Continuous fixed-bed column adsorption of nickel (II) using recyclable three-dimensional cellulose nanocrystals-hydrogel: Bed depth service time, Thomas, Adams-Bohart, and Yoon-Nelson modelling

Heavy metal ions have detrimental impacts on both the environment and human health. Therefore, it is necessary to develop simple, economical water treatment adsorbents that employ easily modifiable, organic, biodegradable polymers like cellulose nanocrystals. This work used Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) to characterize the cellulose nanocrystal hydrogel prepared to remove Ni2+. The hydrogel was established to have two stable degradation points, ranging from 70 to 120 degrees C to 250 to 380 degrees C. Additionally, the principal functionalized groups observed in the hydrogel's molecular structure were C-H, O-H, and C-O, which were uniform distribution and finger-like structures as seen by SEM. It consisted of crystalline and amorphous structures, as shown by XRD patterns, making it a viable option for water filtration. BET showed that the surface area of the hydrogel increased upon modification. The column study involves optimization of pH, flow rate, concentration, and bed depth. According to experimental data, the effects of breakthrough parameters including pH (4, 5, 6) influent concentration (50, 75, and 100 mg/L), feed flow rate (5, 10, and 15 mL/min), and bed height (10, 15, and 20 cm). With an adsorption capacity of 58.65 mg/g, a flow rate of 10 mL/min, a bed depth of 20 cm, an influent concentration of 75 mg/L and a pH of 5 was found. The column experimental data fitted better to the Thomas, Yoon-Nelson, and bed depth service time modelling (R-2 > 0.99) than the Adams-Bohart model with R-2 > 0.90. The adsorbent is economical and environmentally friendly due to its excellent regeneration capacity.