Method for preparing ferrochromium leaching solution and application of ferrochromium leaching solution

Abstract

The invention provides a method for preparing a ferrochromium leaching solution and application, the method comprises the following steps: mixing a ferrochromium-containing raw material with a hydrochloric acid solution, carrying out at least one-stage leaching, and carrying out solid-liquid separation to finally obtain the leaching solution and leaching residues; and the leachate, the leaching residues and ferric trichloride are mixed to be subjected to a hydrothermal reaction, solid-liquid separation is conducted after the reaction is finished, and the ferrochromium leachate is obtained. According to the method, deep extraction of chromium and iron in the ferrochrome raw material is achieved through the two steps of leaching and oxidation, the chromium leaching rate and the iron leaching rate are high and can both reach 99.0% or above, the acidity of the obtained leachate is low, ferrochrome proportion blending is achieved at the same time, the iron-chromium flow battery electrolyte can be directly prepared, and the method has important value for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow batteries, and specifically relates to a method for preparing a chromium-iron leaching solution and its application. Background Art

[0002] As an efficient and large-scale energy storage electrochemical device, the performance of the electrolyte of a ferrochromium flow battery directly determines the energy density and cycle stability of the battery. At present, the key material for the electrolyte of a ferrochromium flow battery is a mixed solution of chromium chloride-ferrous chloride, and its preparation mainly relies on chromium chloride hexahydrate (CrCl 3 ·6H 2 O) and ferrous chloride tetrahydrate (FeCl 2 ·4H 2 O) as raw materials. However, there are some defects in the preparation processes of chromium chloride hexahydrate and ferrous chloride tetrahydrate in the prior art. Chromium chloride hexahydrate is usually prepared from chromite through multiple processes such as oxidative leaching and separation and transformation. In this process, on the one hand, it is necessary to remove iron and other associated components in chromite, and the finally obtained hexavalent chromium salt needs to be further reduced to trivalent chromium salt. This process is not only cumbersome, but also involves high energy consumption and high cost; on the other hand, the iron in chromite is finally discarded in the form of chromite slag containing hexavalent chromium, which is listed as hazardous waste, not only causing waste of iron resources, but also bringing serious environmental problems.

[0003] The prior art has sought some solutions. For example, CN116826127A discloses a method for preparing an electrolyte for a ferrochromium flow battery, in which a chromium-iron raw material is mixed with hydrochloric acid to obtain a leaching solution. The leaching solution has a high acidity, and a large amount of ammonium chloride or ammonium bicarbonate, etc. is required for neutralization in the later production of the electrolyte product; a large amount of hydrogen is generated during the acid dissolution leaching process, which is not suitable for industrial scale-up production and has high risk.

[0004] CN118099495A discloses a method for preparing a ferrochromium electrolyte by leaching carbon chromium iron with ferric chloride. Ferric chloride is used to dissolve carbon chromium iron, then iron powder is added to the solution to precipitate chromium chloride as chromium hydroxide, and then iron is removed, thereby obtaining a ferrous chloride solution and solid chromium hydroxide, and then subsequent treatments are carried out respectively to obtain ferrous chloride crystals and chromium chloride crystals, and finally compounded into a ferrochromium electrolyte. This method requires a series of technological processes to separate and compound iron and chromium respectively, with numerous steps, and is not applicable to high-carbon chromium iron.

[0005] CN115832378A discloses a method for preparing a key material for an electrolyte and its application, in which materials of chromium and iron metals are added to hydrochloric acid for chlorination acidolysis to obtain a key material for the electrolyte. This method only uses hydrochloric acid for acidolysis, and the obtained acidolysis solution has a high acidity. Post-treatment is still required for preparing the electrolyte, and the acid leaching rate of chromium iron is not high, which easily causes waste of resources.

[0006] Therefore, it is of great significance to develop a technical route for preparing electrolyte materials with high efficiency, low cost and environmental friendliness. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for preparing a chromium-iron leaching solution and its application, so as to achieve efficient leaching of chromium-iron metal, reduce the acidity of the leaching solution, and realize the preparation of an iron-chromium redox flow battery electrolyte by blending chromium-iron.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a method for preparing a chromium-iron leaching solution, and the method includes the following steps:

[0010] (1) At least one-stage leaching of the chromium-iron raw material with hydrochloric acid, followed by solid-liquid separation, finally obtaining a leaching solution and a leaching residue;

[0011] (2) Mixing the leaching solution, the leaching residue and ferric chloride for hydrothermal reaction, and performing solid-liquid separation after the reaction ends to obtain the chromium-iron leaching solution.

