During processing of Athabasca oil sands, the finely divided solids form an aqueous suspension, which ultimately stabilizes as a gel-like structure retaining up to 90% of the process water. This gelling phenomenon is believed to be caused by colloidal inorganic components. Kaolinite and mica are the main crystalline minerals in these colloidal solids; swelling clays are present in only trace amounts. Non-crystalline components are more concentrated in the finer fraction of the solids. Although the surfaces of the colloidal solids are virtually free of Fe, some contamination with polar organic matter is observed.

The terms “hydrophobic” and “hydrophilic” are typically used in a non-specific sense and, as such, they have a limited utility. Surface thermodynamic theory, as described here, allows a natural and potentially powerful definition of these terms. The boundary between hydrophobicity and hydrophilicity occurs when the difference between the apolar attraction and the polar repulsion between molecules or particles of material (1) immersed in water (w) is equal to the cohesive polar attraction between the water molecules. Under these conditions, the interfacial free energy of interaction between particles of 1, immersed in water (ignoring electrostatic interactions), exactly zero. When is positive, the interaction of the material with water dominates and the surface of the material is hydrophilic; when is negative, the polar cohesive attraction between the water molecules dominates and the material is hydrophobic. Thus, the sign of defines the nature of the surface and the magnitude of may be used as the natural quantitative measure of the surface hydrophobicity or hydrophilicity.

This study is concerned with the relationship between carbonisation conditions and properties of the resultant bagasse char, and the challenging proposal for the use of fine bagasse char particles as high-performance solar light collectors. Bagasse char was obtained by carbonising raw bagasse at temperatures of 200–900°C for three hours in nitrogen (N2) gas. Characterisation of the resultant bagasse char was performed by elemental analysis (EA), scanning electric microscope (SEM) observation, estimation of colour, nominal bulk density and evaluation of specific surface area and pore structure by N2 gas absorption/desorption. The most typical property of the resultant bagasse char is its unique pore structure, which is clear in SEM observation. The largest specific surface area of bagasse char in this study was about 600 m2/g, which is as large as commercial activated carbon materials. Macro-, meso- and micro-porous structures in the bagasse char induce many important characteristics, such as increased hydrophilicity, very low bulk density and excellent light absorption and accumulation. We also suggest the use of bagasse char as an excellent heat insulation material. The energy used for air conditioning in a private house or office building can be decreased by more than 50–60% by use of this insulator on the roof or walls.