Transcript Diapositiva 1

The Crepuscular Earth. A reference for calculating the depletion of
mineral resources using LCA
Alicia Valero and Antonio Valero
CIRCE - Research Center for Energy Resources and Consumption. Universidad de Zaragoza (Spain)
Introduction
 The Crepuscular Earth or Thanatia is a guess thermodynamic model for a terrestrial “grave”, where all fossil fuels have been burned and
converted into CO2 and with the absence of mineral deposits. The crepuscular crust is composed by the 294 most abundant minerals currently found
on Earth.
Thanatia constitutes a coherent baseline for the assessment of minerals. Any substance like a mineral deposit or a glacier is an exergy resource
with respect to the Crepuscular Earth.
 The exergy analysis allows the assessment of all physical properties of natural resources, such as composition, grade or quantity, with a single
unit of measure (the exergy costs) and in an objective way far removed from market distortions or currency speculation.
Methodology
Exergy/
Exergy cost
Cradle to entry gate
Entry gate to exit gate
Exergy/
Exergy cost
Useful products
Manuf.
costs
Product
manufacture
Man-made stock
 We propose to include one additional step in the
LCA methodology: the grave to cradle stage to
account for abiotic resource depletion.
Man-made mining and
refining process
Mining and
refining costs
Grave to cradle
Exit gate to grave
Recycling
costs
Use and
dispose of
materials
Recycling of
materials
Fuels
Minerals
Mineral deposits
Landfills
Natural conc. and
refining process
 The minimum exergy replacement cost bc of a
mineral to concentrate a substance from Thanatia
is calculated as :


(1  xi )
bc   RT0 ln( xi ) 
ln(1  xi ) 
xi


Natural stock
Avoided costs/
mineral bonus
 The resources are physically assessed as the
energy required to replace them from a
complete degraded state or Thanatia to the
conditions in which they are currently presented in
nature: Replacement costs.
Materials
dispersion and
pollution
The actual exergy replacement costs bt*
consider also the state of technology:
Crepuscular Earth / Thanatia
Reference
Environment
bt *  kc ·bc
Zero Exergy
k
Materials Life cycle
E real _ process
bmin eral
Discussion and Conclusions
This approach helps to solve some unresolved issues in the evaluation of abiotic resource depletion in LCA:
 In the grave to cradle approach, it is not the extraction of materials which is of concern, but rather the dissipative use and disposal of materials.
 A resource is not valued according to its mass or energy content. It is assessed according to its differentiation with the environment. The
greater the ore grade of the mineral with respect to the dispersed state of the Crepuscular planet, the greater its thermodynamic value.
 The temporal, political or social factor does not play any role in our view of Crepuscular Earth, and hence the arbitrariness of assuming static
reserves disappears.
 As opposed to other methodologies which account for abiotic resource depletion as a function of the extraction costs (as with the Eco-indicator
99), the mining of highly concentrated mines (which have low extraction costs) is penalized since they have associated greater replacement costs.
However, high-grade mines do not need so much energy in the mining and concentration steps. Hence, both concepts complement each other and no
double counting occurs.
 The exergy analysis of minerals from Thanatia could constitute a universal and transparent prediction tool for assessing the degradation
degree of non-renewable resources, with dramatic consequences for the future management of the earth’s physical stock.
This study has been carried out under the framework of the ENE2010- 19834 project financed by the Spanish Ministry of Education and Science
CIRCE – Universidad de Zaragoza
Edif. CIRCE, Mariano Esquillor 15, 50018 Zaragoza (Spain)
Tel: (+34) 976 76 18 63. Email: [email protected]