SHS Processing of cyclone ferrosilicium dust

Abstract

This paper offers a review of waste disposal techniques for disposing of dust generated by ferrosilicium industry. The paper examines the possibility of nitriding cyclone ferrosilicium dust through application of a high-pressure infiltration combustion process. The authors describe the key regularities of the ferrosilicium nitride SH-synthesis and demonstrate the potential applicability of the new technique. The findings show that the high-grade dusts resultant from ferrosilicium crushing and screening operations and identified as FeSi65 and FeSi75 consist of iron and silicon disilicides, whereas the dust coming from a 45 % alloy consists of FeSi2 and FeSi. Interaction of the initial alloys with nitrogen in a high-pressure combustion mode results in the generation of high-nitrogen material with the β-phase of silicon nitride at the basis. Such material can be used as unmolded refractory material for application in blast furnaces. Or it can be used to produce nitrogen containing steels, such as transformer steel. Thus, the dust grade PUD-75 would be optimum for application in refractories, and the dust grade PUD-65 — as an alloying component. The paper demonstrates that the composition of the cyclone ferrosilicium dust combustion products can be changed by changing the nitrogen pressure and the dispersity of the burden. Silicon nitride constitutes the main component in the composition of the combustion products (60–85%). It will be iron that will serve as a binder in this composite at the highest nitrogen saturation degree, whereas in the case of a lower nitrogen saturation degree it will iron silicides. It was found that nitrogen is absorbed in two stages during layer-by-layer combustion of ferrosilicium alloys. Passing of the combustion front is followed by the process of bulk post-reaction, during which the share of absorbed nitrogen can increase by 30%. This phenomenon explains why there exists no dependence between the concentration of nitrogen in the combustion products and the applied pressure.