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Organic degradation in uranium and cobalt solvent extraction: The case for aliphatic diluents and anti-oxidants. Deon van Rensburg ChemQuest Africa. Introduction to the Problem. Rössing Uranium experienced organic degradation a number of times.
Organic degradation in uranium and cobalt solvent extraction:The case for aliphatic diluents and anti-oxidants Deon van Rensburg ChemQuest Africa
Introduction to the Problem • Rössing Uranium experienced organic degradation a number of times. • They instituted a program of investigation and remedy. • A number of cobalt/nickel SX plants also experienced organic degradation. • ChemQuest conducted some laboratory testing.
RÖSSING URANIUM • Organic phase breakdown products detected, related to the presence of nitrosamines. • Extensive crud formation, poor stripping efficiency and excessive organic entrainment was noted. • Very expensive to replace degraded organic phase. (1986, 2002, 2005 – latter two included entire inventory)
RÖSSING URANIUM The presence of high levels of nitrosamines directly correlated with the upset conditions on the SX plant.
Possible Reasons • Ingress of nitrates with process water – from the explosives used in the pit. • Nitrates are co-extracted by the amine reagent • [R3NH]2SO4 + mNOx [R3NH]2 [NOx]m + SO42— • High redox potential from the leach process possibly carried over into the SX • Tests show that high Eh causes organic degradation. • Undissolvedpyrolusite carryover?
Oxidation Test Methods • Standard test solution used by Rössing, with addition of 5 mg/l KMnO4 • O:A ratio of 1 • 45°C, constant air injection, 220 rpm, 180 minutes • Used aliphatic and aromatic diluent • With and without 0.2% m/v butyl hydroxy toluene
Conclusion:Uranium • It remains better to tackle the source of the problem, rather than treat the symptoms and effects
Degradation in Cobalt Circuits • Increased viscosity and poorer phase disengagement in both circuits • Actual cobalt and nickel removal in the D2EHPA circuit • High organic entrainment • Poorer extraction kinetics of cobalt in 272 circuit • Linked to high redox potential in incoming PLS
Conclusion:Cobalt • If organic degradation is found or suspected in SX circuits using solvation-type extractants such as Cyanex 272, Ionquest 290, D2EHPA or Versatic 10, then the use of an anti-oxidant is probably indicated.