Separation and spectrophotometric determination of rare earths

At the present time arsenazo appears to be widely used for the spectrophotometric determination of rare earths. Unfortunately, the method is not selective. The separation of rare earths and yttrium from interfering elements has been studied, and the following method is proposed. Rare earths are precipitated as fluorides using calcium fluoride as the carrier. Thorium and zirconium are removed by extraction with thenoyltrifluoroacetone (TTA) in xylene at pH 1·3. Small amounts of residual aluminium, iron, etc., are removed by extraction with 8-quinolinol-chloroform at pH 4·5. Rare earths are separated from calcium by TTA extraction at the same pH, then they are back-extracted into 1M nitric acid. After evaporation of the solution, the rare earths are determined spectrophotometrically with arsenazo.