Sulphide capacity measurements of slag with MgO content up to 18 mass% were carried out at 1713, 1743 and 1773 K to obtain reliable data for the blast furnace process. In the measurement, the slag is equilibrated with copper at a controlled oxygen partial pressure for 24 h. The sulphide capacities are calculated based on the sulphur analyses for both slag and copper.
Experiments were conducted to investigate the possibility of removing sulfur from used ladle slag by oxidation. Slag samples (solid, two-phase mixture, and liquid with a small fraction of solid MgO particles) were subjected to an oxygen-rich atmosphere in the temperature range 1373-1673 K. The sulfur removal from the samples of solid and two-phase mixture was found to be a slow process due to the slow diffusion. The sulfur removal was found to have little dependence on temperature in the range 1373-1573 K. When the slag was mostly liquid (at 1673 K), the sulfur removal was significantly increased. More than 85 % of the sulfur could be removed after 60 min of oxidation in pure oxygen. An increase in oxygen partial pressure was found to increase the desulfurization slightly. Increasing the Al 2 O 3 content in the slag decreased the degree of sulfur removal.
An investigation of the nitrogen pickup of liquid steel from ladle slag after vacuum degassing was made. Nitride capacities, CN, of a number of ladle slags were determined at controlled nitrogen and oxygen potentials at 1873 K. The nitride capacities in the composition range studied were found to be very low. In accordance with the literature, the nitride capacity was found to increase with increasing SiO2 content. Industrial trials were performed. The nitrogen content of the steel was determined before and after vacuum degassing as well as after the waiting period. Three different trends of the variation of nitrogen content in the steel were observed. Both the laboratory study and the industrial trials revealed that the transfer of nitrogen from slag to steel was not the reason for nitrogen pickup in the steel subsequent to vacuum degassing.
During refining of silicon using slag treatment, boron dissolved in the silicon is extracted to a liquid oxide (slag) phase. In this investigation the partitioning of boron between SiO2–CaO–MgO slags and liquid silicon was examined at 1873 K over a range of slag compositions and CO–N2 gas mixtures. It was found that the distribution of boron is strongly dependent on the nitrogen partial pressure as well as the slag composition. The greatest partition ratios were achieved at 0.6 atm CO/0.4 atm N2 with low silica content in the slag. The concentration of MgO in the slag seems to have little or no impact on the boron partition ratio.
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