preferably, in step (b), the volume ratio of the organic phase to the phosphoric acid solution is (5~7):1; and the concentration of the phosphoric acid solution is 35%~38%.

[0012] Preferably, in step (b), the oxidant includes hydrogen peroxide, urea peroxide, sodium percarbonate, and persulfate; the amount of oxidant added is 0.01% to 0.1% of the mass of the phosphoric acid solution; and the concentration of hydrogen peroxide is 15% to 25%.

[0013] Preferably, in step (b), the amount of hydrofluoric acid added is 1% to 3% of the mass of the phosphoric acid solution, and the concentration of hydrofluoric acid is 15% to 25%.

[0014] Preferably, in step (c), the concentration of the ammonium fluoride solution is 25% to 35%; the amount of ammonium fluoride solution added is 0.1% to 0.3% of the mass of the phosphoric acid solution.

[0015] Preferably, in step (d), the washing method is multi-stage countercurrent washing; the washing acid is a phosphoric acid solution with a concentration of 35%~38%, and the volume ratio of the reaction solution to the washing acid is (6~7):1.

[0016] Preferably, in step (d), the back-extraction method is multi-stage countercurrent extraction, and the back-extraction agent is demineralized water; the volume ratio of organic phase to demineralized water is (8~12):1.

[0017] Preferably, step (d) further includes diluting the phosphoric acid solution that has partially removed titanium impurities with deionized water, and then recycling it as the phosphoric acid solution in step (b) or the washing acid in step (d).

[0018] Compared with the prior art, the beneficial effects of the present invention include at least the following: In the removal method of this invention, trace amounts of hydrogen peroxide (H2O2) can transform stable Ti-O-Ti bridge bonds into titanium-peroxide bridge structures [Ti(O2)]. 2+ Or neutral Ti(O2)(OH)2 species; these titanium peroxide complexes exhibit decreased electron cloud density, increased Lewis acidity at the titanium center, increased Ti–O bond length, and greater acceptance of external ligands (such as F) at the titanium center. - The titanium complex participates in coordination exchange, increasing the ligand exchange rate several times. Therefore, this invention utilizes the "reversible weakening" effect of the peroxidation process to temporarily make the coordination environment of titanium "easily attacked by fluorine," thereby significantly increasing the rate of subsequent fluorination reactions. Furthermore, the introduced ammonium fluoride has the following functions: First, NH4+... + The weak complexation of NH4 + Can be used with HF / F - Formation of hydrogen-bonded composites {NH4 + ···F -}、{NH4 + ...HF}, this assemblage has strong local polarization ability, which can improve F... - Nucleophilicity of Ti(O2) species, reduction of reaction transition state energy barrier, and promotion of HF→F - First, NH4F exhibits localized instantaneous dissociation, a characteristic not possessed by HF itself. Second, it has a localized pH fluctuation effect; even with minimal overall pH changes, NH4F instantaneously alters proton activity in specific microenvironments (such as droplets or stirred shear zones), accelerating Ti(O2) species rearrangement, promoting the dissociation of coordinated water / hydroxyl groups, and generating exposed Ti(IV) centers more susceptible to fluorine attack. Third, it has an initiator effect; the small amount of initial [TiF6] formed by NH4F... 2- The product undergoes a dynamic equilibrium migration with the original titanium species, enabling coordination exchange to proceed continuously in a diffusion manner, i.e., a TiF6... 2- NH4F can induce multiple surrounding Ti(IV) groups to enter a state where they can be fluorine-substituted, thus acting as a "reaction initiator" to improve the overall conversion efficiency of the reaction system. Furthermore, while HF is inexpensive, its efficiency is low on its own. However, after initiation with NH4F, HF can participate in the reaction in large quantities and be rapidly consumed. The reasons are as follows: the initial Ti–F bonds formed by a small amount of NH4F increase the overall coordination exchange rate of Ti; HF, as a F donor, can rapidly complete coordination exchange in systems with activated Ti centers; and the high stability of titanium fluoride species is beneficial for HF→F. -The continuous release of NH4F ultimately achieves a "scale-up effect" of a small amount of NH4F initiating a large amount of HF reaction. In summary, the removal method of this invention first uses a trace amount of H2O2 to convert titanium into active peroxy titanium species, then activates the activity of fluoride ions through the initiation effect of NH4F, and finally forms a stable fluorine-titanium complex with HF as the main fluorine source and migrates to the acid phase. After separation, low-titanium purified phosphoric acid is obtained, thus achieving the removal of titanium impurities. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will be described in detail below with reference to the examples. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0020] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] This invention provides a method for removing titanium impurities from a phosphoric acid solution, the method comprising the following steps: (a) Extracting a phosphoric acid solution containing titanium impurities with an organic solvent and collecting the organic phase; (b) The organic phase is mixed with the phosphoric acid solution, and then an oxidant and hydrofluoric acid are added and mixed well to obtain a mixture; (c) Add ammonium fluoride solution dropwise to the mixture to carry out the reaction, and obtain the reaction solution; (d) The reaction solution is washed, clarified and separated into phases, and the organic phase is back-extracted to obtain a phosphoric acid solution with titanium impurities removed.

