Phase equilibria in the system “MnO” – CaO – SiO2 – Al2O3 – K2O relevant to manganese smelting slags

Abstract

Abstract K2O introduced with manganese ore is redistributed by evaporation and condensation within submerged arc ferromanganese smelting furnaces. To characterise the phase equilibria relevant to these slags experimental studies have been carried out to determine pseudo-ternary sections of the form “MnO” – CaO – (SiO2 + Al2O3) with a fixed Al2O3/SiO2 weight ratio of 0.65 and 6.0 wt.% K2O for temperatures in the range 1523 – 1673 K. It was found that the presence of K2O in the slag decreases liquidus temperatures relative to those of K2O-free slags in the anorthite and gehlenite primary phase fields at low MnO concentration; at higher MnO concentration however the KAlSiO4 and KAlSi2O6 phases are formed maintaining the liquidus above 1500 K. The manganosite primary phase field is expanded in the direction of increased (Al2O3 + SiO2) and the liquidus temperatures in the manganosite primary phase field are increased significantly with the presence of K2O in the slag.