Method of treating ferruginous slags

The disclosure is of a method of treating ferruginous metallurgical slags to lower basicity, stabilize their composition, reduce their melting point and stabilize the slag in regard to dusting and slaking. The stabilized slag is useful as an artificial sand or as an aggregated sand useful in the manufacture of concrete and like compositions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to steel making and more particularly relates to 
improving stability of the slag by-product of steel making. 
2. Brief Description of the Prior Art 
As is well known, converter slag is a highly basic slag by-product of a 
converter steel making plant. Table 1 below shows the chemical 
compositions of converter slag and blast furnace slag, their basicity and 
melting points. As is seen in the Table 1 basicity of converter slag 
(CaO/SiO.sub.2) is as high as 2.5 - 4.7. This is a higher range than that 
of blast furnace slag. Also as shown the chemical composition of converter 
slag, particularly calcium dioxide, silicon dioxide and iron contents may 
vary largely depending on operating conditions under which it is formed. 
Table 1 
______________________________________ 
Chemical composition and melting points of 
blast furnace slag and converter slag. 
Chem. Comp. Blast Furnace Slag 
Converter Slag 
______________________________________ 
CaO 40 - 43% 35 - 59% 
SiO.sub.2 32 - 36% 10 - 18% 
Al.sub.2 O.sub.3 
12 - 18% 0.5 - 1.5% 
Fe* (Total) 0.2 - 1.2% 8.0 - 25.0% 
MgO 2.0 - 7.0% 1.2 - 4.0% 
MnO 0.5 - 2.0% 1.0 - 8.0% 
TiO.sub.2 0.5 - 2.2% 0.5- 1.5% 
P.sub.2 O.sub.5 
0.02 - 0.10% 1.5 - 3.0% 
S 0.70 - 1.50% 0.06 - 0.20% 
F tr 0.3 - 0.9% 
CaO/SiO.sub.2 Basicity 
1.1 - 1.3 2.5 - 4.7 
Melting Point .degree. C 
1,360.degree. - 1,430.degree. 
1,450.degree. - 1,630.degree. 
______________________________________ 
*The percentage of Fe, sometimes referred to hereinafter as "Total Fe" or 
"Total iron" and as found throughout the specification and/or used in the 
claims, means the iron content contributed by ferrous oxide and ferric 
oxide. It does not include small iron particles physically mixed in the 
slag. 
As shown in Table 1, the melting point of converter slag is 1,450.degree. 
C. -1,630.degree. C. or 80.degree. C. - 130.degree. C. higher than the 
melting point of blast furnace slag (1,360.degree. C. - 1,430.degree. C.). 
Therefore, fluidity of the converter slag is inferior to blast furnace 
slag fluidity at the same temperature. In fact, converter slag is 
considered a very viscous slag. Because of its relatively high melting 
point, converter slag held in a slag ladle easily forms a solidification 
layer at its surface. Solidification at the contact surface between the 
ladle inside wall and the molten slag also usually proceeds speedily. 
Further, even when thin multiple castings of slag is carried out in a dry 
pit, thin slag flow is difficult due to poor fluidity of the converter 
slag and results in formation of a partially lump type slag. 
Prior hereto, only converter slag of good fluidity was granulated in 
conventional granulation equipment. The amount of converter slag which 
could be safely granulated is only 20 to 40% of the total slag. The 
operation is very dangerous, often resulting in an explosion. The cause of 
the explosion phenomenon is not clearly understood. Theories of the cause 
include the following. First the temperature of converter slag at the time 
of granulation is 1,500.degree. C. - 1,650.degree. C. This temperature is 
very near to the melting point of fine metallic iron particles usually 
found dispersed in molten slag as well as very near to the melting point 
of comparatively large metallic iron grains poured into the ladle and 
inter mixed with the slag at the time of slag tapping. When this metallic 
iron comes into contact with cooling water the following reaction proceeds 
very rapidly: 
EQU Fe + H.sub.2 O .fwdarw. FeO + H.sub.2 
the hydrogen gas formed reacts explosively in air. Secondly, since the 
fluidity of converter slag is very poor compared to blast furnace slag, 
the flow rate of the converter slag from the ladle is not uniform and part 
of the slag becomes the semi-molten lump type in water. Water surrounding 
the lump and water drawn into the lump rapidly vaporizes from the latent 
heat of the lump; rapid expansion of the vapor leads to decomposition. At 
the same time due to the presence of metallic iron particles contained in 
the lump, decomposition will proceed readily. Large explosions may be 
caused by a combination of the effects of these causes. At any rate, 
explosions during granulation of the converter slag indicates clearly that 
the explosion has a close relationship with the presence of metallic iron 
particles in the slag and with slag fluidity. 
