Preparation method of low-chromium tetravalent vanadium electrolyte

Abstract

The invention relates to a preparation method of a low-chromium tetravalent vanadium electrolyte, in particular to the field of flow battery energy storage and vanadium product preparation, and the preparation method comprises the following steps: performing chromium complexing inerting treatment on an acidic tetravalent vanadium and trivalent chromium solution, and then performing extraction and reverse extraction to obtain the low-chromium tetravalent vanadium electrolyte; the molar ratio of the ligand used in the chromium complexing and inerting treatment to chromium in the solution is greater than 8: 1. According to the preparation method provided by the invention, the type and the concentration of the ligand in the solution are adjusted, so that the ligand is combined with chromium to form a water-soluble complex with high stability, the combination of chromium and the extraction agent is inhibited, and the extraction of vanadium is not influenced, so that the deep separation of vanadium and chromium and the short-process preparation of the low-chromium tetravalent vanadium electrolyte are realized through a one-step extraction method; the process of pre-precipitation chromium removal and vanadium precipitation refining is not carried out, the whole process is a liquid process, no solid process exists, the vanadium yield is high, and the content of chromium impurities in the vanadium electrolyte is smaller than 1 mg / L.

Description

Technical Field

[0001] The present invention relates to the fields of energy storage of flow batteries and preparation of vanadium products, and particularly relates to a method for preparing a low-chromium tetravalent vanadium electrolyte, and more particularly to a short-process method for preparing a low-chromium tetravalent vanadium electrolyte. Background Art

[0002] The all-vanadium flow battery is a redox battery with vanadium as the active substance in a circulating liquid state, and has the advantages of high safety, strong expandability, long cycle life, and low full-life cycle cost. It is a flow battery with relatively mature commercialization at present. The vanadium electrolyte is the energy storage medium of the all-vanadium flow battery, which is an acid solution of vanadium ions in different valence states. The positive electrode is +4 / +5 valence vanadium ions, and the negative electrode is +2 / +3 valence vanadium ions. Vanadium ions in different valence states can be converted by electrolysis.

[0003] In order to ensure the stable operation and electrochemical performance of the all-vanadium flow battery, the requirements for impurity ions in the vanadium electrolyte are very strict. Chromium is a common impurity in the vanadium electrolyte, and chromium will have an adverse impact on the electrochemical performance of the vanadium electrolyte, such as reducing the reversibility of the electrode reaction, affecting the reaction activity and diffusivity of vanadium ions, etc. In order to avoid the adverse effects of chromium, the actual industrial applications are often more stringent than the national standard GB / T 37204-2018. When the vanadium concentration ≥ 1.7M, it is required that Cr ≤ 5mg / L (equivalent mass ratio V / Cr ≥ 17320). Therefore, it is of great significance to prepare a low-chromium vanadium electrolyte.

[0004] Vanadium electrolytes are usually prepared from high-purity vanadium pentoxide by chemical reduction or electrolysis methods, but the preparation process of high-purity vanadium pentoxide is complex and costly.

[0005] CN113036198A discloses a method and equipment for preparing an all-vanadium flow battery electrolyte. Vanadium pentoxide and ammonia are generated by pyrolysis of ammonium metavanadate, and the generated ammonia is used to partially reduce vanadium pentoxide, and then the vanadium oxide with mixed valence states is dissolved in acid to obtain a vanadium electrolyte. None of the above methods have a purification step, and the chromium concentration in the vanadium electrolyte product is limited by the chromium content in the vanadium raw material.

