CN117457955B - Method for preparing iron-chromium electrolyte by using carbon ferrochromium - Google Patents
Method for preparing iron-chromium electrolyte by using carbon ferrochromium Download PDFInfo
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Abstract
The invention relates to the technical field of electrolyte production, in particular to a method for preparing an iron-chromium electrolyte by using carbon ferrochromium. The method comprises the following steps: s1, leaching carbon ferrochrome with hydrochloric acid to obtain a ferrochrome solution; s2, evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a ferrous chloride crude product and a first chromium chloride solution; s3, adding water, heating and dissolving the crude ferrous chloride, and recrystallizing to obtain recrystallized ferrous chloride; oxidizing a small amount of ferrous chloride in the first chromium chloride solution, evaporating, concentrating, cooling and crystallizing to obtain chromium chloride crystals containing ferric trichloride; adding water and a reducing agent to reduce ferric trichloride in chromium chloride crystals to obtain a mixed solution for removing impurities; s4, mixing the recrystallized ferrous chloride, the purified mixed solution, hydrochloric acid and water according to a proportion, and compounding into the iron-chromium electrolyte. The method takes the carbon ferrochrome as the raw material, does not introduce impurities in the purification process, can prepare the ferrochrome electrolyte with high purity, and has the advantage of low cost.
Description
Technical Field
The invention relates to the technical field of electrolyte production, in particular to a preparation method of an iron-chromium electrolyte, the electrolyte and application thereof.
Background
As renewable energy sources such as wind energy, solar energy, and the like rapidly develop, development of large-scale energy storage systems is urgently needed to achieve efficient storage and utilization of such renewable energy sources with intermittent and unstable output characteristics. The iron-chromium redox flow battery is the flow battery which is originally proposed and commercially applied, has the remarkable advantages of mutually independent system energy and power, low material cost, easy expansion, high safety, high response speed, long cycle life, high energy efficiency and the like, and is a large-scale energy storage product with huge potential.
The electrolyte is used as a carrier of active substances in the iron-chromium redox flow battery, and plays a vital role in the performance of the battery. NASA in 1974 proposed that ferrous chloride and chromium chloride are dissolved in hydrochloric acid as positive and negative electrolytes respectively, and to continuously improve electrochemical performance of a battery, an iron-chromium flow battery electrolyte has been developed to achieve discharge and charge by using Fe 3+/Fe2+ and Cr 3+/Cr2+ as positive and negative poles respectively and redox coupling in a mixed electrolyte of hydrochloric acid solution. Currently, the key material of the basic electrolyte of the iron-chromium flow battery is a mixed solution of chromium chloride, ferrous chloride and hydrogen chloride.
The prior art discloses a preparation method of a basic electrolyte material of an iron-chromium flow battery, which comprises the following steps: chinese patent CN112993358a discloses a method and system for preparing an electrolyte of an iron-chromium redox battery, which can be obtained by simply compounding the finished products of ferrous chloride, chromium chloride and hydrochloric acid, and the production process of ferrous chloride and chromium chloride is not mentioned. Cr 6+ is involved in the production process of chromium chloride in the prior art, so that the adverse effect on the environment and operators is large, the environmental protection pressure is high, and the selling price of the chromium chloride is 13000-16000 yuan/ton; the production cost is directly influenced by the production raw materials and the purification process of the ferrous chloride, and the selling price of the electronic grade ferrous chloride in the market is 8000-12000 yuan/ton. The method is to compound the produced ferrous chloride, chromium chloride, hydrochloric acid and water according to the required proportion, and the electrolyte produced by the method has high cost.
Chinese patent CN115832379a discloses that after adding a material containing iron metal and chromium metal into an acidic solution, mixing, performing solid-liquid separation to obtain a leachate, and selecting a impurity remover for the leachate to adsorb impurities or generate insoluble solids for removal, thereby obtaining a purified electrolyte. The impurity removing agent selected in the patent is mostly dissolved in water, impurities are removed and introduced, and all impurities can be removed only to within 50mg/L, and when the requirements of certain impurities with strict requirements, such as copper and nickel, are less than 10ppm, the technical means cannot be used.
Chinese patent CN 112234238B discloses a method for preparing an electrolyte of an iron-chromium redox battery, which comprises the steps of carrying out constant-current electrolysis on red mud, ferroferric oxide and the like, discarding impurities which cannot be dissolved in the electrolyte in the red mud to obtain ferrous chloride, and then compounding with purchased chromium chloride and hydrochloric acid. The method only relates to the production and purification of the ferrous chloride part, does not relate to the production of key material chromium chloride, and still can not effectively solve the problem of high cost of electrolyte.
Chinese patent CN 115832378A, CN 115832379A, CN115842148A discloses a preparation method and application of an electrolyte key material, wherein a material containing chromium metal, chromium hydroxide, iron metal, ferric oxide, ferroferric oxide, ferric hydroxide or ferrochrome alkali slag is added with hydrochloric acid solution for chloridizing acidolysis, and the electrolyte key material is obtained through solid-liquid separation and concentration. According to the method, the chromium-containing iron-containing material is subjected to acid dissolution to obtain the iron-chromium mixture, and the iron-chromium mixture is not subjected to purification treatment, so that the impurity content in the electrolyte obtained by the method is very high, and the electric performance requirement of the iron-chromium electrolyte cannot be met.
Chinese patent CN 113564680B discloses a method for purifying an iron-chromium electrolyte and the iron-chromium electrolyte thus obtained, which adopts an electrolysis method to remove impurities from the iron-chromium electrolyte, but the technology can only be applied to high-purity electrolytes. For example, this patent describes that "in the iron-chromium electrolyte to be purified of the present invention, the total concentration of impurity metal ions is 20ppm or less, preferably 10ppm or less, more preferably 5ppm or less, still more preferably 3ppm or less, and most preferably about 1 ppm", however, an iron-chromium electrolyte having a total concentration of impurity ions of < 20ppm is difficult to obtain. Therefore, the technology is only suitable for purifying high-purity electrolyte, and obviously limits the industrial application of the technical scheme.
