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

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

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: Extractant 7% v/o – Alamine 336 Phase Modifier 3% v/o – Isodecanol Diluent 90% v/o – Shellsol 2325

4. 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)

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

6. 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 (MnO2) carryover?

7. RÖSSING URANIUM Strip Eluant Uses Process Water Solvent Stripping Porter Ion Exchange Solvent Extraction Conc Eluate = Pregnant Leach Solution Strip Make-up Uses Process Water • RÖSSING IS IN THE NAMIB DESERT • HAVE TO RECYCLE WATER • WATER CONTAINS TRACE IMPURITIES

8. Redox Monitoring

9. Nitrate Monitoring

10. Nitrate Monitoring

11. Nitrosamine Monitoring

12. Nitrosamine Monitoring

13. Oxidation Test Apparatus

14. 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

15. Oxidation Test Results:Uranium

16. RÖSSING URANIUM~ Plant Changes ~ • Tighter control of water returned from pit, and volumes of recycled water used • Improvements in MnO2 handling • Change from using ±20% aromatic diluent (Shellsol 2325) to <0.5% aromatics (Sasol SSX210)

17. Conclusion:Uranium • It remains better to tackle the source of the problem, rather than treat the symptoms and effects • Work required on oxidation using nitrate as oxidising catalyst

18. Degradation in Cobalt Circuits

19. D2EHPA EXTRACTION CURVES

20. 272 EXTRACTION CURVES

21. 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 in raffinates • Poorer extraction kinetics of cobalt in 272 circuit • Linked to high redox potential in incoming PLS

22. Degradation in Cobalt Circuits> ChemQuest Tests • GC-MS scans showed presence of carboxylic acids in both SX circuits • Presence of stable emulsions seen • Investigation into mixing energies, mixer designs, pH control • Unfortunately plant shut down before completion of testing

23. Oxidation Test ResultsUsing CCC heterogenite concentrateChemorex D2EHPA and Ionquest 290

24. Conclusion 1:Cobalt SX • The use of an aliphatic diluent such as Sasol SSX 210 or Shellsol D70 is indicated

25. Conclusion 2:Cobalt SX • 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.