Abstract:Address to three major technical bottlenecks in the traditional V2O5 production process: first, the purity of precipitated vanadium products is typically lower than 98.5%, making it challenging to meet the demand for high-end applications like electrode materials for new energy batteries; second, a high amount of ammonium salt is consumed (the ammonium coefficient is typically greater than 6), which raises production costs significantly; and third, after the reaction, the residual ammonium ions form nitrogen pollution and ammonia, which can cost much for wastewater treatment. Especially noteworthy is that the conventional washing method makes it difficult to effectively remove the sodium ions entrained in the product, and this key defect has resulted in product purity consistently lower than 98.5%, severely limiting the application of high-end vanadium products in strategic emerging fields such as energy storage and catalysts. Based on this, this study uses the vanadium-rich liquid produced by a plant in Shaanxi Province as a raw material and ingeniously designed a coupled process system of hydrolysis vanadium precipitation and ultrasound-assisted washing to systematically investigate the mechanism of key process parameters on the rate of vanadium precipitation and product purity. A two-stage process optimization strategy was adopted: at the stage of hydrolysis vanadium precipitation, the influences of pH value (0.5—2.4) of solution, reaction temperature (25—100 ℃), and reaction time (0.5—2.5 h) on the vanadium precipitation rate were systematically investigated in a one-way system. At the stage of ammonium washing, ultrasonic enhancement technology was introduced, with a focus on the ammonium addition coefficients (0.3—3.0), the ultrasonic power (200—1 200 W), ultrasonic time (3—20 min), ultrasonic temperature (25—75 °C), and number of washings affect product purity and vanadium loss. SEM-EDS was used to characterize the micromorphological evolution of the products before and after washing, XRD and FTIR were used to analyze the changing rules of physical phase transition and chemical bonding, and particle size distribution was used to investigate the mechanism of ammonium salt washing following ultrasonic intervention. The experimental results show that vanadium precipitation rate is more than 98.98% under the optimal hydrolysis vanadium precipitation process parameters including pH value of solution of 1.8, reaction temperature of 95 ℃ and reaction time of 1.5 h, which demonstrating excellent precipitation efficiency. In the ultrasonic washing step, the purity of the product is enhanced to 99.05% when the ammonium coefficient is 0.5, the ultrasonic power is 400 W, the ultrasonic time is five minutes and wash twice at ultrasonic temperature of 25 ℃ (room temperature). Compared to the typical ammonium salt vanadium precipitation technique, the ammonium salt consumption of this process is reduced by 91.6%. The microscopic morphological study reveals that the ultrasonically treated products are uniformly dispersed, with a clear layered structure, and have much higher crystallinity than the ammonium salt products, which are prone to agglomeration. The ultrasonication products are smaller and more concentrated, with a fraction of 1.2—20 μm particles at 72.4% (52.1% for ammonium salt vanadium precipitation). Physical phase analysis indicates that following ultrasonic washing, NaV3O8?xH2O and Na2SO4 are entirely transformed to a single phase (NH4)2V6O16?1.5H2O to accomplish efficient Na+ removal. Infrared spectroscopy demonstrates the mechanism of ultrasound-induced crystal reconstruction: the V=O bond transformed into a V—O—V bond, the SO42- characteristic signal disappears, and NH4+ is successfully embedded in the crystal lattice. Ultrasonic cavitation strengthens the NH4+ and Na+ ion exchange kinetics and disrupts the electrostatic interaction between Na+ and vanadate by increasing the collision frequency, resulting in a 91.6% increase in washing efficiency and 99.05% purity of V2O5. This procedure creates a new method for producing V2O5 with high purity, low ammonium usage and environmental friendliness. The next step is to reduce the impurity ion content in the raw material by pre-treating the vanadium-rich liquid to remove impurities in depth, to investigate the feasibility of producing higher purity V2O5 products, and to see if ammonium consumption can be reduced further by using the pre-treated vanadium-rich liquid for vanadium precipitation and ultrasonic washing.