The document discusses various processes for extracting aluminum and magnesium from their oxide ores. It describes the direct carbothermal reduction process for aluminum extraction, which involves reacting alumina with carbon to form aluminum oxide and aluminum carbide, then transferring the liquid mixture to a lower zone for aluminum extraction. For magnesium extraction, it discusses the Mintek Thermal Magnesium Process, which operates at atmospheric pressure and 1600-1800°C in an AC submerged arc furnace. It also describes a multi-step solid oxide membrane process for magnesium involving electrolysis between 1150-1300°C and condensing magnesium vapor. The document concludes that direct carbothermal and solid oxide membrane processes can reduce energy requirements for aluminum and magnesium extraction compared to

1. A BRIEF STUDY OF ENERGY EFFICIENCY IN
ALTERNATIVE ROUTES OF EXTRACTION OF
ALUMINIUM AND MAGNESIUM
A P R E S E N T A T I O N B Y
• M A I N A K S A H A
D E P T T O F M E T A L L U R G I C A L A N D M A T E R I A L S E N G I N E E R I N G
N I T D U R G A P U R

2. DIRECT CARBOTHERMAL REDUCTION
PROCESS FOR ALUMINIUM
• I N T H I S P R O C E S S , A C C O R D I N G T O C O C H R A N A N D
F I T Z G E R A L D , A T F I R S T A L U M I N A I S R E A C T E D W I T H
C A R B O N T O O B T A I N L I Q U I D M I X T U R E O F A L U M I N I U M O X I D E
A N D A L U M I N I U M C A R B I D E A N D T H E R E A C T I O N I S
P E R F O R M E D I N A S T A C K T Y P E R E A C T O R A T 2 0 0 0 D E G C A T
U P P E R R E A C T I O N Z O N E .
• S E C O N D L Y , L I Q U I D M I X T U R E O F A L U M I N I U M O X I D E A N D
A L U M I N I U M C A R B I D E A R E F O R M E D W H I C H A R E
T R A N S F E R R E D T O L O W E R R E A C T I O N Z O N E F O R A L
E X T R A C T I O N A T 2 2 0 0 D E G C . B Y T H E I N V E S T I G A T I O N M A D E
B Y T H E A L C O A A N D E L K E M , I N T H E F I R S T S T E P 5 0 % O F
B O T H A L U M I N I U M O X I D E A N D A L U M I N I U M C A R B I D E W A S
P R O D U C E D U S I N G T H E A D V A N C E D R E A C T O R P R O C E S S ( A R P )
R E A C T O R
• B O T H S T E P S I N V O L V E T H E G E N E R A T I O N O F C O W H I C H M A Y
B E U S E D T O P R E H E A T T H E R E A C T A N T S B U T H O W E V E R ,
R E A C T A N T S A R E N O T H E A T E D B Y P A R T I A L C O M B U S T I O N O F
C A R B O N . S O , H E A T I N G T H E R E A C T A N T S R E Q U I R E S A
L A R G E A M O U N T O F E L E C T R I C I T Y .

3. SCHEMATIC OF HALL-HEROULT PROCESS FOR
ALUMINIUM

4. PRIMARY ALUMINIUM ELECTRIC CONSUMPTION
IN THE US

5. HALL-HEROULT CELL CURRENT EFFICIENCY

6. SCHEMATIC OF CARBOTHERMIC REACTOR FOR
ALUMINIUM EXTRACTION

7. DIRECT CARBOTHERMAL PROCESS FOR ALUMINIUM
• The ARP includes a method for vapour recovery for recycling the aluminium and
aluminium sub-oxide vapours generated.
• The rate of formation of Al4C3 from Al2O3 and Al gases in CO is controlled by diffusion
of the reactant gases through the Al4C3 product layer.
• Reactions occurring at ARP (Advanced reactor process) are

8. DIRECT CARBOTHERMAL REDUCTION PROCESS FOR
ALUMINIUM
• So , the first step of the reaction requires large amount of energy due to use of stack-
type reactor which is electrically powered.
• However , the reactor has very less efficiency as only a minor amount of input energy
is converted to electrical energy.
• So , the energy efficient technique is to go for the first step being performed at low
temperature zone and the second step at higher temperature zone with two zones at
different locations but at same levels in an Electric Arc Furnace with integrated shaft
attachment and vacuum conditions.

