Note: Descriptions are shown in the official language in which they were submitted.
` `- 21~8226
The invention relates to a process for producing steel and
hydraulically active binders, such as, e.g., blast furnace
slag, clinker and the like.
When producing steel, steel slag is formed, which has a
relatively high iron oxide content due to the refining process
involved. Conventional steel slag contains MnO and FeO in
amounts up to 33 ~ by weight.
While blast furnace slag is remarkable by its favorable
hydraulic properties and by a substantially lower iron oxide
content, thus being more readily apt for utilization as a -
basic construction material, the disposal of slags from
steelworks has become increasingly difficult, since steelworks
slag in the incurring composition, i.e., without any
metallurgical aftertreatment, cannot be readily used for
construction purposes or the like. It has already been -
proposed to granulate steelworks slags along with blast
furnace slags and use them as bottoming material in road
construction. However, the relatively high CaO content of
steelworks slag allows for the use of only limited amounts of
steelworks slag also in that case. `~ ~ :
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In order to obtain a product of higher quality, the
metallurgical processing of steelworks slag, as a rule,
involves high energy consumption and, therefore, is not really -~ ;
economical. ~;~`, `
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Yet, slags having relatively high contents of iron oxide also -~ -
incur in other metallurgical processes or combustion
processes. In particular, it is known that Cu converter slags
frequently have iron oxide contents of above 50 ~ by weight,
35 and slags from waste and garbage combustion plants that are- -
characterized by relatively high iron oxide contents are also
known.
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21~g22~
The invention aims at further processing steelworks slags and
slags having relatively high iron oxide contents of the
initially defined kind directly in a steelworks and to convert
the same into more readily usable end products, namely
hydraulically active binders. In order to solve this problem,
the process according to the invention consists in that pig
iron is refined by adding slags containing iron oxides in
amounts exceeding 5 ~ by weight, such as, e.g., steel slags,
Cu converter slags after reaction with a lead bath or oxidized
slags from waste combustion plants. In this process, the high
iron oxide content of the liquid slags, such as, e.g.,of the
steel slag, thus is utilized to refine molten pig iron having
relatively high carbon and silicon contents. In doing so, iron
oxide basically reacts with carbon or iron carbide to form
iron and carbon monoxide, whereas the iron oxide of the slag
reacts with the silicon of the pig iron bath to form iron and
SiO2. These reactions partially are exothermic so as to
provide for a high degree of economy. ~ue to the iron oxide
content in the steel slag being reduced, an analysis deviating
from the original slag analysis is obtained, resulting in
substantially more favorable hydraulic properties. The iron
oxide content is utilized to oxidize the pig iron bath, and,
for instance, in the case of steel slags reduction of the iron
oxide content to below one third of the original value may be
achieved, the volume portions of the other components of the
original steel slag thus increasing in respect of their
portions in the overall slag. Hence results a new slag
analysis no longer corresponding to the original steel slag
analysis. The new slag analysis is characterized by a
substantially more favorable hydraulic module and a relatively
high content of alite. Even though the thus obtained slag end
product, which may be denoted as cement clinker, does not
conform to standardized Portland cement clinker, a highest-
~uality alite cement clinker is obtained which is suitable asan extremely favorable base for mixing with other hydraulic or
latent hydraulic substances. The cement clinker to be obtained
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`` 21~822~
in this manner is suitable, in particular, for mixing with
puzzolanes, wherein a particularly high 28-day strength could
be attained.
Analogous considerations as have been made in respect of steel
slag also apply to Cu converter slag and other slags, wherein,
in case of Cu converter slags, care has, of course, to be
taken that copper will not get into the steel bath, being
detrimental to steel. Consequently, copper must at first be
separated above a lead b th, the copper being eliminated from
the slag prior to the iron bath. ~he lead itself subsequently
is reduced in an iron bath reaction, wherein iron and lead can
be drawn off separately in a simple manner, beause iron and
lead together do not enter into solution. Below the iron or
steel bath a sea of lead is formed, steel and lead being
capable of being drawn off separately in such cases.
Due to the possibility, beside the simultaneous recovery or
recuperation of metal fractions, of converting the remaining
slag into a superior product to be reused, a substantial
economic advantage is achieved, slags being disposable for
which no suitable application has existed so far. In order to
enable the desired oxidation of the carbon content within the
pig iron bath and hence the refining to steel, it is
advantageously proceeded in a manner that the iron oxide
content of the slag is chosen to exceed 8 ~ by weight,
preferably 10 ~ by weight.
