Effect of coal ash on hydrazine degradation under stirring and ultrasonic irradiation conditions.

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1-5.0 mmol/L was investigated as a function of amount of coal ash (0.0-5.0 wt%) under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the rate of decrease in the hydrazine concentration depended upon an amount of coal ash under the stirring and ultrasonic irradiation condition. It was considered under the stirring condition that hydrazine was adsorbed and degraded partly on coal ash. Furthermore, the sonochemically formed OH radicals were more effective in the hydrazine degradation than stirring condition in the presence of an intermediate amount of coal ash (0.6-2.4 wt%), whereas the effect of OH radicals disappeared in the presence of coal ash more than 2.4 wt%.

The effect of pH on sonochemical degradation of hydrazine.

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1 and 1.0 mmol/L was investigated as a function of pH under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the hydrazine degradation depended greatly upon pH under the ultrasonic irradiation condition, while it did not take place over the whole pH range (0.8-9) under the stirring condition. The hydrazine degradation was suppressed by the addition of tertial butyl alcohol (t-BuOH) known as a scavenger of OH radicals. This result suggested that OH radicals played an important role in the hydrazine degradation. The pH dependence of the hydrazine degradation was discussed in terms of a dissociating form of hydrazine depending upon pH and the effect of OH radicals.

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 (10mg/L, 100mL) was sonicated at 200 kHz and 200 W with or without coal ash (53-106 microm 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.