Uptake of nickel ions from aqueous solutions using protonated dry alginate beads

Uptake of nickel ions from aqueous solutions using protonated dry alginate beads was studied. Nickel uptake increased with stirring rate, reaching values of 75·9 mg mg^-1 of dry alginate at 300 rev min^-1, at solution pH of 5·0 and 360 min. For a nickel concentration less than 12 mg L^-1, the uptake was complete. The nickel uptake mechanism is explained by ion exchange between Ni ions and protons from the functional groups of the alginate beads. The uptake kinetics was represented by a pseudo-second order model. A rate constant value of 1·1×10^-4 g mg^-1 min^-1 was determined. At equilibrium conditions, the experimental data were fitted to a Langmuir adsorption model, and the highest uptake values were found to be 97·6 and 131·6 mg g^-1 at pH of 4·0 and 5·0, respectively, which were higher than the values reported for different sorbents used for nickel uptake in the literature. Observations obtained by SEM and cross-sectional compositions measured by EDS indicated that the surface of the alginate beads do not suffer any size variation after the experimentation; however, the roughness the surface was lost during the removal.