Process Knowledge, System Dynamics, and Metal Ecology

Abstract

A key principle in industrial ecology is the cyclic use of materials, a characteristic of natural ecosystems but a challenge in economic systems. Indeed, in society, metal retention, that is, the ongoing use or ready availability of metal in the economy between the life‐cycle stages of resource extraction and final disposal back into the lithosphere, is finite because of the limited grade of secondary (recycled) metals. Currently, the utility of metals is maintained through the addition of high primary (virgin) metals, bringing the concentration of the recycled metals to desired levels. This mixing with high‐grade primary metals keeps these recycled metals in the cycle. Long term, this practice of dilution of the undesired substances prevents a closure of the material cycles, whereas recovery without dilution reduces the quality (or quantity) of recycled metals.Metals participate in a system of linked cycles and thus cannot be produced or recovered independently from one another. The metal wheel is introduced in this article as a concise but powerful instrument for the communication of available process knowledge in process metallurgy, the science and technology of producing metals from natural ores and societal raw materials, residues, and end‐of‐life products. It summarizes the chemical and physical linkages between metals found in ores and the set of metallurgical processes that has been developed to accommodate these linkages.A dynamic mass‐flow model is introduced to characterize the global metal cycles. The model facilitates the visualization of the evolution of their structure and technological content.To illustrate the interdependency of metal cycles using the metal wheel and the dynamic model, the transition to lead‐free solder is evaluated. Neglect of metal‐cycle linkages and dynamics in policy formulation may lead to a shortage of lead substitutes. In case of an extended ban on lead, both the availability and recovery of a range of metals will be affected.