A Process for Utilising Acid Sulphates of Soda.
Year: 1893

page_text: Date of Application, 17th Oct., 1893
Complete Specification Left. 19th Apr., 1894-Accepted, 19th May,
1894
PROVISIONAL SPECIFICATION.
A Process for Utilising Acid Sulphates of Soda.
I, ROBERT EDWARD CHATFIELD, of Woodlands, Sewardstone, in the County
of Essex, Manufacturing Chemist, do hereby declare the nature of this invention
to be as follows :-
In the manufacture of nitric acid, as described in my Specification No. 16512
of 1891, and also in the manufacture of other acids, there is a residue consisting of
acid sulphate of soda or sulphate of soda with excess of sulphuric acid. My invention
relates to the utilisation of such residues which I effect as follows. I treat an
aqueous solution of the residue with ammonia blown through it as a gas, or mixed
with it as a liquid, or applied as a carbonate. Sulphate of soda and sulphate of
ammonia are then separated by fractional crystallisation.
Dated this 17th day of October 1893.
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
A Process for Utilising Acid Sulphates of Soda.
I, ROBERT EDWARD CHATFIELD, of Woodlands, Sewardstone, in the County
of Essex, Manufacturing Chemist, 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 :-
In the manufacture of nitric acid, as described in my.Specification No. 16512
of 1891, and alsó in the manufacture of other acids, there is a residue consisting of
acid sulphate of soda or sulphate of soda with excess of sulphuric acid. My
invention relates to the utilisation of such residues which I effect as follows.
treat an aqueous solution of the residue with ammoniacal compounds from gas
liquor or other sources producing mixed sulphates of soda and ammonia from
which sulphate of soda and sulphate of ammonia are separated by fractional
crystallisation. Ammoniacal vapours can be directly passed into the acid sulphate
of soda solution, from which if it be very strong, crystals are deposited while the
liquor is hot and a further quantity when it is cooled.
The process should be conducted in the following manner.
If we take, as our standard, normal bi-sulphate of soda, treated with any of the
above substances with sufficient water to keep the whole in solution, the salts of the
resulting solution contain one equivalent of sulphate of soda to one equivalent of
sulphate of ammonia, equal to about 48% of sulphate of ammonia. This con-
stitutes the proportions of the well known double salt, the ammonio-sodic sulphate,
which salt, though unstable under some conditions, persistingly forms under other
conditions, and it is chiefly owing to its action that the separation of these two
sulphates commercially has hitherto been deemed impossible.
The solution of the mixed sulphates, if required neutral, can be finished off with

page_text: a little ammonia free from sulphur compounds and the insoluble matter, iron &c.
can be removed by filtration or as may be most convenient..
Two processes are now available, (A) and (B). (A) removes one half or a
little more of the sulphate of soda from the mixed sulphates in an anhydrous state,
and (B) removes considerably more than one half as Glauber's salts, in cold
weather.
Process (A). The solution containing salts with 48% sulphate of ammonia,
which in this case is preferably. of considerable strength, is evaporated till a
sample is at about 76° Twaddell at a temperature a little under its boiling
point.
The deposited sulphate of soda can be from time to time fished out and
drained from the mother liquors, the salts of which liquor will then contain
about 65% of sulphate of ammonia to 35% sulphate of soda, or two equivalents
of the former to one equivalent of the latter.
If the liquor, at 76° Twaddell, be further evaporated, sulphate of soda carries
down sulphate of ammonia with it in large quantities as the specific gravity
rises, and thus no further separation can be commercially effected.
The sulphates of soda fished out can be dissolved in water and crystallised.
Process (B). The solution containing salts having 48% sulphate of ammonia is
diluted to a specific gravity of 55° to 60° Twaddell at 90° Fahr. or to corre
sponding specific gravity at other temperatures such as may result from chemical
action, allowance being made for steam going off at higher temperatures.
On cooling, hydrated sulphate of soda (Glauber's salts) crystallises out and is
drained from the mother liquor and covered with water and allowed to soak before
the liquid is run off. These washings can be used for soaking subsequent lots,
until they become too rich. The washed crystals may thus be obtained with less
thanth per cent. of sulphate of ammonia.
The salts of the mother liquor may contain as much as 77% of sulphate of
ammonia if well cooled; the colder the temperature the richer the salts will be in
sulphate of ammonia. If the solution of the mixed sulphates be made too strong
before setting it aside to crystallise, the double sulphates crystallise until the
solution becomes dilute enough to enable the sulphate of soda to obtain its water of
crystallisation and to crystallise.
Any liquors having salts in solution containing 65% and upwards of sulphate of
ammonia are evaporated and the mixed sulphates which are fished out or otherwise
obtained, as well as any crystals rich in sulphate of ammonia, that may result from
the processes herein set forth are brought into contact with cold mother liquors
or sulphate of soda washings or water, by percolation, or agitation, grinding
or otherwise, till the specific gravity of the liquor ceases to rise even though
more solids are added to it. This specific gravity will vary according to the
temperature of the air &c. and the purity of the materials, but will be about
57° Twaddell.
The mixed sulphates will yield up further sulphate of ammonia to weaker
solutions or water and the residue, chiefly sulphate of soda, can be dissolved in
weak liquors or water and treated for separation as herein described.
The salts in the 57° Twaddell liquor should contain about 88 sulphate of
ammonia to 12% sulphate of soda or 8 equivalents of the former to 1 equivalent of
the latter. This liquor being evaporated down, sulphate of ammonia drops and can
be fished.
When this liquor becomes rich in sulphate of soda, which will be at about
76° Twaddell, as much as possible is run off before recharging with fresh lots
of 88% solution.
The liquor run off can be brought round into the circle again or treated
separately. If it be allowed to cool, the mixed sulphates crystallise leaving the
liquor very rich in sulphate of ammonia.
The separation processes above described are applicable to sulphates of soda
containing any excess of sulphuric acid.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The herein described process for treating acid sulphates of soda, by acting on
their solutions with ammoniacal compounds, thereby producing mixed sulphates of
ammonia and soda, and separating sulphate of soda and sulphate of ammonia
therefrom by fractional crystallisation.
2. In the treatment above referred to, the process (A), conducted substantially
as herein described.
3. In the treatment above referred to, the process (B) substantially as herein
described.
4. For recovery of sulphate of ammonia the treatment substantially as herein
described of the liquors resulting from the processes herein set forth.
Dated this 19th day of April 1894.
ABEL & IMRAY,
Agents for the Applicant.