Method for preparing vanadium electrolyte by electrochemistry-ultrasonic synergistic reduction of waste vanadium catalyst

Abstract

The invention discloses a method for preparing a vanadium electrolyte by electrochemistry-ultrasonic synergistic reduction of a waste vanadium catalyst in the technical field of solid waste resource utilization, which comprises the following steps of: roasting the waste vanadium catalyst by NaOH and leaching by sulfuric acid, applying 80Hz pulse current by adopting a titanium-based lead dioxide anode and a graphite cathode in a three-chamber electrolytic bath, synchronously starting a 25kHz and 300W ultrasonic field for synergistic reduction, and controlling the reaction temperature to be 35 + / -2 DEG C until the V < 5 + > concentration is less than 0.05 g / L; and then adding a chitosan-tea polyphenol composite stabilizer, and concentrating through a PVDF (Polyvinylidene Fluoride) ultrafiltration membrane to obtain electrolyte with the vanadium concentration of 1.8 mol / L, wherein the molar ratio of V < 4 + > to V < 3 + > is 1: 1.2, Fe < 3 + > is less than 15 ppm, and Al < 3 + > is less than 10 ppm. In the process, the vanadium recovery rate reaches 95.2%, the energy consumption is 2.8 kWh / kg vanadium and is reduced by 65% compared with that of a traditional process, and the cycle life of the electrolyte is prolonged to 1200 times or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, and particularly relates to a method for preparing vanadium electrolyte by electrochemical-ultrasonic synergistic reduction of waste vanadium catalyst. BACKGROUND

[0002] As a new type of energy storage technology, the preparation process of the core electrolyte of the all-vanadium redox flow battery is crucial to the performance of the battery. At present, the vanadium electrolyte is mainly prepared by chemical reduction method, electrolysis method and solvent extraction method in industry. The chemical reduction method usually uses oxalic acid and other reducing agents to treat vanadium oxide, and reduces pentavalent vanadium to tetravalent vanadium through high-temperature reaction; the electrolysis method relies on electrode reaction to control the valence state of vanadium ions, and realizes the conversion of valence state through electric energy driving; the solvent extraction method uses specific organic reagents to selectively separate vanadium ions, and combines with the reverse extraction process to obtain high-purity solution. These technologies are based on the recycling of waste catalysts and other secondary resources, aiming to realize the efficient extraction of vanadium through processes such as calcination, leaching and separation.

[0003] However, the existing technology still has significant bottlenecks: first, the chemical reduction method relies on a large amount of strong acid (such as concentrated sulfuric acid) and reducing agent (such as oxalic acid), which is easy to produce waste gas such as CO2 and SO2 and waste water containing heavy metals, has high environmental protection cost and long reaction period, and the leaching time needs 4-6 hours; second, the electrolysis method has huge energy consumption, and the energy consumption per ton of product is 5-8 kWh, and the electrode is easy to corrode, resulting in high equipment maintenance cost; third, the solvent extraction method needs multi-stage countercurrent operation, and the process is complex and the organic reagent is easy to remain, which affects the purity of the electrolyte. In addition, the recovery rate of vanadium in the existing process is generally low, and the impurity separation is not complete, which leads to poor cycle stability of the electrolyte and limits the industrial application of the all-vanadium redox flow battery. SUMMARY

[0004] The present application aims to provide a method for preparing vanadium electrolyte by electrochemical-ultrasonic synergistic reduction of waste vanadium catalyst, in order to solve To solve the above technical problems, the present application provides the following technical scheme: a method for preparing vanadium electrolyte by electrochemical-ultrasonic synergistic reduction of waste vanadium catalyst, comprising the following steps: S1, waste vanadium catalyst pretreatment: mixing the waste vanadium catalyst with NaOH at a mass ratio of 1:1-1:2, calcining at 500-600℃ for 2-3 hours, crushing to below 200 mesh after cooling, leaching with 50-60% sulfuric acid at a solid-liquid ratio of 1:3-1:5, leaching temperature 80-90℃, time 4-6 hours, filtering to obtain vanadium-containing leaching solution; S2, electrochemical-ultrasonic synergistic reduction: transferring the leaching solution to an electrolytic cell, using titanium-based lead dioxide as anode and graphite as cathode, applying pulse current, frequency 50-100Hz, 10-20mA / cm 2At the same time, an ultrasonic field is started, with a power of 200-400 W and a frequency of 20-40 kHz, and the reaction temperature is controlled at 30-40 DEG C, until the V 5 + concentration is less than 0.1 g / L. S3, composite stabilizer addition: a chitosan-tea polyphenol composite stabilizer is added to the reduced electrolyte, with an addition amount of 0.05-0.15% of the mass of the electrolyte, and stirring is uniform; S4, membrane concentration: polyvinylidene fluoride ultrafiltration membranes with a molecular weight cut-off of 10,000 Da are used for concentration, with an operating pressure of 0.1-0.3 MPa, to obtain an electrolyte with a vanadium concentration of 1.5-2.0 mol / L.

