Impurity removal method of high-purity ferric chloride

Abstract

The application discloses a method for removing impurities from high-purity ferric chloride, and belongs to the technical field of inorganic chemical separation and purification. The method comprises the following steps: firstly, oxidizing ferric chloride hydrochloric acid liquid containing divalent iron and metal impurities into a feed liquid mainly containing trivalent iron; secondly, contacting the feed liquid with an organic phase containing n-butyl acetate and tributyl phosphate, so that ferric chloride enters the organic phase in the form of a chloro-complex solvation; then, performing backwashing and refining on the loaded organic phase by using a water phase containing tartaric acid, and effectively controlling the co-migration of high-valence impurities by using complexation; then, performing secondary impurity removal on the back-extraction liquid by using an organic phase containing bis(2-ethylhexyl)phosphoric acid and tri-octylamine, so that trace metals are stripped; finally, performing vacuum concentration and removing organic residues, and thus high-purity ferric chloride products are prepared. Through the cooperation of multi-stage extraction and specific complexing agents, the total impurity metal content is effectively controlled, and high-iron yield and high-main-content separation of ferric chloride are realized.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical separation and purification technology, specifically, it relates to a method for removing impurities from high-purity ferric chloride. Background Technology

[0002] High-purity ferric chloride, as an important inorganic iron salt, has wide applications in the electronics industry (such as etching of high-precision printed circuit boards and lead frames), high-end water treatment, fine chemical catalysts, and the synthesis of pharmaceutical intermediates. With the continuous upgrading of downstream industries, the purity requirements for ferric chloride are becoming increasingly stringent. Especially for electronic-grade and specific catalytic applications, high-purity ferric chloride not only requires extremely high main iron content but also extremely low levels of trace heavy metals and transition metal impurities.

[0003] In industrial production, the preparation of ferric chloride from steel pickling waste liquid, titanium dioxide by-products, or other iron-containing hydrochloric acid solutions (such as regenerated pickling systems) is an effective way to achieve resource recycling. However, the composition of these basic solutions is extremely complex. In addition to containing large amounts of ferric and ferrous iron, they are also generally enriched with various metallic impurities. These impurities can be mainly divided into two categories according to their chemical properties: one category is high-valence, easily hydrolyzed metallic impurities (such as titanium, zirconium, and tin); the other category is conventional transition metal impurities (such as copper, zinc, nickel, and chromium).

[0004] Currently, solvent extraction is commonly used in the industry to purify iron-containing solutions. Commonly used extraction systems primarily employ tributyl phosphate (TBP) or methyl isobutyl ketone (MIBK) as the main extractant. While these systems can separate ferric iron from most matrix elements, they still face the following insurmountable technical bottlenecks in practical applications: First, high-valence impurities readily co-migrate with the main salt and are difficult to elute. The complexation forms of high-valence impurities such as titanium, zirconium, and tin in hydrochloric acid media are very similar to those of ferric iron, and they enter the organic phase along with the main salt during extraction. Existing backwashing processes typically use only pure water or dilute hydrochloric acid for simple washing, or use conventional dicarboxylic acids (such as succinic acid) as an aid. However, due to the lack of specific coordination control capabilities, these high-valence impurities cannot be effectively complexed and removed, resulting in high residual levels of titanium, zirconium, and tin in the product.

[0005] Second, it is difficult to simultaneously achieve the removal of trace transition metals at the end of the extraction process and the yield of the main salt. After preliminary extraction and conventional backwashing, trace amounts of transition metals such as copper, zinc, nickel, and chromium often remain in the system. In existing technologies, to deeply remove these trace metals, it is often necessary to significantly increase the acidity or extractant concentration of the purification system. However, this inevitably leads to the unnecessary transfer of a large amount of ferric iron (the main salt), causing a sharp decline in the overall iron yield and resulting in low economic efficiency.

