Process for the preparation of ferrochrome electrolyte and electronic grade ferrous chloride

Abstract

The application provides a preparation method of ferrous chloride for electronic grade and iron-chromium electrolyte, and the method comprises the following steps: taking waste hydrochloric acid containing iron and elemental iron as raw materials, removing impurities by acid consumption, removing sulfate radicals by barium chloride, producing hydroxyl ferric oxide by oxygen oxidation, separating and washing the hydroxyl ferric oxide, acid dissolving and reducing ferrous sulfide, and then separating elemental sulfur, so that the low-impurity ferrous chloride solution can be prepared and can be used for producing the ferrous chloride for electronic grade and preparing the iron-chromium electrolyte. The ferrous chloride prepared through the above steps has high purity and less waste; meanwhile, the electrolyte prepared has good electrical performance, low attenuation rate and low cost, realizes the purpose of comprehensive recycling of resources, and meets the technical improvement trend.

Description

Technical Field

[0001] This invention relates to the field of electrolyte production technology, specifically to a method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride. Background Technology

[0002] Currently, the key materials for the electrolyte in iron-chromium flow batteries are a mixed solution of chromium chloride, ferrous chloride, and hydrochloric acid. The "NB / T 11067—2023 Technical Specification for Electrolytes for Iron-Chromium Flow Batteries" and the proposed industry standard "Iron-Chromium Electrolytes for Flow Batteries" restrict various impurities. "CN 118244131 A A Method for Studying the Influence of Impurities in Electrolytes for Iron-Chromium Flow Batteries," as shown in Figure 2 of this patent, indicates that the more impurities in the electrolyte, the greater the impact on battery performance. High impurity levels in the iron-chromium electrolyte can easily lead to rapid battery capacity decay, affecting the normal operation of iron-chromium flow batteries. Therefore, most iron-chromium flow battery manufacturers have high purity requirements for hydrochloric acid-based iron-chromium electrolytes.

[0003] The chromium chloride in the electrolyte of the iron-chromium redox flow battery is mainly commercially available chromium chloride, which is obtained by reducing chromic anhydride. The chromic anhydride obtained has a very high purity, and most impurities have been removed to within 5 mg / kg or even 1 mg / kg. Therefore, the chromium chloride does not need to be further purified to achieve a very high purity, which meets the requirements of the electrolyte of the iron-chromium redox flow battery.

[0004] However, the bottleneck in obtaining high-purity iron-chromium electrolyte lies in obtaining high-purity ferrous chloride at a low cost. Iron sources mainly include steel and iron powder, and their derivatives such as steel pickling waste liquid, oxide scale, and iron oxide red. These iron sources contain a large number of impurity metals, such as copper, nickel, zinc, chromium, manganese, calcium, and magnesium, which cannot meet the requirements for high-purity ferrous chloride after direct acid dissolution. As described in the literature "Preparation Process of High-End Ferric Chloride," commonly used purification methods for ferrous chloride include crystallization, recrystallization, elemental iron reduction for impurity removal, and sulfide impurity removal. For example, patent CN 110980833 A discloses "a method for preparing electronic-grade ferrous chloride". This patent uses crystallization and recrystallization methods. Most impurities are removed at a rate of 80% to 95% during recrystallization, but the removal rate of manganese is only about 20% to 50%. In Example 1, it is shown that the manganese content in the secondary crystal is 0.008%, and the manganese content in the tertiary crystal obtained after recrystallization is 0.007%, indicating low purification efficiency. Another example is CN 115010185B, which discloses a method for producing battery-grade ferrous chloride. This patent uses iron filings to consume acid, sulfide impurities removal, and PAM flocculation. The supernatant after settling is battery-grade ferrous chloride. As can be seen from its impurity removal principle, this technical solution cannot remove manganese, calcium, magnesium, etc. The test data in Table 1 show that the impurities in ferrous chloride are all relatively high, and it cannot be used to prepare high-purity iron-chromium electrolyte.

[0005] Therefore, another technical solution is needed to find a way to obtain high-purity electronic-grade ferrous chloride and iron-chromium electrolytes. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride. This method uses iron-containing waste hydrochloric acid (a waste liquid containing an iron source generated from cleaning rusted steel surfaces with industrial hydrochloric acid) and elemental iron as raw materials. The process involves acid removal, barium chloride removal of sulfate, oxygen oxidation to produce ferric hydroxide, separation, water washing of the ferric hydroxide, acid dissolution and ferrous sulfide reduction, and solid-liquid separation to obtain solid sulfur and an electronic-grade ferrous chloride solution. This electronic-grade ferrous chloride solution has high purity and can be directly used for producing electronic-grade ferrous chloride and for preparing iron-chromium electrolyte. This technical solution comprehensively utilizes waste materials, turning waste into treasure, and implements a green circular technology route.

