Design of environmentally-benign metal extraction systems: the use of CO_2 in metal extraction

摘要

Recovery of metals from dilute solution, whether the matrix is olid or liquid, remains a considerable technical and financial challenge. Methods currently exist whereby metals can be extracted from either type of matrix, yet these methods consume significant quantities of reagents and can also generate multiple waste streams in the process. Technology developed in our lab allows efficient application of environmentally-benign CO_2 to a number of separation problems involving metals. For example, we have employed biphasic mixtures of CO_2 and water as a green acid leach medium. Metals have been extracted from a steelmaking process residue and then recovered as metal carbonates through depressurization. In this process, metals are extracted and recovered without the use of reagents other than CO_2 and water,a nd CO_2 is sequestered as a solid. In addition, through synthesis of CO_2-miscible phase transfer agents, we have shown that CO_2 can replace the organic solvent currently used in refining of precious metals. The sensitivity to presusre of phase behavior in a CO_2-mixture may allow significant streamlining of the process as well. Finally, CO_2-soluble chelating agents have been used to extract toxic metals from acidic effluent such as that found in plating facilties.