As mentioned above, fine metallic iron particles are usually found 
solidified in converter slag. These iron particles are not included in the 
Fe percent shown in Table 1, supra. During oxygen blowing in the 
converter, fine metallic iron particles are sprayed with the oxygen jet 
into the molten slag, and are physically dispersed, then solidified in the 
slag. Therefore these fine metallic particles are always observed in the 
converter slag tapped. Usually the proportion of these metallic iron 
particles is within the range of from 2 to 10% by weight of the converter 
slag. 
The fine metallic iron particles observed in solidified converter slag are 
oxidized with time to show the characteristic ferruginous red-brown color. 
These iron particles eventually fall off the slag surface, giving an 
undesired effect to the converter slag, limiting its utilization. Although 
some differences are observed depending on cooling speed and treating 
method, slaking phenomenon caused by chemical change of free lime in the 
converter slag is observed with time, both in the case of lump type slag 
and in particle type slag. Dusting phenomenon is also observed, caused by 
expansion of slag from the inside. This occurs with aging. Also when the 
converter slag contacts rain water, large amounts of free lime are leached 
away, dissolved in the water. This is not always desirable for the 
environment. Apparently quick lime charged into the converter during steel 
making is not necessarily completely slagged, but quick lime is known to 
be uniformly dispersed in the slag microscopically. 
After surveying actual converter operation, we confirmed that there was a 
close relationship between slag basicity and unslagged lime content. With 
the increase of slag basicity CaO/SiO.sub.2, unslagged quick lime content 
is increased and if the basicity falls below 2.0, unslagged quick lime is 
not readily observed. Since the basicity of converter slag is as high as 
2.5 - 4.7, formation of complex compounds consisting mainly of 
3CaO.SiO.sub.2 (basicity 2.8) or calcium ferrites (CaO.Fe.sub.2 O.sub.3 or 
2CaO.Fe.sub.2 O.sub.3) among various oxides such as CaO, SiO.sub.2, 
Al.sub.2 O.sub.3, FeO, Fe.sub.2 O.sub.3, MgO, P.sub.2 O.sub.5 occurs. 
These compounds are said to be decomposed into complex compounds mainly 
consisting of 2CaO.SiO.sub.2 (basicity 1.86) and free lime during the 
process of cooling the slag. In the second process, 2CaO.SiO.sub.2, which 
is the main composition of the complex compounds, transform 
.alpha..fwdarw..alpha.'.fwdarw..beta..fwdarw..gamma. in the cooling 
process and is said to become stable .gamma. 2 CaO.SiO.sub.2 at room 
temperature. In the transformation from .beta. type to .gamma. type, a 
volume increase is accompanied therefore by the expansion of the slag 
causing the dusting phenomenon. 
Compositions like MnO and P.sub.2 O.sub.5 have the effect of preventing 
transformation of .beta. type to .gamma. type, but FeO is said to have an 
effect of helping the above transformation. Therefore the fact that total 
Fe is high in the converter slag means that the slag is in the condition 
of encouraging the dusting phenomenon. 
It is very difficult to differentiate between free lime and unslagged lime 
content in the practical converter slag. The lime content may be causing 
the undesired slaking phenomenon by forming stable calcium hydroxide 
[Ca(OH).sub.2 ] in contact with water. 
Although the above are theories not yet proved, converter slag has basic 
properties which result in the undesired dusting phenomenon by expansion 
and the undesired slaking phenomenon by contact with water. These are 
detrimental to effective utilization of the converter slag. 
