From Grave to Cradle

Abstract

Keywords:exergy industrial ecology life cycle assessment (LCA) minerals mining nickel Supporting information is available on the JIE Web site SummaryLife cycle assessment (LCA) is a promising tool in the pursuit of sustainable mining. However, the accounting methodologies used in LCA for abiotic resource depletion still have some shortcomings and need to be improved. In this article a new thermodynamic approach is presented for the evaluation of the depletion of nonfuel minerals. The method is based on quantifying the exergy costs required to replace the extracted minerals with current available technologies, from a completely degraded state in what we term "Thanatia" to the conditions currently found in nature. Thanatia is an estimated reference model of a commercial end of the planet, where all resources have been extracted and dispersed, and all fossil fuels have been burned. Mineral deposits constitute an exergy bonus that nature gives us for free by providing minerals in a concentrated state and not dispersed in the crust. The exergy replacement costs provide a measure of the bonus lost through extraction. This approach allows performing an LCA by including a new stage in the analysis: namely the grave to cradle path. The methodology is explained through the case study of nickel depletion.

Evaluation of Abiotic Resource LCIA Methods

“…Exergoecology, proposed by Valero e Valero [50,51], brings an innovative approach to the LCA community, where the authors try to quantify the depletion of metals and minerals through the exergy cost, which, in a simplified way, would be to make a cumulative exergy consumption assessment, but in the opposite direction, i.e., from grave-to-cradle. The main idea is that the method quantifies the exergy needed to let the metal be ready for extraction through mining, from its reference state (where exergy is zero).…”

“…Exergoecology has an interesting alternative approach, but it is not yet completely operational for LCA, mainly for two reasons: (1) Through the published articles, we were able to quantify only seven CF; and (2) this originates from a scientific area that needs more research, and more CF should be generated. Regarding the latter reason, even though exergy is already established in LCA, the scientific proposal from Valero and Valero [50,51] goes beyond traditional exergy, i.e., they propose accounting for the exergy from grave-to-cradle. For those reasons, Exergoecology received a low score for scope and a medium-high score for scientific robustness.…”

From Theory to Practice: Enhancing the Potential Policy Impact of Industrial Ecology

“…Thermodynamics refers to the relationship between heat, energy and ability to do work within a system, be it open or closed [27]. These laws are important as they describe the physical limits on the work that can be done by an ideal system (with the term "exergy" used sometimes for available work [28]). The energy available in a real system is further limited by a dissipative loss of energy e.g., as friction-generated heat.…”

“…Conventional LCAs may not offer policymakers suitable information on which to base a decision with scarcity implications [35]. Valero and Valero [28] present an exergy-based LCA approach which tries to address that deficiency by considering, for example, the energy implications of using an alternative to the depleted resource in question. However, framing an LCA to prioritise supply of a scarce resource (e.g., to maximise metal recapture from recycling), may discount the environmental impact of relevant processes [74].…”

Thermodynamic Rarity and the Loss of Mineral Wealth

“…Since the grave-to-cradle process is hypothetical, the exergy replacement cost is not truly an embodied exergy. Rather, it can be considered a hidden or avoided cost, and hence, both terms cannot be used as synonyms, as is the case for cradle-to-grave analyses [26].…”