Method for recycling invalid electrolyte

Abstract

The invention relates to a method for recycling invalid vanadium electrolyte, and belongs to the technical field of vanadium chemical industry. The method specifically comprises the following steps: carrying out electrolytic reduction on the invalid vanadium electrolyte to reduce all vanadium to tetravalent vanadium, adding high-purity vanadium water and a pH regulator, carrying out vanadium concentration adjustment, adjusting the pH value to 1.6-2.5, carrying out extraction and separation to obtain an organic phase containing tetravalent vanadium and an ammonium sulfate solution, carrying out reverse extraction on the organic phase containing tetravalent vanadium through an oxalic acid solution to obtain a vanadyl oxalate solution, and carrying out solid-liquid separation to obtain the vanadium oxide. And carrying out cooling crystallization, filtering separation and vacuum drying to obtain a vanadyl oxalate solid phase. According to the method, the vanadium element in the invalid vanadium electrolyte can be effectively recycled, and the resource utilization rate is remarkably increased; compared with a traditional recovery method, the method has the advantages that the use amount of alkali is reduced, so that the cost is reduced, a new application is given to a recovery product of the invalid vanadium electrolyte, and good economic benefits and application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of vanadium chemical industry, and in particular relates to a method for recycling spent electrolyte. Background Art

[0002] The efficient recycling process of spent vanadium electrolyte is an important research direction in the field of all-vanadium redox flow batteries, which aims to recover valuable vanadium elements from spent electrolytes to achieve resource recycling and cost reduction.

[0003] At present, the recovery methods of spent electrolyte include oxidation method, composite precipitation method, regeneration method and so on.

[0004] The oxidation method is to oxidize low-valent vanadium into pentavalent vanadium by adding an oxidant (such as sodium chlorate or potassium permanganate), and then recover the vanadium by a precipitation method. CN111484076A discloses a method for recovering high-purity vanadium from spent vanadium electrolyte, which is to add an oxidant to the spent vanadium electrolyte, oxidize the vanadium ions in the electrolyte into pentavalent ions, and then adjust the pH value of the electrolyte to 2-5; add a vanadium precipitant to the electrolyte to obtain a solid precipitate, and after filtering, washing, drying and calcining, obtain a vanadium pentoxide solid with a purity of more than 95%. This method is easy to operate, environmentally friendly, and has a high vanadium recovery rate, but it needs to add alkali to adjust the pH value to 8, consumes a large amount of alkali, and the addition of the oxidant easily introduces other impurities.

[0005] The composite precipitation method (such as CN110867592A) is to introduce composite precipitants such as organic amine substances into the failed electrolyte, and use conventional alkali solution to adjust the solution to neutrality, and fully stir it at room temperature to completely precipitate the vanadium in the solution. The advantage of this method is that the treatment process is simple, no complicated high temperature and high pressure conditions are required, and the raw materials are relatively easy to obtain. However, the composite precipitation method also has some problems. On the one hand, it is similar to the oxidation method, and the alkali consumption is large, which makes the cost high; on the other hand, for the subsequent treatment of vanadium organic precipitates, the relevant methods do not give clear instructions. It is particularly worth noting that the organic matter is prone to produce irritating odors during the calcination process, which will have an adverse effect on the environment and may cause environmental problems such as air pollution. In practical applications, additional environmental protection measures are needed to deal with it.

[0006] The electrolysis method is a method of electrolyzing the spent vanadium electrolyte to a tetravalent or pentavalent state and then precipitating vanadium. CN102983379A uses spent vanadium electrolyte as raw material, and in an inert environment, charges the battery to raise the valence of vanadium in the electrolyte to pentavalent state, then adds a vanadium precipitator to precipitate the pentavalent vanadium therein, and calcines the removed precipitate at high temperature to obtain vanadium pentoxide. CN105406098A uses an electrolytic cell to electrolyze the vanadium in the spent vanadium electrolyte to a tetravalent state to obtain a vanadium oxysulfate solution; the vanadium oxysulfate solution is evaporated or dissolved and crystallized to obtain vanadium oxysulfate.

