Experimental and Thermodynamic Study of the Partition of Cr, Ni, Cu, Pb, and Mn during Co-combustion of Pickling Sludge and Bituminous Coal

Co-combustion tests of pickling sludge with coal were performed in a high-temperature tubular furnace system. The effect of combustion conditions (combustion temperature from 800 to 1500 °C and sludge ratio from 0 to 100% by weight) on the partitioning of Cr, Pb, Ni, Cu, and Mn in flue gas, fly ash, and bottom ash was investigated. The results showed that the largest part of Cr, Ni, and Mn was retained in bottom ash. The content of Pb in fly ash and flue gas was obviously affected by the temperature. No more than 9% of Cu was emitted with flue gas. Increasing the combustion temperature caused a significant increase in the partitioning of Pb and Cu in bottom ash, while the partitioning of Cr, Ni, and Mn in bottom ash remained stable. The thermodynamic equilibrium calculation was carried out to determine the species of selected heavy metals during co-combustion. The results revealed that Cr, Ni, and Mn were enriched in bottom ash mainly combined with a mineral substance, such as SiO 2, Al 2 O 3, Fe 2 O 3, and MgO, while Cu and Pb were predicted to report to the gas phase in the form of chlorides and oxides. Additionally, the results of principal component analysis (PCA) indicated that the concentration of Mn in the gas phase was positively correlated with the sludge ratio, while Cr and Ni had a weakly negative correlation with the sludge ratio. The sludge ratio seemed irrelevant to Pb and Cu.