Recovery of heavy oil from contaminated sand by using exfoliated graphite

Heavy oil was recovered from contaminated sand through capillary suction into exfoliated graphite with different packed densities by using model sands, alumina powders, with different particle sizes. For efficient recovery it was important to have an appropriate combination of average size of sand particles and packed density of exfoliated graphite. Pumping of heavy oil into exfoliated graphite occurs as a balance in an attracting capillary force between exfoliated graphite and sand, the former being stronger than the latter because of the hydrophobic nature of the surface of graphite.

Heavy oil was able to be recovered from contaminated sand by placing EG on it through capillary pumping. In order to have efficient recovery of heavy oil, it was shown to be important to have an appropriate combination between average size of sand particles and packed density of EG. For coarse sands with large pores, which keep heavy oil, a low-packed density of EG where relatively large pores are formed among worm-like particles is required. Pumping of heavy oil into EG occurs as a balance of an attracting force of capillaries between EG and sand, the former being stronger than the latter supposedly because of the hydrophobic nature of the surface of graphite. The rise of heavy oil into EG from contaminated sand in the present positional relation, the former being in the upper part of the latter, has to overcome gravity. In practical cases, water was expected to be mixed together with heavy oil. However, water was released when heavy oil was dropped onto the EG, which absorbed water in advance, suggesting preferential sorption of heavy oil into EG [12]. Even though water existed in contaminated sand, heavy oil was reasonably supposed to be sorbed preferentially into EG. Carbonized fir fibers and carbon fiber felts were also used as sorbents for heavy oil [14,15]; the former had high sorption capacity, almost comparable with EG, and the latter had excellent recycling performance even though sorption capacity was not high. These carbon materials seem to have a similar ability to pump up heavy oils from contaminated sand. Since carbon fiber felts had a relatively high sorption rate and excellent recycling performance [15], they might have a good possibility for practical processes. As a consequence of capillary pumping, sand could not be completely cleaned up; the white color of the model sand alumina was not completely restored. In the next step of this series of our study, therefore, the decomposition of a small amount of heavy oil remaining in the sand particles is planned by using anatase-type TiO2 fine particles. It has been demonstrated that heavy oil in contaminated sand could be decomposed by anatase powder placed on the sand under UV irradiation [16]. Also heavy oil sorbed into EG could be decomposed by anatase mounted on EG through a sol-gel process [17,18].