The document discusses the life cycle assessment of aluminum production and use, including details on the Bayer process for extracting alumina from bauxite ore and the Hall-Héroult process for smelting aluminum. It analyzes the energy usage and greenhouse gas emissions from primary aluminum production compared to using recycled aluminum. The results suggest that increasing aluminum recycling and use in vehicles can significantly reduce carbon dioxide emissions.

1. Analyse de Cycle de Vie (ACV)
Life Cycle Analysis (ACL)
Benjamin Warr
LCA Part I

2. History of LCA
• Early 1970s US Net Energy Analysis (NEA) and
Materials-Process-Product Models (MPP)
• Society for Environmental Toxicology and
Chemistry (SETAC-Europe or US)
• US environmental Protection Agency (USEPA)
• International Standards Organisation (ISO)
– Promote consensus on framework
– Define inventory methodology
– Provide accreditation for enterprises and organisations
– ISO14000 and ISO19000 series

3. Who uses LCA?
(see Methods and StandardsISO Survey 2003.pdf)
• Industry
– Mostly (cautious) multinationals to identify areas of
improvement, working with suppliers to obtain better
quality or « greener » inputs.
– « Less is best » for useable comparisons
– Do not go «beyond regulatory compliance »
– But, a holistic view of the enterprise is proactive,
avoids potential problems and is good for image
• Governments (for France see DGEMP2003.pdf)
– Defining public policy – lag behind industry
– US DOE « Life Cycle Costing », « Greening of
Industry », (FRED) Framework for Responsible
Environmental Decision Making)

4. From « Cradle to Grave »
4. Considering manufacture, use + disposal implies a temporal horizon
1. Many 2. Complex 3. Consideration of
materials and and linked outputs (allocation to
energy processes air, sea, freshwater,
combinations (linked unit soil)
(exergy) processes)

5. Partnerships and policies that encourage LCA

6. 4 main steps of LCA - (SETAC)
1. Goal Definition and
Scoping
2. Inventory Analysis
3. Impact Assessment
– Classification
– Characterisation
– Valuation
4. Interpretation
Iteration
Refinement

7. Generic Goals
• Education and communication
• Product design (design for environment)
• Product development and improvement
• Pollution prevention
• Assessment and reduction of potential liability
• Strategic planning
• Assessing and improving environmental programs
• Development of policy and regulations
• Individual and organisational purchase and
procurement
• Labeling
• Developing market strategies
• Environmental management systems

8. •Description of
environmental performance
of products - ISO14040
•Improvement of
environmental performance
of products – ISO 14062
•Information about
environmental aspects of
performance – ISO14020
•Communication of
environmental performance
– ISO 14063
•Description of
environmental performance
of organisations – ISO14030
•Information about the
environmental management
system – ISO19011

9. 1. Goal and Definition Scoping
ISO14041 states
• The goal of any study shall unambiguously state
the intended
– application,
– reasons for the study
– target audience
• Recognise limitations of LCA (non-spatial at present)
• Identify, justify rules and conventions (data, averages etc.)
• Consider qualitative impacts (i.e. social)
• Involve interested parties early in process (feedback)
• Evaluation of LCA via peer review (check assumptions)

10. Goal and Scope: Functional Units
A functional unit must be defined.
A reference to which input and output data are
related (intensive variable)
Product systems must be comparable
It is the service/performance that is
compared, NOT the product itself
Example: can’t compare 1L paint with any
other paint, BUT can compare « 1m painted
surface with Xmm coating and service life
of 10 years »

11. Stages Agricultural Life Cycle Index Matrix
Impacts
Functional unit is
YIELD
(rendement)
It can be expressed as
an intensive variable
relative to
quantitative measures
(indices) of the system
state

12. Goal and Scope: Functional Units
• Alternative Product Evaluation (APE) : a product
system (or service) is described by a fixed functional unit
that serves as a reference. Alternative products are then
compared on the basis of their relative environmental
impact.
• Example: What is the environmental impact associated
with the activity of driving different vehicles 1km carrying
1 tonne of goods?
• Environmental functional demand (EFD): Based on an
an acceptable environmental impact (quota) divided by the
function output. Quotas are then goals which serve as the
starting point for the assessment procedure. Different
technical solutions that satisfy the quota are then identified.
• What vehicles can be used to carry 1ton of goods 1km if
the acceptable environmental consequence is limited to a
certain environmental impact?

