Method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride from stainless steel waste liquid

Abstract

The invention provides a method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride by using a stainless steel waste liquid. The method comprises the following steps: firstly, adding elemental iron and / or elemental chromium into the stainless steel waste liquid to obtain a chromium-containing ferrous chloride solution; then, sulfide is added, and nickel is removed; adding iron powder to increase the pH value to obtain chromium hydroxide precipitate and a ferrous chloride solution; dissolving chromic hydroxide in hydrochloric acid to obtain a chromic chloride solution; purifying the ferrous chloride solution to obtain an electronic-grade ferrous chloride crystal; and finally, adding a chromium chloride solution, the electronic-grade ferrous chloride crystal and hydrochloric acid according to a certain proportion, and stirring and mixing to obtain the iron-chromium electrolyte. The ferrous chloride prepared by the steps is relatively high in purity and less in waste; meanwhile, the prepared electrolyte is good in electrical property, low in attenuation rate and low in cost, the purpose of comprehensive recycling of resources is achieved, and the general trend of technical improvement is met.

Description

Technical Field

[0001] The invention relates to the technical field of electrolyte production, and in particular to a method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid, and an iron-chromium electrolyte and an iron-chromium redox flow battery. Background Art

[0002] With the development of iron-chromium redox flow batteries, people try to find a widely available and cheap chromium-containing raw material to prepare the electrolyte of iron-chromium redox flow batteries. At present, the key material of the electrolyte of iron-chromium flow batteries is a mixed solution of chromium chloride, ferrous chloride and hydrochloric acid.

[0003] Stainless steel waste liquid contains a large amount of nickel, chromium and iron resources. With the development of the economy, my country's consumption of nickel, chromium and other metal resources is huge, and the contradiction between supply and demand is becoming increasingly acute. However, the reserves of nickel, chromium and other metal resources are limited. Therefore, it is particularly important to recycle and utilize waste nickel and chromium metal resources.

[0004] Prior art CN 107416959 A discloses a method for removing chromium and nickel from pickling waste liquid, and CN112499802A discloses a method for removing nickel and chromium from pickling waste liquid. The method uses iron powder and nano iron powder to remove chromium and nickel from the waste liquid together. The obtained nickel-chromium mixture is difficult to reuse. The ferrous chloride solution obtained after removing nickel and chromium has low purity and is only used for producing iron salts.

[0005] Prior art CN 114959711 A discloses a method for comprehensive utilization of stainless steel etching waste liquid. This patent first adds iron powder to consume acid and reduce Fe 3+ , add alkali to adjust the pH to obtain ferrochrome precipitate, which is used to produce ferrochromium alloy. After the filtrate is adjusted to pH 1, iron powder is added at 80°C to replace nickel. Nickel is used to prepare ferronickel powder. The ferrochrome precipitate in this process has a high impurity nickel content and cannot be used to prepare ferrochromium electrolyte.

[0006] Prior art CN 114180629 A discloses a method for separation and recovery of chromium and nickel and resource utilization of waste acid in a strong acid environment. In this patent, an organic reducing agent is added to the stainless steel pickling waste liquid at pH = 0.5 to 2.5 to reduce nickel, and phosphate is added to precipitate chromium after separation at pH = 2.0 to 4.0. The solution from which nickel and chromium are removed is used to prepare polyferric sulfate. The nickel and chromium in the solution are generally less than 50 ppm, and the purity of the obtained nickel and chromium products is not mentioned.

[0007] It can be seen that in the prior art, nickel and chromium in stainless steel waste liquid are mainly removed as impurities, and nickel and chromium can rarely be made into high-purity, high-value-added products.

[0008] Prior art CN 117497816 B discloses a method for preparing a low-nickel iron-chromium electrolyte by removing impurities with sulfides. In this patent, sulfides can reduce the key impurity nickel in the iron-chromium mixture to <0.1 mg / L, thereby preparing a low-impurity iron-chromium electrolyte. If this technical method is used to produce electrolyte from stainless steel waste liquid, due to the high iron content and low chromium content, a large amount of expensive chromium chloride needs to be added, which greatly increases the production cost and is not the best solution.

[0009] CN 118099495 B A method for preparing an iron-chromium electrolyte by leaching carbon ferrochrome from ferric chloride. The leaching solution of this patent has high iron content and low chromium content. The chromium is precipitated and enriched, and then crystallized and purified to prepare an iron-chromium electrolyte with low impurities. If the iron-chromium electrolyte is produced by using this technical solution with stainless steel waste liquid, the obtained chromium hydroxide is also enriched with a relatively high content of nickel. The purification efficiency is low only by washing with water and crystallizing and purifying, and it is not suitable for actual production.

[0010] How to recycle the chromium in stainless steel waste liquid and use it in the preparation of iron-chromium electrolyte requires other technical solutions. Summary of the invention

[0011] One of the purposes of the present invention is to provide a method for producing iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid. The method uses stainless steel waste liquid and iron powder as raw materials, removes impurities with sulfide, and can produce low-impurity iron-chromium electrolyte and electronic-grade ferrous chloride, so as to comprehensively utilize waste and turn waste into treasure, and implement a green circular economy route.