[0006] CN103606694A discloses a preparation method of vanadium electrolyte. After redissolving the vanadium-containing raw material with alkali, the pH of the solution is adjusted. Impurities are removed by adding a impurity remover under weak alkaline conditions, and then vanadium is repeatedly precipitated under weak acidic conditions to remove impurities such as iron, chromium, silicon, and manganese therein. Finally, the vanadium oxide obtained by reduction roasting is dissolved with sulfuric acid to obtain vanadium electrolyte. CN103482702A discloses a preparation method of high-purity vanadium oxide and vanadium electrolyte. The industrial crude vanadium oxide is redissolved and filtered under alkaline conditions. First, a magnesium salt is added, and after reacting at 90-100 °C and aging for more than 12 hours, chromium and part of silicon are removed by filtration; then an aluminum salt is added and reacted at 90-100 °C to remove silicon; subsequently, ammonium is added to the solution to precipitate vanadium, and ammonium metavanadate is calcined to obtain high-purity vanadium pentoxide, and vanadium electrolyte is further prepared using it as a raw material. In the above methods, the solid vanadium raw material is first dissolved, and after multiple steps of impurity removal - filtration and other operations, ammonium is added to precipitate vanadium to obtain ammonium metavanadate with low chromium content, then high-temperature roasting is carried out, and finally, it is dissolved with acid to obtain vanadium electrolyte: the solid vanadium raw material is converted into vanadium electrolyte only after multiple steps of "liquid → solid" and "solid → liquid" conversions, with a long process, high energy consumption, low vanadium yield in ammonium salt precipitation of vanadium, a large amount of ammonia nitrogen wastewater generated, and poor precipitation impurity removal effect, especially chromium impurities are difficult to completely remove.

[0007] CN105355955A discloses a preparation method of high-purity vanadyl sulfate solution. Ferrous ions in the vanadyl sulfate solution are oxidized to ferric ions using a pentavalent vanadium solution, and then the pH of the solution is adjusted with ammonia water to form jarosite precipitate and filtered off. Then, ammonia is continuously added to adjust the pH to precipitate vanadium, while low-valent chromium ions form soluble complexes and remain in the solution. Finally, vanadyl hydroxide precipitate is dissolved with sulfuric acid to obtain high-purity vanadyl sulfate solution. This method requires complex iron precipitation and vanadium precipitation operations, generates ammonia nitrogen wastewater and vanadium-containing solid waste, has a low vanadium yield, and vanadyl hydroxide precipitate still entrains a certain amount of chromium, which ultimately enters the product solution.

[0008] CN103515642A and CN103505903A respectively disclose a preparation method of high-purity vanadyl sulfate solution, which are respectively prepared by "preliminary impurity removal → vanadium precipitation → reduction → extraction → oil removal" and "preliminary impurity removal → alkaline extraction → reduction → acidic extraction → oil removal", directly preparing the alkaline pentavalent vanadium solution produced by the vanadium plant into high-purity tetravalent vanadyl sulfate solution. The above methods have a long process, equivalent to "vanadium precipitation + extraction" and "two-step extraction", resulting in a low vanadium yield. Magnesium salts are used to generate precipitates with chromate ions to remove impurity chromium, and it is difficult to completely remove chromium by precipitation; the residual chromium after impurity removal will cause the extraction agent to condense and affect its performance and service life after being extracted, and part of the chromium will enter the vanadyl sulfate solution after back extraction, resulting in an excessive chromium content.

[0009] It can be seen that in order to make the all-vanadium redox flow battery achieve good electrochemical performance, the effective removal of chromium in the vanadium electrolyte is an urgent problem to be solved. Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a low-chromium tetravalent vanadium electrolyte, which regulates the stable coordination of ligands with chromium and inhibits the combination of chromium with the extractant during the extraction process, so that the chromium content in the low-chromium tetravalent vanadium electrolyte is < 1 mg / L, in order to solve the problem that the high chromium concentration in the vanadium electrolyte leads to poor electrical performance of the all-vanadium redox flow battery.

[0011] To achieve this purpose, the present invention adopts the following technical solutions:

[0012] The present invention provides a method for preparing a low-chromium tetravalent vanadium electrolyte, and the preparation method includes:

[0013] Performing chromium complexation inerting treatment on the acidic tetravalent vanadium trivalent chromium solution, and then performing extraction and back-extraction to obtain a low-chromium tetravalent vanadium electrolyte;

[0014] The molar ratio of the ligand used in the chromium complexation inerting treatment to chromium in the solution is > 8:1.