Our invention provides a method which solves the problems described above 
as associated with converter slags. That is, by this invention the 
basicity of the slag is lowered, composition fluctuation is reduced, the 
melting point of the slag is lowered as much as possible and its 
fluctuation is decreased. At the same time, iron particle content in the 
slag is lowered. The result is a reduction in the defects associated with 
basicity of the slag and iron particle content. 
In the past in order to improve the chemical composition of converter slag 
a method of making synthetic slag of desired chemical composition by 
adding powder materials was considered. However, the above method is 
disadvantageous in that large amounts of energy are required to melt the 
solid addition materials. 
Our invention offers a means of using converter slag by removing its basic 
defects. The invention can also be applied widely to ferruginous 
metallurgical slags such as the slag by-product of electric steel making 
and open-hearth furnace processes. 
SUMMARY OF THE INVENTION 
The invention comprises a method of improving a ferruginous metallurgical 
slag, which comrpises; 
(a) adjusting the composition of the molten slag so as to include 2.0 to 
8.0 parts by weight of total Fe and 7.0 to 18.0 parts by weight of Al.sub. 
2 O.sub.3 and a basicity (CaO/SiO.sub.2) of 1.3 - 1.65; 
(b) oxidizing metallic iron in the molten slag; and 
(c) cooling the slag under conditions which yield a lump type slag. 
The invention also comprises the product slag of the method of the 
invention. The product slag is useful as an artificial sand and as an 
aggregate sand for preparing concrete and the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
The following description of the invention will be directed to the 
improvement of converter slag, but the basic principles apply to any 
ferruginous metallurgical slag having a chemical composition similar to 
that of converter slag. 
The first step in the process of the invention calls for adjusting the 
composition of the molten converter slag so that it has a basicity 
(CaO/SiO.sub.2) of from about 1.3 to about 1.65 and contains from about 
2.0 to 8.0 parts of total Fe and from about 7.0 to 18.0 parts of Al.sub.2 
O.sub.3. Preferably adjusting is carried out by mixing blast furnace slag 
with the converter slag to be treated by the method of the invention. 
The chemical composition and melting points of blast furnace slag and 
converter slag used in the invention may be widely varied as shown in 
Table 1. For example, the basicity of blast furnace slag (CaO/SiO.sub.2) 
may be from 1.1 - 1.3, and their melting points may be 1,360.degree. C. - 
1,430.degree. C. The basicity of converter slags (CaO/SiO.sub.2) may be 
from 2.5 - 4.7, and their melting points may be from 1,450.degree. C. - 
1,630.degree. C. 
In the case of converter slag, total Fe content differs largely even for 
slags of the same basicity because of varied operating conditions of the 
converter. Therefore large fluctuations of melting points among the slags 
occurs naturally. 
Blast furnace slags and converter slags having various compositions as 
obtained from actual steel making operations were mixed in various ratios 
and the melting points of the fused synthetic slags obtained were 
measured. The term "synthetic slag" as used herein means a slag whose 
composition is adjusted to that specific herein prior to oxidation 
according to this method of the invention. The results of these 
experiments is shown in FIG. 1. In FIG. 1, the upper limit of melting 
points is shown by the CD curve, and the lower limit is shown by the EF 
curve. Almost all melting points of samples tested were found to lie 
within this temperature range. In the FIG. 1, mixing ratios are shown 
based on the sum of blast furnace slag and converter slag being 100. The 
melting point of synthetic slag obtained for a mixing of from 0% to 20% by 
weight converter slag with blast furnace slag is from 1,360.degree. C. to 
1,410.degree. C. This is almost the same melting point for blast furnace 
slags. The melting point of the synthetic slag increases from 
1,370.degree. C. to 1,450.degree. C. when the proportion of converter slag 
is increased from 20% to 30%. If the proportion of converter slag is more 
than 30% of the mixture, the melting point increases rapidly and the 
difference between maximum value and minimum value becomes large. For 
synthesized slags containing 70% to 80% of converter slag the melting 
point reaches its highest value and may exceed 1,650.degree. C. If the 
proportion of converter slag is over 80% of the slag mixture, the melting 
point is unexpectedly lowered; this is a new finding. The fact that the 
melting point of converter slag fluctuates from 1,630.degree. C. to 
1,450.degree. C. was found to be controlled by its basicity and total Fe 
content by this experiment. The melting point of a synthetic slag formed 
by melting a mixture of converter slag and blast furnace slag at various 
ratios is not predictable from the melting points of both slags and the 
mixing ratios. When the proportion of converter slag is 70% - 80% by 
weight of the synthetic slag, the melting point of the synthetic slag 
shows an extraordinary high value. This was found to be true from basic 
studies separately carried out on quarterly of the equilibrium diagram CaO 
- SiO.sub.2 - Al.sub.2 O.sub.3 - FeO and analysis of the result. 
