Note: Descriptions are shown in the official language in which they were submitted.
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~ he in~ention relates to a metallothermal process
for the simultaneous production of ~agnesium and cement or
calcium and ement.
As known, magnesium and calcium are generally
produced by electrolyzing the melt o:E their salts.
~ he salts /generally chlorides/ are electrolyzed at
about 700 to 900 C. A disad~antage o~ this method is that it
requires extremely pure starting materials 3 completely free
of water, which can be prepared o~ly by a sophisticated and
lengthy procedure requiring much la~our and energy.
Several attempts have been made to elaborate large-
scale methods for the production of magnesium from dolomite
/CaCO3 MgC03/ and calcium from limestone /CaC03/, two ~ -
minerals occurring abundantly in nature. According to these
methods dolomite or limestone are ~irst calci~ed9 and the
resulting calcined products tCaO MgO or CaO/ are subjected
to metallothermal reduction. ~len silicon is applied as `
reducing agent, calcinea dolomite con~erts into magnesium
according to the equation
2/CaO MgO/ ~ Si = 2 CaO SiO2 ~ 2 Mg,
whereas calcined lime yields calcium according to the
equation
4 CaO ~ Si = 2 CaO Si02 t 2 Ca.
~hen aluminium is used as reducing agent in the
metallothermal processes9 magnesium or calcium is formed
according to the equations
3/CaO MgO/ ~ 2 Al = 3 CaO A1203 ~ 3 Mg
6 CaO ~ 2 Al = 3 CaO A12O3 ~ 3 Ca ;~
Up to now these methods could not compete with
electrolytical techniques, since they yield9 beside the aimed
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product, extre~el~ large a~ounts o~ useless slag. According
to theoretical calculations, 3.6 tons of slag with a ~-
composition of 2 GaO SiO2 are formed in the silicothermal
production of l -ton of magnesiu~, whereas in the alumino-
-5 thermal process the production of l ton of magnesium is
acco~panied with the formation of 3.72 tons of slag with a
composition of 3 CaO Al203. In the production of calcium
2.14 tons of 2 CaO SiO2 or 2.24 tons of 3 ~aO A1203 are
formed together wlth one ton of the re~uired product.
~he in~ention aims at -the elimination of the abo~e
disad~antages of the silicothermal or aluminothermal produc
tion of magnesium or calcium by providing an easily perform-
able, economical large-scale method for the metallothermal
production of these two alkaline earth metals.
~ow it has been found that when preparing magnesium ;;
from calcined dolomite or calcium from calcined lime, cement
is obtained as valuable by-product in addition to the two `
metals~ if the reduction is performed with an appropriate
amount of a reducing agent containing silicon and aluminium ;~
in a Si:Al weight ratio of 4:1 to l:l. Tn the process lOO to
200 parts by weight of the reducing agent are applied to
con~er-t 600 to 800 parts by weight of calcined dolomite or
700 to 1000 parts by weight of calcined lime. When magnesium
is to be prepared, one can also proceed by adding not more
than 200 parts by weight of calcined lime to 600 to 800 parts
by weight of calcined dolomite, and reducing this mixture
with 100 to 200 parts by weight of the reducing agent.
Accordingly, the invention is based on the recogni-
tion that if a reducing agent containing silicon and alu-
minium in the weight ratios defined abo~e is applîed, and the
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X ,'
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xa-tio of the reducing agent to the starting substance ls
maintained within the above limits, the silicothermal or
aluminother~al process yields cement as by-product instead
of a useless slag. ~s it appears frorn the above ratios, the
- 5 mixtures of the starting substance and the reducing agent
contain relati~el~ high amounts of calclum oxide~ ~s men-
tioned above~ specific ad~antages arise in the production of
magnesium when an additional amount of calcium oxide is
added to -the calcined dolomite prior to starti~g the
metallother~al reduction. ~hese facts are in stri~ing
contrast with the prior e*forts, where it was attempted to
keep the proportion of calcium oxide at the minimum in order
to decrease the amount of slag. On the contrary, according
to the in~ention, it is essential to process mixtures with
relati~ely high calcium oxide contents, since this ensures
the formation of cement as by-product instead of a slag.