[0015] The preparation method provided by the present invention adjusts the type and concentration of ligands in the solution, so that the ligands combine with chromium to form water-soluble complexes with high stability, inhibit the combination of chromium with the extractant, and do not affect the extraction of vanadium; on this basis, the present invention adopts a one-step extraction method to prepare the vanadium electrolyte with a short process, without going through the processes of pre-precipitation for chromium removal and vanadium precipitation and refining. The whole process is a liquid process without a solid process, realizing the deep separation of vanadium and chromium and the short-process preparation of the low-chromium tetravalent vanadium electrolyte, with a high vanadium recovery rate and the chromium impurity content in the vanadium electrolyte being < 1 mg / L.

[0016] As a preferred technical solution of the present invention, the acidic tetravalent vanadium trivalent chromium solution is obtained by acidifying and reducing an alkaline solution containing pentavalent vanadium and hexavalent chromium or by reducing acid leaching or acid leaching of a crude vanadium compound containing chromium.

[0017] As a preferred technical solution of the present invention, the reducing agent used in the reduction includes a sulfur-containing reducing agent.

[0018] Preferably, the sulfur-containing reducing agent includes 1 or at least 2 combinations of sodium dithionite, sodium sulfide, sodium metabisulfite, thiourea, sodium sulfite or hydroxylamine sulfate.

[0019] Preferably, the acid used in the acidification includes 1 or at least 2 combinations of sulfuric acid, hydrochloric acid or nitric acid.

[0020] The acid used in the acid leaching includes 1 or at least 2 combinations of sulfuric acid, hydrochloric acid or nitric acid.

[0021] As a preferred technical solution of the present invention, the ligands used in the chromium complex inerting treatment include organic ligands and / or inorganic ligands.

[0022] As a preferred technical solution of the present invention, the substances providing the organic ligands include one or a combination of at least two of tartaric acid, tartrate, citric acid, citrate, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, nitrilotriacetic acid, nitrilotriacetate, sulfosalicylic acid, sulfosalicylate, triethanolamine, urea, or guanidine hydrochloride.

[0023] As a preferred technical solution of the present invention, the substances providing the inorganic ligands include sulfuric acid and / or sulfate.

[0024] As a preferred technical solution of the present invention, the extractant used in the extraction includes acidic organophosphorus extractants.

[0025] As a preferred technical solution of the present invention, the pH value of the aqueous phase is controlled to be ≤ 1.9 during the extraction.

[0026] As a preferred technical solution of the present invention, the extraction method includes one or a combination of at least two of mixing and stirring extraction, multi-stage cocurrent extraction, or multi-stage countercurrent extraction.

[0027] As a preferred technical solution of the present invention, the raffinate obtained from the extraction is subjected to evaporation saturation treatment to obtain a recovered salt, and the obtained recovered salt is returned to be used in the chromium complex inerting treatment.

[0028] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0029] The present invention uses a one-step extraction method to prepare vanadium electrolyte with a short process. It does not go through the processes of pre-precipitation for chromium removal and vanadium precipitation and refining. The whole process is a liquid process without a solid process. During the extraction, by adjusting the types and concentrations of ligands in the solution, the ligands combine with chromium to form water-soluble complexes. These complexes have high self-stability and steric hindrance effects, which can inhibit the combination of chromium and the extractant, but the selected ligands do not affect the extraction of vanadium. Through the above treatment, the deep separation of vanadium and chromium and the short-process preparation of low-chromium tetravalent vanadium electrolyte are realized. The vanadium recovery rate is high, and the chromium impurity content in the vanadium electrolyte is < 1 mg / L. Specific Embodiments

[0030] To better illustrate the present invention and facilitate understanding of its technical solutions, the typical but non-limiting embodiments of the present invention are as follows:

[0031] This embodiment provides a method for preparing a low-chromium tetravalent vanadium electrolyte, and the preparation method includes:

[0032] Performing chromium complex inerting treatment on an acidic tetravalent vanadium and trivalent chromium solution, followed by extraction and back-extraction to obtain a low-chromium tetravalent vanadium electrolyte;

[0033] The molar ratio of the ligand used in the chromium complex inerting treatment to chromium in the solution > 8:1.

[0034] In the present invention, the chromium element content in the obtained low-chromium tetravalent vanadium electrolyte < 1 mg / L.

