Migration and distribution of heavy metals during co-combustion of pickling sludge and coal

The experiment on co-combustion of pickling sludge and coal was carried out under different temperatures in a high-temperature tubular furnace. The distribution of ten heavy metals (HMs) including As, Cr, Ni, Cd, Cu, Mn, Pb, Zn, Sb and Se in flue gas, fly ash and bottom slag was analyzed. The results indicate that Cd, Se, and Zn are volatile HMs, which predominate in gas phase and fly ash. As to Cd, the maximum proportion in gas phase reaches 61%, while the proportion of Se in flue gas ranges from 38.58% to 94.612%. When the temperature increases, a large amount of Zn is transferred from flue gas to fly ash. As, Cu, Pb, and Sb are semi-volatile HMs. The distribution rate of Pb in bottom slag changes slightly. However, its percentage in flue gas and fly ash swings from 14.176% to 45.79% and from 9.78% to 32.55%, respectively. The peak distribution rate of Sb in flue gas is 37.64%. On the contrary, the temperature increment inhibits the volatilization of As and Cu. This phenomenon is closely relevant to the reaction between As or Cu and some mineral matter. Ni, Cr, and Mn are anti-volatile HMs. The majority of them enrich in bottom slag; in addition, their distributions are insensitive to the temperature change. The enrichment of Cr and Ni in bottom slag is more than 95% and 97%, respectively. The percentage of Mn in bottom slag is boosted from 71.46% to 96.89% as the temperature rises.