Koleszár, Péter

Kozák, Miklós

Papp, István

University of Debrecen Electronic Archive

ACTA GGM DEBRECINA Geology, Geomorphology, Physical Geography Series DEBRECEN Vol. 4-5, 3–6    2010 
 3
Behaviour of ladle slag minerals in atmospheric conditions regarding utilization 
Üstsalak ásványok viselkedése légköri körülmények között különöse tekintettel az alkalmazásra 
 
Péter Koleszár – István Papp – Miklós Kozák  
 
Department of Mineralogy and Geology, University of Debrecen, H-4032, Debrecen, Egyetem tér 1; email: scoriomin@gmail.com 
 
Abstract – The secondary steelmaking slags contain numerous minerals such as larnite, Ca-aluminates. The formed ladle slags are 
unstable in the atmosphere so they are dissociating to fine powder. The modification change of larnite (C2S) is the main cause of this 
phenomenon. The fresh formed white slag powder is unprotected against wind erosion. The water sprinkling creates a solid layer on it 
instantly. We have found that this layer contains calcium aluminate hydrate that causes rapid binding. This protective layer reduces the 
effects of wind erosion significantly. 
 
Összefoglaló – A szekunder salakok sokféle ásványt tartalmaznak, amilyen például a larnit és a különféle kalcium- aluminátok. A 
képződött salakok a levegőre kikerülve fehér porrá esnek szét, amit főként a larnit módosulása idéz elő. A frissen képződött fehér salak 
fokozottan szélerózió érzékeny. Vízzel történő locsolás hatására viszont szilárd kéreg képződik rajta. Vizsgálataink szerint ez a kötött réteg 
kalcium-aluminát-hidroxidokat tartalmaz, melyek a gyors kötés okozói. E védő burok hatására a szélerózió lehetősége jelentősen csökken. 
 
Keywords – minimill, Ladle Furnace, deoxidisation, oldhamite, calcium-aluminate,gehlenite 
Tárgyszavak – miniacélmű, üstkemence, deozoxidáció, oldhamit, calcium-aluminát,gehlenit 
 
 
Introduction 
 
The first step of steelmaking is the so called primary 
steel metallurgy. By this way the charged material goes 
across oxidization. The result of these stages is the uptake 
of the oxidable nondiserable elements such as Si, Mn, P to 
the slag phase as SiO2, MnO, P2O5. At the same time the 
initial S content of the steel decreases significantly (max. 
50%) while it is absorbed in the slag. As they use the most 
common technology, primary steelmaking is very similar at 
the integrated steelworks, however, it can be different at 
the minimills. At the integrated steelworks mainly basic 
oxygen furnaces (BOF) are in operation which consume 
the hot metal produced by the blast furnace. So at the BOF 
area the main charging material is hot metal (75%) with 
well known quality and the rest of the material contains 
separated scrap (25%), so it contains nondiserable elements 
in relatively low concentration. In this situation the 
theoretical probability of „catch carbon heat” technology is 
given where the heat is under oxygen blasting until the 
carbon content decreases to the diserable level and then the 
heat is tapped. The steel produced in this way contains 
dissolved oxygen in a relatively low concentration resulting 
in the lower consumption of deoxidants. Nowadays these 
methods are becoming widespread worldwide. Most of the 
BOF meltshops use „building up heat” technology that 
means total oxidation of the batch. Therefore the final 
product is steel with almost zero C, Si, P, Mn content that 
is carbonized under tapping, and treated in the ladle. This is 
a reasonable technology because the steelmakers can 
produce relatively clean raw steel from contaminated raw-
material for secondary steelmaking facilities. 
The minimills work with 100% The UHP (Ultra High 
Power) EAF( is the soul of this mill types. The most 
applied method is the one mentioned first, the “building up 
heat” technology. The scrap charge is melted down by the 
electric arc and oxyfuel jetburners such as in the Steelwork 
of Ózd Ltd. (OAM Ltd.). By the end of the heating the 
steel bath becomes oversaturated in oxygen. After casting 
gases would form eraised hollows as gas inclusions in the 
rolled steel products that are harmful. Other problems are 
the high inclusion and sulphur content. These parameters 
do not meet the requirements of the steel standards  
These quality problems can be avoided by secondary 
refining. Secondary steelmaking technologies can be 
separated substantially to two types, the atmospheric and 
vacuum technologies. The mini mill type steelworks to 
meet this requirement use different ladle metallurgical 
technology (for example: vacuum technologies: VOD, 
ASEA-SKF etc) (Szőke 1990). 
The most advanced and fundamental technologies are 
the atmospheric gas purging (AP) technologies where the 
inert gas (N2, Ar) flows into the ladle at the bottom of the 
ladle via a purging plug. The standard technology consists 
of two technological steps. The first step is the 
precipitational deoxidation while the steel is under tapping. 
The next step is the diffusion deoxidation which is carried 
out in a ladle furnace where the steel obtains its final 
composition and the inclusions are floating into the slag 
and there they are absorbed 
 