Blast furnace slag is generally charged into a slag ladle and kept there 
after the slag is tapped from the furnace. After some time, the surface of 
the molten slag is solidified. However, the temperature drop inside the 
ladle is very slow and a molten slag temperature of 1,360.degree. C. - 
1,400.degree. C. may be kept for comparatively long time periods. In 
contradistinction the temperature of converter slag when charged into the 
ladle is from 1,650.degree. C. to 1,750.degree. C. and if the slag is kept 
in the ladle, solidification of the surface layer proceeds rapidly and the 
solidified layer becomes thicker more rapidly. The temperature of such 
molten slag on the inside is usually lowered by 150 - 200.degree. C. very 
rapidly after charging. Therefore, when converter slags and blast furnace 
slags are mixed in the molten state as in the case of the method of this 
invention, converted slag may be directly charged into the ladle 
previously charged with a predetermined amount of blast furnace slag. By 
this method, large amounts of energy contained in the converter slag can 
be effectively utilized and formation of solidified surface layers will be 
insignificant. This invention is not limited to such mixing. The object of 
this invention can also be accomplished by mixing the slags in a container 
which can hold both slags in the required proportions. 
The reason why the chemical composition of the synthetic slag used in the 
process of the invention is limited to specified ranges of specified 
basicity and components is as follows. The first reason is that if 
comparatively large temperature difference exists between the temperature 
of synthetic slag formed by mixing blast furnace slag and converter slag 
and the melting point of the synthetic slag, the succeeding steps of the 
process of the invention can be advantageously carried out. For example 
when blast furnace slag kept at 1,390.degree. C. is mixed with converter 
slag kept at 1,680.degree. C. in a slag ladle uniformly, the temperature 
of the synthetic slag is shown by line AB in FIG. 1. It is nearly a 
straight line relationship with the mixing ratio of the two slags. The 
melting point of the synthetic slag obtained is almost within the 
temperature range contained by the CD curve and the EF curve as was 
described above. Thus, if the temperature of the synthetic slag is 
50.degree. C. - 100.degree. C. higher than the melting point of the 
synthetic slag, succeeding steps of the process of the invention can be 
advantageously carried out. Thus the mixing ratio of slags is desirably 
limited to 40% by weight of converter slag and 60% by weight blast furnace 
slag. The synthetic slag within such range has good fluidity and enables 
one to use a thin, multiple layer flow operation in a pit as described 
hereinafter. 
The second reason is the following. Any prior art converter slag cannot 
avoid the disadvantages of the dusting and slaking phenomena previously 
described because of its chemical composition. By the method of our 
invention, converter slags can be transformed to stable chemical 
compositions. That is, by making the basicity (CaO/SiO.sub.2) of the slag 
less than 1.65, unslagged lime existing in the converter slag may be 
completely dissolved in the slag. Further, complicated compounds 
(consisting mainly of 3CaO.SiO.sub.2) existing in the highly basic slag 
disappear and the amount of complicated compounds consisting mainly of 
2CaO.SiO.sub.2 decreases greatly. Therefore, extraordinary expansion 
associated with the transformation .alpha..fwdarw..beta..fwdarw..gamma. of 
these compounds decreases greatly. 
Most of the total Fe content of converter slag exists in the form of FeO. 
Therefore total Fe content can be decreased easily by mixing with blast 
furnace slag. This is advantageous, particularly from the point of 
preventing dusting of slag. Thus, total Fe content is specified to 2 - 8%. 
