Dual mechanism bifunctional polymers : Class III : Ion exchange/precipitation resins

A third class of dual mechanism bifunctional polymers which operate by mechanisms of ion exchange and precipitation have been developed for specific metal ion recovery. A divinylbenzene crosslinked poly(vinyl-benzyl chloride) copolymer is functionalized with a phosphonic acid ion exchange group and a quaternary amine group containing a counterion capable of precipitation with a targeted metal ion. Selectivity in metal ion extraction can be attained through varying the alkyl groups of the amine and/or the counterion. Bifunctional phosphonic acid/trimethylamine and phosphonic acid/tributylamine resins containing, for example, Cl^-, SCN^-, IO_3-, and SO₄^2- counterions have been synthesized. The performance of these resins in the extraction of various metal ions, such as Ag⁺, Hg²⁺, Pb²⁺, Ni²⁺, and Zn²⁺, has been investigated and compared with that of corresponding monofunctional phosphonic acid and quaternary amine resins. The extraction of Ag⁺ by the bifunctional phosphonic acid/tributylamine resin with the thiocyanate counterion appears to be the first example of synergism in metal ion extraction by polymer-supported reagents. A bifunctional phosphonic acid/dimethylamine resin has also been synthesized and its ability to extract Ag⁺ and Hg²⁺ investigated. This resin can operate by ion exchange and coordination mechanisms and belongs to the second class of dual mechanism bifunctional polymers.