An Improved Process of Manufacturing Sulphuric Acid.
Year: 1898

page_text: Date of Application, 14th Oct., 1898--Accepted, 7th Jan., 1899
COMPLETE SPECIFICATION.
An Improved Process of Manufacturing Sulphuric Acid.
I, AMÉDÉE SEBILLOT, Engineer, of 60. Boulevard de Clichy, Paris, France,
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 follow-
ing statement:—
In the treatment of ores, by the wet process, divers reactions are used in which
acids play the principal part. Sulphuric acid is the most energetic and rapid
agent for producing the solution of the metallic salts from which the metal is
afterwards taken either by precipitation or by an electrolytic process. Especially
for copper ores, the hydro-metallurgical process, permits of the metal being
extracted at a very small cost, in a condition for disposing of large quantities
of water charged with sulphuric acid; in fact, with the oxidised or carbonated
ores the dissolution is complete and the copper is got by precipitating it with
iron.
With the sulphuretted ores, such as copper pyrites, a part of the copper is
transformed into sulphate by the roasting itself whilst the remainder of the
copper passes into the state of oxide and is easily made soluble by means of
dilute sulphuric acid in a cold state.
It is clear that if sulphuric acid could be had at a low price near the mines,
the metals; fit to be converted into sulphate, could be extracted at such a low
cost as would completely change the present condition of affairs.
With regard to copper mines especially the yield is never very high; ores
with 10, 15, or 20% are the exceptions, and it may be said that the average ores do
not yield more than 5% of metal, and often, indeed, the average yield is much
lower. Such ores do not pay when the cost of transport to the works and the
cost of dressing is taken into account and this is the reason why many copper
mines have had to be shut down as the full value of the ore is not realized. The
difficulty then is the production of sulphuric acid at the mines which, at present,
cannot be done owing to the process in vogue requiring the employment of lead
chambers which are very costly to fit up and which require a special staff to work
them and for these reasons it has not been practicable to use them in the proximity
of the mines.
In view of the above facts it is perfectly clear that some other mode of treatment
must be devised for the production of sulphuric acid in which the use
of lead chambers or the employment of nitrate is not necessary. This has been
attempted by various persons some of whom, by their processes, have been par-
tially successful. All the attempts heretofore have, more or less, been founded
upon a due consideration of the following facts:-
When in contact with moist air sulphurous acid is so easily transformed into
sulphuric acid that solutions of sulphurous acid can only be kept with difficulty.
This reaction is facilitated by the presence of porous bodies such as pumice-
stone or coke. Even, when dry, sulphurous acid and oxygen combine when
the mixture is passed over spongy platinum or certain metallic oxides.

page_text: Starting with these data, warks have been established in which the sulphurous
acid is conducted to the base of a column filled with coke and upon which water
is allowed to run. About thirty years ago Mr. Petrie, of England, manufactured
sulphuric acid by this simple process which has however not come into general
use owing to the fact that the result was incomplete; the transformation of the
sulphuric acid was only partial and only a very weak acid could be obtained
which had to be concentrated in order to give it commercial value. Such are
the reasons for the non-adoption of this process by sulphuric acid manufacturers.
The fact however is proved that it is possible to obtain acid waters by this process
which can be used for the metallurgy of copper owing to the fact that sulphuric
acid, for such purpose, is never employed except in dilute solutions.
But, on the other hand, are the defects which attend the process of conversion
by the direct action of the air irremediable? I think, on the contrary, that this
process can be so improved that results equal to those obtained by the use of
lead chambers can be obtained.
Why is the transformation of sulphurous acid into sulphuric acid not complete?
It is, in my opinion, because it is necessary that atmospheric air, sulphurous acid,
and vapour of water should be in the presence of each other and thoroughly
mixed, and that in the proportions required by the composition of the acid.
Moreover it is well known that sulphuric acid decomposes when subjected to
a dull red heat; whereas, on the other hand, the combination is a slow one at
a low temperature. It therefore follows that the mixture of sulphurous acid,
atmospheric air, and vapour of water must be maintained between two degrees
of temperature; the one below the dull red heat, and the other, which must be,
according to theory, above the point of ebullition of monohydratic acid.