13. Alternative Functional Units

14. Service rather than product
Can consider two valid
approaches
1. Service lifetime
2. Raw material life cycle
Functional Units
The System

15. Defining the functional unit,
permits answers to a series
of simple questions:
• What needs to be
accomplished?
• Why does it need to be done?
• When does it need to be
done?
• What conditions must be
considered?
The TEAM must
1. Understand mechanical,
physical, chemical
performance and cost
requirements (need)
2. Develop environmental
requirements and goals
(desire or wish list)

16. Industrial Goals driven by R&D

17. Defining the System Boundaries
• So that product and service systems can be subdivided into
a set of unit processes.
• Inputs and outputs at the boundaries should be elementary
flows linked to unit processes
• There are 2 ways to define the system boundaries (always
considering the goals!)
• narrow system boundaries:
– 1. extraction
– 2. disposal
– 3. manufacture
– 4. use
• extended system boundaries: “cradle to grave”

18. Proposing Engineering Technologies
and Options
• Once requirements and goals are defined, the team should
– Identify technologies that combine to form different options to
provide the desired function
• Technologies include materials and equipment.
Keywords:
Reduce
Recover
Maintain
Upgrade
And Technology Life Cycles

19. Linking Technologies to
Requirements and Goals

20. LCA of Aluminium
• Sponsor: International Aluminium Institute
• Stated objectives:
– Increase use of Al in transportation systems
– reduce energy consumption and associated GHG emissions of Al
production
– Increase use of recycled Al.
• First task: quantification of CO2 and PFC greenhouse gas
(GHG) emissions from the worldwide aluminium industry
• Second Task: estimates of the implications (in terms of
Greenhouse Gas Emissions) of the increased use of
aluminium for the manufacture of cars and trucks.
• Data from over 80% of the worldwide industry including
estimates from Russia and China.

21. AL LCA: System Boundaries

22. Bauxite Mining and Benefication
• Bauxite is washed, ground and dissolved in
caustic soda (sodium hydroxide) at high
pressure and temperature. The resulting
liquor contains a solution of sodium
aluminate and undissolved bauxite
residues containing iron, silicon, and
titanium. These residues sink gradually to
the bottom of the tank and are removed.
They are known colloquially as "red mud".
• Clear sodium aluminate solution is
pumped into a huge tank called a
precipitator. Fine particles of alumina are
added to seed the precipitation of pure
alumina particles as the liquor cools. The
particles sink to the bottom of the tank, are
removed, and are then passed through a
rotary or fluidised calciner at 1100°C to
drive off the chemically combined water.
The result is a white powder, pure alumina.
The caustic soda is returned to the start of
the process and used again.
• The BAYER PROCESS

23. The BAYER PROCESS in REFINERY
• The Bayer process can be considered in three stages:
• Extraction The hydrated alumina is selectively removed from the other (insoluble) oxides by
transferring it into a solution of sodium hydroxide (caustic soda):
– Al2O3.xH2O + 2NaOH ---> 2NaAlO2 + (x+1)H2O
– The process is far more efficient when the ore is reduced to a very fine particle size prior to reaction.
This is achieved by crushing and milling the pre-washed ore. This is then sent to a heated
pressure digester.
– Conditions within the digester (concentration, temperature and pressure) vary according to the
properties of the bauxite ore being used. Although higher temperatures are theoretically favoured
these produce several disadvantages including corrosion problems and the possibility of other
oxides (other than alumina) dissolving into the caustic liquor.
– After the extraction stage the liquor (containing the dissolved Al2O3) must be separated from the
insoluble bauxite residue and purified as much as possible and filtered before it is delivered to the
decomposer. The mud is thickened and washed so that the caustic soda can be removed and
recycled.
• Decomposition Crystalline alumina trihydrate is extracted from the digestion liquor by hydrolysis:
– 2NaAlO2 + 4H2O ---> Al2O3.3H2O + 2NaOH
– This is basically the reverse of the extraction process, except that the product's nature can be
carefully controlled by plant conditions (including seeding or selective nucleation, precipitation
temperature and cooling rate). The alumina trihydrate crystals are then classified into size fractions
and fed into a rotary or fluidised bed calcination kiln.
• Calcination Alumina trihydrate crystals are calcined to remove their water of crystallisation and
prepare the alumina for the aluminium smelting process.
– The mechanism for this step is complex but the process, when carefully controlled, dictates the
properties of the final product.

