IMPROVEMENTS IN OR CONNECTED WITH THE MANUFACTURE OF SULPHITE OF CALCIUM
Year: 1884

page_text: Sulphite of Calcium.
I, JOSIAH WICKLIFF KYNASTON of N° 149 Kensington, Liverpool, in the County
of Lancaster, Analytical Chemist, do hereby declare the nature of my said
invention for "IMPROVEMENTS IN OR CONNECTED WITH THE MANUFACTURE OF
SULPHITE OF CALCIUM," to be as follows:-
My invention relates to an improved process for the manufacture of sulphite of
calcium. The process has the further advantage of effecting the profitable utili-
zation of the sulphur and calcium contained in alkali waste.
To a solution of chloride of calcium I add magnesia equivalent to the chloride of
calcium contained in the solution, and pass sulphurous acid gas into the mixture
when the calcium is converted into a sulphite, whilst the magnesium present
combines with the chlorine to form chloride of magnesium in solution.
After the sulphite of calcium has settled down the solution of chloride of
magnesium thus obtained is decanted, and then digested with tank or alkali waste
and agitated, whereby sulphuretted hydrogen gas is liberated and a solution of
calcium chloride containing an equivalent of magnesia remains behind ready for a
fresh operation.
The sulphuretted hydrogen gas evolved is burnt in suitable apparatus and the
sulphurous acid gas thus obtained is used in preparing a fresh quantity of sulphite
of calcium.
In place of utilizing tank waste for the regeneration of the magnesium chlorido
the same may be boiled down and calcined in the usual manner for the recovery of
the chlorine in the form of hydrochloric acid and the residual oxide of magnesium
may be used over again for the treatment of fresh quantities of calcium chloride.

page_text: Improvements in or Connected with the Manufacture of
Sulphite of Calcium.
J, JOSIAH WICKLIFF KYNASTON of N° 149 Kensington, Liverpool in the County
of Lancaster, Analytical Chemist, do hereby declare the nature of my said
invention for "IMPROVEMENTS IN OR CONNECTED WITH THE MANUFACTUre of
SULPHITE OF CALCIUM and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:—
"
The economical production of sulphite of calcium for the subsequent manufacture
of the bisulphite and also as an agent for use in the recovery of the sulphur from vat
waste, has become a matter of considerable moment, and the improvement I now
describe has the advantage that the calcium contained in vat waste is made
available for the purpose.
I take a solution of chloride of calcium and add thereto, for each equivalent of
real chloride of calcium Ca Cl, present, an equivalent of Magnesia-Mg O-or
preferably I take the mixture of chloride of calcium and magnesia containing also
some carbonate of calcium obtained as a residue of an operation hereinafter
described, and bring it into contact with sulphurous acid gas, strong or dilute as
obtained by means well known. The result is that the calcium of the chloride is
converted into sulphite which is insoluble whilst the magnesium unites with the
chlorine forming chloride of magnesium which remains in solution according to the
equation
Ca Cl, + MgO + SO₂ = Ca SO, + Mg Cl,
If there be carbonate of calcium present in the mixture this is also completely
converted into sulphite if a sufficiency of sulphurous acid bo used and at the same
time carbonic acid gas is liberated.
The sulphurous acid to be used for this purpose may be obtained by the com-
bustion of the sulphuretted hydrogen liberated in the operation hereinafter described,
but inasmuch as sulphuretted hydrogen may be applied to other more valuable
purposes, for example, for the recovery of the sulphur contained therein, in the form
of brimstone, I prefer to use sulphurous acid in its cheapest form, as obtained
largely diluted with other gases, by roasting pyrites in the burners in common use
in vitriol works.
The mode by which the sulphurous acid is brought in contact with the solution
of chloride of calcium with magnesia, is either by drawing the gas through the
mixture by means of an aspirator, an ejector, or an air pump, or by forcing air into
specially constructed burners at such pressure as will overcome the resistance of the
column of absorbing liquid, or, and this is the mode I prefer, I use as the absorbers
a flag-stone tower constructed exactly as the hydrochloric acid towers in common
use in alkali works, except that in place of the usual coke packing, the packing
must be of open or pigeon hole brick-work, the alternate layers crossing each other,
and the one layer partially obstructing the free passage left in the course below.
The mixture of chloride of calcium and magnesia is pumped into a cistern on the
top of the tower and must be kept in agitation. The arrangement for running the
mixture down the tower may be any kind of distributor which will not permit of
the separation or deposition of the insoluble portion from the solution. The dilute
sulphurous acid gas then passing into the tower at the bottom ascends through the
open brickwork packing and meeting the descending current of absorbing mixture,
the sulphurous acid is abstracted from the other gases and the latter are drawn

page_text: away from the top of the tower by a connection with a chimney stack, or other
artificial means of creating a draught through the whole apparatus.
The proportion of the aqueous mixture run down the tower may be so regulated
that from the bottom there runs a mixture of neutral sulphite of calcium suspended
in a solution of chloride of magnesium, but I prefer that as it issues from the tower,
it contain a very slight excess of free sulphurous acid as this ensures the decom-
position of the ferrous sulphide always present, and so prevents the discoloration of
the calcium sulphite obtained.
It is desirable that the sulphurous acid gas, after leaving the burners, be passed
through an ordinary Glover tower, where coming in contact with strong vitriol any
sulphuric anhydride is absorbed. If this latter is present in the gas in only small
proportion, sulphate of lime is formed in the tower and forming crusts, obstructs
the free passage of the gas.
The mixture of sulphite of calcium and chloride of magnesium obtained as above
described is allowed to flow into cisterns or settling tanks and when the insoluble
sulphite of calcium has settled down, the supernatant solution of chloride of
magnesium is drawn off, and concentrated to a density of 'from 40 to 45 degrees
Twaddle.
A quantity of vat or alkali waste is now taken and to it, in a closed iron vessel,
is added the solution of chloride of magnesium obtained as above described, in such
proportion that for each equivalent of real calcium sulphide Ca S contained in the
waste, there shall be used about one and one-half equivalents of real chloride of
magnesium Mg Cl₁. The mixture is kept in agitation and heated by means of a
steam coil until completely decomposed. The result is that the sulphur of the waste
is eliminated as sulphuretted hydrogen, whilst there remains in the still the
mixture of chloride of calcium and magnesia in equivalent proportions together
with some carbonate of lime, cinders and other grosser matters contained in the
original waste. This mixture, whilst still hot, is passed through a strainer of about
60 meshes to the inch and the cinders and grosser matters rejected, and the mixture
of chloride of calcium and magnesium with some carbonate of lime is obtained
ready for treatment with sulphurous acid as before described.
In place of using tank or alkali waste for the regeneration of magnesium chloride,
the latter may be boiled down and calcined in the usual manner for the recovery of
the chlorine in the form of hydrochloric acid, and the residual magnesia may be
used over again for the treatment of fresh quantities of calcium chloride.
Having now described my invention and the best means known to me of carrying
the same into effect I wish it to be understood that I do not bind myself to the
exact details of working as above described, but what I claim as my invention is
1st. The manufacture of sulphite of calcium by treating a solution of chloride of
calcium, having an equivalent of magnesia suspended in it, with sulphurous acid
until the calcium present is converted into sulphite.
2nd. The manufacture of sulphite of calcium by the treatment of vat waste first
with chloride of magnesium so as to eliminate the sulphur, and afterwards treating
the aqueous residuum of chloride of calcium and magnesia with sulphurous acid,
substantially as described.