Metallic solvent extraction of manganese and titanium from ferroalloys
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I.
INTRODUCTION
E L E M E N T S such as manganese, chromium, titanium, and vanadium form very stable oxides which cannot easily be reduced to the pure metal, and the usual procedure is to purify the oxide or chloride prior to reduction with a more reactive element, such as aluminum. This obviously makes these elements relatively expensive when compared to other metals with similar availability in the earth's crust but which can be extracted directly, either carbothermically or electrolytically. It is possible to reduce manganese, chromium, titanium, and vanadium oxides, in the presence of iron, to form ferroalloys containing about 25 wt pct i r o n . [1'2] Due to this ease of preparation, ferroalloys are much cheaper than the pure metals, but the presence of iron precludes their use in many applications. There is, obviously," a need for a process to selectively remove the element from the iron. Examination of the properties of the iron and the other element, present in the ferroalloy, show that iron is the most noble element, and this gives the opportunity for electrochemical separation, t3] However, even in a fused electrolyte, the alloy is likely to be beneath its melting point, so that the removal of manganese is likely to be controlled by diffusion in the solid state, which is usually very slow. As rates of diffusion are much greater in a liquid phase, it is advisable that the ferroalloy is dissolved in a metallic solvent before subsequent processing. A search of the published phase diagrams shows that there are several noble, relatively low melting point metals which have high solubilities for manganese, chromium, vanadium, and titanium, t4] If the specific case of manganese is considered, the phase diagrams for bismuth-manganese and iron-manganese show substan-
A.J. GODSELL, formerly Research Student, Department of Materials Science and Metallurgy, University of Cambridge, is Senior Scientist with the Transport and Road Research Laboratory, Berkshire, United Kingdom. D.J. FRAY, University Lecturer, is with the Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom. This paper is based on a presentation made in the T.B. King Memorial Symposium on "Physical Chemistry in Metals Processing" presented at the Annual Meeting of TMS, Denver, CO, February 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS. This symposium appeared in the April 1989 issue of Metall. Trans. B. METALLURGICAL TRANSACTIONS B
tial solubility for manganese in bismuth, whereas iron is virtually insoluble in bismuth. In this particular case, bismuth seems to be the ideal solvent for both dissolving manganese and also separating the iron from the manganese. Unfortunately, for other elements mentioned in this paper, there does not appear to be a metallic solvent which will only dissolve the desired metal without also taking the iron into solution. Possible solvents for these elements are lead, antimony, and tin. Having taken the desired element into
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