There is a lack of methods in the prior art for producing high purity ferrochrome electrolyte at low cost.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provide a preparation method of an iron-chromium electrolyte, which takes carbon ferrochromium as a raw material, can prepare the iron-chromium electrolyte with high purity under the condition of no impurity introduction, and has the advantage of low cost.
In order to achieve one of the above objects, the present invention provides the following technical solutions:
provides a preparation method of an iron-chromium electrolyte, which comprises the following steps,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation, wherein the obtained liquid is a mixed solution of chromium chloride and ferrous chloride, and is called ferrochrome solution;
s2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride;
s3, adding water to dissolve the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals;
Adding an oxidant into the first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric trichloride, evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric trichloride;
Adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution to reduce ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution with impurities removed, wherein the mixed solution contains chromium chloride and ferrous chloride;
S4, mixing the purified ferrous chloride crystal with the purified mixed solution, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte.
The working principle of the preparation method of the iron-chromium electrolyte is as follows:
The main components of the carbon ferrochrome are chromium and iron, and the carbon ferrochrome comprises carbon and silicon which are insoluble in hydrochloric acid, and also comprises high-content impurities such as calcium, magnesium, manganese, copper, nickel and the like which are soluble in hydrochloric acid, and part of the impurities easily cause hydrogen evolution side reaction of a negative electrode, so that the carbon ferrochrome can be used for preparing an iron-chromium electrolyte after being leached by acid and the impurities are removed. Based on the method, the ferrochrome solution is evaporated, concentrated, cooled and crystallized, and the crude ferrous chloride and the first chromium chloride solution containing a small amount of ferrous chloride are separated, so that the iron content in the first chromium chloride solution is reduced, the first chromium chloride solution with low iron concentration is more beneficial to impurity removal, and the crude ferrous chloride and the first chromium chloride are convenient to purify respectively. Then recrystallizing the crude ferrous chloride to improve the purity of the ferrous chloride; meanwhile, the first chromium chloride solution is oxidized to oxidize ferrous chloride into ferric chloride, when the ferric chloride and chromium chloride are crystallized in a mixture system, impurities such as Ni 2+、Mn2+ and the like are divalent, fe 3+、Cr3+ is trivalent, and the impurities are not easy to enter crystal lattices to form mixed crystals when the ferric chloride and the chromium chloride are crystallized, so that the crystallization and purification of the first chromium chloride solution are facilitated. And then, after the chromium chloride crystal is dissolved, reducing ferric trichloride in the chromium chloride crystal into ferrous chloride, wherein the concentration of the ferric trichloride is low, the consumption of iron powder is small, and the purity of the obtained electrolyte can be ensured by using high-purity iron powder. And finally, mixing the purified ferrous chloride crystal, the impurity-removed mixed solution, hydrochloric acid and water according to a proportion to obtain the compound electrolyte.
In some embodiments, in step S1, the carbon ferrochrome is crushed to a particle size of < 100 mesh before adding the hydrochloric acid.
The leaching efficiency can be improved by crushing the carbon ferrochrome and then leaching.
In some embodiments, in step S1, the hydrochloric acid is warmed to 90 ℃ to 110 ℃ and carbon ferrochrome is leached.
Wherein, the temperature of 90-110 ℃ can effectively leach the iron and chromium elements in the carbon ferrochrome, and generate ferrous chloride and chromium chloride.
In some embodiments, in step S1, the concentration of the hydrochloric acid is 20% to 35%.
In some embodiments, in step S1, the leaching of carbon ferrochrome is ended when pH = -0.5 during the leaching of carbon ferrochrome.
The free acid in the leaching liquid can be controlled by controlling the pH value, and the leaching degree of the carbon ferrochrome can be reacted by using the pH value as an index, so that the production process can be effectively monitored.
In some embodiments, in step S2, the ferrochrome solution is evaporated to a total concentration of iron and chromium of 16% -18%.
The ferrochrome solution with the concentration is convenient for crystallization operation, and the solid-to-liquid ratio is about 1:2.
In some embodiments, in step S2, the ferrochrome solution is cooled to a temperature of 10 ℃ to 30 ℃ during crystallization. The crystallization temperature is optimal to crystallize ferrous chloride with less chromium chloride entrainment.
In some embodiments, in step S3, the oxidizing agent is one or a mixture of any two or more of oxygen, chlorine, hydrogen peroxide, or ozone.
The oxidant oxygen, chlorine, hydrogen peroxide or ozone does not contain impurities, so that the impurities are prevented from being introduced into the electrolyte.
In some embodiments, in step S3, the first chromium chloride solution is concentrated to a total of iron and chromium concentrations of 15% to 17% before cooling to crystallize.
The first chromium chloride solution at this concentration facilitates the crystallization operation and has a solids to liquid ratio of about 1:2.
In some embodiments, in step S3, the first chromium chloride solution is cooled to a temperature of 20 ℃ to 35 ℃ during crystallization.
In some embodiments, in step S3, the crude ferrous chloride is dissolved to a concentration of 19% -20% ferrous chloride, and the dissolution temperature is 50 ℃ -80 ℃.
The ferrous chloride solution of this concentration facilitates recrystallization and the resulting solid to liquid ratio is about 1:2.
In some embodiments, in step S3, after the first chromium chloride solution is cooled and crystallized, a mother solution is obtained, and the mother solution is circularly concentrated and crystallized until the impurity of the mother solution exceeds a threshold value, and the mother solution is discharged for other purposes.
The utilization rate of chromium chloride can be improved after the mother solution is circularly crystallized.
In some embodiments, in step S3, the iron powder is used in an amount of 1.05 to 1.2 times the theoretical amount of iron powder.
The dosage of the iron powder can ensure that Fe 3+ is completely reduced, and is convenient for controlling the reduction speed, so that chromium chloride does not form chromium hydroxide precipitate.
In some embodiments, in step S3, the temperature of the second chromium chloride solution is 60 ℃ to 80 ℃ during the reduction reaction; after dropping hydrochloric acid, the pH value of the second chromium chloride solution is less than 0.
