An investigation of the effect of ultrasonic waves on the efficiency of silicon extraction from coal fly ash

Abstract Burning of coal accounts for an enormous proportion of the current energy supply, especially in developing countries. Burning of coal produces large amounts of coal fly ash, which causes serious environmental problems unless it is managed properly. Using chemical analysis, we found that coal fly ash could be a promising source of Si, Al, Ca and some rare earth elements, especially with the assistance of some measures such as ultrasound. In this study, we extracted silicon from coal fly ash using an alkaline dissolution strategy and investigated the effects of temperature and ultrasonic power on the efficiency of silicon extraction. During a 70 min reaction, the efficiency of silicon extraction increased markedly, from 9.41% to 34.96%, as the reaction temperature increased from 70 °C to 110 °C. With ultrasound assistance, ultrasonic waves enhanced the extraction of silicon at both 80 °C and 110 °C at 720 W ultrasound, increasing the efficiency of silicon extraction from 6.01% to 15.36% and from 34.96% to 54.42%, respectively. However, at 900 W ultrasonic power, extraction was slightly inhibited at both temperatures, causing a little decrease in efficiency.