[0007] To achieve one of the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride includes the following steps:

[0009] S1. Add elemental iron to iron-containing waste hydrochloric acid, heat the reaction until pH > 3.0, add barium chloride to react, and then separate the solid and liquid to obtain ferrous chloride solution;

[0010] S2. The ferrous chloride solution is transferred into a reaction vessel, oxygen is introduced, and positive pressure is maintained inside the reaction vessel to keep the reaction temperature at 85℃~120℃. After the reaction is completed, a mixed slurry is obtained, which contains ferric chloride solution and ferric hydroxide solid.

[0011] S3. The mixed slurry is separated into solid and liquid components, and the iron hydroxide solid is washed with water to obtain purified iron hydroxide solid;

[0012] S4. Slurry the purified iron hydroxide solid, then add industrial hydrochloric acid, and react at 60℃~100℃ until the purified iron hydroxide solid is completely dissolved. Add ferrous sulfide or hydrogen sulfide until Fe... 3+ The reaction was completed, followed by solid-liquid separation to obtain solid sulfur and an electronic-grade ferrous chloride solution.

[0013] In some embodiments, in step S1, the amount of barium chloride added is the theoretical amount, the temperature of the heating reaction is 80℃~100℃, and the reaction time is 0.5h~1h.

[0014] In some embodiments, in step S2, after oxygen is introduced, a catalyst, nitric acid or sodium nitrite, is added to carry out the reaction, wherein the amount of catalyst added is 1‰ to 3‰ of the mass of the ferrous chloride solution.

[0015] In some embodiments, in step S2, the positive pressure inside the reactor is >0.1 MPa.

[0016] In some embodiments, in step S3, the weight of the washing water is 1 to 5 times the weight of the solid iron hydroxyoxide, more preferably 2 to 3 times.

[0017] In some embodiments, in step S4, water is added to the purified iron hydroxyl oxide solid and the mixture is slurried. The amount of water added is 0 to 0.5 times the weight of the iron hydroxyl oxide, and the reaction temperature is 60 to 100°C, more preferably 60 to 80°C.

[0018] In some embodiments, in step S4, the amount of industrial hydrochloric acid added is 1.03 to 1.08 times the theoretical amount.

[0019] In some implementations, the amount of hydrogen sulfide or ferrous sulfide added in step S4 is the theoretical amount.

[0020] In some embodiments, the sulfur solid is purified by washing with water and drying.

[0021] It also provides an iron-chromium electrolyte containing chromium chloride, hydrochloric acid, water and electronic-grade ferrous chloride crystals, wherein the electronic-grade ferrous chloride crystals are obtained by evaporation, concentration and cooling crystallization of the electronic-grade ferrous chloride solution obtained by the above method.

[0022] The beneficial effects of the present invention regarding the preparation method of iron-chromium electrolyte and electronic-grade ferrous chloride are as follows:

[0023] (1) This invention uses elemental iron and iron-containing waste hydrochloric acid as raw materials. After impurity removal, oxidation and reduction, a high-purity electronic-grade ferrous chloride solution is obtained. The purification of this electronic-grade ferrous chloride solution meets the requirements of iron-chromium electrolyte production, has high added value, realizes the purpose of comprehensive resource recycling, and conforms to the general trend of technological improvement.

[0024] (2) The method of the present invention can obtain a ferrous chloride solution with low levels of various impurities, especially low levels of manganese, and the cost is relatively low. If the crystallization purification method is used, the purification cost is about RMB 11,560 per ton, while the cost of the present invention is about RMB 3,300 per ton, which greatly reduces the cost and is suitable for large-scale production and application.

[0025] (3) By controlling the production conditions of ferric hydroxide, the present invention generates ferric hydroxide that is easy to filter and wash. Free impurity ions carried in the ferric hydroxide can be effectively removed by washing with water. The process control conditions are simple, and the steps of using sulfides to remove impurities and crystallization purification are omitted, thereby achieving the purpose of saving process costs.

[0026] (4) This invention uses ferrous sulfide and hydrogen sulfide to reduce Fe 3+ It does not introduce impurity ions, thus ensuring the purity of the product.

[0027] To achieve the second objective mentioned above, the present invention provides the following technical solution:

[0028] A ferrochromium electrolyte is provided by mixing industrial hydrochloric acid, chromium chloride, water, and electronic-grade ferrous chloride in a certain proportion.

