A method for preparing vanadium electrolyte by crystallizing vanadium slag with alumina seed mother liquor

Abstract

The application provides a method for preparing vanadium electrolyte by crystallizing vanadium slag with bayer seed mother liquor, which comprises the following steps: reducing and acid leaching the bayer seed mother liquor crystallized vanadium slag, converting V(V) and As(V) into V(IV) and As(III), adding arsenic removal precipitator to remove arsenic, and further hydrolyzing VO(OH)2; converting the VO(OH)2 into pentavalent vanadate solution through oxidation and alkali leaching, and further removing impurity ions such as arsenic, phosphorus, aluminum and silicon through multiple crystallization to obtain high-purity vanadate; finally, converting the high-purity vanadate into V(IV) solution through reduction and acid leaching, adding arsenic removal precipitator again to realize deep arsenic removal, hydrolyzing to obtain VO(OH)2, and preparing VOSO4 electrolyte through sulfuric acid acid solution.

Description

Technical Field

[0001] The invention relates to the field of preparation of vanadium electrolyte, in particular to a method for preparing vanadium electrolyte by utilizing alumina seed liquor and crystallized vanadium slag. Background Art

[0002] Bauxite is an important potential vanadium resource. The Bayer process is the most widely used method for extracting alumina from bauxite. Alumina is obtained through a series of steps: dissolution, seed crystal decomposition, and high-temperature roasting. During the dissolution process, the aluminum in the bauxite is converted into sodium aluminate and enters the mother liquor. Simultaneously, over 30% of the vanadium in the bauxite, as well as some impurities such as phosphorus, arsenic, and silicon, also dissolve into the mother liquor. These vanadium and impurities continue to accumulate as the mother liquor circulates, posing a threat to the subsequent aluminum hydroxide seed crystal decomposition process.

[0003] Currently, the industry widely uses evaporative cooling crystallization to remove impurities such as vanadium, phosphorus, arsenic, and silicon from the Bayer process mother liquor. The resulting crystals, after further processing, yield vanadium slag with a V2O5 content of 10%-20%. This vanadium slag is known as Bayer process alumina mother liquor crystallization slag. Currently, alumina plants typically treat this vanadium slag by dissolving it in water and then directly precipitating vanadium with ammonium salts to obtain crude ammonium metavanadate. Further roasting yields crude V2O5 with high levels of impurities such as phosphorus, arsenic, silicon, and aluminum, resulting in low purity. Furthermore, the high-salt ammonia nitrogen wastewater produced by ammonium salt precipitation is very expensive to treat, further exacerbating the cost pressures and environmental pollution issues faced by alumina plants.

[0004] Chinese invention patent application publication number CN 116904772 A discloses a process for extracting vanadium from crystallized vanadium slag from the seed liquor of alumina produced by the Bayer process. The vanadium slag is first dissolved in sodium hydroxide, and lead sulfate is added to precipitate vanadium. The precipitated solution is cooled, crystallized, filtered, and returned to the dissolution step. The vanadium-enriched slag is leached with sulfuric acid and a reducing agent to obtain a vanadium-enriched solution. This method eliminates the need for ammonium salt precipitation, thus avoiding the generation of ammonia-nitrogen wastewater. However, the resulting lead-containing wastewater is still harmful to the environment, and the resulting vanadium-enriched solution still requires further treatment, such as extraction. Chinese invention patent application publication number CN 116397112 A discloses a method for separating and extracting vanadium from crystallized vanadium slag from the seed liquor of the Bayer process. The vanadium slag is dissolved in sodium hydroxide, followed by the addition of a barium salt to selectively precipitate vanadium. The precipitated solution is cooled, crystallized, filtered, and returned to the dissolution step. The precipitated vanadium slag is leached with a leaching agent or converted to an acid solution and then leached with a leaching agent to obtain a leached slag and a vanadium-enriched solution. The vanadium-enriched solution is then precipitated with ammonium salt to obtain a vanadium product. This method consumes less acid and alkali and achieves a high vanadium recovery rate, but the recovery of the vanadium product still requires ammonium salt precipitation. Furthermore, these methods are all targeted at deep removal of impurity elements from vanadium slag, resulting in only crude vanadium products with high impurity content and low purity.

[0005] All-vanadium flow battery electrolyte is a high-value vanadium product, primarily produced using expensive high-purity V2O5 as raw material. High-purity V2O5 is typically produced from 98% crude V2O5 through a lengthy purification process, which results in the discharge of large amounts of highly polluting ammonia-nitrogen wastewater. This also contributes to the high cost of vanadium electrolytes. Using vanadium slag crystallized from Bayer process seed liquor as raw material for a shorter, clean production process would not only reduce vanadium electrolyte production costs but also achieve high-value utilization of vanadium slag. However, vanadium electrolytes have high impurity requirements, and vanadium slag is rich in a wide range of impurity elements at high concentrations. Therefore, the in-depth purification and removal of multiple impurities in the preparation of vanadium electrolytes from vanadium slag crystallized from Bayer process seed liquor is crucial.

[0006] A Chinese invention patent application, publication number CN 116404220 A, discloses a method for preparing a high-concentration vanadium electrolyte by crystallizing and purifying vanadates and then chemically reducing them. Using crude vanadium or other vanadium-containing materials as raw materials, the method uses alkali dissolution and crystallization to purify high-purity vanadates, which are then chemically reduced to produce the vanadium electrolyte. This method is an entirely wet process, requiring no reagents such as ammonium salts or impurity removers. However, the raw materials used are industrial products such as crude vanadium and ammonium vanadate, which have high vanadium content and low impurity content. Therefore, it is not suitable for crystallizing vanadium slag from Bayer process seed liquor, which has a high impurity content.

[0007] In summary, the existing methods for extracting vanadium and preparing electrolyte cannot achieve the purification and removal of impurities from the crystallization of vanadium slag from the Bayer process alumina seed liquor and the preparation of vanadium electrolyte. It is urgent to develop a method for purifying and removing impurities from the crystallization of vanadium slag from the Bayer process seed liquor and preparing vanadium electrolyte. Summary of the Invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a vanadium electrolyte by using vanadium slag crystallized from alumina seed liquor. The method aims to achieve the purification and impurity removal of vanadium slag crystallized from alumina seed liquor produced by the Bayer process and the preparation of a vanadium electrolyte, so that the obtained vanadium electrolyte meets the requirements of GB / T 37204-2018 for first-grade quadrivalent vanadium electrolyte, while reducing the production cost of the vanadium electrolyte.

