Process Chemistry and Mineralogy of Brannerite Leaching

Rorie Gilligan and Aleks Nikoloski SAIMM Hydrometallurgy Conference, Cape Town, August 1-3 2016

Introduction

• Brannerite, UTi2O6 is the most common refractory uranium mineral

• Most important uranium mineral after uraninite and coffinite

• Has a general formula of (U,Th,REE,Ca)(Ti,Fe3+)2O6

• Thorium and light rare earth elements substitute uranium

Processing of brannerite and ores

• Leached under more aggressive conditions compared to other U minerals

• >75°C, >25 g/L H2SO4

• Brannerite-rich U ores in Ontario, Canada leached

~75°C

60-75 g/L H2SO4

36-48 h leaching time

• Pressure leaching trialled in South Africa in 1970s-80s

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

Leaching experiments (acid)

• Brannerite leached for 5 hours

• 0.05 mol/L Fe3+

• 0.10-2.00 mol/L H2SO4 or 0.25-1.00 mol/L HCl

• 25-96°C (up to four intermediate values)

• Selected experiments repeated with gangue additives

• 10 g/L fluorapatite or fluorite

• Uranium and titanium dissolution monitored

• Solids characterised by XRD, SEM and EDX

Leaching experiments (alkaline)

• Brannerite leached for 24 hours

• 0.010 - 0.025 mol/L Fe3+ as K3Fe(CN)6

• 1.00 mol/L total carbonate as NaHCO3 and Na2CO3

• 50-90°C (three intermediate values)

• Selected experiments repeated with a high-brannerite ore from Queensland

• Uranium and titanium dissolution monitored

• Solids characterised by XRD, SEM and EDX

Brannerite specimen (Cordoba, Spain)

Brannerite interior

Anatase (TiO2) coating

Anatase and silica filled cracks

Leaching kinetics – acid

Varied temperature, 0.25 mol/L acid Varied acid concentration, 52°C

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H₂SO₄, 96°C HCl, 96°CH₂SO₄, 52°C HCl, 52°CH₂SO₄, 25°C HCl, 25°C

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2.00 M H₂SO₄ 2.00 M HCl1.00 M H₂SO₄ 1.00 M HCl0.50 M H₂SO₄ 0.50 M HCl0.25 M H₂SO₄ 0.25 M HCl0.10 M H₂SO₄

Acid leaching kinetics – effect of apatite

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96°C96°C + fluorapatite52°C52°C + fluorapatite25°C25°C + fluorapatite

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100 g/L H₂SO₄ 50 g/L H₂SO₄ 25 g/L H₂SO₄ 100 g/L H₂SO₄ + fluorapatite 50 g/L H₂SO₄ + fluorapatite 25 g/L H₂SO₄ + fluorapatite

Varied temperature, 0.25 mol/L H2SO4 Varied acid concentration, 52°C

Leaching kinetics – alkaline

Varied temperature, 2:1 HCO3-:CO3

2- Varied bicarbonate:carbonate ratio, 70°C

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90°C80°C70°C60°C50°C

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4:1 2:1 1:1

Final extractions – varied temperature

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Temperature (°C)

0.25 M H₂SO₄ 0.25 M HCl1.00 M CO₃²⁻ (24 h) 1.00 M CO₃²⁻ (5 h)

Brannerite characterisation

Si: Red

U: Green

Ti: Blue

Altered zones along cracks low in U/Ca

Cracks filled with microcrystalline anatase

Si/Pb accumulate at edges of altered zones

Post-leach mineralogy -sulphuric acid

Altered zones susceptible to corrosion. Note the depth of corrosion either side of the anatase inclusions Uranium is shown in green, titanium in blue

Post-leach mineralogy -hydrochloric acid

Uranium drawn out from altered zones Secondary titanium oxide forms within leach pits at higher T Uranium is shown in green, titanium in blue, silicon in red

0.25 M HCl 25°C

0.25 M HCl 96°C

Post-leach mineralogy – apatite interaction

Varied temperature, 25 g/L H2SO4, apatite • Residual apatite

associated with gypsum

• No uranium phosphates were detected

• A phosphorus enriched titanium oxide rim was identified on leached brannerite

Post-leach mineralogy (alkaline)

Minimal corrosion at 50°C Some pitting at 70°C Formation of secondary anatase on surface at 90°C Uranium is shown in green, titanium in blue, silicon in red

Conclusions

• Brannerite leaching strongly dependent on temperature in all lixiviants

• Sulphate media superior to chloride media

• Phosphate minerals inhibit uranium dissolution in acid

• Also contribute to brannerite passivation

• Less of a problem at higher acidities

• Acid and sulphate counteract the effects of phosphate

• Alkaline leaching slow but effective

Further reading

• Gilligan, R., Nikoloski, A.N. 2015. The extraction of uranium from brannerite – A literature review. Minerals Engineering 71, 34-48

• Gilligan, R., Nikoloski, A.N. 2015. Leaching of brannerite in the ferric sulphate system. Part 1: Kinetics and reaction mechanism. Hydrometallurgy 156, 71-80

• Gilligan, R., Deditius, A., Nikoloski, A. N. 2016. Leaching of brannerite in the ferric sulphate system. Part 2: Mineralogical transformations during leaching. Hydrometallurgy 159, 95-106

• Gilligan, R., Nikoloski, A.N., 2016. Leaching of brannerite in the ferric sulphate system. Part 3: The influence of reactive gangue minerals. Hydrometallurgy 164, 343-354

Questions?

Contact us

r.gilligan@murdoch.edu.au

a.nikoloski@murdoch.edu.au