Pressurised Hot Water Extraction of n-Alkanes and Polyaromatic Hydrocarbons in Soil and Sediment from the Oil Shale Industry District in Estonia

• Published in: Journal of soils and sediments 2004-01, Vol.4 (2), p.107-114
• Main Authors: Kronholm, J, Kettunen, J, Hartonen, K, Riekkola, M-L
• Format: Article
• Language: English
• ISSN: 1439-0108
• DOI: 10.1065/jss2004.03.096

Organic pollutants formed during thermal treatment of oil shale and then released from the solid waste (semi-coke) to aquatic life are a major concern in Estonia. Efficient environmentally friendly techniques are being sought for the analysis of soil and sediments for pollutants and for the clean up of contaminated areas. The altered physicochemical properties of pressurised hot water can be exploited in the extraction of organics from solid samples. For example, the relative permittivity, hydrogen bonding ability and viscosity of water are decreased and diffusivity is increased with temperature. In addition, water is environmentally friendly, cheap, non-flammable and readily available. In small-scale or pilot-scale operations, pressurised hot water extraction (PHWE) can also be used in the purification of contaminated soil and sediments. PHWE and conventional Soxhlet extraction were applied to extract organic compounds from soil and sediment samples collected from various locations around a semi-coke mound in a mining district in northeastern Estonia. One important aim was to compare the extraction efficiencies of the two techniques. Another aim was to determine the pollutants in soil in the vicinity of the semi-coke mound and the sediments of two rivers (the Purtse River flowing to the Gulf of Finland and the Kohtla River feeding into the Purtse) and in canals between the Kohtla River and the semi-coke mound. The PHWE equipment was self-constructed and applied with temperatures of 300 and 350 degree C (P = ca. 200 bar). Soxhlet extraction was carried out for 20 h with dichloromethane as a solvent. All extracts were cleaned up with a silica gel column, concentrated and analysed by gas chromatography-mass spectrometry (GC-MS). Organic matter contents of the samples were determined. Alkanes and polyaromatic hydrocarbons (PAHs) were the main compounds found in the GC-MS analysis after PHWE and Soxhlet extractions. In general, recoveries for short-chain n-alkanes (C10-C16) and PAHs with two benzene rings (i.e. naphthalene, acenaphthylene, acenaphthene and fluorene) were better with PHWE at 350 degree C than with Soxhlet extraction. These compounds are relatively volatile and may be lost during Soxhlet extraction. For longer chain n-alkanes, recoveries were better with Soxhlet extraction than with PHWE. The longer chain compounds are less polar than the shorter chain compounds and not so easily recovered by PHWE. For PAHs with more than two benzene rings, PHWE