[0029] To achieve the third objective mentioned above, the present invention provides the following technical solution:

[0030] Provides an iron-chromium redox flow battery containing the aforementioned iron-chromium electrolyte. Detailed Implementation

[0031] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention have been shown, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0032] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0033] Example 1

[0034] This embodiment discloses a method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride, comprising the following steps:

[0035] S1. Add elemental iron to iron-containing waste hydrochloric acid, heat the reaction until pH > 3.0, raise the temperature to above 80℃, add barium chloride and react for 0.5 to 1 hour, separate the solid and liquid to obtain ferrous chloride solution A1.

[0036] The principle behind the above steps: Fe in iron-containing waste hydrochloric acid 3+ =0.1%~1%, Fe 2+ =8%~14%, HCl =2%~5%. Adding elemental iron can remove Fe from iron-containing waste hydrochloric acid. 3+ Reduced to Fe 2+ , restore H +The pH is increased. Simultaneously, metallic impurities such as Sn, Ti, Zr, Al, and Cr are hydrolyzed and removed at a low pH, preventing them from precipitating in ferric hydroxide due to low free acidity during subsequent oxidation. This removes some copper, nickel, and other metal ions that undergo displacement reactions with elemental iron. Since the hydrochloric acid used for pickling steel is mostly a byproduct containing a small amount of sulfate, it forms basic ferric sulfate in ferric hydroxide during oxidation, which cannot be removed by water washing. Therefore, barium chloride is added to remove sulfate. To ensure easy sedimentation and filtration of the generated barium sulfate particles, the reaction temperature must be controlled between 80℃ and 100℃. Below this temperature, sulfate removal is incomplete, and the small-particle barium sulfate formed at low temperatures can penetrate the filter cloth, making solid-liquid separation difficult.

[0037] S2. Transfer ferrous chloride solution A1 into the reactor, introduce oxygen, add catalyst, maintain positive pressure inside the reactor, and keep the reaction temperature above 85℃. React for 1–3 hours until Fe… 2+ <0.1%, a mixed slurry A2 of ferric chloride solution and ferric hydroxide solid is obtained.

[0038] The principle behind the above steps: The free acid content in the ferrous chloride solution A1 is very low. Oxidation with oxygen requires the consumption of hydrochloric acid, but no hydrochloric acid was added. After oxidation, Fe... 3+ Subsequently, hydrolysis occurs due to low acidity, producing ferric hydroxide or ferric hydroxide. By controlling the oxidation rate, all hydrolysis products can be easily filtered and washed with water to obtain ferric hydroxide, with the reaction equation being 12FeCl₂ + 3O₂ + 2H₂O = 8FeCl₃ + 4FeOOH. When the reaction temperature is below 70℃, no catalyst is added, and the reaction pressure is below 0.05MPa, the product obtained is mainly colloidal ferric hydroxide, which is difficult to filter and wash. When the reaction temperature is above 85℃~120℃, a catalyst such as 1‰~3‰ nitric acid or sodium nitrite is added, and the reaction pressure is >0.1MPa, easily filtered and washed ferric hydroxide can be obtained.

[0039] S3. The mixture of ferric chloride solution and ferric hydroxide solid A2 is separated into solid and liquid phases, and washed online with 2 to 3 times the weight of the filter cake to obtain high-purity ferric hydroxide solid A3.

[0040] The principle behind the above steps: Solid-liquid separation is commonly achieved using a plate and frame filter press or centrifuge. After solid-liquid separation, most impurities remain in the ferric chloride solution, while a small amount of impurities are entrained in ferric hydroxide, which can be effectively removed by washing with water. Online washing with approximately 2-3 times the weight of the solid in water can remove entrained free Cu, Ni, Zn, Mn, Ca, Mg, Na, K, and other impurities to <30 mg / kg, or even <1 mg / kg. Increasing the amount of washing water further does not significantly remove impurities. After air blowing and pressing in the filter press, high-purity ferric hydroxide solid can be obtained.

[0041] S4. Add water to the solid iron hydroxide A3 and slurry it. Add 1.03 to 1.08 times the theoretical amount of hydrochloric acid, heat to above 60°C, and react for 1 to 3 hours. Add the theoretical amount of ferrous sulfide or hydrogen sulfide until Fe... 3+ After the reaction was complete, the solid and liquid were separated to obtain an electronic-grade ferrous chloride solution A4 and solid sulfur. The solid sulfur was washed with water, dried, and then sold.

[0042] Electronic-grade ferrous chloride solution A4 can be sold directly or concentrated to Fe by evaporation. 2+ =15%~21%, cooled and crystallized to obtain high-purity electronic-grade ferrous chloride crystals.

