Evolution of aluminum recycling initiated by the introduction of next-generation vehicles and scrap sorting technology
Graphical abstract
Highlights
► World aluminum demand and discard will reach 50 and 45 million tons in 2050. ► Recycling enables future demand to be filled with less primary aluminum than today. ► Rapid penetration of electric vehicles will transiently disturb the recycling. ► Applying scrap sorting to ELV scrap reduces primary aluminum consumption by 15–25%.
Introduction
Current trends in energy supply and consumption are generally regarded as unsustainable: International Energy Agency (IEA) estimates that energy-related greenhouse gas (GHG) emissions will more than double by 2050. The vehicle industry, one of the high CO2-emitting sectors, has been developing next-generation vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and fuel cell vehicles (IEA, 2009). These vehicles are expected to consume less fossil fuel and emit less CO2 during the use phase than conventional vehicles with internal combustion engines (ICEVs) (Lave et al., 2000, Samaras and Meisterling, 2008). In recent years, several governments have announced sales targets for these vehicles, and IEA has proposed a global scenario named “BLUE Map scenario,” which aims at “cutting CO2 emissions levels in 2050 to 30% below 2005 levels” for the transport sector”. (The overall target for the scenario is a 50% reduction in global energy-related CO2 emissions by 2050 compared to 2005 levels.) According to IEA (2009), this ambitious objective can be achieved by the rapid penetration of next-generation vehicles, improvements in energy efficiency, and some other technological developments. Thus, the introduction of next-generation vehicles has often been evaluated from the viewpoint of energy consumption and climate change.
However, the effect of such vehicles on the resource management of metals has not been discussed thoroughly. The expansion of the world economy in the last century has increased an importance of securing various metals (Erdmann and Graedel, 2011), and a still larger amount of metal usage is expected for developing countries. In response to this problem, a number of technologies and policies have been developed to promote the three Rs (reduce, reuse, and recycle); therefore, anthropogenic material stocks and flows are of current interest (Gerst and Graedel, 2008, Graedel et al., 2004, Johnson et al., 2005, Reck et al., 2008, Wang et al., 2007). Researches of the material flow analysis (MFA) have found that the vehicle industry plays a prominent role in the material cycle for various metals (Saurat and Bringezu, 2008, Saurat and Bringezu, 2009, Tabayashi et al., 2009). A notable example is aluminum, whose use has expanded as a means of lowering fuel costs, with a consequent increase in aluminum consumption and recycling.
Aluminum is usually used with the addition of a few elements, in the form of an alloy. The Japanese Standard Association defines 40 or more alloy types (JSA, 2003), and these alloys are commonly categorized into two types according to the concentration of alloying elements: wrought alloys (less than ca. 5%) and cast alloys (ca. 15%). In current aluminum recycling, cast alloy production receives most of its scrap from end-of-life products because it can tolerate a high concentration of foreign elements. This recycling system (called down-cycling or cascading) works well as long as the demand for cast alloy is sufficiently greater than the quantity of scrap generated. However, a recent increase in scrap generation from end-of-life vehicles, buildings, and other products may dictate a change in the recycling system. Gesing (2004) simulated the mass balance in the transport sector and concluded that there would be a large amount of scrap that could not be absorbed by cast alloy production, while not being suitable for wrought alloy production because of its high concentrations of foreign elements. The author stated that “The transportation sector will become a net producer of aluminum scrap rather than, as is the case at present, a consumer.” Gesing also raised the possibility that the expansion of cast alloy demand, economic principles, and technologies in the future would mitigate the generation of this “unrecyclable scrap.” In particular, scrap sorting by alloy type is considered to be an effective means of reducing unrecyclable scrap. If wrought alloys in end-of-life products are identified and collected without much contamination, they can be used as a source for wrought alloy production. To carry out the sorting in a simple, quick, and inexpensive manner, several techniques such as X-ray transmission analysis, apparent density, and three-dimensional sensing, combined with neural network analysis, have been under development (Gaustad et al., 2012, Koyanaka and Kobayashi, 2011, Mesina et al., 2007).
The purpose of this paper is to provide insight into aluminum recycling in the near future, with a focus on clarifying how the next-generation vehicles will affect it. The extent to which scrap sorting can enhance recycling is also discussed. Aluminum demand and discard in Europe, the United States, Japan, and China are modeled using MFA. Then, the necessary amount of primary aluminum and the generation of unrecyclable scrap are derived for three separate scenarios of vehicles and scrap use. The results show the limitations of the current recycling system and confirm the validity of scrap sorting.
Section snippets
Methodology
The present status of the anthropogenic aluminum cycle has been illustrated by some MFA studies (Boin and Bertram, 2005, Chen et al., 2010, Liu et al., 2011, Martchek, 2006). In the previous publication (Hatayama et al., 2009) we projected the aluminum in-use stock, demand, and discard up to 2050 for Japan, the United States, Europe and China, using dynamic MFA. In that study we calculated the concentrations of foreign elements in scrap, considering the alloy types used in respective end uses,
Results
The dynamic MFA provided the information on the source and sink of recycling: scrap volume and its compositions for respective end uses, and production demand for respective alloy types. Then, the minimum requirement for primary aluminum and the generation of unrecyclable scrap were calculated using multimaterial pinch analysis for 2030 and 2050.
Aluminum stock, demand and discard were estimated as shown in Fig. 2, Fig. 3, Fig. 4 for scenarios II and III. (It should be noted that the word
Discussion and conclusions
This paper presents the prospects of aluminum recycling by 2050, quantitatively analyzing the influence of next-generation vehicles and scrap sorting. First, dynamic MFA was used to estimate the stock and flow of aluminum in Europe, the United States, Japan, and China by 2050. The MFA indicated that the increase in aluminum stock and demand in the future are almost all derived from developing China, while aluminum usage in developed countries already seems mature for traditional products. The
Acknowledgments
This study was partly supported by the Japan Society for the Promotion of Science through a Grant-in-Aid for Research Fellowships (No. 219266) and Scientific Research (B) (No. 22360387).
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