And (3) dropwise adding hydrochloric acid to maintain the acidic condition of the solution system, so that chromium chloride does not form chromium hydroxide precipitate to be separated out.
The method for preparing the iron-chromium electrolyte by using the carbon ferrochromium has the following beneficial effects:
(1) According to the preparation method of the iron-chromium electrolyte, the carbon ferrochrome is used as a raw material of chromium and iron, the carbon ferrochrome is only counted by the content of chromium, the iron is relatively donated, the price of 100% chromium is about 18000 yuan/ton, the price of chromium chloride is about 68000 yuan/ton, and the raw material cost is greatly reduced.
(2) The technical scheme is skillfully designed by utilizing the difference of the saturation concentration of ferrous chloride and chromium chloride and the removal rate of impurities in different systems, and the crude ferrous chloride and the chromium chloride solution are separated and purified respectively. The purification only involves the crystallization process, no impurity is introduced, the purity of the electrolyte can be ensured, and the production process cost is low.
(3) The whole production process does not use the traditional chromium salt purification process, does not relate to hexavalent chromium, does not generate harmful substances, is clean, green and environment-friendly, and accords with the great trend of technical improvement.
(4) The method has low requirement on the purity of the raw materials, can obtain better purification even the raw materials with high impurities, is suitable for large-scale production and application, and has wide application range.
In order to achieve the second object, the present invention provides the following technical solutions:
An electrolyte is provided, which contains an iron-chromium electrolyte, and the iron-chromium electrolyte is prepared by the preparation method of the iron-chromium electrolyte.
In order to achieve the third object, the present invention provides the following technical solutions:
an iron-chromium redox flow battery is provided, which contains the electrolyte.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been illustrated, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Example 1
The preparation method of the ferrochrome electrolyte disclosed in the embodiment comprises the following steps,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation to obtain a liquid which is a ferrochrome solution.
Before hydrochloric acid is added into the carbon ferrochrome, the carbon ferrochrome is crushed to be 200 meshes in particle size, and then leaching treatment is carried out after the carbon ferrochrome is crushed, so that the leaching efficiency can be improved, and the recovery efficiency of the carbon ferrochrome can be improved.
The hydrochloric acid is industrial hydrochloric acid, the concentration of the industrial hydrochloric acid is 20%, the industrial hydrochloric acid is heated to 90 ℃ and carbon ferrochrome is leached, and the reaction speed of the heated hydrochloric acid can be effectively improved, so that the leaching efficiency is improved.
Wherein, in the process of leaching the carbon ferrochrome, when the pH value is minus 0.5, the carbon ferrochrome is leached.
S2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride;
The ferrochrome solution is evaporated and concentrated until the sum of iron and chromium concentration is 16%, the temperature of the ferrochrome solution is 10 ℃ when the ferrochrome solution is cooled and crystallized, the cooling and crystallizing temperature is determined according to the characteristics of the ferrochrome solution, and the temperature can efficiently cool and crystallize crystals of the ferrochrome solution.
S3, adding water to dissolve the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals; the ferrous chloride crude product is dissolved until the concentration of ferrous chloride is 19%, the dissolution temperature is 50 ℃, and the optimal temperature is 60 ℃. The crude ferrous chloride is dissolved until the concentration of ferrous chloride is 19%, so that recrystallization is facilitated. Meanwhile, the dissolution temperature is 50 ℃, so that the dissolution can be accelerated.
And after the dissolved ferrous chloride crude product is dissolved, recrystallizing so as to realize secondary purification of ferrous chloride.
Adding an oxidant into the obtained first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric chloride, evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric chloride; wherein, before cooling and crystallizing, the first chromium chloride solution is concentrated to the concentration of iron and chromium which is 16 percent. The temperature of the first chromium chloride solution is 10 ℃ when cooling and crystallizing. And cooling and crystallizing the first chromium chloride solution to obtain mother liquor, circularly concentrating and crystallizing the mother liquor until the impurity of the mother liquor exceeds a threshold value, improving the utilization rate of chromium chloride, and discharging the circularly concentrated mother liquor for other purposes.
The first chromium chloride solution still contains a small amount of ferrous chloride, if the mixture of chromium chloride and ferrous chloride is directly crystallized, impurities such as Ni, mn and the like have poor removal rate in crystallization, eutectic precipitation is easy to form in the mixture, and purification of the chromium chloride is not facilitated, so that the ferrous chloride with the same valence state as Ni and Mn is oxidized into ferric trichloride, and the removal rate of Ni and Mn in a chromium trichloride and ferric trichloride system is good in crystallization, and chromium chloride crystals with high purity can be obtained.
Adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution to reduce ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution with impurities removed, wherein the mixed solution contains chromium chloride and ferrous chloride; wherein,
The consumption of the iron powder is 1.05 times of the theoretical amount of the iron powder, and the consumption of the iron powder is larger than the theoretical value, so that the reduction effect is ensured. Wherein,
In the reduction reaction, the temperature of the second chromium chloride solution is 60 ℃; and (3) after the hydrochloric acid is added dropwise, the pH value of the second chromium chloride solution is less than 0, and the hydrochloric acid is added dropwise to maintain the acidic condition of the solution system, so that chromium chloride does not form chromium hydroxide to precipitate until Fe 3+ is completely reduced.
And dissolving the purified chromium chloride crystal, and carrying out reduction treatment on the purified chromium chloride and ferric chloride solution at the moment so that the ferric chloride can be reduced into ferrous chloride.
The oxidant is one or a mixture of more than two of oxygen, chlorine, hydrogen peroxide or ozone, and the oxygen, the chlorine, the hydrogen peroxide or the ozone of the oxidant are only oxygen atoms and hydrogen atoms, so that the oxidant does not contain impurities and the purity of the electrolyte is effectively ensured.
S4, mixing the purified ferrous chloride crystal with the purified mixed solution, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte.
The purified ferrous chloride crystal and the mixed solution are substances subjected to multiple impurity removal, so that the purity of the iron-chromium electrolyte can be effectively ensured.