According to a fur-ther ~ariant of the in~ention a
reducing agent also containing calcium is applied. ~his is
again in contrast wi-th the former efforts. The significance
of the presence of calcium can èasily be understood on the
basis of the equation
5 lCaO MgO/ t Ca t. 2 Si = 2 /3 CaO ~ Si.02/ + 5 Mg
~his equation shows that calcium also participates in the
reduction of calcined dolomite as a reducing agent. Of
course, in the processing of calcined lime calcium has no
reducing effect but simply increases the yield. ~he reason ~` -
for the use of/calcium-containing reducing agent in the
processing of calcined lime is that CaSi allo~ is the most
; easily a~ailable of the reduoing agents applicable in
30 practice. ~he calcium content o* this reducing agent ~;
.
-............ , : . . ~ ;- . ~ . ..... . .
increases the yield o~ the aimed product.
~s mentioned abo~e, substances containing silicon
and aluminium in a weight ratio of ~:l to 1:1 are applied as ;
reducing agents. ~he total silicon and aluminium content of
the reducing agent may vary between 50 to lO0 % ~his means
that simple mixtures or alloys of silicon and alùminium con-
taining the two metals in the abo~e weight ratio can be
utilized as reducing agents in the process of the invention.
However, reducing agents containing other subs-tances in addi
tion to aluminium and silicon can be utili~ed as well. As
mentioned above, reducing agents also containing calcium are
preferred. ~he calcium content o~ these reducing agents may ;~
amount to 30 % by weight; they contain generally 1 to 30 ~0
by weight of calcium. ~he reducing agents utilized in
practice are generally iron-containing alloys or mixtures of
such alloys. ~he iron content of the reducing agent may
amount to 25 % by weight; the reducing agent contains
generally 0.1 to 25 ~0 by weight of iron. ~s reducing agent
appropriate mi~tures of silicoaluminium, ferrosLlicon,
calciumsilicon, silicoaluminiumcalcium and ferrosilico-
aluminiumcalcium alloys can be used, wherein the ratio of
silicon to alum m ium, the total silicon and aluminium content,
and the calcium and iron content meets the above requirements.
Of course, single alloys with appropriate compositions can `
be used as well.
~ he reduction itself is performed in apparatuses
utili~ed for silicothermal and aluminothermal processes
according to known techniques, at a temperature of 1300 to
1600 C under a pressure o~ less than 10 torr, until the
development of magnesium or calcium vapours ceases.
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The ~ixt~re of the ~tar-ting su~-tances is powdered
and brlquetted. Appropriate briquattes can be formed from
the mixtures generally under a pressure of 500 to 2000
kiloponds/cm2 The briquettes, either as such or op~ionally
after hardening and/or preheating, are filled into the
cobbing chamber, kept at 1300 to 1600 ~, of a furnace
filled with an inert protecting gas. ~he furnace is closed,
the internal pressure is decreased to below 10 *orr, and
heating is continued, whereupon the briquettes warm up to
1300 to 1600 ~ and the metallothermal reaction takes place. ;~
~he magnesium or calcium ~apours formed are collected in the
condenser of the furnace, where magnesium or calcium preci-
pitates in crystalline form. At the end of the process the
temperature of the condenser drops, since no further
~agnesium or calcium vapour precipitates in -the condenser.
Depending on the composition of the mixture of -the
starting substance and the reducing agent, the dimensions of ;
the furnace, the temperature and other parameters, reduction
is completed generally within 4 to 12 hours.
At the end of the reaction the furnace is refilled
with an inert protecting gas, and the cement clinker formed
is removed from the cobbing chamber, whereas crystalline
magnesium or calcium is removed from the condenser. ~he
process can then be restarted. It is preferred to operate
the furnace in cyclic manner.
As protecting gas preferably argon is applied.
~ he cement clinker removed from the cob~:ing chamber
of the furnace contains 20 to 25 yO by weight of SiO2, 6 to
12 % by weight of A1203 and 62 to 69 % by weight of CaO~
furthermore optionally up to 2 % by weight of MgO and/or
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up -to 6 ~0 by welght of iron. hs the composition of this
product corresponds to that of portland cement, it can be
utilized as binding agent in the building lndustry.