[0009] According to one aspect of the present invention, a method for preparing a vanadium electrolyte by crystallizing vanadium slag from an alumina seed liquor is provided, wherein the alumina seed liquor is an alumina seed liquor produced by the Bayer process, and the method comprises the following steps:

[0010] 1) dissolving the crystallized vanadium slag of the Bayer process alumina seed liquor in acid, adjusting the pH value of the solution to 0-5, adding a first reducing agent in an amount of 1.1-3 times the theoretical amount of the first reducing agent required for reducing V(V) and As(V) to V(IV) and As(III), reacting at 25-99° C. for 0.5-5 hours to obtain a V(IV) solution, adjusting the pH value of the V(IV) solution to -1-5, adding an arsenic removal precipitant in an amount of 3-9 times the theoretical amount of the arsenic removal precipitant required for removing As(III) in multiple portions, reacting at 25-99° C. for 0.5-2 hours to obtain an arsenic-removed V(IV) solution, adjusting the pH value of the arsenic-removed V(IV) solution to 5-14, and filtering to obtain a VO(OH)2 solid; wherein the first reducing agent comprises one or more of sodium sulfide, elemental sulfur, sulfur dioxide, sulfite, oxalic acid, oxalate, glucose, fructose, sucrose, and formic acid;

[0011] 2) placing the VO(OH)2 solid obtained in step 1) in an alkaline solution and adjusting the pH to 7-14, adding an oxidant in an amount of 1.5-5 times the theoretical amount required for oxidation of V(IV) to V(V), reacting at 25-99°C for 0.5-2 h to obtain a pentavalent vanadate solution, then cooling the vanadate solution to 0-25°C at a rate of 0.1-5°C / min, and stirring the solution at a rate of 20-200 r / min. The cooled solution is filtered to obtain vanadate crystals; then, step 2) is repeated once or more using the vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain high-purity vanadate crystals with a purity greater than 99.9%;

[0012] 3) dissolving the high-purity vanadate crystals obtained in step 2) in acid and adjusting the pH to 0-5; adding a second reducing agent in an amount of 1.1-3 times the theoretical amount of the second reducing agent required for reducing V(V) and As(V) to V(IV) and As(III); reacting at 25-99° C. for 0.5-5 h; adjusting the pH of the solution to -1-5; adding an arsenic removal precipitant in an amount of 3-9 times the theoretical amount of the arsenic removal precipitant required for removing As(III) in multiple portions; reacting at 25-99° C. for 0.5-2 h to obtain an arsenic-removed solution; adjusting the pH of the arsenic-removed solution to 5-14; filtering to obtain VO(OH)2; washing the VO(OH)2 with acid and water; and dissolving the washed VO(OH)2 with acid to prepare a vanadium electrolyte; wherein the second reducing agent comprises one or more of sodium sulfide, elemental sulfur, sulfur dioxide, sulfite, oxalic acid, oxalate, glucose, fructose, sucrose, and formic acid.

[0013] As a preferred embodiment of the method of preparing vanadium electrolyte by using alumina seed liquor crystallized vanadium slag of the present invention, the alumina seed liquor crystallized vanadium slag produced by the Bayer process includes V2O5 10-20 wt%, Al 0.5-1 wt%, As 0.5-3 wt%, P 1-3 wt%, and Si 0.1-1 wt%.

[0014] As a preferred embodiment of the method of preparing a vanadium electrolyte by using vanadium slag crystallized from alumina seed liquor of the present invention, in step 1), the acid comprises dilute sulfuric acid with a concentration of 40 to 100 g / L, and the solid-to-liquid ratio of the vanadium slag crystallized from the Bayer process alumina seed liquor to the dilute sulfuric acid is 1:1 to 1:10 g / mL.

[0015] As a preferred embodiment of the method of preparing a vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, the pH value is adjusted as follows: when the pH value needs to be lowered, one or more acids including sulfuric acid and hydrochloric acid are added to the solution for adjustment; when the pH value needs to be increased, one or more bases including NaOH and KOH are added to the solution for adjustment.

[0016] As a preferred embodiment of the present invention's method for preparing a vanadium electrolyte using alumina seed liquor crystallized from vanadium slag, the arsenic removal precipitant includes one or more of sodium sulfide, potassium sulfide, ammonium sulfide, hydrogen sulfide, and thiourea. The theoretical amount of the arsenic removal precipitant required to remove As(III) is specifically the theoretical amount required for the reaction of As(III) with the arsenic removal precipitant to produce As2S3.

[0017] As a preferred embodiment of the method for preparing vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, the multiple times in step 1) is 3 to 5 times.

[0018] As a preferred embodiment of the method for preparing vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, in step 2), the oxidant comprises one or more of hydrogen peroxide, sodium peroxide, potassium peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate.

[0019] As a preferred embodiment of the method for preparing vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, in step 2), the alkali solution comprises one or more of NaOH and KOH solutions with a concentration of 50-500 g / L.

[0020] As a preferred embodiment of the method for preparing vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, the multiple times in step 3) is 3 to 5 times.

[0021] As a preferred embodiment of the method for preparing a vanadium electrolyte by crystallizing vanadium slag from alumina seed liquor, in step 3), the reagent used for pickling is dilute sulfuric acid with a pH of 5 to 7, the number of acid pickling washes is 1 to 3 times, and the number of water washes is 2 to 3 times; the reagent used for acid dissolution is sulfuric acid with a concentration of 4 to 6 mol / L.

[0022] The present invention subjects the Bayer process seed denominator liquor crystallized vanadium slag to reduction acid leaching, converting V(V) and As(V) therein into V(IV) and As(III), adding an arsenic removal precipitant for arsenic removal, and further hydrolyzing to produce VO(OH)2; VO(OH)2 is converted into a pentavalent vanadate solution by oxidative alkali leaching, and then further removing impurity ions such as arsenic, phosphorus, aluminum, and silicon through multiple crystallizations to obtain high-purity vanadate; finally, the high-purity vanadate is converted into a V(IV) solution by reduction acid leaching, and an arsenic removal precipitant is added again to achieve deep arsenic removal, and VO(OH)2 is obtained by hydrolysis, which is then dissolved in sulfuric acid to prepare a VOSO4 electrolyte.

