Development of a Process for Dephosphorisation of High Carbon Ferromanganese

The bulk of high carbon ferromanganese produced in India continue to have more than 0.35% phosphorus
since they are produced by carbothermic reduction process. The low phosphorus manganese ores are depleting
fast and ferromanganese manufacturers will have no option but to use medium and low grade ores having
high phosphorus content resulting in high phosphorus in the product. A systematic study was taken up at NML
to solve this problem. Initially, a thermodynamic analysis was carried out for which Ba-P-O ternary predominance
diagrams were constructed at several temperatures to predict the most suitable conditions for selective
removal of phosphorus from high carbon ferromanganese. These conditions required a usage of a flux having
a high level of basicity, moderate oxygen potential as well as low melting temperature. The experimental results
showed that it was possible to remove phosphorus from high carbon liquid ferromanganese 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 subsequent study carried out at the laboratory scale 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 was felt that the handling of pellets under plant conditions would be easier
and also eliminate the loss of flux as a dust, which occurs when powder is added. These pellets were forced
towards the bottom of the melt for better efficiency. For this purpose, a plunging system was designed and
fabricated in-house that helped in reducing the flux consumption to less than 5% and also improved the kinetics
of the process. The desired results were achieved within 10 minutes of the addition of the flux. The
know-how is ready for transfer to interested parties and authors are willing to conduct large scale trials with
them.