[0012] To achieve one of the above purposes, the present invention provides the following technical solutions:

[0013] A method for preparing an iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid is provided, comprising the following steps:

[0014] S1. Add elemental iron and / or elemental chromium to the stainless steel waste liquid, control the pH = 1.2 to 2.2, separate the solid and liquid, and obtain a chromium-containing ferrous chloride solution A1;

[0015] S2. Adjust the chromium-containing ferrous chloride solution A1 to make its Fe 2+ content is less than 14%, adding sulfide to the chromium-containing ferrous chloride solution A1 until nickel is not detected, and separating the solid and liquid to obtain solid nickel sulfide and the chromium-containing ferrous chloride solution A2;

[0016] S3. The chromium-containing ferrous chloride solution A2 is heated to 50°C to 100°C, iron powder is added to obtain a mixed solution,

[0017] The mixed solution is stirred using a dispersive stirring paddle, the mixed solution is first stirred at a first stirring speed to make the pH value of 2.5 to 3.0, and chromium hydroxide precipitation is formed, and then the chromium hydroxide is dispersed at a second stirring speed, wherein the diameter of the dispersive stirring paddle is adapted to the diameter of the container containing the mixed solution so that when stirring at the second stirring speed, the dispersive stirring paddle generates a shear force on the mixed solution, and the shear force reduces the particle size of the polymerized chromium hydroxide, thereby releasing the adsorbed and contained free nickel ions,

[0018] The first stirring speed is less than the second stirring speed, and the second stirring speed is 800-1000 r / min to obtain chromium hydroxide slurry.

[0019] removing excess iron powder from the chromium hydroxide slurry, separating the solid from the liquid, and obtaining a ferrous chloride solution and chromium hydroxide;

[0020] S4. Wash the chromium hydroxide with dilute acid water having a pH value of 2.0 to 2.5, and then dissolve it in hydrochloric acid to obtain a chromium chloride solution;

[0021] The ferrous chloride solution is sequentially evaporated and concentrated, cooled and crystallized to obtain electronic grade ferrous chloride. In some embodiments, in step S1, the stainless steel waste liquid is heated at a temperature of 40 to 90°C;

[0022] The chromium-containing ferrous chloride solution A1 contains Cr 3+ <1%.

[0023] In some embodiments, in step S2, the sulfide is sodium sulfide and / or hydrogen sulfide, and the amount of sodium sulfide / hydrogen sulfide added is calculated based on the theoretical amount of nickel removed, and the remaining S in the solution is - The concentration is 1.4%~2.0%.

[0024] In some embodiments, in step S2, the chromium-containing ferrous chloride solution A1 in step S1 is transferred to another stirring tank, and then the chromium-containing ferrous chloride solution A1 is adjusted.

[0025] In some embodiments, in step S3, the amount of iron powder added is 2% to 5% of the mass of the chromium-containing ferrous chloride solution A2.

[0026] In some embodiments, in step S3, the diameter of the dispersed stirring paddle is 1 / 3 to 1 / 4 of the diameter of the container;

[0027] The first stirring speed is 200-400 r / min. When pH=2.5-3.0, the first stirring speed is increased to the second stirring speed of 800-1000 r / min. The stirring time of the second stirring speed is 1-3 min.

[0028] In some embodiments, in step S3, excess iron powder is removed by an iron remover.

[0029] In some embodiments, in step S4, the temperature of the dilute acid water is set to 60°C to 80°C to wash the chromium hydroxide, and the washing water after washing is returned to step S2 to adjust the Fe content of the chromium-containing ferrous chloride solution A1. 2+ content.

[0030] The beneficial effects of the method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid of the present invention are as follows:

[0031] (1) The present invention uses hazardous waste liquid stainless steel waste liquid as raw material, recovers nickel through sulfide, enriches and recovers chromium for the preparation of iron-chromium electrolyte, and ferrous chloride can reach electronic grade product standards after crystallization and purification, thereby obtaining three products with high purity, achieving the purpose of comprehensive resource recovery and utilization, and conforming to the general trend of technological improvement.

[0032] (2) The present invention adds iron powder to adjust the pH to precipitate chromium, and the dispersed stirring paddle shears the chromium hydroxide into small molecules, and the hot dilute acid water washing can effectively remove Fe at the same time. 2+ 、Ni 2+ Plasma, omitting the crystallization purification and reduction of Fe 3+ steps to achieve the purpose of saving process costs.

[0033] (3) The raw material used in the present invention is hazardous waste stainless steel waste liquid, with a cost of less than 0 yuan and a purification cost of less than 1,000 yuan / ton. The existing technology uses carbon ferrochrome as raw material, with a raw material cost of about 1,400 yuan / ton and a purification cost of less than 2,000 yuan, which is significantly lower than the cost of the existing technology.

[0034] (4) The present invention uses sulfide as a means of impurity removal to remove about 25 impurities in the chromium-containing ferrous chloride solution, and the impurity content can be reduced to less than 0.1 mg / L. In addition, no impurities are introduced when iron and chromium are separated. The purification method is simple and the production process cost is low, and the purity of the iron-chromium electrolyte and ferrous chloride can be guaranteed.

[0035] (5) The entire production process of the present invention does not use the traditional chromium salt purification process and does not involve hexavalent chromium; although sulfide is used as an impurity remover, S 2- By converting into solid nickel sulfide, sulfur can be efficiently utilized and the production process is clean, which is in line with the general trend of technological improvement.

[0036] To achieve the second objective above, the present invention provides the following technical solutions:

[0037] Provided is an iron-chromium electrolyte, which is prepared by mixing industrial hydrochloric acid, the chromium chloride solution prepared above and electronic grade ferrous chloride in proportion to obtain the iron-chromium electrolyte.

[0038] To achieve the third objective above, the present invention provides the following technical solutions:

[0039] Provided is an iron-chromium redox flow battery comprising the above-mentioned iron-chromium electrolyte. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0041] The terminology used in the present invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention.

[0042] Example 1

[0043] The method disclosed in this embodiment for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid comprises the following steps:

[0044] S1. Add elemental iron and / or elemental chromium to the stainless steel waste liquid, control the pH = 1.2 to 2.2, separate the solid and liquid, and obtain a chromium-containing ferrous chloride solution A1;

[0045] The principle of the above steps: Stainless steel waste liquid contains Fe 2+ =4%~8%,Fe 3+ =6%~9%, Fe=10%~14%, HCl=0.5%~3%, adding elemental iron and / or elemental chromium can reduce Fe 3+ Reduction to Fe 2+ , while reducing H + To increase pH. - When pH is less than 1.2, the solution will overflow easily, and the S - The utilization rate of chromium chloride in chromium-containing ferrous chloride solution is easy to form chromium hydroxide precipitation when pH>2.2, so it is necessary to control pH=1.2~2.2.

