How Much Sorting Is Enough

Abstract

One strategy for mitigating the effects of rapidly growing global materials consumption is intensified recycling. A key barrier to recycling is the ability to segment or sort constituents within end-of-life products. Various sorting technologies hold promise, but each must demonstrate added value to achieve wide-scale deployment. Potential factors affecting such value include the mix of scrap supply, the nature and mix of finished goods demand, sorting technology performance, and costs. This article examines the use of optimization models to identify economically efficient sorting strategies and their impact on scrap usage. Using this method, this article attempts to identify the conditions that amplify and mute the value of sorting to facilitate recycling.When this method is applied to a case representative of European aluminum secondary production, it is clear that sorting methods can add value in a broad range of conditions. Although better sorting performance (in the form of segmentation efficiency, referred to as recovery rate) correlates positively with cost savings and scrap utilization, it does not always vary monotonically with optimal sorter utilization (i.e., the fraction of scrap sorted rather than unsorted). Furthermore, the case analysis indicates that the value of sorting is more strongly dependent on recovery rate for the more heterogeneous fraction, which, in the case of aluminum, is the cast-like fraction. Ultimately, sorting increases production flexibility, making a recycler more economically resilient in the face of changing supply and production conditions.

Performance evaluation of material separation in a material recovery facility using a network flow model

“…Several papers have studied the costs and operations of an MRF in various contexts: Metin et al estimated the investment and operating costs of different municipal MRFs in Turkey using city-wide aggregate data (Metin et al, 2003); Kang and Schoenung examined the cost drivers of an existing e-waste MRF (Kang and Schoenung, 2006); Li et al considered how sorting strategies can impact the utilization of scrap in a secondary aluminum production process. (Li et al, 2011). However, these papers do not model the material flows through the individual separation units, but rather assume a given material recovery rate.…”

The Materials Science behind Sustainable Metals and Alloys

“…The former refers to mixed and often quite highly chemically contaminated scrap from consumer products, infrastructures, buildings, machinery, appliances, etc. The latter refers to in-line industrial scrap that is collected already during production and downstream manufacturing, thus also referred to as in-line, “runaround”, or pre-consumer scrap. ,,− Examples are waste materials produced during casting, blanking, stamping or chipping. The amount of in-production scrap can be as small as a few percent for some special steels as well as for many precious metals, but it can be also as high as 90% and more, as for instance in the case of titanium when it is chipped into parts for aerospace vehicles. ,, New scrap has usually a known and well-defined chemical composition and can be collected sort-specifically.…”

In-depth analysis of aluminum flows in Austria as a basis to increase resource efficiency

“…Potential limits in Al scrap recycling, especially for end-of-life vehicles, have also been analyzed by Modaresi and Müller (2012) and Løvik et al (2014). The economic benefits of advanced sorting technologies in Al recycling were presented by Li et al (2011). Furthermore, the MFA studies conducted provide a database for the calculation of greenhouse gas emissions along the Al life-cycle Liu and Müller, 2013;McMillan, 2011).…”