[0023] In the technical solution of the present invention, all contents are by mass unless otherwise specified, As(V) refers to pentavalent arsenic, As(III) refers to trivalent arsenic, V(V) refers to pentavalent vanadium, and V(IV) refers to tetravalent vanadium.

[0024] Compared with the prior art, this invention has the following beneficial effects:

[0025] 1. This invention uses vanadium slag, crystallized from the seed liquor of alumina produced by the Bayer process, as raw material to produce vanadium electrolyte, realizing resource utilization and high-value utilization of vanadium in bauxite. Furthermore, the washing liquid obtained from acid and water washing can be used to dissolve high-purity vanadate crystals. Calculations show that compared to the traditional production process of vanadium electrolyte produced from vanadium slag obtained from vanadium-titanium magnetite, the production cost of vanadium electrolyte can be reduced by more than 50%.

[0026] 2. The three-stage synergistic precipitation-crystallization-precipitation process deeply removes impurities such as arsenic, aluminum, and silicon from the crystallized vanadium slag from the Bayer process seed liquor. This achieves a high impurity removal rate and produces a high-purity vanadium electrolyte that meets the first-grade requirements for quadrivalent vanadium electrolyte specified in GB / T 37204-2018. The vanadium electrolyte obtained using the present invention has impurity contents of As ≤ 0.8 ppm, Al ≤ 1.8 ppm, and Si ≤ 1.2 ppm.

[0027] 3. The entire process of the present invention is a wet process, which does not require high-temperature calcination, has low energy consumption, low cost, is easy to operate, and does not produce difficult-to-treat wastes such as ammonia nitrogen wastewater and organic pollutants. In addition, the solution in the entire process can be recycled through purification, and the process is clean. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the preparation method of the present invention

[0029] Figure 2 Actual picture of the vanadium electrolyte obtained by the preparation method of the present invention DETAILED DESCRIPTION

[0030] The following will be a clear and complete description of the technical solutions in the embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 7.7% V, 18.4% Na, 1.4% As, 1.3% P, 0.6% Al, and 0.3% Si. The method comprises the following steps:

[0033] 1) 200 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 80 g / L dilute sulfuric acid at a solid-liquid ratio of 1:3, and the pH value of the solution was adjusted to 1 with sulfuric acid. 27 g of oxalic acid was added and the mixture was reacted at 60°C for 2 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH value of the V(IV) solution to 2. A total of 27 g of sodium sulfide (9 g each time) was gradually added in three portions and the mixture was reacted at 60°C for 1 h to obtain an arsenic-removed V(IV) solution. NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 7, and the solution was filtered to obtain VO(OH)2 solid.

[0034] 2) The VO(OH)2 solid obtained in step 1) was mixed with 10.2 g of hydrogen peroxide, dissolved in 300 ml of a 100 g / L NaOH solution, and adjusted to pH 9 using dilute sulfuric acid. The mixture was reacted at 60°C for 1 h to obtain a pentavalent sodium vanadate solution. The sodium vanadate solution was then cooled to 20°C at a rate of 1.4°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain sodium vanadate crystals. Step 2) was then repeated twice using sodium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 55.2 g of high-purity sodium vanadate crystals with a purity of 99.93% and an As content of 0.06 wt%.

[0035] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 1. 30.24 g of sodium sulfite was added and the reaction was carried out at 60° C. for 2 h. NaOH was added to adjust the pH value of the solution to 2. 0.3 g of sodium sulfide (0.1 g each time) was added in three portions and the reaction was carried out at 60° C. for 1 h to obtain an arsenic-free solution with an arsenic content of 3.4 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 7. The solution was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed twice with water. The washed VO(OH)2 was then dissolved in 150 mL of 4.2 mol / L sulfuric acid to prepare a 1.6 mol / L vanadylic sulfate electrolyte.

[0036] The vanadyl sulfate electrolyte prepared in this embodiment was determined to contain 42 ppm of Na, 0.2 ppm of As, 1 ppm of Al, and 1.2 ppm of Si, meeting the requirements of GB / T 37204-2018 for first-grade tetravalent vanadium electrolyte.

[0037] Example 2

[0038] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 8.2% V, 17.3% Na, 1.2% As, 1.5% P, 1% Al, and 0.4% Si. The method comprises the following steps:

[0039] 1) 200 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 70 g / L dilute sulfuric acid at a liquid-solid ratio of 1:5, and the pH value of the solution was adjusted to 3 using KOH. 5.14 g of elemental sulfur was added, and the mixture was reacted at 40°C for 5 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to 0, and a total of 21.12 g of potassium sulfide (5.28 g each time) was gradually added in 4 portions, and the mixture was reacted at 40°C for 1 h to obtain an arsenic-free V(IV) solution. NaOH was added to adjust the pH value of the arsenic-free V(IV) solution to 9, and VO(OH)2 solid was obtained by filtration.

[0040] 2) The VO(OH)2 solid obtained in step 1) was mixed with 52.8 g of potassium peroxide, dissolved in 300 ml of a 150 g / L KOH solution, and the pH was adjusted to 12 using KOH. The mixture was reacted at 80°C for 1 h to obtain a pentavalent potassium vanadate solution. The potassium vanadate solution was then cooled to 10°C at a rate of 2.5°C / min. During the cooling process, the solution was stirred at a rate of 100 r / min. The cooled solution was filtered to obtain potassium vanadate crystals. Step 2) was then repeated twice using potassium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 59.4 g of high-purity potassium vanadate crystals with a purity of 99.91% and an As content of 0.08 wt%.

[0041] 3) The high-purity potassium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 3. 17.28 g of oxalic acid was added and the mixture was reacted at 40° C. for 5 h. Sulfuric acid was added to adjust the pH value of the solution to 0. 0.418 g of potassium sulfide (0.1054 g each time) was added in four portions and the mixture was reacted at 40° C. for 1 h to obtain an arsenic-free solution having an arsenic content of 5.2 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 10. The solution was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed twice with water. The washed VO(OH)2 was then dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 2 mol / L vanadium oxysulfate electrolyte.

