Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1977-02-07
1985-02-19
Lewis, Michael L.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 84, 75 21, 423 58, 423 61, 423118, 423378, C22B 102
Patent
active
045003505
ABSTRACT:
In the disintegration of a chromite or chromium-containing residue, wherein the chromium-containing material is disintegrated with an alkaline compound in the presence of oxygen and a diluent at a temperature above about 800.degree. C. and thereafter leached, the improvement which comprises pre-roasting the chromium-containing material prior to addition of the alkaline compound. Pre-roasting can be effected at 400.degree. to 1200.degree. C. with addition of certain amounts of silica dioxide and/or aluminum oxide and such additives, depending on the chromium containing material, if still required, are added--prior to disintegration and leaching--in such a quantity to establish a ratio of SiO.sub.2 : AL.sub.2 O.sub.3 of about 2:1 and further a ratio, calculated on the basis of NaOH as the alkaline compound, of SiO.sub.2 : Na.sub.2 O of about 1:0.5 plus a Cr.sub.2 O.sub.3 : Na.sub.2 O ratio of about 1:2 to 1:4. Residues from previous leaching cycles can be present during disintegration as solid diluents but their contents of SiO.sub.2 and/or Al.sub.2 O.sub.3 are not taken into account in calculating the SiO.sub.2 :AL.sub.2 O.sub.3 ratios. The process gives excellent results even with starting materials relatively high in SiO.sub.2 which are difficult to disintegrate to materials of desirable properties by other methods.
REFERENCES:
patent: 3510256 (1970-05-01), Shafer
patent: 3812234 (1974-05-01), Shafer et al.
patent: 3859412 (1975-01-01), Okabe et al.
Udy, M. J., Chromium, vol. I, Rheinhold Pub. Corp., p. 265, (1956).
Bockelmann Wolfgang
Meussdoerffer Johann-Nikolaus
Nieder-Vahrenholz Hans-Georg
Niederprum Hans
Bayer Aktiengesellschaft
Lewis Michael L.
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