[0005] Further, the NaOH roasting in step S1 is used to convert V2O5 in the waste vanadium catalyst into soluble NaVO3, and 0.5-1.0 g / L of sodium thiosulfate is added during sulfuric acid leaching to reduce Fe 3 + in the leaching solution.

[0006] Further, the duty cycle of the pulse current in step S2 is 60%-80%, and the ultrasonic field uses an intermittent working mode, working for 30 minutes and pausing for 10 minutes, until the electrolyte color changes from yellow to blue-violet.

[0007] Further, the degree of deacetylation of the chitosan in step S3 is greater than or equal to 90%, the purity of the tea polyphenol is greater than or equal to 95%, and the composite stabilizer needs to be previously dissolved in deionized water with a concentration of 5-10 g / L before being added to the electrolyte.

[0008] Further, the mass ratio of the chitosan-tea polyphenol composite stabilizer in step S3 is 1:1-1:3.

[0009] Further, the ultrafiltration membrane in step S4 needs to be pre-filtered before concentration, with a 5-micron filter core being used to remove suspended impurities, and the content of impurity ions (Fe 3 +, Al 3 +) in the electrolyte after concentration is less than or equal to 50 ppm.

[0010] Further, the molar ratio of V 3 + / V 4 + in the electrolyte is 1:1.2-1:1.5, the pH value is 1.5-2.0, the conductivity is greater than or equal to 0.8 S / cm, and the precipitation rate is less than or equal to 1.5% after storage at 50 DEG C for 30 days.

[0011] The beneficial effects of the present application are: 1. Through the electrochemical and ultrasonic synergistic process, the leaching and reduction efficiency of vanadium elements in the waste vanadium catalyst is significantly improved, the vanadium recovery rate can reach more than 90%, which is 10-15 percentage points higher than that of the traditional process, and the leaching time is shortened from 6-8 hours to 4 hours.

[0012] 2. The coupling of ultrasonic cavitation effect and pulse current reduces the overpotential of electrochemical reduction, reduces the energy consumption of ton product from 5-8 kWh to 2.8 kWh, reduces the energy consumption by 65%, and avoids the use of toxic reagents such as oxalic acid in traditional chemical reduction method, realizing green production without wastewater pollution.

[0013] 3. Using chitosan-tea polyphenol composite stabilizer, without additional impurity removal process, the content of Fe 3 +、Al 3 + and other impurities in the electrolyte can be controlled below 15 ppm, the electrolyte conductivity reaches 0.9 S / cm, and the cycle life is prolonged to more than 1200 times, which is 50% higher than the traditional process.

[0014] 4. The process realizes the synchronous recovery of titanium, potassium and other components in waste catalyst throughout the whole process, the leaching residue can be reused as titanium dioxide raw material, and a closed-loop system of "solid waste resourceization-high value utilization-clean emission" is constructed, which not only reduces the raw material cost of energy storage industry, but also provides an efficient path for harmless disposal of waste catalyst, and meets the collaborative development needs of new energy and environmental protection industry under the "double carbon" goal. DETAILED DESCRIPTION

[0015] EMBODIMENT: A method for preparing vanadium electrolyte by electrochemical-ultrasonic synergistic reduction of waste vanadium catalyst, comprising the following steps: Step 1: Pretreatment of waste vanadium catalyst Raw material preparation: Take 1000 g of waste vanadium catalyst (containing V2O58 wt%, TiO275 wt%, K2O3 wt%, from waste SCR catalyst of steel industry) and crush it to below 200 mesh.

