Recovery of hydrocarbons and heavy metals from contaminated soils and wastes

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In the past and still today, land is contaminated with both petroleum hydrocarbons (such as gasoline, diesel oil, crude oil and bitumen) and heavy metals. This contamination is a result of accidental spills and improper waste disposal practices and poses a threat to the environment, public health and the economy. Contaminants present in soil may move into the water, contaminating the water we drink and the water we use for agricultural or recreational purposes. Contaminants may also move into the air we breathe. Contaminants may also be taken up by plants and thus find their way into the food chain, contaminating the food we eat. Finally, contaminated land also poses an economic burden because their cleanup represents an economic liability and unused land represents a loss in revenue. There are thousands of contaminated sites in Canada and hundreds of thousands of contaminated sites around the world that must be cleaned up. In addition to contaminated soils, there are many other contaminated wastes that contain both petroleum hydrocarbons and heavy metals. An example of such a waste is oil sands tailings i.e. tailings that are produced after the extraction of bitumen from oil sands. These tailings contain residual bitumen, other hydrocarbons and heavy metals and must be cleaned up in order to protect the surrounding environment and to not leave a legacy of contaminated tailings for years to come. To clean up these contaminated soils and wastes, innovative technologies that can clean up both petroleum hydrocarbons and heavy metals effectively, quickly, in a cost-effective manner are desperately needed. Supercritical fluid extraction (SFE) is a technology that could potentially deal with these types of contaminated materials. SFE is a solvent extraction process that uses a supercritical fluid as a solvent. A supercritical fluid is any fluid that is at a pressure and temperature above its critical pressure and temperature. One of the most commonly used supercritical fluids is carbon dioxide, owing to the fact that it is non-toxic, non-flammable, readily available and relatively inexpensive. Carbon dioxide also has a relatively easily achievable critical temperature and pressure, making it a good supercritical fluid of choice for many applications, even at a large scale. This proposal outlines a research program which will investigate the efficiency of supercritical carbon dioxide, on both a laboratory-scale and pilot-scale, at extracting petroleum hydrocarbons and heavy metals from contaminated soils and wastes.  Experiments will investigate the effect of important parameters, such as pressure, temperature, solids content, solids (soil) type and water content, on the amount of contaminant extracted. It is expected that the results will provide important information that will lead to the design of a SFE system that can effectively clean many heavy metal and petroleum hydrocarbon contaminated soils and wastes in Canada and around the world.