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

•Alginate beads in Ca2+ and H+ form were prepared for Cu2+ sorption from solutions.•Protonated alginate beads were favored over Ca-alginate for Cu2+ sorption.•Ca2+ acted as a competing ion towards Cu2+ during sorption onto alginate beads.•No early breakthrough of Cu2+ occurred using H+-alginate beads in column test.•High reusability was confirmed for 10 cycles with no loss of sorption capacity.

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 (Qmax) of calcium and hydrogen alginates (abbreviated as CA and HA, respectively) were found to be 107 mg/g and 189 mg/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, Qmax was drastically decreased to 20 mg/g. A faster equilibrium time (24 h) was also observed for HA beads compared to CA beads (48 h). 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 (αCu/Ca, 10.3) of HA beads. In addition, their reusability was confirmed via ten regeneration cycles.

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