Refining of Secondary Aluminum: Important Chemical Factors

Abstract

There are important economic and environmental incentives to recycling. Unfortunately, secondary aluminum frequently contains undesirable impurity elements. These limit the amount of secondary material that can be recovered, since the usual practice has been to meet alloy specifications by dilution (that is, by blending with primary metal). In 2019, China curtailed the importation of scrap metal, which changed the scrap market in North America. The price differential between secondary and primary metal suddenly became 20 or 30 cents a pound, sometimes more. This differential was large enough that producers began to ask: “Is there a refining process we can we use to recover this scrap?” This paper is an attempt to answer this question. Chemical factors which make it possible (or impossible) to remove an impurity are reviewed in detail. Example calculations are presented and some important alloying elements are considered individually.