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

无论是过去还是现在，土地都受到汽油、石油、农药、多氯联苯和炸药等有机化合物的污染，也受到重金属和放射性化合物等无机化合物的污染。这种污染是由于意外泄漏和不当的废物处理做法造成的，对环境、公共卫生和经济构成威胁。土壤中的污染物可能会进入水中，污染我们饮用的水以及我们用于农业或娱乐目的的水。污染物也可能进入我们呼吸的空气。污染物也可能被植物吸收，从而进入食物链，污染我们所吃的食物。最后，受污染的土地也给公司和政府带来了经济负担，因为它们的清理工作意味着经济责任，而未使用的土地意味着收入的损失。加拿大有数千个受污染的地点，世界各地有数十万个受污染的地点必须清理。要做到这一点，我们需要新的创新技术，能够以经济有效的方式快速清理这些地点。迄今为止，大部分努力都集中在开发技术，以清理受有机化合物污染的场所，特别是汽油和石油。研究还调查了处理重金属污染场地的技术。然而，很少有技术能够同时处理被有机化合物和重金属污染的场地。超临界流体萃取是一种有可能处理这类污染土壤的技术。超临界流体萃取是一种以超临界流体为溶剂的溶剂萃取工艺。超临界流体是压力和温度高于临界压力和温度的任何流体。超临界流体比传统溶剂有许多优点。例如，超临界流体具有类似液体的密度和粘度以及类似气体的扩散率，使其成为从固体基质（如土壤）中提取污染物的理想溶剂。超临界流体的另一个优点是，萃取后只要简单地降低压力，超临界流体就很容易从土壤中分离出来。本提案概述了一项研究计划，该计划将在实验室规模和中试规模上调查超临界流体萃取从混合污染土壤（即被石油碳氢化合物和重金属污染的土壤）中提取污染物的效率。二氧化碳将被用作超临界流体，感兴趣的污染物将是石油碳氢化合物（柴油）和重金属（铜、锌和镉）。实验将考察压力、温度、土壤类型和土壤含水量等重要参数对污染物提取量的影响。预计研究结果将提供重要信息，有助于设计超临界流体萃取系统，有效处理加拿大和世界各地许多具有挑战性的污染场地。

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.