<![CDATA[This study aims to determine the effect of varying HCl concentrations and microwave irradiation times on the adsorption capacity of kaolin to absorb Fe(II) ions from water, as well as to determine the optimum adsorption time. Kaolin was activated using HCl solutions with concentrations of 0.5, 1.0, and 1.5 N, followed by microwave irradiation for 35, 45, and 55 minutes. The adsorbent was characterized using Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). The adsorption process was conducted on a Fe(II) solution with an initial concentration of 10 ppm and contact times of 30, 60, 90, 120, and 150 minutes. The results showed that for the 1.0 N HCl-activated kaolin adsorbent with a contact time of 90 minutes—as determined by Atomic Absorption Spectrophotometry (AAS), which indicated a Fe concentration in the water after adsorption of 0.0063 mg/L—and for the 35-minute microwave irradiation treatment with a contact time of 90 minutes—as determined by Atomic Absorption Spectrophotometry (AAS), showed an iron concentration in the water after adsorption of 0.0280 mg/L. This adsorbent was able to effectively adsorb Fe(II) metal ions as contact time increased until reaching an optimum condition, after which the adsorption rate tended to stabilize due to surface saturation of the adsorbent. Adsorption kinetics analysis indicates that the adsorption process follows a pseudo-second-order kinetic model, as evidenced by a coefficient of determination (R²) approaching 1 and the agreement between theoretical and experimental adsorption capacities. Thus, HCl- and microwave-activated kaolin has the potential to be used as an effective, economical, and environmentally friendly adsorbent for reducing Fe(II) concentrations in water. Keywords: kaolin, HCl activation, microwave, adsorption, Fe(II), adsorption kinetics. ]]>
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