Optimization of mixing behaviors in a multistage vanadium shale leaching tank by a double-layer impeller at different speeds

Background: Multistage vanadium-containing shale leaching tanks often suffer from uneven solid phase distribution and mineral deposition at the bottom of the tank, leading to low leaching efficiency. Methods: In this study, the solid-liquid flow, tracer diffusion and power consumption in a multistage vanadium shale leaching tank with an inlet and outlet were numerically investigated and compared, the samples were stirred by a double-layer impeller with the same and different speeds, and the numerical model was validated by water model experiments. Significant Findings: The results showed that the maximum velocity near the liquid surface increased from 1.24 m/ s to 1.47 m/s and the average velocity increased from 1.15 m/s to 1.24 m/s when the lower impeller speed increased from 34 r/min to 44 r/min. The volume of the low-speed region decreased from 1.15 m3 to 0.63 m3, and the stirring power was reduced by 14.7%. In addition, increasing the lower impeller speed could effectively shorten the response time and increase the peak molar concentration of the tracer. A stirring speed of 34 rpm for the upper impeller and 44 rpm for the lower impeller could achieve good stirring efficiency with proper stirring power.