Investigating Pathways to Circular Manufacturing Industry Using Material Flow Analysis

Abstract

The circular economy can address the issues of low resource efficiency and large waste generation in the linear production and consumption systems. Part of the sectors play crucial roles to close the loops in supply chains. A comprehensive material flow analysis can shed light on what the key players are for a material of concern. However, most of the material flow studies focus either on specific micro-level business that can hardly grasp the entire lifecycle or on the whole economy in which the industry-specific inputs/outputs are aggregated into several life cycle stages or one economic system as a black box.

To explore how the flows of magnesium (Mg) go circular in Taiwan, we conducted a material flow analysis with an overview of highly-detailed supply chains. Magnesium and its alloy are widely used in various products and components due to its lightness and strength. We present the network with elaborate economic activities as nodes and the flows of magnesium as links within and between several life cycle stages adapted from the stocks and flows framework (STAF) proposed by Thomas Graedel’s team in the Yale University. Our study encompasses five stages of the material’s lifecycle, import and export, and reverse logistics.

The inventory of material flows is based on publicly available data, and the estimation of distributional flows into the downstream sectors by input-output modeling. Also, we interviewed a secondary Mg alloy smelting and casting factory. Two indicators of circularity are given for comparison with the EU’s End-of-life Recycling Input Rates (EoL-RIR) and the Circular Material Use Rate (CMUR).

Our results show that Taiwan imported 64 kilotons of Mg through aluminum (Al) alloy, processed Mg, Mg alloy, Al scrap, and Mg scrap. Each Mg-containing material accounts for 31%, 20%, 18%, 7%, and 2%, respectively. Among all imported Mg, 30 kilotons were consumed for Al alloy products. The casting of Mg alloy consumes 19 kilotons of Magnesium. Quality scrap from Mg alloy castings can by smelt down and manufacture new Mg alloy ingot. Among the 5.1 kilotons of secondary Mg ingot refined in Taiwan in 2017, 80% were exported, and 20% were for domestic usage. The EoL-RIR and CMUR in Taiwan are 20% and 48 %, respectively. Taiwan’s circulation of Mg is equal or better to that in the European Union.

This study investigates the variety of Ma’s circular pathways and concludes the alternative of high priority to retain the value of Mg in end-of-life products and scrap from metal fabrication. The Mg in Al products can be recycled and used as raw material for Al alloy again, but for Mg alloys. On the other hand, the Mg in end-of-life products cannot be circulated due to the current recycling system. In the interview with Mg metalworking factories, the manager stated the concern for not using the ingot from the secondary smelter. The secondary Mg smelting factories might need to have their quality certified with international standard to gain buyers of secondary Mg alloy ingot and circulate majority of high-quality Mg scrap.

Keywords: material flow analysis, circular economy, magnesium