How to Process Slags: Classifications, Components and Applications
2025/2/14 14:53:58 Other22205
What is slag?
Slag is fully named ground-granulated
blast-furnace slag (GGBFs), a by-product produced by metallurgical smelting plants.
In addition to iron ore and fuel (coke), appropriate limestone and dolomite
should also be mixed to lower the smelting temperature in the smelting process.
Calcium oxide in the limestone, magnesium
oxide in the dolomite, waste minerals in the iron ore, and ash in the coke are
smelted in the blast furnace to produce a melt containing silicate and
aluminate.
Slags
The melt floating on the surface of molten
iron is discharged from the port. After being quenched by the air and water, it
forms the granular particles (GGBFs).
The discharged slag has a large volume. And
it varies with ore grade and smelting method. For example, when producing 1 ton
of pig iron, 1 to 1.2 tons of slag is discharged from lean iron ore, but only
0.25 tons of slag discharged from high-grade iron ore.
With the improvement of modern
beneficiation and smelting technology, the amount of slag produced from per ton
of pig iron has been reduced significantly.
The composition and properties of slag are
different under different smelting processes and raw materials. And there are
mainly two methods for the classification of slags.
Classification of slag
By the types of smelted pig iron
Casted slag: slag discharged during
smelting and casting process.
-
Steelmaking slag: slag discharged when
smelting the pig iron for steelmaking.
-
Special slag: slag discharged when
smelting pig iron with other metal components.
By the basicity of slag
The ratio of the basic oxides and the
acidic oxides of the slag is called the basicity of the blast furnace slag ("B"
in short), B%=(CaO%+MgO%)/(SiO%+Al2O3%).
According to basicity, the slag can be
divided into three types:
Alkaline slag: B>1.
-
Neutral slag: B=1.
-
Acidic slag: B<1.
This is the most commonly used
classification method for blast furnace slag. The basicity ratio intuitively
reflects the relationship between the composition of basic oxides and acidic
oxides in slag.
Composition of slag
Composition of slag
The main chemical components in the slag
are SiO2, Al2O3, CaO, MgO, MnO, FeO, S, etc. Besides, some slags also contain
traces of TiO2, V2O5, Na2O, BaO, P2O5, Cr2O3, etc. The amount of CaO, SiO2, and
Al2O3 accounts for more than 90% of the total slags.
2
31-44
22-35
19-32
Al2O3
6-18
7-22
13-17
MgO
1-16
1-9
7-9
MnO
0.05-2.6
3-24
0.3-1.2
FeO
0.2-1.5
1.2-1.7
1.2-1.9
S
0.2-2
0.17-2
0.2-0.9
TiO2
-
-
6-31
V2O5
-
-
0.06-1
Comprehensive application of slag
Slag cement
Slag cement production process
Portland slag cement (PSC) is made of portland
cement clinker, granulated blast furnace slag, and 3% to 5% gypsum.
When Crusher, the amount of
blast furnace slag can account for 20% to 85% of the total cement weight, which
is very beneficial for improving the quality and reducing the production cost
of cement.
First, it has a strong resistance to dissolution and erosion, so it
can be used in water conservancy, seaports, and underground projects.
However, the corrosion resistance of slag cement is worse
than that of ordinary cement in acid water and magnesium saltwater.
Second, PSC has a lower hydration heat, which is suitable for pouring
concrete with large volume.
Third, with stronger heat resistance, it performs better than
ordinary cement in high-temperature workshops and blast furnace foundations.
Gypsum slag cement is a hydraulic
cementitious material obtained by mixing and grinding dry slag and gypsum, PSC
or lime in a certain ratio.
In the formulation of gypsum slag cement,
blast furnace slag is the main raw material, accounting for about 80% of the
total components.
This gypsum slag cement has low cost and
good resistance to sulfate attack and permeability, and is suitable for
hydraulic construction and making various prefabricated blocks.
Lime slag cement is a hydraulic
cementitious material obtained by mixing and granulating dry slag, quick lime,
and natural gypsum in an appropriate ratio.
