Preparation of highly pure thorium nitrate via thorium sulfate and thorium peroxide

Abstract

A simple alternative and selective method has been proposed for the preparation of thorium nitrate using as raw material a hydrated crystalline technical grade thorium sulfate. This salt was produced industrially [1] from the alkaline chemical processing of monazite sand in S. Paulo. From a crude thorium hydroxide as the raw material containing uranium and rare earth elements was prepared a technical grade thorium sulfate [Th(SO4)2.9H2O]. A typical analysis of this salt had shown the following composition: ThO2 47-53%, R2O3 (rare earth oxides) 0.5-0.9%, and UO3 0.01% and minor amounts of iron, titanium, phosphorus, and silicon oxides. The thorium sulfate is dissolved into water and the thorium peroxide is precipitated from acidic medium by addition of hydrogen peroxide. The thorium peroxide is filtered, washed and finally dissolved with nitric acid. Samples of the thorium peroxide were dried and fired to ThO2 and aliquot of the thorium nitrate solution was evaporated to dryness and calcined to obtain the ThO2. Both ThO2 have high purity (>99.5%). The content of total rare earth elements is very low (0.23% as oxide). Uranium was not detected. The great majority of the RE is precipitated and recovered from the filtrate by oxalic acid.