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Патент USA US2118353

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2,118,353‘
Patented May 24, 1938
"UNITED STATES
PATENT.’ OFFICE
‘2,118,353 7
PROCESS FOR OBTAINING MAGNESIUM '
_ >
Y “
OXIDE FROM DOLQMITIC ROCK
Walter
'
'Ma'clnltlre, Knoxville, Tenn, assignor
to American Zinc, Lead & Smelting Company,
St. Louis, Mo., a corporation of Maine
No Drawing.‘ Application February 15, 1937,
Serial N0. 125,930
,
v
‘
8 Claims.
(Cl. 23—201) .
This invention relates to the production of sub
stantially pure magnesium oxide-‘and has for its
object to obtain a product of this character from
dolomitic rock, such as dolomite or dolomitic
5
limestone, at a minimum cost.
. '
-
CaO may be e?ected in any suitable way, as by
injection of a small amount of carbon dioxide
gas to convert the CaO ‘to calcium carbonate‘
(CaCOs). or‘ by the addition of the requisite
amount of magnesium sulfate to convert the CaO
to calcium sulfate (CaSO4). Or any other ap
propriate means for eliminating the lime ((390)
In practicing the invention dolomite or dolo
mitic limestoneis calcined to produce ‘a mixture
of substantially three parts CaCOa and one part may be employed. '
After the_“free” lime content has been con
MgO and a" minimal amount of CaO. This soft
10 calcine is comminuted and'a cold water suspen ' verted to either calcium carbonate or' sulfate in,
sion of the three components of the-mixture is the suspensioml-lzS gas is injected into this‘ lime
‘then formed. Thesuspension is ?rst made by free cold suspension until the H28 gas comes
the addition to the calcine of about one-fourth to a pseudoequilibriuin with the cold ‘suspension,
at which point about 80%-90% of the MgO con
of the ?nal volume of. added water'to effect hy
tent of the suspension will be found to have
' dration of the MgO of the calcine. The hydra
entered into solution. When this point is reached,
tion maybe accomplished by aging the suspen
- sion but preferably is'eXp‘edited by application if there is further injection of the HzS gas, said
of heat. The remaining three-fourths of the full gas will pass on-through the suspension, with
quantity of water is then added,‘ the preferred out being absorbed. When the point is reached
where no further absorption of H28 gas takes
20 ?nal ratio of calcine to water being ‘within the
- range _of 1 to 16 and 1 to 20.‘ Such a suspension place,.the solution is permitted to stand for a
few hours, say over night, after which additional
haspractically'no solvent action on the carbon
ate and MgO solids. which are merely held in HzS gas is injected until no more will be absorbed.
This results in a. practically. complete solution
suspension in the cold water. Into this suspen
of the MgO content of the calcine in the suspen
25 sion hydrogen sul?de gas (HzS) is injected. The
hydrogen sul?de gas combines with the hydrated sion. When such practically complete solution
MgO in‘ suspension‘ to produce a cold solution of the initial MgO content of the calcine has
been secured, the solutionv is clari?ed as above
of MgHzSz, the CaCOz remaining as a solid sus
pended in this solution of MgHzSz. This cold described and then subjected to heating, and it
solution of MgHzSz is then separated from'the' breaks down into substantially pure solid hy
inert calcium carbonate (CaCOa) by ?ltration,
gas being recovered and held ready for use in
ter solution of MgHZSZ is obtained.
repeating the operation.
This clari
tion and then applying extraneous heat in any
suitable way. This heat causes the MgHzSa
solution to break down into solid hydrated mag
nesia (Mg(OH)2) and the gas. Has. The heat
40 ing of the solution is carried'on in a closed cham
her, to the complete evolution of H23 so that
this HzS gas is recovered for use in repeating the
operation.
As thus far described,the small amount of
45 caustic, or “free” lime in the calcine mixture has
been ignored, and the ?nal MgO product, while
being of high quality, is not absolutely pure, since
the free lime would also react with and be dissolved by the injected gas, H28, and the ,result
50 ant hydrated MgO product would be contami
nated thereby. To produce pure MgO the small
“free” lime content of the calcine mixture (MgO,
, CaCOa_ and some CaO), is eliminated fromv the
cold water suspension before injection of the
55 H25 gas.
This elimination of active or “free”
15
20
25
drated magnesia (Mg(OH)2) ' and H28 gas, the
centrifuging or otherwise and a clari?ed cold wa
?ed solution is then heated to the boiling point,
35 preferably by ?rst injecting steam into the solu
10
'
‘
The resultant precipitate, after ?ltration or.
centrifuging, may then be dried and lightly cal
cined in asingleoperation to convert the hy
drated oxide, Mg(OH)2 to the oxide, MgO.
Having thus described the invention, what is.
claimed is:
1. A process which consists in forming a cold
water suspension of a comminuted dolomitic cal
cine comprising CaCOs and MgO, permitting hy- dration of the‘ suspended MgO to ensue, then
bringing the hydrated MgO content of the cal
cine into solution by injecting hydrogen sulfide
gas into the suspension,- clarifying the solution
and boiling the clari?ed solution.
