Thermo-chemical conversion and kinetic evaluation of Casuarina equisetifolia pines to biochar and their utilization in sequestering toxic metal ions

The thermal degradation and kinetics behavior of coastal She-oak plant, i.e., Casuarina equisetifolia pines, were investigated using thermo-gravimetric analysis (TGA). C. equisetifolia pines (CeP) were applied for pyrolytic decomposition at four varying rates of heating (1.25, 15, 20, and 40 °C/min). Underlying kinetic mechanisms were elucidated using iso-conversional or model-free kinetics (Kissinger-Akahira-Sanose, Flynn-Waal-Ozawa, and Starink), and the corresponding activation energies were evaluated. The biomass undergone thermo-chemical decomposition in two distinct regimes where moisture, volatiles, and other biochemical constituents got volatilized between 400 and 900 K. Microscopic and elemental analyses were performed to characterize the elemental and morphological features of the biomass and biochar. The utility of CeP-biochar in removing toxic heavy metal ions from a composite metal solution was tested, and the biochar exerted complete removal (99%) within 24 h.