[0006] Third, the state of the feed solution in the initial stage has a significant impact on the stability of the subsequent separation process. Complex hydrochloric acid feed solutions often contain high concentrations of ferrous iron. If the pre-oxidation in the existing process is incomplete, the distribution behavior of ferrous iron in the extraction system will seriously interfere with the balance between main salt extraction and impurity separation, resulting in large fluctuations in the quality of the final product.

[0007] In summary, existing technologies lack a synergistic process capable of simultaneously targeting and separating both "high-priced, easily hydrolyzable impurities" and "transition metal impurities," while ensuring extremely high main salt yields and extremely low impurity residues. Therefore, developing a high-purity ferric chloride purification method with high main salt transfer efficiency and thorough removal of trace impurities has become a pressing technical challenge in this field. Summary of the Invention

[0008] To address the technical challenges in the purification of high-purity ferric chloride from iron-containing feed solutions, such as the easy co-migration of highly valence and easily hydrolyzable impurities (e.g., titanium, zirconium, tin) with the main salt and their difficulty in removal by conventional backwashing, the difficulty in deeply removing trace transition metal impurities (e.g., copper, zinc, nickel, chromium) at the end of the extraction process leading to significant loss of the main salt (low iron yield), and the poor separation stability of the entire extraction system due to incomplete oxidation at the front end, this invention provides a method for removing impurities from high-purity ferric chloride. This method, based on the differences in the valence state and complexation chemistry of impurity metals, combines the preferential transfer of the main salt with the removal of trace impurities at the end, constructing a single closed-loop route for segmented targeted impurity removal.

[0009] The present invention adopts the following technical solution: a method for removing impurities from high-purity ferric chloride, comprising the following steps: oxidizing a ferric chloride hydrochloric acid feed solution containing ferrous iron and metallic impurities into a feed solution mainly composed of ferric iron; contacting the feed solution with an organic phase containing n-butyl acetate and tributyl phosphate, so that ferric chloride enters the organic phase in a chlorine complex solvated form; backwashing or purifying the loaded organic phase with an aqueous phase containing tartaric acid; subsequently performing a second impurity removal with an organic phase containing bis(2-ethylhexyl)phosphoric acid and trioctylamine; and then performing vacuum concentration and removal of organic residues to obtain high-purity ferric chloride.

[0010] Preferably, the oxidation step uses hydrogen peroxide or chlorine as the oxidant, the oxidation temperature is 20-35℃, and the oxidation is followed by aging for 10-40 minutes. The oxidation step is carried out under the protection of an inert gas to inhibit the hydrolysis of the liquid and the introduction of moisture from the air.

[0011] Preferably, the total iron mass fraction in the feed liquid is 25-35%, the free hydrochloric acid mass fraction is 12-22%, and the primary extraction step adopts two to four stages of countercurrent extraction with a single-stage contact time of 3-8 minutes.

[0012] Preferably, the weight ratio of n-butyl acetate (CAS No.: 123-86-4) to tributyl phosphate (CAS No.: 126-73-8) in the primary extraction organic phase is 100:(10-35), and the ratio of the primary extraction steps is 1:(0.8-1.5).

[0013] Preferably, in the backwashing or refining step, tartaric acid (CAS No.: 87-69-4) is added in the form of a 0.5-3.0% hydrochloric acid aqueous solution (where the mass fraction of tartaric acid is 0.5-3.0% and the mass fraction of hydrogen chloride is 5.0-6.0%), the backwashing stage is one to two, and the amount of backwash solution is 0.15-0.40 times the volume of the loaded organic phase.

[0014] Preferably, the weight ratio of bis(2-ethylhexyl)phosphoric acid (CAS No.: 298-07-7) to trioctylamine (CAS No.: 1116-76-3) in the secondary impurity removal organic phase is (5-20):(2-12), and n-butyl acetate or kerosene is used as the dilution medium to ensure that the secondary impurity removal organic phase and the back-extraction solution are in contact for 1 to 3 stages at a ratio of (0.3-0.9):1.

