Uranium Ores Processing

Ibrahim (Abe) Gundiler igundiler@nmgb.nmt.edu

Uranium Minerals

Mining Methods

https://geoinfo.nmt.edu/resources/uranium/mining.html

• Open Pit • Underground • In-Situ Recovery or In-Situ Leaching

Open Pit Uranium Mine

Reclaimed Tailings Piles

Uranium ore processing

• Drying • Crushing • Blending • Fine Ore Storage • Roasting

to remove carbonaceous matter to convert vanadates to soluble form to alter clay minerals

Processing Methods

• Agitation Leaching (Selective Dissolution) – Acid leach – Basic Carbonate Leach

• Percolation Leach • Pressure Leach • Heap Leaching • In-Situ Leach

Solubility of Uranium Minerals

• Hexavalent uranium oxides dissolve in acids UO3 + 2 H+ = UO2

++ + H2O

• Tetravalent Oxides require an oxidant 2Fe3+ + 2e = 2Fe++

UO2 = UO2++ + 2e

Overall reaction:

UO2 + 2Fe3+ = UO2++ + 2Fe++

Stability domain of water

2H2O = O2(g) + 4H+ + 4e E = E0 + {RT/nF}ln{[O2][H+]4 / [H2O]2} E = 1.23 – 0.059 pH (b)

H2(g) = 2H+ +2e (a) E = 0.0 – 0.059 pH

H2O = H2O2 + 2H+ + 2e E = 1.77 – 0.059 pH + 0.0295 log (H2O2)

Oxidation of Ferrous Ions

• 6Fe++ + NaClO3 = Fe3+ + NaCl + 3H2O • 2Fe++ + MnO2 + 4H+ = 2 Fe3+ + Mn++ + 2H2O

Oxidizing Agents • H2O2 + 2 H+ + 2e = 2 H2O E° = 1.77 V • MnO4¯+ 8 H+ +5e = Mn2+ + 4 H2O E° = 1.52 V • ClO3¯ + 6 H+ + 5e = ½ Cl2 (g) + 3 H2O E° = 1.47 V • MnO2 (s) + 4 H+ + 2e = Mn2+ + 2 H2O E° = 1.23 V • O2 (g) + 4 H+ + 2e = 2 H2O E° = 1.23 V • NO3¯ + 4 H+ + 3e = NO (g) + 2 H2O E° = 0.96 V • ClO¯+ H2O + 2e = Cl¯ + 2 OH¯ E° = 0.89 V • Fe3+ + e = Fe2+ E° = 0.77 V • Cu2+ + 2e = Cu (s) E° = 0.34 V • 2 H+ + 2e = H2 (g) E° = 0.0 V • Fe2+ + 2e = Fe E° = -0.44

• Acid Leaching – Low carbonate ores

UO3 + 2H+ = UO2++ + H2O

UO2 + 2Fe+++ = UO2++ + 2Fe++

Uranyl ion forms complexes with sulfate ions UO2

++ + SO4¯ ¯ = UO2 SO4

UO2 SO4 + SO4¯ ¯ = [UO2 (SO4)2]2¯

[UO2 (SO4)2]2¯ + SO4¯ ¯ = [UO2 (SO4)3]4¯

Acid Consuming Reactions

• Carbonates • Sulfides • Phosphates • Vanadates • Phosphates • Some oxides • Clays

Autoclave Leaching

Pressure Oxidation of Pyritic Ores

• 2FeS2 + 7.5 O2 + H2O = Fe2(SO4)3 + H2SO4

• UO2 + Fe2(SO4)3 = UO2SO4 + 2FeSO4

• 4FeSO4 + 2H2SO4 + O2 = 2Fe2(SO4)3 + 2H2O

• CuFeS2 + 2H2SO4 + O2 = FeSO4 + CuSO4 + 2H2O

Heap Leaching

• FeS2 + H2O + 3.5O2 = FeSO4 + H2SO4

• 2FeSO4 + H2SO4 + ½ O2 = Fe2(SO4)3 + H20 – Thiobacillus Ferrooxidants – Thiobacillus Thiooxidants – Ferrobascillus Ferrooxidants Bacteria oxidize Ferrous ions to Ferric and help

dissolve uraninite

UO2 + 2Fe3+ = UO2++ + 2Fe2+

Abandoned Injection Well

Recovery of Uranium from Acidic Solutions

• Solvent Extraction with both cationic (alkyl phosphoric acids) or anionic (tertiary amine) liquid ion exchangers:

• UO2++ + 2(RH)2(org) = UO2R4H2(org) + 2H+

• 4R3N(org) + 2H2SO4 + UO2(SO4)34- =

(R3NH)4UO2(SO4)3(org) + 2SO42-

• Uranium stripped with Na2CO3 solution and precipitated

as Na2U2O7

Carbonate Leaching

• 2UO2 + O2(dissolved) = 2UO3 (or H2O2)

• UO3 + Na2CO3 + 2NaHCO3 = 4Na+ + UO2(CO3)3

4- + H2O

Sodium carbonate hydrolyzes in water to produce highly basic solutions. Bicarbonate added to neutralize excess OH¯ to prevent precipitation of sodium diuranate (Na2U2O7 - yellowcake).

Ion Exchange Resins

• Both acidic or basic carbonate solutions

4RX + [UO2(SO4)3]4- = R4UO2(SO4)3 + 4X¯

4RX + [UO2(CO3)3]4- = R4UO2(CO3)3 + 4X¯

X : NO3¯>CN¯>HSO4¯>Cl¯>HCO3¯>OH¯

Ion Exchange Resin

Uranium Leaching, Counter Current Decantation, Solvent Extraction, Precipitation

Uranium Precipitation and Purification

• Yellow cake (>70% U3O8) precipitated from carbonate solutions by MgO, NaOH or ammonia is dissolved

• Phosphates, arsenates, molybdates, vanadates etc. removed by various methods

• Uranium repreciptated with ammonia • Ammoniun diuranates decomposed • Oxides reduced by H2(g) to UO2

• UO2 converted to UF4 then UF6 (g) • U235 enriched from U238 by gaseous diffusion or

centrifuge

Uranium Enrichment Centrifuges