Pyrolysis of textile dyeing sludge in fluidized bed and microwave-assisted auger reactor: Comparison, migration and distribution of heavy metals

Abstract

This study compared products distribution, heavy metals migration and distribution of textile dyeing sludge (DS) pyrolysis in microwave-assisted auger pyrolyser (MWAP) and fluidized bed pyrolyser (FBP). FBP had higher gas and CO2 yields, while MWAP was beneficial to production of condensates. The yields of FBP char (FC) and MWAP char (MC) decreased while the non-condensable gas yields increased with temperature. Condensates yield reached maximum at 650 °C for both MWAP and FBP. Kaolin decreased condensate yield for FBP and increased it for MWAP. However, kaolin achieved the highest condensate and gas yields compared with other additives. CaO reduced gas yield by sorption of CO2 and FBP had better sulfur retention ability than MWAP. Cu, Zn, Ni were enriched in MC, and Zn, Ni were enriched in FC. The residue ratios (RRs) of the enriched heavy metals were 73.91–100% and 75.28–100% for FBP and MWAP, respectively, indicating good stability of these heavy metals. CaO, kaolin and Ca-bentonite retained Zn, Ni and Pb at various degrees with maximum RRs of Zn and Ni up to 97.96% and 100%, respectively. All heavy metal contents in FCs and MCs met requirements of national standard (CJ/T 362 2011, China), showing slight potential ecological risks.