Effective removal of uranium via phosphate addition for the treatment of uranium laden process effluents

Abstract

We have investigated the suitability of phosphate addition, in the form MH2PO4 (M = Na+, K+ or NH4+), for the selective removal of uranium from a complex waste effluent. The effluent in question is generated as part of a treatment strategy for a spent uranium catalyst, used in the production of acrylonitrile (Sohio process), which has been in temporary storage in Korea since 2004. Both pH (3.0–11.0) and phosphate dosages (0.25–10 mM) have been screened to identify the optimal conditions of 6.25 and 1 mM, respectively, for an initial uranium concentration of 0.16 mM. Precipitation kinetics have been investigated revealing the rapid removal of uranium from solution, with 30 min found to be optimal. The effluent was effectively decontaminated via Meta-ankoleite (K(UO2)(PO4)·3H2O) formation to uranium levels below the Korean release limit of 1 ppm for uranium-bearing liquid wastes, with KH2PO4 addition being chosen for the real process. Final decontamination factors of the order of ≥ 8000 were readily achieved. Aluminium, calcium and iron containing coagulants were screened for the clean-up of the remaining supernatant, post-uranium removal, ensuring the final effluent meets the relevant release criteria (pH, total suspended solids, total phosphate and turbidity) for general, non-radioactive, effluents. A process scheme is presented and discussed for adaptation to similar uranium containing effluents.