The role of natural surfactants in bitumen extraction from oil sands has been extensively researched, but these studies have focused primarily on surfactants that are soluble in the water phase. Recent work at CETC-Devon has shown strong correlations between bitumen weathering or oxidation and poor recoveries. The reason for the poor recoveries has been shown to be an increase of surfactant concentration in the hydrocarbon phase. With oxidized ores, this hydrocarbon-phase surfactant concentration increases, resulting in a stronger association between the mineral and bitumen components in the ore. This association between the mineral and bitumen components results in a decrease in bitumen recovery, poorer froth quality, or both.
Quantification of the surfactant partitioning between the hydrocarbon and water phases has been related to bitumen recovery for a variety of naturally occurring oxidized ores, as well as for ores that were oxidized under controlled laboratory conditions. Optimal recoveries were correlated directly to surfactant concentration in the water phase and inversely to surfactant concentration in the bitumen.
The CANMET Energy Technology Centre-Devon (CETC-Devon) at Devon, Alberta has evaluated a variety of extraction protocols over the years in order to systematically investigate the parameters affecting the extraction process. An effective batch extraction test protocol needs to be reproducible, correlate with commercial experience, and permit extraction assessments using core samples that are sometimes small. The CETC-Devon protocol meets all of these criteria and, although it seems unlikely given the vast differences in scale, very good correlations have been established between the industrial experience (at 500,000 tonnes per day) and the 500-g batch extraction test. In any case, regardless of the details of the batch extraction procedure, a consistently executed procedure will allow for the identification of extraction trends in terms of the impacts of clays, water chemistry, temperature, or other variables(1–3). Typically, bitumen recovery and bitumen froth quality are the most important processability parameters investigated, although tailings properties (both fluid fine tailings and sand tailings) also vary and can have important operational consequences depending upon the ore feed and the extraction conditions. The focus of this paper is the partitioning of natural surfactants between the bitumen and water phases in the extraction process. Many factors affect surfactant partitioning, including temperature and water chemistry. Over the range of extraction temperatures that is typically evaluated (20 to 80 ° C), surfactant partitioning is more-orless unaffected by temperature variations. Water chemistry variations, however, can be extremely important in the release of naphthenic acids (the major surfactant component in bitumen) at elevated pH, or in the precipitation of naphthenic acids from solution in hard water (high calcium or magnesium concentrations)(2–7).
Relationships have been established between the fines content, (commonly defined by the industry as the minus 44-:m mineral fraction) and bitumen content in the Athabasca oil sands ore. Positive correlations between the bitumen content and recovery are also well established, as is the negative correlation between fines content and bitumen recovery.
