Development of a supercritical fluid extraction (SFE) process for the treatment of mixed contaminated soils

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In the past and still today, land is contaminated with both organic compounds such as gasoline, oil, pesticides, PCBs and explosives, as well as inorganic compounds such as heavy metals and radioactive compounds. 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 to companies and governments 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. To do this, we need new innovative technologies that can clean up these sites quickly, in a cost-effective manner. Most effort to date has concentrated on developing technologies that cleanup sites contaminated with organic compounds, in particular gasoline and oil. Research has also investigated technologies to treat sites contaminated with heavy metals. However, few technologies are able to treat sites contaminated with both organic compounds and heavy metals. Supercritical fluid extraction is a technology that could potentially deal with these types of contaminated soils. Supercritical fluid extraction 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. Supercritical fluids have many advantages over conventional solvents. For example, supercritical fluids have liquid-like densities and viscosities and gas-like diffusivities, making them ideal solvents for extracting contaminants from solid matrices such as soil. Another advantage is that the supercritical fluid is easy to separate from the soil after the extraction by simply lowering the pressure.**This proposal outlines a research program which will investigate the efficiency of supercritical fluid extraction, on both a laboratory-scale and pilot-scale, at extracting contaminants from mixed contaminated soils, that is, soil contaminated with both petroleum hydrocarbons and heavy metals. Carbon dioxide will be used as the supercritical fluid and the contaminants of interest will be petroleum hydrocarbons (diesel oil) and heavy metals (copper, zinc and cadmium). Experiments will investigate the effect of important parameters, such as pressure, temperature, soil type and soil water content, on the amount of contaminant extracted. It is expected that the results of will provide important information that will lead to the design of a supercritical fluid extraction system that can effectively deal with many of the challenging contaminated sites across Canada and around the world.