The reason why Al.sub.2 O.sub.3 content in the synthetic slag is limited 
to less than 18% is to lower the melting point of the slag. If the 
proportion of converter slag mixed with blast furnace slag is chosen so 
that the synthetic slags have the composition specified herein, the 
succeeding steps of the process of the invention will achieve the desired 
result. In general, 1.5 to 9.5 parts of blast furnace slag weight is 
required for mixing with 1 part of converter slag. If the synthetic slag 
thus produced is rapidly cooled or slowly cooled, slag comparable to blast 
furnace slag in properties (which is small in free lime) and has almost no 
slaking and dusting disadvantages may be obtained. However, even after 
mixing blast furnace slag with converter slag within the specified 
composition range, fine metallic iron particles dispersed in the original 
converter slag still exist as a problem. To remove these fine, metallic 
iron particles we discovered that metallurgical oxidation by blowing 
oxygen containing gas into the molten slag is effective. The fine metallic 
iron particles are burnt to oxide and slagged. Since the molten slag is 
vigorously agitated by the oxygen containing gas, uniform mixing of blast 
furnace slag and converter slag (which have different viscosity, specific 
gravity and temperature) is effectively carried out. 
In blowing an oxygen containing gas into the molten slag through a lance, 
the higher the O.sub.2 content in the gas the stronger is the oxidation 
reaction. There is an increase in the temperature of the synthetic slag 
proportional to oxidation. If the temperature of the resulting oxidized 
slag is too high it may be lowered by adding a less oxidative gas to the 
oxygen containing gas, for example by the addition of air or nitrogen. 
By the method of the invention, oxygen containing gas is specified to be 
blown into the molten slag through a lance. The lance is preferably 
immersed in the molten slag, but it may also be positioned above the slag 
surface. 
The process of the invention is further described in the following. Fine 
metallic iron particles in the molten slag are kept at 1,400.degree. C. - 
1,450.degree. C. since they are heated by contact with the synthetic 
molten slag. Therefore if they come into contact directly with oxygen they 
are oxidized instantaneously. The FeO in the molten synthetic slag is 
oxidized to Fe.sub.2 O.sub.3. Therefore fine metallic iron particles 
dispersed in molten synthetic slag are very speedily removed by oxidation. 
The iron oxide formed by oxidation of the fine metallic iron particles is 
transformed into the slag, and helps to decrease the free lime content 
when the slag is solidified. 
In this invention, by blowing an oxygen containing gas into the synthetic 
molten slag, oxidation of metallic iron and admixtures of the molten slags 
are simultaneously carried out. This is an advantage of the method of the 
invention. 
The fluidity of the oxidized molten slag after fine metallic iron particles 
are removed becomes as good as that of blast furnace slag. Therefore if it 
is desired to granulate the slag, the hazard of explosion is reduced. 
Thus, the conventional equipment for blast furnace slag granulation can be 
used without danger. The granulated slag thus formed has greater strength 
than blast furnace granulated slag, since basicity, total Fe content, 
specific gravity and density of the product slag are improved over blast 
furnace slag. The free lime content of 0.05 - 0.08% is almost the same as 
that of blast furnace slag, and is much lower than the free lime content 
(0.3 - 1.5%) of converter granulated slag. Thus the granulated slag 
obtained by the method of this invention has a high value. 
When thin multiple layer casting of slag after oxidation treatment is 
carried out in a pit the obtained lump type slag has very superior 
physical properties, particularly in mechanical strength in comparison to 
blast furnace slag, since the free lime content is lower. 
According to the above described method of this invention, if chemical 
composition of tapped molten converter slag is supposed, and blast furnace 
slag volume is pre-set to obtain synthetic molten slag having the desired 
chemical composition, we can obtain slag which may be effectively applied 
without any danger, regardless of the basicity and the composition of the 
converter slag. 
The following example is given to describe the manner and process of making 
and using the invention and sets forth the best mode contemplated by the 
inventors of carrying out the invention but is not to be construed as 
limiting. 