[0046] In step S1, the stainless steel waste liquid is heated at a temperature of 40 to 90° C., preferably 50° C. The chromium-containing ferrous chloride solution A1 is adjusted to Cr<1%. Heating is beneficial to the reaction, but when the temperature is too high, the reaction speed is too fast and chromium hydroxide precipitation is likely to occur. Therefore, it is better to control the temperature at 40 to 90° C.

[0047] S2. Adjust the chromium-containing ferrous chloride solution A1 to make its Fe 2+content is less than 14%, adding sulfide to the chromium-containing ferrous chloride solution A1 until nickel is not detected, preferably, the sulfide is sodium sulfide and / or hydrogen sulfide, and performing solid-liquid separation to obtain solid nickel sulfide and the chromium-containing ferrous chloride solution A2;

[0048] The principle of the above steps is to add sulfide to remove nickel from the solution until it is undetectable, and then separate the solid and liquid to recover the nickel mud. 2+ =0.1%~2%. Nickel easily enters chromium hydroxide during subsequent chromium precipitation, making the nickel content in chromium hydroxide very high and difficult to remove. Therefore, nickel needs to be removed before chromium precipitation. In this step, it is necessary to control the Fe content in the solution. 2+ <14%,Fe 2+ High concentrations easily form FeS precipitation, which has a poor nickel removal effect and reduces the purity of nickel sulfide. The amount of sulfide added is calculated based on the theoretical amount of nickel removed, and the remaining S in the solution is - The concentration is 0.14%~0.20%.

[0049] Preferably, the chromium-containing ferrous chloride solution A1 is transferred to another stirring tank and then the chromium-containing ferrous chloride solution A1 is adjusted.

[0050] The chromium-containing ferrous chloride solution is transferred to another stirring tank because there is an excess of elemental iron / chromium in the reaction tank S1, which will continue to react with the solution, and the pH will continue to rise when the sulfide is used to remove nickel, resulting in chromium hydroxide precipitation, which cannot achieve the purpose of completely separating nickel and chromium. In addition, if sulfide is added to the same reaction tank, when the next batch of materials enters the reaction tank, the acid in the stainless steel waste liquid reacts with the remaining sulfide at the bottom of the tank to generate hydrogen sulfide gas, which is likely to cause damage to workers and the environment, and increase the amount of tail gas treatment.

[0051] S3. Raise the temperature of the chromium-containing ferrous chloride solution A2 to 50°C to 100°C, preferably 60°C, add iron powder, preferably, the amount of iron powder added is 2% to 5% by mass of the solution, preferably 3%, so that pH = 2.5 to 3.0, to obtain a mixed solution,

[0052] The mixed solution is stirred using a dispersive stirring paddle, the mixed solution is first stirred at a first stirring speed until a chromium hydroxide precipitate is formed, and then the chromium hydroxide is dispersed at a second stirring speed, wherein the diameter of the dispersive stirring paddle is adapted to the diameter of a container containing the mixed solution so that when the mixed solution is stirred at the second stirring speed, the dispersive stirring paddle generates a shear force on the mixed solution, and the shear force reduces the particle size of the chromium hydroxide, thereby releasing the adsorbed and contained free nickel ions.

[0053] The first stirring speed is less than the second stirring speed, and the second stirring speed is 800-1000 r / min to obtain chromium hydroxide slurry.

[0054] removing excess iron powder from the chromium hydroxide slurry, and then separating the solid and liquid to obtain a ferrous chloride solution and chromium hydroxide;

[0055] The principle of the above steps is: the temperature of the chromium-containing ferrous chloride solution for nickel removal is raised, and iron powder is added to increase the pH, so that the chromium chloride forms a chromium hydroxide precipitate. When the pH is greater than 2.5, the Cr in the solution is less than 50ppm. In this step, a dispersed stirring paddle must be used as a stirring device. The dispersed stirring paddle has a toothed structure. When the pH is low, a first stirring speed with a low rotation speed is selected, which mainly plays a stirring role. After the chromium hydroxide precipitate is formed, a second stirring speed with a high rotation speed is used. By setting the adaptability between the diameter of the dispersed stirring paddle and the diameter of the container, a shear force is generated between the second stirring speed and the container. The shear force shears the polymerized chromium hydroxide to form chromium hydroxide with a small particle size, so that the free nickel ions (from the iron powder) adsorbed and contained in the colloidal chromium hydroxide are released, which is convenient for removal during subsequent water washing. If a high rotation speed is always used, Fe 3+ Rapid increase, need to increase Fe removal 3+ process steps.

[0056] In step S3, the diameter of the dispersed stirring paddle should be 1 / 3 to 1 / 4 of the diameter of the container;

[0057] The first stirring speed is 200-400 r / min. When the pH value is 2.5-3.0, the first stirring speed is increased to the second stirring speed of 800-1000 r / min. The stirring and dispersing time of the second stirring speed is 1-3 min.

[0058] In addition, excess iron powder is removed by a magnetic separator.

[0059] S4. Wash the chromium hydroxide with dilute acid water having a pH value of 2.0 to 2.5, and then dissolve it in hydrochloric acid to obtain a chromium chloride solution;

[0060] The ferrous chloride solution is sequentially evaporated and concentrated, and cooled and crystallized to obtain electronic grade ferrous chloride.