[0022] The present invention does not impose strict limitations on the phosphoric acid solution containing titanium impurities. It can be a phosphoric acid solution containing titanium impurities that is common in the art, such as wet-process industrial phosphoric acid; high-concentration phosphoric acid (50%~70%), phosphoric acid containing extractant residues, etc.

[0023] In this invention, the form in which titanium impurities exist in the phosphoric acid solution containing titanium impurities is not specifically limited, and can be colloidal titanium dioxide, polynuclear hydroxy titanium complexes, organic titanium in the waste sulfuric acid after extraction, etc.

[0024] In one embodiment, in step (a), the organic solvent is selected from at least one of methyl isobutyl ketone, n-butanol, isooctyl alcohol, nonanol, TBP, and dimethylheptyl methylphosphonate; the volume ratio of the organic solvent to the phosphoric acid solution containing titanium impurities is (3~5):1; preferably, the organic solvent is a mixture of methyl isobutyl ketone and dimethylheptyl methylphosphonate in a mass ratio of (3.2~3.8):1.

[0025] In one embodiment, in step (a), the extraction is a multi-stage countercurrent extraction, and the extraction temperature is less than 50°C.

[0026] In one embodiment, in step (b), the volume ratio of the organic phase to the phosphoric acid solution is (5~7):1; the concentration of the phosphoric acid solution is 35%~38%.

[0027] In one embodiment, in step (b), the oxidant includes hydrogen peroxide, urea peroxide, sodium percarbonate, and persulfate; the amount of oxidant added is 0.01% to 0.1% of the mass of the phosphoric acid solution; and the concentration of hydrogen peroxide is 15% to 25%.

[0028] In one embodiment, in step (b), the amount of hydrofluoric acid added is 1% to 3% of the mass of the phosphoric acid solution, and the concentration of hydrofluoric acid is 15% to 25%.

[0029] In one embodiment, in step (c), the concentration of the ammonium fluoride solution is 25% to 35%; the amount of ammonium fluoride solution added is 0.1% to 0.3% of the mass of the phosphoric acid solution.

[0030] In one embodiment, in step (d), the washing method is multi-stage countercurrent washing; the washing acid is a phosphoric acid solution with a concentration of 35%~38%, and the volume ratio of the reaction solution to the washing acid is (6~7):1.

[0031] In one embodiment, in step (d), the back-extraction method is multi-stage countercurrent extraction, and the back-extraction agent is demineralized water; the volume ratio of organic phase to demineralized water is (8~12):1.

[0032] In one embodiment, step (d) further includes diluting the phosphoric acid solution that has partially removed titanium impurities with deionized water, and then recycling it as the phosphoric acid solution in step (b) or the washing acid in step (d).

