On the interactions between naphthenic acids and inorganic minerals

Naphthenic acids are a family of carboxylic acids that are found in oil sands bitumen. These compounds partition to the aqueous phase during extraction and refining and are toxic to various biota. The removal of these acids from solution is difficult due to their low concentrations, complexity of the mixture and poor understanding of the behaviour of the mixed compounds. In particular, partitioning of these organic acids to solid surfaces is not well understood. Knowledge of this equilibria would be helpful for potential process development. The research presented here describes the adsorption of two surrogate naphthenic acids onto inorganic minerals (copper sulphide and copper hydroxide). Decanoic acid and cyclohexane pentanoic acid were found to be insoluble in water at pH 3, leading to hydrophobic adsorption onto the minerals and the reaction vessel surfaces. At pH 8.5, both acids formed insoluble copper-carboxylate complexes when mixed with the minerals. The hypothesized 2:1 acid:copper stoichiometry was confirmed. The mechanism of complexation varied with the reaction conditions; both chelating and bridging complexes were observed in the resultant metallo-organic solids. The relative hydrophobicity of the two NA surrogates was also found to contribute to the different adsorption trends. During the pH 8.5 reactions, the solution pHs were found to drop. The uncontrolled decreases in pH had significant effect on the water-solid partition and on the apparent mineral loading of the organics. It appears that soluble copper cations have a higher extent of reaction with the carboxylate anions than does copper contained in the mineral solids. Quantification of these reactions is difficult; however this research does enable conclusions about how the organic acids and inorganic minerals interact and sets the stage for future research.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat