Organic degradation in uranium and cobalt solvent extraction:
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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.

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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


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Introduction to the Problem extraction:

  • 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.


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RÖSSING URANIUM extraction:

  • 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)


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RÖSSING URANIUM extraction:

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


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Possible Reasons extraction:

  • 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?


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Nitrate Monitoring extraction:


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Nitrate Monitoring extraction:




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Redox Monitoring extraction:



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Oxidation Test Methods extraction:

  • 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


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Oxidation Test Results: extraction:Uranium


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Conclusion: extraction:Uranium

  • It remains better to tackle the source of the problem, rather than treat the symptoms and effects





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Degradation in Cobalt Circuits extraction:

  • 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



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Conclusion: extraction: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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