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Патент USA US2403939

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2,403,939
Patented July 16,1946
UNITED STATES PATENT OFFICE
2,403,939
PRGCESS FOR TREATMENT OF DOLOMITE
AND HIGH-CALCIC LIMESTONES
Walter H. MacIntire, Knoxville, Tenn, assignor to
American Zinc, Lead & Smelting Company,
St. Louis, Mo., a corporation of Maine
No Drawing. Application May 31, 1944,
Serial No. 538,207
11 Claims. (Cl. 23-134)
1
This invention pertains to a process by which
magnesium oxide is obtained from dolomite or
dolomitic limestone, duly calcined, with con
comitant recovery of the calcium component of
the calcine as either calcium pentasul?de, cal
cium chloride, or calcium carbonate; and par
2
the processing of the generated pentasul?de solu
tion to a desired concentration or in the obtain
ing of the solid pentasul?de (Case) or in the re
covery of dissolved calcium in the forms of salts
and sulfur as such from the solution of the penta
sul?de,
The initial step in my process when applied to
dolomite is to calcine the dolomite to a composi
tion of lime (CaO) and magnesia (MgO). Such
as the agency for the selective dissolution of CaO
from a calcine containing that oxide and MgO. 10 calcination can be effectuated by any suitable
niethodthat assures the calcination of dolomite
The process is also applicable to high calcic lime
ticularly is a process in which a solution of ele
mental sulfur in ammonium hydroxide is used
to its component oxides without “over-burning,”
although I prefer to burn the dolomite at a tem
into which combination the sulfur of the added
perature of approximately 700° C. in an atmos
ammonium sul?de solution is completely con
15 phere of steam to assure a lime component of
verted.
unusual reactivity, as set forth in my Patent No.
I am aware of the fact that sulfuric acid has
2,212,446.
been used to accomplish the dissolution of the
The calcine is then suspended in an aqueous
magnesium carbonate content of raw dolomite
solution of ammonium sul?de, which is a solute
with resultant lay-product carbon dioxide gas and
of elemental sulfur in an ammoniacal solution
waste calcium sulfate; that hydrogen sul?de gas
resultant from the injection of hydrogen sul?de
has been used for the'selective dissolution of mag
(I-IzS) into a suspension of elemental sulfur in an
nesium hydroxide from an aqueous suspension of
aqueous solution of ammonia. This ammoniacal
dolomite calcined selectively to a composition of
solution of sulfur may be prepared directly or
CaCoa and MgO, as set forth in. U. S. Patent No.
2,118,353, in which case the ready reactivity of the 25 obtained as a by-product from industrial opera
tions. One part of the dolomitic calcine to twelve
hydrogen sul?de toward MgO and inertia toward
to ?fteen parts of the ammonium sul?de solution
calcium carbonate are implemented; and that hy
by weight is preferred. Empirical determination
drogen sul?de has been used to effect the dissolu
has established the desirability of this ratio of
tion of the lime (CaO) component of a completely
calcined dolomite to the exclusion of similar dis 30 calcine to solution, but since this proportion can
be varied somewhat for speci?c adaptations I do
solvent action upon the magnesia (MgO) com
not limit myself thereto.
ponent as set forth by Murray U. S. Patent No.
The “milk of dolomitic lime” solution-suspen
2,317,396. I am also aware that elemental sulfur
sion in the ammoniacal sul?de system thus pro
has been utilized to separate the calcic and mag
vided is boiled in a closed container and is kept
nesic oxide components of a completely calcined
in a state of agitation at approximately 100° C.
dolomite, as set forth in the Drewsen Patent No.
stones for the production of calcium pentasul?de,
1,628,311, by which, however, the sulfur was not
This is done conveniently and preferably by the
passage of a current of steam to expedite reaction
fully and effectively utilized inasmuch as one
between the hydrated calcium oxide, Ca(OH) 2, of
sixth of it was lost in the undesired form of cal
cium thiosulfate (CaSzOa). Such a procedure, 40 the dolomitic calcine and the additive solution of
sulfur, with which the hydrated lime reacts to
characterized by the same wastefulness of sulfur
form the soluble calcium pentasul?de. This ef
through the formation of the undesired thiosul
fectuate-s a dissolution of the calcium hydroxide
fate, is also disclosed in British Patent No. 536,
by the ammonium sul?de with concomitant and
The primary objective of the present invention 45 expeditious liberation of the ammonia, which is
670/1942.