[0007] In addition, some researchers have used the advantages of low-valent vanadium in spent electrolytes to synthesize other vanadium compounds, further expanding the recycling methods of spent vanadium electrolytes. CN114142077A discloses a method for preparing vanadium sulfide, which is to oxidize low-valent vanadium ions in spent vanadium electrolytes into pentavalent vanadium using the positive electrode of an electrolytic cell, and then add an appropriate amount of sulfur source and reducing agent to prepare a high-purity vanadium sulfide nanomaterial through high-temperature and high-pressure reaction. The advantage of this method is that it can make full use of the vanadium resources in spent electrolytes to prepare vanadium sulfide nanomaterials with special properties and broad application prospects. However, its disadvantage is that it requires high-temperature and high-pressure reaction conditions, which places high demands on the pressure resistance, high-temperature resistance and operational safety of the equipment, and may increase the investment cost and operational risk of production equipment. CN106299361A discloses a method for preparing vanadyl phosphate, which first electrolyzes vanadium ions in spent vanadium electrolyte into pentavalent vanadium ions; then adds excess phosphate to the electrolyzed pentavalent vanadium ion electrolyte, and produces a yellow-green precipitate after stirring; finally, the precipitate is filtered and washed with an organic solvent, and dried in air to obtain a vanadyl phosphate solid. The advantage of this method is that it avoids the problems of low solubility of vanadium pentoxide in phosphoric acid and long reaction time, and the reaction time is short, but the limitations of the application field of vanadyl phosphate need to be considered. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for recycling spent electrolyte, which can effectively recover the vanadium element in the spent vanadium electrolyte and significantly improve the resource utilization rate.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for recycling spent vanadium electrolyte, the method comprising the following steps:

[0010] (1) electrolytically reducing the spent vanadium electrolyte to reduce all vanadium in the spent vanadium electrolyte to tetravalent vanadium, and then adding high-purity vanadium water and a pH regulator to the spent vanadium electrolyte to adjust the vanadium concentration and the pH value to 1.6-2.5;

[0011] (2) mixing an extractant and sulfonated kerosene to obtain an organic phase, performing multi-stage extraction on the spent vanadium electrolyte, and separating to obtain an organic phase containing tetravalent vanadium and an ammonium sulfate solution;

[0012] (3) subjecting the organic phase containing tetravalent vanadium to multi-stage countercurrent stripping with an oxalic acid solution to obtain a vanadium oxalate solution;

[0013] (4) cooling the vanadium oxalate solution for crystallization, filtering and separating, and vacuum drying to obtain vanadium oxalate crystals.

[0014] In step (1) of the present invention, the pH regulator is any one or more of ammonia water, ammonium bicarbonate and ammonium carbonate, and the vanadium concentration is adjusted to 10-40 g / L.

[0015] In step (2) of the present invention, the extractant is any one or more of P204, P507, P253, TBP and Cyanex 923, the volume fraction of the extractant is 5-40%, the volume ratio of the organic phase to the aqueous phase is 1-5:1, and the extraction temperature is 20-50°C.

[0016] In step (3) of the present invention, the concentration of oxalic acid is 0.5-4 mol / L, the volume ratio of the organic phase to the aqueous phase is 1-8:1, and the stripping temperature is 20-60°C.

[0017] The cooling crystallization conditions in step (4) of the present invention are stirring speed of 50 to 300 r / min, cooling temperature of 20 to 30° C., and cooling time of 3 to 12 h.

[0018] The chemical composition of the vanadyl oxalate in step (4) of the present invention is: VOC2O4·5H2O, with a purity of ≥99.5%.

