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Title: Chemical characterisation and repellency-inducing effects of organic compounds isolated from sandy soils
Author: Mainwaring, K. A.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2005
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A study of the chemical factors determining the hydrophobicity of 14 water repellent soils and 5 wettable controls from Australia, Greece, Portugal, the Netherlands and UK has been made. Isopropanol: aqueous ammonia (IPA/NH3; 7:3 v:v) Soxhlet extraction rendered 12 of the 14 repellent samples wettable. Extracts from both sample types induced repellency when added to acid washed sand (AWS). Detailed Gas Chromatography-Mass Spectrometry analysis of the chloroform soluble IPA/NH3 extracts showed fatty acids (C16-C24), amides (C14-C24), alkanes (C25-C33), aldehydes/ketones (C23-C31) and complex ring-containing structures in all samples. Sequential extraction using chloroform, IPA/NH3, water and aqueous sodium hydroxide was more effective in terms of mass extracted than a single-step IPA/NH3 technique. However extraction with IPA/NH3 is most effective in removing soil hydrophobicity, suggesting that amphiphilic compounds are important in determining hydrophobicity. Repellency and mass extracted were poorly related, suggesting that only a fraction of the extract causes repellency. Sonication/flotation extractions suggest mineral bound organics, as opposed to particulate organic material, are the main contributor to repellency. A linear correlation (R2 = 0.79) between Molarity of an Ethanol Droplet test results and In(Water Drop Penetration Time), WDPT, values was found. Repellency assessments using aqueous linear (C1-C5) oxygen-containing compound solutions and simple ionics (NaCl, HCl and NaOH) showed droplet penetration times to be determined primarily by solution surface tension rather than solute molecular structure, although aqueous phenol penetrates the soils faster than expected on this basis. Compounds, of the type found in soils, were added singly and as mixtures over a range of loading to AWS and wettable Portuguese soil, and WDPT measured. The simple presence or absence of individual compounds is an insufficient explanation for soil hydrophobicity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available