Use of poly(vinylidene fluoride-co-vinyl dimethylphosphonate) copolymers for efficient extraction of valuable metals

Abstract

The radical copolymerisation of vinylidene fluoride (VDF) with vinyl dimethyl phosphonate (VDMP) initiated by various kinds of initiators is presented. First, an optimisation of the nature of the initiator on the yield of the reaction was achieved showing that 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane was the most efficient one, leading to the best yields (81%). Under similar radical conditions, VDMP does not homopolymerise. The microstructure and molar masses of such resulting poly(VDF-co-VDMP) copolymers were monitored by ¹⁹F and ¹H nuclear magnetic resonance and infra-red spectroscopy and by gel permeation chromatography. In all cases, surprisingly, the lower VDF content in the copolymer than that of VDF in the comonomer feed revealed the lower reactivity of this fluorinated alkene. These poly(VDF-co-VDMP) copolymers were hydrolysed into original PVDFs bearing phosphonic acid moieties in 80% yields and were quite stable in strongly acidic media (6 M HNO₃ and 6 M HCl). Both series of copolymers were used for precious metal (Au) and rare earth element extraction processes (La, Nd, Dy, Yb and Sc) in acidic media. Such copolymers displayed a satisfactory separation of the metallic cations and their selectivity can be tuned according to the nature of the copolymer.