9. DIRECT CARBOTHERMAL REDUCTION PROCESS FOR
ALUMINIUM
• The EAF is the main reactor where liquid aluminium is produced and the
shaft acts as condenser for the Al and Al2O vapours. By carrying out the
process under vacuum, the formation of aluminium rich vapour will be
favoured over Liquid aluminium.
• The process can also be carried out at lower temperatures, e.g at 1500oC
at 10 Pa pressure.
• Experimental study may be carried out using a solar furnace to
demonstrate the process. At temperatures 1027 to1727oC and pressures
350 to 1200Pa, Al (up to 19%) along with Al4C3and Al4O4.

10. MINTEK THERMAL MAGNESIUM PROCESS(MTMP)
• This process may be used as an alternative for Magnetherm process which requires
a temperature of 1550degC in vacuum atmosphere in AC submerged arc surface.
• Magnetherm process was developed in 1950s and served as an advanced version of
Pidgeon’s process(the Pidgeon process is carried out in retorts and at 1100-1200°C,
where the pressure is kept near vacuum).
• In this process , magnesium extraction is carried out in an AC submerged arc
furnace. The magnesium vapour is condensed in a surface condenser, largely to a
solid phase.
• When the condenser is full, the operation is stopped to remove the condenser and to
replace it with an empty one.
• In 1980s , the developments in DC arc furnace technology led to the development of
Mintek process.

11. MINTEK THERMAL MG PROCESS PROCESS (MTMP)
The MINTEK process is a silicothermic process operating at atmospheric
pressure and at a temperature of about 1600-1800degC.
Thus , there is a fairly high chance of more energy consumption by this
process as compared to that in case of Magnetherm process
In order to minimise the energy requirements for the process , while charging
magnesia or dolime into smelter, they may be kept at high temperature
and also that the smelters may be integrated.
The energy efficiency of DC electric arc furnace is about 51.5% while the
efficiency of coal fired furnace is only about 12%.

12. MINTEK THERMAL MAGNESIUM PROCESS
• In this method, Condensation to a liquid phase for volatile Mg in
condenser vessel reduces the energy requirements in the cleaning and
refining stages, as re-melting of the crude magnesium is not required .
Besides, high condensation efficiency may also be achieved by increasing
the partial pressure of Mg vapour, Improving the sealing facility of
equipment to keep the air ingressed to a minimum and steady operation of
plant for long
• As metal condensation is controlled by energy transfer, bath agitation
contributes to the improved condenser efficiency by quickly dissipating
the energy of condensation and thus maintaining a uniform temperature
throughout the condenser crucible, particularly the condensing surface
temperatures.

13. SCHEMATIC OF MINTEK PILOT PLANT

14. MULTI-STEP SOLID OXIDE MEMBRANE(SOM) PROCESS
FOR MAGNESIUM
• In this process,reduction of magnesium oxide dissolved in fluoride-based electrolytes
(MgF2-CaF2-MgO) is carried out by passing electric current at 1150 to 1300 degC. When
electric field is applied, magnesium oxide dissociates into magnesium and oxygen. Ions
. Oxygen ions are pumped out through Yttrium Stabilised Zirconia (YSZ) membrane to
the anode. The magnesium vapour evolves at the cathode and condenses in a separate
chamber. The reported energy demand is 10 kWh/kg Mg.
• The energy efficiency of the present process is attributed, in part, to the combination of
two steps, one in which a metal oxide is reduced to form highly reactive metal and
another in which a metal compound of interest is reduced while the highly reactive metal
is oxidized. In one or more embodiments, it takes significantly less electrical energy to
reduce the highly reactive metal ion and use it to produce the desired metal from the
metal oxide of interest than it does to reduce the metal compound of interest to produce
the desired metal in an alternate, single-step process.

