IMPROVEMENTS IN THE MANUFACTURE FROM DOLOMITES AND MAGNESIAN LIMESTONES. OF PRODUCTS RICH IN MAGNESIA, AND FREE FROM CAUSTIC LIME
Year: 1881

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for an Invention of
"IMPROVEMENTS
IN THE MANUFACTURE FROM DOLOMITES AND MAGNESIAN LIMESTONES. OF
PRODUCTS RICH IN MAGNESIA, AND FREE FROM CAUSTIC LIME." A commu-
nication from abroad by Jean Baptiste Marie Prosper Closson, of 29, Avenue
Trudaine, Paris, France.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 20th April 1881.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN THE MANUFACTURE FROM DOLOMITES AND
MAGNESIAN LIMESTONES OF PRODUCTS RICH IN MAGNESIA, AND FREE FROM
CAUSTIC LIME." [A communication from abroad by Jean Baptiste Marie Prosper
Closson, of 29, Avenue Trudaine, Paris, France.]
This Invention relates to the manufacture of products rich in magnesia, and free
from caustic lime.
Double carbonates of lime and magnesia, more or less pure, are frequently found
in nature in large masses. Amongst the most pure may be found some dolomites,
containing, for example:
Carbonate of Magnesia
-
44.50
which is equal to 21·19 per cent. of magnesia. If this dolomite be calcined at a
suitable temperature (300°, 400°, 500° C., according to circumstances), the carbonate
of magnesia only is decomposed, and a product is obtained containing 27.63 per
cent. of caustic magnesia.
Dolomites, richer in magnesia, are also found, but they are generally much more

page_text: impure. Take, for example, those of carigeract, which have the following
composition
Carbonate of magnesia
Carbonate of lime
61
22
which gives 29 per cent. of magnesia.
If this dolomite be calcined at a proper temperature (which may vary, according
to the method of operating and the kind of dolomite, from 650° to 850° C., or to a
red heat, at which limestone decomposes) the carbonates of magnesia and iron are
decomposed, and a product is obtained which contains 45 per cent. of magnesia.
By operating in a similar way with the dolomites or argillaceous magnesites of Italy
and other countries, one may attain 70 per cent. of magnesia.
By pulverising more or less finely, according to circumstances, before or after
calcination I am able, by separating and sorting by means of a blast, or, in most
cases better still, by washing, to render the products still richer in magnesia.
I am thus able to obtain products containing, according to circumstances, from
50 to 90 per cent. of pure magnesia. I may even obtain, commercially, pure
magnesia by carrying the separation by washing far enough.
The enrichment of the product is effected more or less easily, according to the
chemical and physical composition of the dolomite. There are some dolomites
which, by being merely washed and allowed to settle, are freed in a few minutes of
a great part of their impurities, and there are others for which the operation is very.
difficult.
I employ, according to circumstances, the separation by air blast, or the washing
and settling, or the various sifting apparatus or jiggers; or, in short, the various
washing and separating apparatus employed in mining. If any lime remains in the
product, and its presence is objectionable, I eliminate it in the various methods
described in the Specifications of former Letters Patent, dated respectively Oct. 20,
1879, No. 4253, and 17th Feb. 1881, No. 701. I may absorb it by means
of sugar, or by muriate of ammonia; or if I do not care to obtain a pure product,
and if the presence of carbonate of lime is not objectionable, I treat with carbonate
of soda or potash, which forms with the lime carbonate of lime, the soda or potash
remaining in the water, and being able to be used for another operation.
By the method herein described, that is to say, by calcination at a suitable
temperature, by separation by a blast, or suitable washings, by purification by
means of either hydrochlorate of ammonia, sugar, or carbonate of soda, as the case
may be, I am able to obtain either caustic magnesia, or products rich in caustic
magnesia, and containing no caustic lime, the objectionableness or otherwise of the
carbonate of lime and silica for the purposes for which the product is intended
being the consideration which governs the details of manufacture above set
forth.
Thus, if the magnesian product obtained is to be employed either to make mortar,
with sand, or to mould masses together by means of chloride of magnesium, the
presence of carbonate of lime, silica, &c. is not objectionable, they will merely make
the mortar leaner, or, in other words, will require the addition of less sand. If, on
the other hand, the product is to be employed for the manufacture of refractory
products, the presence of carbonate of lime and silica would be objectionable, and
in this case they are-to be removed as above described.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the
20th October 1881.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent.
"IMPROVEMENTS IN THE MANUFACTURE FROM DOLOMITES AND
MAGNESIAN LIMESTONES OF PRODUCTS RICH IN MAGNESIA, AND FREE FROM
CAUSTIC LIME." A communication from abroad by Jean Baptiste Marie Prosper
Closson, of 29, Avenue Trudaine, Paris, France.
This Invention relates to the manufacture of products rich in magnesia, and
free from caustic lime.
Double carbonates of lime and magnesia, more or less pure, are frequently found
in nature in large masses. Amongst the most pure may be found some dolomites
containing, for example:
Carbonate of magnesia
-
44.50
which is equal to 21.19 per cent. of magnesia. If this dolomite be calcined at a
suitable temperature (500° to 600° C., according to circumstances) the carbonate of
magnesia only is decomposed, and a product is obtained containing 27.63 per cent.
of caustic magnesia.
Dolomites, richer in magnesia, are also found, but they are generally much more
impure. Take, for example, those of carigeract, which have the following
composition
•
which gives 29 per cent. of magnesia. If this dolomite be calcined at the
temperature hereinbefore indicated the carbonates of magnesia and iron are
decomposed, and a product is obtained which contains 45 per cent. of magnesia.
By operating in a similar way with the dolomites or argillaceous magnesites of
Italy and other countries, one may attain 70 per cent. of magnesia.
By pulverising more or less finely, according to circumstances, before or after
calcination, I am able by separating and sorting by means of a blast, or in most
cases, better still, by washing, to render the products still richer in magnesia. I am
thus able to obtain products containing, according to circumstances, from 50 to 90
per cent. of pure magnesia. I may even obtain, commercially, pure magnesia by
carrying the separation by washing far enough.
The enrichment of the product is effected more or less easily, according to the
chemical and physical composition of the dolomite. There are some dolomites
which, by being merely washed and allowed to settle, are freed in a few minutes of
a great part of their impurities, and there are others for which the operation is very
difficult.
I employ, according to circumstances, the separation by air blast, or the washing
and settling, or the various sifting apparatus or jiggers; or in short the various

