Extraction of Hydrocarbons from Clay Soils by Sonication and Soxhlet Techniques

Abstract

The contamination of soil due to the presence of petroleum hydrocarbons is an important environmental issue. In Australia, there are a number of methods that are employed for such analysis, all of which are widely accepted. In this study, we specifically focused on the sonication and the soxhlet extraction techniques, which are two of the common methods of extracting semi-volatile Total Petroleum Hydrocarbons (TPH). The components that fall within this fraction are the hydrocarbons with their carbon index number ranging between 10 and 36 (i.e. C₁₀ to C₃₆). The C₁₀ to C₃₆ TPH fraction was further broken up into sub-fractions, which were C₁₀-C₁₄, C₁₅-C₂₈ and C₂₉-C₃₆, in order that specific details regarding the extent of the contamination could be assessed. The TPH extractions were carried out on 84 homogenized clay soil samples collected from service station sites. The soils were then classified and confirmed to contain greater than 50% clay in all cases. The moisture content of the soil varied with a minimum of 6.9% and a maximum of 32.7%. These soils were extracted in duplicate by the sonication and the soxhlet extraction techniques. The extracts were analysed by gas chromatography with flame ionisation detection (GCFID). After performing the relevant statistical analysis it was concluded that the soxhlet extraction generated higher semi-volatile TPH concentrations than the sonication extraction technique for the clay soil samples. This variation was significant and therefore should be an important factor to consider since TPH analysis is mostly conducted using the sonication extraction technique.