Understanding the processes of thickening and filtration of yellow cake slurry (ammonium polyuranate) generated by in-situ uranium leaching sites

Abstract

One of the key stages in the in-situ leaching of uranium includes thickening of yellow cake slurry to obtain washed uranium concentrate. Russian in-situ leaching sites tackle this by using membrane filter presses. In spite of their high performance, filter presses have one major drawback – the filtration is done periodically. This paper describes the results of a laboratory study suggesting that, together with membrane filter presses, continuous band vacuum filters could also be used in this application. The yellow cake slurry obtained after precipitation of ammonium polyuranate from Dalur JSC’s eluates has the density of 1060–1065 kg/m3. In laboratory conditions, the slurry was thickened by adding 1 g/dm3 of Praestol 2530 slurry. The settling rate was 5.4 m/h, the thickening performance – 2.8 t/(m2.day). The resultant thickened product with a density of 1600 kg/m3 was filtered in a band filter with a three-stage counter-current washing cycle at a fresh water flow rate of 1 m3/t solid and a vacuum of –49 kPa. The process resulted in an average filtration performance of 8–9 t/(m2.day) and a 17–18 mm thick washed precipitate with 41–43% humidity. The duration of the overall filtration and washing cycle was 110–140 sec. The maximum concentration of sulphate-ion in the washed and dried yellow cake precipitate did not exceed 2.0%, which is significantly lower than the 4% allowed. It is noted that, if necessary, these indicators can be improved by raising the rinse water flow rate.