Processing of xenotime concentrate by sulphuric acid digestion and selective thorium precipitation for separation of rare earths

A process is described for the recovery of rare earths from xenotime concen trate by digestion with sulphuric acid. A low grade xenotime concentrate (t ypically assaying 57% light rare earths, 27% Y2O3 and 15.6% heavy rare eart h) and a high grade xenotime (assaying 38% light rare earths, 41.8% Y2O3 an d 20.55% heavy rare earths) is routinely being produced in India. Both type s of materials have been tested and > 98% solubilisation of metal values ha s been achieved. Xenotime sulphate leach liquor has been processed for remo val of thorium by selective precipitation with ammonia and sodium pyrophosp hate. Although in both systems thorium removal was almost complete, the amm onia precipitation was found suitable since it facilitates the preferential precipitation of lighter rare earths along with thorium. Consequently, the heavy rare earths have been enriched in the filtrate. Other impurities suc h as iron, uranium, sulphate and phosphate have been effectively removed by precipitation of rare earths with oxalic acid. It has been shown possible to recover rare earths along with yttrium (similar to 99% recovery) by thes e processes. (C) 2001 Elsevier Science B.V. All rights reserved.