Ultrasound-Assisted Leaching of Vanadium and Yttrium from Coal Ash: Optimization, Kinetic and Thermodynamic Study

Vanadium (V) and yttrium (Y) were extracted from coal fly ash by a leaching process utilizing sulfuric acid with assistance of ultrasonic and hydrogen peroxide. Response surface methodology was applied to optimize main factors including solid-to-liquid (S/L) ratio, H2SO4 percentage, and H2O2 percentage. Under optimal conditions recovery rates for V and Y were 100 % and 97 %, respectively. A modified shrinking core model to study the kinetic leaching showed that the mass diffusion step controlled the reaction rate. The enthalpies for V and Y recovery indicated that the process was endothermic. Gibbs energy for both metals was negative, i.e., the process was spontaneous. Field emission scanning electron microscopy was applied to determine the effects of acid concentration and ultrasound on the surface of coal fly ash. Results demonstrated that the leaching agent could degrade and diffuse to coal ash particles.