For decontamination of surroundings (in particular, soils) from heavy metals and radionuclides very promising are the technologies developed for extraction of complexes, containing the contaminating elements and chemically active β-diketones, into the supercritical carbon dioxide (SC-CO2). Their efficiency and ecological purity is connected with a considerably reduced - in comparison with usual deactivation technologies – volume of secondary liquid wastes. However, these technologies, to be introduced, require further studies of the complex-formation chemistry and thorough optimization of physical-chemical SFE parameters in the course of preliminary laboratory investigations.
In 2006 SPE RESST in cooperation with the V.N.Karazin Kharkov National University (KNU) have developed and put into operation the laboratory apparatus USFE-1 to study SFE of rare-earth metals (REM) by β-diketones in the SC-CO2 medium (see Fig.1). The apparatus can be used for SFE of samples in the semi-automatic mode of operation in the temperature range from 20°C to 150°Ñ and under pressures from 0.1 to 20 MPa with unlimited number of extraction cycles.
Fig.1. External view of the supercritical fluid extraction apparatus USFE-1
The apparatus USFE-1 was in the test measurements on SFE of cuprum ions Cu2+ and in the series of experiments on SFE of complexes including cerium, lanthanum, gadolinium, europium, neodymium, yttrium and β-diketones (acetylacetone) in the presence of modifiers . The results have shown that formation of complexes with β-diketones intensifies SFE of REM, and the attainable degree of REM extraction depends on the physical state of the matrix material. It is demonstrated that in the interval of 50…200 atm the degree of REM extraction increases linearly with pressure and under constant pressure there is an optimum extraction temperature determined by the thermal destruction of β-diketone complexes of REM.