[0033] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0034] Example 1 This embodiment describes a method for removing titanium impurities from a phosphoric acid solution. The method includes the following steps: (a) A multi-stage countercurrent extraction was performed in five mixing and clarifying tanks on a phosphoric acid solution containing titanium impurities (123 ppm titanium impurities and 52% phosphoric acid content) using an organic solvent (a mixture of methyl isobutyl ketone and dimethyl heptyl methylphosphonate in a mass ratio of 3.5:1). The extraction temperature was 40°C and the volume ratio of organic solvent to phosphoric acid solution containing titanium impurities was 4:1. The organic phase was collected. (b) The organic phase and the phosphoric acid solution (phosphoric acid content 36.5%) were mixed at a volume ratio of 6:1. Then, 20% hydrogen peroxide (0.05% of the mass of the phosphoric acid solution) and 20% hydrofluoric acid (2% of the mass of the phosphoric acid solution) were added and mixed well to obtain a pale yellow mixture. (c) Add ammonium fluoride solution (ammonium fluoride solution concentration is 30%, the amount added is 0.2% of the mass of phosphoric acid solution in step (b)) to the mixture and react for 10 min until the pale yellow color disappears; (d) The reaction solution is subjected to five-stage countercurrent washing (the washing acid is a 36.5% phosphoric acid solution, and the volume ratio of the reaction solution to the washing acid is 6.5:1), clarified and separated, and the organic phase is subjected to five-stage countercurrent extraction (the solvent is demineralized water, and the volume ratio of the organic phase to the demineralized water is 10:1) to obtain a phosphoric acid solution with titanium impurities removed. The phosphoric acid solution with titanium impurities removed is partially diluted with demineralized water to a phosphoric acid concentration of 36.5%, and then recycled as the phosphoric acid solution in step (b) and the washing acid in step (d).

[0035] Example 2 This embodiment describes a method for removing titanium impurities from a phosphoric acid solution. The method includes the following steps: (a) A multi-stage countercurrent extraction was performed in five mixing and clarifying tanks on a phosphoric acid solution containing titanium impurities (123 ppm titanium impurities and 52% phosphoric acid content) using an organic solvent (a mixture of methyl isobutyl ketone and dimethyl heptyl methylphosphonate in a mass ratio of 4:1). The extraction temperature was 40°C and the volume ratio of organic solvent to phosphoric acid solution containing titanium impurities was 4:1. The organic phase was collected. (b) The organic phase and the phosphoric acid solution (phosphoric acid content 36.5%) were mixed at a volume ratio of 6:1. Then, 20% hydrogen peroxide (0.08% of the mass of the phosphoric acid solution) and 25% hydrofluoric acid (3% of the mass of the phosphoric acid solution) were added and mixed well to obtain a pale yellow mixture. (c) Add ammonium fluoride solution (ammonium fluoride solution concentration is 25%, the amount added is 0.3% of the mass of phosphoric acid solution in step (b)...) to the mixture and react for 10 min until the pale yellow color disappears; (d) The reaction solution is subjected to a 5-stage countercurrent washing process (the washing acid is a 36.5% phosphoric acid solution, and the volume ratio of the reaction solution to the washing acid is 7:1), followed by clarification and phase separation. The organic phase is then subjected to a 5-stage countercurrent extraction process (the solvent is demineralized water, and the volume ratio of the organic phase to the demineralized water is 10:1) to obtain a phosphoric acid solution with titanium impurities removed. The phosphoric acid solution with titanium impurities removed is partially diluted with demineralized water to a phosphoric acid concentration of 36.5%, and then recycled as the phosphoric acid solution in step (b) and the washing acid in step (d).

