Microwave irradiation for the recovery enhancement of fly ash components: Thermodynamic and kinetic aspects

•Full recoveries of V and Ni were obtained under the conventional leaching condition using H2O2.•Full recovery of V and Ni is attainable using microwave irradiation without using additives.•Both H2O2 and microwave energy increased the thermodynamic tendency of dissolution reactions.•Microwaves assist the leaching process by removing kinetic barriers. This study investigated the use of microwave-assisted leaching to recover the vanadium (V) and nickel (Ni) of fly ash collected from power plants. The fly ash sample was characterized using XRF, ICP-OES, powder X-ray diffraction, FESEM, and a laser particle size analyzer. The sample was found to be valuable as well as hazardous due to the presence of a considerable amount of base and heavy metals with an 80% passing particle size of 70 micrometers. Conventional leaching tests were performed using sulfuric acid (H2SO4), which resulted in 91.2% V, 80.5% Ni, and 57.6% Fe recoveries. Full recovery of the aforementioned components was achieved by adding 10% v/v hydrogen peroxide (H2O2). Microwave-assisted leaching showed promise, with comparable recoveries for Ni and V (complete recovery) at a microwave power of 700 W and a retention time of 30 mins, without the addition of any chemical additive. The study provided thermodynamic and kinetic justification for the efficient dissolution of V and Ni, which occurs via rapid boiling of the sulfuric acid solution (19.5% v/v) overcoming the chemical and liquid diffusion kinetic barriers. This work concludes that microwave-assisted leaching is an effective method for recovering heavy metals from fly ash samples as a complex solid waste. [Display omitted]