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High affinity for heavy metal cations over alkali or alkaline earth metals. The macroporous (macroreticular) polystyrene based resin derivatized with iminodiacetic acid groups provides high resistance to osmotic shock and short ion diffusion paths resulting in improved kinetics. The apparent selectivity for a given metal depends upon concentration, the presence of other species, and pH. The affinity of the resin for a given metal can be increased or decreased by adjusting the pH. Many feed streams contain particular matter which can clog the exchanger bed. Backwashing is necessary at regular intervals. If glass columns are used, the swelling (hydraulic expansion) of the resin must be considered.
The resin swells 100 % during change from the hydrogen to monovalent salt form; regeneration is best done in a funnel first with 10 % acid, then 10 % caustic and finally water to neutrality of the eluent.
To obtain the desired pH, buffer solutions are preferably used.
As an example, for pH 4, 10 bed volumes of a 0.5 M solution of NaH2PO4/Na2HPO4 adjusted to pH 4 and finally10 volumes of water are percolated. As SERDOLIT® Chelite® CHE has an extremely high affinity for polyvalent cations, the amount of regenerant is higher than required for conventional weakly acidic ion exchange resins.
Maximum working temperature:
90 °C Na+ form; 70 °C H+ form