[0042] It was determined that the vanadyl sulfate electrolyte prepared in this example contained 36 ppm of Na, 0.5 ppm of As, 1.8 ppm of Al, and 1 ppm of Si, which met the requirements of GB / T 37204-2018 for first-grade tetravalent vanadium electrolyte.

[0043] Example 3

[0044] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 6.8% V, 15.4% Na, 1.9% As, 2% P, 2% Al, and 1% Si. The method comprises the following steps:

[0045] 1) 200 g of vanadium slag crystallized from Bayer process mother liquor of alumina production with liquid-solid ratio of 1:7 was dissolved in 80 g / L dilute sulfuric acid, the pH value of the solution was adjusted to 0 using sulfuric acid, 20.16 g of sodium sulfite was added, and the reaction was carried out at 25°C for 5 h to obtain a V(IV) solution, the pH value of the V(IV) solution was adjusted to 0 using sulfuric acid, a total of 52.65 g of sodium sulfide (10.53 g each time) was added in 5 steps, and the reaction was carried out at 25°C for 2 h to obtain a V(IV) solution from which arsenic was removed, the pH value of the V(IV) solution from which arsenic was removed was adjusted to 11 using NaOH, and filtration was performed to obtain VO(OH)2 solid;

[0046] 2) The VO(OH)2 solid obtained in step 1) was mixed with 52.65 g of sodium peroxide, dissolved in 250 ml of 200 g / L NaOH solution, and the pH value was adjusted to 7 using sulfuric acid, and the reaction was carried out at 40°C for 1 h to obtain a sodium vanadate solution, then the sodium vanadate solution was cooled to 2°C at a rate of 0.5°C / min, and the solution was stirred at a rate of 100 r / min during the cooling process, and the cooled solution was filtered to obtain sodium vanadate crystals; then step 2) was repeated twice with sodium vanadate crystals replacing VO(OH)2 solid as raw material to obtain 40 g of high-purity sodium vanadate crystals with a purity of 99.95% and an arsenic content of 0.04 wt%;

[0047] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid, and the pH value was adjusted to 0, 9.72 g of formic acid was added, and the reaction was carried out at 25°C for 5 h, the pH value of the solution was adjusted to 0 using sulfuric acid, 0.22 g of sodium sulfide (0.044 g each time) was added in 5 steps, and the reaction was carried out at 25°C for 2 h to obtain an arsenic-removed solution with an arsenic content of 6.4 ppm, the pH value of the arsenic-removed solution was adjusted to 14 using NaOH, and filtration was performed to obtain VO(OH)2, which was washed with dilute sulfuric acid with a pH of 6.5 twice and water twice, then the washed VO(OH)2 was dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 1.7 mol / L vanadyl sulfate electrolyte.

[0048] It was determined that the vanadyl sulfate electrolyte prepared in this embodiment had Na 23 ppm, As 0.5 ppm, Al 1.6 ppm, and Si 0.7 ppm, which met the requirements of GB / T 37204-2018 for 4-valent vanadium electrolyte first-grade products.

[0049] Example 4

[0050] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 10.5% V, 15.5% Na, 1% As, 2.4% P, 1.2% Al, and 0.4% Si. The method comprises the following steps:

[0051] 1) 500 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 40 g / L dilute sulfuric acid at a solid-liquid ratio of 1:9, and the pH value of the solution was adjusted to 0 with sulfuric acid. 97.6 g of potassium sulfite was added and the reaction was carried out at 30°C for 5 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to -1, and a total of 20.4 g of ammonium sulfide (5.1 g each time) was gradually added in 4 portions and the reaction was carried out at 30°C for 2 h to obtain an arsenic-removed V(IV) solution. NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 13, and VO(OH)2 solid was obtained by filtration.

[0052] 2) The VO(OH)2 solid obtained in step 1) was mixed with 70 g of hydrogen peroxide, dissolved in 1 L of 330 g / L KOH solution, and adjusted to pH 8 using sulfuric acid. The mixture was reacted at 30°C for 2 h to obtain a pentavalent potassium vanadate solution. The potassium vanadate solution was then cooled to 2°C at a rate of 0.1°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain potassium vanadate crystals. Step 2) was then repeated three times using potassium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 200 g of high-purity potassium vanadate crystals with a purity of 99.91% and an As content of 0.09 wt%.

[0053] 3) The high-purity potassium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to -1. 61.8 g of potassium oxalate was added and the mixture was reacted at 30°C for 5 h. Sulfuric acid was added to adjust the pH value of the solution to -1. 0.75 g of ammonium sulfide (0.25 g each time) was added three times and the mixture was reacted at 30°C for 2 h to obtain an arsenic-free solution with an arsenic content of 3.2 ppm. KOH was added to adjust the pH value of the arsenic-free solution to 13. VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was washed once with dilute sulfuric acid at a pH of 6.5 and washed three times with water. The washed VO(OH)2 was then dissolved in 270 mL of 6 mol / L sulfuric acid to prepare a 3 mol / L vanadylic sulfate electrolyte.

[0054] It was determined that the vanadyl sulfate electrolyte prepared in this example contained 46 ppm of Na, 0.8 ppm of As, 1.2 ppm of Al, and 0.8 ppm of Si, which met the requirements of GB / T 37204-2018 for first-grade tetravalent vanadium electrolyte.

[0055] Example 5

[0056] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 9.6% V, 13.2% Na, 1.2% As, 2% P, 1.3% Al, and 0.5% Si. The method comprises the following steps:

[0057] 1) 300 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 40 g / L dilute sulfuric acid at a solid-liquid ratio of 1:10, and the pH value of the solution was adjusted to 5 with NaOH. 82.3 g of sodium oxalate was reacted at 90 °C for 0.5 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to -1. A total of 16.8 g of sodium sulfide (4.2 g each time) was gradually added in 4 portions and reacted at 90 °C for 0.5 h to obtain an arsenic-free V(IV) solution. KOH was added to adjust the pH value of the arsenic-free V(IV) solution to 5, and VO(OH)2 solid was obtained by filtration.

[0058] 2) The VO(OH)2 solid obtained in step 1) was mixed with 80.64 g of sodium peroxide, dissolved in 500 ml of 400 g / L NaOH solution, and adjusted to pH 11 using sulfuric acid. The mixture was reacted at 95°C for 0.5 h to obtain a pentavalent sodium vanadate solution. The sodium vanadate solution was then cooled to 2°C at a rate of 5°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain sodium vanadate crystals. Step 2) was then repeated once using sodium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 82.5 g of high-purity sodium vanadate crystals with a purity of 99.91% and an As content of 0.06 wt%.

