| Summary: | 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 of === Chemical and Biological Engineering, Department of === Graduate
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