Cerium oxalate precipitation: effect of process and operating parameters on cerium oxalate particle size distribution

Abstract

The oxalate precipitation process has been adopted for the reconversion of plutonium nitrate present in nitric acid solution to plutonium oxide powder at the backend of nuclear fuel cycle. Due to the radioactivity associated with plutonium, the testing and development of plutonium oxalate precipitator can be conveniently performed using a non-radioactive surrogate such as cerium. In the present work, the effect of various operating and process parameters such as the concentration of nitric acid, cerium nitrate and oxalic acid, impeller design and speed, mode of precipitation on the particle size distribution of cerium oxalate was investigated. The results showed that the concentration of nitric acid and mode of precipitation were found to affect the particle size distribution of cerium oxalate to a significant extent. The D ₅₀ of the cerium oxalate particles increased nearly five times (21–98 µm) with increasing the nitric acid concentration from 0.5 to 4.0 M. Forward strike mode of precipitation doubled the D ₅₀ of cerium oxalate from 34 to 74 µm as compared to the typical batch precipitation. The cerium ion concentration in feed solution showed the negligible effect on D ₅₀ of cerium oxalate, whereas width of the particle size distribution increased from 0.9 to 2.0 with increase of cerium in nitric acid from 3 to 43 g L⁻¹. Lowering the concentration of oxalic acid produced smaller sized particles with broad particle size distribution. For real applications, the surrogate studies showed that it is important to control the concentration of nitric acid in the feed solution for producing bigger plutonium oxalate particles, which is required for facile operation, and to minimize the loss of residual plutonium in the filtrate.