A NEW METHOD OF TREATING THE RESIDUES FROM SODA WORKS
Year: 1884

page_text: I GEORGE FREDERICK REDFERN of the General Patent Office, No 4, South Street,
Finsbury, in the county of Middlesex, Patent Agent do hereby declare the nature
of the said invention for "A NEW METHOD OF TREATING THE RESIDUES FROM SODA
WORKS" and in what manner the same is to be performed, to be particularly.
described and ascertained in and by the following statement:
This invention relates to a new process for extracting hydrate of lime and
sulphur from the residues from soda-works.
By a well known process the sulphide of calcium contained in the said residues
from soda-works can be easily converted into hydrosulphuret of calcium which is
soluble in water, such. result being obtained by treating with carbonic acid or
with hydro-sulphuric acid the sulphide of calcium suspended in water, or by
heating the said sulphide and water under a pressure of about five atmospheres.
The lye of hydrosulphuret of calcium thus prepared contains the whole amount
of sulphur which existed within the residues in the form of sulphides. Now, by a
reaction heretofore unknown to manufacturing chemists the said lye can be
decomposed into hydrate of lime which precipitates, and into pure hydrosulphuric
acid which escapes. In order to promote the said reaction, the lye is poured into
an iron boiler or other suitable vessel, provided with a stirrer and is heated by a
furnace or by bigh pressure steam. When the lye begins to boil, hydrate of lime
precipitates in the form of a fine crystalline powder, whilst hydrosulphuric acid
escapes through pipes provided for the purpose.
To free this acid from aqueous vapour it is made to pass through a suitable
condenser whence it is conducted in a perfectly pure state into a gasometer. The
hydrate of lime is separated from its lye by means of a filter-press and the
remaining lye is again placed in the boiler.
The hydrate of lime thus prepared is perfectly pure and fit to be used for all
purposes.
Before leading the hydro-sulphuric acid into the gasometer it is made to pass
through a vessel containing fresh residues from the manufacture of soda suspended
in water. In this water half the quantity of hydro-sulphuric acid prepared cach
day is absorbed as it serves for dissolving a fresh quantity of sulphide of calcium
and converting the same into a lye of hydrosulphuret of calcium which is again
passed into the boiler and there decomposed in the manner above described. The

page_text: following formulas
process are represented by C
=
Ca SHS Ca SH, S
Ca SH, S + 2 H₂O
=
Ca OH, O + 2 H, S
The prepared hydrosulphuric acid may be burnt to sulphurous acid and this
latter may be converted into sulphuric acid, or sulphur may be extracted therefrom
by any of the known processes.
Compared with other methods heretofore employed or proposed the above
described process offers the following advantages;
Firstly. Apart from the unavoidable losses arising in every manufacturing
process, the whole sulphur contained in the residues from soda manufacture is
Baved in the form of hydro-sulphuric acid.
Secondly. The bulk of the lime is likewise saved and moreover it is saved in the
useful form of hydrate of lime.
Thirdly. The carrying into practice of the process is very simple and of small
cost, as fuel is the only material required to be used.
Fourthly. The definitive residues resulting from this process are only 35 per cent.
of the original residues and for this reason the outlay for the transport of residues
and for storage are considerably reduced.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that What is
claimed is
The herein described process of manufacturing hydrate of lime and hydro-
sulphuric acid from a lye of hydrosulphuret of calcium, the said process consisting
in placing the said lye in a closed boiler or other suitable vessel, provided with a
stirrer, and in heating the same by means of a furnace or high pressure steam,
substantially as described.
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