Recycling of Dusts from Iron Foundries by Incorporation into Silicon Carbide Briquettes

Dusts from iron foundries are considered hazardous waste due to increased heavy metal contents. They are nowadays often landfilled, although they contain valuable constituents such as iron and quartz which could be recycled. Silicon carbide (SiC) briquettes are used in iron foundries to provide silicon and carbon as alloying elements. In this study, the incorporation of iron foundry dusts in SiC briquettes is investigated. Eight dust types originating from distinct process steps in two foundries were investigated. Their chemical and mineralogical characteristics were determined through X-ray fluorescence, X-ray diffraction, and ICP–OES analyses, supported by wet-chemical determination of iron valence states and carbon–nitrogen–sulfur measurements used to quantify SiC content. Dusts enriched in quartz or iron-bearing phases were selected for briquette formulation trials. In parallel, ground cupola furnace slag and ground granulated electric arc furnace slag were introduced as partial cement replacements to reduce binder consumption and associated CO2 emissions. The mechanical performance of the briquettes was evaluated using compressive strength testing after 48 h and 21 days, as well as a 1.5-m drop test to assess structural integrity. The findings indicate that several dust types can be successfully integrated into SiC briquettes, particularly when combined with slag-based binder substitution. Nevertheless, the substantial variability in Fe and Si phase distributions, the generally low abundance of metallic Fe, and the complex interactions between raw materials, basicity, and strength development underscore the challenges of implementing a robust closed-loop recycling system for heterogeneous foundry dust streams.