is Do effect the complete reaction of the added
sulfur and its full recovery in the form of cal
recovered for cyclic operation, as indicated by the
equation
‘
cium pentasul?de (Cass) through complete in
hibition of the formation of calcium thiosulfate,
a salt that results in waste of a substantial part 50
At the end of the reaction period of forty-?ve
of the starting sulfur and which has no known
minutes or less the boiled and ammonia-freed
usage. Further, the thiosulfate is not only re
solution of calcium pentasul?de (Cass) is ?ltered
sponsible for the incomplete recovery of the start
from the undissolved magnesia (MgO) , which is
ing sulfur in the desired form of calcium penta
sul?de but is also a‘diluent and an obstruction in 55 partly in the hydrated form (Mg(OH)a). The
2,403,939
3
4
?ltrate of pentasul?de (Cass) can be concen
trated, or the solute can be brought to solid phase
calcium and magnesium components of a dolo
mitic calcine in the form of calcium pentasul?de
and magnesium oxide which comprises calcining
the dolomite to its’constituent oXides of calcium
and magnesium, suspending the calcine in an
aqueous solution of ammonium sul?de, boiling the
by evaporation and then constitutes, in both
phases, the valuable economic spray product avail
able for appropriate dilution and usage as a
fungicide particularly adapted to the control of
the San Jose scale and other orchard handicaps.
suspension in a closed system until the ammonia
As noted, dissolution of the calcium oxide of
is liberated completely, ?ltering and concentrat
the dolomitic calcine is conducted preferably
ing the solution of the calcium pentasul?de, ‘and
with requisite agitation in a closed system in 10 gently calcining the ?ltered magnesic residuum.
which air has been replaced by steam, and which
2. The process of making a separation of the
system is heated either internally or externally.
calcium and magnesium components of a dolo
Further, it is advantageous to use a fresh hot cal
mitic calcine in the form of calcium pentasul?de
cine and thus conserve both stored heat and heat
and magnesium oxide which comprises calcining
of CaO hydration in the chamber in which the 15 the dolomite to its constituent oxides of calcium
ammoniacal solution of sulfur is brought into
and magnesium, suspending the calcine in an
reaction with the dolomitic calcine solution-sus
aqueous solution of ammonium sul?de, boiling the
.
suspension in a closed steam-swept system until
Empirical determination has established the
the ammonia is liberated completely, ?ltering and
necessity for boiling the ammoniacal polysul?de 20 concentrating the solution of the calcium penta
solution containing the calcine until complete re
sul?de, and gently calcining the ?ltered mag
moval of ammonia is effectuated. It has been
nesic residuum_
found desirable to expedite the removal of the
3. The process of making a separation of the
pension.
liberated ammonia by the passage of a current of
calcium and magnesium components of a dolo
steam through the boiling system. The pre 25 mitic calcine in the form of calcium pentasul?de
scribed step of boiling in a closed system precludes
and magnesium oxide which comprises calcining
any oxidation of the dissolved sulfur.
the dolomite to its constituent oxides of calcium
The present process eifectuates the complete
and magnesium, suspending the calcine in an
removal of the calcium oxide component of the
aqueous solution of ammonium sul?de in the
starting dolomitic calcine and full utilization of
proximate proportion of one part of calcine to
the added sulfur, the cost of which is compen
twelve to ?fteen parts of solution by weight,
boiling the suspension in a closed system for
sated for by its complete conversion into a highly
desirable commercial fungicide; and with con
forty-?ve minutes or less until the ammonia is
liberated completely, ?ltering and concentrating
comitant recovery of the magnesia of that calcine.
If desired, the sulfur of the pentasul?de can be "
recovered as elemental sulfur through addition of
muriatic acid, HCl, as indicated by the equation
CaS5-|-2I-ICl=4=S+I-IzS+CaClz. Also the calcium
of the chloride solution ?ltered from the ele
mental sulfur liberated by the HCl can be recov
ered as calcium carbonate (CaCOa) by the injec
tion of carbon dioxide (CO2) and ammonia into
the ?ltrate from the precipitated sulfur, as indi
the calcium pentasul?de solution, and gently cal
cining the ?ltered magnesic residuum.