Example 2
The preparation method of the ferrochrome electrolyte disclosed in the embodiment comprises the following steps,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation, wherein the obtained liquid is ferrochrome solution;
before hydrochloric acid is added into the carbon ferrochrome, the carbon ferrochrome is crushed to be 200 meshes in particle size, and then leaching treatment is carried out after the carbon ferrochrome is crushed, so that the leaching efficiency can be improved, and the recovery efficiency of the carbon ferrochrome can be improved.
The hydrochloric acid is industrial hydrochloric acid, the concentration of the industrial hydrochloric acid is 35%, the industrial hydrochloric acid is heated to 110 ℃ and carbon ferrochrome is leached, and the reaction speed of the heated hydrochloric acid can be effectively improved, so that the leaching efficiency is improved.
Wherein, in the process of leaching the carbon ferrochrome, when the pH=0.5, the carbon ferrochrome is leached.
S2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride;
The ferrochrome solution is evaporated and concentrated until the sum of iron and chromium concentrations is 18%, and is properly concentrated, so that the crystallization speed can be increased, and the ferrochrome solution with the concentration is convenient for cooling and crystallization.
When cooling and crystallizing, the temperature of the ferrochrome solution is 30 ℃, the cooling and crystallizing temperature is determined according to the characteristics of the ferrochrome solution, and the temperature can efficiently cool and crystallize crystals of the ferrochrome solution.
S3, adding water to dissolve the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals; the ferrous chloride crude product is dissolved until the concentration of ferrous chloride is 20%, the dissolution temperature is 80 ℃, and the optimal temperature is 70 ℃. The ferrous chloride solution at this concentration facilitates recrystallization. The crude ferrous chloride is dissolved until the concentration of ferrous chloride is 20%, so that recrystallization is convenient to occur. Meanwhile, the dissolution temperature is 80 ℃, so that the dissolution can be accelerated.
The dissolved ferrous chloride crude product can be recrystallized, so that the ferrous chloride is secondarily purified.
Adding an oxidant into the obtained first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric chloride, evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric chloride; wherein, before cooling and crystallizing, the first chromium chloride solution is concentrated to 17 percent of the sum of the iron and chromium concentrations. The temperature of the first chromium chloride solution is 35 ℃ when cooling and crystallizing. And the first chromium chloride solution is cooled and crystallized to obtain mother liquor, the mother liquor is circularly concentrated and crystallized until the impurity of the mother liquor exceeds a threshold value, the circularly concentrated mother liquor is discharged, and the mother liquor is circularly crystallized to recover and crystallize to the greatest extent, so that substances are recovered on one hand, and the discharge of pollutants is effectively reduced on the other hand.
The oxidant is one or a mixture of more than two of oxygen, chlorine, hydrogen peroxide or ozone, and the oxidant is only oxygen atoms and hydrogen atoms, and does not contain impurities, so that the purity of the electrolyte is effectively prevented from being influenced by the introduction of other chemical atomic impurities into the electrolyte, and the purity of the electrolyte is effectively ensured.
The first chromium chloride solution still contains a small amount of ferrous chloride, if the mixture of chromium chloride and ferrous chloride is directly crystallized, impurities such as Ni, mn and the like have poor removal rate in crystallization, eutectic precipitation is easy to form in the mixture, and purification of the chromium chloride is not facilitated, so that the ferrous chloride with the same valence state as Ni and Mn is oxidized into ferric trichloride, and the removal rate of Ni and Mn in a chromium trichloride and ferric trichloride system is good in crystallization, and chromium chloride crystals with high purity can be obtained.
Adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution to reduce ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution with impurities removed, wherein the mixed solution contains chromium chloride and ferrous chloride; wherein,
The amount of the iron powder is 1.2 times of the theoretical amount of the iron powder. Wherein,
In the reduction reaction, the temperature of the second chromium chloride solution is 80 ℃; and (3) dropwise adding hydrochloric acid to maintain the acidic condition of the solution system, so that chromium chloride does not form chromium hydroxide to precipitate until Fe 3+ is completely reduced.
S4, mixing the purified ferrous chloride crystal with the purified mixed solution, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte.
The purified ferrous chloride crystal and the mixed solution are substances subjected to multiple impurity removal, so that the purity of the iron-chromium electrolyte can be effectively ensured.
Example 3
The preparation method of the ferrochrome electrolyte disclosed in the embodiment comprises the following steps,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation, wherein the obtained liquid is ferrochrome solution;
Before hydrochloric acid is added into the carbon ferrochrome, the carbon ferrochrome is crushed to 300 meshes in particle size, and then leaching treatment is carried out after the carbon ferrochrome is crushed, so that the leaching efficiency can be improved, and the recovery efficiency of the carbon ferrochrome can be improved.
The hydrochloric acid is industrial hydrochloric acid, the concentration of the industrial hydrochloric acid is 30%, the industrial hydrochloric acid is heated to 100 ℃ and carbon ferrochrome is leached, and the reaction speed of the heated hydrochloric acid can be effectively improved, so that the leaching efficiency is improved.
Wherein, in the process of leaching the carbon ferrochrome, when the pH=0.3, the carbon ferrochrome is leached.
When the pH value is slightly acidic, the excessive hydrochloric acid indicates that the carbon ferrochrome is leached, and the leaching degree of the carbon ferrochrome can be accurately checked by using the pH value as an index, so that the production process can be effectively monitored.
S2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride;
the ferrochrome solution is evaporated and concentrated until the sum of iron and chromium concentrations is 17%, and is properly concentrated, so that the crystallization speed can be increased, and the ferrochrome solution with the concentration is convenient for cooling and crystallization.
When cooling and crystallizing, the temperature of the ferrochrome solution is 25 ℃, the cooling and crystallizing temperature is determined according to the characteristics of the ferrochrome solution, and the temperature can efficiently cool and crystallize crystals of the ferrochrome solution.