[0061] The principle of the above steps: After solid-liquid separation, the free Fe in chromium hydroxide 2+ The content is very high and Cr 3+ The content is very low, so water washing is required to remove iron to Cr 3+ Content>Fe 2+ content, and remove impurities that cannot be replaced by iron powder (such as Mn 2+ , Ca 2+ Mg 2+ The washing water can be used to control the Fe content of the chromium-containing ferrous chloride solution in step S2. 2+ <14%. Due to the slow solid-liquid separation and Fe 2+Easily oxidized to Fe at high pH 3+ , when washing, you need to use dilute acid water with pH = 2.0 ~ 2.5 instead of tap water directly. After washing with dilute acid water, No need for recrystallization to purify the product The washing effect will be better when the dilute acid water is heated to 60-80℃.

[0062] The ferrous chloride solution is purified by sulfide and iron powder removal and then crystallization. The resulting ferrous chloride crystals have high purity and can be sold as electronic grade products.

[0063] In step S4, the chromium hydroxide is washed with dilute acid water with a pH of 2.0 to 2.5.

[0064] Finally, industrial hydrochloric acid, the chromium chloride solution prepared above and electronic grade ferrous chloride are mixed in proportion to obtain an iron-chromium electrolyte.

[0065] The prepared iron-chromium electrolyte can be applied to iron-chromium redox flow batteries.

[0066] To further illustrate the effect of the present invention, the following test was performed:

[0067] Test Example 1

[0068] The present application discloses a method for producing iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid, comprising the following steps:

[0069] S1. Add 0.7 tons of iron powder to 10 tons of stainless steel waste liquid, heat to 40 ° C, and react until the pH of the solution is 1.2 to obtain a chromium-containing ferrous chloride solution A1;

[0070] S2. 0.2 tons of 60% solid sodium sulfide was added to the chromium-containing ferrous chloride solution A1, and the reaction was stirred for 30 minutes to remove nickel until it was undetectable, followed by solid-liquid separation to obtain solid nickel sulfide and chromium-containing ferrous chloride solution A2;

[0071] S3. The chromium-containing ferrous chloride solution A2 was heated to 50°C, 0.5 tons of iron powder was added, a dispersed stirring paddle was used as a stirring device, the speed was 400r / min, the reaction was carried out for 60min, pH = 2.8, the speed was adjusted to 800r / min, the reaction was carried out for 3min, and chromium hydroxide slurry was obtained. The chromium hydroxide slurry was passed through an iron remover to remove excess iron powder to obtain chromium hydroxide slurry after iron powder removal, and the chromium hydroxide slurry after iron powder removal was subjected to solid-liquid separation;

[0072] S4. Wash the chromium hydroxide with 2 tons of 60°C pH = 2.0 dilute acid water, dissolve 1.0 tons of chromium hydroxide after washing with 0.6 tons of industrial hydrochloric acid to obtain a chromium chloride solution, which has a low chromium concentration and is concentrated to Cr = 7.4% and then compounded with an electrolyte;

[0073] 9.0 tons of ferrous chloride solution was evaporated and concentrated to Fe 2+ =20.0%, cooled to 20°C, and after solid-liquid separation, 2.1 tons of electronic grade ferrous chloride crystals were obtained;

[0074] S5. Add chromium chloride solution, electronic grade ferrous chloride crystals, industrial hydrochloric acid in the desired proportion, and stir to obtain an iron-chromium electrolyte;

[0075] Finally, the product testing data of each step is summarized in Table 1.

[0076] Table 1 Product testing data for each step of Example 1

[0077] Substance name <![CDATA[Cr 3+ ,%]]> <![CDATA[Fe 2+ ,%]]> Cu, % Ni, % Mn, mg / L Stainless steel waste liquid 0.97 2.39 0.0316 1.2478 597 Nickel Sulfide Solid 0.41 14.6 0.92 36.46 / Chromium chloride solution 7.40 3.86 0.0003 Not detected 14 Ferrous chloride crystals Not detected 27.4 Not detected 0.00012 283 Iron-chromium electrolyte 5.5 5.1 0.0002 0.00001 33

[0078] Test Example 2

[0079] The present application discloses a method for producing iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid, comprising the following steps:

[0080] S1. 0.4 tons of solid containing elemental iron and a small amount of elemental chromium were added to 10 tons of stainless steel waste liquid, heated to 60 ° C, and reacted until the pH of the solution was 1.8 to obtain a chromium-containing ferrous chloride solution A1;

[0081] S2. 0.12 tons of 60% solid sodium sulfide was added to the chromium-containing ferrous chloride solution A1 to remove nickel until it was undetectable, followed by solid-liquid separation, solid nickel sulfide and chromium-containing ferrous chloride solution A2;

[0082] S3. The chromium-containing ferrous chloride solution A2 was heated to 70°C, 0.3 tons of iron powder was added, a dispersed stirring paddle was used as a stirring device, the speed was 300r / min, the reaction was carried out for 50min, pH = 2.5, the speed was adjusted to 1000r / min, the reaction was carried out for 1min, and chromium hydroxide slurry was obtained. The chromium hydroxide slurry was passed through an iron remover to remove excess iron powder to obtain chromium hydroxide slurry after iron powder removal, and the chromium hydroxide slurry after iron powder removal was subjected to solid-liquid separation;

[0083] S4. Wash the chromium hydroxide with 2.5 tons of 70°C pH = 2.3 dilute acid water, add 0.66 tons of industrial hydrochloric acid to dissolve 0.9 tons of chromium hydroxide after washing to obtain a chromium chloride solution. If the chromium concentration of this solution is low, it can be concentrated and then the electrolyte is compounded;

[0084] 9.1 tons of ferrous chloride solution was evaporated and concentrated to Fe 2+ =20.3%, cooled to 30°C, and after solid-liquid separation, 2.2 tons of electronic grade ferrous chloride crystals were obtained;

[0085] S5. Add chromium chloride solution, electronic grade ferrous chloride crystals, industrial hydrochloric acid in the desired proportion, and stir to obtain an iron-chromium electrolyte;

[0086] Finally, the product testing data of each step is summarized in Table 2.

