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The primary goal of the current research was predicting the optimum operational parameters for removing of Fe (II) from aqueous solutions by Exhausted Coffee Husk (ECH) biochar, through batch mode experiments using a Box-Behnken Design (BBD) within a Response Surface Methodology (RSM) framework. The effect operational factors for instance, pH, contact time and the dosage of ECH-biochar were investigated in a certain range, prior to conducting the BBD experiments. The pH was in a range of 4–9, while the contact time was in between 30 and 150 minutes and the dosage 0.05–2.5 g. The results showed that the optimum operational parameters for ECH biochar as biosorbent for Fe ions removal were 7, 0.102 g, 54.49 minutes for pH, contact time and dosage, respectively, with the RE and biosorption capacity (qt) were 99.91 % and 73.09 mg/g. The validation test showed the similar results were obtained for RE and qt with %RSD were 0.7 %. The process of Fe biosorption corresponds effectively with a modified Langmuir isotherm model, and the prediction of the rate constant is reliably achieved using the pseudo-second-order kinetic model. Furthermore, analyses of scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction (XRD) showed ion exchange as the Fe removal mechanism by the ECH-BC, while Fourier-transform infrared spectroscopy (FT-IR) also showed the role of structural alterations on the surface of ECH-BC subsequent to the biosorption of Fe.

This research focuses on optimizing the carbonization parameters of Exhausted Kahwa Coffee (EKC) for enhanced biosorption of Cu(II) from aqueous solutions. Utilizing the Box-Behnken design (BBD), the study systematically investigates the combined effects of carbonization temperature, time, and gradient on EKC biochar (EKC-BC) formation, maintaining a constant initial copper concentration. The BBD demonstrates statistical significance through ANOVA testing. The optimized carbonization conditions obtained are at 575.42 °C, 2.59 hours, and a gradient of 19.52 °C/min, yielding a maximum predicted biosorption capacity of 6.62 mg/g. Experimental values for Cu2+ removal rate and adsorption capacity confirm the model's accuracy, with a 2% deviation from predictions. Response surface methodology effectively enhances the preparation conditions of EKC-BC, leading to improved biosorption capacity. Copper biosorption aligns well with a linearly transformed Langmuir isotherm model, while the pseudo-second-order kinetic model accurately forecasts the rate constant. Instrumental analyses, including scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), provide insights into the surface structural modification of EKC-BC after adsorption of Cu2+.