[0035] In the present invention, the molar ratio of the ligand used in the chromium complex inerting treatment to chromium in the solution > 8:1, for example, it can be 8.1:1, 8.2:1, 8.4:1, 8.6:1, 8.8:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 11.5:1 or 12:1, etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0036] Among them, the acidic tetravalent vanadium trivalent chromium solution is obtained by acidifying and reducing an alkaline solution containing pentavalent vanadium and hexavalent chromium, or by reducing acid leaching or acid leaching of a crude vanadium compound containing chromium.

[0037] Furthermore, the acidic tetravalent vanadium trivalent chromium solution can also be directly prepared by preparing a solution, or a related vanadium chromium solution generated in other industrial processes, by adjusting the pH value and reducing or oxidizing.

[0038] Among them, the reducing agent used in the reduction includes a sulfur-containing reducing agent, including one or at least a combination of two or more of sodium dithionite, sodium sulfide, sodium metabisulfite, thiourea, sodium sulfite or hydroxylamine sulfate.

[0039] Exemplarily, the combinations of the sulfur-containing reducing agents include: the combination of sodium dithionite and thiourea, the combination of thiourea and sodium sulfite, the combination of sodium sulfite and hydroxylamine sulfate, the combination of sodium dithionite and sodium sulfite, the combination of hydroxylamine sulfate and thiourea, etc.

[0040] Among them, the acid used in the acidification includes one or at least a combination of two or more of sulfuric acid, hydrochloric acid or nitric acid.

[0041] Exemplarily, the combinations of the acids used in the acidification include the combination of sulfuric acid and hydrochloric acid, the combination of sulfuric acid and nitric acid, the combination of hydrochloric acid and nitric acid, etc.

[0042] Among them, the acid used in the acid leaching includes one or at least a combination of two or more of sulfuric acid, hydrochloric acid or nitric acid.

[0043] Exemplarily, the combinations of the acids used in the acid leaching include the combination of sulfuric acid and hydrochloric acid, the combination of sulfuric acid and nitric acid, the combination of hydrochloric acid and nitric acid, etc.

[0044] Among them, when nitric acid is used in acid reduction and reductive acid leaching, there may be pollutants such as nitrogen oxide gases. Therefore, it is preferred to use sulfuric acid and / or hydrochloric acid, but a small amount of nitric acid complex treatment scheme is not excluded. Under the condition of ensuring the limited requirements, nitric acid is also feasible.

[0045] Furthermore, when the acids used in acidification and acid leaching meet the requirements of effective separation and recovery of vanadium and chromium, organic acids can also be used for substitution, such as oxalic acid, acetic acid, etc.

[0046] Among them, the ligands used in the chromium complex inerting treatment include organic ligands and / or inorganic ligands.

[0047] Among them, the substances providing the organic ligands include one or at least a combination of 2 of tartaric acid, tartrate, citric acid, citrate, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, nitrilotriacetic acid, nitrilotriacetate, sulfosalicylic acid, sulfosalicylate, triethanolamine, urea, or guanidine hydrochloride.

[0048] Exemplarily, the combinations of the organic ligands include: the combination of tartaric acid and tartrate, the combination of citric acid and citrate, the combination of ethylenediaminetetraacetic acid and ethylenediaminetetraacetate, the combination of nitrilotriacetic acid and nitrilotriacetate, sulfosalicylic acid and sulfosalicylate, the combination of triethanolamine and urea, the combination of guanidine hydrochloride and urea, the combination of citric acid and ethylenediaminetetraacetic acid, the combination of nitrilotriacetic acid and sulfosalicylic acid, etc.

[0049] Among them, the substances providing the inorganic ligands include sulfuric acid and / or sulfate.

[0050] Among them, the extractants used in the extraction include acidic organophosphorus extractants.

[0051] Exemplarily, if the extractants used include one or at least a combination of 2 of bis(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA), or bis(2,4,4-trimethylpentyl) phosphonic acid (Cyanex 272).

[0052] Exemplarily, the combinations of the extractants used include: the combination of D2EHPA and EHEHPA, the combination of EHEHPA and Cyanex 272, the combination of D2EHPA and Cyanex 272, etc.

