A Process for Recovery of Sulphur, Carbonate of Soda, and Iron Oxide from Double Sulphide of Sodium and Iron.
Year: 1891

page_text: Date of Application, 9th May, 1891
Complete Specification Left, 15th Jan., 1892-Accepted, 27th Feb., 1892
PROVISIONAL SPECIFICATION.
A Process for Recovery of Sulphur, Carbonate of Soda, and Iron
Oxide from Double Sulphide of Sodium and Iron.
We, GEORGE LUNGE, of Zürich, Switzerland, Professor of Chemistry, and
JAMES DEWAR, of The Royal Institution, Albemarle Street, in the County of
London, Professor of Chemistry, do hereby declare the nature of this invention to
be as follows:-
:-
According to a process for the production of caustic soda from sulphate of soda
the sulphate is first converted into sodium sulphide, and this sulphide, in aqueous
solution, is filtered through or digested with ferrate or ferrite of soda, which latter
substance is obtained by roasting at a red heat carbonate of soda and sesqui-oxide
of iron, the result of this treatment being the production of a solution of caustic
soda and of a residue consisting mostly of a double sulphide of sodium, and iron.
The object of our invention is to treat this residue, which it is at present difficult
to utilise, in such a manner as to recover from it a proportion of free sulphur, and
also carbonate of soda and hydrated oxide of iron, both of which are available for
the soda process above referred to. According to our process, we act on the residue
(consisting as above stated, mostly of double sulphide of sodium and iron) in a moist
state, or state of more or less fluid mud, with a mixture of carbonic acid gas and
air, which may be applied in various proportions, but we practically find about
1 volume of carbonic acid gas to 4 volumes of air a very suitable mixture.
apply this at ordinary temperatures either by blowing the mixed gases through the
semifluid residue, or by causing them to pass over the moist residue which is spread
out so as to expose a large surface, and from time to time turned over.
We
The carbonic acid gas employed may be obtained from any source such as a lime
kiln or from a furnace, notwithstanding its admixture with nitrogen and other gases,
and thus the carbonic acid evolved in the operation of reducing sulphate of soda to
sodium sulphide is available for treatment of the residue according to our process.
By this treatment the double sulphide of sodium and iron is decomposed producing
carbonate and a little hyposulphite of soda, hydrated iron oxide, and free sulphur
which can be separated by well known means. The carbonate of soda and iron
oxide are available in the process above referred to for production of caustic soda,
or for other uses.
Dated this 9th day of May 1891.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
A Process for Recovery of Sulphur, Carbonate of Soda, and Iron
Oxide from Double Sulphide of Sodium and Iron.
We, GEORGE LUNGE, of Zürich, Switzerland, Professor of Chemistry, and
JAMES DEWAR, of The Royal Institution, Albemarle Street, in the County of
London, Professor of Chemistry, do hereby declare the nature of this invention and
in what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement:-
According to a process for the production of caustic soda from sulphate of soda,
the soda is first converted into sodium sulphide, and this sulphide in aqueous
solution, is filtered through or digested with ferrate or ferrite of soda, which latter
Price 77