S3, adding water to dissolve the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals; the ferrous chloride crude product is dissolved until the concentration of ferrous chloride is 19.5%, the dissolution temperature is 70 ℃, and the optimal temperature is 65 ℃. The ferrous chloride solution at this concentration facilitates recrystallization. The crude ferrous chloride is dissolved until the concentration of the ferrous chloride is 19.5%, so that recrystallization is convenient to occur. Meanwhile, the dissolution temperature is 60 ℃, so that the dissolution can be accelerated.
The dissolved ferrous chloride crude product can be recrystallized, so that the ferrous chloride is secondarily purified.
Adding an oxidant into the obtained first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric chloride, evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric chloride; wherein, before cooling and crystallizing, the first chromium chloride solution is concentrated to the concentration of iron and chromium which is 16 percent. The temperature of the first chromium chloride solution is 25 ℃ when cooling and crystallizing. And cooling and crystallizing the first chromium chloride solution to obtain mother liquor, circularly concentrating and crystallizing the mother liquor until the impurity of the mother liquor exceeds a threshold value, improving the utilization rate of chromium chloride, and discharging the circularly concentrated mother liquor for other purposes.
The oxidant is one or a mixture of more than two of oxygen, chlorine, hydrogen peroxide or ozone, and the oxidant is only oxygen atoms and hydrogen atoms, does not contain impurities and effectively avoids other impurities from being introduced into the electrolyte.
The first chromium chloride solution still contains a small amount of ferrous chloride, if the mixture of chromium chloride and ferrous chloride is directly crystallized, cu, ni, mn and other impurities have poor removal rate during crystallization, eutectic precipitation is easy to form in the mixture, and purification of the chromium chloride is not facilitated, so that the ferrous chloride with the same valence state as Cu, ni and Mn is oxidized into ferric trichloride, and the Cu, ni and Mn removal rate during crystallization is good in a chromium trichloride and ferric trichloride system, so that chromium chloride crystals with high purity can be obtained.
Adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution to reduce ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution with impurities removed, wherein the mixed solution contains chromium chloride and ferrous chloride; wherein,
The consumption of the iron powder is 1.1 times of the theoretical amount of the iron powder, and the consumption of the iron powder is larger than the theoretical value, so that the reduction effect is ensured. Wherein,
The temperature of the second chromium chloride solution is 70 ℃ during the reduction reaction; and (3) dropwise adding hydrochloric acid to maintain the acidic condition of the solution system, so that chromium chloride does not form chromium hydroxide to precipitate until Fe 3+ is completely reduced.
And dissolving the purified chromium chloride crystal, and carrying out reduction treatment on the purified solution of chromium chloride and ferric trichloride at the moment, so that the ferric trichloride can be reduced into ferrous chloride, and recovering to obtain the ferrous chloride.
S4, mixing the purified ferrous chloride crystal with the purified mixed solution, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte.
The purified ferrous chloride crystal and the mixed solution are substances subjected to multiple impurity removal, so that the purity of the iron-chromium electrolyte can be effectively ensured.
Example 4
The preparation method of the ferrochrome electrolyte disclosed in the embodiment comprises the following steps,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation, wherein the obtained liquid is ferrochrome solution;
Before hydrochloric acid is added into the carbon ferrochrome, the carbon ferrochrome is crushed to 250 meshes in particle size, and then leaching treatment is carried out after the carbon ferrochrome is crushed, so that the leaching efficiency can be improved, and the recovery efficiency of the carbon ferrochrome can be improved.
The hydrochloric acid is industrial hydrochloric acid, the concentration of the industrial hydrochloric acid is 28%, the industrial hydrochloric acid is heated to 109 ℃ and carbon ferrochrome is leached, and the reaction speed of the heated hydrochloric acid can be effectively improved, so that the leaching efficiency is improved.
Wherein, in the process of leaching the carbon ferrochrome, when the pH=0.4, the carbon ferrochrome is leached.
When the pH value is slightly acidic, the excessive hydrochloric acid indicates that the carbon ferrochrome is leached, and the leaching degree of the carbon ferrochrome can be accurately checked by using the pH value as an index, so that the production process can be effectively monitored.
S2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride;
the ferrochrome solution is evaporated and concentrated until the sum of iron and chromium concentrations is 17%, and is properly concentrated, so that the crystallization speed can be increased, and the ferrochrome solution with the concentration is convenient for cooling and crystallization.
When cooling and crystallizing, the temperature of the ferrochrome solution is 20 ℃, the cooling and crystallizing temperature is determined according to the characteristics of the ferrochrome solution, and the temperature can efficiently cool and crystallize crystals of the ferrochrome solution.
S3, adding water to dissolve the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals; the ferrous chloride crude product is dissolved until the concentration of ferrous chloride is 19.1%, and the dissolution temperature is 60 ℃. The ferrous chloride solution at this concentration facilitates recrystallization. The crude ferrous chloride is dissolved until the concentration of the ferrous chloride is 19-20%, so that recrystallization is convenient to occur. Meanwhile, the dissolution temperature is 60 ℃, so that the dissolution can be accelerated.
The dissolved ferrous chloride crude product can be recrystallized, so that the ferrous chloride is secondarily purified.
Adding an oxidant into the obtained first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric chloride, evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric chloride; wherein, before cooling and crystallizing, the first chromium chloride solution is concentrated to 17 percent of the sum of the iron and chromium concentrations. The temperature of the first chromium chloride solution is 20 ℃ when cooling and crystallizing. And cooling and crystallizing the first chromium chloride solution to obtain mother liquor, circularly concentrating and crystallizing the mother liquor until the impurity of the mother liquor exceeds a threshold value, improving the utilization rate of chromium chloride, and discharging the circularly concentrated mother liquor for other purposes.
The oxidant is one or a mixture of more than two of oxygen, chlorine, hydrogen peroxide or ozone, and the oxidant is only oxygen atoms and hydrogen atoms, does not contain impurities and effectively avoids other impurities from being introduced into the electrolyte.
