PROCESSING OF RARE EARTH PHOSPHATE CONCENTRATES: A COMPARATIVE STUDY OF PRE-LEACH ALTERNATIVES

摘要

Phosphate rocks such as fluorapatite often contain significant amount of rare earth minerals and considered as a rare earth ore. They can be processed to produce phosphoric acid as well as rare earth metals. The mineralization however commonly associated with other rare earth minerals such as monazite ((Ce,La,Th,Nd,Y)P04), florencite ((La,Ce)AB(PO4)2(OH)6), xenotime (YPO4) and cheralite ((Ca,Ce)(Th,Ce)(P04)2). The treatment of fluorapatite for rare earth extraction commonly requires a pre-leach stage with a mineral acid. Calcium, sodium, magnesium, aluminum, potassium, iron, manganese and a range of other metals such as uranium and thorium may enter the solution depending upon the oxide/phosphate/silicate mineralogy. Further processing may involve partial neutralisation to precipitate any rare earth metals which may have solubilised during pre--leach, acid bake of the residue/precipitate with sulphuric acid, water leach followed by purification and precipitation.This paper describes results from a comparative study conducted on pre-leaching a phosphate rare earth concentrate using sulphuric, hydrochloric and phosphoric acids under various leach conditions. Through thermodynamic and kinetic data including measured and predicted solubility of relevant metal ions, the study presents an alternative process route leading to a potentially more efficient and less complex downstream process.