Antimony(III/V) removal from industrial wastewaters: treatment of spent catalysts formally used in the SOHIO acrylonitrile process.

A treatment and volume reduction process for a spent uranium-antimony catalyst has been developed. Targeted removal, immobilization and disposal of the uranium component has been confirmed, thus eliminating the radiological hazard. However, significant concentrations of antimony ([Sb] ≥ 25-50 mg L-1) remain in effluent from the process, which require removal in compliance with Korean wastewater regulations. Antimony(III/V) removal via co-precipitation with iron has been considered with optimal pH, dose and kinetics being determined. The effect of selected anions - Cl-, SO4 2- and PO4 3- - have also been considered, the latter present due to a prior uranium removal step. Removal of Sb(III) from both Cl- and SO4 2- media and Sb(V) removal from Cl- media to below release limits were found to be effective within 5 minutes at an iron dose of 8 mM (molar ratio, [FeIII]/[Sb] = 20) and a target pH of 5.0. However, Sb(V) removal from SO4 2- was significantly hampered requiring significantly higher iron dosages for the same removal performance. Phosphate poses significant challenges for the removal of Sb(V) due to competition between PO4 3- and Sb(OH)6 - species for surface binding sites, attributed to similarities in chemistries and a shared preference for an inner vs outer binding mechanism.

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

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.