Improvements in Separating Salts of Soda and Potash, and particularly Common Salt, from Solutions of Magnesium Chloride.
Year: 1893

page_text: Date of Application, 25th May, 1893
Complete Specification Left, 23rd Feb., 1894-Accepted, 24th Mar.,
1894
PROVISIONAL SPECIFICATION.
Improvements in Separating Salts of Soda and Potash, and
particularly Common Salt, from Solutions of Magnesium
Chloride.
I, THOMAS HUGH BELL of Middlesbrough, in the County of York, Iron
Master (a communication to me from abroad by Théophile Schloesing of 67 Quai
d'Orsay, Paris in the Republic of France) do hereby declare the nature of this
invention to be as follows:-
"
Solutions of magnesium chloride which require to be concentrated by heat in
order to obtain in a solid state the chloride, which in a former Specification
No. 11469 in the year 1891 I have called "chloride of magnesium in grains
generally contain salts of sodium or potassium which are precipitated in the
form of crystals during concentration and may then be separated by various
processes.
The crystals thus produced are generally very small unless concentration has
been conducted very slowly.
But the more bulky the crystals the easier are the operations of collecting and
separating them by washings from the magnesium solution with which they
are impregnated. Hence it has occurred to my correspondent to obtain such
rystals by means other than slow evaporation and for this object he has studied
the solubility of sodium and potassium chlorides at different temperatures in solutions
of magnesium chloride of various strengths. He found that sodium chloride when
in the presence of considerable quantities of magnesium chloride is much more
soluble hot than cold, so that a large proportion may be crystallized out by simply
cooling the solution previously concentrated to the point at which sodium chloride
commences to precipitate.
This salt is then deposited in relatively large crystals.
It is well known to chemists that in pure water sodium chloride is scarcely more
soluble when heated than when cold, but this is no longer so in the presence of
magnesium chloride. It is this unexpected fact which leads to a solution of the
problem.
For example suppose that it is required to heat a solution of magnesium chloride
obtained after having distilled upon magnesia the mother liquor resulting from the
manufacture of carbonate of soda by the ammonia process; this solution contains as
is well known a large proportion of sodium chloride.
After having separated the excess of magnesia from the distilled liquor let them
be concentrated by heat in pans similar to those in use in salt works or other boiler
of any suitable form, until saturation by sea salt is shown either by the density
acquired or by the appearance of small crystals. The solution is then set to cool
either spontaneously or artificially as for example by the aid of an outer flow of
cold water, in suitable vessels; it deposits about half of its sodium chloride, which
forms in bulky crystals, after which the solution is run off and again submitted to
concentration by heat, cooling and crystallization. The solution is then so far con-
centrated that it retains only a small proportion of sodium chloride, which is collected
in the form of fine crystals during a final concentration, by fishing in the manner
usual in salt works. These fine crystals mixed with the crystals already obtained
form a mixture which can without difficulty be washed and dried.
In the course of the manufacture of chlorine from magnesium chloride a certain
proportion of this chloride is decomposed into magnesia and hydrochloric acid; and
if this acid is to be again utilised in the manufacture it must be saturated by
magnesia to form magnesium chloride. But the hydrochloric acid being dissolved
[D 0.77

