ADSORPTION OF QUATERNARY AMMONIUM-COMPOUNDS ON THE SURFACE OF SODIUM OXALATE - FTIR ATR INVESTIGATION UNDER HIGH-IONIC-STRENGTH, HIGHLY ALKALINE CONDITIONS/

Using a recently developed method for the in situ investigation of the surface of sodium oxalate-a Bayer process solid-in highly alkaline, h igh-ionic-strength, aqueous media, ''dose-response'' curves for a seri es of alkyltrimethylammonium bromides on the surface of sodium oxalate have been obtained. These curves show the extent of adsorption increa sing with alkyl chain length until the point is reached where the alky l chain of the adsorbed compound adopts a coil-like orientation at the oxalate surface, thereby reducing the amount adsorbed compared with t hose for the shorter chain homologues. These shorter chain compounds a re adsorbed to the oxalate surface in a predominantly perpendicular ma nner, while the longer chain compound may adopt a more tilted surface orientation. Results obtained for a synthetic oxalate stabilizer formu lation suggest that the compound is adsorbed in a manner analogous to that of the shorter chain compounds. Decreased adsorption observed at higher initial concentrations is due to the formation of large cylindr ical or lamellar micelles, which exhibit increased stability relative to that of the adsorbed form. The formation of these large micellar ag gregates is a result of the high ionic strength of the adsorption matr ix. We believe this to be the first instance in which FTIR/ATR has bee n used to obtain both qualitative and quantitative information as to t he nature of the interfacial layer of dispersed particulate matter.