Study on the Pyrolysis Characteristics, Kinetics and Mineral Transformation of Paper Sludge

To effectively utilize paper sludge and allow for energy recovery, the thermal behaviors of two paper sludge (PS) were studied by thermogravimetric analysis (TGA). The kinetic analysis was conducted according to Coats-Redfern (CR) method. The evolution of pore structure and surface morphology was investigated by N2 adsorption and scanning electron microscopy (SEM), respectively. The mineral transformation was analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Derivative thermogravimetry (DTG) curves of PS show two different stages. The first stage was due to devolatilization (200–400 °C) and the second stage (650–800 °C) accounted for the mineral decomposition and char degradation. It was found that a large number of pores formed during pyrolysis because of char fragmentation. The specific surface areas increased from 5.161 to 22.894 m2 g−1 for PSA and from 9.007 to 16.126 m2 g−1 for PSB with the increase of temperature. The intense absorption bands of calcite (1426, 875 and 712 cm−1) in raw material indicated that calcite was the main mineral of PS. The decomposition of calcite at 700 °C and the further production of gehlenite (916 cm−1) at 900 °C, and the dehydration of kaolinite at 500 °C and further transformation into mullite (996 cm−1) at 900 °C were observed by both FTIR and XRD. The XRD results were generally consistent with FTIR analyses.