Dephosphorization of Mn‐based alloys

Abstract

The critical oxygen partial potential of dephosphorization in liquid Mn‐base alloys under oxidizing or reducing conditions has been determined by thermodynamic analysis. Under oxidizing conditions, thermodynamic conditions to achieve dephosphorization and avoid manganese oxidizing were given. The results of thermodynamic analysis show that BaO‐base slag can be an effective dephosphorization agent for Mn‐base alloys. Under reducing conditions, the high degree of dephosphorization in Mn‐base alloys can be obtained based on thermodynamic analysis. In experimental work, BaCO3 was added to remove phosphorus from Mn–Fe–C melts. The time needed for equilibration of the dephosphorization reaction of Mn–Fe–C melts was determined at 1573, 1623 and 1673 K. The refining results were experienced as dephosphorization efficiency ≠p = (%[P]0 − %[P])/%[P]0. Moreover, the effect of the initial content of Si and C on ≠p was investigated. ≠p in the Mn–Fe–C melts was also given as a function of temperature. Dephosphorization reaction in Mn–Fe–C melts is of first order.

Thermal physical properties and dephosphorisation kinetics of rare earth oxides containing slags

“…Dephosphorisation in the gaseous form is not applicable because the partial pressure of manganese is higher than that of phosphorus at smelting temperature [3]. The reaction product of dephosphorisation under reducing conditions is phosphide, which produces toxic phosphine when it comes in contact with atmospheric moisture [4].…”

“…Several investigations have been carried out to identify the most adequate composition of the slag for oxidation dephosphorisation. Of the various flux systems reported in the literature [1][2][3][4][5][6][7][8][9][10], CaO-based slags have been considered to yield a low overall efficiency, with a degree of dephosphorisation that never exceeds 15%, due to their low phosphate capacity. The Na 2 O bearing agent is usually considered to be much more basic than CaO, but it is unstable at high temperatures, resulting in a high oxygen potential and consequent loss of manganese from the original ferromanganese.…”

“…BaO-based slags have been those most commonly used for the dephosphorisation of ferromanganese because of their high phosphate capacities [6]; however, they have not been applied in the industry because the silicon content in ferromanganese affects the dephosphorisation efficiency too strongly. It is known that a silicon content above 0.25 wt.% hinders the dephosphorisation efficiency [4]. For these reasons, it is necessary to develop a ferromanganese dephosphorisation slag that has a low melting point, high phosphate capacity, and whose physicochemical properties are not significantly affected by the ferromanganese composition.…”

Phosphorus distribution between rare earth oxides containing slags and ferromanganese alloy

“…The removal of phosphorus in the gaseous form is not possible because the partial pressure of manganese is higher than that of phosphorus at smelting temperature [3]. The dephosphorisation product under reducing conditions is phosphide, which produces toxic phosphine when it comes in contact with moisture [4]. Dephosphorisation under oxidising conditions contributes to manganese loss because manganese oxide is more stable than phosphorus oxide [3].…”

Thermodynamic Assessment of Liquid Mn–Fe–Si–C–Ca–P System by Unified Interaction Parameter Model

“…[2][3][4][5][6] Several investigations had been carried out about the oxidizing de-P of ferromanganese with slags containing BaO. [7][8][9][10][11][12][13] However, the conventional oxidizing dephosphorization (de-P) is not feasible for manganese ferroalloys, especially for silicomanganese ferroalloys, due to the inevitable prior oxidation of manganese and silicon. Thus, reducing de-P should be applied for manganese ferroalloys using alkaline earth metals or their compounds, [14][15][16][17][18][19] for example, Ca-Si alloy.…”