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Hazardous and Radioactive Waste Treatment Technologies Handbook - Chapter 5

Dung môi chiết là một trong những kỹ thuật được sử dụng rộng rãi nhất để tập trung, tách, và làm sạch của một loạt các chất trong hoạt động công nghiệp. Thông thường quá trình tách chiết dung môi thường yêu cầu sử dụng các chất lỏng hữu cơ, các giải pháp có tính axit hoặc kiềm, hoặc một sự kết hợp của các, tạo ra các vấn đề môi trường để xử lý và xử lý các dung môi đã qua sử dụng | Chapter Five Non-Thermal Treatment Technologies 2001 by CRC Press LLC Supercritical Fluid Extraction Technology for Nuclear Waste Management Chien M. Wai Department of Chemistry University of Idaho Moscow Idaho Introduction Solvent extraction is one of the most widely used techniques for concentration separation and cleaning of a variety of substances in industrial operations. Conventional solvent extraction processes usually require using organic liquids acidic or alkaline solutions or a combination of these generating environmental problems for handling and disposal of used solvents. In the past two decades there has been considerable interest in developing techniques utilizing supercritical fluids as solvents for chemical extraction separation synthesis and cleaning.1 2 The reasons for developing supercritical fluid extraction SFE technologies are mostly due to the changing environmental regulations and increasing costs for disposal of conventional liquid solvents. Supercritical fluids exhibit gas-like mass transfer rates and yet have liquidlike solvating capability. The high diffusivity and low viscosity of supercritical fluids enable them to penetrate and transport solutes from porous solid matrixes. Furthermore the solvation power of a supercritical fluid depends on density thus one can achieve the optimum conditions for a particular separation process by manipulating the temperature and pressure of the fluid phase. Carbon dioxide CO2 is widely used in SFE because of its moderate critical constants Tc 31.1 c Pc 72.8 atm ọc 0.471 g mL inertness low cost and availability in pure form Figure 5.1.1 . In SEE processes compounds dissolved in supercritical CO2 are separated by reducing the pressure of the fluid phase causing precipitation of the solutes. The fluid phase is usually expanded into a collection vessel to remove the solutes and the gas is recycled for repeated use. The unique properties of supercritical CO2 have found many new applications in industrial