gilligan and nikoloski 2016 the extraction of uranium from brannerite - alta conference 2016 perth
TRANSCRIPT
The extraction of uranium from brannerite
Rorie Gilligan, Aleks Nikoloski
ALTA Uranium Conference, Perth, May 26-27 2016
Background• Brannerite, UTi2O6 is a multiple oxide of
uranium and titanium• General formula (U,Th,REE,Ca)(Ti,Fe3+)2O6
• Thorium and light REE substitute uranium• Common in uranium/REE deposits• Most important U source after uraninite,
UO2 and coffinite, U(SiO4)1-x(OH)4x
Current Industrial practice
• Requires aggressive conditions to leach~75°C60-75 g/L H2SO4
36-48 h leaching timeProcessed at a few former mines in
Ontario, Canada• Pressure leaching trialled in South Africa
Mineralogy• Associated in ores with titanium minerals
rutile (TiO2), ilmenite (FeTiO3) and titanite (CaTi(SiO4)O)
• Brannerite in ores is amorphous and altered, due to its own radioactivity
• Altered brannerite is more susceptible to leaching
Locations
Mount Isa (Valhalla, Skal)
Olympic Dam
Curnamona Province(Crocker Well and others)
Ranger
Methods used in this study• Brannerite (0.5 g) was leached in 10-200 g/L H2SO4
solution containing 2.8 g/L Fe3+
• Leaching at 25-96°C • Uranium and titanium dissolutions monitored• Effect of gangue minerals (apatite, fluorite) tested• Solids characterised by XRD, SEM and EDX
Brannerite sample (Cordoba, Spain)
Brannerite interior
Anatase (TiO2) coating
Anatase and silica filled cracks
SEM/EDX
Si: RedU: GreenTi: Blue
Altered zones along cracks low in U/CaCracks filled with microcrystalline anataseSi/Pb accumulate at edges of altered zones
Leaching kinetics Effect of acid concentration
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 52°C
200 g/L H₂SO₄100 g/L H₂SO₄50 g/L H₂SO₄25 g/L H₂SO₄10 g/L H₂SO₄
Time (h)
Ura
nium
ext
racti
on
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
96°C
200 g/L H₂SO₄100 g/L H₂SO₄50 g/L H₂SO₄25 g/L H₂SO₄10 g/L H₂SO₄
Time (h)
Ura
nium
ext
racti
on
Leaching kinetics Effect of temperature
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 25 g/L H₂SO₄
96°C79°C63°C52°C36°C25°C
Time (h)
Ura
nium
ext
racti
on
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 100 g/L H₂SO₄
96°C79°C63°C52°C36°C25°C
Time (h)
Ura
nium
ext
racti
on
Leach reaction mechanisms• Current reported reaction mechanism1,2:
UTi2O6 + 2 Fe3+ → 2 TiO2 + UO22+ + 2 Fe2+
Observed in this study at low temperature and acidity only (Ea = 36 kJ/mol). TiO2 then attacked by acid:
TiO2 + 2H+ + SO42- → TiOSO4
0 + H2O • Evidence points to a new reaction mechanism at high
temperature3:UTi2O6 + 2 FeSO4
+ + 4 H+ + 2 SO42- →
UO2(SO4)22- + 2 Fe2+ + 2 TiOSO4
0 + 2 H2OChange in reaction mechanism (Ea = 23 kJ/mol). TiOSO4
0 then hydrolyses to anatase:
TiOSO40 + H2O ↔ TiO2(anatase) + 2 H+ + SO4
2-
1. Gogoleva, E. M. 2012.The leaching kinetics of brannerite ore in sulfate solutions with iron (III). J Radioanal Nucl Chem 293 (2012) 185-1912. Smits, G. 1984. Behaviour of minerals in Witwatersrand ores during the leaching stage of the uranium extraction process. Applied Mineralogy, 599-6163. Gilligan, R., Nikoloski, A.N., 2015b. Leaching of brannerite in the ferric sulphate system. Part 1: kinetics and reaction mechanism. Hydrometallurgy 156, 71–80
Post-leach mineralogy• Residue shows formation of pits• Deeper pits around anatase inclusions
suggest altered zones are more susceptible to leaching
• Uranium oxide inclusions more readily leached
