Extraction and Tailings | Optimizing the Extraction Process
The severity of the extraction process can determine not only extraction recovery, but also the degree of clay dispersion, which is the major factor in determining tailings properties. The greater the energy input to the extraction process, the better the recovery for a given ore type. In general, the severity of the extraction process is a combination of thermal (process temperature), mechanical (mixing/pipelining), and chemical (process aids) factors.
Characterization of the bitumen recovery and the tailings properties defines the processability of a given ore. Ultimately the processability is determined by a combination of the severity of the extraction process and the ore properties. Ore properties, including hydrocarbon and clay properties, determine processability. The characterization of hydrocarbon and clay properties is the cornerstone of the extraction oil sands and heavy oil research effort. Optimizing these fundamental processability factors is an essential part of maintaining the economic and environmental sustainability of the oil sands and heavy oil industries.
The fundamental approach to oil sands and heavy oil research issues spans from basic science through to laboratory and pilot scale demonstrations of commercially important processes. CanmetENERGY’s in-house research program is integrated with a very active contract research effort to ensure efficient technology transfer. The role of water chemistry and clay properties in determining oil sands extraction behaviour is well known, and less attention is generally paid to the bitumen chemistry impacts on recovery.
The following graph shows summaries of some extraction test data sets. The low energy ore grade to recovery relationship might be considered typical, with a clear shift to higher recoveries as the energy input to the extraction process is increased. Significant deviations from these grade-recovery relationships can occur when the bitumen chemistry changes.
The higher the mechanical energy of the extraction process the greater the recovery for a given ore. Unusual ore properties or the addition of process aids can significantly change the grade to recovery relationship. The black bars represent the average uncertainty in this data set.
The following picture shows a series of microscopic images of bitumen froth from a "normal" ore, an ore with distinctly different (and undesirable) bitumen chemistry, and the undesirable bitumen ore after treatment. These undesirable bitumen properties lead to significantly stronger interactions with the minerals and water in the extraction process, resulting in lower recovery and a poorer bitumen product. Surfactants in the bitumen are responsible for these negative properties and with the appropriate chemical treatments or extraction additives, the surfactants can be moved from the hydrocarbon to the water.
In the series of photographs hereof, the bitumen is shown in green, the water in black, and the mineral components in red.
Bitumen recovery from the oil sands is optimized when the surfactants in the hydrocarbon are minimized as shown in the graph below. The chemically different, oxidized bitumen has significantly more mineral carried with the froth. This can have serious processability consequences. With the appropriate chemical treatment of the bitumen component, the oxidized ore can be converted to normal bitumen.
This graph shows the relationship between napthenic acids (the major surfactant in oil sands bitumen) in the water and bitumen components, as a function of bitumen recovery under standard conditions. (In this figure the surfactants in the bitumen are noted as degree of bitumen oxidation).
