Iron removal from kaolin using thiourea assisted by ultrasonic wave

In the present study a bleaching process of a kaolinite was carried out using thiourea as the leachant agent in the iron removal process, in the absence and presence of ultrasound. The effect of thiourea was investigated together with other factors, such as thiourea concentration, temperature, treatment time, and ultrasonic parameters. The optimum conditions for the maximum whiteness of 89% with ultrasound were determined as follows: reaction temperature, 20 °C; ultrasound frequency, 80 kHz; ultrasound power, 500 W; thiourea concentration, 0.4 wt.%; pH, 3.0; reaction time, 20 min. The assistance of ultrasound led to a remarkable acceleration for the iron leaching process, and dramatic reduction in the concentration of leach reagent, irradiation time, and reaction temperature, when compared with the conventional bleaching method using thiourea in the absence of ultrasound.