The improvements which I am now going to describe are based upon the afore-
said fundamental rules and the rigorous carrying of them out will essentially
modify the reactions in such a manner as to realize the complete transformation
of the sulphurous acid into sulphuric acid at a degree of concentration analogous
to the acids produced by the use of lead chambers.
These improvements are represented in vertical section at Fig. 1 and in plan
at Fig. 2 of the annexed drawings.
In the system represented there are two distinct stages; the production of
the sulphurous acid and its transformation into sulphuric acid. Whilst I will
subsequently return to the description of the special furnace, as represented in
the drawing for the production of the sulphurous acid, I may say that the
sulphurous acid, mixed with atmospheric air more or less deprived of oxygen,
passes from the roasting furnace A, (which latter may be of any suitable kind
such as either the pyrite furnace in use in sulphuric acid works, a reverberatory
furnace, or the special type of furnace shown in the drawings) through the pas-
sage B into a chamber C divided horizontally by perforated plates D, D, D,
made of ceramic material or volvic stone (i.e. lava). These plates or shelves
each carry a layer of coke or pumice-stone or a metallic oxide capable of facili-
tating the reaction. The mixture of gases passes subsequently through the lower
passage E into a second chamber arranged in the same manner as the first one,
but, in this case, the gases pass upwards from below and escape through the
flue to the chimney G which may be the chimney for the boiler of the works.
In order that the draught in the chimney may not be interfered with the gases
pass out by the vertical flue M and by it are directed upwards.
With the apparatus arranged as aforesaid the gaseous mixture (which, at this
initial stage, is at a temperature usually of from 400° to 500° and is composed
of sulphurous acid, nitrogen, and a variable quantity of air not burnt) is first
conducted to the top layer of pumice-stone in the chamber C and, as it is now
necessary to give the mixture oxygenated air and vapour of water in the pro-
portions required for the proper formation of sulphuric acid in a state of hydra-
tion the most suitable for the condensation of the sulphuric acid, this is effected
by allowing vapour to pass through the pipe H into the vapour receptacle i

page_text: from which the vapour escapes through numerous small nozzles, and, at the
same time, air, in suitable proportions, is conducted through the pipe J to the
air receptacle from which it issues through numerous orifices corresponding to
the vapour nozzles. As a result of this treatment a mixture is obtained which
contains all the constitutive elements of sulphuric acid. The tentperature is
regulated by the volume of air introduced and the volume of vapour which be-
comes superheated and absorbs a portion of the heat in excess.
The mixture in its passage downwards from the first layer of pumice-stone to
the second one and from the second to the third traverses free spaces in which air
pipes K or vapour pipes L are arranged by means of which the temperatura
and the composition of the mixture can be regulated. The mixture must arrive
at the bottom of the chamber at a temperature which varies according to the
degree of concentration required-the water in excess of that required to
form SO, HO remains in a state of vapour in the passage leading from the
first to the second chamber. The function of this second chamber is to condense
any acid which may not have been transformed in the first chamber and thus
the last traces of acid will be transformed and can be gathered together by con-
densing the vapours which penetrate through the bottom of the chamber. To
effect this condensation water is allowed to fall in a spray at the top of the
chamber in a quantity just sufficient to condense the vapour and obtain acid
solutions for diluting. The surplus gases escape by the chimney as aforestated.
It may be here stated that the transformation of sulphurous acid into sul-
phuric acid is brought about even when cold but in this case less energetically.
The apparatus afore described constitutes an essential part of the system and
its arrangement is both necessary and invariable; such however is not the case
when making sulphurous acid.
Two things have to be distinguished; the manufacture properly so-called of
sulphuric acid viewed from an industrial standpoint, with the object of
obviating the use of lead chambers, in which case the ovens used may be those
generally employed for burning pyrites, although, when ores have to be treated,
reverberatory furnaces can be used on the condition that they are provided with
means for producing a very strong draught, such as a draught chimney or a fan
or blower, but the difficulty of regulating the draught, owing to the opening
and shutting of the doors, is well known whilst it is absolutely necessary that
the quantity of air and vapour admitted should be carefully regulated; and,
also, the new type of furnace which completes the transforming apparatus. This
furnace in every case possesses great advantages both from the point of view of
workmanship and fuel combustion, and it is, in many cases, absolutely in-
dispensable.
