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

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.

Automated summary

This study examined the use of microwave-assisted leaching to recover vanadium (V) and nickel (Ni) from fly ash. The study found that the fly ash sample contained valuable but also hazardous base and heavy metals, with a particle size of 70 micrometers. Conventional leaching tests using sulfuric acid resulted in high recovery rates for V, Ni, and Fe, and complete recovery was achieved by adding hydrogen peroxide. Microwave-assisted leaching showed potential for efficient recovery of V and Ni without the need for additional chemicals, with thermodynamic and kinetic justification provided.