page_text: .
washing and separating apparatus employed in mining. If any lime remains in
the product, and its presence is objectionable, I eliminate it by the various methods
described in the Specifications of former Letters Patent, respectively dated
October 20th 1879, No. 4253, and February 17th 1881, No. 701. I may absorb it
by means of sugar or by muriate of ammonia; or if I do not care to obtain a pure
product, and if the presence of carbonate of lime is not objectionable, I treat with
carbonate of soda or potash, which forms with the lime carbonate of lime, the
soda or potash remaining in the water, and being able to be used for another
operation.
By the method herein described, that is to say, by calcination at such a
temperature that the carbonate of magnesia is decomposed, but not the carbonate
of lime; by separation, by a blast or suitable washings; by purification, by means
of either hydrochlorate of ammonia, sugar, or carbonate of soda, as the case may be,
I am able to obtain either caustic magnesia, or products rich in caustic magnesia,
and containing no caustic lime, the objectionableness or otherwise of the carbonate
of lime and silica for the purposes for which the product is intended being the
consideration which governs the details of manufacture above set forth. Thus, if
the magnesian product obtained is to be employed, either to make mortar with
sand, or to mould masses together by means of chloride of magnesium, the presence
of carbonate of lime, silica, &c. is not objectionable, they will merely make the
mortar leaner, or in other words will require the addition of less sand. If, on the
other hand, the product is to be employed for the manufacture of refractory
products the presence of carbonate of lime and silica would be objectionable, and
in this case they are to be removed, as above described.
Having described the nature of the said Invention, and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the
herein-before in part recited Letters Patent is,-
The manufacture from dolomite and magnesian limestones of magnesia, or
products rich in magnesia, and free from caustic lime, by calcination (at such a
temperature that the carbonate of magnesia is, but the carbonate of lime is not
decomposed), in combination with all or some of the other operations, viz., the
separation of the impurities by a blast or by washing, the carbonation of any
caustic lime that may have been produced by means of alkaline carbonates, or the
removal of the lime by the methods referred to, substantially as herein before
specified.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Twentieth day of October, A.D. 1881.