[0087] Table 2 Product testing data for each step of Example 2

[0088] Substance name <![CDATA[Cr 3+ ,%]]> <![CDATA[Fe 2+ ,%]]> Cu, % Ni, % Mn, mg / L Stainless steel waste liquid 0.8 2.04 0.0234 0.9718 560 Nickel Sulfide Solid 0.49 16.7 0.78 32.77 / Chromium chloride solution 7.6 3.2 0.0004 Not detected 10 Ferrous chloride crystals Not detected 27.5 Not detected 0.00016 266 Iron-chromium electrolyte 5.5 5.1 0.0002 0.00001 35

[0089] Test Example 3

[0090] The present application discloses a method for producing iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid, comprising the following steps:

[0091] S1. 0.2 tons of solid containing elemental iron and a small amount of elemental chromium were added to 10 tons of stainless steel waste liquid, heated to 90 ° C, and reacted until the pH of the solution was 2.2 to obtain a chromium-containing ferrous chloride solution A1;

[0092] S2. The hydrogen sulfide gas is passed through a gas distributor into the chromium-containing ferrous chloride solution A1, so that the pH of the solution is 2.05 to 2.10, nickel is removed until it is undetectable, and then solid-liquid separation is performed to obtain solid nickel sulfide and chromium-containing ferrous chloride solution A2;

[0093] S3. The chromium-containing ferrous chloride solution A2 was heated to 90°C, 0.2 tons of iron powder was added, a dispersed stirring paddle was used as a stirring device, the speed was 200 rpm, the reaction was performed for 60 min, pH = 2.8, the speed was adjusted to 900 r / min, the reaction was performed for 2 min, and chromium hydroxide slurry was obtained. The chromium hydroxide slurry was passed through an iron remover to remove excess iron powder to obtain chromium hydroxide slurry after iron powder removal, and the chromium hydroxide slurry after iron powder removal was subjected to solid-liquid separation;

[0094] S4. The chromium hydroxide was washed with 1.5 tons of 80°C pH = 2.5 dilute acid water, and the washed chromium hydroxide was dissolved by adding 0.68 tons of industrial hydrochloric acid to obtain a chromium chloride solution, which was concentrated to Cr = 6.68% and then the electrolyte was compounded;

[0095] 9.2 tons of ferrous chloride solution was evaporated and concentrated to Fe 2+ =20.5%, cooled to 40°C, and after solid-liquid separation, 2.1 tons of electronic grade ferrous chloride crystals were obtained;

[0096] S5. Add chromium chloride solution, electronic grade ferrous chloride crystals, industrial hydrochloric acid in the desired proportion, and stir to obtain an iron-chromium electrolyte;

[0097] Finally, the product testing data of each step is summarized in Table 3.

[0098] Table 3 Product testing data for each step of Example 3

[0099] Substance name <![CDATA[Cr 3+ ,%]]> <![CDATA[Fe 2+ ,%]]> Cu, % Ni, % Mn, mg / L Stainless steel waste liquid 0.6 2.11 0.0287 0.4937 487 Nickel Sulfide Solid 0.18 2.4 2.83 48.6 / Chromium chloride solution 6.68 6.15 0.0005 Not detected 23 Ferrous chloride crystals Not detected 27.4 Not detected 0.00019 283 Iron-chromium electrolyte 5.5 5.1 0.0004 Not detected 19

[0100] The reaction conditions of Test Examples 1, 2, and 3 and the test data of the obtained products were analyzed:

[0101] (1) The nickel sulfide solid obtained by using sulfide to remove nickel has a high nickel content and contains ferrous sulfide. When hydrogen sulfide gas is used for impurity removal, the ferrous content is significantly reduced, indicating that the Fe in the nickel sulfide solid is 2+ Mainly due to the formation of Fe(OH) 2 precipitation;

[0102] (2) The nickel in the obtained chromium chloride solution was not detected, indicating that the washing effect of hot dilute acid water was good. The more dilute acid water was used, the higher the Fe content in the chromium chloride solution. 2+ , Mn 2+ The less, the lower the impurities in the chromium chloride solution, and no recrystallization purification is required;

[0103] (3) After chromium is precipitated from iron powder, a small amount of nickel is present in the ferrous chloride solution. After crystallization and purification, the nickel content in the ferrous chloride crystals is less than 0.0002%.

[0104] Comparative test example 1

[0105] Take 2000g of the chromium-containing ferrous chloride solution (pH=1.2, Fe=13.98%, Cr=0.97%) obtained in step S1 of Example 1, take three 500g solutions and add solid chromium chloride hexahydrate to make Cr 1.2%, 1.5% and 2.0%, respectively, heat the four solutions to 60°C, add 10g of iron powder respectively, react to different times to measure pH and Cr content, and the experimental data are summarized in Table 4.

[0106] Table 4 Summary of the pH increase of ferrous chloride solution with different chromium concentrations using iron powder

[0107]

[0108] Analyze the experimental data in Table 4:

[0109] When the chromium concentration in the chromium-containing ferrous chloride solution is higher, the pH at which chromium chloride precipitation occurs is lower. When the pH cannot be raised to above 1.2, the effect of removing impurities with sulfide is poor. Therefore, it is necessary to control the chromium concentration in the chromium-containing ferrous chloride solution. When the chromium concentration is high, the ferrous chloride solution in step S4 can be added to dilute the chromium concentration to less than 1.0% before the pH can be raised with iron powder. Otherwise, liquid alkali needs to be used to raise the pH, such as CN117497816B, a method for preparing a low-nickel iron-chromium electrolyte using sulfide removal, but this method will introduce a large amount of sodium chloride, and a sodium chloride removal step needs to be added.

[0110] When Cr is less than 1.0%, no chromium hydroxide precipitation occurs when elemental iron is used to raise the pH to 2.2, which meets the pH requirement for impurity removal with sulfides.