The first chromium chloride solution still contains a small amount of ferrous chloride, if the mixture of chromium chloride and ferrous chloride is directly crystallized, impurities such as Ni, mn and the like have poor removal rate in crystallization, eutectic precipitation is easy to form in the mixture, and purification of the chromium chloride is not facilitated, so that the ferrous chloride with the same valence state as Ni and Mn is oxidized into ferric trichloride, and the removal rate of Ni and Mn in a chromium trichloride and ferric trichloride system is good in crystallization, and chromium chloride crystals with high purity can be obtained.
Adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution to reduce ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution with impurities removed, wherein the mixed solution contains chromium chloride and ferrous chloride; wherein,
The consumption of the iron powder is 1.1 times of the theoretical amount of the iron powder, and the consumption of the iron powder is larger than the theoretical value, so that the reduction effect is ensured. Wherein,
The temperature of the second chromium chloride solution is 70 ℃ during the reduction reaction; and (3) dropwise adding hydrochloric acid to maintain the acidic condition of the solution system, so that chromium chloride does not form chromium hydroxide to precipitate until Fe 3+ is completely reduced.
And dissolving the purified chromium chloride crystal, and carrying out reduction treatment on the purified solution of chromium chloride and ferric trichloride at the moment, so that the ferric trichloride can be reduced into ferrous chloride, and recovering to obtain the ferrous chloride.
S4, mixing the purified ferrous chloride crystal with the purified mixed solution, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte.
The purified ferrous chloride crystal and the mixed solution are substances subjected to multiple impurity removal, so that the purity of the iron-chromium electrolyte can be effectively ensured.
Test examples
To illustrate the quality of the iron-chromium electrolyte prepared by the invention, specific test examples are used for illustration:
Test example 1
The test example provides a method for producing electrolyte by using carbon ferrochrome, which comprises the following steps:
s1: crushing 1t of carbon ferrochrome to 200 meshes, adding 4.8t of industrial hydrochloric acid, heating to 90 ℃ to leach the carbon ferrochrome, reacting for 3 hours, dissolving until the pH of the solution is minus 0.5-0.5, and performing filter pressing to perform solid-liquid separation to obtain a mixed solution of chromium chloride and ferrous chloride, wherein the experimental example is recorded as a ferrochrome solution;
S2: evaporating and concentrating the ferrochrome solution to 17% of the sum of iron and chromium concentration, cooling to 20 ℃ for crystallization and centrifuging to obtain 1.1t of crude ferrous chloride and 3.7t of chromium chloride solution, wherein the chromium chloride solution contains a small amount of ferrous chloride;
S3, oxidizing ferrous chloride in the chromium chloride solution into ferric trichloride, concentrating to 16% of the sum of the iron and chromium concentration, cooling to 30 ℃ and crystallizing to obtain 1.1t of chromium chloride crystal qualified in impurity, and carrying out discharging treatment when the mother liquor is concentrated and crystallized in a circulating way until the impurity exceeds a preset value;
S4: adding 0.55t of water into 1.1t of chromium chloride crystal, heating to 60 ℃ to dissolve, adding 15kg of reduced iron powder to reduce ferric iron, dropwise adding hydrochloric acid in the reduction process to control the pH value to be less than 0 until the ORP value in the solution is less than 200mv, and carrying out solid-liquid separation on excessive iron powder to obtain a purified chromium chloride and ferrous chloride mixed solution;
S5: adding water for 0.35t into 1.1t of the crude ferrous chloride product obtained in the step S2, heating to 70 ℃ to melt, cooling to 20 ℃ to crystallize, and centrifugally separating to obtain purified ferrous chloride crystals for 0.5t;
S6: weighing a proper amount of products obtained by S4 and S5, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte with the required concentration.
Finally, the content of the purified substances in each step is shown in Table 1.
Table 1 test example 1 product test data for each step
The main components of the carbon ferrochrome are chromium and iron, and also contain Ca, mg, mn, cu, ni and other impurities which can be dissolved in hydrochloric acid, and some impurities easily cause hydrogen evolution side reaction of the cathode, so that the service life of the electrolyte is influenced. After the carbon ferrochrome is purified by the step of the test 1, the impurities of Ca, mg, mn, cu, ni in the obtained ferrochrome electrolyte 1 are lower than 50ppm, the purity is higher, and the chromium chloride and the ferrous chloride in the ferrochrome solution are used for preparing the electrolyte after being purified.
Test example 2
The test example provides a method for producing electrolyte by using carbon ferrochrome, which comprises the following steps:
S1: crushing 1t of carbon ferrochrome to 300 meshes, adding 4.8t of industrial hydrochloric acid, heating to 100 ℃ to leach the carbon ferrochrome, reacting for 2 hours, dissolving until the pH of the solution is minus 0.5-0.5, and performing filter pressing to perform solid-liquid separation to obtain a mixed solution of chromium chloride and ferrous chloride, wherein the experimental example is recorded as a ferrochrome solution;
S2: evaporating and concentrating the ferrochrome solution until the sum of iron and chromium concentration is 16.5%, cooling to 10 ℃ for crystallization and centrifugation to obtain 1.3t of crude ferrous chloride and 3.6t of chromium chloride solution, wherein the chromium chloride solution contains a small amount of ferrous chloride;
S3, oxidizing ferrous chloride in the chromium chloride solution into ferric trichloride, concentrating to 16.5% of the sum of the iron and chromium concentration, cooling to 30 ℃ for crystallization to obtain 1.2t of chromium chloride crystal, and discharging the mother liquor after circulating concentration crystallization until the impurity exceeds a preset value;
S4: adding 0.25t of water into 1.2t of chromium chloride crystal containing ferric trichloride, heating to 80 ℃ to dissolve, cooling to 30 ℃ to crystallize, obtaining 0.6t of chromium chloride crystal qualified in impurities, and carrying out outward discharge treatment when the mother liquor is concentrated and crystallized in a circulating way until the impurities exceed a preset value;
S5: adding 0.6t of qualified chromium chloride crystal containing ferric trichloride into 0.3t of water, heating to 80 ℃ to dissolve, adding 7.5kg of reduced iron powder to reduce ferric iron, dropwise adding hydrochloric acid in the reduction process to control pH to be less than 0 until ORP value in the solution is less than 200mv, and carrying out solid-liquid separation on excessive iron powder to obtain a purified chromium chloride and ferrous chloride mixed solution;
S6: adding water for 0.35t into 1.3t of the crude ferrous chloride product obtained in the step S2, heating to 70 ℃ to melt, cooling to 15 ℃ to crystallize, and centrifugally separating to obtain purified ferrous chloride crystals for 0.6t;
s7: weighing a proper amount of products obtained by S4 and S5, adding hydrochloric acid and water, and compounding into the iron-chromium electrolyte with the required concentration.
