Presentation on theme: "Organic degradation in uranium and cobalt solvent extraction: The case for aliphatic diluents and anti-oxidants Deon van Rensburg."— Presentation transcript:
1Organic degradation in uranium and cobalt solvent extraction: The case for aliphatic diluents and anti-oxidantsDeon van Rensburg
2Introduction 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.
4RÖSSING URANIUMOrganic 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)
5RÖSSING URANIUMThe presence of high levels of nitrosamines directly correlated with the upset conditions on the SX plant.
6Possible ReasonsIngress 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 SXTests show that high Eh causes organic degradation.Undissolved pyrolusite (MnO2) carryover?
7RÖSSING URANIUM Porter Ion Exchange Solvent Extraction Strip Eluant Uses Process WaterPorterIon ExchangeSolvent ExtractionSolvent StrippingConc Eluate= Pregnant Leach SolutionStrip Make-up Uses Process WaterRÖSSING IS IN THE NAMIB DESERTHAVE TO RECYCLE WATERWATER CONTAINS TRACE IMPURITIES
14Oxidation Test Methods Standard test solution used by Rössing, with addition of 5 mg/l KMnO4O:A ratio of 145°C, constant air injection, 220 rpm, 180 minutesUsed aliphatic and aromatic diluentWith and without 0.2% m/v butyl hydroxy toluene
16RÖSSING URANIUM ~ Plant Changes ~ Tighter control of water returned from pit, and volumes of recycled water usedImprovements in MnO2 handlingChange from using ±20% aromatic diluent (Shellsol 2325) to <0.5% aromatics (Sasol SSX210)
17Work required on oxidation using nitrate as oxidising catalyst Conclusion: UraniumIt remains better to tackle the source of the problem, rather than treat the symptoms and effectsWork required on oxidation using nitrate as oxidising catalyst
21Degradation in Cobalt Circuits Increased viscosity and poorer phase disengagement in both circuitsActual cobalt and nickel removal in the D2EHPA circuitHigh organic entrainment in raffinatesPoorer extraction kinetics of cobalt in 272 circuitLinked to high redox potential in incoming PLS
22Degradation in Cobalt Circuits > ChemQuest Tests GC-MS scans showed presence of carboxylic acids in both SX circuitsPresence of stable emulsions seenInvestigation into mixing energies, mixer designs, pH controlUnfortunately plant shut down before completion of testing
23Oxidation Test Results Using CCC heterogenite concentrate Chemorex D2EHPA and Ionquest 290
24Conclusion 1: Cobalt SXThe use of an aliphatic diluent such as Sasol SSX 210 or Shellsol D70 is indicated
25Conclusion 2: Cobalt SXIf 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.