[0015] Preferably, the operating temperature of the secondary impurity removal step is 15-25°C, the single-stage contact time is 2-6 min, and the settling and stratification time is 3-15 min, so as to limit the unnecessary transfer of the main salt in the secondary impurity removal stage.

[0016] Preferably, the vacuum concentration step is carried out at -0.06 to -0.095 MPa and 40 to 65°C to concentrate to a purified solution with a ferric chloride mass fraction of 40% to 65%; after concentration, nitrogen gas is introduced for 5 to 20 minutes, and the solution is filtered through a 0.22 μm filter to remove residual organic matter and mechanical particles.

[0017] Preferably, the purified ferric chloride solution after vacuum concentration is used directly as a high-purity ferric chloride solution product; or it is aged at 20-30°C for 2-6 hours to crystallize, separated from solids, and vacuum dried at 35-45°C to obtain a water-containing ferric chloride solid or ferric chloride crystal product.

[0018] In this application, the oxidation step uses the residual amount of ferrous iron in the feed solution as the endpoint control index; when the Fe in the feed solution after oxidation... 2+ The proportion of Fe in the total iron mass is not higher than 0.10%, or the Fe content calculated based on the final product. 2+When the residual amount is not higher than 150 mg / kg, oxidation is considered to have reached the state required for subsequent extraction. The change in iron content in the loaded organic phase is used as the endpoint control index for the back-extraction step; back-extraction is considered complete when the change in iron concentration in the aqueous phase obtained from the two back-extractions is less than 5%, or when the residual iron in the organic phase after back-extraction is not higher than 3.0% of the initial loaded iron content. When comparisons are involved in any step, volume ratios are preferred; when the examples express the feed amount in mass, the comparison is determined by converting the density of the corresponding material at the operating temperature to volume. The actual volume of the loaded organic phase is based on the volume of the organic phase collected after extraction and stratification.

[0019] Compared to existing technologies, this invention offers at least the following advantages: Targeted removal of high-value impurities: The innovative introduction of tartaric acid utilizes its unique configuration of dicarboxyl groups and adjacent hydroxyl groups for specific complexation, completely solving the problem of co-migration of easily hydrolyzable impurities such as titanium, zirconium, and tin with the main salt. Non-destructive removal of trace metals: A two-component associative extraction system constructed with acidic organophosphorus compounds and tertiary amines precisely intercepts trace amounts of transition metals such as copper, zinc, nickel, and chromium, effectively preventing the loss of the main salt during the impurity removal process. High purity and high yield: Through a closed-loop design of preferential transfer of the main salt and multi-stage synergistic impurity removal, the final product achieves a main salt content of over 99.92%, with total impurity metals strictly controlled below 40.0 mg / kg, and an iron yield maintained above 97.1%. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall process flow of the high-purity ferric chloride purification method of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. For those skilled in the art, equivalent substitutions or conventional adjustments to the source of raw materials, equipment models, operating sequences, and process details without departing from the concept of the present invention should be considered as falling within the scope of protection of the present invention. It should be noted that the raw materials used in the following embodiments can all be purchased through conventional commercial channels; equipment not specifically mentioned is conventional equipment in the art; parameters not listed are the same as in Example 1. The "ferric chloride hydrochloric acid solution" described below is taken from the same batch of regenerated pickling system and packaged for use after pre-analysis. The term "purity" in the text refers to the main content after conversion to ferric chloride, and "total impurity metals" refers to the total amount of titanium, zirconium, tin, copper, zinc, nickel, and chromium. It should be noted that three-stage countercurrent means using three single-stage tanks in series, and two-stage countercurrent means using two single-stage tanks in series. The kerosene generally used is No. 260 solvent oil.