[0016] Mix the waste catalyst powder with NaOH at a mass ratio of 1:1.5, and place it in a muffle furnace at 550°C for 2 hours to convert V2O5 to soluble NaVO3.

[0017] Sulfuric acid leaching: After cooling, add 3000 mL of 50% sulfuric acid solution, with a solid-liquid ratio of 1:3, and stir at 85°C for 4 hours. During the process, add sodium thiosulfate 1.0 g / L to reduce Fe 3 +.

[0018] Filter the leaching solution through a 5 μm filter cartridge to obtain a vanadium-containing leaching solution with a V 5 + concentration of 1.2 mol / L and a pH of 1.2.

[0019] Step 2: Electrochemical-ultrasonic synergistic reduction Electrolytic cell setting: A three-compartment electrolytic cell was used, with a titanium-based lead dioxide electrode in the anode compartment and a graphite electrode in the cathode compartment, both with an area of 100 cm 2 The compartments were separated by a proton exchange membrane.

[0020] The leachate was injected into the cathode compartment and diluted with deionized water to a volume of 2000 mL, with the reaction temperature controlled at 35°C ± 2°C.

[0021] Synergistic reduction operation: Ultrasonic conditions: Turn on the ultrasonic generator, power 300W, frequency 25kHz, use intermittent mode, work for 30 minutes, pause for 5 minutes, continuous action for 2 hours.

[0022] Electrochemical conditions: Apply pulse current, frequency 80Hz, current density 15mA / cm 2 , duty cycle 70%, real-time monitoring of solution color change, from yellow to blue-violet.

[0023] End point control: When the concentration of V 5 + in the solution is <0.05g / L (detected by UV-visible spectrophotometer), stop the reaction, obtain V 4 + / V 3 + mixed solution, molar ratio 1:1.3.

[0024] Step 3: Composite stabilizer addition Stabilizer preparation: Weigh 5g of chitosan (degree of deacetylation 92%) and 4g of tea polyphenol, dissolve in 100mL of deionized water, pH=4.5, ultrasonic dispersion for 30 minutes, to prepare a composite stabilizer solution.

[0025] Add and mix: Slowly add the stabilizer solution to the reduced electrolyte, stirring speed 200rpm, continuous mixing for 30 minutes, control the amount of stabilizer added to be 0.1wt% of the electrolyte mass.

[0026] Step 4: Membrane concentration and finished product Ultrafiltration concentration: Use polyvinylidene fluoride ultrafiltration membrane with a molecular weight cutoff of 10000Da, operating pressure 0.2MPa, concentrate to a volume of 500mL, to obtain high-concentration vanadium electrolyte.

[0027] Finished product parameters: Vanadium concentration 1.8mol / L, V 4 + / V 3 + molar ratio 1:1.2; Impurity content: Fe 3 + <15ppm, Al3+ <10ppm, K+ <50ppm; Electrical conductivity 0.9 S / cm (25℃), pH=1.8.

[0028] Step 5: By-product treatment Titanium slag recycling: After being acid-washed with 5% HF, the leaching residue is calcined at 900℃ for 2 hours to obtain rutile TiO2. After washing and drying, it can be reused as a raw material for titanium dioxide in catalyst production.

[0029] Wastewater treatment: After neutralization and precipitation, the concentration of heavy metal ions in the anolyte of the electrolytic cell is lower than the GB25467-2010 emission standard, and it can be discharged into the municipal pipe network.

[0030] Key process parameters and innovations:

[0031] Implementation effect verification Electrochemical performance testing: The prepared electrolyte was used as the positive electrode liquid, and V was commercially available. 3 + The solution was used as the negative electrode liquid to assemble a 5kW all-vanadium redox flow battery stack.

[0032] At 80mA / cm 2 The results of the cyclic test at current density are as follows: Energy efficiency: 83.5% (78% for conventional processes); capacity retention: 92% after 1000 cycles (85% for conventional processes).

[0033] Impurity tolerance test: Artificial addition of Fe to the electrolyte 3 +to 50ppm, after ultrasonic-electrochemical synergistic treatment for 30 minutes, Fe 3 The concentration of impurities decreased to 8 ppm, indicating that the process has a self-cleaning ability for impurities.

