Reduction of Zinc-Magnesium Alloy Coating Waste by In-House Dross Management

摘要

In a continuous galvanizing process, zinc is added to steel sheet to enhance the corrosion resistance and extend the operational life of the end products on which it is used. Correspondingly, galvanized steel is the largest market segment for global zinc ingot consumption, and zinc is the highest consumable cost for a galvanizing operation. Through the typical hot dip galvanizing process, dross and skimmings are removed from the coating pot as a natural waste product of the coating operation. Research has shown that more than 70% of these skimmings are actually viable zinc from the bath that are sold to traders and recyclers at a loss (compared to the true value of the zinc). Analogously, many continuous galvanizing plants are evaluating the possibility of processing these skimmings in-house and retaining the functional zinc for immediate reuse in the coating pot. Hence, the skimmings from zinc-magnesium coating alloys were evaluated for the possibility of metal recovery through in-house dross processing. First, the characteristics of the skimmings were found to contain higher levels of entrained magnesium and aluminum oxide films in addition to inter-metallic particles. Next, zinc alloy recovery tests identified a generally higher level of metal reclamation than typical GI skimmings recovery (90% versus 80%, respectively).