[0019] The beneficial effects produced by adopting the above technical scheme are: 1. The present invention can effectively recover the vanadium element in the spent vanadium electrolyte through specific electrolytic reduction, extraction, stripping and other steps, thereby improving resource utilization. 2. Compared with traditional oxidation methods, composite precipitation methods, etc., the amount of alkali used is reduced, and the cost is reduced. 3. Compared with evaporation crystallization, the cooling method is used to crystallize vanadium oxalate, which has the characteristics of lower energy consumption and simple operation. 4. The successful preparation of vanadium oxalate crystals provides a new application direction for the recovery products of spent vanadium electrolytes, which has high economic value and environmental significance. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below in conjunction with specific implementation methods.

[0021] Example 1

[0022] (1) Electrolytic reduction and adjustment: Take a certain amount of spent vanadium electrolyte and perform electrolytic reduction until all the vanadium in the electrolyte is reduced to tetravalent. Then add high-purity vanadium water and ammonia water as pH adjusters to adjust the pH value to 2.0, and adjust the vanadium concentration to 20 g / L.

[0023] (2) Extraction: P204 extractant is mixed with sulfonated kerosene, wherein the volume fraction of P204 is 5%, to prepare an organic phase. The adjusted spent vanadium electrolyte is subjected to multi-stage extraction, with the volume ratio of organic phase to aqueous phase being 3:1 and the extraction temperature being 30°C, to separate the organic phase containing tetravalent vanadium and the ammonium sulfate solution.

[0024] (3) Stripping: The organic phase containing tetravalent vanadium is stripped by multi-stage countercurrent stripping with an oxalic acid solution having a concentration of 2 mol / L, the volume ratio of the organic phase to the aqueous phase being 1:1, and the stripping temperature being 40° C., to obtain a vanadium oxalate solution.

[0025] (4) Crystallization and drying: The vanadyl oxalate solution is cooled and crystallized under the conditions of a stirring speed of 200 r / min, a cooling temperature of 25° C., and a cooling time of 8 h, and then filtered, separated, and vacuum dried to obtain vanadyl oxalate crystals.

[0026] After testing, the chemical composition of vanadium oxalate is: VOC2O4·5H2O, with a purity of 99.63%. The composition of vanadium oxalate is shown in the following table.

[0027] element Al As Ca Cr Fe K Mg content(%) 0.0035 0.0136 0.0126 0.0008 0.0042 0.0028 0.0002 element Mn Na P S Si Ti V content(%) 0.0002 0.0078 0.0036 0.0117 0.0039 0.0001 21.7393

[0028] Example 2

[0029] (1) Electrolytic reduction and adjustment: After electrolytic reduction of the spent vanadium electrolyte, high-purity vanadium water and a mixed solution of ammonium carbonate and ammonium bicarbonate (mixing ratio of 1:1) were added as pH adjusters to adjust the pH to 1.6 and the vanadium concentration to 10 g / L.

[0030] (2) Extraction: P507 and TBP were mixed in a ratio of 1:1 as an extractant (volume fraction of the extractant was 30%) and mixed with sulfonated kerosene to form an organic phase. The spent vanadium electrolyte was subjected to multi-stage extraction, with the volume ratio of the organic phase to the aqueous phase being 1:1 and the extraction temperature being 40°C, to obtain an organic phase containing tetravalent vanadium and an ammonium sulfate solution.

[0031] (3) Stripping: The organic phase containing tetravalent vanadium is stripped with oxalic acid solution having a concentration of 4 mol / L, the volume ratio of the organic phase to the aqueous phase is 4:1, and the stripping temperature is 60° C. to obtain a vanadium oxalate solution.

[0032] (4) Crystallization and drying: The vanadyl oxalate solution was cooled and crystallized under the conditions of a stirring speed of 50 r / min, a cooling temperature of 20° C., and a cooling time of 3 h, and then filtered, separated, and vacuum dried to obtain vanadyl oxalate crystals.

[0033] After testing, the chemical composition of vanadyl oxalate is: VOC2O4·5H2O, with a purity of 99.54%. The composition of vanadyl oxalate is shown in the following table.

