The level of undesirable residual elements (Cu, Sn, Ni , Mo, P) is
increasing to an unacceptable level and it is anticipated that other
elements such as (Pb, As, Sb, Bi) will become a problem in the future.
At present this problem is avoided by steelmakers by careful selection
of scrap, but this may not be possible in the future.
There are a number of processes proposed in the past, for the removal
of residuals, but none have been seen as sufficiently attractive for
adoption by the industry. One such process involves the use of high
calcium fluoride fluxes under highly reducing conditions for the removal
of Sn, Pb, Sb, As and Bi. The thermodynamics of this process have been
thoroughly investigated and successful removal of the element M, can be
achieved by the reaction:
xCaO + yM = CaxMy + x/2O2
This study will employ calcium injection to ensure an extremely low
local oxygen potential and rapid reaction kinetics, in combination with
a top slag to absorb the reaction products.
Each of the following critical components will be studied
The rate of reversion from the top slag at higher oxygen potentials
is seen as critical to the process and will comprise a major part of
this study. Data from this phase of the investigation will then be used
in conjunction with kinetic data from injection experiments to develop a
model of the entire process. With positive results from this phase of
the work, plant trials will be proposed.
To investigate the feasibility of tin removal using a combination of,
deep injection of calcium, and a basic top-slag, and ultimately to
develop a process that will allow a greater proportion of high tin scrap
to be used by steelmakers. In order to evaluate such a process the
following questions must be answered:
1. Are the kinetics of such a process sufficiently fast? Whilst
extensive thermodynamic investigations indicate that the process is
feasible there has been no study of the kinetics.
2. Is it necessary to employ high fluoride fluxes?
3. Can a sufficiently low oxygen potential be achieved? Very high
partition ratios have been measured but these required an oxygen
potential of 10-24 and to achieve acceptable partitions
10-22 would be required.
4. Can magnesium be used as a substitute for, or in addition to
calcium and what are the relative advantages?
Benefits of Proposed Research
The "problem" of residuals has been discussed for a number of years,
but in general steelmakers have managed to avoid the problem by
selecting appropriate scrap. Whether the problem can be circumvented for
the foreseeable future is not clear, nor is the cost of avoiding the
problem as opposed to confronting it. Therefore, currently it is not
possible to put a dollar value on the outcome of this proposal but it is
clear that current trends will serve to make the problem worse, and a
solution of the type proposed more attractive.
As the percentage of the worlds steel from electric steelmaking
increases, the ability of steelmakers to pick and choose scrap will
decrease, and the capacity to control residuals will be required to
provide a level of flexibility. In addition, the proposed process will
increase the percentage of total product that can be recycled, a
requirement that is continually being increased by governments.
The research program will be conducted in three phases, two
laboratory based and one in-plant. The details of the plant study are
dependent on the results from the laboratory work but will essentially
be a validation stage. The industrial sponsors have expressed a
willingness to carry out full-scale plant trials. The possibility of
using pilot plant facilities available at Argonne National Labs is also
The laboratory studies to be carried out in parallel, will
1) a fundamental study of slag metal reversion kinetics under a
controlled atmosphere, as a function of slag composition, and oxygen
and 2) a study of reaction kinetics during calcium injection with and
without a top slag.