Humic acid, its colloidal and solution properties and relevance to bitumen recovery from oil sands.

This work considers interactions occurring between humic acid (HA) and other representative components of oil sands such as sand and clays, and their potential effect on bitumen recovery. Further, it considers the characterisation of oil sand components in terms of physico-chemical and dielectric properties. The study focuses on a combination of artificially prepared systems analysed using a variety of techniques, including dielectric spectroscopy (DS), UV-Vis spectrophotometry (UV-Vis), sedimentation analysis and adsorption isotherms. Finally, it talks about HA extraction from natural oil sands, HA behaviour in solution and its interactions with oil sand components. Dielectric properties arise from electronic and atomic polarisation or dipole, ionic or dielectric relaxation mechanisms. The particular sensitivity of basic electrical measurements, e.g. resistivity, to the presence of water made the original use of this approach most relevant to the determination of water-filled porosity in model oil sand samples. The present study builds on recent developments in the literature, and, specifically determines the extent to which the potentially dominant effects of water can be overcome in order to access additional information, such as wettability. DS was used to study physico-chemical and structural characteristics of artificially prepared simplified oil sand systems. At the low-frequency DS analysis (10-3 – 107 Hz) yields complex properties, which revealed contributions from underlying processes in materials, including electronic, ionic and interfacial polarisation. Dielectric measurements undertaken on a range of artificially prepared samples revealed strong, regular dependencies on the composition of the systems. This model study proved DS to be a valid method for the analysis of complex systems such as synthetically prepared oil sands. The results indicated wettability change in a systematic manner in samples made up of varying combinations of sand, clays, water and bitumen. It has been considered that water-soluble organic species can influence the recovery of bitumen by having an effect on parameters such as wettability or surface charge, thereby altering interactions between oil sand components. HA is of considerable environmental significance, being a major component of soil. However, its structure and colloidal properties continue to be the subject of debate, largely owing to its molecular complexity and association with other humic substances and mineral matter. Natural oil sand (NOS) samples obtained from Alberta, Canada were separated into solid, oil and water fractions. HA was further extracted out of water fractions using a range of procedures. The obtained organic species were identified mainly using Fourier Transform infrared (FTIR) spectroscopy and compared against standard components. The presence of aromatics, alcohols, phenols, ketones and aliphatic and aromatic amines was confirmed in the extracted HA samples. An adsorption study of HA on mineral surfaces was done by means of conductivity measurements. The adsorption of various concentrations of NaHA from the aqueous solutions onto the surface of sand, clay and sand-clay mixtures with varying ratios was studied by means of DS and the UV-vis absorption measurements. The results showed a strong affinity of the HA present in the solutions to the surface of sand and clay. The calculations based on the results obtained proved the significance of clay in the HA-solids interactions. Although the sand surface covered in HA remains naturally hydrophilic (slightly less than a natural sand), it hinders the adsorption of asphaltenes onto the surface. The HA adsorbs onto the asphaltenes coated sand, making the surface increasingly more hydrophobic over time. Colloid and interfacial properties were studied by means of conductivity, surface tension and zeta potential measurements. a class, HA is considered to comprise supramolecular assemblies of heterogeneous species, and herein, a simple route for the separation of some HA sub-fractions was considered. A commercial HA sample has been fractionated into two soluble (S1, S2) and two insoluble (I1, I2) fractions by successive dissolution in deionised water at near-neutral pH. These sub-fractions have been characterised by solution and solid-state methods. Using this approach, the HA has been shown to contain non-covalently bonded species with different polarity and water solubility. The soluble and insoluble fractions have different chemical structures, as revealed particularly by their solid-state properties (13C Nuclear Magnetic Resonance (NMR) and FTIR spectroscopies, and thermogravimetric analysis (TGA)); in particular, S1 and S2 were characterised by higher carbonyl and aromatic content, compared with I1 and I2. The soluble fractions were shown to behave as hydrophilic colloidal aggregates. It was found that HA dissolution is not affected by the temperature change or increase of agitation and it was reduced by the presence of mono- and divalent ions. The negative nature of HA was confirmed and it was found that it flocculates by addition of cationic surfactant. The presence of HA in the solution also showed stabilisation of clay dispersions.

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