Biosorption of aqueous cadmium using chemically delignified lignocellulose from industrial hemp stalks: kinetics, isotherms, and thermodynamics

Biosorbents present a cost-effective alternative to expensive fossil-based ion-exchange resins for addressing the challenge of heavy metal contamination in wastewater treatment. Among these contaminants, cadmium poses a significant health threat, even at low concentrations. This study investigated the potential of hemp stalks, processed through chemical treatment to remove lignin, as effective biosorbents for cadmium removal from aqueous solutions. This study examined the effects of initial pH, biosorbent dosage, cadmium concentration, temperature, and contact time on biosorption. The kinetics, isotherms, and thermodynamics of biosorption were analyzed. Biosorbents before and after biosorption were characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). The findings indicate that the biosorption process follows a pseudo-second-order kinetic model, with intraparticle diffusion as the rate-limiting step. The maximum cadmium adsorption capacity of the biosorbent was determined to be 213.4 mg/g, according to Langmuir isotherm. Both kinetics and isotherms demonstrated cadmium biosorption was monolayer chemical adsorption. Furthermore, the biosorption process was spontaneous and endothermic, highlighting the potential of these biosorbents as cost-effective alternatives to synthetic sorbents.