Mineralogical effects of secondary metallurgy 
 
By the process the EAF getting tap the described 
quantity of steel, while at the same time the ladle treatment 
of the steel starts. In this way flux additives and deoxidant 
agents are given to the steel flow. These deoxidants are 
ferroalloys (FeMn, FeSi, FeSiMn, etc.) and aluminium. Flux 
additives are: lime, alumina, alu-slag, fluorspar and coke 
breeze as carburizing agent. The ferroalloys and the 
aluminium are reacted with the active dissolved oxygen 
resulting in dropping down (20ppm) of the initial oxygen 
content. This technological step is called precipitation 
deoxidation, where the oxygen forms different oxides and 
silicates thus precipitating itself. The eraised particles in the 
bath are different minerals such as fayalite-knébelite-
cristobalite, corundum, herczynite, etc. They have different 
density and grain diameter. This results in the different 
floating velocity of the slag. This phenomenon can be 
easily calculated by the formula of Stokes. But the 
remaining particles are the inclusions of steel. These 
residual minerals cause the clogging of the wellblock such 
ACTA GGM DEBRECINA Geology, Geomorphology, Physical Geography Series Vol. 4-5       2010 
 
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as corundum and mayenite so the casting becomes 
disturbed and problematic. The dilatation of the inclusions 
is different and they cause structural stress resulting in the 
deterioration of the steel product. 
 
Figure 1: schematic diagram of the ladle furnace at OAM Ltd. 
1. ábra: Az OAM Kft üstkemencéjének sematikus 
folyamatábrája 
 
The function of lime flux are either to absorb these 
deoxidation products or to transform them to another non 
harmful ductile inclusion. These compounds are different. 
The basic slag, the high lime content and the reductive 
environment perform good desulphurisation (Figure 2). In 
this way the sulphur content of the steel melt is precipitated 
as metal sulphides such as FeS (troilite), MnS (alabandine), 
CaS (oldhamite) and MgS (niningerite) floating up to the  
slag. There are some purging plugs at the bottom of the 
ladle. The gas purging generates circulation in the melt 
towards the slag and down to the bottom. In this way – 
while ladle being transported to the Ladle Furnace stand – 
the inclusions and other reaction products are floating up 
and the dissolved gas content (CO, H2) decreases as well.  
Usually three graphite electrodes are set in the melt so 
they heat the bath until the temperature reaches that the 
casting needs (Figure 1). At the same time, circulation of the 
melt is continuous and the remaining oxygen content 
decreases further. 
The process last mentioned is the diffusion 
deoxidation, because the equilibrium of the FeO, MnO 
concentration in the metal/slag phase is modified. That 
means lower FeO, MnO concentration is kept in the slag 
by the addition of deoxidation agents such as, Al, FeSi 
powder, CaSi and coke powder (SIMON et al. 1980). The 
reduced metal content of the slag flows into the steel bath. 
The desulphurisation is a similar process. Temperature 
is high (6000-7000°C) close around the electrodes. In these 
conditions carbides might have eraising (CaC2, Mg4C3, SiC, 
Al4C3 etc.), but hypothetically, different fullerens, 
metallokarboeders can be eraised to. The added lime flux 
forms clinker like minerals with the non-decompositive 
products of deoxidising like corundum and a few silicates. 
 
 
Figure 2: The situation of the ladle slag in the CaO-Al2O3-SiO2 
ternary system 
2. ábra: Az üstsalak a CaO-Al2O3-SiO2 háromszögdiagramban 
 
 dissociated White lumpy Brownish 
grey lumpy 
gehlenite + + + 
lime + + + 
merwinite + + + 
larnite + +  
bredigit + + + 
mayenit + +  
periklase + +  
ferdisilicite +   
Table 1: The XRD detected minerals from the slag types (analysed by 
P. Kovács- Pállfy – P. Kónya) 
1. táblázat: A salaktípusokban RTG vizsgálattal kimutatható 
ásványok (elemezte: Kovács-Pálffy P. – Kónya P.) 
 