~he most important advantage of the new process
accordlng to the in~ention is that it pro~ldes an econo~ical
method for the large-sc~le production of magneslum and cal-
cium. Utilizing the process of the in~ention the disadvantage
of the prior silicothermal and aluminother~al processes, i.e.
the formation of large amounts of useless slag, also causing
environ~ental protection problems, can be avoided
completely, since all of the products formed in the new
process can be utilized.
~ he process of the invention is easy to per~orm and
requires no specific technological operations or specific
equipment. ~he process can be performed in the apparatuses
commonly used for silicothermal and aluminothermal opera-
tions, pro~ided that a pressure lower than 10 torr and
te~peratures of 1300 to 1600 ~ can be maintained in them.
The invention is elucida-ted in detail by the aid of
the ~ollowing non-limiting Examples.
xample 1
,~1
638 parts by weight of calcined dolomite and 71 parts
by weight o~ calcined lime are admixed with 100 parts by
weight of a reducing agent containing 70 % by weight of
silicon and 30 % by weight of aluminium, and the mixture is
pul~erized by grinding. ~he powder is briquetted, and the
briquettes are cobbed at 1500 C under a pressure of 10 2
torr. As a min product of this process 155 parts by weight
of magnesium separate in the condenser of the furnace. As
by-product, 656 parts by weight of cement containing 66 ~o
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8 - ~ r~r~
by weight of CaO, 23.5 % by weight of SiO21 9 ~0 by weight of
A1203 and 1~5 ~0 by weight o~ MgO re~ain in the cobbing
chamber of the furnace.
xample 2
699 parts by weight of calcined dolomite are admixed
with 125 parts by weigh-t of a reducing agent con-taining 56 ~o
by weight o~ silicon, 24 % by ~eight of aluminium and 20
by weight of calcium, and the mixture is pul~erized by
grindingO ~he powder is briquetted 9 and the briquettes are
cobbed at 1400 C under a pressure of 10 3 torr until the
e~olution of magnesium vapours cease. As a main product 173
par-ts by weight of magnesium are obtained. ~he by-product
i.s 660 parts by weight of cement containing 66.5 % by weight
of aaO, 23 % by weight of SiO25 10 % by weight of A1203 and5 0.5 % by weight of MgO,
~xample 3
668.5 parts by weight of calcined dolomite and
35.5 parts by weight of calcined lime are admixed with
112.5 parts by weight of a reducing agent c~ntaining 62 %
by weight of silicon, 27 % by weight of alu~inium and 11 %
by weight of calcium, and the mixture is ground. ~he resulting
powder is briquetted~ and the briquettes are cobbed at ;~-
1600 a under a pressure of 10 torr until the de~elopment ;
of magnesium vapour ceases. As a main product 164 parts by
weight of magnesium are obtained. As a by-product 665 parts
by weight of cement are formed with essentially the same
composition as indicated in Example 1.
Example 4
638 parts by weight of calcined dolomite and 71
30 parts by weight of calcined llme are admixed with 123 parts - ;
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by weight of a reducing agent con-taining 57 % by weight of
silicon, 24.~ yO by weight of aluminium and 18.6 ~0 by weight
of iron. ~he mixture is pulveri~ed by grinding, and the
powder is briquetted~ ~he br1quettes are cobbed at 130G a
- 5 under a pressure of 10 4 torr until the de~elopment of
~agnesiu~ vapours ceases. 156 parts by weigh-t of magnesium
are obtained as a main product. As a by-product, 675 parts
by weight of cement containing 68.4 ~0 by weight of CaO,
21.0 ~0 by weight of SiO2, 7.0 ~o by weight of A1203, 0.5 yo
by weight of ~gO and 3.1 ~o by weight of iron are obtained.