For the initially mentioned basic reactions as they occur in
the pig iron bath, the observance of relatively high
temperatures is essential. Despite the at least partially
exothermic reactions, the temperature required may drop on
account of thermal losses, the lost heat being reintroducible
via bath electrodes in a particularly simple manner. Due to
its chemical composition, the molten bath may be used as an
electric resistance in a particularly simple manner, the pig
iron h~th }eing us~ble as the counter electrode. In order to
2148226
be able to carry out the process according to the invention in
a particularly economic manner and, above all, to terminate
the desired reactions within acceptable periods of time, it is
required in any case to use the liquid steel slag at
temperatures of above 1550C, in particular 1600C, and molten
pig iron at temperatures ranging from 1450 to 1550C, wherein
it is advantageously proceeded in a manner that the liguid
phases together are maintained at temperatures of above
1550C, in particular 1660C to 1800C, for 3 to 8 hours, in
particular about 6 hours. The upper limit of 1800C is chosen
in consideration of the upper limit of the stability of alite.
The pig iron used as a reducing agent must be overheated to at
least 1350C in order to render the formation of alite
feasible at all. According to a preferred process control it
is provided to use the liquid steel slag at temperatures
exceeding 1550C in order to ensure the optimum phase
formation for any further use of the slag.
Due to the reduction of the iron bath, the iron oxide content
of the slag, for instance, is lowered to about 5 ~ by weight,
the process advantageously being conducted in a manner that
the slag is converted into a sinter phase consisting of 15 to
25 % by weight of molten phase (aluminates, ferrites) and
clinker phase (minerals, alite, belite).
The required overheating, which partially results from the
exothermic reactions of the slag with the pig iron bath, may
be effected by external heating, advantageously by proceeding
in a manner that an electrically heatable tilting converter is
employed as the mixing vessel. Another way of ensuring the
appropriate temperature in addition to a relatively high iron
oxide content in the slag consists in maintaining the slag at
overheating temperature by blowing in or up oxygen. In
particular, if the slag is to be maintained at overheating
temperature by blowing up oxygen, it is advantageously
proceeded in a manner that the slag bath height for the
reaction with pig iron is chosen to be between 2 and 8 cm,
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` 21~822~
preferably 2 to 6 cm, whereby it is ensured that merely the
slag, but not the iron bath located therebelow is refined by
means of oxygen.
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The sinter phase floats on the iron bath, reduced iron
droplets sedimenting into the iron bath from the slag or
sinter phase. Since there is a high resistance to
sedimentation in the sinter phase, it is again advantageous,
as already pointed out above, to limit the thickness of the
slag or sinter phase to 2 to 6 cm, metallic iron being
removable from the slag almost completely at residence times
ranging between 3 and 8 hours.
Another way of adjusting the desired slag parameters consists
lS in that basic poor ores are added to the slags in order to
increase their iron oxide contents to above 8 ~ by weight. ;~ -
Preferably, also CaC03, A1203 and/or SiO2 are used as
additives. In particular, when using such further additives,
the waste heat from the process, i.e., both the sensible and
20 the chemical heat, may be applied for preheating these -- ~ -
substances. ~
: .
In addition to recovering copper by means of the lead bath, it
is, of course, also feasible to recover zinc advantageously by -
proceeding in a manner that, when using Cu converter slags,
lead is drawn off below the steel bath and Zn is condensed
from the gas phase.
To supplement the lost heat, it is advantageously proceeded in
a manner that an electrically heatable tilting converter is
used as a mixing vessel.
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The iron oxide content of the slag is reduced as a function of
the volume ratio of slag to pig iron, wherein, naturally, only
balance reactions are brought about such that the complete
reaction of the iron oxide content is not readily feasible. A
particularly economic and efficient mode of operation results
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214822~
if molten pig iron is added to the liquid slag phase in
amounts by weight ranging from 1 to 2 to 1 to 3.
The sintered cement clinker can be processed further according
to conventional technology. Advantageously, the reduced slag
is supplied to a clinker cooling and granulating means, the
clinker being cooled by air according to the direct method in
a particularly simple manner.
Also the refined molten pig iron already largely conforming to
a steel composition subsequently may be further processed
according to known steel aftertreatment procedures.
In the following, the invention will be explained in more
detail by way of exemplary embodiments.
ExamDle 1:
0.5 parts by weight of molten pig iron were added to a portion
of steel slag, the two phases together having been maintained
at 1660C for 6 hours. During the reaction, 35 g carbon
~onoxide, corresponding to 28 standard liters, formed per kg
steel slag melt. The steel slag had the following analysis:
sio2 8
A12O3 7
CaO 45
MgO 5
MnO + FeO 30.5
TiO2 1
~he pig iron had the following analysis:
Si 4
C 5
Fe 91
- 21~822~
- 7 -
After six hours of reaction, the slag analysis and the steel
analysis had changed in the following manner~
Slaa analvsis (~)
SiO2 13
Al203 8.9
CaO 60
MgO 6.4
MnO ~ FeO 10.5
Tio2 1.3
Steel analvsis (~
si O .-.
