Uptake of copper ion using protonated dry alginate beads from dilute aqueous solutions

This research aimed to identify the copper ion removal mechanism when using protonated dry alginate beads. This mechanism was explained through ion exchange between Cu ions and the protons from the functional groups of the alginate beads. Copper removal increased with stirring velocity, reaching values of 97.5 mg g^-1 (97.5×10^-3 kg/kg of PDAB) of dry alginate at 200 rev min^-1, at a solution pH of 6.0 and a run time of 360 min. For the lowest level of copper concentrations, at 10 mg dm^-3 (10×10-6 kg dm^-3), full removal was attained. The removal kinetics was represented by a pseudofirst order model. A value of 0.0131 min^-1 was found for the velocity constant. Under equilibrium conditions, the experiment data was fit to the Langmuir adsorption model, and the highest removal values were 270.3, 222.2 (222.2×10^-3 kg/kg of PDAB) and 49 mg g^-1 (49×10^-3 kg/kg of PDAB) for pH values of 5.0, 3.5 and 2.5, respectively. These are higher than most sorbents used in the literature for copper removal. Increased temperature leads to higher Cu removal. The activation energy was calculated at 9.3 kJ mol^-1 for the temperature range of 283 to 343K. Observations using SEM and composition measurements of the alginate cross-section taken by EDS showed a uniform distribution of the copper concentration through the structure of the alginate beads, independent of the solution pH, contact time and temperature.