[0022] In this application, the basic composition of the ferric chloride hydrochloric acid solution, by mass, is as follows: 41.8g of divalent iron, 263.6g of trivalent iron, 156.4g of free hydrochloric acid, 0.42g of titanium, 0.30g of zirconium, 0.21g of tin, 0.55g of copper, 0.47g of zinc, 0.33g of nickel, 0.28g of chromium, and 535.64g of water, for a total mass of 1000.0g. The above composition serves as the basic feed composition for Examples 1 to 5 and Comparative Examples 1 to 5.

[0023] Example 1 This embodiment is a preferred implementation method, and its operation process is as follows: Figure 1 As shown.

[0024] Step (1) Oxidation: Take 1000.0g of the above ferric chloride hydrochloric acid solution and add it to a 2L jacketed glass reactor. Stir with a mechanical stirrer at a speed of 320r / min, and purge with nitrogen for 15min. Control the temperature of the reactor jacket at 25℃, and add 42.4g of hydrogen peroxide solution (hydrogen peroxide mass fraction 30.0%) dropwise over 30min. After the addition is complete, continue aging for 20min. Then filter with a polypropylene filter element with a nominal pore size of 5.0μm to obtain the oxidized feed solution. During the process, Fe... 2+ The oxidation endpoint was confirmed by residual weight determination. Oxidation endpoint: Fe 2+ The proportion of total iron ≤0.10% or Fe 2+ Residual amount ≤150mg / kg.

[0025] Step (2) Primary Extraction: Prepare organic phase A according to the following formula: 750.0g of n-butyl acetate and 150.0g of tributyl phosphate, mix thoroughly and set aside. The oxidized feed solution is then contacted with organic phase A using a three-stage countercurrent mixing and clarification method (tank material is polytetrafluoroethylene or borosilicate glass, effective volume of the single-stage mixing chamber is 500mL, and the clarification chamber volume is 1000mL). The mixing temperature for each stage is 25℃, the mixing time is 5min, the stirring speed is 350r / min, and each stage is allowed to stand for 10min to separate into layers. After the three-stage extraction is completed, the loaded organic phases are combined. After the three-stage extraction is completed, the loaded organic phase is collected, its actual volume is recorded, and this volume is used as the basis for subsequent backwashing solution dosage and comparison calculation.

[0026] Step (3) Tartaric acid backwash: Prepare backwash solution: 3.0 g L-(+)-tartaric acid, 27.0 g industrial hydrochloric acid (hydrogen chloride mass fraction 37.0%), 150.0 g deionized water, total mass 180.0 g. Perform two-stage countercurrent backwashing with the above backwash solution, mixing each stage for 4 min (e.g., IKA Eurostar series or equivalent, equipped with PTFE-coated agitator), temperature 20℃, let stand for 8 min to separate the layers, and collect the purified loaded organic phase after backwashing.

[0027] Step (4) Back-extraction: Prepare the back-extraction solution: 80.0 g of industrial hydrochloric acid (hydrogen chloride mass fraction 37.0%) and 1360.0 g of deionized water, totaling 1440.0 g. The purified loaded organic phase obtained in step (3) is subjected to two-stage countercurrent contact with the back-extraction solution, mixing for 5 min at each stage at 25°C, and allowed to stand for 10 min to separate into layers. The intermediate purified ferric chloride solution obtained from the back-extraction is collected. Back-extraction endpoint: The residual iron content in the organic phase after back-extraction is ≤ 3.0% of the initial loaded iron content.

[0028] Step (5) Secondary deep impurity removal: Prepare organic phase B according to the following formula: kerosene 180.0g, bis(2-ethylhexyl)phosphoric acid 24.0g, trioctylamine 12.0g, total mass 216.0g. The intermediate purified liquid obtained in step (4) is subjected to two-stage countercurrent contact with organic phase B, each stage is mixed for 4min, temperature 20℃, stirring speed 300r / min, and allowed to stand for 8min to separate into layers, and the aqueous phase is collected.