C 2
Fe 97
When assessing the slag, which was used as a cement clinker, a
conventional cement-technological assessment was made, `~
yielding the following values. For comparison, the Table below
20 also indicates the typical ranges for Portland clinker. `
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Criterion Value Typical Range ~ -
(Portland clinker)
Hydraulic module 1.85 1.7 - 2.3
Silicate module0.67 1.8 - 3.2
Silicic acid module 1.46 2.5 - 3.5 ~ -
Alumina module0.85 1,5 - 2.5 ;
hime standard1.12 0.8 - 0.95 i~
'- Alite content (C3S) 70.7
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In total, a highest-quality alite cemènt clinker was obtained.
The 28-day strength according to DIN 1164 was 62 N/mm2, which
may be classified as extremely high. However, this is no ;~
standard Portland cement clinker, yet continued reduction of
the iron oxide and slight addition of additives, such as, for ~ ;~
instance, clays, for increasing the SiO2 and A12O3 contents are
21~822~
-- 8 --
feasible if Portland cement clinker according to standards is
desired.
Exam~le 2:
s
To react the steel slag already indicated in Example 1 to a
target slag which might be denoted as blast furnace slag
having the following composition: -
~ Taraet Sla~
10 SiO2 36.5
Al2O3 8.5
CaO 48
MgO 5 5
MnO + FeO 0
15 Tio2 1.5
the original steel slag is reduced to the target slag. 733 g
pig iron are reauired per kg steel slag with 950 g steel being
formed and 60 g CO, or 48 standard liter CO, being released.
In addition, 225 g auartz sand were admixed to produce the
above-mentioned target slag. The pig iron and steel
compositions are indicated in the Table below:
~ Pia Iron Steel
Si 4 0
C 5 1.5
Fe 91 98
The melting temperature was approximately 1600C, a redox time
of approximately 4.5 hours having been observed. The blast
furnace slag formed is excellently usable as a hydraulically
30 active binder. The relevant characteristic data have been ~ ~-
determined to be as follows:
Hydraulic index (wedge) = 92 ~ (very good)
Puzzolanity (ASTM C 618) = 118 (excellent)
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21~8226
g
ExamDle 3: -
Using Cu slag from a converter, a starting slag having the
following chemical analysis was used: ~ `
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~ain com~onent Portion (~) $econdarv com~onent Portion (~
SiO2 28 S03 0-5
Al2O3 6 ~2 0.13
Fe23 Na20 0.64
CaO 8 Ti02 0.36
MgO 2 Cr23 1.4
Mn2O3 0-35
P2O5 0.27
Cl + F 1 ~
Nonferrous M~tal Portion (p~m) ;~ :
Cu 11'000
Pb 6'800
Zn 3'760
Due to the high copper content of the slag, copper was removed
from the slag prior to the iron bath by previously arranging a
lead bath. As a result, lead was reduced, wherein iron and ` -
lead together do not enter into solution such that a lead sea
formed below the iron or steel bath. Steel ànd lead could be
drawn off separately.
The relatively high portion of zinc in the slag was reduced
above the iron bath and condensed in the vapor phase.
The remaining heavy metal concentration was within the range
of cement clinker raw material. After reduction of the slag by
aid of the carbon dissolved in the iron bath, the following
slag analysis was obtained:
21~i822~
-- 10 --
Com~onent Portion (~)
SiO2 60
Al203 13
Fe203 0.5
CaO 17
MgO 4
The slag was cooled in the water bath and exhibited excellent
puzzolanic properties. Simultaneously with the recovery of the
metal fraction zinc from the gas phase by condensation and
with the recovery of copper as well as recovery of the lead
bath, a hydraulically active material was obtained, which
exhibited a high final strength, a low hydration heat and a
high chemical resistance on grounds of its favorable
puzzolanic properties.
Example 4:
:'
Copper was extracted from liquid oxidized waste slag by means
of the redox reaction described in Example 3 at a period of
reaction of 3.5 hours and a melting temperature of lS00C.
The starting slag had the following analysis:
ComDonent Portion (~) ~onferrous Netals Portion (~) :
SiO2 42 Cu 1.2
A1203 8 Pb 0.25
Fe203 28 Zn 0.3
CaO 11 Sn 0.1 ~ ;
NgO 2 Ni 0.1
K20 1 ;,. `.~'`~.. ,
Na20 3 .. .