[0036] Comparative Example 1 This comparative example illustrates a method for removing titanium impurities from a phosphoric acid solution. The method includes the following steps: (a) A multi-stage countercurrent extraction was performed in five mixing and clarifying tanks on a phosphoric acid solution containing titanium impurities (123 ppm titanium impurities and 52% phosphoric acid content) using an organic solvent (a mixture of methyl isobutyl ketone and dimethyl heptyl methylphosphonate in a mass ratio of 3.5:1). The extraction temperature was 40°C and the volume ratio of organic solvent to phosphoric acid solution containing titanium impurities was 4:1. The organic phase was collected. (b) The organic phase and the phosphoric acid solution (phosphoric acid content 36.5%) were mixed at a volume ratio of 6:1. Then, 20% hydrogen peroxide (0.05% of the mass of the phosphoric acid solution) and 20% hydrofluoric acid (2% of the mass of the phosphoric acid solution) were added and mixed well to obtain a pale yellow mixture. (c) The yellow mixture was subjected to a 5-stage countercurrent washing process (the washing acid was a 36.5% phosphoric acid solution, and the volume ratio of the reaction solution to the washing acid was 6.5:1), followed by clarification and phase separation. The organic phase was then subjected to a 5-stage countercurrent extraction process (the solvent was demineralized water, and the volume ratio of the organic phase to the demineralized water was 10:1) to obtain a phosphoric acid solution with titanium impurities removed. The phosphoric acid solution with titanium impurities removed was partially diluted with demineralized water to a phosphoric acid concentration of 36.5%, and then recycled as the phosphoric acid solution in step (b) and the washing acid in step (d).

[0037] Comparative Example 2 This comparative example illustrates a method for removing titanium impurities from a phosphoric acid solution. The method includes the following steps: (a) A multi-stage countercurrent extraction was performed in five mixing and clarifying tanks on a phosphoric acid solution containing titanium impurities (123 ppm titanium impurities and 52% phosphoric acid content) using an organic solvent (a mixture of methyl isobutyl ketone and dimethyl heptyl methylphosphonate in a mass ratio of 3.5:1). The extraction temperature was 40°C and the volume ratio of organic solvent to phosphoric acid solution containing titanium impurities was 4:1. The organic phase was collected. (b) The organic phase and the phosphoric acid solution (phosphoric acid content 36.5%) were mixed at a volume ratio of 6:1. Then, 20% hydrofluoric acid (2% of the mass of the phosphoric acid solution) was added and mixed well to obtain a mixture. (c) Add ammonium fluoride solution (ammonium fluoride solution concentration is 30%, the amount added is 0.2% of the mass of phosphoric acid solution in step (b)) dropwise to the mixture and react for 10 min; (d) The reaction solution is subjected to five-stage countercurrent washing (using a 36.5% phosphoric acid solution, with a volume ratio of reaction solution to washing acid of 6.5:1), followed by clarification and phase separation. The organic phase is then subjected to five-stage countercurrent extraction (using demineralized water as solvent, with a volume ratio of organic phase to demineralized water of 10:1) to obtain a phosphoric acid solution with titanium impurities removed. The phosphoric acid solution with titanium impurities removed is partially diluted with demineralized water to a phosphoric acid concentration of 36.5%, and then recycled as the phosphoric acid solution in step (b) and the washing acid in step (d).

[0038] Comparative Example 3 This comparative example illustrates a method for removing titanium impurities from a phosphoric acid solution. The method includes the following steps: (a) A multi-stage countercurrent extraction was performed in five mixing and clarifying tanks on a phosphoric acid solution containing titanium impurities (123 ppm titanium impurities and 52% phosphoric acid content) using an organic solvent (a mixture of methyl isobutyl ketone and dimethyl heptyl methylphosphonate in a mass ratio of 3.5:1). The extraction temperature was 40°C and the volume ratio of organic solvent to phosphoric acid solution containing titanium impurities was 4:1. The organic phase was collected. (b) The organic phase and the phosphoric acid solution (phosphoric acid content 36.5%) were mixed at a volume ratio of 6:1. Then, 20% hydrogen peroxide (0.05% of the mass of the phosphoric acid solution) and 20% hydrochloric acid (2% of the mass of the phosphoric acid solution) were added and mixed well to obtain a mixture. (c) Add ammonium fluoride solution (ammonium fluoride solution concentration is 30%, the amount added is 0.2% of the mass of phosphoric acid solution in step (b)) dropwise to the mixture and react for 10 min; (d) The reaction solution is subjected to five-stage countercurrent washing (the washing acid is a 36.5% phosphoric acid solution, and the volume ratio of the reaction solution to the washing acid is 6.5:1), clarified and separated, and the organic phase is subjected to five-stage countercurrent extraction (the solvent is demineralized water, and the volume ratio of the organic phase to the demineralized water is 10:1) to obtain a phosphoric acid solution with titanium impurities removed. The phosphoric acid solution with titanium impurities removed is partially diluted with demineralized water to a phosphoric acid concentration of 36.5%, and then recycled as the phosphoric acid solution in step (b) and the washing acid in step (d).

