Rare earth elements (REEs) are a collection of 17 chemical elements that are critical to the functionality of a host of modern commercial industries including emerging clean energy technologies, electronics, medical devices, and national defense applications. Despite their key importance in multiple industries, to-date there has been little emphasis on environmental systems analysis of REE production. Rapid growth in these industrial sectors could result in heightened global demand for REE. As such, assessing the broader ramifications of REE production on human health and the environment is crucial for guiding the sustainable development of these industries. In this study, life cycle assessment (LCA) is performed to evaluate the environmental impacts and resource intensity of producing rare earth oxides (REO) from the Bayan Obo mine located in Inner Mongolia, China. Analysis indicates that the mining, as well as extraction and roasting phase(s), had the greatest contribution to overall life cycle environmental impacts. Additionally, the results reveal that the production of heavy REO consumes over 20 times more primary energy as compared to steel (per unit mass). The high primary energy consumption and life cycle environmental impacts of REO production highlight the critical need for development of REE recycling operations and infrastructure.

BackgroundMicroalgae are touted as an attractive alternative to traditional forms of biomass for biofuel production, due to high productivity, ability to be cultivated on marginal lands, and potential to utilize carbon dioxide (CO2) from industrial flue gas. This work examines the fossil energy return on investment (EROIfossil), greenhouse gas (GHG) emissions, and direct Water Demands (WD) of producing dried algal biomass through the cultivation of microalgae in Open Raceway Ponds (ORP) for 21 geographic locations in the contiguous United States (U.S.). For each location, comprehensive life cycle assessment (LCA) is performed for multiple microalgal biomass production pathways, consisting of a combination of cultivation and harvesting options.ResultsResults indicate that the EROIfossil for microalgae biomass vary from 0.38 to 1.08 with life cycle GHG emissions of −46.2 to 48.9 (g CO2 eq/MJ-biomass) and direct WDs of 20.8 to 38.8 (Liters/MJ-biomass) over the range of scenarios analyzed. Further anaylsis reveals that the EROIfossil for production pathways is relatively location invariant, and that algae’s life cycle energy balance and GHG impacts are highly dependent on cultivation and harvesting parameters. Contrarily, algae’s direct water demands were found to be highly sensitive to geographic location, and thus may be a constraining factor in sustainable algal-derived biofuel production. Additionally, scenarios with promising EROIfossil and GHG emissions profiles are plagued with high technological uncertainty.ConclusionsGiven the high variability in microalgae’s energy and environmental performance, careful evaluation of the algae-to-fuel supply chain is necessary to ensure the long-term sustainability of emerging algal biofuel systems. Alternative production scenarios and technologies may have the potential to reduce the critical demands of biomass production, and should be considered to make algae a viable and more efficient biofuel alternative.

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Holistic evaluation via a life cycle based approach is critical for guiding the environmentally conscious development of emerging microalgal biofuel pathways. This study models the energy return on investment (EROI) and life cycle greenhouse gas (GHG) emissions for producing algal derived biodiesel and renewable diesel under different production pathways—consisting of a combination of algal cultivation, harvesting, extraction, and coproduct utilization scenarios. The results indicate that in the base‐case scenario(s) the EROI for microalgae fuels range from 0.26 to 1.20 with GHG emissions ranging from 50 to 240 gCO2 equivalent/MJ‐fuel depending on the choice of cultivation variables, coproduct utilization options, and processing technologies. In the improved scenario(s), algal fuels have an EROI ranging from 0.81 to 2.01 and GHG emissions ranging from 30 to 90 gCO2 eq./MJ‐fuel. Furthermore, improved scenarios with favorable EROI and GHG emissions profile for microalgal biofuels are plagued with high technological uncertainty. This suggests that broad advances in algal technologies are required if algal fuels are to be competitive with other leading second generation and advanced biofuels. The choice of fuel conversion technology was found to have a comparatively small impact on overall life‐cycle energy use and GHG emissions. Therefore, the choice of fuel product may be based on other criteria such as fuel storage stability and compatibility with transportation fuel infrastructure. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 926–936, 2013

Well-to-wheel (WTW) life cycle assessment (LCA) of multistage torrefaction and in situ catalytic upgrading: overview of unit operations, modeling tools, and data sources.