Concentration of rare earth elements from monazite by selective precipitation

Abstract

Pure rare earth elements and their compounds play a unique role in a wide range of green technology and different industrial applications such as medicine, aerospace and clean energy production. The aim of this study was to concentrate and separate rare earth elements from the monazite matrix. Monazite was digested using a mixture of Na2HPO4/NaH2PO4·H2O fluxes at 900 °C. Precipitation of rare earth elements was investigated with biphenyldicarboxylic acid and acetyl acetone chelating agents. The precipitates were re-dissolved in sulphuric acid and analysed together with the filtrate solutions using inductively coupled plasma optical emission spectrometry. Analytical results indicated selective precipitation of rare earth elements with both biphenyldicarboxylic acid and acetyl acetone. The results also revealed a negative Na+ influence (from the flux) on the rare earth elements recovery in solution which is attributed to easily ionisable behaviour of Na which affects the flame properties of the inductively coupled plasma optical emission spectrometry. Na was removed as NaCl by addition of concentrated HCl prior rare earth elements precipitation. This step improved the rare earth elements recovery in the precipitate from 90.2(1) and 101.68(3) %, while the impurities concentrations remained below 30 %. These results indicated the successful concentration and separation of most rare earth elements from monazite by selective precipitation.