The leaching behavior of cadmium, arsenic, zinc, and chlorine in coal and its ash from coal-fired power plant

The leaching experiment of feed coal (C) and its laboratory high-temperature ash (HA), fly ash (FA), and bottom ash (BA) from a Chinese coal-fired power plant were carried out using column leaching under different pH conditions (pH = 2.0, 4.0, 6.0, and 7.5, respectively) and different leaching durations (up to 80 h). The leaching behaviors of As, Cd, Zn, and Cl were investigated. The results showed that the elements occurring in water-soluble, ion-exchangeable, and Fe-Mn oxide phases are potentially leachable, whereas those in association with organic matter and silicate are less likely to be leached. The cumulative percent of Zn, As, Cl, and Cd leached from C and ash samples increase with decrease in pH. The leaching rate of As and Cl in C and ash samples are higher in comparison with Zn and Cd. However, the maximum concentrations of Cd in the leachate from C, HA, FA, and BA are in excess of or very close to the maximum standard concentrations permitted in the Chinese Standards for Drinking Water and Surface Water. The ultimate concentrations of As, Cd, and Cl in the leachates did not attain equilibrium after the leaching of 80 h; therefore, longer leaching experiments are necessary to evaluate the impact of these hazardous trace elements on aqueous environment.