Improved Process for Purifying Salt.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improved Process for Purifying Salt.
I, HAMILTON YOUNG CASTNER, of 13, Abchurch Lane, London, Chemist, do
hereby declare the nature of this invention to be as follows:-
For many chemical purposes a very pure form of salt is a great advantage,
and in some electrolytic processes where salt in solution is used as an electrolyte
an almost pure solution is sometimes essential. At present to produce pure
salt necessitates the use of expensive chemicals, and these greatly add to the
cost of the product. Ordinary brine from which salt is obtained by evaporation
contains a proportion of calcium and magnesium sulphates.
According to this invention ordinary brine is treated with a small proportion
of lime and then with sodium carbonate and heated so as to precipitate all the
magnesia together with the calcium and also the added lime. The clear brine
then only contains sodium salts, i.e., sodium chloride and sulphate. This brine
is then evaporated in the usual manner, producing a solid salt, which contains
besides the sodium chloride a proportion of sodium sulphate usually from 1
to 2 per cent. depending upon the amount of mixed sulphates in the original
brine. A brine which may or may not have been freed of sulphates of the
alkaline earth metals but which is a saturated solution so far as sodium chloride
is concerned will dissolve about 6% of sodium sulphate at a temperature of
34° Cent.
According to the present invention the salt which contains only sodium
sulphate as an impurity is treated by successive or fractional washings with the
saturated brine (preferably after the preliminary treatment with lime and sodium
carbonate as above described) so as to remove by solution the sodium sulphate
and leave pure salt, while the brine used as a wash liquor gradually increases as
regards its contained sodium sulphate up to 5% to 6%, when it may be dis-
carded or evaporated to produce an inferior quality of salt.
Dated 10th October 1898.
I, HAMILTON YOUNG CASTNER, of 13, Abchurch Lane, London, 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 follow-
ing statement:-
For many chemical purposes a very pure form of salt is a great advantage,
and in some electrolytic processes where salt in solution is used as an electrolyte

page_text: an almost pure solution is sometimes essential. At present to produce pure
salt necessitates the use of expensive chemicals, and these greatly add to the
cost of the product. Ordinary brine from which salt is obtained by evaporation
contains a proportion of calcium and magnesium sulphates.
According to this invention ordinary brine is treated in the ordinary way with
a small proportion of lime and then with sodium carbonate and heated so as to
precipitate all the magnesia together with the calcium and also added lime, or
other means are employed to purify the brine until it only contains sodium
salts, i.e., sodium chloride and sulphate. This brine is then evaporated in the
usual manner, producing a solid salt, which contains besides the sodium chloride
a proportion of sodium sulphate usually from 1 to 2 per cent. depending upon the
amount of mixed sulphates in the original brine.
Now I have ascertained that a brine which is a saturated solution so far as
sodium chloride is concerned and consequently incapable of dissolving more
sodium chloride, is still capable of dissolving and taking up about 6 per cent.
of sodium sulphate when the solution is at a temperature of about 34° Centi-
grade, and I utilize this capability of absorption for the purpose of removing
the sodium sulphate from the solid salt. I find by experiment that the process
may be conveniently carried out by treating the solid salt which only contains
the sodium sulphate as an impurity to successive or fractional washings with
the saturated solution of sodium chloride and preferably but not necessarily
after its preliminary treatment with lime and sodium carbonate as previously
described, thus removing by solution the sodium sulphate and leaving the pure
salt of chloride of sodium in a solid state.
In practice it has been found that when using a saturated brine the amount
required to remove the sodium sulphate will vary with different qualities of
salt from say 60 to 190 gallons for each barrel of salt, and the time required will
vary from say 2 to 5 hours.
The brine used as a wash liquor will gradually increase as regards its con-
tained sodium sulphate until the amount reaches about 5 to 6 per cent. when
it may be discarded or evaporated to produce an inferior quality of salt, or cooled
to about 0° Centigrade when most of the contained sodium sulphate will crys-
tallize out and may be recovered in its solid form, while the brine run off there-
from may be again utilized for carrying on the fractional washings above
described.
Having now particularly described and ascertained the nature of the said in-
vention and in what manner the same is to be performed I declare that what I
claim is:-
1. The process of purifying salt containing sodium chloride and sodium sul-
phate which consists in subjecting such salt while in a solid state. to the action
of a brine solution saturated as to sodium chloride and containing only a small
percentage of sodium sulphate..
2. The process of purifying salt solutions which consists in first removing
therefrom all contained materials except solutions of sodium chloride and sodium
sulphate and then evaporating such solutions until solid salt is obtained and
finally removing the sodium sulphate by subjecting said salt to the action of a
brine solution saturated as to sodium chloride and containing only a small per-
centage of sodium sulphate.
PHILIP M. JUSTICE,
55 and 56, Chancery Lane, London, Chartered Patent Agent,
For the Applicant.