Two-step alkaline thorium dioxide precipitation A low waste method for highly sinterable ThO2

We precipitated thorium in a two-step process with ammonia and carbonates. In contrast to single step ammonia or carbonate precipitation, the two-step process precipitates >99.9% of Th and removes >99.5% of Ra alongside. Filterability is strongly affected by pH variations in the ammonia step, and under well-controlled conditions, the precipitated ThO₂ filters quickly and calcines to crystalline ThO₂ at low temperatures. As-precipitated ThO₂ contains significant quantities of adsorbed H₂O and CO₂, which are removed during calcination. The calcination temperature greatly affects the green density of produced pellets, but for all calcination temperatures investigated, the sintered densities are in excess of 96% with grain sizes within the range applied for nuclear fuels at 10–16 μm.