Microwave pyrolysis of textile dyeing sludge in a continuously operated auger reactor: Char characterization and...

Textile dyeing sludge (DS) contains toxic organic and inorganic substances, and needs to be disposed by appropriate technologies. This paper investigated an auger pyrolyser under microwave irradiation for treatment and disposal of DS. Microwave power, temperature, gas and solid residence times, addition of catalysts were studied. The results showed that the char yield gradually decreased with microwave power. The residence times of solid and gas have slight effects on char yields in the temperature range of 450-750°C. Addition of CaO and Fe increased char yield, decreased non-condensable gas yield and increased H₂ content. CaO promoted decomposition of DS and capture of CO₂. In the meantime, CaO retained more sulfur in the solid phase compared to MWP without addition of CaO. The content of C, H and N in DS and sludge char (SC) decreased with temperature while S increased. The maximum BET (Brunauer-Emmett-Teller) surface area of 91.9m²/g was observed for SC at 550°C, consistent with Scanning Electron Microscopy (SEM) observations. X-Ray fluorescence (XRF) analysis showed existence of some heavy metals, and leaching characteristics of heavy metals in the SC meet the requirements of national standards in China and will not pose a threat to the environments.