I
,
' j 2. A process which consists in forming a col
water suspension of a comminuted dolomitic cal
cine comprising 03.003 and MgO, permitting hy 50
dration of the suspended MgO to ensue; subject
ing the hydrated magnesium oxide in the sus
pension to treatment with H2S to cause the
Mg(OH)-z to pass into solution in the cold 1U
drogen-sul?de-impregnated water, clarifying the. 56
2,118,858
solution‘ and heating the clari?ed solution to pre
cipitate hydrated magnesium oxide, and convert
ing the Mg(OHz) ‘ to MgO by heat.
3. A process which consists in forming a cold
water suspension of a comminuted dolomitic cal
water suspension oi.’ a comminuted dolomitic cal
cine comprising CaCOa and MgO, permitting hy
dration of the suspended MgO to ensue, elimi
nating any free lime from the suspension, then
injecting hydrogen sul?de gas (HzS) into the
cine comprising CaCOa and MgO, permitting hy
suspension until no more of the injected gas is
dration of the suspended MgO to ensue, elimi
nating the CaO content of the calcine from the
absorbed thereby, then permitting the suspen
sion to stand for a short period of, time, then
again injecting hydrogen sul?de gas into the
suspension, subjecting the hydrated magnesium
10 oxide in the suspension to treatment with H2S
to cause the Mg(OH)2 to‘ pass into solution in
the cold hydrogen-sul?de-impregnated water,
clarifying the solution and heating it to pre
cipitate hydrated magnesium oxide, and con
15 verting the Mg(OH)2 to MgO by heat.
4. A process which consists in forming a cold
water suspension of a comminuted dolomitic cal
cine comprising CaCOa and MgO, permitting
hydration of the suspended MgO to ensue, con
verting any "free” lime ((3210) in the suspension
‘to ‘calcium carbonate, (CaCOs), then injecting
hydrogen sul?de gas (HzS) into the suspen
sion, whereby the hydrated magnesium oxide
(Mg(OH)2) in the suspension is brought into
solution in the cold hydrogen-sul?de-impreg
nated water, clarifying the solution by removing
solids therefrom, then heating the clari?ed solu
tion and collecting the resultant hydrated mag
nesium oxide and hydrogen sul?de gas, and con
30 verting the Mg(OH) 2 to MgO by heat.
5. A process which»; consists in forming a cold
water suspension of a comminuted dolomitic cal
cine comprising CaCOa and MgO, permitting
hydration of the suspended MgO to ensue, con
verting any “free” lime. (C80) in the suspension
to calcium sulfate (CaSOii), then injecting hy
drogen sul?de gas
(H28)
into the suspen
sion, whereby the hydrated magnesium oxide
(Mg(OH) 2) in the suspension is brought into so
40 lution in the cold hydrogen-sul?de-impregnated
water, clarifying the solution by removing solids
therefrom, then heating the clari?ed solution’
and collecting the resultant hydrated magnesium
oxide and hydrogen sul?de gas and converting
45 the Mg(OH) 2 to MgO by heat.
6., A process which consists in forming a cold
suspension, whereby the hydrated magnesium 10
oxide (Mg(OH)z) in the suspension is dissolved
in the cold hydrogen-sul?de-impregnated water,
clarifying the solution by removing solids there
from, and then boiling the clari?ed solution and
collecting the resultant hydrated magnesium 16
oxide and hydrogen, sul?de gas and lightly cal
cining the Mg(OH)z to produce MgO.
7. A process which consists in forming a cold
water suspension of a comminuted dolomitic cal
cine comprising CaCOa and MgO, permitting hy 20
dration of the suspended MgO to ensue, convert
ing any free lime of the suspension into calcium
carbonate, injecting hydrogen sul?de gas into the
suspension, whereby a cold solution of MgHzSz
is formed with calcium carbonate as a solid sus 25
pended therein, eliminating the calcium car
bonate from the MgHzSz solution, then boiling
the solution, collecting the resultant hydrated
magnesium oxide and the hydrogen sul?de gas
and lightly calcining the recovered Mg(OH)z to 30
produce MgO.
‘
8. The process of obtaining an approximately
pure magnesium oxide which‘ consists in forming
in cold water a suspension of dolomitic calcine
comprising CaCOa and MgO by ?rst adding to the 35
calcine only approximately enough cold water to
hydrate the MgO and then adding enough cold
water to complete the suspension, then subject
ing the hydrated magnesium oxide of the calcine
suspension to treatment with Has to cause the 40
MgiOH): to pass into solution in the cold hydro
gen-sul?de-impregnated water, clarifying the
solution and heating it to precipitate hydrated
magnesium oxide, and converting the Mg(0H)2
to MgO by heat.
WALTER H. MACIN'I'IRE.
45
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