[0043] Adding chromium chloride, hydrochloric acid, and water to the above-mentioned electronic ferrous chloride solution A4 yields a high-purity iron-chromium electrolyte product.

[0044] The principle behind the above steps: Fe in solid iron hydroxyoxide A3 3+ =35%~40%, add water to make a slurry, add hydrochloric acid. Ferric hydroxyl is poorly soluble in hydrochloric acid at room temperature and requires heating to aid dissolution; the dissolution rate is faster above 60℃. The solution contains an excess of 0.03~0.08 times the amount of hydrochloric acid, i.e., the free acid content in the solution is 0.5~1.5%, which helps decompose the poorly soluble ferrous sulfide to release sulfur. - To reduce Fe 3+ Increasing the temperature also facilitates the reduction process. In this step, ferrous sulfide is used to reduce Fe. 3+ Without introducing impurities, Fe can also be reduced using hydrogen sulfide. 3+ However, the high level of free acid in the reduced solution limits the applications of this ferrous chloride solution. The reaction equation for this step is:

[0045] FeOOH + 3HCl = FeCl3 + 2H2O

[0046] 2FeCl3 + FeS = 3FeCl2 + S↓

[0047] 2FeCl3 + H2S = 2FeCl2 + S↓ + 2HCl

[0048] The sulfur solids obtained in this step are easy to separate from liquid and wash, and can be sold as sulfur after drying.

[0049] To further illustrate the effects of the present invention, the following experiments were conducted.

[0050] Experimental Example 1

[0051] This experimental example provides a method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride, including the following steps:

[0052] S1. Add 0.4 tons of iron powder to 10 tons of iron-containing waste hydrochloric acid, stir and heat to react until pH=3.02, raise the temperature to 80℃, add 0.101 kg of industrial barium chloride and react for 1 hour. Separate the solid and liquid to obtain 10.3 tons of ferrous chloride solution A1.

[0053] S2. Transfer ferrous chloride solution A1 into a reactor, add 20 kg of concentrated nitric acid as a catalyst, and purge with oxygen. Maintain the pressure inside the reactor at 0.1–0.15 MPa and the reaction temperature at 85°C. React for 2 hours until Fe… 2+ <0.1%, ferric chloride and ferric hydroxide slurry A2 is obtained;

[0054] S3. The mixture of ferric chloride solution and ferric hydroxide solid A2 was separated by a filter press and washed online with 3.5 tons of water to obtain 1.29 tons of high-purity ferric hydroxide solid A3;

[0055] S4. Add 1.29 tons of solid iron hydroxide to 3.4 tons of hydrochloric acid, heat to 60°C, stir and react for 3 hours. The free acid in the solution is about 0.55%. Add 0.405 tons of ferrous sulfide, stir and react for 2 hours until Fe... 3+ The reaction was completed, and the solid and liquid were separated to obtain 4.7 tons of ferrous chloride solution A4 and 0.17 tons of sulfur solid. The sulfur solid was washed with water, dried and then sold.

[0056] Ferrous chloride solution A4 can be sold directly or concentrated to Fe by evaporation. 2+ =16%~21%, cooled to 30℃ to crystallize, to obtain high-purity electronic-grade ferrous chloride crystals A5.

[0057] Adding chromium chloride, hydrochloric acid, and water to ferrous chloride solution A4 yields high-purity ferrochromium electrolyte A6.

[0058] Finally, the product testing data for each step are summarized in Table 1.

[0059] Table 1. Product testing data for each step in Example 1.

[0060] Iron-containing waste hydrochloric acid 12.04 356 127 219 685 1297 566 78 102 Ferrous chloride solution A1 14.66 18 25 186 670 9 547 70 93 Iron hydroxyoxide solid A3 39.13 32 2.6 0.5 1.6 24 1.1 13 19 Ferrous chloride solution A4 15.85 9.8 0.9 0.50 0.54 6.2 0.6 2.7 3.1 Ferrous chloride crystals A5 27.57 2.2 0.05 0.02 0.06 0.02 0.03 0.12 0.17 Iron-chromium electrolyte A6 5.1 55000 0.64 0.17 0.24 1.6 0.78 1.6 1.8

[0061] Note: The unit for impurities in the table is mg / kg.

[0062] It is evident that the final ferrous chloride solution A4 has low levels of various impurity metals, meeting the requirements for use as an iron-chromium electrolyte.