EXAMPLE 1 
To a ladle, in which 12 tons of blast furnace molten slag having the 
composition shown in Table 2, CaO/SiO.sub.2 basicity 1.21 temperature at 
1,410.degree. C., and specific gravity 2.91 is held, 4 tons of molten 
converter slag, having the chemical composition shown in Table 2, basicity 
(CaO/SiO.sub.2) 3.95, temperature 1,650.degree. C. and specific gravity 
3.79 is charged and mixed. Then the ladle is moved to a molten slag 
treating place. 
Table 2 
__________________________________________________________________________ 
Chemical composition % Metal- 
Temperature 
Item Basicity Total lic* 
at mixing 
Kind CaO/SiO.sub.2 
SiO.sub.2 
CaO 
Al.sub.2 O.sub.3 
Fe MnO 
TiO.sub.2 
MgO 
P.sub.2 O.sub.5 
S iron% 
time .degree. C 
__________________________________________________________________________ 
blast furnace slag 
1.21 35.09 
42.46 
14.02 
0.80 
0.56 
0.73 
2.46 
0.04 
1.45 
-- 1,410 .degree. C 
converter slag 
3.95 13.12 
51.83 
0.82 
17.62 
4.11 
1.55 
3.14 
2.32 
0.20 
4.5 1,650 
__________________________________________________________________________ 
*Metallic iron content, which is physically mixed in the converter slag 
and which is different from total Fe as previously defined. 
After 7 minutes the resulting slag is cast into a smooth pit having a 
section of width 3 m .times. length 6 m., and slowly cooled to solidify. 
Then the slag in the pit is divided into 18 equal parts. Slag samples are 
taken from each part and analyzed for chemical composition. The results 
are shown in Table 3 below. 
Table 3 
__________________________________________________________________________ 
Chemical composition % 
Item Basicity Total Metallic iron* 
Kind CaO/SiO.sub.2 
SiO.sub.2 
CaO Al.sub.2 O.sub.3 
Fe MnO TiO.sub.2 
MgO P.sub.2 O.sub.5 
S % 
__________________________________________________________________________ 
Theoretical 
chemical 
composition 
1.51 29.60 
44.80 
10.72 
5.01 
1.45 
0.94 
2.63 
0.61 
1.14 
1.13 
of 
synthetic 
slag 
__________________________________________________________________________ 
Actual 
chemical 
composition 
1.46.about. 
28.20.about. 
43.55.about. 
8.26.about. 
3.95.about. 
1.16.about. 
0.79.about. 
2.50.about. 
0.39.about. 
0.90.about. 
0.65.about. 
of 1.61 31.15 
45.90 
13.15 
6.09 
1.74 
1.08 
2.86 
0.82 
1.42 
2.72 
synthetic 
slag 
__________________________________________________________________________ 
*Metallic Iron, supra. 
The theoretical chemical composition described in Table 3 means the 
chemical composition predicted from the mixing ratio of blast furnace slag 
and converter slag on the assumption that both are completely mixed. 
Actual chemical composition of the synthetic slag showed considerable 
variation depending on sampling places as shown in Table 3. This shows 
that uniform compositional structure cannot be obtained by natural mixing. 
Particularly physically mixed metallic iron content variation is marked. 
To the remaining 12 tons of synthetic slag after the first casting into the 
pit, pure oxygen is blown through 3/4" diameter steel pipe for 8 minutes 
at 4 Nm.sup.3 per minute. After oxidation and agitation is carried out 
completely, about 6 tons of slag is cast into a smooth pit of the same 
dimensions previously described. The slag is slowly cooled and solidified. 
Sampling of synthetic slag was made from 18 parts as before, and their 
chemical compositions were analyzed. The result is shown in Table 4. 
Table 4 
__________________________________________________________________________ 
Metallic iron 
Chemical composition % particle 
Item Basicity Total content 
Kind CaO/SiO.sub.2 
SiO.sub.2 
CaO Al.sub.2 O.sub.3 
Fe MnO TiO.sub.2 
MgO P.sub.2 O.sub.5 
S % 
__________________________________________________________________________ 
Theoretical 
chemical 
composition 
1.51 29.60 
44.80 
10.72 
6.14 
1.45 
0.94 
2.63 
0.61 
1.14 
0 
of 
synthetic 
slag 
__________________________________________________________________________ 
Chemical 
composition 
of 1.49.about. 