page_text: substance is obtained by roasting at a red heat carbonate of soda and sesqui-oxide
of iron, the result of this treatment being the production of a solution of caustic
soda and of a residue consisting mostly of a double sulphide of sodium and iron, or,
it may be, of several such double sulphides, the composition of which is not exactly
known. In what follows the term "residue" is to be understood as indicating the
substance just described.
The object of our invention is to treat this residue which it is at present difficult to
utilise, in such a manner as to decompose it as far as possible, producing free sulphur,
carbonate of soda, and hydrated oxide of iron, which are separated by suitable means,
and of which the latter are suitable for being utilised again in the soda process above
referred to.
According to our process, we act on the residue in a moist state, or in the state of
more or less fluid mud, with a mixture of carbonic acid gas and atmospheric air,
which may be applied in various proportions, but we practically find about one
volume of carbonic acid gas to four volumes of air a very suitable mixture. We
apply this at ordinary temperatures or temperatures only slightly differing from
that of the surrounding locality, either by forcing or drawing the mixed gases
through the more or less fluid residue or by causing the mixed gases without any
great pressure to pass over the moist residue, which is spread out so as to expose a
large surface, and from time to time or continuously turned over so as to expose new
surfaces to the action of the gases.
The carbonic acid gas employed may be obtained in a very cheap way, since the
admixture of nitrogen, carbon monoxide, or other gases which render crude carbonic
acid gas useless for many other manufacturing purposes, is in our process of no
consequence, so long as the proportion of oxygen is not excessive. We may there-
fore employ any cheap source of carbonic acid gas, such as lime kiln gases or furnace
gases or the carbonic acid evolved in the operation of reducing sulphate of soda to
sodium sulphide, which is available for treatment of the residue according to our
process.
Where the proportions of carbonic acid and oxygen in the gaseous mixture
employed are not approximately suitable for the decomposition to be effected, they
may be corrected by mixing with another gas, richer in carbonic acid or with
atmospheric air or gases containing less carbonic acid, as the case may require.
By operating on the residues as above described, the sulphides are decomposed
in such manner that no sulphuretted hydrogen, or only a trace of this gas, is
evolved.
The gases passing away from the decomposing apparatus may, therefore in most
cases, be allowed to escape freely.
Where, however, special precautions are called for in order to absorb the last
traces of sulphuretted hydrogen, the gases which pass. off may be treated by any
known process or apparatus for dealing with sulphuretted hydrogen. We prefer,
however, to pass these gases through residue decomposed in a previous operation,
and therefore containing hydrated oxide of iron which absorbs and retains
sulphuretted hydrogen.
If the process is carried out according to the above description, the decomposition
differs from processes dealing with similar double sulphides by taking place in such
manner that the sodium is mostly converted into carbonate, and the iron into
hydrated sesqui-oxide, most of the sulphur being separated in the free state. A
certain quantity of soda is also converted into hyposulphite (thiosulphate); but this
quantity is comparatively slight and does not interfere with the utilisation of the
carbonate of soda, forming the bulk of the soda recovered in the soluble state.
Another quantity of soda is usually left behind in an insoluble state, probably in
that of a special double sulphide or of sulphides of sodium and iron.
The quantity of this insoluble soda is the less, the longer the treatment of the
residue with the mixture of carbonic acid and oxygen is carried on, but it is
unnecessary to aim at a complete decomposition, which would cost more than it is
worth, since the comparatively slight quantity of soda left in the insoluble state

page_text: does not interfere with the utilisation of the insoluble part of the residue as a
whole.
When the gaseous treatment of the residue has been carried on as far as it is
desirable, the product of the operation is treated by well known means, in order to
separate from one another the soluble sodium salts, the free sulphur and the
hydrated oxide of iron, containing some admixture of insoluble sodium compounds.
A convenient way of effecting this separation is as follows:-
The soluble sodium salts are extracted by lixiviation and are utilised as an
ordinary commercial solution of sodium carbonate, either for the production of
caustic soda or for that of commercial carbonate, or for renewed use in the original
process for manufacturing "ferrite of soda."
The insoluble residue left behind on lixiviation is dried, and the sulphur is
extracted therefrom either by means of disulphide of carbon, or by melting it out,
or by distillation, or by burning it into sulphur dioxide, or in any other suitable
way. According to the way in which the extraction of sulphur is effected, the last
residue contains the oxide of iron either in a hydrated or in a partially or entirely
anhydrous state, mixed with any undecomposed sodium, iron sulphide, and other
accidental impurities.
"
It can be utilised for the manufacture of "ferrite of soda or for other purposes.
If desired, the soda can be completely extracted from it by roasting it with air
and lixiviating the sulphate of soda thus formed.
If the sulphur has been previously extracted by burning into sulphurous acid,
the residue left does not require a special roasting for converting the soda into
sulphate.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed we declare that what we
claim is:-
•
The herein described process for recovery of sulphur, carbonate of soda, and iron
oxide from the residue obtained in the soda process above referred to, by acting on
the said residue in a moist condition with a suitable mixture of carbonic acid and
oxygen.
Dated this 15th day of January 1892.
ABEL & IMRAY,
Agents for the Applicants.