[0029] Step (6) Concentration, Residue Removal, Filtration, and Solidification Sampling: The aqueous phase obtained in step (5) was transferred to a 1L glass vacuum evaporator and concentrated at -0.085MPa and 55℃ until the system became noticeably viscous. Heating was then stopped, and nitrogen gas was introduced for 10 minutes. The solution was then filtered through a 0.22μm polyvinylidene fluoride membrane. A portion of the filtrate was allowed to stand at 25℃ for 4 hours to allow ferric chloride crystals to precipitate. After solid-liquid separation, the resulting wet crystals were dried in a 40℃ vacuum drying oven to constant weight to obtain a solid ferric chloride sample containing water. This solid sample was used for the detection of impurity metals, residual ferrous iron, volatile organic compounds, and water-insoluble matter. The main content of the product was calculated based on ferric chloride.

[0030] Example 2 As shown in Table 1, this embodiment illustrates the effect of increasing the dosage within a limited range on the primary extraction stage. The remaining raw materials, equipment, and operating steps are the same as in Example 1, except that the primary extraction formulation in step (2) is adjusted.

[0031] Table 1. Changes in parameters of Example 2 compared to Example 1 Example 3 As shown in Table 2, this embodiment illustrates the effect of reducing the dosage within a limited range on the backwashing effect of high-priced impurities. The remaining raw materials, equipment, and operating steps are the same as in Example 1, except that the composition of the backwash solution in step (3) is adjusted.

[0032] Table 2. Parameter changes in Example 3 compared to Example 1 Example 4 As shown in Table 3, this embodiment illustrates the effect of increasing the dosage of both within a limited range on the removal effect of trace metals at the end. The remaining raw materials, equipment and operating steps are the same as in Example 1, except that the composition of organic phase B in step (5) is adjusted.

[0033] Table 3. Parameter changes in Example 4 compared to Example 1 Example 5 As shown in Table 4, this embodiment illustrates that the technical solution of this application can still be achieved by switching the oxidant to chlorine. The remaining raw materials, equipment and operating steps are the same as in Example 1, only the conditions of steps (1) and (6) are adjusted. Specifically: in step (1), 26.5g of chlorine is used to replace the hydrogen peroxide solution, the introduction time is 25min, the reaction temperature is 22℃, and the aging time is 25min; in step (6), the reduced pressure concentration conditions are adjusted to -0.090MPa, 50℃, and the nitrogen removal time is 15min.

[0034] Table 4. Parameter changes in Example 5 compared to Example 1 Comparative Example 1 This comparative example is used to illustrate the effect of missing components on the removal of high-priced impurities. The remaining raw materials, equipment and operating steps are the same as in Example 1, except that tartaric acid is not added in step (3), and the composition of the backwash solution is adjusted to 27.0g of industrial hydrochloric acid and 153.0g of deionized water, with a total mass of 180.0g.

[0035] Comparative Example 2 This comparative example is used to illustrate the effect of the secondary deep purification step composed of two materials on the trace metal at the end. The remaining raw materials, equipment and operating steps are the same as in Example 1, except that step (5) is omitted and the intermediate purified solution obtained in step (4) directly enters step (6).

[0036] Comparative Example 3 This comparative example is used to illustrate the effect of material dosage below the lower limit on primary extraction and iron recovery. The remaining raw materials, equipment and operating steps are the same as in Example 1, except that the organic phase A in step (2) is adjusted to: 850.0g of n-butyl acetate, 50.0g of tributyl phosphate, and a total mass of 900.0g.

[0037] Comparative Example 4 This comparative example is used to illustrate the effect of oxidation conditions below the lower limit on the residual amount of ferrous iron and the stability of subsequent separation. The other raw materials, equipment and operating procedures are the same as in Example 1, except that step (1) is adjusted to: reaction temperature 10°C, hydrogen peroxide solution 8.0 g, dropping time 10 min, aging for 5 min.

