This study demonstrates the efficacy of FeS2/Chitosan composites as adsorbents for removing cadmium (Cd) from wastewater, showcasing a promising approach for environmental pollution treatment. The hydrothermal synthesis method successfully produced FeS2 and FeS2/Chitosan composites with desirable properties obtained from XRD, FTIR, SEM EDX, XPS, and UV–Vis DRS, including a pyrite crystal structure, 15 nm crystalline size, and a 2.77 eV bandgap energy. The optimized conditions for maximum Cd(II) removal were determined to be a pH of 6, a 12 mg/L Cd(II) solution, a 40 mg adsorbent loading, and a 40 min contact time, achieving complete removal through a pseudo-first-order process. Moreover, the biological studies indicated that the FeS2/Chitosan composite shows significant antibacterial activity against E.coli, further enhancing its utility in wastewater treatment applications. The composite’s dual functionality in heavy metal adsorption and antibacterial efficacy highlights its potential for comprehensive wastewater management solutions. Future research could explore the scalability of this approach and its application to other heavy metals and contaminants, further contributing to sustainable environmental practices.