[0012] The method provided by the present invention first realizes partial extraction of chromium and iron in the chromium-iron raw material through multi-stage leaching, and then adds the oxidant ferric chloride under hydrothermal conditions to deeply extract chromium and iron in the residue. On the one hand, it realizes efficient leaching of chromium and iron in the chromium-iron raw material, with high leaching rates of chromium and iron, and low chromium and iron contents in the obtained leaching residue, which is general industrial solid waste and can be directly used as building materials, reducing resource waste; on the other hand, the obtained leaching solution can be directly used to prepare an iron-chromium redox flow battery electrolyte, avoiding hexavalent chromium pollution, and at the same time realizing the blending of chromium-iron ratio, and having low acidity. The low-acidity leaching solution does not require a large amount of ammonium chloride or ammonium bicarbonate for neutralization during the later production process of preparing the electrolyte product, and can directly prepare the iron-chromium redox flow battery electrolyte, which has important value for industrial production.

[0013] Preferably, the chromium-iron raw material in step (1) includes any one or at least two combinations of chromium-iron, chromium-based alloy, chromium-containing cast iron or chromium-iron-containing slag. Typical but non-limiting combinations include the combination of chromium-iron and chromium-based alloy, the combination of chromium-containing cast iron and chromium-iron-containing slag, the combination of chromium-iron, chromium-based alloy and chromium-containing cast iron, the combination of chromium-based alloy, chromium-containing cast iron and chromium-iron-containing slag, or the combination of chromium-iron, chromium-based alloy, chromium-containing cast iron and chromium-iron-containing slag.

[0014] Preferably, the particle size of the chromium-iron raw material in step (1) is 20 - 300 μm, for example, it can be 30 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] Preferably, the mass fraction of the hydrochloric acid solution in step (1) is 10-37%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35% or 37%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0016] Preferably, the mass ratio of the hydrochloric acid solution to the chromium-containing iron raw material in step (1) is (4-20):1, for example, it can be 4:1, 5:1, 8:1, 10:1, 12:1, 15:1, 18:1 or 20:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0017] Preferably, the temperature of the leaching in step (1) is 40-120°C, for example, it can be 40°C, 50°C, 60°C, 80°C, 100°C or 120°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0018] Preferably, the time of the leaching in step (1) is 0.5-10 h, for example, it can be 0.5 h, 1 h, 3 h, 5 h, 8 h or 10 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0019] Preferably, the leaching method in step (1) includes countercurrent leaching.

[0020] Preferably, the dosage of ferric chloride in step (2) is 0.2-0.8 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue, for example, it can be 0.2 times, 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times or 0.8 times, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] The theoretical dosage is calculated according to the stoichiometric coefficients of the reaction equations of ferric chloride with chromium and iron respectively. The reaction equations are as follows:

[0022] 3FeCl 3 +Cr→3Fe 2+ +Cr 3+ +9Cl -

[0023] 2FeCl 3 +Fe→3Fe 2+ +6Cl -

[0024] Preferably, the temperature of the hydrothermal reaction in step (2) is 60-180 °C, for example, it can be 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 150 °C, 160 °C or 180 °C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the time of the hydrothermal reaction in step (2) is 2-8 h, for example, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0026] Preferably, the hydrogen ion concentration of the ferrochrome leaching solution in step (2) is 0.01-0.3 M, for example, it can be 0.01 M, 0.05 M, 0.1 M, 0.15 M, 0.2 M, 0.25 M or 0.3 M, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0027] As a preferred technical solution of the method provided by the present invention, the method comprises the following steps:

[0028] (1) Mix a hydrochloric acid solution with a mass fraction of 10-37% and a chromium-iron-containing raw material with a particle size of 20-300 μm in a mass ratio of (4-20):1, and perform at least one-stage countercurrent leaching. The temperature of each stage of the leaching is 40-120 °C, and the time of each stage of the leaching is 0.5-10 h, finally obtaining a first-stage leaching solution and leaching residue;

[0029] (2) Mix the first-stage leaching solution, leaching residue and ferric chloride for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.2-0.8 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The temperature of the hydrothermal reaction is 60-180 °C, the time is 2-8 h, and after the reaction, solid-liquid separation is carried out to obtain a ferrochrome leaching solution and a final residue. The hydrogen ion concentration of the ferrochrome leaching solution is 0.01-0.3 M.

