Characterization of an atypical intermediate layer formed in Vanyukov furnaces during smelting of charges with a high content of technogenic materials

The growing need for recycling, along with the depletion of high-grade ore concentrates, has led to the inclusion of previously accumulated technogenic materials — such as metallurgical slags, sludge from settling ponds of recirculating water systems, and similar waste – into the charge of primary smelting units. The share of such feedstock in the furnace charge now reaches approximately 25 %, which has resulted in serious technological disruptions to the stable operation of primary autogenous smelting units. In Vanyukov furnaces, this is manifested by the appearance – alongside the typical smelting products (matte and slag) – of a new atypical phase, the so-called intermediate layer. The formation of this layer leads to adverse effects, including the obstruction of flow paths from the furnace hearth to the slag and matte siphons, ultimately causing a complete shutdown of the unit. A sample of this abnormal product, collected from an industrial furnace during a period of process instability, was analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). These methods allowed the determination of temperature ranges corresponding to phase transformations of the components comprising the intermediate layer. The results obtained can be used to define optimal parameters for stable smelting operation and to develop technical solutions that prevent conditions favorable for the formation of refractory accretions.