A consecutive reaction model and kinetics of cr2o3 reduction from slag by carbon dissolved in molten iron

A first-order, consecutive, two-stage reaction model for the reduction of cr2o3 from slag was developed. The model was applied to the results obtained by studying the effect of various parameters on the rate of reduction of cr2o3 from a CaO-SiO2-Al2o3 slag, by carbon dissolved in molten iron, at temperatures 1400-1550 degrees celcius.The parameters studied were: varying the furnace atmosphere; cr2o3 concertration in slag; metal chromium content; the experimental temperature; slag and metal volume;the presence of the surface-active elements, S or Se and adding FeO and CaF2 to the slag. The progress of the reactions was monitored by taking slag samples at predetermined time intervals, and analyzing them for the relevant species. The results showed that the reduction of cr2o3 from slag takes place primarily at the slag/metal interface, and follows a first-order, consecutive, reversible, two-stage reaction scheme in which (cr2+)is the intermediary product. The rate of (cr3+) reduction remained the same in an argon or carbon monoxide atmosphere whilst an argon atmosphere increased the rate of (cr2+) reduction by a factor of about 1.4,compared to a carbon monoxide atmosphere. The rate of reduction of the chronium species increased with increase in temperature and activation energies obtained were 54.16,27.15 and 81.33 kcal/mol for (cr3+),(cr2+) and cr2o3 reduction. Addition of S or Se to the system markedly increased the attendant increase in the Feo content of the slag. Metal emulsification, which is a consequence of reduced surface-tension of the metal,is thought to be responsible for the increase in the rate of cr2o2 reduction. Addition of FeO to slag decreased the reduction rates of all the chromium species whilst CaF2 addition increased the rate of reduction of the chronium species.The reduction in slag viscosity due to CaF2 addition is thought to be responsible for the increased rates of reduction.