Recovery of Palladium from Acidic Solution Using Polyethylenimine-Crosslinked Calcium Silicate Hydrate Derived from Oyster Shell Waste: Adsorption and Mechanisms

In this work, a new adsorbent with effective Pd(II) adsorption ability was synthesized using an oyster shell and fumed silica as the matrix materials and polyethyleneimine as the functional ligand. The adsorption performance of the developed adsorbent was evaluated for the recovery of palladium chloride ions (Pd(II)) from strong acid solutions. To understand the characteristics of the materials used in the study, samples were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and zeta potential analysis. Zeta potential analysis revealed that the isoelectric point of polyethylenimine-crosslinked calcium silicate hydrate (PEI-CSH) was 9.85. Isotherm experiments revealed that the maximum Pd(II) uptake estimated by the Langmuir model was 156.03 mg/g, which was 22.4 and 35.6 times higher than that of the oyster shell powder (OSP) and calcium silicate hydrate (CSH), respectively. The Pd(II) adsorption equilibrium was established in 180 minutes, according to kinetic experiments. These results suggested the possibility of Pd(II) recovery from oyster shell-based adsorbent. Through five adsorption and desorption cycles, the reusability of PEI-CSH was confirmed. PEI-CSH can therefore be considered a potential adsorbent for Pd(II) recovery.