[0063] Experimental Example 2

[0064] This experimental example provides a method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride, including the following steps:

[0065] S1. Add 0.8 tons of iron rings to 10 tons of iron-containing waste hydrochloric acid, heat to react until pH=1.82, add 0.1 tons of iron powder, heat and stir to react until pH=3.73, raise the temperature to 85℃, add 0.340 kg of industrial barium chloride and react for 0.5 h, separate the solid and liquid to obtain 10.3 tons of ferrous chloride solution A1;

[0066] S2. Transfer ferrous chloride solution A1 into a reactor, add 10.5 kg of concentrated nitric acid as a catalyst, and introduce oxygen. Maintain the pressure inside the reactor at 0.2–0.25 MPa, and the reaction temperature at approximately 100°C. React for 1 hour until Fe… 2+ <0.1%, ferric chloride and ferric hydroxide slurry A2 is obtained;

[0067] S3. The slurry of ferric chloride and ferric hydroxide A2 was separated by a filter press and washed online with 3.3 tons of water to obtain 1.13 tons of high-purity ferric hydroxide solid A3;

[0068] S4. Add 1.13 tons of solid iron hydroxide to 0.4 tons of water and slurry. Then add 2.9 tons of hydrochloric acid, heat to 80°C, and stir for 1 hour. The free acid in the solution is about 1%. Add 0.35 tons of ferrous sulfide and stir for 1 hour until Fe... 3+ The reaction was completed, and the solid and liquid were separated to obtain 4.6 tons of ferrous chloride solution A4 and 0.15 tons of sulfur solid. The sulfur solid was washed with water, dried and sold.

[0069] Ferrous chloride solution A4 can be sold directly or concentrated to Fe by evaporation. 2+ =15%~21%, cooled to 30℃ to crystallize, to obtain high-purity electronic-grade ferrous chloride crystals A5.

[0070] Adding chromium chloride, hydrochloric acid, and water to ferrous chloride solution A4 yields high-purity ferrochromium electrolyte A6.

[0071] Finally, the product testing data for each step are summarized in Table 2.

[0072] Table 2. Product testing data for each step in Example 2.

[0073] Iron-containing waste hydrochloric acid 11.38 10138 576 5974 782 4366 1290 327 566 Ferrous chloride solution A1 13.77 9.2 83 1336 716 11 1297 287 531 Iron hydroxyoxide solid A3 38.74 20.5 4.3 7.8 1.8 27 0.8 14 26 Ferrous chloride solution A4 14.16 5.2 1.3 2.80 0.59 7.0 0.5 1.8 6.9 Ferrous chloride crystals A5 27.66 1.06 0.13 0.19 0.08 0.03 0.05 0.21 0.28 Iron-chromium electrolyte A6 5.1 55000 0.97 1.03 0.24 1.8 0.63 3.6 4.7

[0074] Note: The unit for impurities in the table is mg / kg.

[0075] It is evident that the final ferrous chloride solution A4 has low levels of various impurity metals, meeting the requirements for use as an iron-chromium electrolyte.

[0076] Experimental Example 3

[0077] This application provides a method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride, comprising the following steps:

[0078] S1. Add 0.6 tons of sheet iron to 10 tons of iron-containing waste hydrochloric acid, stir and heat to react until pH=3.50, raise the temperature to 90℃, add 0.044 kg of industrial barium chloride and react for 0.5 h, then separate the solid and liquid to obtain 10.2 tons of ferrous chloride solution A1;

[0079] S2. Transfer ferrous chloride solution A1 into a reactor, add 30 kg of concentrated nitric acid as a catalyst, and purge with oxygen. Maintain the pressure inside the reactor at 0.05–0.1 MPa, and the reaction temperature at 105 °C. React for 2 hours until Fe… 2+ <0.1%, ferric chloride and ferric hydroxide slurry A2 is obtained;

[0080] S3. The slurry of ferric chloride and ferric hydroxide A2 is separated by a filter press and washed online with 2.5 tons of water to obtain 1.2 tons of high-purity ferric hydroxide solid A3;

[0081] S4. Add 1.2 tons of solid iron hydroxide to 0.4 tons of water and slurry. Then add 3.21 tons of hydrochloric acid, heat to 80°C, and stir for 1 hour. The free acid in the solution is about 1.5%. Add 0.38 tons of ferrous sulfide and stir for 0.5 hours until Fe... 3+ The reaction was completed, and the solid and liquid were separated to obtain 5.0 tons of ferrous chloride solution A4 and 0.16 tons of sulfur solid. The sulfur solid was washed with water, dried and sold.

[0082] Ferrous chloride solution A4 can be sold directly or concentrated to Fe by evaporation. 2+ =15%~21%, cooled and crystallized to obtain high-purity electronic-grade ferrous chloride crystals A5.

[0083] Adding chromium chloride, hydrochloric acid, and water to ferrous chloride solution A4 yields high-purity ferrochromium electrolyte A6.

[0084] Finally, the product testing data for each step are summarized in Table 3.