TiO2 1
P20s 0.1
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21~822& ~
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At a copper activity in the lead bath of 30 to 40 % and a slag
layer height of 3.5 cm, the equilibrium concentration of
copper in the slag amounted to 200 ppm.
From the decoppered liquid slag, the remaining heavy metals
lead, zinc, tin, nickel and iron were subsequently reduced and
separated.
Separation of the two metal phases iron/lead assured the
recovery of hiqh-grade pig iron practically free of copper and
having the following analytical data:
Nonferrous Metal Portion (%) ~ -
Ni 0.34
Sn 0.13
Cu 0.07
Cooling, granulating and grinding of the liquid slag enriched
with heavy metals yielded the slag product ~puzzolane~ having ~ `
the following analysis:
Com~onent Portion (%) -
SiO2 59
Al2O3 12
Fe2O3 0.5
CaO 16
MgO 2.5 ~ `~
K2O 1.5
Na2O 4.5
Tio2 1.5
P2O5 0.2
On account of the relatively high Al2O3 content, the puzzolane
cement has a high early strength. Its wedge index is about
95 ~
- 214822~
- 12 -
On the whole, optimized blast furnace slags may be produced by
the addition of SiO2 and, if required, A12O3 carriers, such as
clays, quartz sand and bauxite, the melt viscosity being
considerably lowered at the same time. When reducing such
melts, steel droplets are more easily eliminated by
sedimentation such that the free iron content in the hydraulic
binder can be substantially lowered.
The process according to the invention may be realized in a
steelworks in a simple manner. On the assumption of about 15 t
of slag incurring per hour, a converter having an active
weight of about 125 t, or an active volume of 35 m3, would
have to be employed in order to be able to mix 90 t, or about
m3, of steel slag each with approximately 34 t
(approximately 5 m3~ of pig iron. The clinker phase is drawn
off separately from steel and is tapped into a mixing vessel
to be completed there. In that mixing vessel, processing to
Portland cement clinker may be effected, for instance, by the
addition of additives, such as, for instance, clays, and
further reduction. Yet, such a mixing vessel, in the first
place, also may serve to balance out slag fluctuations.
The clinker cooling and granulating means may be cooled by air
in the direct method. In such cases, air at temperatures of
20C is heated to about 1100C, the clinker being cooled from
approximately 1600C to 250C.
The amount of CO formed constitutes a further source of
energy. CO incurs at temperatures of about 1600C, thus also
containing sensible heat in addition to the latent chemical
thermal energy. If a thermal loss of 30 ~ at the most is taken
into account with a suitably well insulated metallurgical
vessel, this means that the process according to the invention
might be operated exothermally for the production of steel and
clinker, provided the combustible gases formed could be
utilized to the optimum degree.
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- 13 -
The process according to the invention renders feasible in a
particularly simple manner the conversion of a hardly reusable
steel slag to ore cement clinker under simultaneous refining.
The process according to the invention, furthermore, enables
the utilization of heat amounts not readily applicable in
conventional processes and, in this way, also the decrease of
emissions of gases, in particular, CO2.
Within the scope of the process according to the invention,
the decisive reactions each occur on the interfaces of the
melts, the process being realizable in a sintering furnace.
- The carbon monoxide evoluting from the interface reduces
dissolved iron oxide in the slag bath layer, the CO2 portion
of the reducing gas in the slag layer naturally increasing.
From a volume portion of about 15 ~ by vol. of CO2, the gas
looses its reducing effect, wherein, however, further
energetic use remains possible at least partially, since such
gases may be burnt by ventilation or oxygen or air-oxygen
mixtures above the slag layer. Heat transfer to the slag and
iron phases in that case occurs practically exclusively
through radiation procedures.
As already mentioned, the waste heat developing may be used
for preheating additives, the sinter phase floating on the
surface being withdrawable separately. The temperature control
according to the invention is adjusted to the stability range
of alite, from which the initially demanded overheating
results. The alite sinter formed may be frozen to alite
clinker by conventional clinker cooling technique, the main
target in that context having to be the minimization of the
content of free lime.
Optionally desired introduction of carbon for controlling the
melting temperature of pig iron and the reduction potential
may be effected by saturation with carbon in the bath, for
instance, by means of immersed lances or the like. Carbon
introduction may be effected on several points in counterflow
.
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- 14 -
or in co-current flow. In doing so, the iron bath not only
functions as a reductant carrier, but also acts as a conveying
medium for the slag and sinter phases, particularly simple
furnace constructions being applicable.
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