Study of vacuum thermal treatment of galvanized steel scrap in view of optimized recycling (ULiège)

Abstract

A recycling process of galvanized steel scrap to recover zinc has been studied. Development of the recycling process of galvanized steel scrap is important to mitigate the waste accumulation due to the increasing demand of this material. Furthermore, recycling process can be one of the alternatives to produce zinc from secondary materials. The process used vacuum heat treatment process to separate zinc from the galvanized steel scrap. In the present investigation, a thermodynamic study of dezincing process, kinetic evaluation, economic feasibility, and environmental impact assessment through life cycle analysis have been carried out. Variation temperature from 450C to 600C and pressure from 0.3 mbar to 4.5 mbar are used in this study. As a result, up to 96% of zinc can be separated and recovered from the galvanized steel scrap. The vacuum treatment process produces high quality of zinc product up to 4N grade (>99.99%) and the economic study provides an analysis that the process is profitable with an adjustment on the vacuum pump. Environmental impact assessment has been conducted and it shows that the process does not produce direct emission of CO2. A process simulation-based life cycle assessment with thermochemical simulation software (HSC Chemistry 10) has been done to compare the currently available process of galvanized zinc recycling with the proposed process in the focus of zinc recovery. With the new proposed process, the CO2-eq can be reduced up to 73.5% per kg of zinc produced. The possibility of zero CO2 emission in the proposed system can be achieved by implementing clean energy sources in the processing system.