Iron losses during calcium carbide based hot metal desulphurisation have been studied via large scale investigations of slag from the slag pit as well as slag sampling during desulphurisation at SSAB EMEA in Luleå . The desulphurisation slag, after injection of calcium carbide, is normally solid and contains large amounts of iron. An alkali containing mineral, nepheline syenite, was mixed together with the calcium carbide to form a more fluid slag as the iron losses originate from enclosed metal droplets in the slag as well as drawn off hot metal during slag skimming. The slag amount after slag skimming decreased from 28?1 to 25?1 kg t 21 hot metal with addition of 5 wt-% nepheline syenite to the calcium carbide, and the magnetic fraction of the slag from the slag pit decreased from 2?5 to 1?9%. Finally, no negative effect on the reagent efficiency was observed during the trials with addition of nepheline syenite.

In order to gain an insight into the mixing behaviour of slag and metal under different stirring conditions, samples of slag/metal interface were collected from an industrial 65 ton ladle furnace using a new sampling technique. Different stirring conditions and sampling positions in the ladle were chosen. Complementary cold model experiments were also performed. The experimental results strongly suggested that the shear force between the two liquids played an important role in slag-metal mixing. Evidence for the existence of slag droplets each surrounded by a very thin metal film was found in the samples taken under both gas stirred and induction stirred conditions. This observation strongly suggested that slag-metal system behaved similarly as oil-water system, wherein, the shear force owing to the bulk flow led to a packed 'sphere bed' of oil droplets each coated by a thin water film above the water bath. On the basis of the experimental results, preliminary mathematical models were developed to describe the rate of mass exchange at the slag/metal interface.

The thermodynamic activities of SiO(2) in Al(2)O(3)-SiO(2) liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863-2169 K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF(2) standard. The mass spectra obtained for pure SiO(2) were in agreement with earlier data. The activities of silica, measured in the present work at 2150 K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al.

Laboratory experiments were carried out to study the phenomena related to open‐eye formation in ladle treatment. Ga‐In‐Sn alloy with a melting temperature of 283 K was used to simulate the liquid steel, while MgCI2‐Glycerol(87%) solution as well as HCl solution were used to simulate the ladle slag. No open‐eye was formed at lower gas flow rates, but, occurred when gas flow reached a critical rate. This critical gas flow rate was found to depend significantly on the height of the top liquid. No noticeable amount of top liquid was observed in any of the samples taken from the metal bulk during gas stirring. To confirm this aspect, samples of slag‐metal interface were taken around the open‐eye in an industrial gas stirred steel ladle. No entrapped slag droplet was found in the solidified steel within the region between the interface and 2 cm from the interface. The accordance of the laboratory and industrial results suggests that the entrainment of slag into the steel bulk around the open‐eye cannot be considered as the major contribution to inclusion formation.

Experiments on a vanadium recovery method from vanadium containing BOF‐slag using both a Tamman furnace (3 kg scale) and an induction furnace (150 kg scale) were conducted. The vanadium was extracted into the slag phase by bubbling oxidation gas into a metal bath consisting mainly of V (1–10 mass%), Si (less than 1 mass%) and P (about 1 mass%). The first experiments revealed that the slag formed during oxidation reaction had considerably high phosphate capacity. High phosphorus content would rule out the possibility of using the slag as a raw material for the production of ferrovanadium of high quality. In order to reduce the P‐content in the slag, addition of slag former to reduce phosphate capacity was necessary. A suitable slag system (having the initial composition 40 mass% Al2O3 ‐ 25 mass% CaO ‐ 35 mass% SiO2) and a suitable atmosphere, by using CO2, that enhanced the oxidation of vanadium, but limit the oxidation of iron and phosphorus was found. However, more efforts should be put forward, e.g. study of the phase diagram, the viscosity of the slag and even oxide activities to gain more insight into the slag formed by selective oxidation.