Comparison of Silica Polyamine Composites and Crosslinked Polystyrene Resins

The development of silica polyamine composites (SPC) was inspired by the need for more environmentally benign ways of extracting and recovering technologically important and environmentally dangerous metals from waste streams. These solid phase adsorbents are designed to endure the extreme conditions associated with environmental remediation and the metal processing industry. In order for the silica polyamine composites to be viable in industry, their performance must meet or exceed the current methods of metal extraction from aqueous media. A study was undertaken to compare three silica polyamine composites: WP-2, BPAP, and CuWRAM, with their closest crosslinked polystyrene resin analogs. The studies undertaken consisted of tests of industrial relevance: metal ion capacity, pH dependence of capacity, mass transfer kinetics, metal ion selectivity, and the efficiency of recovering the metal from the adsorbent. To further compare these ion exchange matrices, some new synthetic procedures for making analogs of existing polystyrene resins on the silica polyamine matrix were explored. These in-depth studies have demonstrated that while crosslinked polystyrene chelator resins sometimes exhibit higher equilibrium batch capacities, SPCs exhibit faster mass transfer kinetics and equivalent flow capacities, with higher or similar purity. Explorations into developing direct analogs of polystyrenes chelator resins led to a new reaction pathway for a currently commercially produced SPC that is simpler and more cost effective. A study aimed at understanding the nature of the polymer-surface interface in SPCs was undertaken. This study explored the influence of changing the structure of the silane linker between the silica surface and the polyamine on metal ion selectivity. It was found that substituting the more rigid and bulkier chlormethylphenyltrichlorosilane linker for the chloropropyltrichlorosilane resulted in a marked increase in the selectivity of Fe3+ over Cu2+, but only in the case of the linear polymer polyallylamine (PAA). In the case of the branched polymer polyethyleneimine (PEI), no such change in selectivity was observed. While these results are not well understood at this time, this allows the Rosenberg group and Purity Systems Inc. another way of fine tuning the metal selectivities of silica polyamine composites