Co-combustion of dried waste activated sludge (WAS) and lignite was conducted in a horizontal tube furnace system. The mineral transformation and emission behaviors of Cd, Cr, Ni, Pb, and Zn during combustion were examined. The above heavy metals (HMs) were selected because they are more abundant in WAS than in lignite. In the combustion condition of 1000 degrees C-21% O-2-30 min, the minerals in lignite ash were mainly anorthite (CaAl2Si2O8), quartz (SiO2), pyroxene [Ca(Mg, Fe) Si2O6], and albite (NaAlSi3O8). By contrast, the minerals in WAS ash were mainly quartz (SiO2), anorthite (CaAl2Si2O8), and hematite (Fe2O3). When 90% lignite and 10% WAS were co-combusted, hematite was hardly detected in the combustion product because hematite reacted with quartz and calcium oxide, which are abundant in lignite ash, and generated a large amount of pyroxene. Anorthite and pyroxene were generated continuously during the combustion process, but albite was mainly generated during the first 5 min of combustion. High temperature promoted the generation of complex components, such as sodian anorthite [(Ca, Na)(Si, Al)(2)Si2O8 or (Ca, Na)(Si, Al)(4)O-8]. High O-2 concentration promoted the reaction among the three main mineral elements, i.e., silicon, aluminum, and calcium, and generated a large amount of anorthite. During the co-combustion of WAS and lignite, the volatilization percentages of Cd, Pb, and Zn exceeded 30% after a combustion time of 30 min, and the order was Cd > Pb > Zn. By contrast, the volatilization percentages of Cr and Ni were lower than 15%. High temperature caused an increase in the volatility of HMs, especially Zn and Ni, although the volatilization percentage of Ni remained low. High O-2 concentration also caused an increase in the volatility of HMs, except for Cr and Ni, which showed a slight increase or decrease with increasing O-2 concentration in the inlet atmosphere. (C) 2017 Elsevier Ltd. All rights reserved.