Recycling MgO–C refractories and dolomite fines as slag foaming conditioners: experimental and thermodynamic evaluations

Abstract The slag foaming process is currently applied in the steel production due to its greater benefits, i.e., reduction of energy losses, enhancement of the refractory service life and productivity, etc. Lime/dolomite, oxygen and carbon are usually added during an electric arc furnace (EAF) operation to adjust the liquid basicity and saturation and also provide suitable conditions for foam generation. Considering the high concentration of MgO and C contained in spent MgO–C refractories and dolomite fines (derived from rotary kilns), one good alternative consists of recycling those materials as slag conditioners. In this work, experimental tests and thermodynamic calculations (phase equilibrium, viscosity and isothermal solubility diagrams) were carried out in order to define the impact of some mixtures (comprised mainly of ground MgO–C spent bricks, dolomite fines and coke) on the foaming behavior of a molten synthetic slag at 1700 °C. Based on the attained results, recycling MgO–C bricks and dolomite fines led to faster slag saturation and provided suitable conditions for foam formation. Furthermore, the increase in FeO content in the liquid portion of the slag compositions presented a clear correlation with the measured foam height, indicating that this oxide plays a major role in the foaming phenomenon.