Lecture 11 Flashcards
1
Q
Extractive Metallurgy types
A
- Pyrometallurgy
- Hydrometallurgy
- Electrometallurgy
2
Q
Pyrometallurgy
A
- Extraction/refinement of metals from minerals/ores through physical/chemical changes due to high T
- e.g.: Hydrogen reduction (green steel); Carbothermal reduction (silicon)
3
Q
Hydrometallurgy
A
- Extraction/refinement of metals using aqueous or organic solvent
-e.g.: Leaching, Aqueous solving (ionic liquids)
4
Q
Electrometallurgy
A
- Extraction/refinement of metals using electrical energy to drive a chemical process in an ionically conducting media
5
Q
OIL - RIG
A
- Oxidation is Loss of electrons
- Reduction is Gain of electrons
6
Q
Ellingham diagram
A
- shows the temperature dependence of the stability of compounds
- more negative ∆G indicates a reaction is more spontaneous
- Where lines intersect shows the temperature from which reduction with a given reducing agent is possible
7
Q
Types of Electrolysis
A
- Molten Salt Electrolysis (MSE)
- Hall-Hérault
- FFC
- Molten regolith Electrolysis
- Ionic Liquid Electrolysis
8
Q
Hall-Hérault process (MSE)
A
- major process for aluminium extraction
- aluminium acts as cathode
- criolite (Na3AlF6) as electrolyte; Al2O3 dissolved
- Fluoride-based salts, T≈1000°C
- Molten aluminium forms at bottom
9
Q
MSE - Pro
A
- no beneficiation required
- Landing site agnostic, more components can be reduced than thermo-chemical methods
- High oxygen yield
- Direct metal (alloy) production possible
- Electrolyte doesn’t get used up
10
Q
MSE - Con
A
- Energy intensive (high T)
- Non-indigenous electrolyte -> import from Earth
- Complex multiphase behavior
- Key Challenges:
- Ident. of suitable oxygen evolving inert anode
- Salt recycling & purification
- Regolith handling & continuous processing
- Material selection to withstand extreme corrosive environment
- Regolith management in the salt
- Impact of low-gravity environments on the system
11
Q
Molten salts as electrolytes
A
- Reasonable melting point
- High electrical conductivity
- Large electrochemical window -> many oxides can be reduced b4 salt breaks down
- High regolith/oxide solubility
- Appropriate saturated vapor pressure (clogging & recycling)
- Low viscosity & density
- Low cost
12
Q
Hall-Hérault Challenges for aerospace applications
A
- Solubility & bath poisoning
- esp. imp. since regolith is made up of many different minerals/oxides
- since CaO can be turned into CaF2 (c<5wt% to avoid poisoning) -> CaO can be treated as pollutant
13
Q
Inert anode requirements (MSE)
A
- Sufficient electrical conductivity
- Thermal (cycling) stability at op. temp. (1000°C9
- Corrosion resistance to molten salt (cryolite)
- Resistance to gases (O2)
- Facilitates O2 formation
- Machinability
- Cost (less critical for extraterrestrial applications)
14
Q
Inert Anode materials (MSE)
A
- Metallic anode
- High electrical conductivity
- High mechanical strength
- e.g.: Cu-Al, Cu-Fe-Ni
- Ceramic/metallic anode
- High corrosion resistance
- High chemical resistance
- e.g.: SnO2, NiFe2O4
- Cermets
- High stability
- good electrical conductivity
15
Q
FFC process (MSE)
A
- electrochemical process to produce Titan from TiO2
- Chloride-based salts (CaCl2-CaO), nec. bc of Calcium based intermediates in reaction; T≈950°C
- Solid-state regolith pellets as cathode
- oxygen yield of 40-45wt%
- Landing-site agnostic, no beneficiation
- CaO content decreases & then recovers over time; inverse in regolith
- Careful management of CaO -> expulsion from salt if too high, free Cl2 if Ca2+ has to be sourced from CaCl2
16
Q
Three-phase interline model (3PI) (MSE)
A
- reduction of regolith requires a three-way contact point between salt-regolith-metal (at cathode)
- reduction starts at initial contact point & propagates from there
17
Q
Requirements for inert anode in FFC (MSE)
A
- Sufficient electrical conductivity
- Thermal(cycling) stability at op. T
- Corrosion resistance to molten salt
- Resistance to gases (O2;Cl2)
- Machinability
- Cost
18
Q
Molten Regolith Electrolysis (MRE)
A
- also known as Molten Oxide Electrolysis (MOE)
- processes regolith into oxygen & metals
- No beneficiation required
- Landing-site agnostic
- Higher T than MSE (1600-2000°C)
- Oxygen yields ca. 35% possible
19
Q
MRE reactor design challenges
A
- material has to withstand extreme environment
- cold-wall reactor concept to protect reactor walls
- issues with solid cathode failure
- Composition-dependent properties (melting point, viscosity, & conductivity challenge reactor control
- Issues with reactor start-up (solid regolith not conductive enough for Joule heating -> ext heating required for start-up)
- Marangoni effect: molten regolith climbing complicates reactor design
20
Q
Inert Anode Requirements (MRE)
A
- Sufficient electrical conductivity
- Thermal (cycling) stability at op T
- Corrosion resistance to molten regolith
- Resistance to gases
- Facilitates O2 formation
- Machinability
- Cost
21
Q
Low-gravity impact (MRE)
A
- Oxygen is removed from the system as gas
- inhibits the removal of bubbles from the surface of the electrode
- lowers processes efficiency, specially in viscous media
- Typical bubble removal techniques challenging in high T processes
22
Q
MRE - Pro
A
- Landing-site agnostic, more components can be reduced than thermo-chemical methods
- Direct metal (alloy) production possible
- No non-indigenous chemicals/reagents required
23
Q
MRE - Con
A
- Energy intensive (high T)
- Complex multiphase behaviour
- Hard to start-up
24
Q
MRE - Key Challenges
A
- Material selection to withstand extreme corrosive environment
- Identification of suitable oxygen-evolving inert anode
- Regolith handling & continuous processing
- Impact of low-gravity environments on the system
25
Q
Ionic Liquid Electrolysis (IL)
A
- Three-step process:
- Dissolving regolith in an aqueous solution with acidic ionic liquid yields water ( can be accelerated by diluting the IL with water)
- Electrolysis of the solution
- Regeneration of the IL (electrochemically reducing the dissolved metal ions & restoring its acidity
26
Q
Desirable properties of ionic liquids
A
- Liquid at “room” T (<100°C)
- Large electrochemical window & thermochemical stabilty
- High regolith/oxide solubility
- Very low volatility
27
Q
IL - Pro
A
- Low T process
- Well-known process in industrial metal refining
28
Q
IL - Con
A
- Low oxygen yield
- Restricted solubility of regolith in IL (might require beneficiation)
- Non-indigenous IL (must be brought from earth)
29
Q
IL - Key Challenges
A
- IL recycling & purification
- Regolith handling & continuous processing
- Regolith management in the IL
- Impact of low-gravity environments on the system