[0030] In the second aspect, the present invention provides an application of the method for preparing a ferrochrome leaching solution described in the first aspect, and the method for preparing a ferrochrome leaching solution is applied to the preparation of an iron-chromium flow battery;

[0031] The ferrochrome leaching solution is used to prepare an electrolyte for an iron-chromium flow battery.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] The method provided by the present invention realizes the deep extraction of chromium and iron in ferrochrome raw materials through two steps of leaching and oxidation. The leaching rates of chromium and iron are high, both reaching more than 99.0%. The obtained leaching solution has a low acidity, and at the same time, the chromium-iron ratio is adjusted, and the electrolyte of the iron-chromium flow battery can be directly prepared, which has important value for industrial production. Detailed Embodiments

[0034] The technical solution of the present invention will be further described below through specific embodiments.

[0035] For clearly illustrating the technical solution of the present invention, in the specific embodiments, the composition of ferrochrome includes: Cr 50 wt%, Fe 30 wt%, Si 3 wt%, C 7 wt%, and the balance is other metal impurities such as Al, V, Mg, Mn.

[0036] The composition of the chromium-based alloy includes: Cr 50 wt%, Fe 5 wt%, Si 0.5 wt%, C 0.3 wt%, and the balance is other metal impurities such as Ni, Mo, Co, Al.

[0037] The composition of chromium-containing cast iron includes: Cr 15 wt%, Fe 70 wt%, Si 1 wt%, C 3 wt%, and the balance is other metal impurities such as Mo, Ni, Mn.

[0038] Example 1

[0039] This example provides a method for preparing a ferrochrome leaching solution, and the method includes the following steps:

[0040] (1) A hydrochloric acid solution with a mass fraction of 30% and ferrochrome with a particle size of 40 μm are subjected to two-stage countercurrent leaching according to a mass ratio of 6:1. The temperature of each stage of leaching is 90 °C, and the time of each stage of leaching is 4 h. The specific process of countercurrent leaching is: ferrochrome is subjected to the first-stage leaching with the second-stage leaching solution to obtain a first-stage leaching solution and a first-stage leaching residue. The first-stage leaching residue is subjected to the second-stage leaching with hydrochloric acid to obtain a second-stage leaching solution and a second-stage leaching residue, and finally a first-stage leaching solution and a second-stage leaching residue are obtained;

[0041] (2) The obtained first-stage leaching solution, the second-stage leaching residue and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.46 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 120 °C for 5 h. After completion, filtration is carried out to obtain a ferrochrome leaching solution and a final residue at the same time.

[0042] Example 2

[0043] This example provides a method for preparing a ferrochrome leaching solution, and the method includes the following steps:

[0044] (1) A hydrochloric acid solution with a mass fraction of 10% is subjected to three-stage countercurrent leaching with a chromium-based alloy having a particle size of 300 μm at a mass ratio of 4:1. The temperature for each stage of leaching is 40 °C, and the time for each stage of leaching is 0.5 h. The specific process of countercurrent leaching is as follows: The chromium-based alloy is subjected to the first-stage leaching with the second-stage leaching solution to obtain the first-stage leaching solution and the first-stage leaching residue. The first-stage leaching residue is subjected to the second-stage leaching with the third-stage leaching solution to obtain the second-stage leaching solution and the second-stage leaching residue. The second-stage leaching residue is subjected to the third-stage leaching with hydrochloric acid to obtain the third-stage leaching solution and the third-stage leaching residue. Finally, the first-stage leaching solution and the third-stage leaching residue are obtained;

[0045] (2) The obtained first-stage leaching solution, third-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.2 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 60 °C for 2 h. After completion, filtration is carried out to obtain the chromium-iron leaching solution, and at the same time, the final residue is obtained.

[0046] Example 3

[0047] This example provides a method for preparing a chromium-iron leaching solution, and the method includes the following steps:

[0048] (1) A hydrochloric acid solution with a mass fraction of 37% is mixed with chromium-containing cast iron having a particle size of 20 μm for one-stage countercurrent leaching. The specific process is as follows: The hydrochloric acid solution and chromium iron are subjected to the first-stage countercurrent leaching at a mass ratio of 20:1 at 120 °C for 10 h, and solid-liquid separation is carried out to obtain the first-stage leaching solution and the first-stage leaching residue;

[0049] (2) The obtained first-stage leaching solution, first-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.8 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 180 °C for 8 h. After completion, filtration is carried out to obtain the chromium-iron leaching solution, and at the same time, the final residue is obtained.

