Valorization of Invasive Faxonius limosus Shell Waste as a Biosorbent for Zn(II) and Cd(II) Removal from Aqueous Solutions

The increasing contamination of aquatic environments by heavy metals and the need for sustainable management of invasive aquatic species have stimulated interest in low-cost biosorbents derived from biological waste. In this study, minimally processed shells of the invasive crayfish Faxonius limosus were evaluated for Zn(II) and Cd(II) removal from aqueous solutions. FTIR, SEM, and BET/BJH analyses revealed an organic-mineral material containing amino, hydroxyl, amide, and carbonate functional groups with a predominantly mesoporous structure. Batch experiments showed rapid metal uptake, with equilibrium reached within approximately 60 min. The pseudo-second-order model provided the best fit to the kinetic data, while equilibrium behavior was best described by the Temkin model for Zn(II) and the Langmuir model for Cd(II). Langmuir maximum adsorption capacities were 70.69 mg/g for Zn(II) and 302.12 mg/g for Cd(II). Metal removal was influenced by both initial pH and biosorbent dose, with 2.5 g/L providing high removal efficiencies for both metals. Calcium-release experiments showed increased Ca concentrations in the presence of Zn(II) and Cd(II), supporting the involvement of the Ca-rich mineral fraction in metal removal. Overall, F. limosus shell waste represents a promising low-cost biosorbent and a sustainable valorization route for invasive biomass.