Example 5
699 parts by weight of calcined dolomite are ~ -
admixed with 148 parts by weight of a reducing agent
containing ~7 % by weight of silicon, 20 % by weight of
aluminiu~, 17 yO by weight of calcium and 16 % by weight of
iron. ~he mixture is pulverized by grinding, and the powder
is briquetted. ~he briquettes are cobbed at 1550 C under a
pressure o~ 10 1 torr until the development of magnesium
vapours cease~.~he process yields 171 parts by weight of
magnesium as main product and 677 parts by weight of cement,
containing 64.0 ~0 by weight of CaO, 19.7 % by weight of
SiO2, 11.3 % by weight of A1203, 1.8 % by weight of MgO and
3.1 ~0 by w~ight of iron, as by-product.
Exarnple 6
668.5 parts by weight of calcined dolomi-te and 35.5
parts by weight of calcined lime are admixed with 135 5
parts by weight o~ a reducing agent containing 51.7 yo by
weight of silicon, 22 1 ~0 by weight of aluminium, 9.2 yO by
weight of calcium and I7 % by weight of iron. ~he mixture is
pulverized by grinding, and the powder is briquetted. ~he
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- 10 ~ b~ ~i
briquettes are cobbed at 1450 C under a pressure of 10 2
torr un-til the development of magnesium vapours ceases. ~he
process yields 166 parts by welght of magnesium as main
product and 671 parts by weight of cement, containing 65.0 %
by weight of CaO, 24 0 ~0 by weight of SiO2, 7.7 ~0 by weight
of A1203, 0.2 % by weight of MgO and 3~ O by weight of iron
as by-product.
~ `~,
~14 parts by weight of calcined lime are admixed
with 100 parts by weight of a reducing agent con-taining 70 %
by weight of silicon and 30 ~0 by weight of alu~inium. ~he
mixture is pulveri~ed by grinding, the powder is briquetted,
and the briquettes are cobbed at 1500 C under a pressure of
10 3 torr until the development of calcium vapours ceases.
~he process yields 258 parts by weight of calcium as main
product and 656 parts by weight of cement, containing 64.5 %
by weight of CaO, 23.6 % by weight of SiO2, 11.4 % by weight
of A1203 and 0.5 % by weight of MgO, as by-product.
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814 parts by weight of calcined lime are admixed ~-
with 135 parts by weight of a reducing agent containing
52 % by weight of silicon, 22 % by weight of aluminium and
26 % by weight of calcium. ~he mixture is ground, the result-
ing powder is briquetted, and the briquettes are oobbed at
1600 C under a pressure of 10 1 torr until the development
of calcium vapours ceases. ~he process yields 294 parts by
weight of calcium as main product and 650 parts by weight of
cement, containing 66.7 yO by weight of CaO, 22.8 ~ by weight
of SiO2, 9.9 % by weight of A1203 and 006 % by weight of
MgO, as by-product.
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hxc~mple 9
814 parts by weight of calcined lime are admixea
with 123 parts by weight of a reducing agent containing 57 %
by weight of silicon 9 24 % by weight of aluminium and 19 %
- 5 by weight of iron. The mixture is pulveri~ed by grinding) the
resulting powder is briquetted, and the briquettes are cobbed
at 1450 C under a pressure of 10 4 -torr until the develop-
~ent of calcium vapours ceases. ~he process yield~ 254 parts
by weight of calcium as main product and 680 parts by weight
of cement, containing 64.8 yO by weight of CaO, 22.7 yO by
weight of SiO2, 8.5 % by weight of A1203, 0.3 % by weight of is
MgO and 3.7 yO b~ weight of iron, as by-product.
.
814 parts by weigh-t of calcined lime are admixed
with 158 parts by weight of a reducing agent containing
44.3 yO by weight of silicon, 19.0 yO by weight of aluminium
22.2 yO by weight of calcium and 14.5 % by weight of iron.
~he mixture is pul~eri~ed by grinding, the resulting powder
is briquetted, and the briquettes are cobbed at 1550 C under
a pressure bf 10 3 torr. ~he process yields 298 parts by
weight of calciu~ as main product and 675 parts by weight of
cement, containing 62.9 % by weight of CaO, 23.5 % by weight
of SiO2, 9.6 yO by weight of ~1203, 0.7 % by weight of MgO
and 3.3 ~o b~ weight of iron, as by-product.
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