Equilibrium and kinetic studies of copper ion uptake by calcium alginate

Equilibrium and kinetic experiments of copper ion uptake by calcium alginate beads were carried out under different values of pH, ionic strength, initial concentration of copper ion, and amount of calcium alginate. The removal efficiency increases with increasing pH and decreasing ionic strength and initial concentration. The removal of copper occurs rapidly in the first hour, followed by a slow process that takes about 15 h. The copper ion uptake becomes faster with increasing pH and decreasing initial copper concentration and ionic strength. Mass transport of copper ions plays an important role in the kinetics of uptake. Equilibrium experiments show that surface complex formation is the major mechanism for copper ion uptake. Modeling of equilibrium and kinetics was also conducted based on a surface complexation approach. Modeling results showed that the two-pK Basic Stern model can successfully describe the effect of pH on equilibrium uptake. A diffusion-controlled model can also predict the effect of pH on the kinetics.