[0034] The above specific embodiment constructs an efficient and green vanadium electrolyte preparation system through a whole-process technology of waste vanadium catalyst pretreatment-electrochemistry-ultrasonic synergistic reduction-composite stabilizer addition-membrane concentration. Through the synergistic effect of ultrasonic cavitation effect and pulse current, the efficiency bottleneck of traditional leaching-reduction process is broken, the vanadium recovery rate is increased to more than 90%, and the energy consumption is reduced. The introduction of natural polymer composite stabilizer solves the residual pollution problem of traditional chemical reducing agent, ensures that the impurity content of electrolyte is lower than the industry standard, and prolongs the cycle life to more than 1200 times. In addition, the whole process realizes the full recovery of vanadium, titanium and other elements in waste catalyst, and the treated wastewater meets the discharge standard, forming a closed-loop mode of "solid waste resourceization-clean production-high value utilization". This method not only provides a new path for harmless disposal of waste vanadium catalyst, but also provides a low-cost and high-performance electrolyte preparation technology, which effectively supports the application and promotion of all-vanadium redox flow battery in the field of large-scale energy storage, and has significant environmental, economic and industrial innovation value.

[0035] The above is only an embodiment of the present application, and the common knowledge of specific structures and characteristics in the scheme is not described in detail. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be regarded as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst, characterized in that, Includes the following steps: S1. Pretreatment of waste vanadium catalyst: Mix waste vanadium catalyst with NaOH at a mass ratio of 1:1 to 1:2, calcine at 500 to 600°C for 2 to 3 hours, cool and crush to below 200 mesh, leach with 50 to 60% sulfuric acid at a solid-liquid ratio of 1:3 to 1:5, leach at 80 to 90°C for 4 to 6 hours, and filter to obtain vanadium-containing leachate; S2. Electrochemical-ultrasonic synergistic reduction: The leachate is transferred to an electrolytic cell, with titanium-based lead dioxide as the anode and graphite as the cathode. A pulsed current is applied at a frequency of 50-100Hz and a current density of 10-20mA / cm². 2 Simultaneously, the ultrasonic field is activated with a power of 200-400W and a frequency of 20-40kHz, and the reaction temperature is controlled at 30-40℃ until the solution reaches V 5 +Concentration < 0.1 g / L; S3. Addition of composite stabilizer: Add chitosan-tea polyphenol composite stabilizer to the reduced electrolyte at a concentration of 0.05-0.15% of the electrolyte mass and stir until homogeneous. S4. Membrane Concentration: Concentration is performed using a polyvinylidene fluoride ultrafiltration membrane with a molecular weight cutoff of 10000 Da at an operating pressure of 0.1-0.3 MPa to obtain an electrolyte with a vanadium concentration of 1.5-2.0 mol / L.

2. The method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst according to claim 1, characterized in that: In step S1, NaOH roasting is used to convert V2O5 in the waste vanadium catalyst into soluble NaVO3. During sulfuric acid leaching, 0.5-1.0 g / L of sodium thiosulfate is added to reduce Fe in the leachate. 3 +.

3. The method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst according to claim 2, characterized in that: In step S2, the duty cycle of the pulse current is 60%-80%, and the ultrasonic field adopts an intermittent working mode, working for 30 minutes and pausing for 10 minutes, until the electrolyte color changes from yellow to blue-purple.

4. The method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst according to claim 3, characterized in that: In step S3, the degree of deacetylation of chitosan is ≥90%, the purity of tea polyphenols is ≥95%, and the composite stabilizer needs to be dissolved in 5-10 g / L deionized water before being added to the electrolyte.

5. The method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst according to claim 4, characterized in that: In step S3, the mass ratio of chitosan-tea polyphenol composite stabilizer is 1:1 to 1:

3.

6. The method for preparing vanadium electrolyte by electrochemical-ultrasound synergistic reduction of waste vanadium catalyst according to claim 5, characterized in that: In step S4, pre-filtration is required before ultrafiltration membrane concentration. A 5μm filter element is used to remove suspended impurities. After concentration, the electrolyte contains impurity ions (Fe2+). 3 +、Al 3 +) content ≤50ppm.

7. The vanadium electrolyte prepared according to any one of claims 1-6, characterized in that: V in electrolyte 3 + / V 4 The molar ratio is 1:1.2-1:1.5, the pH value is 1.5-2.0, the conductivity is ≥0.8S / cm, and the precipitation rate is ≤1.5% after storage at 50℃ for 30 days.

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