[0039] Experimental Example Titanium impurities in phosphoric acid solution were removed according to the methods of Examples 1-2 and Comparative Examples 1-3, respectively. The titanium content in the phosphoric acid solution after removing titanium impurities in step (d) of Examples 1-2 and Comparative Examples 1-3 was detected by ICP-OES and ICP-MS, and the results are shown in Table 1. Table 1

[0040] As shown in Table 1: Compared to the comparative example, the embodiments of the present invention can better remove titanium impurities from phosphoric acid solution with high removal efficiency.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for removing titanium impurities from a phosphoric acid solution, characterized in that, The removal method includes the following steps: (a) Extracting a phosphoric acid solution containing titanium impurities with an organic solvent and collecting the organic phase; (b) The organic phase is mixed with the phosphoric acid solution, and then an oxidant and hydrofluoric acid are added and mixed well to obtain a mixture; (c) Add ammonium fluoride solution dropwise to the mixture to carry out the reaction, and obtain the reaction solution; (d) The reaction solution is washed, clarified and separated into phases, and the organic phase is back-extracted to obtain a phosphoric acid solution with titanium impurities removed.

2. The removal method according to claim 1, characterized in that, In step (a), the organic solvent is selected from at least one of methyl isobutyl ketone, n-butanol, isooctyl alcohol, nonanol, TBP and dimethylheptyl methylphosphonate; the volume ratio of the organic solvent to the phosphoric acid solution containing titanium impurities is (3~5):1; Preferably, the organic solvent is a mixture of methyl isobutyl ketone and dimethylheptyl methylphosphonate in a mass ratio of (3.2~3.8):

1.

3. The removal method according to claim 1, characterized in that, In step (a), the extraction is a multi-stage countercurrent extraction, and the extraction temperature is less than 50°C.

4. The removal method according to claim 1, characterized in that, In step (b), the volume ratio of the organic phase to the phosphoric acid solution is (5~7):1; the concentration of the phosphoric acid solution is 35%~38%.

5. The removal method according to claim 1, characterized in that, In step (b), the oxidant includes hydrogen peroxide, urea peroxide, sodium percarbonate and persulfate; the amount of oxidant added is 0.01% to 0.1% of the mass of the phosphoric acid solution; the concentration of hydrogen peroxide is 15% to 25%.

6. The removal method according to claim 1, characterized in that, In step (b), the amount of hydrofluoric acid added is 1% to 3% of the mass of the phosphoric acid solution, and the concentration of hydrofluoric acid is 15% to 25%.

7. The removal method according to claim 1, characterized in that, In step (c), the concentration of ammonium fluoride solution is 25% to 35%; the amount of ammonium fluoride solution added is 0.1% to 0.3% of the mass of phosphoric acid solution.

8. The removal method according to claim 1, characterized in that, In step (d), the washing method is multi-stage countercurrent washing; the washing acid is a phosphoric acid solution with a concentration of 35%~38%, and the volume ratio of the reaction solution to the washing acid is (6~7):

1.

9. The removal method according to claim 1, characterized in that, In step (d), the back-extraction method is multi-stage countercurrent extraction, and the back-extraction agent is demineralized water; the volume ratio of organic phase to demineralized water is (8~12):

1.

10. The removal method according to claim 1, characterized in that, Step (d) further includes diluting the phosphoric acid solution that has partially removed titanium impurities with deionized water, and then recycling it as the phosphoric acid solution in step (b) or the washing acid in step (d).

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