Kinetics, adsorption isotherms, thermodynamics, and desorption studies of cadmium removal from aqueous solutions using bamboo sawdust/rice husk biochar

The adsorption mechanisms of Cd²⁺ removal from synthetic water using blended biochar from bamboo sawdust (BSD) and rice husk (RH) feedstocks at BSD/RH ratios 1:1, 1:3, and 3:1 were investigated. The equilibrium isotherms (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) and kinetics (pseudo-first order, pseudo-second order, Elovich, and intra-particle diffusion kinetic adsorption models) and thermodynamics were examined. The BSD/RH biochar ratio of 1:1, 1:3, and 3:1 produced the Cd²⁺ removal of 99.2%, 98.3%, and 97.24% respectively. The adsorption investigation found insignificant differences in removal efficiency across the biochar ratio combinations. Furthermore, the equilibrium isotherm analyses for the BSD/RH ratio of 3:1 and 1:1 are best described by in favor of the Freundlich model, whereas for BSD/RH biochar ratio of 1:3 best matched the Langmuir model. The thermodynamic study revealed that the process is non-spontaneous, endothermic, and dominated by the physisorption mechanism. Generally, physisorption was discovered to be the dominant process controlling the Cd²⁺ removal from the solution.