Solid–liquid extraction of rare earths with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester using paraffin wax as solvent

Abstract

The solid–liquid extraction of rare earths with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507, HL) has been studied in molten paraffin wax from hydrochloric acid. The mechanism of extraction was investigated by a slope analysis method and the composition of the extracted complex was further determined by a saturation volumetric method. The gelatinous extracted complex was separated from the wax phase and studied by IR spectroscopy. From the IR spectra the chemical bonding in the extracted complex is postulated. The extraction constants K ex of fifteen rare earths have been evaluated. The plots of log K ex and pH ( E = 50%) versus atomic number Z show a tetrad effect. The mean separation factor of adjacent rare earths is 2.78. All experimental results agree with those of the extraction with P507 in n-dodecane. This proves that the same principles can be applied to both solid–liquid and liquid–liquid extraction systems. But the extraction using molten wax as a solvent has some merits, such as accuracy, simplicity, rapidity, safety and economy.