Preparation of porous materials by ultrasound-intensified acid leaching of high-carbon component in coal gasification fine slag

Coal gasification fine slag is one of the by-products from clean and efficient utilization of coal, and its resource utilization is extremely urgent. In this work, a high carbon fraction with a fixed carbon content higher than 60% was obtained by simple sieving of gasification fine slag, from which a porous material was prepared by ultrasonic acid leaching method. The adsorption performance of porous materials, being used as treatment of radioactive iodine in nuclear wastewater, is characterized by iodine adsorption value. The effects of ultrasound time, ultrasound power, acid concentration, and temperature on the iodine adsorption performance and compositional structure of the porous materials were systematically investigated by combining the results of SEM, BET, XRD, and FTIR. The mechanisms of ultrasound-enhanced acid leaching on compositional structure of residual carbon and migration and transformation laws of the ash constituents were explored and summarized. The results show that the porous material prepared under conditions of acid concentration of 4 mol/L, acid immersion temperature of 50 ℃, ultrasonic power of 210 W, and ultrasonic time of 1.5 h has the best iodine adsorption performance of 468.53 mg/g, with a specific surface area of 474.97 m²/g, and possesses a rich pore structure with predominant mesopores. The order of each factor on the iodine adsorption performance is: sonication time > acid concentration > sonication power > acid immersion temperature. The mechanism of ultrasonic enhanced acid leaching is that ultrasonic cavitation and mechanical wave action firstly enhance dissociation of carbon-ash adherent particles, thus making desorption of ash particles blocked in pore channels of the gasification slag to increase its connectivity; secondly, lead to generation of cracks on surface of the carbon and ash particles to enhance accessibility of inorganic components inside the carbon particles; and thirdly, enhance the acid leaching process by increasing mass transfer rate to strengthen leaching effect of inorganic components in the gasification slag.