[0038] Comparative Example 5 This comparative example illustrates the effect of replacing conventional dicarboxylic acids on the backwashing effect of high-valence impurities. The remaining raw materials, equipment, and operating procedures are the same as in Example 1, except that 3.0 g of tartaric acid in step (3) is replaced with 3.0 g of succinic acid, and the amounts of industrial hydrochloric acid and deionized water remain unchanged.

[0039] The test methods are as follows. Determination of main content and iron yield: Take 0.5000g of the solid test sample obtained by step (6) of each sample, add a small amount of hydrochloric acid solution to dissolve and then make up to volume. The total iron is determined by potassium dichromate volumetric method, and then the main content is converted by ferric chloride. The iron yield is calculated as the ratio of the total amount of iron finally recovered by each sample to the total amount of iron in the basic feed. Each sample is measured in parallel 3 times and the average value is taken. Determination of trace metals: Take 0.2000g of solid test sample, dissolve in 50.0mL hydrochloric acid solution, and then make up to 250.0mL with deionized water. The contents of titanium, zirconium, tin, copper, zinc, nickel and chromium are determined by inductively coupled plasma atomic emission spectrometry. The instrument model is Agilent 5110ICP-OES; radio frequency power 1.20kW; plasma gas flow rate 12.0L / min; nebulizer temperature 20℃. The matrix matching standard curve is used for calibration, and the average value is taken after 3 consecutive measurements. Determination of ferrous iron residue: 0.3000 g of solid sample was dissolved and the ferrous iron was determined by the o-phenanthroline spectrophotometric method. The instrument used was a Shimadzu UV-2600 UV-Vis spectrophotometer, with a measurement wavelength of 510 nm. Each sample was measured in triplicate, and the average value was taken. Determination of volatile organic compound residue: 1.0000 g of solid sample was added to a 20 mL headspace vial, dissolved in 5.0 mL of pure water, and then injected into the headspace. An Agilent 8890 gas chromatograph with an FID detector was used. The chromatographic column was a DB-WAX 30 m × 0.32 mm × 0.25 μm column. The column temperature program was 40 °C for 3 min, then increased to 180 °C at a rate of 10 °C / min. Results were expressed as n-butyl acetate, in mg / kg. Determination of water-insoluble matter: Take 50.0 g of sample solution, filter it through a 0.45 μm microporous membrane, dry the membrane at 105 °C to constant weight, and calculate the water-insoluble matter content based on the increase in membrane weight, with the result expressed in mg / kg. For solution products, the total iron content is converted to ferric chloride content after sampling; for hydrated ferric chloride solid or crystalline products, the total iron content is determined after weighing, dissolving, and adjusting the volume of the sample, and then the ferric chloride content is converted to the ferric chloride content. Unless otherwise specified, the purity or ferric chloride content mentioned in this application are converted values ​​based on ferric chloride and do not necessarily indicate that the product is anhydrous ferric chloride.

[0040] The test results are shown below.

[0041] Table 5. Results of impurity metals in each embodiment and comparative example. Table 6. Main content and process-related results for each embodiment and comparative example. As shown in Tables 5 and 6, Examples 1 to 5 all achieved low total impurity metal content and high iron yield. Compared with Example 1, Comparative Example 1, without the addition of tartaric acid, showed a significant increase in titanium, zirconium, and tin content, indicating that tartaric acid has a complexing and backwashing effect on high-valence, easily hydrolyzable impurities. In Comparative Example 2, omitting the secondary impurity removal step significantly increased the total content of copper, zinc, nickel, and chromium, indicating that the secondary impurity removal system composed of bis(2-ethylhexyl)phosphoric acid and trioctylamine can remove trace transition metals at the end. In Comparative Example 3, the amount of tributyl phosphate was lower than the specified range, resulting in a significant decrease in iron yield, indicating that the composition of the primary extraction organic phase has a significant impact on the transfer efficiency of ferric chloride. The above results show that there is a synergistic effect between the key components and process steps of this application, which can achieve a balance between low impurities, high primary metal content, and high iron yield. In Example 2, increasing the proportion of tributyl phosphate increased the iron yield, but the total content of copper, zinc, nickel, and chromium increased slightly, which may be related to the increased co-migration of a small amount of impurities due to the enhanced primary extraction ability. In Example 4, increasing the amount of secondary impurity remover reduced the total content of copper, zinc, nickel, and chromium, but slightly decreased the iron yield, indicating that enhanced secondary impurity removal may lead to a small loss of the main salt. Furthermore, in Comparative Example 4, the significant loss of unoxidized ferrous iron resulted in a substantial decrease in the total iron yield.