[0050] Example 4

[0051] This example provides a method for preparing a chromium-iron leaching solution, and the method includes the following steps:

[0052] (1) The hydrochloric acid solution with a mass fraction of 37% is subjected to three-stage countercurrent leaching with ferrochrome having a particle size of 20 μm at a mass ratio of 20:1. The temperature of each stage of leaching is 40 °C, and the time of each stage of leaching is 10 h. The specific process of countercurrent leaching is as follows: The ferrochrome is subjected to the first-stage leaching with the second-stage leaching solution to obtain the first-stage leaching solution and the first-stage leaching residue. The first-stage leaching residue is subjected to the second-stage leaching with the third-stage leaching solution to obtain the second-stage leaching solution and the second-stage leaching residue. The second-stage leaching residue is subjected to the third-stage leaching with hydrochloric acid to obtain the third-stage leaching solution and the third-stage leaching residue. Finally, the first-stage leaching solution and the third-stage leaching residue are obtained;

[0053] (2) The obtained first-stage leaching solution, the third-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.6 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 180 °C for 7 h. After completion, filtration is carried out to obtain the ferrochrome leaching solution and the final residue at the same time.

[0054] Example 5

[0055] This example provides a method for preparing a ferrochrome leaching solution, and the method includes the following steps:

[0056] (1) The hydrochloric acid solution with a mass fraction of 10% is subjected to four-stage countercurrent leaching with a chromium-based alloy having a particle size of 40 μm at a mass ratio of 18:1. The temperature of each stage of leaching is 110 °C, and the time of each stage of leaching is 8 h. The specific process of countercurrent leaching is as follows: The chromium-based alloy is subjected to the first-stage leaching with the second-stage leaching solution to obtain the first-stage leaching solution and the first-stage leaching residue. The first-stage leaching residue is subjected to the second-stage leaching with the third-stage leaching solution to obtain the second-stage leaching solution and the second-stage leaching residue. The second-stage leaching residue is subjected to the third-stage leaching with the fourth-stage leaching solution to obtain the third-stage leaching solution and the third-stage leaching residue. The third-stage leaching residue is subjected to the fourth-stage leaching with hydrochloric acid to obtain the fourth-stage leaching residue and the fourth-stage leaching solution. Finally, the first-stage leaching solution and the fourth-stage leaching residue are obtained;

[0057] (2) The obtained first-stage leaching solution, the fourth-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.3 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 170 °C for 8 h. After completion, filtration is carried out to obtain the ferrochrome leaching solution and the final residue at the same time.

[0058] Example 6

[0059] This example provides a method for preparing a ferrochrome leaching solution, and the method includes the following steps:

[0060] (1) A hydrochloric acid solution with a mass fraction of 35% and chromium-containing cast iron with a particle size of 100 μm are subjected to two-stage countercurrent leaching at a mass ratio of 20:1. The temperature of each stage of leaching is 100 °C, and the time of each stage of leaching is 9.5 h. The specific process of countercurrent leaching is as follows: The chromium-containing cast iron is subjected to the first-stage leaching with the second-stage leaching solution to obtain the first-stage leaching solution and the first-stage leaching residue. The first-stage leaching residue is subjected to the second-stage leaching with hydrochloric acid to obtain the second-stage leaching solution and the second-stage leaching residue, and finally the first-stage leaching solution and the second-stage leaching residue are obtained;

[0061] (2) The obtained first-stage leaching solution, second-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.5 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 150 °C for 6 h. After completion, filtration is carried out to obtain the chromium-iron leaching solution, and at the same time, the final residue is obtained.

[0062] Example 7

[0063] This example provides a method for preparing a chromium-iron leaching solution, and the method includes the following steps:

[0064] (1) A hydrochloric acid solution with a mass fraction of 30% and chromium-iron with a particle size of 40 μm are mixed for one-stage countercurrent leaching. The liquid-solid mass ratio of leaching is 6:1, the temperature is 90 °C, and the time is 4 h. The specific process is as follows: The hydrochloric acid solution and chromium-iron are subjected to the first-stage countercurrent leaching, and solid-liquid separation is carried out to obtain the first-stage leaching solution and the first-stage leaching residue;

[0065] (2) The obtained first-stage leaching solution, first-stage leaching residue, and ferric chloride are mixed for hydrothermal reaction. Among them, the dosage of ferric chloride is 0.46 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the leaching residue. The reaction is carried out at 120 °C for 5 h. After completion, filtration is carried out to obtain the chromium-iron leaching solution, and at the same time, the final residue is obtained.

