Metal ion complexation using solvent impregnated resins and bifunctional interpenetrating polymer networks

Solvent impregnated resins (SIRs) and bifunctional interpenetrating polymer networks (IPNs) are described in this work, and evaluated for metal-ion recovery. Special attention is directed toward identification of synergistic extraction systems. Preparative schemes for SIRs are discussed, including both wet and dry impregnation methods. The presence of synergism is determined by comparing metal-ion distributions in bifunctional systems, with distributions obtained by contacting the metal-ion solution with each of the functionalities individually.

SIRs prepared using a carboxylic acid resin impregnated with liquid extractants (di-n-hexylsulfide, 3,6-di-thiaoctane) showed positive results suggesting synergistic extraction of Hg²⁺ at pH 6.0 in 0.10 N acetic acid. A diethylester resin impregnated with Cyanex 272 also exhibited synergistic extraction of europium(III), at pH 2.0.

A bifunctional vinylpyridine/acrylic acid IPN synergistically complexed several first-row transition metal-ions, including Zn²⁺, Ni²⁺, and Co²⁺, at pH 6.0 from a 0.6-N acetic acid matrix. Cu²⁺ and Hg²⁺ were also readily extracted, however, both the vinylpyridine and the acrylic acid ligands extracted the ions equally as well as the bifunctional polymer.

Based on results with selected metal cations, synergistic extraction systems have at least two features in common. First, the ligand which does not ion- exchange, is in the same hard/soft Lewis acid/base category as the metal ion of interest. For example, a ligand such as di-n-hexylsulfide, which binds through sulfur, could be expected to complex with Hg²⁺, a very soft Lewis acid. Second, the operative pH is one at which the metal ion is likely to occur as a cation, rather than a metal hydroxide. These conclusions warrant further investigation, to facilitate the design of bifunctional extraction systems which effectively isolate target metal ions from aqueous media.