Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Investigation of the Solid/Aqueous Interface of Low Surface Area, Water-Soluble Solids in High Ionic Strength, Highly Alkaline, Aqueous Media

A new method for the investigation of the adsorption of the series of surface active quaternary ammonium (QA) compounds, dodecyltrimethylammonium bromide (C12), tetradecyltrimethylammonium bromide (C14), and hexadecyltrimethylammonium bromide (C16) on the surface of sodium oxalate a Bayer process solid has been developed using Fourier transform infrared (FTIR) attenuated total reflection (ATR) spectroscopy. The technique involves the use of a finely ground sodium oxalate combined with an appropriate adsorption matrix and, for the first time, permits the in situ investigation of adsorption from high ionic strength, highly alkaline (pH 12), aqueous media onto a water soluble, low surface area solid: sodium oxalate (a compound traditionally treated as ligand or adsorbate). Spectroscopic results show the formation of surfactant aggregate clusters on the surface of sodium oxalate and suggest adsorption in the order C16 > C14 > C12. This new method will allow the acquisition of “dose−response” curves for the C12, C14, and C16 QAs on sodium oxalate (under the aforementioned conditions), while also leading to the in situ investigation of the surface of sodium oxalate in synthetic and process Bayer liquors (high ionic strength, extremely alkaline media). Our results suggest that this method will be well suited to interfacial research in other similar areas involving complex, nonideal industrial systems which also depend upon chemical processes occurring at the solid/aqueous and solid/liquid interfaces.