[0059] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 5. 60.48 g of oxalic acid was added and the reaction was carried out at 90 ° C for 0.5 h. Sulfuric acid was added to adjust the pH value of the solution to -1. 0.24 g of sodium sulfide (0.06 g each time) was added in 4 portions and the reaction was carried out at 90 ° C for 0.5 h to obtain an arsenic-free solution with an arsenic content of 3.2 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 11, and VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed three times with water. The washed VO(OH)2 was then dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 2.5 mol / L vanadyl sulfate electrolyte.

[0060] The vanadyl sulfate electrolyte prepared in this embodiment was determined to contain 58 ppm of Na, 0.6 ppm of As, 0.8 ppm of Al, and 0.6 ppm of Si, which met the requirements of GB / T 37204-2018 for first-grade tetravalent vanadium electrolyte.

[0061] Example 6

[0062] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 5.7% V, 13.2% Na, 2% As, 2.4% P, 2.2% Al, and 1% Si. The method comprises the following steps:

[0063] 1) 400 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 100 g / L dilute sulfuric acid at a solid-liquid ratio of 1:1, and the pH value of the solution was adjusted to 4 with KOH. 52.3 g of potassium oxalate was added, and the mixture was reacted at 80 °C for 1 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to 0. A total of 88 g of potassium sulfide (17.6 g each time) was gradually added in 5 portions, and the mixture was reacted at 80 °C for 1 h to obtain an arsenic-removed V(IV) solution. NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 10, and VO(OH)2 solid was obtained by filtration.

[0064] 2) The VO(OH)2 solid obtained in step 1) was mixed with 69.3 g of potassium peroxide, dissolved in 450 ml of a 500 g / L KOH solution, and adjusted to a pH of 10 using sulfuric acid. The mixture was reacted at 80°C for 0.5 h to obtain a pentavalent potassium vanadate solution. The potassium vanadate solution was then cooled to 5°C at a rate of 4°C / min. During the cooling process, the solution was stirred at a rate of 20 r / min. The cooled solution was filtered to obtain potassium vanadate crystals. Step 2) was then repeated twice using potassium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 78 g of high-purity potassium vanadate crystals with a purity of 99.93% and an As content of 0.05 wt%.

[0065] 3) dissolving the high-purity potassium vanadate crystal obtained in step 2) in sulfuric acid and adjusting the pH value to 1, adding 30.24 g of oxalic acid, reacting at 70 °C for 1 h, adding sulfuric acid to adjust the pH value of the solution to 0, adding 0.27 g of ammonium sulfide in 5 times (0.054 g each time), and reacting at 80 °C for 1 h to obtain an arsenic-removed solution containing 4 ppm of arsenic, adding KOH to adjust the pH value of the arsenic-removed solution to 5, and filtering to obtain VO(OH)2, which is washed with dilute sulfuric acid at pH 5 for 2 times and water for 2 times, and then the washed VO(OH)2 is dissolved with 100 mL of 6 mol / L sulfuric acid to prepare a 3.5 mol / L vanadyl sulfate electrolyte.

[0066] It is determined that the vanadyl sulfate electrolyte prepared in the embodiment contains 40 ppm of Na, 0.3 ppm of As, 0.9 ppm of Al, and 0.5 ppm of Si, which meets the requirements of GB / T 37204-2018 for the first-grade product of the 4-valence vanadium electrolyte.

[0067] Comparative Example 1

[0068] A method for preparing a vanadium electrolyte by crystallizing vanadium slag from a Bayer process alumina seed mother liquor, the main components of the vanadium slag from the Bayer process alumina seed mother liquor crystallization including V 7.7%, Na 18.4%, As 1.4%, P 1.3%, Al 0.6%, and Si 0.3%, the method comprising the following steps:

[0069] 1) dissolving 200 g of vanadium slag from the Bayer process alumina seed mother liquor crystallization in 80 g / L dilute sulfuric acid at a solid-liquid ratio of 1:3, adjusting the pH value of the solution to 1 with sulfuric acid, adding 27 g of oxalic acid, and reacting at 60 °C for 2 h to obtain a V(IV) solution, adjusting the pH value of the V(IV) solution to 2 with sulfuric acid, adding a total of 4.32 g of sodium sulfide in 3 times (1.44 g+1.44 g+1.44 g, 1 times the theoretical reaction amount), and reacting at 60 °C for 1 h to obtain an arsenic-removed V(IV) solution, adjusting the pH value of the arsenic-removed V(IV) solution to 7 with NaOH, and filtering to obtain VO(OH)2 solid;

[0070] 2) The VO(OH)2 solid obtained in step 1) was mixed with 10.2 g of hydrogen peroxide, dissolved in 300 ml of a 100 g / L NaOH solution, and adjusted to pH 9 using dilute sulfuric acid. The mixture was reacted at 60°C for 1 h to obtain a pentavalent sodium vanadate solution. The sodium vanadate solution was then cooled to 20°C at a rate of 1.4°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain sodium vanadate crystals. Step 2) was then repeated twice using sodium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 55.2 g of high-purity sodium vanadate crystals with a purity of 99.43% and an As content of 0.55 wt%.

[0071] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 1. 30.24 g of sodium sulfite was added and the reaction was carried out at 60° C. for 2 h. NaOH was added to adjust the pH value of the solution to 2. 0.3 g of sodium sulfide (0.1 g each time) was added in three portions and the reaction was carried out at 60° C. for 1 h to obtain an arsenic-free solution with an arsenic content of 17 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 7. VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed twice with water. The washed VO(OH)2 was then dissolved in 150 mL of 4.2 mol / L sulfuric acid to prepare a 1.6 mol / L vanadylic sulfate electrolyte.

[0072] The results show that the contents of Na 57 ppm, As 5.6 ppm, Al 1.2 ppm and Si 1.3 ppm in the vanadium sulfate electrolyte prepared in this comparative example do not meet the requirements of GB / T 37204-2018 for first-class vanadium electrolyte. Compared with Example 1, the amount of arsenic removal precipitant added in this comparative example is too low, and the As in the V(IV) solution cannot be removed. 3+ Deep removal results in excessive arsenic ion content in the arsenic removal V(IV) solution. Arsenic ions are mixed in high-purity vanadates, reducing their purity. In subsequent processes, arsenic ions are mixed in VO(OH)2 and enter the vanadium electrolyte, causing the arsenic content of the vanadium electrolyte to exceed the standard.

