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

and anti-oxidantsand anti-oxidants

Deon van Rensburg

Introduction to the ProblemIntroduction 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.

RÖSSING URANIUMRÖSSING URANIUM

ORGANIC PHASE:ORGANIC PHASE:Extractant 7% v/o – Alamine 336Extractant 7% v/o – Alamine 336

Phase Modifier 3% v/o – IsodecanolPhase Modifier 3% v/o – IsodecanolDiluent 90% v/o – Shellsol 2325Diluent 90% v/o – Shellsol 2325

RÖSSING URANIUMRÖSSING 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)

RÖSSING URANIUMRÖSSING URANIUM

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

SX plant.SX plant.

Possible ReasonsPossible 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 + SO4

2—

• 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?

RÖSSING URANIUMRÖSSING URANIUMStrip Eluant Uses Process Water

Strip Make-up Uses Process Water

• RÖSSING IS IN THE NAMIB DESERT• HAVE TO RECYCLE WATER• WATER CONTAINS TRACE IMPURITIES

Conc Eluate = Pregnant Leach Solution

Redox MonitoringRedox MonitoringPreg vs SX Redox

440

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Preg Raff 1 Raff 2 SX Conc

Nitrate MonitoringNitrate MonitoringNitrates and Chlorides Monitoring

Conc Eluate StreamConc. Chlorides and Nitrates

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ate

s (g

/l)

Cl- NO3-

Nitrate MonitoringNitrate MonitoringNitrates Monitoring

Ammonium Sulphate and Strip solvent stream

Amm. sulph and Strip Solv Nitrates

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Amm. Sulph Strip Solvent Target

Nitrosamine MonitoringNitrosamine MonitoringComponent composition of Impurities in Stripped Solvent

(Excluding Carrier & Modifier)

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are

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Imp 1 Imp 2 Imp 3 Imp 4 Imp 5 Nitros 1

Imp 6 Imp 7 Imp 8 Imp 9 Nitros 2 Imp 11

Imp 12 Nitros 3 Imp 14 Imp 16 Solvent Addition (m3)

Nitrosamine

Nitrosamine MonitoringNitrosamine Monitoring

Oxidation Test ApparatusOxidation Test Apparatus

Oxidation Test MethodsOxidation 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

Oxidation Test Results:Oxidation Test Results:UraniumUranium

Extraction of Uranium, % Phase disengagement time, secs Before

oxidation After oxidation Before oxidation After oxidation

Shellsol 2325 73.1 33.8 35 95 Sasol SSX 210 72.9 54.9 38 78 Shellsol 2325 with 0.2% BHT 72.2 63.8 35 51 Sasol SSX 210 with 0.2% BHT 72.9 71.8 36 40

RÖSSING URANIUMRÖSSING URANIUM~ Plant Changes ~~ 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)

• It remains better to tackle the It remains better to tackle the source of the problem, rather than source of the problem, rather than

treat the symptoms and effectstreat the symptoms and effects• Work required on oxidation using Work required on oxidation using

nitrate as oxidising catalystnitrate as oxidising catalyst

Conclusion:Conclusion:UraniumUranium

Degradation in Cobalt CircuitsDegradation in Cobalt Circuits

DD22EHPA EXTRACTION CURVESEHPA EXTRACTION CURVES

272 EXTRACTION CURVES272 EXTRACTION CURVES

• 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 Linked to high redox potential in

incoming PLSincoming PLS

Degradation in Cobalt CircuitsDegradation in Cobalt Circuits

• 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

Degradation in Cobalt CircuitsDegradation in Cobalt Circuits> ChemQuest Tests> ChemQuest Tests

Oxidation Test ResultsOxidation Test ResultsUsing CCC heterogenite concentrateUsing CCC heterogenite concentrateChemorex DChemorex D22EHPA and Ionquest 290EHPA and Ionquest 290

Extraction of Zinc, % Phase disengagement time, secs Before

oxidation After oxidation Before oxidation After oxidation

Shellsol D70 88.2 81.3 27 45 Sasol SSX 210 87.0 80.1 29 49 Shellsol D70 with 0.2% BHT 88.1 88.2 28 33 Sasol SSX 210 with 0.2% BHT 87.4 87.9 28 34

• The use of an aliphatic diluent The use of an aliphatic diluent such as Sasol SSX 210 or Shellsol such as Sasol SSX 210 or Shellsol

D70 is indicatedD70 is indicated

Conclusion 1:Conclusion 1:Cobalt SXCobalt SX

• If organic degradation is found or If organic degradation is found or suspected in SX circuits using suspected in SX circuits using

solvation-type extractants such as solvation-type extractants such as Cyanex 272, Ionquest 290, DCyanex 272, Ionquest 290, D22EHPA EHPA or Versatic 10, then the use of an or Versatic 10, then the use of an

anti-oxidant is probably indicated.anti-oxidant is probably indicated.

Conclusion 2:Conclusion 2:Cobalt SXCobalt SX