Ash flotation of dispersed oil droplets : a model system for bituman flotation from tar sand

The recovery of bitumen from tar sand tailings is an important problem that must be solved in order to achieve both economic and environmental benefits. Some bitumen is lost to the tailings as a fine dispersion of bitumen droplets which should be recovered. The recovery of such bitumen droplets from tar sand tailings is, though somewhat complex, a typical example of the general problem of oil separation from water. Air sparged hydrocyclone (ASH) flotation is a promising technology for the recovery of such bitumen. The high capacity, directed fluid flow, and small air bubbles are characteristic of the ASH technology and make it an interesting process alternative. In order to begin to evaluate the potential of ASH flotation in tar sand processing a simple system containing only dispersed oil, without solids, was examined with respect to both surface chemistry considerations and ASH operation. Two fundamental surface chemistry aspects of the problem were considered: 1. the necessary conditions, with respect to surfactant concentration (sodium dodecyl sulfate, SDS), for oil filming at the air bubble surface; and; 2. the emulsion stability, which was determined by the kinetics of gravity separation of the oil droplets, and correlated with the zeta potential and size distribution of the dispersed oil. Of particular significance in this phase of the thesis research was the demonstration for the first time that the spreading coefficient for oil at the air/water interface goes through a maximum with respect to the SDS concentration and that both the extent and rate of oil filming is greatest under these conditions. The dispersed oil was floated in the ASH and the effects of additives and flow conditions on the separation efficiency were studied. Oil recovery from ASH flotation was found to be dependent on the surface chemistry and a maximum in separation efficiency was observed at the best conditions for air bubble filming by oil and at conditions for which the dispersed oil is at its isoelectric point. The appropriate operating conditions for the ASH flotation system were found to be dependent upon the desired quality of the underflow water.