Carboxymethyl Cellulose/ Microfibrillated Cellulose Hydrogel Beads for Phosphate Recovery: Templating Effects of in Situ-Grown CaCO3 Nanoparticles from CO2

Carboxymethyl cellulose (CMC) hydrogel is a promising adsorbent. However, its weak chemical interaction with phosphate restricts the adsorption capacity and selectivity for nutrient recovery. In this study, CaCO 3 nanoparticles were grown with microfibrillated cellulose using CO 2 before crosslinking CMC into hydrogel beads to improve phosphate adsorption through chemical interactions. Scanning electron microscope showed the rough surface with wrinkles and the slightly porous surface after removing CaCO 3 . Fourier -transform infrared spectroscopy confirmed calcite formation in CMC hydrogel and the removal through chelation based on the calcite peak at 852 cm -1 . However, the calcite crystallinity was absent in the X-ray diffraction analysis due to the hindrance of the amorphous hydrogel. The phosphate adsorption capacity was increased to 109.87 mg/g by growing CaCO 3 nanoparticles instead of blending. After removing CaCO 3 nanoparticles, the phosphate adsorption capacity was further raised to 132.21 mg/g due to the increment of active sites and surface area. The adsorption was stable between pH 3 and pH 7, and it was only significantly affected by HCO 3 - due to alkalinity changes. The selective phosphate adsorption was driven by chemical interaction, as proven by the pseudosecond -order kinetic model and Langmuir isotherm. After 6 cycles, the adsorption capacity was maintained more than 80 %.