Effect of coal ash on sonochemical degradation of phenol in water

The influences of coal ash on the degradation of phenol in water were investigated under the stirring or ultrasonic irradiation conditions. Phenol solution (10 mg/L, 100 mL) was sonicated at 200 kHz and 200 W with or without coal ash (53–106 μm in particle size and concentration of 0.0–1.5 wt%). It was found that the sonochemical degradation of phenol in the presence of coal ash was faster than that in the absence of coal ash, and the optimum amount of coal ash was a maximum at 0.4–0.6 wt%. It was confirmed that the phenol degradation did not occur by the addition of hydrogen peroxide and nitric acid under the stirring conditions. The sonochemical degradation with coal ash was depressed by the addition of tertiary butyl alcohol as a radical scavenger. These results indicated that the coal ash accelerated the phenol degradation due to the increase in the amount of hydroxyl radicals under the ultrasonic irradiation. Since the coal ash used had a porous and uneven surface, which was observed by SEM, it was assumed that the coal ash led to the increase in the nucleation site for cavitation bubble due to its surface roughness.