These are the following: calcium-aluminates e.g. C2A, 
C3A and mayenite, silicates such as C2S (larnite), C3S 
(hatrurite), gehlenite-akermanite, etc. The sulphur content 
forming MnS alabandine – CaS oldhamite – MgS 
niningerite – (Fe,Mg,Ca)S kielite series. The precipitated 
calcium-aluminate grains affect the sulphides as 
mineralizators, as floating aluminate inclusions adsorb 
sulphides on their grain surface as oldhamite coatings 
(SEILEROVÁ et al. 2004). 
 
Figure 3: The white lumpy LF slag 
3. ábra: A fehér darabos üstkemence salak 
Koleszár et al.: Behaviour of ladle slag minerals in atmospheric conditions       MINERALOGY, GEOCHEMISTRY 
 
 5
We have carried out X-ray diffraction analysis to 
describe the mineralogical composition of the slag. We 
have found that the predicted main minerals occur in the 
investigated slags, except for the hatrurite and spinell. 
Perhaps they are in the slags but in subcrystal state or they 
form stable silicates such as gehlenite, bredigite, Merwinite. 
 
 
Figure 4: The lumpy brownish gray Lf slag 
4. ábra: Barnásszürke darabos üstkemence salak  
 
The sulphides form pyro sols and they are dispersed in the 
slag as colloid scale particles which cannot be detected by 
XRD method, but the effect of water smells like hydrogen 
sulphide thus it can be suggested that they are present in 
the dissociated and in the white lumpy slags as well. We 
have found ferdisilicite in traces. This originates from 
residual Ferrosilicon deoxidising agent.  
 
 
 Mineralization of secondary slags 
 
The cooling slag in the presence of larnite tend to 
disintegrate, that can be explained by the larnite β-γ, 
structural transformation that increases volume (approx. 
10%) of the larnite crystal. This structural stress turns the 
slag into slag powder. The eraisement of this powder is an 
advantage and a disadvantage at the same time. The 
advantage of this phenomenon is the easy metal recycling 
because metal residues can be extracted by sieving and 
electromagnetic separation without crushing. Disadvantage 
of this material is the presence of fine particles because the 
fresh powder is exposed to wind erosion so it is hard to 
manipulate this material without air pollution. The most 
common method of avoiding pollution is water sprinkling. 
The hydrated material makes a bonded solid bark of the 
sprinkled surface. Water dissociates carbides, sulphides, 
nitrides, phosphides while small amount of acetylene, 
methane, ammonia, hydrogen sulphide phosphine eraises 
which cause no health risk 
 
 The effect of moisture and watering the slag powder 
is bounded. At the beginning, existing relatively loose 
material (breakable by hand) solidifies in a few months by 
the effect of calcium-aluminate (UKRAINCZYK et al. 2007) 
and free lime content. This process finally forms 
carbonates such as calcite, aragonite, (Figure 3). The sulphur 
content is solved out and  
 
LF slags -H2O 
% 
+H2O 
% 
SiO2 
% 
FeO
% 
TiO2
% 
Al2O3 
% 
CaO 
% 
MgO
% 
Na2O
% 
K2O
% 
MnO 
% 
S 
% 
other
(SiC)
% 
B3 
 
Dissociated  0.27 -1.03 20.55 1.30 0.05 17.56 48.34 7.27 0.03 0.35 0.32 0.67 3.00 1.46
White  
lumpy 
0.64 -0.49 16.07 0.67 0.03 16.92 55.10 5.83 0.06 0.35 0.00 1.89 2.00 1.85
Brownish  
Greyish 
lumpy 
0.36 -0.34 25.74 1.11 0.02 20.98 37.97 8.31 0.10 0.34 1.19 0.09 3.00 0.99
Table 2: The main element composition of the ladle furnace slags 
2. táblázat: Üstkemence salakok főelem összetétele  
  
the residual sulphur content is only hundred part of the 
starting total content. The ratio of the residual non-
dissociated material to the total mass is about 5-10% 
because these material phases are saturated or over 
saturated in silicon dioxide (SiO2) and alumina (Al2O3) i.e. 
brownish-greyish lumpy slags (Table 1) belong to that 
group. The definition of basicity is as follows: 
  
 Basicity B3= CaO%+MgO% 
                      SiO2%+Al2O3%  (1) 
 
B3<1 acid B3=1 intermediate  B3>1 basic (ideal) 
 
This type of slag is intermediate and slightly acid B3=0.99. 
It is an inefficient and harmful melt, as it cannot absorb 
any sulphur but corrodes the refractory lining of the ladle. 
 
