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

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.

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

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)

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

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?

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

Redox Monitoring

Nitrate Monitoring

Nitrate Monitoring

Nitrosamine Monitoring

Nitrosamine Monitoring

Oxidation Test Apparatus

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

Oxidation Test Results: Uranium

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)

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

Degradation in Cobalt Circuits

D2EHPA EXTRACTION CURVES

272 EXTRACTION CURVES

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

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

Oxidation Test Results Using CCC heterogenite concentrate Chemorex D2EHPA and Ionquest 290

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

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.