[0111] Comparative Test Example 2

[0112] Take 2000g of the chromium-containing ferrous chloride solution obtained in step S1 of Experimental Example 2, take three appropriate portions of the solution and add ferrous chloride tetrahydrate solid to make the ferrous Fe 2+ 14.5%, 15.0%, 15.5% respectively. Take 500g of each portion, heat to 60℃, add 6g of industrial sodium sulfide (Na 2 S=60%), stirred for 30min, filtered, recorded the filtration time, and detected the concentrations of nickel, ferrous iron and chromium in the filtrate. The experimental data are summarized in Table 5.

[0113] Table 5 Summary of experimental data on nickel removal using sodium sulfide in chromium-containing ferrous chloride solutions with different ferrous concentrations

[0114]

[0115] Analyze the experimental data in Table 5:

[0116] With the increase of iron concentration, the nickel removal effect is worse when the same amount of sodium sulfide is used for nickel removal. The higher the iron concentration, the slower the filtration speed is, which is not conducive to industrial production. In order to ensure the nickel removal effect, reduce iron loss, and improve the purity of nickel mud, it is necessary to control the Fe content of the solution before adding sodium sulfide. 2+ <14%.

[0117] Comparative Test Example 3

[0118] Take 2000g of the chromium-containing ferrous chloride solution A2 obtained in step 2 of Example 1, from which nickel is removed until no chromium is detected, heat it to 70°C, add 30g of reduced iron powder (Fe=98.3%, Ni=0.06%) respectively, use an anchor stirring paddle to stir at a speed of 250r / min, react until the pH value is 2.5-2.6, and obtain a chromium precipitation slurry. Take an appropriate amount of the chromium precipitation slurry for the following 7 groups of comparative tests.

[0119] ⑨-1: Take 300g of chromium precipitation slurry and add it to a 250mL measuring cylinder. Use a 12000GS magnetic rod to magnetically absorb until there is no magnetically absorbed object. Filter until there is no filtrate. Collect the filtrate. Add 300g of tap water to the filter cake and continue to filter. Collect the washing liquid and the chromium hydroxide after washing.

[0120] ⑨-2: Take 500g of the chromium precipitation slurry and stir it with an anchor stirring paddle at 1000r / min for 2min, then take 300g and add it to a 250mL measuring cylinder. Use a 12000GS magnetic rod to magnetically absorb until there is no magnetically absorbed object, filter until there is no filtrate, and collect the filtrate and chromium hydroxide.

[0121] ⑨-3: The difference from ⑨-2 is that a propeller stirring paddle is used to stir at 1000 r / min for 2 minutes.

[0122] ⑨-4: The difference from ⑨-2 is that a gear-dispersed stirring paddle is used to stir at 1000 r / min for 2 minutes.

[0123] ⑨-5: The difference from ⑨-4 is that after collecting the filtrate, the chromium hydroxide is further filtered and washed with 300 g of tap water.

[0124] ⑨-6: The difference from ⑨-5 is that the chromium hydroxide is continuously filtered and washed with 300 g of dilute acid water at 20° C. with a pH of 2.5.

[0125] ⑨-7: The difference from ⑨-6 is that the temperature of the dilute acid water is 60°C.

[0126] Experiment ⑨-8: Take 300g of ferrous chloride solution A2 obtained in step 2 of Example 1, in which nickel is removed until no chromium is detected, and adjust the pH of the solution to 3.0 with 20% sodium hydroxide solution. The filtrate is free of Cr. 3+ Green, filter, and wash the chromium hydroxide with 300g of 60℃ dilute acid water.

[0127] The experimental data are summarized in Table 6.

[0128] Table 6 Effects of different types of stirring blades and different detergents on impurities in chrome mud

[0129]

[0130]

[0131] Analyze the experimental data in Table 4:

[0132] (1) From the data of nickel in chromium hydroxide in experiment ⑨-1, it can be seen that the nickel in the chromium-containing ferrous chloride solution has been removed by sodium sulfide to the point where it is undetectable. However, the chromium hydroxide obtained after the reaction with iron powder to precipitate chromium, the iron removal and replacement of solid nickel by magnetic rod adsorption, and the removal of free nickel by water washing still contains nickel. The analysis shows that the nickel is introduced by the iron powder and the trace amount of H in the solution + Reaction to free Ni 2+ Afterwards, it may undergo a replacement reaction with iron powder or be adsorbed by chromium mud. It needs to be explored whether the nickel in chromium hydroxide is in solid state or in free state.

[0133] (2) Experiments ⑨-2, ⑨-3, and ⑨-4 show that after the chromium precipitate slurry is stirred for 2 minutes with different types of stirring paddles, the nickel in the chromium hydroxide and the filtrate obtained after filtration is different, indicating that the nickel in the chromium hydroxide is in a free state. For the chromium hydroxide precipitated by the anchor stirring paddle, increasing the speed or using a propeller stirring paddle cannot shear the polymerized molecules of the chromium hydroxide into small molecules, and the particle size of the chromium hydroxide is larger. However, the gear-dispersed stirring paddle can achieve this goal. After high-speed dispersion, the particle size of the chromium hydroxide is smaller, thereby releasing the free nickel adsorbed and contained during the precipitation of the chromium hydroxide, causing the nickel in the filtrate to increase and the nickel in the chromium hydroxide to decrease.

[0134] (3) From experiments ⑨-5, ⑨-6, and ⑨-7, it can be seen that after chromium hydroxide is washed with dilute acid water, Ni, Fe 3+ The nickel in chromium hydroxide can be reduced to undetectable level after washing with dilute acid water heated to 60°C, and there is no need to add crystallization purification process later.

