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Organic degradation in uranium and cobalt solvent extraction: The case for aliphatic diluents and anti-oxidants

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.

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Organic degradation in uranium and cobalt solvent extraction: The case for aliphatic diluents and anti-oxidants

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  1. Organic degradation in uranium and cobalt solvent extraction:The case for aliphatic diluents and anti-oxidants Deon van Rensburg ChemQuest Africa

  2. 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.

  3. 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)

  4. RÖSSING URANIUM The presence of high levels of nitrosamines directly correlated with the upset conditions on the SX plant.

  5. 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?

  6. Nitrate Monitoring

  7. Nitrate Monitoring

  8. Nitrosamine Monitoring

  9. Nitrosamine Monitoring

  10. Redox Monitoring

  11. Oxidation Test Apparatus

  12. 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

  13. Oxidation Test Results:Uranium

  14. Conclusion:Uranium • It remains better to tackle the source of the problem, rather than treat the symptoms and effects

  15. Degradation in Cobalt Circuits

  16. Degradation in Cobalt Circuits

  17. Degradation in Cobalt Circuits

  18. 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

  19. Oxidation Test Results

  20. 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.

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