| Summary: | Factors influencing the equilibrium phosphorous distribution, Lp, and phosphide
capacity, CP
3-, of ferromanganese smelting slags in highly reducing atmospheres were
studied in this research work at 1500oC (1773oK). The research work seeks to extend
the concept of slag capacities to submerged electric arc furnace operations used in the
production of ferromanganese alloys. The concept of slag capacities has been used
fairly widely in the steelmaking industry particularly in ladle technology processes to
control various impurities including sulphur and phosphorous.
Equilibrium experimental runs were conducted in graphite crucibles under two
different atmospheres, CO and Ar/CO mixture at 1500oC. The resultant partial
pressure of oxygen in the two atmospheres was 1.223x10-16atm. and 7.826x10-19 atm.
respectively at 1500oC. The compositions of the slag samples were determined using
the extreme vertices design method for mixture experiments. The composition of
ferromanganese slag samples was in the following range, MnO 5-10 wt. %, SiO2 36-
54 wt. %, CaO 18-36 wt. %, P2O5 1-4 wt. %, and Al2O3 and MgO were fixed at 5 wt.
% and 10 wt. % respectively. Three types of alloy samples were made and their
composition was in the following range Mn 70-85 wt. %, Fe 6-18 wt. %, Si 1.5-4.5
wt. % and C was fixed at 7.5 wt. %.
The analytical results of the final equilibrium slag and metal samples were used to
calculate the equilibrium phosphorous distribution ratios, Lp, and these were used in
turn to calculate the slag CP
3-. The results for Lp, and CP
3-, were further used to derive
empirical models to predict Lp and CP
3- as functions of slag composition using
statistical modeling. Graphs were compiled to determine the effect of varying the slag
composition on Lp and CP
3- parameters. Increasing the SiO2 content in the slag
reduced slag basicity which led to a decrease of the slag Lp and CP
3- parameters.
Increasing the slag basicity under both atmospheres led to an increase of both Lp and
CP
3-. Increasing slag CaO content, a basic oxide, led to an increase in both Lp and
iv
CP
3- parameters of the slag. The ferromanganese slag Lp and CP
3- parameters
decreased with a reduction of Po2 in the controlling atmosphere. Therefore an overall
increase in slag basicity resulted in an increase of Lp and Cp3- under both
atmospheres. An overall decrease in slag basicity resulted in a decrease of Lp and
Cp3-.
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