[0073] Comparative Example 2

[0074] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 8.2% V, 17.3% Na, 1.2% As, 1.5% P, 1% Al, and 0.4% Si. The method comprises the following steps:

[0075] 1) 200 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 70 g / L dilute sulfuric acid at a liquid-solid ratio of 1:5, the pH value of the solution was adjusted to 3 with KOH, 5.14 g of elemental sulfur was added, and the mixture was reacted at 40°C for 5 h to obtain a V(IV) solution, sulfuric acid was added to adjust the pH of the V(IV) solution to 0, 21.12 g of potassium sulfide was added at once, and the mixture was reacted at 40°C for 1 h to obtain an arsenic-removed V(IV) solution, NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 9, and VO(OH)2 solid was obtained by filtration;

[0076] 2) The VO(OH)2 solid obtained in step 1) was mixed with 52.8 g of potassium peroxide, dissolved in 300 ml of a 150 g / L KOH solution, and the pH was adjusted to 12 using KOH. The mixture was reacted at 80°C for 1 h to obtain a pentavalent potassium vanadate solution. The potassium vanadate solution was then cooled to 10°C at a rate of 2.5°C / min. During the cooling process, the solution was stirred at a rate of 100 r / min. The cooled solution was filtered to obtain potassium vanadate crystals. Step 2) was then repeated twice using potassium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 59.4 g of high-purity potassium vanadate crystals with a purity of 99.34% and an As content of 0.64 wt%.

[0077] 3) The high-purity potassium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 3. 17.28 g of oxalic acid was added and the mixture was reacted at 40° C. for 5 h. Sulfuric acid was added to adjust the pH value of the solution to 0. 0.418 g of potassium sulfide (0.1054 g each time) was added in four portions and the mixture was reacted at 40° C. for 1 h to obtain an arsenic-free solution having an arsenic content of 20.6 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 10. The solution was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed twice with water. The washed VO(OH)2 was then dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 2 mol / L vanadium oxysulfate electrolyte.

[0078] The results show that the contents of Na 42 ppm, As 6 ppm, Al 2 ppm and Si 1.3 ppm in the vanadium sulfate electrolyte prepared in this comparative example do not meet the requirements of GB / T 37204-2018 for first-class vanadium electrolyte. Compared with Example 2, the arsenic removal precipitant in this comparative example is added once, resulting in the S in the V(IV) solution being 1.3 ppm. 2- The concentration increases instantly, S 2- With H in solution + Rapidly generate H2S gas, thereby reducing the S content in the solution 2- The amount of As in V(IV) solution 3+Failure to remove vanadates deeply reduced the purity of high-purity vanadates and caused the arsenic content in the vanadium electrolyte to exceed the standard.

[0079] Comparative Example 3

[0080] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 6.8% V, 15.4% Na, 1.9% As, 2% P, 2% Al, and 1% Si. The method comprises the following steps:

[0081] 1) 200 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 80 g / L dilute sulfuric acid at a liquid-solid ratio of 1:7, and the pH value of the solution was adjusted to 0 using sulfuric acid. 20.16 g of sodium sulfite was added, and the mixture was reacted at 25°C for 5 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH value of the V(IV) solution to 0, and a total of 52.65 g of sodium sulfide (10.53 g each time) was gradually added in 5 portions, and the mixture was reacted at 25°C for 2 h to obtain an arsenic-free V(IV) solution. NaOH was added to adjust the pH value of the arsenic-free V(IV) solution to 11, and VO(OH)2 solid was obtained by filtration.

[0082] 2) The VO(OH)2 solid obtained in step 1) was mixed with 52.65 g of sodium peroxide, dissolved in 250 ml of a 200 g / L NaOH solution, and adjusted to pH 7 using sulfuric acid. The mixture was reacted at 40°C for 1 h to obtain a pentavalent sodium vanadate solution. The sodium vanadate solution was then cooled to 2°C at a rate of 0.5°C / min. During the cooling process, the solution was stirred at a rate of 250 r / min. The cooled solution was filtered to obtain sodium vanadate crystals. Step 2) was then repeated twice using sodium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 40 g of high-purity sodium vanadate crystals with a purity of 99.68% and an As content of 0.12 wt%.

[0083] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 0. 9.72 g of formic acid was added and the mixture was reacted at 25° C. for 5 h. Sulfuric acid was added to adjust the pH value of the solution to 0. 0.22 g of sodium sulfide (0.044 g each time) was added in 5 portions and the mixture was reacted at 25° C. for 2 h to obtain an arsenic-free solution having an arsenic content of 19.3 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 14. VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed twice with dilute sulfuric acid at a pH of 6.5 and washed twice with water. The washed VO(OH)2 was then dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 1.7 mol / L vanadyl sulfate electrolyte.

[0084] The vanadyl sulfate electrolyte prepared in this comparative example was determined to contain 23 ppm Na, 2.5 ppm As, 15 ppm Al, and 10 ppm Si, failing to meet the requirements for first-grade tetravalent vanadium electrolytes specified in GB / T 37204-2018. Compared to Example 3, the crystallization process in this comparative example exhibited excessive stirring speed, small crystal size, and large residual liquid inclusions. Impurity elements such as As, Al, and Si in the solution were not fully removed, resulting in excessive levels of As, Al, and Si in the resulting vanadium electrolyte.

[0085] Comparative Example 4

[0086] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 10.5% V, 15.5% Na, 1% As, 2.4% P, 1.2% Al, and 0.4% Si. The method comprises the following steps:

[0087] 1) 500 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 40 g / L dilute sulfuric acid at a solid-liquid ratio of 1:9, and the pH value of the solution was adjusted to 0 with sulfuric acid. 97.6 g of potassium sulfite was added and the reaction was carried out at 30°C for 5 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to -1, and a total of 20.4 g of ammonium sulfide (5.1 g each time) was gradually added in 4 portions and the reaction was carried out at 30°C for 2 h to obtain an arsenic-removed V(IV) solution. NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 13, and VO(OH)2 solid was obtained by filtration.

