Complexation properties of a homologous series of linear polythioethers grafted onto macroporous polystyrene matrices. Selective binding of mercury(II) and silver(I)

Abstract

The binding properties towards some metal salts of a series of ten chelating resins prepared by grafting mono- or dithiol oligoethylene sulfides with two, three or four sulfur atoms onto macroporous chloromethlated polystyrene matrices are described. The evolution of the formation of the complexes as a function of the length, grafting ratio and mono- or di-linkage of the ligand is analyzed. Very high capacities ranging from 4.4 to 7.3 meq/g and high selectivities are obtained for Hg(II) chloride and silver(I) salts. It is shown that the main parameter governing the stoichiometry of the complexes formed is the crowding within the resin. Two types of complexes are formed. One metal is coordinated to each sulfur atom when the sulfur content is lower, as in the case of short ligands or long ligands at low ratios of grafting. At very high sulfur content, one metal becomes coordinated to two sulfur atoms. In the intermediate range, a mixture of both stoichiometries is observed. Mono- or di-linked (pseudo-cyclic) ligands show the same behavior. From isotherms, a stability constant of 60 ± 20 l mol −1 is obtained for the mercury complexes. In the presence of a high concentration of chloride or in nitrate and sulfate solutions, the binding capacities decrease, showing that the complexed species is mainly covalent HgCl 2.