Pyrolysis of textile dyeing sludge in fluidized bed: Analysis of products, and migration and distribution of heavy metals

Fluidized bed pyrolysis (FBP) is a promising technique for disposal of textile dyeing sludge (DS) owing to its unique characteristics, economic and environmental benefits. However, only a limited number of relevant studies have been found. This work investigated pyrolysis characteristics of DS in a fluidized bed at different operation conditions. The results showed the non-condensable gas yield increased and FBP char (FC) yield gradually decreased with increasing temperature. The maximum oil yield (i.e. 3.52 wt%) was achieved at 650 degrees C. Higher temperatures promoted release of heavy metals and FCs retained heavy metals with residue ratios (RRs) ranging from 64 to 89 wt% at 450-850 degrees C. CaO, kaolin and Ca-bentonite contributed to enrichment of Pb, Zn, Ni and Cr in FCs at various degrees. Ca-bentonite achieved the highest RRs of 98.08% for Ni, 97.96% for Zn and 96.08% for Pb, K3NiO2, ZnAl2O4, ZnS, PbSiO3 and Pb3SO6 were detected in FCs, while only ZnAl2O4 was found in DS. The extraction results by BCR (Community Bureau of Reference) four-step methods displayed that higher temperature (e.g. 650 degrees C) and addition of catalysts (e.g. Ca-bentonite) converted heavy metals (e.g. Cr and Ni) from oxidizable fraction to residual fraction, thus realizing less environmental toxicity. All heavy metals contents in FCs conformed to national standard. (C) 2019 Elsevier Ltd. All rights reserved.