A solid composition comprises: - MnO2; and - a compound represented by the general formula (I) wherein: R is a polymer; each Y is independently a hydrogen or a negative charge; Z is either hydrogen or is not present; each n is independently 1, 2, 3, 4, 5 or 6; wherein the MnO2 is bound to the compound of formula (I) so as to coat the surface thereof. Such a composition may be used for the separation of polyvalent metal species, such as Mo, from one or more accompanying impurities.