• No signs of titanium oxide coating• Secondary titanium oxide seen at high
temperature and low acidity
Post-leach mineralogyOutline
Post-leach mineralogyAltered zones
Altered zones susceptible to corrosion.Note the depth of corrosion either side of the anatase inclusionsUranium is shown in green, titanium in blue
50 g/L H2SO4, 25°C
10 g/L H2SO4, 52°C
Post-leach mineralogy Uraninite inclusions
Uraninite inclusions susceptible to corrosion.Note the direction of corrosion, parallel to the uraninite inclusionsUranium is shown in green, titanium in blue
10 g/L H2SO4, 52°C
100 g/L H2SO4, 36°C
Post-leach mineralogy Reaction front
• Pitted brannerite particle leached in 50 g/L H2SO4 at 63°C
• The base of the leach pits was cracked and porous
• U:Ti ratio near constant across the reaction front
Post-leach mineralogy Secondary anatase
Precipitate formed in 10 g/L H2SO4, at 96°CAnatase formed as a product of leaching.Lower solubility at higher temperature.Iron from the lixiviant often incorporated into the anatase – according to both EDX and XRDIron is shown in red, uranium in green, titanium in blue
Gangue interferences• Associated gangue minerals affect the leaching• Simple interferences from acid consumers• More complicated from phosphates and fluorides• Selected leaches repeated with fluorite, CaF2 and
fluorapatite, Ca5(PO4)3F• 5 g of gangue added to leach along with 0.5 g
brannerite
Gangue interferences Apatite and phosphate• Associated with brannerite in:
1. Curnamona province (SA, Aust)2. Mount Isa (QLD, Aust) 3. Central Ukrainian Uranium Province
• Phosphate: 1. binds to iron (III), inhibiting uranium oxidation2. can form uranyl phosphates, but unlikely at the
higher acid concentrations3. suppresses the dissolution of titanium – a
brannerite-specific effect
Gangue interferences Kinetics
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%96°C96°C + fluorapatite52°C52°C + fluorapatite25°C25°C + fluorapatite
Time (h)
Uran
ium
ext
racti
on
0 1 2 3 4 50%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%100 g/L H₂SO₄50 g/L H₂SO₄25 g/L H₂SO₄100 g/L H₂SO₄ + fluorapatite50 g/L H₂SO₄ + fluorapatite25 g/L H₂SO₄ + fluorapatite
Time (h)
Uran
ium
ext
racti
on
Varied temperature, 25 g/L H2SO4 Varied acid concentration, 52°C
Gangue interferences Post-leach mineralogy
25 g/L H2SO4,10 g/L Ca5(PO4)3FResidual apatite associated with gypsumNo uranium phosphates were detectedA phosphorus enriched titanium oxide rim was identified on leached branneriteThis suggests that the effects of phosphate on brannerite leaching are more complex than general uranium leaching
Gangue interferences Fluorite• Fluorite promotes the dissolution of brannerite,
likely through the formation of HF
0 1 2 3 4 50%
10%20%30%40%50%60%70%80%90%
100%
25 g/L H₂SO₄, 96°C + fluorite100 g/L H₂SO₄, 52°C + fluorite25 g/L H₂SO₄, 52°C + fluorite25 g/L H₂SO₄, 96°C100 g/L H₂SO₄, 52°C25 g/L H₂SO₄, 52°C
Time (h)
Uran
ium
ext
racti
on
Conclusions• Brannerite dissolved under practicable
conditions• Dissolution strongly dependent on temperature,
slightly on acidity• Altered brannerite zones leached more readily• Fluorite promotes uranium extraction• Phosphates suppress uranium dissolution,
promote formation of a titanium oxide coating• Increased acidity reduces the negative effect of
phosphate
Further reading
Further reading
Further reading
Further reading• Part 3 on the gangue interaction study is
currently under review• Studies on alternative leaching systems in
forthcoming papers
