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

introduction to the problem
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.
r ssing uranium
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)
r ssing uranium4
RÖSSING URANIUM

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

possible reasons
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
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
Conclusion:Uranium
  • It remains better to tackle the source of the problem, rather than treat the symptoms and effects
degradation in cobalt circuits18
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
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.