Bestimmung der Löslichkeit von Metallchelaten in überkritischem Kohlendioxid

In the present work the bases for a direct reactive extraction of the metals palladium and rhodium were determined. The metals were converted thereby by addition of suitable ligands into chelates. Enormous differences in solubility of the chelates formed with the ligands DPDC and THD could be determined which is a basis for the selective extraction of metals. The most important basis for a selective extraction of a mixture of metal chelates is the knowledge of the
solubility of the individual chelates in the extracting agent. For the investigation of this basis a dynamic-spectroscopic method was developed for the solubility determination of metal-organic compounds in supercritical carbon dioxide. The equipment used consisted in its core of a modified MPS 225 of the company Suprex, which was connected to a scanning UV detector. The calibration took place via an off-line quantification.
With this equipment the solubility of chelates was determined as a function of the temperature and the density of the supercritical fluid. The temperatures, at which the isotherms were measured, were 50, 60 and 70 °C. The examined area of the reduced density extended from 1,1 to 1,9. The used model substances were chelates of the heavy metals palladium, rhodium and lead. As ligands 2.2.6.6 Tetramethylheptandione (THD), Diisopropyldithiocarbamate (DPDC) and the Methylthioglykolate (MTG) were selected.