[0088] 2) The VO(OH)2 solid obtained in step 1) was mixed with 70 g of hydrogen peroxide, dissolved in 1 L of a 330 g / L KOH solution, and adjusted to pH 8 using sulfuric acid. The mixture was reacted at 30°C for 2 h to obtain a pentavalent potassium vanadate solution. The potassium vanadate solution was then cooled to 2°C at a rate of 0.1°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain 225 g of potassium vanadate crystals with a purity of 99.6% and an As content of 0.2 wt%.

[0089] 3) The high-purity potassium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to -1. 61.8 g of potassium oxalate was added and the mixture was reacted at 30°C for 5 h. Sulfuric acid was added to adjust the pH value of the solution to -1. 0.75 g of ammonium sulfide (0.25 g each time) was added three times and the mixture was reacted at 30°C for 2 h to obtain an arsenic-free solution with an arsenic content of 9.1 ppm. KOH was added to adjust the pH value of the arsenic-free solution to 13. VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was acid-washed once with dilute sulfuric acid at a pH of 6.5 and washed three times with water. The washed VO(OH)2 was then dissolved in 270 mL of 6 mol / L sulfuric acid to prepare a 3.5 mol / L vanadylic sulfate electrolyte.

[0090] The vanadyl sulfate electrolyte prepared in this comparative example was measured to contain 56 ppm Na, 1.4 ppm As, 63 ppm Al, and 23 ppm Si, failing to meet the requirements for first-grade tetravalent vanadium electrolytes specified in GB / T 37204-2018. Compared to Example 4, the number of crystallizations in this comparative example was too low, and impurity elements such as As, Al, and Si in the solution were not fully removed, resulting in excessive levels of these impurities in the resulting vanadium electrolyte.

[0091] Comparative Example 5

[0092] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 9.6% V, 13.2% Na, 1.2% As, 2% P, 1.3% Al, and 0.5% Si. The method comprises the following steps:

[0093] 1) Dissolve 300 g of Bayer process alumina seed liquor crystallized vanadium slag in 40 g / L dilute sulfuric acid at a solid-liquid ratio of 1:10. Adjust the pH of the solution to 5 with NaOH. Add 82.3 g of sodium oxalate and react at 90 °C for 0.5 h to obtain a V(IV) solution.

[0094] 2) The VO(OH)2 solid obtained in step 1) was mixed with 80.64 g of sodium peroxide, dissolved in 500 ml of a 400 g / L NaOH solution, and adjusted to a pH of 11 using sulfuric acid. The mixture was reacted at 95°C for 0.5 h to obtain a pentavalent sodium vanadate solution. The sodium vanadate solution was then cooled to 2°C at a rate of 5°C / min. During the cooling process, the solution was stirred at a rate of 200 r / min. The cooled solution was filtered to obtain sodium vanadate crystals. Step 2) was then repeated once using the sodium vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain 82.5 g of high-purity sodium vanadate crystals with a purity of 99.4% and an As content of 0.58 wt%.

[0095] 3) The high-purity sodium vanadate crystals obtained in step 2) were dissolved in sulfuric acid and the pH value was adjusted to 5. 60.48 g of oxalic acid was added and the mixture was reacted at 90°C for 0.5 h. Sulfuric acid was added to adjust the pH value of the solution to -1. 0.24 g of sodium sulfide (0.06 g each time) was added in four portions and the mixture was reacted at 90°C for 0.5 h to obtain an arsenic-free solution having an arsenic content of 29.5 ppm. NaOH was added to adjust the pH value of the arsenic-free solution to 11. VO(OH)2 was filtered to obtain VO(OH)2. The VO(OH)2 was washed twice with dilute sulfuric acid at a pH of 6.5 and three times with water. The washed VO(OH)2 was then dissolved in 120 mL of 5 mol / L sulfuric acid to prepare a 2.5 mol / L vanadyl sulfate electrolyte.

[0096] The vanadyl sulfate electrolyte prepared in this comparative example was measured to contain 22 ppm Na, 5 ppm As, 0.4 ppm Al, and 0.4 ppm Si, failing to meet the requirements for first-grade tetravalent vanadium electrolytes in GB / T 37204-2018. Compared to Example 5, this comparative example lacked the first precipitation arsenic removal step, allowing most of the arsenic in the feedstock to enter the vanadate solution. Crystallization and the second precipitation arsenic removal process were unable to completely remove the excess arsenic, resulting in an excessive arsenic concentration in the resulting vanadium electrolyte.

[0097] Comparative Example 6

[0098] A method for preparing a vanadium electrolyte by using vanadium slag crystallized from a Bayer process alumina seed liquor, wherein the main components of the vanadium slag crystallized from the Bayer process alumina seed liquor include 5.7% V, 13.2% Na, 2% As, 2.4% P, 2.2% Al, and 1% Si. The method comprises the following steps:

[0099] 1) 400 g of Bayer process alumina seed liquor crystallized vanadium slag was dissolved in 100 g / L dilute sulfuric acid at a solid-liquid ratio of 1:1, and the pH value of the solution was adjusted to 4 with KOH. 52.3 g of potassium oxalate was added, and the mixture was reacted at 80 °C for 1 h to obtain a V(IV) solution. Sulfuric acid was added to adjust the pH of the V(IV) solution to 0. A total of 88 g of potassium sulfide (17.6 g each time) was gradually added in 5 portions, and the mixture was reacted at 80 °C for 1 h to obtain an arsenic-removed V(IV) solution. NaOH was added to adjust the pH value of the arsenic-removed V(IV) solution to 10, and VO(OH)2 solid was obtained by filtration.

