IN THE MANUFACTURE OF MAGNESIA."
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by the said Thomas Twynam at the
Office of the Commissioners of Patents on the 10th October 1881.
THOMAS TWYNAM; of 22, Addison Gardens North, Kensington.
IN THE MANUFACTURE OF MAGNESIA."
"IMPROVEMENTS
My Invention relates to improvements in the production of magnesia for
employment in metallurgical and other operations.
In the Weldon process, in which manganese chloride is decomposed by milk of
lime, so as to formi chloride of calcium and a compound of manganese dioxide with
lime, I employ, instead of the pure lime at present in use, dolomitic lime, that is,
the compound of lime and magnesia obtained by burning dolomite.
I add to the solution of chloride of manganese dolomitic lime in such quantity as
shall contain so much lime as is ordinarily used in the Weldon process, that is,
sufficient to effect the complete decomposition of the chloride solution, and also to
leave such an amount of lime in excess as is required to form the compound Ca O.
Mn O, with the manganese, while the magnesia of the dolomitic lime remains
unacted upon, air being blown through in the usual way. In the ordinary process,
after the complete decomposition of the chloride has taken place, it is usual to add
an additional quantity of manganese chloride solution, termed "final liquid," which
by reacting on the compound of one molecule of lime with one molecule of manganese
dioxide removes half of the lime as chloride of calcium, forming a compound
corresponding nearly to the formula Ca O2 Mn O,, that is, one molecule of lime with
two molecules of manganese dioxide, at the same time manganese monoxide is pre-
cipitated. In my process I add not only such a quantity of manganese chloride as
is sufficient to effect the above purpose, but also sufficient to react upon the
magnesia present in the precipitate forming magnesic chloride and manganese
nonoxide; this reaction is facilitated by continuing the injection of air, the
manganese monoxide becoming partly oxidized to dioxide, and combining with
itself to form compounds, probably corresponding to Mn O Mn O, and Mn O,
.n .

page_text: Mn O₂, but this further oxidation of the manganese monoxide is very incomplete
and slow. This objection is completely overcome however by an additional
operation, which consists in adding to the solution such a quantity of pure milk of
lime as is required to combine with the manganese monoxide precipitated by the
magnesia, and likewise with that formed by the action of the first addition of final
liquid on the compound of lime and manganese dioxide at first formed. In
practice I prefer to run off as much as possible of the calcic chlorido solution before
adding any final liquid, and thus to obviate having too great a bulk of liquid.
Thus the practical working of my process differs from the ordinary Weldon process
in the addition of a much larger quantity of final liquid, and then further adding
an additional quantity of lime, while the chemical reactions in the final operation
differ considerably from those in present use. The mixed solution of calcic and
magnesic chlorides is run off after settling in the usual way, and digested upon
lime or dolomitic lime in order to precipitate the magnesia.
I sometimes find it preferable to proceed in a manner somewhat different but
dependent on the same chemical reactions. Instead of commencing the process by
adding dolomitic lime to the manganese chloride solution, I add at once a sufficient
quantity of magnesia, or preferably of hydrate of magnesia, obtained subsequently
by precipitation from its chloride, to decompose all the manganese chloride; no
excess of magnesia should be used, air is blown in until the decomposition is
complete. When a test shows that the manganese chloride is decomposed, a
quantity of pure line is added, sufficient to form with the precipitated manganese
oxide, a compound of one molecule of lime with one molecule of manganese dioxide;
the blowing is then continued. When oxidation has ceased to advance the usual
quantity of final liquid is added, and the process continued exactly in the usual
manner. By proceeding thus 1 obtain a solution consisting chiefly of magnesic
chloride, which when run off from the settled precipitate is decomposed either by
digesting it on lime, or dolomitic lime, or by evaporating and decomposing, or
partially decomposing it by heat, so as to obtain magnesia and recover the greater
part of the hydrochloric acid at present completely wasted.
I also prepare magnesia by digesting an excess of dolomitic or magnesian lime,
and agitating with crude acetic or pyroligneous acid so that the magnesia at first
taken up by the acid is reprecipitated by the excess of lime, giving a solution
containing chiefly acetate of lime, the inagnesia being left behind. The solution of
acetate of lime is then treated with sulphate of magnesia solution, with formation
of acetate of magnesia, and precipitation of the lime as sulphate. The acetate of
lime is reformed by digesting the acetate of magnesia on dolomitic lime, and the
operation is repeated by again adding sulphate of magnesia. The sulphate of
magnesia may be produced by digesting magnesian lime or dolomite with the
sulphate of lime produced as above, with or without the presence of carbonic acid.