[0135] Comparison of Fe in chromium hydroxide after washing in experiments ⑨-1, ⑨-5, ⑨-6, and ⑨-7 3+ , Fe in chromium hydroxide washed with dilute acid water 3+ Very low, no further reduction is required to prepare the iron-chromium electrolyte. Chromium hydroxide contains a large amount of free Fe 2+ , when washing, Fe 2+ At higher pH, it is easily oxidized and hydrolyzed to Fe(OH) 3 , mixed in chromium hydroxide, washing with dilute acid water can significantly reduce Fe 2+ The oxidation rate verifies that when washing chromium hydroxide with dilute acid water of pH=2.0-2.5 at 60-80℃, chromium hydroxide will not dissolve and be lost. 3+ Both are lower than 0.05%, and the higher the temperature, the better the impurity removal effect.

[0136] (4) Experiment ⑨-8 shows that when chromium is precipitated with liquid alkali, the resulting chromium hydroxide contains no impurity nickel, but after washing with hot dilute acid water, Fe 2+ It is still very high. The reason is that when sodium hydroxide is added to the solution, the local over-alkalinity will form Fe(OH) 2 The precipitate cannot be removed by water washing, resulting in high iron and low chromium in chromium hydroxide. If it is used to produce iron-chromium electrolyte, a large amount of expensive chromium chloride needs to be added, which greatly increases the production cost. Therefore, when precipitating chromium, liquid alkali is not used, and iron powder is used. Although nickel will be introduced, it can be removed by water washing. The raw materials for the final electrolyte are all derived from chromium-containing waste liquid, and no additional chromium chloride needs to be added.

[0137] Comparative Test Example 4

[0138] Experiment ⑩: Take 1000g of the chromium-containing ferrous chloride solution A2 obtained in step 2 of Example 1, in which nickel is removed until no chromium is detected, heat it to 70°C, add 30g of reduced iron powder (Fe=98.3%, Ni=0.06%) respectively, use a dispersed stirring paddle to stir at a speed of 1000r / min, react for different times, take samples and filter, detect nickel in the filtrate, react to pH=3.4-3.5, obtain chromium precipitation slurry, take 300g of the chromium precipitation slurry and add it to a 250mL measuring cylinder, use a 12000GS magnetic rod to magnetically absorb until there is no magnetically absorbed object, filter until there is no filtrate, detect the components in the chromium mud, and the experimental data are summarized in Table 7 below.

[0139] Table 7 Summary of experimental data on nickel replacement using dispersion disk

[0140]

[0141] Analyze the data in Table 7:

[0142] The dispersion disk has been used as a stirring device for chromium precipitation and nickel replacement, but the nickel in the filtrate cannot be completely replaced. 3+ The reason is that when the dispersed stirring paddle rotates quickly, the particle size of chromium hydroxide is small, which avoids the inclusion of free nickel. Increasing the amount of iron powder helps to replace the free nickel into solid nickel, which is easy to remove by magnetic attraction. However, due to the high speed and high pH of the material, the Fe in the slurry 2+ It is easily oxidized by oxygen in the air, making Fe 3+ Increased Fe 3+ It can undergo redox reaction with solid nickel to increase the free nickel. Therefore, in order to increase the Fe 3+ The content of nickel is relatively low, so it is not suitable to use the dispersion disk for a long time. The pH value of the chromium precipitation slurry is preferably 2.5-3.0.

[0143] From experiment ⑩, it can be seen that if the free nickel is to be completely replaced, it is necessary to increase the pH and release the nickel contained in the chromium hydroxide. It is necessary to use a dispersed stirring blade when the chromium hydroxide precipitates. However, after increasing the pH, Fe 3+ The solid nickel is dissolved due to the increase of pH. The technical idea of ​​completely replacing nickel and then removing it by magnetic attraction is not feasible. Therefore, the present invention adopts a technical solution of removing free nickel by washing with hot dilute acid water. This technical solution only needs to precipitate the chromium, and does not need to increase the pH to avoid the formation of Fe 3+ , while saving iron powder.

[0144] Comparative Test Example 5

[0145] Experiments A-K: In a small test, chromium hydroxide slurry was prepared according to the process flow. In each experiment, 2 kg of slurry was taken into a 3 L glass beaker with a diameter of 17 cm. The slurry was dispersed for 3 minutes using dispersing stirring paddles of different diameters and at different rotation speeds, and the particle size of the chromium hydroxide was detected.

[0146] Experiment L: 500 kg of chromium hydroxide slurry was prepared according to the pilot process. The diameter of the stirring tank was 1 m, the diameter of the dispersion disk was 35 cm, and it was dispersed at 800 r / min for 2 min. Samples were taken to detect the particle size of the chromium hydroxide.

[0147] The experimental data are summarized in Table 8.

[0148] Table 8 Effect of different impeller sizes and speeds on chromium hydroxide particle size

[0149]

[0150] Analyze the experimental data in the above table:

[0151] (1) From experiments A and B, it can be seen that when the size of the stirring paddle is too small, increasing the rotation speed can increase the shear force, thereby reducing the particle size of chromium hydroxide;

[0152] (2) Experiments J and K show that when the size of the stirring paddle is too large, the shear force is weak, and the shear force decreases when the rotation speed is increased. The reason for this is that the solution rotates with the stirring paddle, and the relative movement is small, which cannot achieve the purpose of shearing chromium hydroxide.

[0153] (3) From experiments C to G, it can be seen that increasing the rotation speed reduces the particle size of chromium hydroxide, and a rotation speed of 800 to 1000 r / min can make the particle size of chromium hydroxide reach the required level;

[0154] (4) From experiments H to I, we can see that the particle size data are close to those of D and G, indicating that the dispersion effects of the 4.5 cm and 6 cm dispersion disks on this solution are similar.

[0155] Summarizing and analyzing the small-scale experiments A to K, the diameter of the dispersed stirring paddle should match the diameter of the container, and the diameter of the stirring paddle should be 1 / 3 to 1 / 4 of the container diameter, and the speed should be 800 to 1000 r / min. The rules summarized in the small-scale experiment are applied to the pilot test, and the effect is similar, which can be applied to production.