[0053] In the present invention, phase adjustment agents and diluents and other extraction auxiliary reagents are also combined with the extractants in the extraction to achieve the efficient and reasonable use of the extractants.

[0054] Exemplarily, the phase adjustment agents used include tributyl phosphate (TBP), etc., and the diluents include kerosene and / or sulfonated kerosene and other commonly used diluents and phase adjustment agents in the art.

[0055] Among them, in the extraction, the pH value of the aqueous phase is controlled to be ≤ 1.9.

[0056] In the present invention, for the control of the pH value of the aqueous phase during the extraction process, the material can be treated with a pH adjuster, such as adding an acid, a base, a carbonate, etc. to adjust the pH value of the solution.

[0057] In the present invention, the volume ratio of the extractant to the aqueous phase during the extraction process can be reasonably selected specifically according to the concentration of the extractant in the extractant and the concentration of vanadium in the aqueous phase, and can be designed specifically with reference to the operating parameters of conventional vanadium extraction in the art.

[0058] In the present invention, the extraction method can be selected as mixed stirring extraction, single-stage cocurrent or single-stage countercurrent extraction, or multi-stage cocurrent extraction, multi-stage countercurrent extraction and other extraction methods.

[0059] Among them, the raffinate obtained after extraction is subjected to evaporation saturation treatment to obtain a recovered salt, and the obtained recovered salt is returned to be used in the chromium complex inerting treatment. Further, the remaining liquid after the evaporation saturation treatment is subjected to subsequent treatment such as further recovering chromium, or being reused after purification treatment.

[0060] Among them, the organic phase obtained by extraction can be optionally washed before stripping to remove water-soluble ions such as Na and K in the organic phase, so as to further reduce the impurity ions in the stripping solution.

[0061] Among them, the stripping reagent used in the stripping can be selected from the commonly used stripping reagents in the art, such as acid solutions, such as hydrochloric acid, sulfuric acid or nitric acid, etc. The phase ratio during the stripping process is determined according to the dosage and concentration of the raw material and the extractant and the concentration of the vanadium electrolyte product. The concentration of hydrogen ions in the acid used is 7 - 10 mol / L, the time is ≥ 5 min, and the temperature is 20 - 40 °C.

[0062] In the present invention, the limited time for both extraction and stripping is the single-stage operation time.

[0063] Furthermore, in order to illustrate that the concentration of chromium ions in the low-chromium tetravalent vanadium electrolyte obtained by the preparation method of the low-chromium tetravalent vanadium electrolyte provided by the present invention is significantly reduced, actual examples are used for illustration, as follows:

[0064] Example 1

[0065] This example provides a preparation method of a low-chromium tetravalent vanadium electrolyte, and the preparation method includes:

[0066] Performing chromium complex inerting treatment on an acidic tetravalent vanadium trivalent chromium solution, and then performing extraction and stripping to obtain a low-chromium tetravalent vanadium electrolyte;

[0067] The acidic tetravalent vanadium and trivalent chromium solution is obtained by acidifying and reducing an alkaline solution containing pentavalent vanadium and hexavalent chromium; in the reduction, sodium sulfite and hydroxylamine sulfate are used as reducing agents in a molar ratio of 5:1; in the acidification, sulfuric acid and hydrochloric acid are used as acids in a molar ratio of 1:1;

[0068] In the chromium complex inerting treatment, the molar ratio of the ligand used to chromium in the solution is 12:1; the ligand used in the chromium complex inerting treatment is an organic ligand, provided by a combination of citric acid and triethanolamine in a molar ratio of 1:1; the main elemental composition of the solution after chromium complex inerting treatment is: V(IV) 22.05 g / L, Cr(III) 3.47 g / L, Na 42.50 g / L, Si 0.16 g / L, K 0.09 g / L, Ca 0.12 g / L.