[0066] Example 8

[0067] This example provides a method for preparing a chromium-iron leaching solution. Compared with Example 1, the temperature of the hydrothermal reaction in step (2) is controlled at 40 °C, and the rest are the same as in Example 1.

[0068] Example 9

[0069] This example provides a method for preparing a chromium-iron leaching solution. Compared with Example 1, the temperature of the hydrothermal reaction in step (2) is controlled at 200 °C, and the rest are the same as in Example 1.

[0070] Example 10

[0071] This example provides a method for preparing a chromium-iron leaching solution. Compared with Example 1, the dosage of ferric chloride in step (2) is controlled at 1 times the theoretical dosage, and the rest are the same as in Example 1.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a chromium-iron leaching solution. Compared with Example 1, in step (2), ferric chloride is not added, and the rest are the same as in Example 1.

[0074] Comparative Example 2

[0075] This comparative example provides a method for preparing a chromium-iron leaching solution, and the method includes the following steps:

[0076] A hydrochloric acid solution with a mass fraction of 30%, chromium iron with a particle size of 40 μm, and ferric chloride are mixed for hydrothermal reaction. Among them, the liquid-solid mass ratio of the hydrochloric acid solution to the chromium iron is 6:1, and the dosage of ferric chloride is 0.46 times the theoretical dosage of ferric chloride for reacting with chromium and iron in the chromium iron. The reaction is carried out at 120 °C for 5 h. After completion, filtration is carried out to obtain the chromium-iron leaching solution, and at the same time, the final residue is obtained.

[0077] That is, hydrochloric acid, ferric chloride, and chromium iron are subjected to hydrothermal reaction in one step, and the rest of the process parameters are the same as in Example 1.

[0078] The chromium and iron leaching rates of the chromium-iron leaching solutions prepared in the examples and comparative examples are calculated, and the chromium, iron, and hydrogen ion concentrations in the leaching solutions and the chromium and iron contents in the leaching residues are measured. The results are listed in Table 1.

[0079] The measurement method is as follows:

[0080] The chromium and iron contents in the leaching residue: The leaching residue is melted with a mixed flux of sodium carbonate and sodium tetraborate and then dissolved in hydrochloric acid. The obtained dissolved solution is diluted to a chromium and iron concentration of 1-10 ppm, and the chromium and iron contents are measured by inductively coupled plasma atomic emission spectrometry. The chromium and iron contents are calculated according to the proportion of the solution volume.

[0081] Chromium and iron leaching rates: The leaching solution is diluted to a chromium and iron concentration of 1-10 ppm, and the chromium and iron contents are measured by inductively coupled plasma atomic emission spectrometry. The chromium and iron contents therein are calculated according to the proportion of the solution volume, and the chromium and iron leaching rates are calculated through the chromium and iron contents in the raw materials, leaching residues, and leaching solutions.

[0082] Chromium concentration in the leaching solution: The ferric iron ions in the chromium-iron leaching solution obtained in step (2) are shielded with a phosphoric acid-sulfuric acid mixture, and the concentration of trivalent chromium ions is measured by using the ultraviolet-visible absorption characteristic wavelength of trivalent chromium ions. According to the different absorbances of different trivalent chromium ion concentrations, the chromium concentration is calculated by matching with the standard test curve.

[0083] Iron concentration in the leaching solution: The Fe in the leaching solution is reduced to Fe by hydroxylamine hydrochloride 3+ by 2+, in sulfuric acid and phosphoric acid media, using sodium diphenylamine sulfonate as an indicator, titrate with a standard potassium dichromate titrant solution, and calculate the concentration of iron.

[0084] H+ concentration in the leachate: Add sodium fluoride masking agent to the leachate, then titrate with a standard sodium hydroxide solution using an automatic potentiometric titrator. The turning point of the titration curve (E-V curve) is the stoichiometric point, and calculate the H+ concentration. + concentration: Add sodium fluoride masking agent to the leachate, then titrate with a standard sodium hydroxide solution using an automatic potentiometric titrator. The turning point of the titration curve (E-V curve) is the stoichiometric point, and calculate the H+ concentration. + concentration.