page_text: in a relatively large proportion of water, the chloride is somewhat dilute, and the
solution must be concentrated by heat; to do this, this solution may be poured into
the solution obtained from the mother liquors of ammonia soda works, at the
moment of its entering the concentration boilers. But it may be put to a better
use as follows:-This solution of magnesium chloride being free from sodium
chloride, can be concentrated very far in a separate boiler without inconvenience
from the formation of deposits of alkaline chloride and then it can be poured into
the above mentioned solution containing magnesium and sodium chlorides, and
concentrated to the point at which sodium chloride will precipitate; the mixture is
allowed to cool, but as the percentage of magnesium chloride has been greatly
increased by the addition of the highly concentrated solution, the solubility when
cool of the sodium chloride is found to be greatly decreased, so much so that after
cooling about three quarters of the whole sodium chloride is obtained in the form
of large crystals.
The cooled solutions are run off and concentrated; the remainder of the sodium
chloride is then precipitated in fine crystal which are fished and are mixed with the
crystals already obtained.
In thus operating, there is no need of cooling and concentrating several times;
one single crystallization is sufficient.
T. HUGH BELL.
COMPLETE SPECIFICATION.
Improvements in Separating Salts of Soda and Potash, and
particularly Common Salt, from Solutions of Magnésium
Chloride.
I THOMAS HUGH BELL of Middlesborough in the County of York, Iron
Master, (a communication to me from abroad by Théophile Schloesing of 67 Quai
d'Orsay, Paris, in the Republic of 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 following statement :—
"
Solutions of magnesium chloride which require to be concentrated by beat in
order to obtain in a solid state the chloride which in a former Specification
No. 11469 in the year 1891 I have called "chloride of magnesium in grains
generally contain salts of sodium or potassium which are precipitated in the
form of crystals during concentration and may then be separated by various
processes.
The crystals thus produced are generally very small unless concentration has
been conducted very slowly.
But the more bulky the crystals the easier are the operations of collecting and
separating them by washings from the magnesium solution with which they are
impregnated. Hence it has occurred to my correspondent to obtain such crystals
by means other than slow evaporation and for this object he has studied the
solubility of sodium and potassium chlorides at different temperatures in solutions
of magnesium chloride of various strengths. He found that sodium chloride when
in the presence of considerable quantities of magnesium chloride is much more
soluble hot than cold, so that a large proportion may be crystallized out by simply
cooling the solution previously concentrated to the point at which sodium chloride
commences to precipitate.
This salt is then deposited in relatively large crystals.
It is well known to chemists that in pure water sodium chloride is scarcely more
soluble when heated than when cold but this is no longer so in the presence of
magnesium chloride. It is this unexpected fact which leads to a solution of the
problem.
For example suppose that it is required to treat a solution of magnesium chloride

page_text: obtained after having distilled upon magnesia the mother liquor resulting from the
manufacture of carbonate of soda by the ammonia process; this solution contains
as is well known a large proportion of sodium chloride.
After having separated the excess of magnesia from the distilled liquors let them
be concentrated by heat in pans similar to those in use in salt works or other boiler
of any suitable form until saturation by sea salt is shewn either by the density
acquired or by the appearance of small crystals. The solution is then set to cool
either spontaneously or artificially as for example by the aid of an outer flow of
cold water, in suitable vessels; it deposits about half of its sodium chloride which
forms in bulky crystals, after which the solution is run off and again submitted to
concentration by heat, cooling and crystallization. The solution is then so far con-
centrated that it retains only a small proportion of sodium chloride which is
collected in the form of fine crystals during a final concentration by fishing in the
manner usual in salt works. These fine crystals mixed with the crystals already
obtained form a mixture which can without difficulty be washed and dried.
In the course of the manufacture of chlorine from magnesium chloride a certain
proportion of this chloride is decomposed into magnesia and hydrochloric acid;
and if this acid is to be again utilized in the manufacture it must be saturated by
magnesia to form magnesium chloride. But the hydrochloric acid being dissolved
in a relatively large proportion of water the chloride is somewhat dilute, and the
solution must be concentrated by heat; to do this; this solution may be poured
into the solution obtained from the mother liquors of ammonia soda works, at the
moment of its entering the concentration boilers. But it may be put to a better
use as follows:-This solution of magnesium chloride being free from sodium
chloride can be concentrated very far in a separate boiler without inconvenience
from the formation of deposits of alkaline chloride and then it can be poured into
the above mentioned solution containing magnesium and sodium chlorides and
concentrated to the point at which sodium chloride will precipitate; the mixture
is allowed to cool but as the percentage of magnesium chloride has been greatly
increased by the addition of the highly concentrated solution, the solubility when
cool of the sodium chloride is found to be greatly decreased, so much so that after
cooling about three quarters of the whole sodium chloride is obtained in the form
of large crystals.
The cooled solutions are run off and concentrated; the remainder of the sodium
chloride is then precipitated in fine crystals which are fished and are mixed with
the crystals already obtained.
In thus operating there is no need of cooling and concentrating several times;
one single crystallization is sufficient.
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
claim is :-
1. The method substantially as described for separating salts of soda and potash
(and particularly common salt.) from solutions of magnesium chloride, which
consists in concentrating the mixed solutions until the common salt or the salt of
the alkali commences to separate and then ceasing the concentration whereby large
crystals are caused to be deposited on cooling.
2. The method substantially as described for separating salts of soda and potash
(and particularly common salt) from solutions of magnesium chloride which
consists in concentrating the mixed solutions until the common salt or the salt of
the alkali commences to separate, then ceasing the concentration and adding a
concentrated solution of magnesium chloride free from alkaline salt, thereby
facilitating the separation of the alkaline salt in large crystals on cooling.
ليدم
2004
T. HUGH BELL.