[0034]

[0035]

[0036] Example 3

[0037] (1) Electrolytic reduction and adjustment: After the electrolytic reduction operation of the spent vanadium electrolyte is completed, high-purity vanadium water and ammonia water are added (the adjustment amount is determined according to the actual situation) to make the final pH value reach 2.5 and the vanadium concentration is adjusted to 40 g / L.

[0038] (2) Extraction: P253 and Cyanex 923 were mixed in a ratio of 2:1 as the extractant (volume fraction of the extractant was 35%) and mixed with sulfonated kerosene to prepare the organic phase. The spent vanadium electrolyte was subjected to multi-stage extraction, with the volume ratio of the organic phase to the aqueous phase being 5:1 and the extraction temperature being 20°C, and the organic phase containing tetravalent vanadium and the ammonium sulfate solution were separated.

[0039] (3) Stripping: The organic phase containing tetravalent vanadium is stripped by multi-stage countercurrent stripping with 0.5 mol / L oxalic acid solution, the volume ratio of organic phase to aqueous phase is 8:1, and the stripping temperature is 35° C. to obtain a vanadyl oxalate solution.

[0040] (4) Crystallization and drying: The vanadyl oxalate solution was cooled and crystallized under the conditions of a stirring speed of 300 r / min, a cooling temperature of 30° C., and a cooling time of 12 h. After filtration and separation, and vacuum drying, vanadyl oxalate crystals were obtained.

[0041] After testing, the chemical composition of vanadium oxalate is: VOC2O4·5H2O, with a purity of 99.60%. The composition of vanadium oxalate is shown in the following table.

[0042] element Al As Ca Cr Fe K Mg content(%) 0.0025 0.0108 0.0097 0.0009 0.0028 0.0017 0.0002 element Mn Na P S Si Ti V content(%) 0.0001 0.0078 0.0118 0.0005 0.0049 0.0002 20.7330

[0043] Example 4

[0044] (1) Electrolytic reduction and adjustment: The spent vanadium electrolyte is electrolytically reduced to ensure that all vanadium is converted to tetravalent vanadium. High-purity vanadium water and ammonium carbonate are then added as pH regulators to adjust the pH to 2.2, and the vanadium concentration is adjusted to 25 g / L.

[0045] (2) Extraction: P204 and P507 were mixed in a ratio of 3:2 as an extractant (the volume fraction of the extractant was 25%), and fully mixed with sulfonated kerosene to form an organic phase. Then, the adjusted spent vanadium electrolyte was subjected to a multi-stage extraction operation, with the volume ratio of the organic phase to the aqueous phase set at 3.5:1, and the extraction temperature controlled at 35°C.

[0046] (3) Stripping: The organic phase containing tetravalent vanadium was stripped by multi-stage countercurrent stripping using 2.5 mol / L oxalic acid solution. The volume ratio of the organic phase to the aqueous phase was 4.5:1, and the stripping temperature was set at 45°C.

[0047] (4) Crystallization and drying: The vanadium oxalate solution is placed in a crystallization device and cooled and crystallized under the conditions of a stirring speed of 180 r / min, a cooling temperature of 26° C., and a cooling time of 9 h. After the crystallization is completed, the vanadium oxalate crystal wet material is obtained by filtration and separation through a filtration device. Finally, the wet material is placed in a vacuum drying oven for vacuum drying to obtain a finished vanadium oxalate crystal.

[0048] After testing, the chemical composition of vanadium oxalate is: VOC2O4·5H2O, with a purity of 99.51%. The composition of vanadium oxalate is shown in the following table.

[0049] element Al As Ca Cr Fe K Mg content(%) 0.0015 0.0108 0.0143 0.0008 0.0033 0.0017 0.0003 element Mn Na P S Si Ti V content(%) 0.0002 0.0063 0.0103 0.0115 0.0032 0.0000 21.7143

[0050] Example 5

[0051] (1) Electrolytic reduction and adjustment: First, electrolytic reduction is performed on the spent vanadium electrolyte to reduce all the vanadium to tetravalent state. Then, high-purity vanadium water and ammonium bicarbonate are added to the electrolyte as pH regulators to adjust the final pH value to 1.9 and the vanadium concentration to 30 g / L.

