Effect of boron oxide additives on viscosity and melting point of the CaO – SiO2 – Al2O3 – MgO system

The share of local iron ore raw materials of metallurgical enterprises of the Ural region is 50 – 60 %. The rest is brought from Central Russia, the Kola Peninsula and Kazakhstan. The issue of replacing imported raw materials with local, cheaper ones, is very relevant. The extraction of siderite iron ore of the Bakalskoye deposit (Southern Urals), the reserves of which are about 1 billion tons, is many times less than the mining and geological conditions allow because of the insignificant demand for this raw material due to its low quality. The high content of magnesium oxide in the ore makes blast furnace smelting difficult or impossible using more than 20 % of siderites in the charge. The basis of any blast furnace slag is a four-component system CaO – SiO 2 – Al 2 O 3 – MgO with the following composition, wt. %: 30 – 40 SiO 2 , 31 – 49 CaO, 3 – 18 MgO, 7 – 20 Al 2 O 3 . The melting point of such slags is 1280 – 1320 ℃. At a temperature of 1450 °C, their viscosity is about 0.5 Pa·s. An increase in the magnesium oxide content (>20 %) leads to a sharp increase in melting point of the slags, reduces the crystallization interval and makes them unstable. In this regard, the materials made from siderite ore using various technologies for preparing them for blast furnace smelting (raw ore, roasting-magnetic separation, agglomeration) are introduced into the blast furnace charge only as additives. Their share does not exceed 20 %. The effect of boric anhydride on the viscosity of high-magnesia blast furnace slags containing 15 – 36 % MgO was studied using modern methods of statistical processing of experimental data. It was shown that addition of boric anhydride to the initial charge allows to reduce the melting point of the slag and to increase the crystallization interval. This makes it possible to conduct blast furnace smelting on slags containing about 40 % MgO, which corresponds to a siderite share of 40 – 50 % in the initial charge.