[0069] In the extraction, the extractant used is an acidic organophosphorus extractant, which is a combination of bis(2,4,4-trimethylpentyl) phosphonic acid and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester in a molar ratio of 2:8. The total concentration of the acidic organophosphorus extractant is 30 vol%, the phase modifier tributyl phosphate is 3 vol%, and the diluent is sulfonated kerosene with a concentration of 67 vol%; the extraction phase ratio O / A = 1.2:1, the number of extraction stages is 3, the extraction time is 15 min, and the extraction temperature is 25 °C; in the extraction, the pH value of the aqueous phase is controlled to be 1.87; the extraction method is multi-stage countercurrent extraction;

[0070] In the stripping, the phase ratio is O / A = 5:1, the concentration of sulfuric acid used is 4.6 mol / L, the number of stripping stages is 3, the time is 10 min, and the temperature is 25 °C.

[0071] Example 2

[0072] This example provides a method for preparing a low-chromium tetravalent vanadium electrolyte, and the preparation method includes:

[0073] Performing chromium complex inerting treatment on the acidic tetravalent vanadium and trivalent chromium solution, followed by extraction and stripping to obtain a low-chromium tetravalent vanadium electrolyte;

[0074] The acidic tetravalent vanadium and trivalent chromium solution is obtained by reduction acid leaching of crude ammonium polyvanadate containing chromium; in the reduction, thiourea and sodium sulfite are used as reducing agents in a molar ratio of 1:4; the acid used in the acidification is hydrochloric acid;

[0075] The molar ratio of the ligand used in the chromium complexation inerting treatment to chromium in the solution is 9:1; the ligand used in the chromium complexation inerting treatment is an organic ligand, provided by a combination of sulfosalicylic acid and guanidine hydrochloride with a molar ratio of 2:1; the main elemental composition of the solution after the chromium complexation inerting treatment is: V(IV) 30.05 g / L, Cr(III) 45.00 mg / L, Na 11.80 g / L, Si 14.50 mg / L, K 0.52 g / L, Ca 0.09 g / L, Fe 6.50 mg / L.

[0076] The extractant used in the extraction is an acidic organophosphorus extractant, which is a combination of bis(2-ethylhexyl) phosphoric acid and bis(2,4,4-trimethylpentyl) phosphonic acid with a molar ratio of 8:2. The total concentration of the acidic organophosphorus extractant is 32.5 vol%, and the diluent is 260# solvent naphtha with a concentration of 67.5 vol%; the extraction phase ratio O / A = 1.5:1, the number of extraction stages is 3, the extraction time is 20 min, and the extraction temperature is 30 °C; the pH value of the aqueous phase is controlled to be 1.77 in the extraction; the extraction method is mixing and stirring extraction;

[0077] The phase ratio in the stripping is O / A = 4.5:1, the acid used is a mixed acid of sulfuric acid and hydrochloric acid, the hydrogen ion concentration is 8.2 mol / L, the number of stripping stages is 3, the time is 15 min, and the temperature is 25 °C.

[0078] Example 3

[0079] This example provides a method for preparing a low-chromium vanadium(IV) electrolyte, and the preparation method includes:

[0080] Performing chromium complexation inerting treatment on the acidic vanadium(IV) chromium(III) solution, followed by extraction and stripping to obtain a low-chromium vanadium(IV) electrolyte;

[0081] The acidic vanadium(IV) chromium(III) solution is obtained by acidifying and reducing the sodium roasting and water leaching solution of chromium-containing vanadium slag; the reducing agent used in the reduction is a combination of sodium dithionite and sodium metabisulfite with a molar ratio of 1:3; the acid used in the acidification is a combination of sulfuric acid and hydrochloric acid with a molar ratio of 24:1;

[0082] The molar ratio of the ligand used in the chromium complexation inerting treatment to chromium in the solution is 19:1; the ligand used in the chromium complexation inerting treatment is an inorganic ligand sulfate radical, provided by sulfuric acid and sodium sulfate; the main elemental composition of the solution after the chromium complexation inerting treatment is: V(IV) 27.15 g / L, Cr(III) 2.02 g / L, Na 50.13 g / L, Si 0.15 g / L, K 0.52 g / L, Ca 0.11 g / L, Fe 5.30 mg / L.

