Selective removal of phosphorus from high carbon ferromanganese - an improved process

Abstract

The presence of phosphorus is known to deteriorate the mechanical properties of cast steel and other metallic products. Ferromanganese, used as the last additive during steel making, is one of the main sources of phosphorus contamination. Therefore phosphorus has to be removed from the ferromanganese before it is used as a deoxidizing and alloying agent. The bulk of high carbon ferromanganese produced in India continues to have more than 0.35% phosphorus since they are produced by carbothermic reduction process. A systematic study by NML showed that it was possible to remove phosphorus from high carbon liquid ferromanganese successfully from 0.56% to 0.18% using BaCO3 based fluxes at the rate of 16-wt% of the ferromanganese charged. However, the Mn loss varied in the range of 2-5%. The objective of the present study was to optimize the flux consumption as well as minimize the Mn loss with effective dephosphorization by using BaO based calcined pellets instead of BaCO3 based powders. It is easier to handle pellets under plant conditions and eliminate the loss of flux as a dust, which occurs when powder is added. These pellets can be forced towards the bottom of the melt for better efficiency. Another advantage of using pellets is that it utilizes manganese ore fines, which is a waste material in the ferromanganese industry. The results have shown that the addition of moderate amount of MnO into the pellets reduces the Mn loss while it helps dephosphorization. The results achieved indicate that it is possible to achieve more than 60% phosphorus removal using flux addition at 5% by weight of the ferromanganese charged.