[0085] Table 1

[0086]

[0087]

[0088] It can be seen from Table 1 that:

[0089] (1) The preparation method of the low-acid ferrochrome leachate provided in Examples 1-10 of the present invention first undergoes multi-stage countercurrent leaching, and then hydrothermal leaching with the oxidant ferric chloride is carried out to achieve efficient leaching of chromium and iron in the raw materials. The leaching rates of chromium and iron are >99%, and the H+ concentration in the leachate is <0.15 M. In Examples 8-10, when the hydrothermal temperature is too high or too low, and when the amount of ferric chloride used is too high, the leaching effect decreases slightly.

[0090] (2) Comparing Example 1 with Comparative Example 1, when ferric chloride is not added, chromium and iron in the n (n≥1)-stage leaching residue cannot be completely leached, the leaching rates of chromium and iron in the ferrochrome leachate decrease, and the H+ + concentration increases, increasing the cost of the subsequent production of the electrolyte. In Comparative Example 2, hydrothermal reaction is directly carried out without leaching ferrochrome, and the leaching effect is also poor.

[0091] In summary, the method provided by the present invention realizes the deep extraction of chromium and iron in the ferrochrome raw materials through two steps of leaching and oxidation. The leaching rates of chromium and iron are high, both reaching over 99.0%. The obtained leachate has a low acidity, and at the same time, the chromium-iron ratio is adjusted, and the iron-chromium flow battery electrolyte can be directly prepared, which has important value for industrial production.

[0092] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a ferrochrome leaching solution, characterized in that: The method comprises the following steps: (1) using hydrochloric acid to perform at least one stage of leaching on the chromium-containing raw material, and performing solid-liquid separation to finally obtain a leachate and a leaching residue; (2) The leaching solution, leaching residue and ferric chloride are mixed for hydrothermal reaction, and after the reaction is completed, solid-liquid separation is performed to obtain the ferrochrome leaching solution.

2. The method according to claim 1, characterized in that The ferrochromium-containing raw material in step (1) comprises any one of ferrochromium, chromium-based alloy, chromium-containing cast iron or ferrochromium-containing slag, or a combination of at least two thereof; Preferably, the particle size of the ferrochrome raw material in step (1) is 20-300 μm.

3. The method according to claim 1 or 2, characterized in that: The mass fraction of the hydrochloric acid solution in step (1) is 10-37%; Preferably, the mass ratio of the hydrochloric acid solution in step (1) to the ferrochromium-containing raw material is (4-20):

1.

4. The method according to any one of claims 1 to 3, characterized in that: The leaching temperature in step (1) is 40-120° C. Preferably, the leaching time in step (1) is 0.5-10 h.

5. The method according to any one of claims 1 to 4, characterized in that: The leaching method in step (1) includes countercurrent leaching.

6. The method according to any one of claims 1 to 5, characterized in that: The amount of ferric chloride used in step (2) is 0.2-0.8 times the theoretical amount of ferric chloride required to react with chromium and iron in the leached residue.

7. The method according to any one of claims 1 to 6, characterized in that: The temperature of the hydrothermal reaction in step (2) is 60-180°C; Preferably, the hydrothermal reaction time in step (2) is 2-8 hours.

8. The method according to any one of claims 1 to 7, characterized in that: The hydrogen ion concentration of the ferrochrome leaching solution in step (2) is 0.01-0.3M.

9. The method according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: (1) mixing a hydrochloric acid solution having a mass fraction of 10-37% and a chromium-containing ferrochrome raw material having a particle size of 20-300 μm in a mass ratio of (4-20):1, and performing at least one stage of countercurrent leaching, wherein the leaching temperature of each stage is 40-120° C., and the leaching time of each stage is 0.5-10 h, and finally obtaining a first-stage leachate and a leaching residue; (2) mixing the first-stage leachate, the leach residue and ferric chloride for a hydrothermal reaction, wherein the amount of ferric chloride used is 0.2-0.8 times the theoretical amount of ferric chloride for reacting with the chromium and iron in the leach residue, the temperature of the hydrothermal reaction is 60-180° C., the time is 2-8 hours, and after the reaction, the solid and liquid are separated to obtain a ferrochrome leachate and a final slag, and the hydrogen ion concentration of the ferrochrome leachate is 0.01-0.3M.

10. An application of the method for preparing ferrochrome leaching solution according to any one of claims 1 to 9, characterized in that: The method for preparing ferrochromium leaching solution is applied to preparing iron-chromium flow battery; The ferrochromium leaching solution is used to prepare an electrolyte for an iron-chromium liquid flow battery.

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