Calcium and hydrogen effects during sorption of copper onto an alginate-based ion exchanger: Batch and fixed-bed column studies

The characteristics of alginate beads in calcium (Ca²⁺) and hydrogen (H⁺) form were studied with respect to the uptake of copper ions (Cu²⁺) via batch and fixed-bed column experiments. The maximum Cu²⁺ sorption capacities (Q_max) of calcium and hydrogen alginates (abbreviated as CA and HA, respectively) were found to be 107mg/g and 189mg/g, respectively. At pH 5, more than 95% of Cu²⁺ was removed, but the amount of Cu²⁺ sorbed onto CA beads was significantly lowered at pH 2 owing to the pKa value of carboxylic acid. When Ca²⁺, as a competing ion, was present in solution at a molar ratio of Ca²⁺ to Cu²⁺ equal to 8, Q_max was drastically decreased to 20mg/g. A faster equilibrium time (24h) was also observed for HA beads compared to CA beads (48h). In a fixed-bed column packed with CA beads, the breakthrough of Cu²⁺ occurred immediately with the presence of Ca²⁺ in the model wastewater. Using HA beads, however, the first breakthrough of Cu²⁺ appeared after 900 bed volumes. These results suggested that HA beads were more effective than CA beads in reducing the adverse influence of competing cations such as Ca²⁺ during the initial period of Cu²⁺ sorption. Moreover, the breakthrough of Cu²⁺ occurred later than that of Ca²⁺ due to a higher selectivity of Cu²⁺ over Ca²⁺, which was confirmed by a separation factor (α_Cu/Ca, 10.3) of HA beads. In addition, their reusability was confirmed via ten regeneration cycles.