Non-Isothermal Kinetic Decomposition Characteristic of Gracilaria corticata Biomass and Its Biochar Utilization for Efficient Heavy Metals Remediation

The present study utilizes differential thermo-gravimetric (TGA-DTG) based approach for iso-conversional kinetic thermal decomposition of the red seaweed; Gracilaria corticata biomass. The biomass undergone different heating rates (1.25, 2.5, 5, 10, and 15 °C/min) under nitrogen atmosphere and differential thermo-gravimetric analysis showed multistage decomposition of biomass in five different zones. The iso-conversional methods, namely Starink, Kissinger–Akahira–Sunose, and Flynn–Wall–Ozawa, were applied to estimate the apparent activation energies, which found to be 146.70, 142.72, 147.43 kJ/mol respectively. The decomposition of complex biochemical constituents, i.e., polysaccharides, proteins, lipids, pigments, fatty acid, vitamins, hemicellulose, and lignin, occur between 400 and 700 K. The proteins and other cellular components are further decomposed from 900 to 1200 K. The prepared biochar from Gc-biomass were employed for the remediation of toxic heavy metals (cadmium, cobalt, copper, nickel, zinc, mercury, and lead) from mixture of solutions. Kinetic characteristics were evaluated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion adsorption models. Among the models tested, pseudo-second-order was best-fitted to explain the kinetic characteristics of Co²⁺, Ni²⁺, and Cd²⁺ removal by GcB-biochar. The study revealed the importance of biomass as a feed stock and biochar utilization as efficient sorbent in environmental remediation.

Graphical Abstract