Effect of temperature and oxygen on oleate adsorption by fluorite

Abstract

The effect of temperature and oxygen on the adsorption of oleate by fluorite was investigated in alkaline solution using a radiotracer technique. In these experiments, aqueous-phase precipitated calcium oleate was distinguished from surface oleate compounds and adsorption density was established as a function of system variables. The adsorption isotherms are characterized by three distinct regions: a chemisorbed plateau region; a surface calcium oleate precipitate region with significantly higher adsorption density reaching an adsorption maximum; and a third region, a region which exhibits a decrease in adsorption density at higher equilibrium oleate concentrations. Based upon the experimental evidence, adsorption seems to involve a chemisorbed layer at low equilibrium oleate concentrations which can be distinguished from a surface calcium oleate precipitate which forms at equilibrium concentrations exceeding 5 × 10 −6 M . Of greater importance, however, is the conclusion that these modest changes in adsorption density at higher temperatures and higher oxygen potentials do not provide a satisfactory explanation for the significant increase in hydrophobicity observed under similar conditions.