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E-Rad > Uranium Mining and Extraction > Flashcards

Uranium Mining and Extraction Flashcards

1
Q

What is open pit mining?

A

Mine open at the surface for extraction of minerals close to the surface.

  • Used for ore bodies with large lateral extents
  • Quick extraction but large amounts of spoils/tailings
  • Low Grade
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2
Q

What in underground mining?

A
  • Access via ramp/shaft
  • More expensive
  • Higher Grade

e.g., Raise boring, jet boring

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3
Q

What is in-situ mining?

A

Pump in chemicals to create dissolved U(6+) and cause leaching.

  • can extract U from liquid
  • known as manipulation oxidation state chemistry
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4
Q

What is Uranium Ore Milling?

A

Involves taking uranium form and ore to something you can trade, called ‘yellow cake’

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5
Q

What does the sequence for U ore milling depend on?

A
  • Ore mineralogy
  • Gangue minerals
  • Desired product
  • Environmental precautions
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6
Q

What are the 6 stages to U ore milling?

A
  1. Crushing and grinding
  2. Pre-concentration
  3. Leaching
  4. Liquid-solid separation
  5. Ion exchange and solvent extraction
  6. Product recovery
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7
Q

What does crushing and grinding involve in U ore milling?

A

Size reduction is required to expose minerals and make susceptible to leaching.

  • Primary and fine crushing lead to 3/4” fragments
  • Fine grinding leads to fragments max 0.5mm
  • Dust collection is important
  • Don’t have to completely separate from gangue
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8
Q

What does pre-concentration involve in U ore milling?

A

Separating U bearing minerals from gangue through a series of separation processes.

  • Enhances grade
  • Removes minerals that may hinder leaching
  • Produces clean tailings

Separated by radiometric sorting, photometric sorting, size/shape, gravity etc.

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9
Q

What does leaching involve in U ore milling?

A

Can use either acid or alkali leaching depending on:

  • Ore type
  • Ore grade
  • Time for solubilisation
  • Operating/capital costs

Want to go from U(4+) to U(6+), insoluble to soluble.

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10
Q

Characteristics of Acid Leaching?

A

pH 2, Fe(3+) used as oxidant.
Can be accelerated by bacteria.
Generally has environmental concerns.

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11
Q

Characteristics of Alkaline Leaching?

A

Oxidant is O2, where uranyl forms soluble carbonate complex.
Generally less common, but fewer environmental concerns.

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12
Q

What does Liquid-Solid separation involve in U ore milling?

A

Separating solids (U poor) and liquids (U rich).

Carried out using:

  • High rate thickeners (wash flocculants)
  • Cyclones (Crude phase separation)
  • Belt filters (Small mesh sieve)
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13
Q

What does Ion exchange and solvent extraction involve in U ore milling?

A

Aims to purify the separated U-rich leach solution.

Methods include:

  • Direct ppt.
  • 2 stage ppt.
  • Solvent extraction and ion exchange (best for ores with Ni, Co and As)
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14
Q

What is ion exchange in U ore milling?

A

Concentrates and purifies uranium.

- Leachate solution contains U(VI), gets sorbed to resins and leaves other metals dissolved in leachate

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15
Q

What does Product recovery involve in U ore milling?

A

The end product of milling is Uranium Diuranate (Yellow Cake).

  • Highly purified
  • Suits enrichment and fuel fabrication
  • Get harmful by-products in ppt. reaction
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16
Q

What is removed from yellow cake to purify it and prepare for isotope enrichment?

A

1) Reactor poison elements
- These can capture neutrons and prevent fission

2) Volatile fluorides
- Can contaminate UF6

3) Impurity elements
- Such as Th

17
Q

What are the stages of going from yellow cake to UF6?

A

1) Yellow cake
2) Acid dissolution
3) Solvent extraction
4) UO2 production
5) Hydrofluorination

18
Q

What is the process of going from yellow cake to UF6? (in detail)

A

a) Yellow cake is dissolved in HNO3 at 90 degrees to create a slurry.
b) Purified uranyl nitrate solution is then evaporated to create a salt, in the form of UO3.
c) UO3 is hydrated and reacted with hydrogen, forms UO2.
d) UF4 is produced by anhydrous hydrofluoric acid (HF)
e) UF6 is produced from reacting HF4 with F2

UF6 is gaseous, filtered and then condensed into a solid.

19
Q

What are the two types of enrichment techniques?

A

1) Gaseous diffusion

2) Centrifuge enrichment

20
Q

What is centrifuge enrichment?

A

Separation by spinning gas at a high velocity.

  • Solid UF6 is heated to return it to gaseous state
  • Heavy U-238 moves to the outside, lighter U-235 to the middle of the centrifuge.
  • Want the enriched U from the centre, outside is depleted.

Requires a cascade of centrifuges for max enrichment, where the level of enrichment depends on the rate of fission chain reactors.

21
Q

What are the two types of nuclear fuel?

A

Nuclear fuel is from 3-5% U-235 enriched U.

  1. Metal Fuel - mainly U-metal
  2. Oxide Fuel (UO2)

E-Rad (10 decks)

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