Efficient Removal of Cd(II) Using Potassium Permanganate Modified Spent Coffee Grounds: Kinetics, Equilibrium, and Adsorption Mechanism Studies

ABSTRACT The disposal of spent coffee grounds (SCG) not only represents a significant waste of resources but also poses environmental challenges, highlighting the need for effective pretreatment strategies to mitigate potential adverse effects. Incorporating metal oxides into biomass‐based adsorbents can enhance their adsorption capacity for heavy metal ions by enhancing electrostatic attraction and increasing the number of accessible active sites. In this study, KMnO 4 ‐modified spent coffee grounds (KMnO 4 ‐SCGS) were successfully synthesized and applied for the removal of Cd(II) from aqueous solution. Key process parameters, including contact time, pH, initial Cd(II) concentration, temperature, and adsorbent dosage, were systematically investigated. Characterization using scanning electron microscopy (SEM), Fourier‐transform infrared spectroscopy (FTIR), and x‐ray photoelectron spectroscopy (XPS) confirmed that KMnO 4 treatment increased the abundance of oxygen‐containing functional groups and promoted the deposition of manganese oxides (MnO x ) on the adsorbent surface. The adsorption isotherm followed the Langmuir model, and the kinetics were well fitted by the pseudo‐second‐order model. The maximum Langmuir adsorption capacity of KMnO 4 ‐SCGS for Cd(II) was determined to be 49.54 mg/g at pH 5.0, and 298 K. Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. The enhanced Cd(II) uptake was primarily attributed to the synergistic effect of MnO x and oxygen‐containing functional groups, which facilitated the formation of surface complexes. In conclusion, KMnO 4 modification represents an effective strategy for developing high‐performance adsorbents for Cd(II) removal.