15. MULTI-STEP SOLID OXIDE MEMBRANE(SOM) PROCESS
FOR MAGNESIUM
Schematic of SOM process for Mg

16. MULTI-STEP SOLID OXIDE MEMBRANE(SOM) PROCESS
FOR MAGNESIUM
• In the second step of the multi-step process, no substantial amount of
energy is needed to reduce the metal ion of interest because the highly
reactive metal in the metal compound facilitates a chemical reaction.
• In sum, less energy is used to reduce a selected amount of the metal
oxide of interest in multi-step process than would be used in a
comparable single-step electrolysis process.

17. CHEMICAL STABILITY OF
ALUMINIUM,MAGNESIUM AND IRON OXIDES
THROUGH GIBB’S FREE ENERGY AND ENTHALPY
OF FORMATION

18. CONCLUSIONS
•As compared to Bayer’s and Hall-Heroult’s process , direct carbothermic
production of Al using EAF with integrated shaft attachment as condensor (for Al
and aluminium sub-oxide vapours) , thereby allowing only Al vapour instead of
liquid Al and high vacuum atmosphere can reduce energy requirements 35% below
those of the best Bayer-Hall technology.Implementation of carbothermic reduction
processes in aluminium production may lead to energy savings of up to 21 %, GHG
emissions reductions of up to 52 % and energy efficiency increase of up to 10%.
•The energy consumption for producing metal from ore is strongly linked to the
chemical stability of mineral being processed, availability and the richness of ore,
and process route. The chemical stability of an oxide compound can be reflected
by the Gibbs free energy while the enthalpy of formation determines the minimum
energy requirement of a process. So , as Gibbs free energy of magnesium oxide is
low , it indicates that magnesium oxide is highly stable and requires high energy to
extract the metal. The difference between the theoretical energy requirements and
the actual energy usage reflects the different aspects of the process route.

19. CONCLUSIONS
•The Pidgeon process urgently needs improvement in order to reduce energy
consumption and greenhouse gas emissions.Improvement that has been
proposed includes utilisation of cleaner energy source (e.g. natural gas) for
reducing GHG emissions and integrating small smelters to improve energy
efficiency.
•The solid oxide membrane electrolytic process has a lower Global Warming
Potential compared to the Pidgeon process (47.3 kg CO2/kg Mg to 62.7 kg
CO2/kg Mg), but suffers from low productivity and high capital costs.
•In case of Mintek process (for Mg) charging magnesite or dolomite as hot as
possible into the smelters and even integrating the smelters may lead to
significant energy reduction . At the same time , condenser efficiency may be
improved by increasing the partial pressure of Mg vapour ,improving the
sealing facility of condenser, maintaining a uniform temperature of condenser
and proper bath agitation to quickly dissipate energy of condensation.

20. REFERENCES
• S. Namboothiri, M. P. Taylor, J. J. J. Chen, M. M. Hyland, M. Cooksey,
“Aluminium Production Options with a Focus on the Use of a Hydrogen
Anode: A Review”, Asia-Pacific Journal of Chemical Engineering, Vol.2,
(2007), pp. 442-7.
• I.M. Morsi, K.A. El Barawy, M.B. Morsi, S.R. Abdel-Gawad, Silicothermic
reduction of Dolomite Ore under Inert Atmosphere, Canadian Metallurgical
Quarterly, Vol. 14, No. 1,(2002),p.15.
• Brooks, G., Trang, S., Witt, P., Khan, M.N.H , Nagle, M, 'Carbothermic
Route to Magnesium', Journal of Minerals, Metals and Materials Society,
Vol.58, no. 5, p.51-55.
• R.T. Jones, Computer Simulation of Pyrometallurgical Processes,
Proceedings of the Twentieth International Symposium on the Application
of Mathematics and Computers in the Minerals,Industries, Vol. 2,(
1987),p.265.

21. THANK YOU