Process for Treating Sulphureous Zinc Ores in Blast Furnaces by the Addition of Ferriferous Substances.
Year: 1894

page_text: Date of Application, 18th Aug., 1894-Accepted, 1st June, 1895
COMPLETE SPECIFICATION.
Process for Treating Sulphureous Zinc Ores in Blast Furnaces by the
Addition of Ferriferous Substances.
I, ROBERT BIEWEND of Clausthal in the Kingdom of Prussia, Empire of
Germany, Professor of the School of Mines, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
Heretofore, in extracting zinc from zine ores, it has been necessary to first of all
subject the ores to a preliminary treatment with the object of driving out the
sulphuric acid contained in same and which preliminary treatment generally consisted
in roasting the ore in lumps in the open.
This system has very great disadvantages. In the first place, owing to the
sulphureous acid gas given off, all vegetation in the district in which the roasting is
carried on is destroyed; secondly, the time and space required for the operation
are very considerable, and, finally, owing to these and other indirect causes, the
cost of production of zine is very heavy-and this not to speak of the unhealthy
nature of the work.
Attempts have, it is true, been made to carry out the complete process of zine
extraction in a blast furnace so as to do away with the necessity for outside roasting,
but these attempts have not ended satisfactorily owing to the zinc vapors becoming
oxidized by the carbonic acid from the charge or being burned by ferric oxide before
they could be condensed.
The object of any invention is to enable a complete process of zinc extraction
from zinc ores to be carried out in a blast furnace, that is to say without its being
necessary to first roast the ore in the open.
It is a known fact that, at a high temperature, sulphide of zinc is decomposed by
iron in such way that metallic zinc and sulphide of iron are formed and it is on this
fact that I base my process. In other words, my said process is a precipitation
process in that the sulphureous zine ores are directly reduced to metallic zinc in a
blast furnace by the addition of ferriferous substances. These ferriferous sub-
stances can be added either as iron itself or as ferric oxide; in the latter case, the
process is somewhat more complicated as the ferric oxide must first be reduced to
metallic iron.
The main difficulty to be overcome is to prevent the zinc vapors from becoming
oxidized by the carbonic acid from the charge on coming in contact with the air or
from being burned by the ferric oxide when this is used as the addition, and, there-
fore, care must be taken to free the furnace gases of carbonic acid before they enter
the condensing chamber and to fully reduce the ferric oxide before it is allowed to
come in contact with the zinc vapors.
For this purpose, I require a furnace similar to an ordinary blast furnace having
openings for the blast above as well as below, the upper openings being located
preferably near the charging hopper or cone. In this furnace the passages or
canals serving to conduct the gases to the condensers are not placed in the upper
out in the lower part of the shaft and at about one third of its height. The
purpose of this arrangement is to effect the reduction of the ferric oxide in the
apper part of the furnace and to reduce the carbonic acid thus formed by forcing
ame through a sufficiently strong incandescent heat downwards towards the gas
passages or outlet canals. Meanwhile, the zinc vapors passing upwards from
below are also caused to pass through an incandescent heat and are freed of

page_text: carbonic acid before they meet the gases coming from above at the level of the gas
outlet canals.
Any ordinary blast furnace would be suitable for carrying out my process
providing the dimensions of same were sufficient; but, for the sake of clearness, I
herewith give illustration in which A is the shaft, bb, the blast pipes in the under
portion of the shaft, those in the upper portion of the shaft, D the gas outlet
canal, B B' the condensers, C a reserve condenser and a the slag-duct.
When the ferriferous addition is iron, the process is, as previously stated, simple,
and can be carried out as well without as with a blast according to the chemical or
physical nature of the ores. But where ferric oxide is used, there must be a blast
and the reduction of the ferric oxide must be complete after passing through the
incandescent beat on its way down to the gas outlet canals.
In retorts and the like, an excess of coal has a disadvantageous influence on the
process, but this is not the case in a blast furnace as the principal function of
the coal in a blast furnace is to produce the necessary temperature for the process
and not merely to reduce the ferric oxide. Seeing, however, that. a very high
temperature is required, the slag must be of a nature not to melt too easily and I
may here mention that I prefer for the purpose a calcium-aluminium-silicate or a
singulo-bisilicate slag.
Beyond the ore, the ferriferous additions, and the coal, further additions are not
necessary unless the quantity or quality of the earths is otherwise insufficient to
form a suitable slag. If the amount of slag is small, it can be tapped periodically;
but as a rule it can be allowed to run continuously.
The furnace gases which, after the carbonic acid has been reduced, consist of
vapor of zinc, carbonic oxide, and nitrogen, must enter the condensers at a
temperature of not less than 800° C. In order to maintain the gases, at this
temperature, they should not be kept too long in contact with the charge as this
draws the heat from them and it is preferable, therefore, not to place the outlet
canals too high up in the shaft. There ought to be at least two or three outlet
canals for the passage of the gases to the condenser or condensers and they should
be placed at equal distances apart.
As previously mentioned, carbonic acid is likely to be present in the upper part
of the shaft about the twyers; I obtain the necessary incandescent heat for
reducing this carbonic acid by strengthening the blast and by placing the twyers
sufficiently high over the gas outlet canals so that the course of the gases is not too
short. The reduction of the carbonic acid both in the upper and lower part of the
furnace is carried out according to the formula CO2 + C = 2 CO.
As condensers, I prefer perpendicular or inclined shafts of masonry provided at
one end with a coverable opening for filling with coal, coke or other such lumpy
filtering material. The condensers should be roomy and should preferably be
provided with openings underneath whereby they can be emptied and cleaned
periodically.
If one condenser is not sufficient to absorb all the zinc contained in the gases, a
second, and, if necessary, a third condenser must be used, and as the filtering
substance has for its function more in mechanically facilitating the deposit of the
zinc particles than in reducing any oxide of zinc still contained in the gases or any
escaped carbonic acid, it must be such that the gases can leave the condensers
perfectly dust free.
The fluid zinc can be tapped periodically from the condensers.
The zinc-freed gases in the condensers contain only nitrogen and carbonic oxide
and can thus advantageously be used as combustible material for re-heating the
blast or for producing spongy iron or for like services.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed I declare that what I
claim is :-
A process for extracting zine from zinc ores in a blast furnace without the ores

page_text: having to be previously roasted in the open and consisting in smelting the ores with
the addition of ferriferous substances and in reducing any carbonic acid contained
in the furnace gases by passing said gases through an incandescent beat before they
enter the condensers substantially as described.
Dated this 17th day of August 1894.
J. E. EVANS-JACKSON & Co.,
Agents for the Applicant.