One of the major environmental issues today is waste pollution, particularly non-biodegradable wastes such as polystyrene waste. Furthermore, heavy metal contamination is a major environmental threat. Mercury is one of the most hazardous and poisonous contaminants, and its usage in various industrial processes has resulted in contaminated effluents being released into surface runoff and groundwater. Because of the beneficial physical properties of polystyrene foam, this non-biodegradable waste was used in this study as a suitable medium for chemical modification. The polystyrene foam was first modified using crosslinked chitosan, and then it was reacted with carbon disulfide to improve its performance for the removal of Hg2+. The prepared composite was used for the removal of mercury ions from contaminated water. The adsorbent's physical, chemical, and morphological properties were determined using energy-dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), and Brauer-Emmett-Teller (BET) analyses. Specific surface area, porosity, and average pore diameter were determined to be 314.8m2/g, 0.345 cm2/g, and 1.96 nm, respectively. Experiments were designed to investigate the effects of pH, contact time, and contaminant concentration by the Box-Behnken response surface methodology. The maximum removal percentage of 79.85% was achieved for the initial mercury concentration of 50mg/L at pH 4. Moreover, the adsorption was observed to follow the Dubinin-Radushkevich isotherm. Studies on adsorbent recovery also showed that the adsorbent can be recovered and reused for at least three cycles.