Abstract
This paper presents the results of a study of the strengthening of iron ore raw materials obtained by oxidative roasting of granules and pellets using gaseous fuel and agglomeration with combustion of solid fuel in the agglomeration layer. Differences in the mechanisms of mineral formation of granules, pellets and agglomerates appear at the stage of liquid-phase strengthening and are due to the different role of iron in forming the strengthening melt. At the same time, in the agglomerate, granules and pellets, iron is in different valence states, affecting the processes' features. Iron can be in a trivalent state in the iron-silicate melt of granules and pellets and is not a silicate-forming component of the charge. The silicate compositions of the binders in the entire studied range of basicities (0.3-1.5) are located along the line of the CaO–SiO2 connection, which is determined using the phase diagram of the CaO–Fe2O3–SiO2 system. During agglomeration, the silicon-containing melt is formed under conditions of excess FeO, which directs the process of mineral formation during the creation of the iron-silicate binder of the agglomerate. Under standard agglomeration conditions, silicate binders with a basicity of 1.0-1.5 are formed in the olivine field of the CaO–FeO–SiO2 phase diagram, covering a wide range of compositions. The processes of mineral formation in batches, by hardened methods, both during the firing of granules, pellets, and during agglomeration, have shown that changing the oxidation potential of the gas phase is an effective lever on the path not only to improving the properties of ferrous sand - a waste product of alumina production, but also to creating both new binders and new types of iron ore raw materials suitable for smelting ferrosilicon.