Improved methods for the extraction or dissolution of metals, metalloids or their oxides, especially lanthanides, actinides, uranium or their oxides, into supercritical solvents containing an extractant are disclosed. The disclosed embodiments specifically include enhancing the extraction or dissolution efficiency with ultrasound. The present methods allow the direct, efficient dissolution of UO.sub.2 or other uranium oxides without generating any waste stream or by-products.
STATEMENT OF GOVERNMENT SUPPORT
This invention was funded in part by the Department of Energy Office of Environmental Management, DE-FG07-98ER14913. The United States Government may have certain rights in this invention.