[0083] The extractant used in the extraction is an acidic organophosphorus extractant, which is a combination of bis(2-ethylhexyl)phosphoric acid and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester with a molar ratio of 2:8. The total concentration of the acidic organophosphorus extractant is 30 vol%, the phase modifier is tributyl phosphate with a concentration of 6 vol%, and the diluent is sulfonated kerosene; the extraction phase ratio O / A = 1.5:1, the number of extraction stages is 4, the extraction time is 25 min, the extraction temperature is 25 °C, and the pH value of the aqueous phase is controlled to be 1.67 during extraction; the extraction method is multi-stage countercurrent extraction;

[0084] The phase ratio in the stripping is O / A = 5:1, the concentration of hydrochloric acid used is 8 mol / L, the number of stripping stages is 4, the time is 20 min, and the temperature is 25 °C.

[0085] Example 4

[0086] This example provides a method for preparing a low-chromium tetravalent vanadium electrolyte, and the preparation method includes:

[0087] Performing chromium complexation and passivation treatment on the acidic tetravalent vanadium and trivalent chromium solution, and then performing extraction and stripping to obtain a low-chromium tetravalent vanadium electrolyte;

[0088] The acidic tetravalent vanadium and trivalent chromium solution is obtained by reduction and acid leaching of a crude vanadium compound containing chromium; the reducing agent used in the reduction is a combination of thiourea and sodium metabisulfite with a molar ratio of 1:4; the acid used in the acid leaching is sulfuric acid; the main elemental composition of the solution after chromium complexation and passivation treatment is: V(IV) 40.70 g / L, Cr(III) 31.00 mg / L, Na 28.20 g / L, Si 2.90 mg / L, K 0.09 g / L, Ca 0.08 g / L, Fe 12.30 mg / L.

[0089] The molar ratio of the ligand used in the chromium complexation and passivation treatment to chromium in the solution is 25:1; the ligand used in the chromium complexation and passivation treatment is an organic ligand; the organic ligand includes a combination of sodium tartrate and nitrilotriacetic acid with a molar ratio of 1:1;

[0090] The extractant used in the extraction is bis(2-ethylhexyl)phosphoric acid, the total concentration of the acidic organophosphorus extractant is 25 vol%, and the diluent is 260# solvent naphtha with a concentration of 75 vol%; the extraction phase ratio O / A = 2.5:1, the number of extraction stages is 2, the extraction time is 10 min, the extraction temperature is 35 °C; the pH value of the aqueous phase is controlled to be 1.81 during extraction; the extraction method includes mixing and stirring extraction;

[0091] The phase ratio in the stripping is O / A = 5.5:1, the acid used is a mixed acid of sulfuric acid and hydrochloric acid, the hydrogen ion concentration is 8.6 mol / L, the number of stripping stages is 2, the time is 5 min, and the temperature is 25 °C.

[0092] Comparative Example 1

[0093] It is only different from Example 1 in that no chromium complexation passivation treatment is carried out, that is, the solution is directly extracted.

[0094] Comparative Example 2

[0095] It is only different from Example 1 in that the molar ratio of the ligand used in the chromium complexation passivation treatment to chromium in the solution is 3:1.

[0096] Comparative Example 3

[0097] It is only different from Example 1 in that the molar ratio of the ligand used in the chromium complexation passivation treatment to chromium in the solution is 1:1.

[0098] Comparative Example 4

[0099] It is only different from Example 1 in that the substance providing the ligand in the chromium complexation passivation treatment is replaced with an equal amount of sodium chloride.

[0100] Comparative Example 5

[0101] It is only different from Example 1 in that the acidic tetravalent vanadium trivalent chromium solution is replaced with a tetravalent vanadium solution of the same concentration and pH value.

[0102] Comparative Example 6

[0103] It is only different from Example 1 in that the acidic tetravalent vanadium trivalent chromium solution is replaced with a trivalent chromium solution of the same concentration and pH value.

[0104] Comparative Example 7

[0105] It is only different from Comparative Example 5 in that no chromium complexation passivation treatment is carried out.

[0106] Comparative Example 8

[0107] It is only different from Comparative Example 6 in that no chromium complexation passivation treatment is carried out.

