Abstract: The invention relates to ureido or carbamate derivatives of crown ethers and of silicon of formula: These derivatives can be grafted to silica gel for the purpose of obtaining supports for the chromatographic separation of cations or of molecules comprising amine functional groups, such as amino acids.

Abstract: The invention relates to ureido or carbamate derivatives of crown ethers and of silicon of formula: These derivatives can be grafted to silica gel for the purpose of obtaining supports for the chromatographic separation of cations or of molecules comprising amine functional groups, such as amino acids.

Abstract: An apparatus for the extraction of constituents present in a substance by means of an extraction fluid constituted by a supercritical fluid or a pressurized liquid. According to this apparatus, in an exterior (3) contacting takes place between the substance and the extraction fluid in order to dissolve the constituents in fluid. The fluid leaving the extractor is then treated to separate the extracted constituents. The fluid is expanded at a pressure p.sub.1. Firstly, the less volatile constituents are separated in a liquid-gas separator (41), the separated gas is then liquefied in gas separator-liquefier (13) and the thus liquefied gas is rectified in column (19) to concentrate the extracted constituents in the liquid phase. The extraction fluid can be carbon dioxide gas.

Abstract: A chemical process of isotopic enrichment of uranium makes use of isotopic exchange between an aqueous phase loaded with uranium III and another phase charged with uranium IV. Reduction and oxidation of uranium in aqueous phase are carried out using the same electrolyzer. Reduction may be by zinc amalgam which is later electrolytically reduced.