[0042] In summary, the above embodiments and comparative examples demonstrate that a high-purity ferric chloride product can only be stably obtained when the above components and steps are coordinated with each other. The data show that the present invention can stably achieve a balance between high purity (main content ≥ 99.92%), low impurities (total impurities ≤ 40.0 mg / kg), and high yield (≥ 97.1%).

Claims

1. A method for removing impurities from high-purity ferric chloride, characterized in that: The process includes the following steps: oxidizing a ferric chloride hydrochloric acid feed solution containing ferrous iron and metallic impurities into a feed solution mainly composed of ferric iron; contacting the feed solution with an organic phase containing n-butyl acetate and tributyl phosphate, allowing ferric chloride to enter the organic phase in a chlorine complex solvated form; backwashing or purifying the loaded organic phase with an aqueous phase containing tartaric acid; subsequently performing a second impurity removal process with an organic phase containing bis(2-ethylhexyl)phosphoric acid and trioctylamine in the back-extraction solution; and finally, performing vacuum concentration and removal of organic residues to obtain high-purity ferric chloride.

2. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The oxidation step uses hydrogen peroxide or chlorine as the oxidant, the oxidation temperature is 20-35℃, and the oxidation is followed by aging for 10-40 minutes. The oxidation step is carried out under the protection of an inert gas to inhibit the hydrolysis of the liquid and the introduction of moisture from the air.

3. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The feed liquid contains 25-35% total iron and 12-22% free hydrochloric acid. The primary extraction step employs two to four stages of countercurrent extraction, with a single-stage contact time of 3-8 minutes.

4. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The weight ratio of n-butyl acetate to tributyl phosphate in the primary extraction organic phase is 100:(10-35), and the ratio of the primary extraction steps is 1:(0.8-1.5).

5. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: In the backwashing or refining step, tartaric acid is added in the form of a hydrochloric acid aqueous solution with a mass fraction of 0.5-3.0%, the backwashing stage is one to two, and the amount of backwash solution is 0.15-0.40 times the volume of the loaded organic phase.

6. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The weight ratio of bis(2-ethylhexyl)phosphoric acid to trioctylamine in the secondary impurity removal organic phase is (5-20):(2-12), and n-butyl acetate or kerosene is used as the dilution medium to make the secondary impurity removal organic phase and the back-extraction solution contact each other for 1 to 3 stages at a ratio of (0.3-0.9):

1.

7. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The operating temperature of the secondary impurity removal step is 15-25℃, the single-stage contact time is 2-6 min, and the settling and stratification time is 3-15 min, in order to limit the unnecessary transfer of the main salt in the secondary impurity removal section.

8. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The vacuum concentration step is carried out at -0.06~-0.095MPa and 40-65℃. After concentration, nitrogen gas is introduced for 5-20 minutes and the mixture is filtered through a 0.22μm filter to remove residual organic matter and mechanical particles.

9. The method for removing impurities from high-purity ferric chloride according to claim 1, characterized in that: The purified ferric chloride solution after vacuum concentration is aged at 20-30℃ for 2-6 hours, followed by solid-liquid separation and vacuum drying at 35-45℃ to obtain a solid ferric chloride product; or it can be directly retained as a high-purity ferric chloride solution product.

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