29.49.about. 
44.50.about. 
10.18.about. 
5.72.about. 
1.12.about. 
0.82.about. 
2.38.about. 
0.52.about. 
0.50.about. 
0.02.about. 
synthetic 
1.54 30.45 
45.43 
11.61 
6.58 
1.59 
1.06 
2.81 
0.73 
0.77 
0.04 
slag after 
oxygen 
mixing 
__________________________________________________________________________ 
As is shown in Table 4, variation of the chemical composition of synthetic 
slag cast into the pit after oxygen blowing is very small. Particularly, 
metallic iron particles physically mixed in the slag showed low value, 
since they were removed by oxidation. 
Right after No. 2 casting, 3 tons of the remaining synthetic molten slag is 
granulated slagged by granulated slag treating equipment. The fluidity of 
the molten slag is good and constant volume flow easily obtained without 
explosion. The chemical composition of the granulated slag is shown in 
Table 5. Variation of composition and physically mixed metallic iron 
particles showed very low values. 
Table 5 
__________________________________________________________________________ 
Metallic iron 
Chemical composition % particle 
Item Basicity Total content 
Kind CaO/SiO.sub.2 
SiO.sub.2 
CaO Al.sub.2 O.sub.3 
Fe MnO TiO.sub.2 
MgO P.sub.2 O.sub.5 
S % 
__________________________________________________________________________ 
Theoretical 
chemical 
composition 
1.51 29.60 
44.80 
10.72 
6.14 
1.45 
0.94 
2.63 
0.61 
1.14 
0 
of 
synthetic 
slag 
Chemical 
composition 
1.48.about. 
29.06.about. 
44.40.about. 
10.22.about. 
5.74.about. 
1.44.about. 
0.78.about. 
2.39.about. 
0.37.about. 
0.48.about. 
0.02.about. 
of 1.53 29.94 
45.28 
11.42 
6.48 
1.86 
1.04 
2.62 
0.64 
0.65 
0.03 
granulated 
slag 
__________________________________________________________________________ 
In the above example, properties of solidified product slag after oxidation 
treatment and slow cooling and those of solidified slags cast into the 
same pit of blast furnace slag and converter slag are shown in Table 6. 
Free lime content of the product slag and that of blast furnace slag are 
almost the same. That of converter slag is about 20 times greater. The 
physical strength of the product slag is much greater than that of blast 
furnace slag. 
Properties of product slag and blast furnace slag after granulation are 
shown in Table 7. The difference of free lime content is hardly 
noticeable. The free lime content of the product slag was proved to be far 
smaller than that of converter slag (0.3%- 1.5%). The product slags 
produced by the method of the invention have stabilized chemical 
compositions and they can be utilized without pollution problems. 
Table 6 
__________________________________________________________________________ 
Physical properties 
Compression 
One direction 
fracture 
compression 
Item Basicity 
Free lime 
Weight of unit 
True specific 
strength 
strength 
Kind (CaO/SiO.sub.2) 
% volume kg/l 
gravity 
kg/cm.sup.3 * 
kg/cm.sup.2 
__________________________________________________________________________ 
blast 
furnace slag 
1.21 0.182 1.84 2.91 122.1 22.0 
converter slag 
3.95 4.145 2.90 3.79 -- -- 
Product slag 
1.52 0.195 2.10 3.14 240.5 35.1 
__________________________________________________________________________ 
*By Brazilian strength test 
Table 7 
__________________________________________________________________________ 
Particle Size 
Item Basicity 
Free lime less than 
Average 
Kind (CaO/SiO.sub.2) 
% 5 - 3 mm 
3 - 2 mm 
2 - 1 mm 
1 - 0.5 mm 
0.5 mm 
mm 
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Blast 
furnace 
1.21 0.05 2.9% 14.8% 46.8% 27.5% 8.0% 1.41 
slag 
Product 
slag 1.50 0.07 3.0 15.1 46.7 27.6 7.6 1.43 
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