Advances in Uranium Precipitation

摘要

Precipitation is a key step in uranium processing, however, it is often neglected. A poor precipitation can give a product with lots of fines, which is difficult to handle in downstream processing, and may generate dust, leading to potential exposure to operators. Generally, either ammonia or hydrogen peroxide is used to precipitate uranium, producing respectively ammonium diuranate or uranium peroxide. Ammonia precipitates are calcined at high temperature to produce U3O8, whilst peroxide precipitates are dried at low temperature. Precipitation commonly occurs in tanks, as either a continuous or batch process. The product formed generally has a jagged shape and a large amount of fines, which can become dust upon drying. Product bulk densities are approximately 1.7 kg/L for peroxide, and 2.4 kg/L for calcined U_3O_8. A new process developed by AREVA is continuous fluid bed precipitation. The fluid bed works with any precipitation technique to produce a superior product. The precipitation plant is simpler to operate and maintain, leading to lower production costs. Increased recovery of uranium is possible. The technology gives particles which are more spherical and up to three times larger (D50 44 versus 13 μm). There are very few fines produced, which lowers dust and reduces the risk of exposure to operators. Product bulk densities are 2.2 kg/L for peroxide and up to 3.0 kg/L for calcined U_3O_8. The increased bulk density allows more product to be packed per drum, lowering transport costs by up to 25 per cent (up to 50 per cent with a dryer upgrade). The fluid bed product shows higher uranium content and fewer impurities. Dewatering is more efficient, resulting in lower dryer energy consumption (up to 40 per cent) or higher throughput. The product also flows better and the solids are easier to handle.