Roasting Sulphurous Iron-Ore. [Volume: 8, Issue: 4, 1889, pp. 208-218]

No. 4.]

CHARCOAL IRON WORKERS.

211

the oxygen of the SO2 is used for the higher oxidation of the iron,
basic sulphates of iron oxide are formed, and SO2 vaporized; on
still further raising the temperature, the basic iron salt is also decomposed, SO2 driven off, and oxide of iron remains behind."
In general, the above-described experiments agree with this statement of Ledebur. But it must be remembered, that in saying that
" half the sulphur is volatilized " at a low heat, he evidently means
the one atom of sulphur in FeS2. This, however, only reduces the
sulphur from 53.33 per cent. in FeS2 to 39.66 per cent. in Fe8S9.
My tests have shown that this is the actual result, although with a
white heat, without air, I have succeeded in reducing the sulphur
to a somewhat lower point.
From the two tables given it appears that, for proper desulphurization of pyrites air is absolutely necessary, and of greater importance than an excessively high temperature.
Experiments made by Dr. F. Menges, of Pennsylvania College,
Gettysburg, Pa., as to the amount of air needed for proper desulphurization of FeS,, show that with ample air-current all sulphur volatilized will readily burn to SO2, and that in a deficient
air-current any sulphur condensed will be subsequently removed.
In view of the fact that many furnace-men are under the impression that pyritiferous ores can be largely desulphurized in the upper
part of the blast-furnace, the following experiments were made:
Samples of pyrite were heated in a current of gas taken from the
" down-take " flue of a furnace. The gas had the following composition by weight, and gave results as below:
Per cent.
Carbonic oxide,. 31.17
Carbonic acid,..... 10.06
Nitrogen,........ 58.72

Approximate Duration Per Cent. Per Cent. of
Temperature of Sulphur in Loss. Total Sulphur
in Deg. Fahr. Heat. Residue. Expelled.
Original Pyrites............................ 53.42....................................
1250 10 min. 41.14 12.22 22.98"
"d 1 hr. 33.93 19.48 36.68
1800 25 min. 33.88 19.54 36.58