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> 1 Addressing the issue of uncertainty in MFA: an application to rare earth elements in the EU-28 Dominique GUYONNET (French Geological Survey, BRGM, FR)
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Addressing the issue of uncertainty in MFA:
an application to rare earth elements in the EU-28
Dominique GUYONNET (French Geological Survey, BRGM, FR)
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Presentation outline
1. Objectives of the ASTER project
2. MFA and uncertainty
3. Some results
4. Conclusions
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1. Objectives of the ASTER project
• ASTER (Systemic Analysis of REEs – flows and stocks)
• Explore, using MFA, flows and stocks of certain rare earths at the
scale of the EU-28
• Build Sankey diagrams to visualize flows and stocks along the
value chain
• Help appreciate criticality and recycling potentials
• Develop innovation with respect to two aspects:
Account for “lithospheric stocks” (geological potentialities)
Account for “epistemic” uncertainties (related to the incomplete/imprecise
nature of available information)
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• Motivation
REE flows and stocks have been studied primarily at a global
scale
A systemic analysis associating both primary and secondary
sources, is required for reliable decision-making regarding raw
material management and policy-making
MFA can help identify recycling potentials and highlight the
complementarity between primary and secondary sources of
raw materials
The issue of uncertainty treatment in MFA (as in LCA) is an
important technical and scientific issue
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• Primary focus of ASTER: applications for which there exist
recycling potentials
Phosphor powders (Eu, Tb, Y)
Permanent magnets (Pr, Nd, Dy)
NiMH batteries (Pr, Nd)
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• Main deliverables
Estimates of primary resource potentials in the EU
Sankey diagrams of flows/stocks along the value chain
A methodology for data reconciliation in MFA with “epistemic”
uncertainties
Prospective analysis of REE supply/demand trends at a 2020
horizon
Dissemination (web page, conferences, journals, etc.)
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• Data collection involves multiple sources of uncertainty
Lack of specificity of HS codes (customs) used to identify imported or
exported products containing rare earths (EUROSTAT, WTA)
Choice of certain countries not to communicate their data to EUROSTAT
Customs data-entry errors
Estimations of quantities of rare earths in components (e.g. Nd in
permanent magnets), but also quantities of components in products
(e.g. magnets in hard-disk drives or in wind-power turbine generators)
Losses of rare earths in industrial processes (manufacture)
Variations over time
Etc…
2. MFA and uncertainty
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• Such uncertainty is typically of an epistemic nature
(reflecting knowledge gaps), rather than a stochastic nature
(reflecting random variability)
• Hence the choice of relying on a possibilistic representation
of data and associated uncertainty
• Motivation:
consistency between available information
and the way it is represented in MFA
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3. Principle of proposed methodology
• “Classical” approach to uncertainty representation in MFA:
assume normal probability distributions
• Reconciliation of MFA: least-squares minimization
2
1
*2 1
n
i
ii
i
FF
• Methodological choice in ASTER: represent uncertain data
by “nested intervals” (fuzzy sets) (well suited for “expert
information”)
• Reconciliation under constraints (mass balances, data
boundaries, etc.)
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Illustration 1: min-max interval
Process
Inflow expert Outflow expert
Reconciliation under constraints:
• Flow in = flow out
• Reconciled flows lie within
boundaries of initial estimates
Flow 10 20 30 40 50 60 70
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intersection0
0,2
0,4
0,6
0,8
1
40 45 50 55 60 65 70
Poss
ibil
ity
Flux
Flux in
Flux out
Illustration 2: “Nested intervals”
• Preferences can be expressed within intervals (fuzzy sets)
• Find maximum level of possibility which satisfies constraints of
mass balance and membership
Flow
Flow in
Flow out
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• For more complex “real-world” examples: need linear programming
algorithms
, 43(8): 787-809.
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• Primary resources: > 400 occurrences of REE in Continental
Europe & Greenland, described in terms of typology and potential
3. Some results
> 14 Charles et al. (2014), Tuduri et al. (in prep)
• Geodynamic interpretation of typology
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Nd 2010 • Sankey diagrams
Tons Nd metal
2010 in-use
stock = 16 ktons
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Tb
Tons Tb metal
2010 in-use
stock = 140 tons
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Nd
Tons Nd metal
2010 in-use
stock = 600 tons
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• Estimated uncertainty ranges for several REE flows
• Details in:
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• Based on hypotheses regarding manufacture of REE and
extraction sector in EU
Whether Norra Kärr enters production or not
Major trends in industry:
Dy optimisation in magnets (and/or substitution)
Phasing out of phosphor lamps by LEDs
…
• Results highlight the importance of demand on the relative
contribution of recycling to supply
Prospective analysis at 2020 horizon
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Nd 2020
Tons Nd metal
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• Only a very limited number of REEs currently present supply
risks (primarily the REEs related to NdFeB magnets)
• The situation could change if extraction projects outside China
were no longer viable due to Chinese competition (e.g.
Molycorp, Lynas, …)
• With respect to the proposed uncertainty methodology: the
objective is “consistency with available information”
• A project is foreseen in order to further develop the
methodology within a platform that would allow researchers to
test different methodologies
• Associating primary and secondary sources of RMs is essential for a
analyzing RM supply and demand
Some conclusions