[0085] Table 3. Product testing data for each step in Example 3.

[0086] Iron-containing waste hydrochloric acid 13.13 166 17 22 437 560 13 33 43 Ferrous chloride solution A1 13.79 12 14 19 479 8 19 30 41 Iron hydroxyoxide solid A3 39.42 29 0.3 0.4 1.1 20 0.3 6 8 Ferrous chloride solution A4 14.31 7.2 0.3 0.48 0.42 5.2 0.4 1.9 2.4 Ferrous chloride crystals A5 27.43 3.2 0.02 0.02 0.05 0.02 0.02 0.10 0.13 Iron-chromium electrolyte A6 5.1 55000 0.52 0.19 0.20 1.1 0.66 1.2 0.9

[0087] Note: The unit for impurities in the table is mg / kg.

[0088] The reaction conditions and test data of the products obtained in Experiments 1, 2, and 3 were analyzed:

[0089] (1) When the pH of iron-containing waste hydrochloric acid is increased by elemental iron, Cr can be effectively removed to less than 20 mg / kg. The higher the pH, the lower the chromium in ferrous chloride, which can remove some Cu and Ni. Adding barium chloride to remove sulfate can remove S to less than 20 mg / kg. Other impurities have no obvious removal effect.

[0090] (2) Iron hydroxyl oxide is generated and washed with water. Cu, Ni, Zn, Mn, Ca, and Mg can be washed to a lower concentration during the water washing process. Among them, the water washing removal effect of Cu, Ni, Zn, and Mn is very significant, while the water washing effect of Ca and Mg is mainly affected by the difference in content in tap water in the north and south regions.

[0091] (3) In the ferrous chloride solution A4 after acid dissolution of ferric hydroxyoxide and reduction by ferrous sulfide, all impurities are <15mg / kg, of which Cu, Ni, Zn and Mn are <3mg / kg. No impurities were introduced during the reduction process.

[0092] (4) All impurities in the electrolyte prepared by the ferrous chloride solution and commercially available chromium chloride hexahydrate obtained by this process are <5mg / kg, especially Mn <1mg / kg, which is much lower than the manganese content in the iron-chromium electrolyte in the prior art.

[0093] It is evident that the final ferrous chloride solution A4 has low levels of various impurity metals, meeting the requirements for use as an iron-chromium electrolyte.

[0094] Comparative Test Example 1

[0095] Take 1 kg of iron-containing waste hydrochloric acid from Experiment Example 2, and use the oxidation conditions in Experiment Example 2. After the reaction is completed, filter the solution with a Buchner funnel until there is no obvious filtrate. Collect the filtrate and use ferric chloride for testing. Wash the filter residue with 3 times its weight of water and filter it. Collect the washed filter residue for testing. The experimental data are summarized in Table 4.

[0096] Table 4. Summary of experimental data on the oxidation of iron-containing waste hydrochloric acid at different pH values.

[0097]

[0098] Analyze the experimental data in Table 4:

[0099] Iron-containing waste hydrochloric acid is oxidized without being purified by raising the pH with elemental iron. Cr and Sn will hydrolyze and precipitate in ferric hydroxide, while S will mainly be in the form of SO4. 2- The form of basic ferric sulfate is generated and cannot be removed by washing with water in the iron hydroxide. Comparing the data of iron hydroxide in Experiment ① and Experiment 2, it can be seen that if impurities are not removed, the impurity content in iron hydroxide is very high. Therefore, in order to obtain high-purity iron hydroxide, impurities that can be hydrolyzed at low pH or whose oxidation products are solids must be removed in advance before oxidation.

[0100] Comparative Test Example 2

[0101] Take 1 kg of iron-containing waste hydrochloric acid from Experiment Example 2, heat it to 80℃, add 80 g of iron powder, and take samples for filtration when the reaction reaches different pH values. Detect the composition and impurities of the filtrate. The experimental data are summarized in Table 5.

[0102] Table 5. Summary of impurity data in ferrous chloride solutions at different pH values.

[0103]

[0104] Analyze the experimental data in Table 5:

[0105] During the process of consuming iron powder in waste hydrochloric acid containing iron, the iron content in the solution continuously increases, and impurities such as Cr and Sn are continuously hydrolyzed. At pH ≈ 3.0, most of the impurities that can be hydrolyzed at low pH have been removed to below 30 mg / kg. If an even lower impurity content is required, the reaction can be carried out at a higher pH to meet the requirements, but SO4... 2- Impurities such as Mn that do not hydrolyze or displace are almost ineffective at removal, and other impurity removal methods need to be considered.

