Modified acidic leaching for selective separation of thorium, phosphate and rare earth concentrates from Egyptian crude monazite

Abstract

The objective of the present work was oriented to develop a technological separation process of phosphate, thorium and rare earth element (REE) concentrates from Egyptian monazite. In this respect, monazite digestion was carried out in sulfuric acid media with low or high acid/monazite ratio. These two ratios were designed to explore the acid efficiency for leaching Th and REE) in the presence of high phosphate media (P2O5≈25%). The original monazite sample (grade 50%) was analyzed by XRF to evaluate the existing elements and their concentrations. A series of experiments was firstly applied to remove various element impurities (such as Na, Ca, and Si) which exist in the monazite sample and create a series of interferences with the main product (REEs). The results are likely promising for removal of the interfering ions specially Na, Ca and Si. These elements usually complicate the separation of the main elements (REEs). A series of experiments was constructed to digest the monazite sample with a low amount of concentrated H2SO4 and to explore the separation possibility of Th from REEs in successive steps at different BaCl2 weights that act as precipitating agent. The results demonstrated that, firstly selective thorium precipitation (99.3%) was obtained at pH0.9. Secondly, the phosphate ions (83.3%) could be successfully separated from the mixed REE cake. Thirdly, separation of light REEs (LREEs) from the mixed cake was then performed by disodium sulfate. The precipitation efficiency of double sulfate for LREEs reached 92, 79 and 82% for Ce, Nd and La respectively. Finally, the remaining REE-phosphate was converted to REE-hydroxide precipitate at pH7 then leached with dilute HCl at pH3 and treated with 3% oxalic acid to precipitate Y and the other HREEs as HREE-oxalate. The results indicated that all Y and other REEs are completely precipitated.