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

摘要

The characteristics of alginate beads in calcium (Ca~(2+)) and hydrogen (H~+) form were studied with respect to the uptake of copper ions (Cu~(2+)) via batch and fixed-bed column experiments. The maximum Cu~(2+) sorption capacities (Q_(max)) of calcium and hydrogen alginates (abbreviated as CA and HA, respectively) were found to be 107 mg/g and 189mg/g, respectively. At pH 5, more than 95% of Cu~(2+) was removed, but the amount of Cu~(2+) sorbed onto CA beads was significantly lowered at pH 2 owing to the pKa value of carboxylic acid. When Ca~(2+), as a competing ion, was present in solution at a molar ratio of Ca~(2+) to Cu~(2+) equal to 8,Q_(max) 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 Cu~(2+) occurred immediately with the presence of Ca~(2+) in the model wastewater. Using HA beads, however, the first breakthrough of Cu~(2+) 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 Ca~(2+) during the initial period of Cu~(2+) sorption. Moreover, the breakthrough of Cu~(2+) occurred later than that of Ca~(2+) due to a higher selectivity of Cu~(2+) over Ca~(2+), 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.