I also use the chloride of iron solutions, produced as a residue in the wet copper
processes, for the production of magnesia by precipitating the iron with magnesian
lime or with dolomite, and reprecipitating the magnesia by digesting on dolo-
mitic lime. So too in the manufacture of chlorato of potassium I use dolomitic
lime. Chlorine gas is introduced into the cylinder containing dolomitic lime in the
usual way. Both the line and the magnesia are acted upon by the chlorine forming
chlorates and chlorides, the solution is run off and mixed with potassium chloride
in proper proportion, and the chlorate obtained by evaporation. On further
evaporation the unacted upon chloride of potassium crystallises out as a double
chloride of potassium and magnesium; thus the loss of potassium salts, which as the
process is at present conducted is considerable, is very much lossened, as the double
chloride may be reused in place of part of the potassium chloride required for the
next operation. The magnesia is recovered from the mother liquors by digestion
with dolomitic lime.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Twynam in the Great Seal Patent Office on the 6th April
1882.
THOMAS TWYNAM, of 22, Cromwell Houses, Fellows Road, South Hampstead,
N.W. "IMPROVEMENTS IN THE MANUFACTURE OF MAGNESIA."
My Invention relates to improvements in the production of magnesia for
employment in metallurgical and other operations. In the Weldon process, in
which manganese chloride is decomposed by milk of lime, so as to form chloride of
calcium and a compound of manganese dioxide with lime, I employ, instead of the
pure lime at present in use, dolomitic lime, that is, the compound of lime and
magnesia obtained by burning dolomite. I add to the neutralized solution of
chloride of manganese dolomitic lime in the form of milk in such quantity as shall
contain so much lime as is ordinarily used in the Weldon process, that is, sufficient
to effect the complete decomposition of the chloride solution, and also to leave such
an amount of lime in excess as is required to combine with the protoxide of man-
ganese precipitated to effect its conversion into dioxide; if the solution of chloride
of manganese contain also chloride of magnesium a further excess of lime will be
required sufficient to effect the decomposition of this chloride of magnesium into
magnesia and chloride of calcium. The operation can be conducted in the ordinary
oxidizers at present in use, and air is forced in in the usual manner. After the
oxidation has ceased to advance it is the custom to add an additional quantity of
chloride of manganese solution, termed "final liquor," which by reacting upon the
compound of lime and manganese dioxide previously formed removes part of the
lime as chloride, manganeso monoxide being at the same time precipitated. In my
process I add not only such a quantity of manganese chloride as " final liquor" as is
sufficient to effect the above purpose, but also sufficient to react upon all the
magnesia present in the precipitate, forming therewith magnesium chloride and
manganese monoxide. If air be blown through the manganese monoxide thus
precipitated becomes converted into higher oxides, but this further oxidation is
incomplete and slow. This objection can be overcome however by an additional
operation, which consists in adding to the solution such a quantity of pure milk of
lime as is required to combine with the manganese monoxide precipitated by the
magnesia, and likewise with that formed by the action of the final liquor on the
compound of lime and manganese dioxide at first produced, air being forced through
in the usual way after the addition of the lime until the oxidation ceases to
advance. In practice I prefer when possible to run off as much as possible of the
calcic chloride solution before adding any final liquor, and thus to obviate having
too great a bulk of liquid. It will be seen that my process differs from the Weldon
process as ordinarily carried out in the substitution of dolomitic lime for pure lime,
in the addition of a much larger quantity of final liquor, and in making a further
addition of lime. After the solution containing the inanganese in suspension has
been allowed to settle in the usual settlers the clear solution of chloride of calcium
and chloride of magnesium is run off into a tank, where it is digested upon lime
or dolomitic lime in order to precipitate the magnesia; the lime used must be added
in quantity just sufficient to effect this purpose.