24. Additional Info. on the Bayer Process
• The amount of residue « red mud » generated, per tonne of alumina produced,
varies greatly depending on the type of bauxite used, from 0.3 tonnes for high
grade bauxite to 2.5 tonnes for very low grade.
• The following data gives some idea of the wide range in chemical composition that
can be found in residue from different bauxites.
• Fe2O3 30 - 60%
• Al2O3 10 - 20%
• SiO2 3 - 50%
• Na2O 2 - 10%
• CaO2 - 8%
• TiO2
• Trace - 10%
• Apart from the alkalinity that is imparted by liquors in the process, the residue is
chemically stable and non-toxic.
• Bauxite residue is most often disposed of on land using one of a variety of
methods. Once such land has been decommissioned is can be used to grow crops or
other vegetation. Alternatively the land can be used for building, depending upon
the moisture of the residue.

25. Al Smelting: the Hall-Heroult Process
• Alumina is dissolved in an electrolytic bath of molten cryolite
(sodium aluminium fluoride) within a large carbon or graphite lined
steel container known as a "pot". An electric current is passed through
the electrolyte at low voltage, but very high current, typically 150,000
amperes. The electric current flows between a carbon anode
(positive), made of petroleum coke and pitch, and a cathode
(negative), formed by the thick carbon or graphite lining of the pot.
• Molten aluminium is deposited at the bottom of the pot and is
siphoned off periodically, taken to a holding furnace, often but not
always blended to an alloy specification, cleaned and then generally
cast.
• Across all technologies, electricity consumption averaged 15.95 kWh
per kg of molten metal. The consumption of fuels to produce this
electricity generated 5.8 metric tonnes of CO2 per tonne of metal. An
additional 1.6 metric tonnes of CO2 per metric tonne are generated in
the electrolytic process.

26. Smelting System Diagram
2Al2O3 + 3C -----> 4Al + 3CO2
Incremental improvements
have reduced energy
intensity.
•PFC emissions at 0.30 kg of
CF4 and 0.03 kg of C2F6 per mt
per metric tonne of Al.
•Equivalent to 2.2 metric tonnes
of CO2 for every tonne of Al.

27. Thermodynamic inefficiency in
smelter
2Al2O3 + 3C -----> 4Al + 3CO2

28. LCA Results: For a target audience?
• Estimates from car manufacturers and others range from 5-10% of
fuel economy savings per 10% weight reduction for today's average
vehicles.
• Thus an automobile driven for 200,000 km could save 6-13 litres of
gasoline for every kg of aluminium used to replace 2 kg of heavier
materials
• Modelling indicates the potential to save over 20 metric tonnes of
CO2 equivalents for each tonne of additional automotive aluminium
products from enhanced vehicle fuel efficiency over the vehicle's
lifetime.
• Modelling was also conducted to quantify the effect of using either all
recycled or all primary aluminium. The table below shows that even
with all virgin (primary) metal, net carbon dioxide savings are
substantial.
Metal Used All Primary 30% Recycled 60% Recycled 95% Recycled
Tonnes CO2e 13.9 18.1 22.9 26.7
saved
per tonne of Al

29. Future Efforts
• Easier dismantling of aluminium components from cars to
improve the recovery of aluminium.
• Recycling rates for transport applications range from 60-90
per cent.
• Close to 40% of the global demand for aluminium in all
markets is based on recycled metal from process scrap and
scrap from old products.
• Increasing use of recycled metal saves on both energy and
mineral resources needed for primary production.
• Recycling of aluminium requires only 5% of the energy to
produce secondary metal as compared to primary metal and
generates only 5% of the green house gas emissions.