Effect of B2O3 on viscosity of high-magnesia blast furnace slag

Metallurgical companies in the Urals account for 50 – 60 % of local raw materials. Its deficit is compensated by the use of materials imported from Central Russia, the Kola Peninsula and Kazakhstan. Replacing them with the local raw materials would increase the competitiveness of metal produced in the Urals, so the question of assessing the possibility of replacing imported raw materials with local ones is very relevant. Such raw materials could be siderite ores from the Bakal deposit. They are not in demand by metallurgists because of their low iron content and high magnesium content. With growth of siderites in a charge the magnesium oxide content in slag increases that influences its viscosity and makes it difficult or impossible to smelt using more than 20 % of siderites. The use of boron oxide has been suggested to liquefy the slag. The synthetic slag containing 26.8 % CaO, 38.1 % SiO2 , 11.8 % Al2O3 , 23.6 % MgO, simulating composition of slag from MMK blast-furnace smelting with the addition of 30 % of burnt siderites is short and unstable. The temperature corresponding to the slag viscosity at the blast furnace outlet (0.5 Pa·s) is 1390 °C and the temperature corresponding to the melting point (viscosity 2.5 Pa·s) is 1367 °C. If boric anhydride is added to such a slag, it becomes long and stable. In the melts, when the proportion of B2O3 is increased from 0 to 12 %, the temperature at which the slag viscosity is 0.5 Pa·s and 2.5 Pa·s decreases to 1260 °C, and 1100 °C, respectively. This makes it possible to significantly increase the siderite content in blast furnace charge.