Co-thermal conversion, atmosphere, and blend type controls over heavy metals in biochars and bottom slags of textile dyeing sludge and durian shell

Abstract

The co-thermal conversions of textile dyeing sludge ((TDS) with biomass may be turned into a feasible and green technology to valorize energy and products, but the transformation behavior of heavy metals remains unclear. This study aimed to quantify the migrations and distributions of HMs in biochars and bottom slags and their environmental risks in response to the co-pyrolysis and co-combustion of durian shell (DS) and TDS, atmosphere type, blend ratio, and temperature. The co-combustion interaction of DS and TDS raised the residual HM contents of the bottom slag. Co-pyrolysis reduces the environmental risks of HMs of the TDS, and the effect of CO2 atmosphere is better. In 80N220O2, Cr, Zn, and Cu in the TDS bottom slag had the highest leaching toxicity concentrations at 900 °C. At 800 °C, the leaching toxicity concentrations of HMs were Cr > Cu > Zn > Mn in TDS. The O2 concentration and atmosphere type did not significantly affect the HM morphology and transformation. K increased the temperature of converting solid-phase Ni to slag-phase NiO in DS sample and affected the transformation temperature and strength of Ni, Zn, and Pb in other sample at the high temperature. The combined results of all the three optimizations of HM contents, forms, and risks pointed to add 50 % DS in the N2 atmosphere and add 50 % DS in 50N250O2 and 80CO220O2 atmospheres as the optimal co-pyrolysis/combustion settings, respectively.