A bio-mimetic cadmium adsorbent: Design, synthesis, and characterization

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Abstract
A cadmium‐binding adsorbent has been designed based on insights gained from the study of cadmium‐binding molecules isolated from living organisms. Cadmium‐chelating thiolate groups—common in proteins that bind cadmium—have been covalently attached to a commercially available ion‐exchange resin. The new adsorbent exhibits a favorable affinity (2 × 10−10M), selectivity (25‐fold greater affinity for Cd2+ than Zn2+), and capacity (1.4 mmol Cd2+/g dry resin) for cadmium ion. Adsorbed Cd2+ may be released with 20mM pyro‐phosphate at pH 2. The adsorbent also recovers Cd2+ in the presence of NH4CI and KCN. The apparent adsorption rate at pH 7.0 (2M−1 min−1) increases 30‐fold as pH is increased to 11. The rate dependence on pH may be due to the inhibition of adsorbent‐metal association by intramolecular hydrogen bonding at neutral pH.