Dissolution Methods for the Quantification of Metals in Oil Sands Bitumen

Seven different dissolution methods proposed in the literature to prepare oil samples for metal analysis by inductively coupled plasma optical emission spectrometry (ICP-OES) were evaluated for V, Ni, Fe, and Ca analysis of bitumen. The dissolution methods evaluated were direct dilution, dry ashing, sulfated ashing, ultrasound assisted extraction, extraction induced emulsion breaking, detergentless microemulsification, and acid decomposition in closed vessels. The types of bitumen samples evaluated were raw bitumen, bitumen with emulsified water, and diluted bitumen. Only direct dilution and sulfated ashing could be recommended for the dissolution of all types of bitumen samples to quantify V and Ni content. Of these two methods, only sulfated ashing resulted in samples with good storage stability. Typical values for these elements in raw Athabasca bitumen were 224–226 (±14) μg V/g and 94 (±4) μg Ni/g. No firm recommendation about the most appropriate dissolution methods for analysis of Fe and Ca in bitumen could be made, and the values were typically around 10 μg/g or less for both Fe and Ca. When bitumen was stored as diluted bitumen in a toluene solution, it was found that 40–50% of the V-containing species separated from the bulk solution during a 28 day storage period. Over the same storage period