Thesis supervisors: Prof Toomas Tenno, Institute of Chemistry, University of
Tartu, Estonia PhD Natalya Irha, National Institute of Chemical Physics and Biophysics, Estonia
Opponent: Prof Jyri-Pekka Mikkola, Department of Chemistry, Umeå Univeristy, Sweden
The largest industrially used oil shale basin in the world is based in Estonia. Due to the high content of mineral matter in oil shale a significant amount of oil shale processing waste is formed. Spent shale – the waste from oil shale retorting, oil shale ash – the waste from oil shale combustion and oil shale processing waste-based products were in¬vestigated in terms of organic and inorganic pollutant leaching (PAHs and metals). The deposit and/or reuse of oil shale processing wastes may be detrimental for both the environment and human health because of entrained organic (polycyclic aromatic hydrocarbons – PAHs) and inorganic (heavy metals) pollutants. In general, the environmental impact of the pollutants is related to their availability for transport and bio-uptake, rather than their total concentrations in waste material. The long-term fate of PAHs and heavy metals in the environment from oil shale processing waste disposal at field conditions was investigated. A simple and effective low-cost field sampling method was used. Results from the present study indicate an increased leachibility of PAHs with time from spent shale deposits, however important to note that their concentrations were low. Although the concentration of PAHs and heavy metals in field leachates were below permissible limits, the spent shale deposit may represent a constant source of low concentrations of potentially hazardous PAHs and metals. The application of fluorinated PAHs as internal standards in GC-MS analysis for PAHs in oil shale wastes was per¬formed. New Solid Phase Microextraction (SPME) method coupled with GC-MS was developed and opti¬mised for determination of the bioavailable fraction of PAHs. Bioavailable fraction (Cfree) of PAH is small, indicating strong association of PAHs with organic and mineral (colloid, clay) matter. Only 0.01–2.7% of total concentration of studied PAHs in the leachate samples comprised for Cfree. A com¬pa¬rative study of the ash and ash-based materials originating from the new cir¬culating fluidized bed combustion (CFB) com-bustion technology and the old pulverized-fired (PF) was conducted. The leaching characteristics from both granular and monolithic waste-based materials were assessed. New method of monolith leaching (CEN/TC 15862, 2012) was applied and performed. The leaching properties of oil shale ash – based material depended on the specific characteristics of ash and hardening time. The obtained results enlarge our knowledge about the environmental pro¬perties of oil shale processing wastes and waste-based materials.