[0052] (2) Extraction: P253 and TBP were mixed in a ratio of 1:2 as the extractant (the volume fraction of the extractant was 40%) and mixed with sulfonated kerosene to form an organic phase. The spent vanadium electrolyte was subjected to multi-stage extraction, with the volume ratio of the organic phase to the aqueous phase being 2.5:1 and the extraction temperature being 50°C.

[0053] (3) Stripping: Stripping the organic phase containing tetravalent vanadium with 3.5 mol / L oxalic acid solution, the volume ratio of organic phase to aqueous phase was 5.5:1, and the stripping temperature was 20°C.

[0054] (4) Crystallization and drying: The vanadium oxalate solution is cooled and crystallized, the stirring speed is controlled at 220r / min, the cooling temperature is 24°C, and the cooling time is 7h. After the crystallization is completed, the vanadium oxalate crystal crude product is obtained by filtration and separation using a filtration device. The crude product is then placed in a vacuum drying device for drying to obtain a vanadium oxalate crystal product.

[0055] After testing, the chemical composition of vanadium oxalate is: VOC2O4·5H2O, with a purity of 99.56%. The composition of vanadium oxalate is shown in the following table.

[0056] element Al As Ca Cr Fe K Mg content(%) 0.0018 0.0095 0.0135 0.0004 0.0021 0.0013 0.0002 element Mn Na P S Si Ti V content(%) 0.0001 0.0089 0.0076 0.0012 0.0089 0.0001 21.7247

[0057] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for recycling spent vanadium electrolyte, characterized in that: The method comprises the following steps: (1) electrolytically reducing the spent vanadium electrolyte to reduce all vanadium in the spent vanadium electrolyte to tetravalent vanadium, and then adding high-purity vanadium water and a pH regulator to the spent vanadium electrolyte to adjust the vanadium concentration and the pH value to 1.6-2.5; (2) Mixing the extractant and sulfonated kerosene to obtain an organic phase, performing multi-stage extraction on the spent vanadium electrolyte, and separating the organic phase containing tetravalent vanadium and the ammonium sulfate solution; (3) using an oxalic acid solution to perform multi-stage countercurrent stripping on the organic phase containing tetravalent vanadium to obtain a vanadium oxalate solution; (4) Cooling the vanadium oxalate solution for crystallization, filtering and separating, and vacuum drying to obtain vanadium oxalate crystals.

2. The method for recycling spent vanadium electrolyte according to claim 1, characterized in that: In step (1), the pH regulator is any one or more of ammonia water, ammonium bicarbonate, and ammonium carbonate, and the vanadium concentration is adjusted to 10-40 g / L.

3. The method for recycling spent vanadium electrolyte according to claim 1, characterized in that: In the step (2), the extractant is any one or more of P204, P507, P253, TBP and Cyanex 923, the volume fraction of the extractant is 5-40%, the volume ratio of the organic phase to the aqueous phase is 1-5:1, and the extraction temperature is 20-50°C.

4. The method for recycling spent vanadium electrolyte according to claim 1, characterized in that: In the step (3), the oxalic acid concentration is 0.5-4 mol / L, the volume ratio of the organic phase to the aqueous phase is 1-8:1, and the stripping temperature is 20-60°C.

5. The method for recycling spent vanadium electrolyte according to claim 1, characterized in that: The cooling crystallization conditions in step (4) are as follows: a stirring speed of 50-300 r / min, a cooling temperature of 20-30° C., and a cooling time of 3-12 h.

6. A method for recycling spent vanadium electrolyte according to any one of claims 1 to 5, characterized in that: The chemical composition of the vanadyl oxalate is: VOC2O4·5H2O, with a purity of ≥99.5%.

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