[0106] Comparative Test Example 3

[0107] Following the method in Comparative Experiment Example 2, 2 kg of ferrous chloride solution with pH = 3.0 was prepared, divided into 4 equal portions of 500 g each, heated to different temperatures, and the theoretical amount of barium chloride was added. Samples were taken after reacting for 0.5–1 h, the filtration status was recorded, and the S of the filtrate was tested. The experimental data are summarized in Table 6.

[0108] Table 6 Summary of experiments on barium chloride removing sulfate at different temperatures

[0109]

[0110] Analyze the experimental data in Table 6:

[0111] (1) Temperature has a significant effect on the removal of sulfate by barium chloride. The higher the temperature, the higher the sulfate removal rate. After the temperature exceeds 80℃, the removal rate is basically stable.

[0112] (2) Temperature has a significant effect on the filtration of barium sulfate. Theoretically, high temperature is conducive to the formation of large barium sulfate crystals, which is beneficial to filtration and separation. Considering the effect of sulfate removal, the reaction temperature is 80℃.

[0113] (3) Extending the reaction time does not significantly improve the efficiency of barium chloride in removing sulfate; 0.5 h is sufficient.

[0114] Comparative Test Example 4

[0115] The ferrous chloride solution A1 obtained in Experimental Example 2 was taken in portions of 1 kg each and oxidized under different reaction temperatures, catalyst dosages, and reaction pressures until Fe was obtained. 2+ The reaction was stopped when the concentration was less than 0.1%. The reaction time was recorded. 200g of solution was taken and filtered using a 5cm diameter Buchner funnel and a 10μm filter membrane. The filtration was continued until no filtrate dripped within 30s. The filtration time was recorded. The experimental data are summarized in Table 7.

[0116] Table 7. Effects of different oxidation conditions on the solid-liquid filtration separation rate

[0117]

[0118] Analyze the experimental data in Table 7:

[0119] (1) The longer the oxidation reaction time, the longer the filtration time, indicating that the solid is more difficult to filter and separate, the product is iron hydroxide, and it is also more difficult to wash and remove impurities with water.

[0120] (2) Comparing the data of ⑦-1 and ⑦-2, the catalyst can significantly improve the reaction rate;

[0121] (3) Comparing ⑦-1, ⑦-2, ⑦-3 and ⑦-4, ⑦-5, ⑦-6, ⑦-7, when the oxidation reaction time is <3h, the filtration time is significantly shortened. The reaction rate can be increased by increasing the reaction temperature, increasing the amount of catalyst, and increasing the reaction pressure, so as to obtain ferric hydroxy oxide that is easy to filter and wash with water.

[0122] Comparative Test Example 5

[0123] Approximately 2.5 kg of the solution obtained from dissolving solid iron hydroxide A3 in water and 1.0 times the amount of hydrochloric acid in step 3 of Experimental Example 2 was divided into four portions of 500 g each. Different amounts of hydrochloric acid were added to each portion to achieve acidities of 0.5, 1, and 1.5. Fe was then reduced with an equivalent amount of ferrous sulfide at different temperatures. 3+ The fifth part introduces hydrogen sulfide to reduce Fe. 3+ The experimental data are summarized in Table 8.

[0124] Table 8. Reduction of Fe by ferrous sulfide under different temperatures and acidity conditions. 3+ Experimental Data Summary Table

[0125] Analyze the experimental data in Table 8:

[0126] (1) Increasing the reaction temperature and the concentration of hydrochloric acid in the solution helps to shorten the reaction time. 3+ The reduction time is important because ferrous sulfide is sparingly soluble in water but readily soluble in dilute acid, requiring dilute acid to promote its dissolution and electrolysis to release sulfur. -That is, the free acid concentration in the ferrous chloride solution should be maintained at 0.5% to 1.5%, and the reaction can be completed in 1 to 3 hours at 60℃ to 70℃.

[0127] (2) When hydrogen sulfide is introduced to reduce Fe 3+ When the ferrous chloride solution is obtained, the free acid content is high. It can be compounded with water, hydrochloric acid, and chromium chloride to form an electrolyte. However, if it is used for evaporation and concentration to produce ferrous chloride crystals, the evaporator must be highly corrosive, which limits its industrial application.

[0128] Comparative Test Example 6

[0129] Electrical performance testing

[0130] The electrolytes obtained from Experiments 1, 2, and 3, as well as electrolytes with various impurity concentrations, were subjected to electrical performance tests. The charge / discharge mode was set to constant current charge / discharge, and the current was 120 mA / cm². 2 The charging cutoff voltage was 1.2V, the discharging cutoff voltage was 0.3V, and the number of charge-discharge cycles was 20. The data obtained are shown in Table 9. The iron-chromium electrolyte contained Fe = 1.2M, Cr = 1.4M, and HCl = 2.5M.

