Production of lanthanon and thorium compounds from monazite. III.† Preparation of pure thorium nitrate

A precipitation process is described for converting crude thorium oxalate or crude thorium phosphate into substantially pure thorium nitrate. The process is based on the use of a sulphuric acid-oxalic acid mixture to ‘leach’ the bulk of the phosphate from a thorium oxalate complex. A phosphate concentrate can be treated similarly, but is first treated with oxalic acid to convert it into an oxalate complex. Residual phosphate and sulphate are removed from the acid-treated products by precipitation of thorium oxalate under specified conditions. Residual lanthanons, together with any remaining impurities, are separated from thorium by precipitation of a granular form of thorium ‘peroxynitrate’. Variables in the process have been studied and material flow sheets, based on laboratory investigations, are presented. If mechanical losses are ignored the yield of thorium from monazite exceeds 90%. Application of the process to any type of thorium oxalate or phosphate concentrate is discussed, and details are given of the analytical determination in various thorium compounds of small quantities of phosphorus, cerium and mixed lanthanons.