Effects of pH, Ionic Strength, Temperature, and Complexing Anions on the Sorption Behavior of Cobalt on Hydrous Silica

Abstract

Sorption of Co(II) on SiO2.xH2O (silica gel) has been investigated as a function of time, amount of silica gel (0.10–1.00g), cobalt concentration (5.00 × 10−5–1.20 × 10−3 M), ionic strength (0.20–1.40 M NaClO4), pH (∼6.80–10.80), and temperature (273–318 K). Using the sorption kinetics data, the diffusion coefficient of Co(II) was calculated to be 6.86(±0.44) × 10−12 m2sec−1 under particle diffusion-controlled conditions. The sorption rate was determined as 2.61(±0.19) × 10−3 sec−1 at 298 K, pH 6.70(±0.05) and 0.20 M NaClO4. The sorption data followed the Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) isotherms. Cobalt sorption decreased with increased ionic strength. A gradual decrease in pH with increased ionic strength supported the sorption of Co(II) by an ion exchange mechanism. The effects of different ligands such as , F−, and on the sorption of Co(II) were studied in the pH range 6.50 to 8.50. The sorption of cobalt on silica gel increased with increased temperature and had an endothermic enthalpy change (ΔH = 23.60(±0.57) kJ/mol).