[0100] 2) The VO(OH)2 solid obtained in step 1) is mixed with 69.3 g of potassium peroxide, dissolved in 450 ml of a 500 g / L KOH solution and adjusted to a pH of 10 using sulfuric acid, and reacted at 80°C for 0.5 h to obtain a pentavalent potassium vanadate solution, and then the vanadate solution is cooled to 5°C at a rate of 4°C / min, and the solution is stirred at a rate of 20 r / min during the cooling process, and the cooled solution is filtered to obtain potassium vanadate crystals; then the step 2) is repeated twice by replacing the VO(OH)2 solid with the potassium vanadate crystals as raw material, and 78 g of high-purity potassium vanadate crystals with a purity of 99.93% and an As content of 0.05 wt% are obtained;

[0101] 3) The high-purity potassium vanadate crystals obtained in step 2) are dissolved in sulfuric acid and adjusted to a pH of 1, 30.24 g of oxalic acid is added, and reacted at 70°C for 1 h to obtain a V(IV) solution with an arsenic content of 30 ppm, and the pH of the V(IV) solution is adjusted to 5 by adding KOH, and filtered to obtain VO(OH)2, which is washed with dilute sulfuric acid with a pH of 5 for 2 times and water for 2 times, and then the washed VO(OH)2 is dissolved with 100 mL of 6 mol / L sulfuric acid to prepare a 3.5 mol / L vanadyl sulfate electrolyte.

[0102] It is determined that the vanadyl sulfate electrolyte prepared in the present example has Na 0 ppm, As 10 ppm, Al 0.9 ppm, and Si 0.5 ppm, which does not meet the requirements of GB / T 37204-2018 for the first-grade product of the 4-valence vanadium electrolyte. Compared with Example 6, the present example lacks the second precipitation arsenic removal process, and the residual arsenic in the V(IV) solution is included in the VO(OH)2, resulting in an arsenic concentration exceeding the standard in the final prepared vanadium electrolyte.

[0103] It should be noted that according to the above embodiments of the present application, those skilled in the art can fully realize the entire scope of the independent claim and the dependent claims of the present application, and the implementation process and method are the same as the above embodiments; and the part not described in detail in the present application belongs to the commonly known technology in the art. However, the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing vanadium electrolyte by using alumina seed solution to crystallize vanadium slag, characterized in that: The method comprises the following steps: 1) dissolving the crystallized vanadium slag of the Bayer process alumina seed liquor in acid, adjusting the pH value of the solution to 0-5, adding a first reducing agent in an amount of 1.1-3 times the theoretical amount of the first reducing agent required for reducing V(V) and As(V) to V(IV) and As(III), reacting at 25-99° C. for 0.5-5 hours to obtain a V(IV) solution, adjusting the pH value of the V(IV) solution to -1-5, adding an arsenic removal precipitant in an amount of 3-9 times the theoretical amount of the arsenic removal precipitant required for removing As(III) in multiple portions, reacting at 25-99° C. for 0.5-2 hours to obtain an arsenic-removed V(IV) solution, adjusting the pH value of the arsenic-removed V(IV) solution to 5-14, and filtering to obtain a VO(OH)2 solid; wherein the first reducing agent comprises one or more of sodium sulfide, elemental sulfur, sulfur dioxide, sulfite, oxalic acid, oxalate, glucose, fructose, sucrose, and formic acid; 2) placing the VO(OH)2 solid obtained in step 1) in an alkaline solution and adjusting the pH to 7-14, adding an oxidant in an amount of 1.5-5 times the theoretical amount required for oxidation of V(IV) to V(V), reacting at 25-99°C for 0.5-2 h to obtain a pentavalent vanadate solution, then cooling the vanadate solution to 0-25°C at a rate of 0.1-5°C / min, and stirring the solution at a rate of 20-200 r / min. The cooled solution is filtered to obtain vanadate crystals; then, step 2) is repeated once or more using the vanadate crystals instead of the VO(OH)2 solid as a raw material to obtain high-purity vanadate crystals with a purity greater than 99.9%; 3) dissolving the high-purity vanadate crystals obtained in step 2) in acid and adjusting the pH to 0-5; adding a second reducing agent in an amount of 1.1-3 times the theoretical amount of the second reducing agent required for reducing V(V) and As(V) to V(IV) and As(III); reacting at 25-99° C. for 0.5-5 h; adjusting the pH of the solution to -1-5; adding an arsenic removal precipitant in multiple portions in an amount of 3-9 times the theoretical amount of the arsenic removal precipitant required for removing As(III); and reacting at 25-99° C. for 0.5-2 h to obtain an arsenic-removed solution; adjusting the pH of the arsenic-removed solution to 5-14; filtering to obtain VO(OH)2; washing the VO(OH)2 with acid and water; and dissolving the washed VO(OH)2 with acid to prepare a vanadium electrolyte; wherein the second reducing agent comprises one or more of sodium sulfide, elemental sulfur, sulfur dioxide, sulfite, oxalic acid, oxalate, glucose, fructose, sucrose, and formic acid.

2. The method according to claim 1, wherein The Bayer process alumina seed liquor crystallization vanadium slag includes V2O5 10-20 wt%, Al 0.5-1 wt%, As 0.5-3 wt%, P 1-3 wt%, and Si 0.1-1 wt%.

3. The method according to claim 1, wherein In step 1), the acid comprises dilute sulfuric acid with a concentration of 40-100 g / L, and the solid-liquid ratio of the Bayer process alumina seed liquor crystallization vanadium slag to the dilute sulfuric acid is 1:1-1:10 g / mL.

4. The method according to any one of claims 1 to 3, wherein The pH value is adjusted specifically by adding one or more acids including sulfuric acid and hydrochloric acid to the solution for adjustment when the pH value needs to be lowered, and adding one or more bases including NaOH and KOH to the solution for adjustment when the pH value needs to be increased.

5. The method according to any one of claims 1 to 3, wherein The arsenic removal precipitant includes one or more of sodium sulfide, potassium sulfide, ammonium sulfide, hydrogen sulfide, and thiourea.

6. The method according to any one of claims 1 to 3, wherein: The multiple times in step 1) is 3 to 5 times.

7. The method according to any one of claims 1 to 3, wherein: In step 2), the oxidant includes one or more of hydrogen peroxide, sodium peroxide, potassium peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate.

8. The method according to any one of claims 1 to 3, wherein: In step 2), the alkali solution includes one or more of NaOH and KOH solutions with a concentration of 50-500 g / L.

9. The method according to any one of claims 1 to 3, wherein: The multiple times in step 3) is 3 to 5 times.

10. The method according to any one of claims 1 to 3, wherein In step 3), the acid washing reagent is dilute sulfuric acid with a pH of 5 to 7, the acid washing times are 1 to 3 times, and the water washing times are 2 to 3 times; the acid dissolution reagent is sulfuric acid with a concentration of 4 to 6 mol / L.

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