4. The process of treating limestone which
comprises calcining the limestone, suspending
the calcine in an aqueous solution of ammonium
sul?de, boiling the suspension in a closed sys
tem until the ammonia is liberatedcompletely,
?ltering and concentrating the calcium penta
sul?de solution, treating the calcium pentasul
?de ?ltrate with muriatic acid and recovering
the sulfur liberated in elemental form and the
cated by the equation
45 calcium as chloride.
The magnesia obtained as a residue from the
5. The process of treating a limestone which
?ltration of the calcium pentasul?de from the
processed lime-freed calcine is comprised of
MgO' and Mg(OH) 2, the last mentioned being in
preponderance at a ratio of about 4 to 1. When
lightly calcined to dispel water of hydration this
residue gives a magnesia (MgO) of relatively high
concentration, or purity; and, when derived from
a good grade of dolomite, is of quality superior to
that of the magnesia obtained from sea water.
As heretofore noted one part of the dolomitic
calcine to twelve to ?fteen parts of the am
monium sul?de solution by weight is preferred.
comprises calcining the limestone, suspending
tem until the ammonia is liberated, ?ltering
and concentrating the calcium pentasul?de solu
tion, treating the calcium pentasul?de solution
with muriatic acid (HCl) and recovering the
sulfur liberated in elemental form and the cal
cium as chloride, and treating the calcium chlo
ride (CaClz) solution by injecting carbon di
oxide and ammonia and recovering calcium
carbonate (CaCOa) and ammonium chloride
calcine to 20 to 30 parts of solution by weight in
from limestone which comprises calcining the
the calcine in an aqueous solution of ammonium
sul?de, boiling the suspension in a closed sys
(NHiCl).
When the process is used with high grade calcic '
6. The process of making calcium pentasul?de
limestone, however, I prefer a ratio of one part of 60
limestone, suspending the calcine in an aqueous
asmuch as such a high-calcic limestone might
solution
of ammonium sul?de, boiling the sus
contain as much as 99 per cent of 02.003.
When used on high-calcic limestones the chief > x pension in a closed system until the ammonia
is liberted completely, and ?ltering and con
objective of my ammonium sul?de process is to
centrating the solution of the calcium penta—
sul?de.
sulfur in the form of calcium pentasul?de (Cass) ,
7. The process of making calcium pentasul?de
in either solute or solid phase. The process could from limestone which comprises calcining the
be directed also to the attainment of either cal 70 limestone, suspending the calcine in an aqueous
cium chloride or carbonate of high purity through
solution of ammonium sul?de, boiling the sus
the stipulated processing of the .polysul?de solu
pension in'a closed steam-swept system until
tion.
_
the ammonia is liberated completely, and ?lter
attain full reaction and recovery of the additive
What is claimed is:
.
‘ ing and concentrating the solution of the cal
1. The process of making a separation of the 76 cium pentasul?de.
2,403,939
5
in an aqueous solution of ammonium sul?de in
10. The process of making calcium penta
sul?de from limestone which comprises calcin
ing the limestone, suspending the calcine in an
aqueous solution of ammonium sul?de, boiling
the proximate proportion of one part of calcine
the suspension in a closed system until the am
to twenty to thirty parts of solution by weight,
monia is liberated completely, and ?ltering and
evaporating the solution to secure solid calcium
8. The process of making calcium pentasul?de
from a high-calcic limestone which comprises
calcining the limestone, suspending the calcine
boiling the suspension in a closed system until
the ammonia is liberated completely, and ?lter
ing and concentrating the solution of the calcium
pentasul?de.
9. The process of making calcium pentasul?de
from a high-calcic limestone which comprises
pentasul?de.
11. The process of making calcium penta
10 sul?de from a high-calcic limestone which com
prises calcining the limestone, suspending the
calcine in an aqueous solution of ammonium sul
?de in the ‘proximate proportion of one part of
calcine to twenty to thirty parts of solution by
in an aqueous solution of ammonium sul?de in
the proximate proportion of one part of calcine 15 weight, boiling the suspension in a closed system
to twenty to thirty parts of solution by‘weight,
until the ammonia is liberated completely, and
?ltering and evaporating the solution to secure
boiling the suspension in a closed steam-swept
solid calcium pentasul?de.
system until the ammonia is liberated completely,
and ?ltering and concentrating the solution of
the calcium pentasul?de.
WALTER H. MACINTIRE.
20
calcining the limestone, suspending the calcine
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