Finally, the content of the purified substances in each step is shown in Table 2.
Table 2 test example 2 results of product detection at each step
The main components of the carbon ferrochrome are chromium and iron, and also contain Ca, mg, mn, cu, ni and other high-content impurities which can be dissolved in hydrochloric acid, and some impurities easily cause hydrogen evolution side reaction of the cathode, so that the service life of the electrolyte is influenced. After the carbon ferrochrome is purified by the step of test example 2, particularly after the chromium chloride crystal is recrystallized, the impurity content is obviously reduced, the Ca, mg, mn, cu, ni impurities in the obtained ferrochrome electrolyte 2 are all lower than 15ppm, the purity is higher, and the chromium chloride and the ferrous chloride in the ferrochrome solution are purified and then used for preparing the electrolyte.
Comparative example 1
To compare the impurity removal effects of fractional crystallization and oxidized ferrous chloride crystallization, the ferrochrome solution obtained in step S1 of test 2 was directly crystallized and oxidized and then crystallized, respectively, to obtain the data shown in Table 3.
TABLE 3 detection data of crystals and mother liquor obtained by direct crystallization and post-oxidation crystallization of ferrochrome solution
As shown in Table 3, the crystal and mother liquor of direct crystallization of ferrochrome solution are analyzed, in the mixed solution of chromium chloride and ferrous chloride, ferrous chloride is separated out before the crystallization of chromium chloride, and Ni and Mn are separated out along with the formation of mixed crystal of ferrous chloride, so that the impurity Ni and Mn of the crystal is higher than that of mother liquor, at this time, a small amount of ferrous chloride remains in the mother liquor of chromium chloride, and a small amount of iron element is beneficial to the crystallization and purification of chromium chloride, therefore, the fractional crystallization is designed in the technological process, and the crystallization and the purification of ferrous chloride are carried out after the crystallization and separation of the ferrous chloride.
Analyzing the data of impurities in crystals and mother liquor crystallized after ferrochrome solution oxidation, crystallizing in a mixed solution of chromium chloride and ferric chloride, wherein iron and chromium are distributed in the crystals and the mother liquor in almost equal proportion, ni and Mn do not form mixed crystals to enter the crystals, each impurity accords with the general rule of crystallization and purification, namely, the concentration of the impurity in the crystals is low, the impurity is enriched in the mother liquor, but the removal rate of each impurity is poor, the analysis reason is that the concentration of ferric trichloride is higher, the viscosity of ferric trichloride is higher, so that more mother liquor is entrained in the obtained crystals, the purification of the crystals is unfavorable, and the reasonable deduction can be realized, because the impurity removal rate is poor in the crystallization in the system, even if the oxidized crystallization crystal 1 is recrystallized after being added with water, the impurity is still very high, and the content of ferric trichloride in the obtained crystal is unfavorable for the subsequent reduction to ferrous chloride, so that the purification is not carried out by adopting the process route.
Comparative example 2
Using the direct crystallization mother liquor 1 obtained in comparative example 1 as a raw material (i.e. mother liquor obtained after crystallization of ferrochrome solution), half of the direct crystallization mother liquor is directly concentrated and crystallized to obtain direct crystallization crystals 2 and direct crystallization mother liquor 2; the other half was oxidized and then concentrated and crystallized to obtain oxidized crystal 2 and oxidized crystal mother liquor 2, and the obtained data are shown in Table 4.
TABLE 4 direct crystallization of mother liquor direct crystallization and crystallization after oxidation and mother liquor detection data
The direct crystallization mother liquor 1 is the mother liquor after crystallization of comparative example 1, and the iron concentration of the mother liquor is low, however, crystallization is performed when the ferrous chloride concentration is low, the removal effect of Ni and Mn is not good, and the removal effect of Ni and Mn is good after oxidation of the direct crystallization mother liquor 1. The reason is that: after ferrous chloride is oxidized, the ferrous chloride is easy to separate from impurity metals due to low iron content and low viscosity, and in a chromium chloride and ferric trichloride system, ni and Mn are not mixed to be separated out, so that the impurity removal effect is good during crystallization. Therefore, the technological process is designed to oxidize the mother solution with lower iron concentration after crystallization and then concentrate and crystallize again so as to obtain chromium chloride crystals with lower impurities.
Electrical performance testing
The electrolytes obtained in test examples 1 and 2 and electrolytes of various impurity concentrations were subjected to electric performance test, and the charge/discharge modes were set to constant current charge/discharge, current was set to 120mA/cm 2, charge cut-off voltage was set to 1.2V, discharge cut-off voltage was set to 0.3V, and the number of charge/discharge times was set to 20, and the obtained data are shown in table 5. fe=1.2M, cr =1.4M, HCl =2.5M in the iron chromium electrolyte.
TABLE 5 Table of electrical property test data for various impurity concentration electrolytes
As is clear from the data in table 5, the level of the impurity concentration directly affects the energy efficiency and the attenuation rate when the electrolyte is used, and the difference in attenuation rate is large. It is prescribed in the industry that when the discharge amount of the electrolyte decreases to the initial 60%, the electrolyte needs to be regenerated. After the carbon ferrochrome is leached and when the impurities are not removed, the attenuation rate is as high as 3.6 percent, and the electrolyte only needs to be regenerated after being charged and discharged for 11 times, so that the carbon ferrochrome cannot be applied to engineering; the impurity in the product of the prior art CN115832379A is still high, and electrolyte only needs to be regenerated after being charged and discharged for 17 times, so that the product cannot be applied in engineering; the electrolyte in the embodiment 2 of the technical scheme has the advantages that the purity and the configuration of the analytically pure reagent are close, the energy efficiency and the attenuation rate are also close, the electrolyte can be regenerated after 133 times of stable operation, the regeneration times of the electrolyte are greatly reduced, the utilization rate of the electrolyte is greatly improved, and the cost of the electrolyte produced by the technical scheme is far lower than that of the analytically pure reagent, so that the electrolyte has the advantages of low cost and high quality.
