In-situ FT-IR/IRS investigation of double-bond reactions of adsorbed oleate at a fluorite surface

Abstract

Previous experimental results have shown that an increase in temperature and/or oxygen concentration leads to an increase in the hydrophobicity of fluorite with adsorbed oleate as collector. Subsequently, ex-situ Fourier transform infrared (FT-IR) transmission studies suggested that this increase in hydrophobicity was the result of double-bond reactions between adjacent oleate species adsorbed at the fluorite surface. Now, an in-situ FT-IR study on single crystals of fluorite has been used to monitor this phenomenon using internal reflection spectroscopy (IRS) with the crystals serving as reactive internal reflection elements (IREs). The double-bond reaction has been correlated with in-situ adsorption density measurements from spectral data. These results demonstrate that only the monolayer of chemisorbed oleate undergoes the double-bond reaction at an appreciable rate. At higher concentrations multilayers of surface precipitated calcium oleate form, and under these conditions, no reaction of the double bond could be detected even for oxygen-saturated solutions at elevated temperatures.