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.
• 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 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 carryover?
Cl-
4
2.5
2
0
0.6
1.5
0.4
1
0.5
0.2
0
Nitrates (g/l)
20
06
20 /01
06 /0
1
20 /01
06 /1
5
20 /01
06 /2
9
20 /02
06 /1
2
20 /02
06 /2
6
20 /03
/
06 1
2
20 /03
06 /2
6
20 /04
06 /0
9
20 /04
/
06 2
3
20 /05
06 /0
7
20 /05
06 /2
1
20 /06
06 /0
4
20 /06
06 /1
8
20 /07
06 /0
2
20 /07
06 /1
6
20 /07
06 /3
0
20 /08
/
06 1
3
20 /08
06 /2
7
20 /09
06 /1
0
20 /09
06 /2
4
20 /10
06 /0
8
20 /10
06 /2
2
20 /11
06 /0
5
20 /11
06 /1
9
20 /12
/
06 0
3
20 /12
06 /1
7
20 /12
07 /3
1
20 /01
07 /1
/0 4
1/
28
Chlorides (g/l)
Nitrate Monitoring
Nitrates and Chlorides Monitoring
Conc Eluate Stream
Conc. Chlorides and Nitrates
NO31.2
3.5
1
3
0.8
2007/01/28
2007/01/14
2006/12/31
2006/12/17
2006/12/03
2006/11/19
2006/11/05
2006/10/22
Strip Solvent
2006/10/08
2006/09/24
2006/09/10
2006/08/27
2006/08/13
2006/07/30
Amm. Sulph
2006/07/16
2006/07/02
2006/06/18
2006/06/04
2006/05/21
2006/05/07
2006/04/23
2006/04/09
2006/03/26
2006/03/12
2006/02/26
2006/02/12
2006/01/29
2006/01/15
g/l
2006/01/01
Nitrate Monitoring
Nitrates Monitoring
Ammonium Sulphate and Strip solvent
stream
Amm. sulph and Strip Solv Nitrates
Target
8
7
6
5
4
3
2
1
0
Nitrosamine Monitoring
Nitrosamine Monitoring
Redox Monitoring
Preg vs SX Redox
620
600
580
560
540
520
500
480
460
Preg
Raff 1
Raff 2
SX Conc
09
/0
2/
20
07
04
/0
2/
20
07
30
/0
1/
20
07
25
/0
1/
20
07
20
/0
1/
20
07
440
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
Shellsol 2325
Sasol SSX 210
Shellsol 2325 with 0.2% BHT
Sasol SSX 210 with 0.2% BHT
Extraction of Uranium, %
Phase disengagement time, secs
Before
Before
After oxidation
After oxidation
oxidation
oxidation
73.1
33.8
35
95
72.9
54.9
38
78
72.2
63.8
35
51
72.9
71.8
36
40
Conclusion:
Uranium
• It remains better to tackle the
source of the problem, rather
than treat the symptoms and
effects
Degradation in Cobalt Circuits
Degradation in Cobalt Circuits
Degradation in Cobalt Circuits
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
Oxidation Test Results
Shellsol D70
Sasol SSX 210
Shellsol D70 with 0.2% BHT
Sasol SSX 210 with 0.2% BHT
Extraction of Zinc, %
Before
After oxidation
oxidation
88.2
81.3
87.0
80.1
88.1
88.2
87.4
87.9
Phase disengagement time, secs
Before
After oxidation
oxidation
27
45
29
49
28
33
28
34
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.