Effect of addition of rice husk on the fate and speciation of heavy metals in the bottom ash during dyeing sludge incineration

Bottom ash obtained from the incinerated dyeing sludge is rich in heavy metals, leaching of which is harmful to the environment. In this investigation, an in situ passivation technology based on co-firing of dyeing sludge and rice husk is proposed to inhibit the mobility of heavy metals from bottom ash. However, the fate of heavy metals under different dosages of rice husk and the passivation mechanism are still unclear. In this study, the effect of rice husk on the characteristics of heavy metals (Cr, Cu, Ni and Zn) in bottom ash was investigated, and the passivation mechanism of the in situ technology has been revealed. After co-combustion using the addition of 30% rice husk, the leaching concentrations of Cu, Ni and Zn have been found to meet the threshold as prescribed by the integrated wastewater discharge standard (GB8978-1996), while the leaching of Cr remains at an undesirable level. Interaction within the constituents inhibited the leaching of heavy metals during the co-combustion process, especially under a high dosage of rice husk. The newly formed silicoaluminate mineral during co-combustion is the heavy metal-bearing phase, and the generation of which is significantly related to the passivation of heavy metals. (C) 2019 Elsevier Ltd. All rights reserved.