Cost analysis
The cost is calculated according to the production mode of the complex distribution electrolyte of the purchased finished chromium chloride and ferrous chloride, and the Fe=1. M, cr =1. M, HCl =2.5M in the ferrochromium electrolyte, and the data are shown in table 6.
TABLE 6 raw material cost accounting table for purchasing finished chromium chloride and ferrous chloride compound electrolyte
| Material name | Price per ton | Quantity per ton | Single cost, yuan/ton |
| Chromium chloride hexahydrate | 15000 | 0.307 | 4605 |
| Ferrous chloride tetrahydrate | 12000 | 0.189 | 2268 |
| Industrial hydrochloric acid | 400 | 0.240 | 96 |
| Totalizing | / | / | 6969 |
Purchasing the finished product of the compound electrolyte, wherein the cost of the light raw material is close to 7000 yuan/ton; when the carbon ferrochrome is used as the raw material, the cost of the raw material is about 900 yuan/ton, the cost of the dissolving and purifying process is lower than 2000 yuan/ton, and the cost of the electrolyte is reduced to below 50% in the prior art on the premise of purifying to the same purity, so that the method has remarkable economic benefit, has popularization significance and accords with the trend of technical development.
The present invention will be described with reference to the following examples, but the present invention is not limited to the above-described detailed methods, and it is not intended that the present invention be limited to practice with the above-described detailed methods. It will be apparent to those skilled in the art that any modifications of the present invention, equivalent substitutions of the various materials in the process of the present invention, i.e., the addition of auxiliary components, the selection of specific modes, etc., fall within the scope of the invention and the disclosure without departing from the principles of the invention.
Claims (10)
1. A method for preparing ferrochrome electrolyte by using carbon ferrochrome is characterized by comprising the following steps of,
S1, adding carbon ferrochrome into hydrochloric acid, leaching the carbon ferrochrome, and then carrying out solid-liquid separation, wherein the obtained liquid is ferrochrome solution;
S2, sequentially evaporating, concentrating, cooling and crystallizing the ferrochrome solution to obtain a crude ferrous chloride product and a first chromium chloride solution, wherein the first chromium chloride solution contains chromium chloride and ferrous chloride, and the temperature of the ferrochrome solution is 10-30 ℃ during cooling and crystallizing;
s3, adding water, heating and dissolving the ferrous chloride crude product, and recrystallizing the dissolved ferrous chloride to obtain purified ferrous chloride crystals, wherein the dissolution temperature of the ferrous chloride crude product is 50-80 ℃;
Adding an oxidant into the first chromium chloride solution to oxidize ferrous chloride in the first chromium chloride solution into ferric chloride, sequentially evaporating, concentrating, cooling and crystallizing the oxidized first chromium chloride solution to obtain chromium chloride crystals, wherein the chromium chloride crystals contain chromium chloride and ferric chloride, and the temperature of the first chromium chloride solution is 20-35 ℃ during cooling and crystallizing;
adding water to dissolve the chromium chloride crystal to obtain a second chromium chloride solution, adding iron powder into the second chromium chloride solution, and dripping hydrochloric acid to ensure that the pH value of the second chromium chloride solution is less than 0; reducing ferric trichloride in the second chromium chloride solution into ferrous chloride to obtain a mixed solution for removing impurities, wherein the mixed solution contains chromium chloride and ferrous chloride;
S4, mixing the purified ferrous chloride crystal, the mixed solution, hydrochloric acid and water according to a proportion, and compounding into the iron-chromium electrolyte.
2. The method for preparing ferrochrome electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S1, before the carbon ferrochrome is added with hydrochloric acid, the carbon ferrochrome is crushed to a particle size of < 100 meshes; the hydrochloric acid is heated to 90-110 ℃ and carbon ferrochrome is leached out; the concentration of the hydrochloric acid is 20% -35%.
3. The method for preparing ferrochrome electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S1, when ph= -0.5, the leaching of carbon ferrochrome is finished.
4. The method for preparing ferrochrome electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S2, the ferrochrome solution is evaporated and concentrated until the sum of iron and chromium concentrations is 16% -18%.
5. The method for preparing ferrochrome electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S3, the oxidant is one or a mixture of any two or more of oxygen, chlorine, hydrogen peroxide or ozone.
6. The method for preparing ferrochrome electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S3, the first chromium chloride solution is concentrated until the sum of iron and chromium concentrations is 15% -17% before cooling and crystallization;
the ferrous chloride crude product is dissolved until the concentration of the ferrous chloride is 19% -20%;
And cooling and crystallizing the first chromium chloride solution to obtain mother liquor, circularly concentrating and crystallizing the mother liquor until the impurity of the mother liquor exceeds a threshold value, and discharging the mother liquor after the circularly concentrating.
7. The method for preparing an iron-chromium electrolyte by using carbon ferrochrome according to claim 1, wherein in the step S3, the amount of iron powder is 1.05-1.2 times of the theoretical amount.
8. The method for preparing ferrochrome electrolyte using carbon ferrochrome according to claim 1, wherein the temperature of the second chromium chloride solution is 60 ℃ to 80 ℃ during the reduction reaction in step S3.
9. An electrolyte comprising an iron-chromium electrolyte, wherein the iron-chromium electrolyte is prepared by the method for preparing an iron-chromium electrolyte by using carbon ferrochromium according to any one of claims 1 to 8.
10. An iron chromium redox flow battery comprising the electrolyte of claim 9.
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