I sometimes find it preferable to proceed in a manner somewhat different but
dependent on the same chemical reactions. Instead of commencing the process by
adding dolomitic lime to the manganese chloride solution I add a sufficient quantity
of magnesia, preferably in the state of hydrate, to decompose all the manganese
chloride; no excess of magnesia need be used, as it forms no compound with man-
ganese oxide in the wet way; the temperature employed may be the same as that'

page_text: used in the ordinary process, but a higher temperature even to boiling is preferable
for the speedy decomposition of the chloride by the magnesia. The time required
to effect the decomposition varies according to the physical state of the magnesia
employed; if it be the hydrate of magnesia obtained by decomposing a solution
containing chloride of magnesium by means of lime or dolomitic lime that is
employed the decomposition is rapidly effected; the decomposition need not
be carried out in the oxidizers as it is not necessary to force air through at
this stage. When the decomposition is found to be complete, or nearly so,
I add such a quantity of strained milk of lime as is required to form what is
technically known as "base," and air is then forced through in the usual way, the
manganeso protoxide in the presence of the free lime becoming rapidly oxidized by
the current of air. The amount of limo added to form the base should be less
than 06 equivalent of the manganese present, but if any considerable amount of
chloride of manganese has remained undecomposed by the magnesia, sufficient lime
should be added in excess to effect its decomposition. A final quantity of chloride
of manganese solution may be added after the oxidation has ceased to advance,
both in this method and in the method in which dolomitic lime is employed, as
previously described, to react upon part of the lime in the base, and the oxidation
continued as in the ordinary process until the manganese monoxide has absorbed
as much oxygen as it will. By proceeding thus I obtain a solution consisting
chiefly of magnesium chloride, which when run off from the settled precipitate of
manganese mud may be decomposed either by digesting it on lime or dolomitic
lime, or by evaporating and decomposing, or partially decomposing, it by heat, so
as to obtain magnesia (mixed with some chloride of calcium and undecomposed
chloride of magnesium, both of which may be washed out), and to recover part of
the hydrochloric acid at present wasted.
I also prepare magnesia by digesting an excess of dolomitic or magnesian lime
and agitating with crude acetic or pyroligneous acid, so that the magnesia at first
taken up by the acid is reprecipitated by the excess of lime giving a solution
containing chiefly acetate of lime, the magnesin remaining undissolved. The
solution of acetate of lime thus formed is then treated with a sufficient quantity
of a solution of sulphate of magnesia to precipitate all the lime as sulphate,
and forming at the same time acetate of magnesium. The acetate of lime is
reformed from this solution of acetate of magnesium by digesting it on lime or
dolomitic lime, and the operation repeated by again adding sulphate of magnesia.
The sulphate of magnesia required may be most conveniently produced by digesting
dolomitic lime or dolomite with the sulphate of lime produced as above, with or
without the presence of carbonic acid. The decomposition may be effected by
forming the sulphate of lime and dolomite in heaps, and letting them be exposed
in a moist state to the air for a sufficiently long time.
'
I also use the chloride of iron solutions produced as a residue in the wet copper
extraction processes for the production of magnesia by precipitating the iron con-
tained in them by dolomite or dolomitic lime and reprecipitating the magnesia by
digesting on dolomitic lime. Also for neutralizing the chloride of manganese
liquors and freeing them from iron before running them into the oxidizers I use
dolomite in place of carbonate of lime at present used.
So too in the manufacture of chlorate of potassium I use dolomitic lime in place
of the ordinary lime at present in usc. Chlorine gas is introduced into the
cylinders containing dolomitic lime in the usual way. Both the lime and magnesia
are acted upon by the chlorine, forming chlorates and chlorides; the solution is
then mixed with potassium chloride in proper proportion exactly in the ordinary
way, and the chlorate of potassium obtained by evaporation. On still further
evaporating the mother liquor, from which the chlorate has been separated, the
chloride of potassium remaining in the liquor crystallizes out as a double chloride
of potassium and magnesium; thus the loss of potassium salt, which as the process
is at present conducted is considerable, is very much lessened, as the double
chloride may be reused in place of part of the potassium chloride required for the.

page_text: next operation. The magnesia is recovered from the mother liquor by digesting on
dolomitic lime.
Having thus particularly described and ascertained the nature of my Invention,
and in what manner the same is to be performed, I claim,-
The herein described improvements in the manufacture of magnesia, and in the
processes described therein.
In witness whereof, I, the said Thomas Twynam, have hereunto set my hand
and seal, this Sixth day of April, in the year of our Lord One thousand
eight hundred and eighty two.
THOMAS TWYNAM. (L.S.)