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.
Undissolved pyrolusite (MnO2) carryover?

7. RÖSSING URANIUM Porter Ion Exchange Solvent Extraction
Strip Eluant Uses Process Water
Porter
Ion Exchange
Solvent Extraction
Solvent Stripping
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. Work required on oxidation using nitrate as oxidising catalyst
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 Results Using CCC heterogenite concentrate Chemorex 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.