Figure 5: Derivatogram of 1 year old, bonded LF slag (OAM Ltd.) 
(measurement: heating velocity: 10°C/min, ceramic crucible, air 
atmosphere 
5. ábra: Az 1 éves, kötött LF salak (OAM Kft.) derivatogramja 
(mérés: felfűtési sebesség: 10°C/min, kerámia tégely, levegő 
atmoszféra) 
ACTA GGM DEBRECINA Geology, Geomorphology, Physical Geography Series Vol. 4-5       2010 
 
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Utilization possibilities 
 
Utilization of the above slags is limited, because the 
dissociation of these materials is very slow and takes place 
even if samples are kept at dry places the room 
atmosphere. We have observed that the solid, stable 
looking pieces of slag kept on air tend to turn into slag 
powder by “self-powderising” within one year (i.e. white 
lumpy slag). This process can be beneficial for utilization 
as retarded slag fertilisers because the useful trace elements 
are digested slowly and gradually. Its sulphide content can 
be useful when the material is used as fungicide agent in 
desirable quantity (LOCH & NOSTICZIUS 2004). The 
sulphur content and slightly basic pH can be beneficial for 
the cultivation of brassicacea and fabaceaea families such 
as cabbage, rape, alfalfa bean, pea, etc. 
Ideal utilization of the material is the metallurgical 
utilization, because the conditioned slag contains sulphur 
as a trace element and abundant lime and alumina. The 
product can be sold as syntetic slag for secondary 
steelmaking after briquetisation or pelletisation and final 
calcination.  
According to Italian experiences (CAVALOTTI et al. 
2007) the white slag powder is ideal for slag foaming flux 
at EAF steelmaking, because the blowed slag powder 
without coke breeze under the slag forms numerous 
crystal rudiments that make cohesive foam structure. So 
the growing number of gas bubbles causes larger slag 
foam volume. This slag foam helps to make larger heat 
transfer of arc toward the batch and give good sound 
insulation capacity, thus noise pollution can be decreased 
(CAVALOTTI et al. 2007). The most beneficial fact is the 
lower consumption of lime flux making the budget of 
production reduced as well. 
The pelletisation of the slag powder can be simple. So 
the handling of the pellets is easier than that of the 
powders. Pellets can be sold easily as road construction 
material or in other forms of utilization. 
The first mentioned undissociated lumpy slags are 
valuable for the cement industry because they have 
saturated composition with low ratio of contaminants (i.e. 
S, Mn, K, Na) for producing cement. This material is ideal 
to set the aluminate content of the clinker. It requires, 
however, numerous other examinations to decide on this 
type of utilization. The easiest utilization would be to use 
the material as crushed stone for road construction 
(MÁRKUS & GREGA 2006). 
 
References 
CAVALOTTI, P.L., MAPELLI, C., MEMDI, F., PUSTORINO, 
F. (2007): Recycling of LF-white slag. – AIM-
Federacciai-VDEh joint meeting Seminar on 
Metallurgical Fundamentals, Dalmine 15 September, 
41–48. 
LOCH J., NOSTICZIUS Á. (2004): Agrokémia és 
növényvédelmi kémia (Agrochemistry and plant protection 
chemistry). – Mezőgazda Press, Budapest, 399 p. 
MÁRKUS R., GREGA O. (2006): Electric-arc furnace slag 
utilization in the consruction industry. – microCAD 
2006 International Scientific Conference, Miskolc, 
71–76. 
SEILEROVÁ, K., MIHOK, L., DOMOVEC, M., BALKO, K. 
(2004): Influencing of steelcleaness in ladle furnace. 
Acta Montanistica Slovaca, 10, 102–110. 
SIMON S., SZIKLAVÁRI J., SZŐKE L. (1980): Újabb 
technológiai eljárások az acélgyártásban (Recent 
technological procedures in steel production). – Műszaki 
Press, Budapest, 403 p. 
SZŐKE L. (1990): Elektroacélgyártás (Electric steel 
production), – MAVE and Műszaki Press, Budapest, 
361 p. 
UKRAINCZYK, N., MATUSINOVIC, T., KURAJICA, S., 
ZIMMERMANN, B., SIPUSIC, J. (2007): Dehydration of 
a layerd double hydroxide – C2AH8. Thermochimica 
Acta, 464, 7–15. 


Behaviour of ladle slag minerals in atmospheric conditions regarding utilization

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Behaviour of ladle slag minerals in atmospheric conditions regarding utilization

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