Thermal decomposition mechanism and pyrolysis products of waste bischofite calcined at high temperature

Abstract

The thermal behavior of bischofite waste and MgCl2•6H2O was investigated by thermogravimetric analysis–derivative thermogravimetry (TGA-DTG) and X-ray diffraction (XRD). TGA-DTG results showed that the pyrolysis behavior and weight loss of bischofite were different from those of MgCl2•6H2O due to large number of impurities. The effects of temperature, atmosphere, and heating rate on the pyrolysis mechanism and products of bischofite were studied in detail by using XRD. The pyrolysis temperature remarkably affected the pyrolysis products. The mixture of MgO and Mg(OH)Cl coexisted at high temperatures of 550 and 600 °C. However, the presence of MgCl2 was confirmed by calcination at 650 and 700 °C for 0.5 h except MgO. Through calcination at 700 °C for up to 2.0 h, the pyrolysis products of bischofite and MgCl2•6H2O were predominantly MgO, and the atmosphere had no effect on the content of MgO. Low heating rate was favorable for pyrolyzing bischofite into MgO, and the content of MgO reached 94.1% at the heating rate of 5.0 °C/min. After further purification by washing, the content of MgO in the final product increased to 99.0%. This study provided an effective route for the comprehensive utilization of bischofite resources in salt lakes.