[0108] The vanadium electrolytes obtained from the examples and comparative examples were subjected to ion concentration detection. The vanadium recovery rate was calculated based on the vanadium in the stripping solution and the vanadium in the acidic tetravalent vanadium trivalent chromium solution. The results are shown in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] As can be seen from Table 1, in the solution provided by the present invention, through Comparative Examples 1-3, it can be seen that the concentration of the selected ligand has an obvious influence on the efficiency of inhibiting chromium extraction; through Comparative Example 5 and Comparative Example 7, it can be seen that the selected ligand has no influence on the extraction of vanadium; through Comparative Example 6 and Comparative Example 8, it can be seen that the selected ligand inhibits the extraction of chromium, while when there is no ligand passivation, a certain amount of chromium will be extracted, resulting in a very high chromium content in the stripping solution. Through Examples 1-4 and Comparative Examples 1-8, it can be seen that by performing chromium complex passivation treatment on the acidic tetravalent vanadium and trivalent chromium solution, that is, by preferably selecting the type and concentration of the ligand in the solution, the selected ligand combines with chromium to form a water-soluble complex with high stability, inhibits the combination of chromium with the extractant, and does not affect the extraction of vanadium, thereby realizing the deep separation of vanadium and chromium and the short-process preparation of a low-chromium tetravalent vanadium electrolyte. The vanadium recovery rate is above 99%, and the chromium impurity content in the vanadium electrolyte is <1 mg / L.

[0113] It is declared that the present invention uses the above-mentioned embodiments to illustrate the detailed structural features of the present invention, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0114] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0115] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0116] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of a low-chromium tetravalent vanadium electrolyte, characterized in that, The preparation method includes the following steps: Carrying out chromium complexation and passivation treatment on an acidic vanadium(IV) and chromium(III) solution, followed by extraction and back-extraction to obtain a low-chromium vanadium(IV) electrolyte; In the chromium complexation and passivation treatment, the molar ratio of the ligand used to chromium in the solution > 8:

1.

2. The preparation method according to claim 1, characterized in that, The acidic vanadium(IV) and chromium(III) solution is obtained by acidifying and reducing an alkaline solution containing vanadium(V) and chromium(VI), or by reduction acid leaching or acid leaching of a crude vanadium compound containing chromium.

3. The preparation method according to claim 1, wherein The reducing agent used in the reduction includes a sulfur-containing reducing agent; Preferably, the sulfur-containing reducing agent includes one or at least two combinations of sodium dithionite, sodium sulfide, sodium metabisulfite, thiourea, sodium sulfite, or hydroxylamine sulfate; Preferably, the acid used in the acidification includes one or at least two combinations of sulfuric acid, hydrochloric acid, or nitric acid; Preferably, the acid used in the acid leaching includes one or at least two combinations of sulfuric acid, hydrochloric acid, or nitric acid.

4. The preparation method according to claim 1, characterized in that, The ligand used in the chromium complexation and passivation treatment includes an organic ligand and / or an inorganic ligand.

5. The preparation method according to claim 4, characterized in that, The substance providing the organic ligand includes one or at least two combinations of tartaric acid, tartrate, citric acid, citrate, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, nitrilotriacetic acid, nitrilotriacetate, sulfosalicylic acid, sulfosalicylate, triethanolamine, urea, or guanidine hydrochloride; 6. The preparation method according to claim 4, characterized in that, The substance providing the inorganic ligand includes sulfuric acid and / or sulfate.

7. The preparation method according to claim 1, characterized in that, The extractant used in the extraction includes an acidic organophosphorus extractant.

8. The preparation method according to claim 1, characterized in that, In the extraction, the pH value of the aqueous phase is controlled ≤ 1.

9.

9. The preparation method according to claim 1, characterized in that, The extraction method includes one or at least two combinations of mixing and stirring extraction, multi-stage cocurrent extraction, or multi-stage countercurrent extraction.

10. The preparation method according to claim 1, characterized in that, The raffinate obtained from the extraction is subjected to evaporation saturation treatment to obtain a recovered salt, and the obtained recovered salt is returned to the chromium complexation and passivation treatment for use.

Images