The new furnace, which is illustrated at Figs. 1 and 2 of the drawings, con-
sists of a chamber A of rectangular section in which the ore is charged alter-
nately with the fuel in the same manner as in ordinary blast furnaces. At a
convenient height the openings P', are arranged which serve as passages for
the air introduced by the pipe Q or forced in by a fan. Slide valves R, R, R,
are so placed as to distribute the air at the proper height according to the
working condition of the furnace. The air thus introduced must be sufficient
to burn the fuel and roast the ore. The products produced by the roasting
escape through the passages S, S, S, into the reaction apparatus in order to be
treated in the manner already described.
The descent of the charge is regulated by the extraction of the roasted ore
that falls down and is drawn,out through the doors T, T.
This roasting furnace can be used whenever the ore contains sufficient sulphur
to make it worth while transforming it into sulphuric acid. When there is
only a small proportion of sulphur in the ore it is better to lose the sulphurous
acid. This is the case with some ores of mercury.
This furnace will be found of great advantage when treating ores to obtain
mercury as it is well known that mercurial emanations are very dangerous, and,

page_text: の
further, it is also known that very great loss occurs through the doors and fissures
of such furnaces as are used in connection with the mines of Idria, Almaden,
and other places.
com-
The improved furnace obviates these inconveniences and drawbacks
pletely. Fig. is an illustration of the furnace as arranged for treating mer-
curial ores.
In this case the furnace A, which is similar to that illustrated
at Figs. 1 and 2, is enclosed in a casing of sheet iron, the chambers with the
porous material therein are done away with and the flue B is so arranged as to
lead the products produced by the roasting directly into the condenser U in
which the gases travel downwards between the inclined plates V as indicated
by the arrows. The plates are made of sheet iron and a water spray falls
upon them from the perforated pipe X. The mercury collects in the reservoir Y.
In the case of other ores from which sulphuric acid has been obtained by
roasting it is only necessary to effect the sulphatation of the metallic oxides and
the precipitation of the metal. For instance, in the case of copper, the roasted
product contains a part of the copper in the state of sulphate. If the roasting
has been performed with the ore in pieces the ore must be pulverized and the
operations performed methodically with the pparatus illustrated in Figs. 4
and 5. In these figs. the reference letters have no relation whatever to those of
the preceding illustrations.
"
A, A¹, are two tanks arranged one beside the other the one being an attack-
ing" tank and the other a solving tank, the agent used being sulphuric acid.
Each of these tanks receives, in turn, charges of new ore, and the water pro-
ceeding from the filtering tank B, where the dressed ares are deposited and
washed with pure water, is distributed to the tanks, in turn, by means of the
valves C, C. When the attacking action is completed in one of the tanks they
are allowed to rest and the solutions are run off into one of the precipitation
tanks D, D, by means of the valves E, E, E¹, E¹, The mother waters, con-
sisting of solutions of sulphate of iron, are run off by the channels F, F, into
the tank G where the sulphate of iron can be crystallized if there is any use
for it.
The other tanks are built of bricks or masonry and are covered or lined with
cement or asphalt.
The filtering tank B has a false bottom made of perforated planks covered
with asbestos cloth which allows the water used for washing to pass through it.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I consider novel and desire to claim is:
1. The improved process or mode of manufacturing sulphuric acid from
sulphurous acid gas by the action of air and especially the arrangements herein-
before described for ensuring the perfect mixture of the gas with water and air
and the regulation, at will, of the supply of air and water-vapour as well as the
temperature, substantially as herein before set forth.
2. In a process of manufacturing sulphuric acid from sulphurous acid gas
the use of a blast furnace for the roasting of the ores constructed and arranged
substantially as hereinbefore described with reference to the drawings annexed.
Dated this 12th day of October 1898.
H. D. FITZPATRICK,
100, Wellington Street, Glasgow, Agent.