[0156] Electrical performance test

[0157] The electrolytes obtained in Experimental Examples 1, 2, and 3 and electrolytes with various impurity concentrations were subjected to electrical performance tests, and the charge and discharge mode was set to constant current charge and discharge, with a current of 120 mA / cm 2, the charging cut-off voltage is 1.2V, the discharging cut-off voltage is 0.3V, the charging and discharging times are 20 times, and the obtained data are shown in Table 9. In the iron-chromium electrolyte, Fe=1.2M, Cr=1.4M, and HCl=2.5M.

[0158] Table 9 Electrical performance test data record table of various impurity concentration electrolytes

[0159]

[0160] It can be seen from the data in Table 9 that the purity of the electrolyte in this technical solution is close to that of the analytical pure reagent configuration, and the energy efficiency and attenuation rate are better. Compared with the prior art CN117497816B, the manganese content is lower, and the energy efficiency and attenuation rate are similar.

[0161] Cost Analysis

[0162] The cost of purchasing finished products of chromium chloride and ferrous chloride for compounding electrolyte production is calculated based on Fe=1.2M, Cr=1.4M, HCl=2.5M in the ferrochromium electrolyte. The data are shown in Table 10.

[0163] Table 10 Cost accounting table for purchasing finished chromium chloride and ferrous chloride composite electrolyte raw materials

[0164]

[0165]

[0166] It can be seen from Table 10 that the raw material cost of purchasing finished compound electrolyte is close to 7,000 yuan / ton. The cost of carbon ferrochrome in the existing technology CN118099495B is less than 1,400 yuan / ton, and the purification process cost is less than 2,000 yuan / ton. When stainless steel waste liquid is used as raw material, the raw material cost is less than 0 yuan, and the purification process cost is less than 1,000 yuan / ton. The cost of electrolyte is greatly reduced, the economic benefit is significant, and it has promotion significance, which is in line with the trend of technological development.

[0167] The present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. It should be clear to those skilled in the art that any improvement of the present invention, the equivalent replacement of each raw material in the method of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention without departing from the principle of the present invention.

Claims

1. A method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride using stainless steel waste liquid, characterized in that: The following steps are involved: S1. Add elemental iron and / or elemental chromium to the stainless steel waste liquid to make the solution pH = 1.2 to 2.2, separate the solid and liquid, and obtain a chromium-containing ferrous chloride solution A1; S2. Adjust the chromium-containing ferrous chloride solution A1 to make its Fe 2+ content is less than 14%, adding sulfide to the chromium-containing ferrous chloride solution A1 until nickel is not detected, and separating the solid and liquid to obtain solid nickel sulfide and the chromium-containing ferrous chloride solution A2; S3. The chromium-containing ferrous chloride solution A2 is heated to 50°C to 100°C, iron powder is added to obtain a mixed solution, The mixed solution is stirred using a dispersive stirring paddle, and the mixed solution is first stirred at a first stirring speed to make the pH value of 2.5 to 3.0 to form a chromium hydroxide precipitate, and then the chromium hydroxide is dispersed at a second stirring speed, wherein the diameter of the dispersive stirring paddle is adapted to the diameter of the container containing the mixed solution so that when stirring at the second stirring speed, the dispersive stirring paddle generates a shear force on the mixed solution, and the shear force reduces the particle size of the polymerized chromium hydroxide, thereby releasing the adsorbed and contained free nickel ions. The first stirring speed is less than the second stirring speed, and the second stirring speed is 800-1000 r / min to obtain chromium hydroxide slurry. removing excess iron powder from the chromium hydroxide slurry, separating the solid from the liquid, and obtaining a ferrous chloride solution and chromium hydroxide; S4. Wash the chromium hydroxide with dilute acid water having a pH value of 2.0 to 2.5, and then dissolve it in hydrochloric acid to obtain a chromium chloride solution; The ferrous chloride solution is sequentially evaporated and concentrated, and cooled and crystallized to obtain electronic grade ferrous chloride.

2. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S1, the stainless steel waste liquid is heated at a temperature of 40 to 90° C.; The chromium-containing ferrous chloride solution A1 contains Cr 3+ <1%.

3. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by utilizing stainless steel waste liquid according to claim 1, characterized in that: In step S2, the chromium-containing ferrous chloride solution A1 in step S1 is transferred to another stirring tank, and then the chromium-containing ferrous chloride solution A1 is adjusted.

4. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S2, the sulfide is sodium sulfide and / or hydrogen sulfide; The amount of sodium sulfide / hydrogen sulfide added is calculated based on the theoretical amount of nickel removed, and the remaining S in the solution is - The concentration is 1.4%~2.0%.

5. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S3, the amount of iron powder added is 2% to 5% of the mass of the chromium-containing ferrous chloride solution A2.

6. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S3, the diameter of the dispersed stirring paddle is 1 / 3 to 1 / 4 of the diameter of the container; The first stirring speed is 200-400 r / min. When the pH value is 2.5-3.0, the first stirring speed is increased to the second stirring speed of 800-1000 r / min. The dispersion time of the second stirring speed is 1-3 min.

7. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S3, excess iron powder is removed by an iron remover.

8. The method for preparing iron-chromium electrolyte and electronic-grade ferrous chloride by using stainless steel waste liquid according to claim 1, characterized in that: In step S4, the temperature of the dilute acid water is set to 60°C to 80°C to wash the chromium hydroxide, and the washing water after washing is returned to step S2 to adjust the Fe content of the chromium-containing ferrous chloride solution A1. 2+ content.

9. An iron-chromium electrolyte, characterized in that: Industrial hydrochloric acid, the chromium chloride solution prepared according to any one of claims 1 to 8 and electronic grade ferrous chloride are mixed in proportion to obtain an iron-chromium electrolyte.

10. An iron-chromium redox flow battery, characterized in that: Containing the iron-chromium electrolyte according to claim 9.

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