[0131] Table 9. Record of Electrolyte Performance Test Data for Various Impurity Concentrations

[0132]

[0133] Analyzing the experimental data in Table 9, (1) compared with test examples 1, 2 and 3 of this technical solution, CN117497816B has lower copper and nickel content, but much higher manganese content, resulting in low energy efficiency and high decay rate; (2) compared with the examples of this technical solution, CN118099495B has similar copper content, but slightly higher nickel and manganese content, resulting in high decay rate; (3) compared with the examples of this technical solution, the iron-chromium electrolyte prepared with analytical reagent has slightly higher copper, nickel and manganese content, resulting in low energy efficiency and high decay rate.

[0134] Based on the comprehensive analysis of the above data, the electrolyte in this technical solution has a lower manganese content and better energy efficiency and decay rate compared with the existing technology.

[0135] Cost Analysis

[0136] The production cost of ferrous chloride in this technical solution and the existing technology "CN 110980833 A A method for preparing electronic grade ferrous chloride" is calculated based on the production of 1 ton of ferrous chloride crystals. The data is shown in Table 10.

[0137] Table 10 Cost Calculation Table for Ferrous Chloride Crystal Production

[0138]

[0139]

[0140] As shown in Table 10, the production of low-manganese electronic-grade ferrous chloride using this technical solution saves approximately 8,000 yuan / ton compared to the existing technology that uses multiple recrystallization methods. This significantly reduces costs, thereby lowering the preparation cost of low-manganese ferrochromium electrolyte. The economic benefits are significant, and the solution is worthy of promotion and aligns with the trend of technological development.

[0141] The present invention has been illustrated with the above embodiments to explain the detailed method of the present invention. However, the present invention is not limited to the detailed method described above, that is, it does not mean that the present invention must rely on the detailed method described above to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials in the method of the present invention, the addition of auxiliary components, the selection of specific methods, etc., without departing from the principle of the present invention, all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing electronic-grade ferrous chloride, characterized in that, Includes the following steps: S1. Add elemental iron to iron-containing waste hydrochloric acid, heat the reaction until pH > 3.0, add barium chloride to react, and then separate the solid and liquid to obtain ferrous chloride solution; S2. The ferrous chloride solution is transferred into a reaction vessel, oxygen is introduced, positive pressure is maintained inside the reaction vessel, the reaction temperature is 85℃~120℃, and the reaction time is controlled to be <3h. After the reaction is completed, a mixed slurry is obtained, which contains ferric chloride solution and ferric hydroxide solid. S3. The mixed slurry is separated into solid and liquid components, and the iron hydroxide solid is washed with water to obtain purified iron hydroxide solid; S4. Slurry the purified iron hydroxide solid, then add industrial hydrochloric acid, and react at 60℃~100℃ until the purified iron hydroxide solid is completely dissolved. Add ferrous sulfide or hydrogen sulfide until Fe... 3+ The reaction was completed, followed by solid-liquid separation to obtain solid sulfur and an electronic-grade ferrous chloride solution; In step S1, the amount of barium chloride added is the theoretical amount, the temperature of the heating reaction is 80℃~100℃, and the reaction time is 0.5h~1h after adding barium chloride. In step S3, the weight of the washing water is 1 to 5 times the weight of the solid iron hydroxyoxide.

2. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, In step S2, after oxygen is introduced, nitric acid or sodium nitrite is added as a catalyst to carry out the reaction. The amount of catalyst added is 1‰ to 3‰ of the mass of the ferrous chloride solution.

3. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, In step S2, the positive pressure inside the reactor is >0.1 MPa.

4. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, In step S4, water is added to the purified iron hydroxyoxide solid and the mixture is slurried. The amount of water added is 0 to 0.5 times the weight of the iron hydroxyoxide, and the reaction temperature is 60 to 100°C.

5. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, In step S4, the amount of industrial hydrochloric acid added is 1.03 to 1.08 times the theoretical amount.

6. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, In step S4, the amount of hydrogen sulfide or ferrous sulfide added is the theoretical amount.

7. The method for preparing electronic-grade ferrous chloride according to claim 1, characterized in that, The sulfur solid was purified by washing with water and drying.

8. A method for preparing an iron-chromium electrolyte, characterized in that, The electronic-grade ferrous chloride solution prepared by the method described in any one of claims 1 to 7 is concentrated by evaporation and cooled to crystallize, resulting in electronic-grade ferrous chloride crystals. Chromium chloride, hydrochloric acid, and water are then added to prepare the iron-chromium electrolyte.

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