The amount of lime is generally added about
10% to 30%. It plays the role of stimulating the active ingredients in the slag
so as to produce hydrated calcium aluminate and hydrated calcium silicate.
Lime slag cement can be used for various
pre-products of steam curing concrete, unreinforced concrete in water,
underground or pavement, and industrial and civil building mortar.
Slag bricks
Slag brick production process
Slag brick is made by mixing, watering,
grinding and pressing slag and limestone. In the production process of slag
brick, the particle size of the slag is generally smaller than 8 mm, and the steam
temperature injected into the Crusher is about 80 ¡æ to 100 ¡æ, the maintaining time
is about 12 hours.
The brick made of 87% to 92% of granulated
blast furnace slag, 5% to 8% of cement, and 3% to 5% of water has a high
hardness that can reach up to 10 MPa, which can be used in the common house and
underground construction.
In addition, the brick with higher hardness
can be made by mixing 40% of slag powder and 60% of ground-granulated
blast-furnace slag and autoclaved curing for about 6 hours under the steam
pressure of 1.0 MPa to 1.1 MPa.
Slag bricks
Fly ash, slag, sand, and stone powder are
the main raw materials. The materials can be taken locally, which has a high
utilization rate, low cost, and high profit.
The materials such as slag, fly ash and
sand are polymerized by gas making agent and reinforcing agent, and then easily
formed by special equipment.
The simple industrial shed can be used as a
factory, and the products can be stored in the open air without a warehouse.
The business can start with a small
investment and scale. And It can be produced on a fixed plant or can be
produced on the movable site.
Slag concrete
Wet and ground slag concrete is made with
slag as the main raw material. The producing method is to grind slag and
activators (water, cement, lime, and gypsum), and mix them with coarse
aggregate.
The producing process of slag and gravel
concrete is similar to ordinary concrete, but water consumption is slightly
higher. The added water is generally measured by the weight of slag, accounting
for about 1% or 2% of the total slag weight.
Generally, When the strength of the
concrete prepared by slag and gravel is the same as that of the concrete
prepared by the natural aggregate, the amount of concrete can be saved by 20%.
It can effectively improve the seawater resistance of concrete,
especially suitable for seawater engineering.
-
It can significantly reduce the hydration heat of concrete, suitable
for the preparation of large volume concrete.
-
It can inhibit the alkali-aggregate reaction and improve the
durability of concrete.
-
It can greatly increase the strength of concrete.
-
It can improve the density of concrete and improve the
impermeability of concrete.
-
It can reduce the cost of concrete.
Slag ballast road engineering
Slag and gravel have hydraulic properties,
which can be used when constructing highways.
The Crusher contains
many small holes, which has good diffuse reflection performance and a large
friction coefficient.
It also has higher heat resistance than
ordinary crushed stone and is more suitable for the runway at the airport.
Slag cotton
Slag cotton is mainly made of slag, which
has the properties of heat preservation, sound, and cold insulation. The
chemical composition and physical properties are shown in the following tables.
2
Al203
CaO
MgO
S
Content/%
32-42
8-13
32-43
5-10
0.1-0.2
-1¡¤k-1
Sintering temperature/¡æ
Density/g¡¤cm-3
Fiber density /¦Ìm
Applicable temperature range /¡æ
0.033-0.041
780-820
0.13-0.15
4-6
-200-800
There are two methods for producing slag
cotton: blowing method and centrifugal method. Blowing method: the melted and flowed raw materials are blowing by
the spraying steam or compressed air to produce cotton.
Centrifugal
method: the raw material is melted in the furnace
and falls on the rotating disc to produce slag cotton.
The main raw material of slag cotton is
blast furnace slag, accounting for about 80% to 90%. and other materials are dolomite,
fluorite, or others such as red bricks, pebbles, etc. The fuel for producing
slag cotton is coke.
Injection process to produce slag cotton
Slag cotton can be used for thermal
insulation, sound absorption, and fireproofing.
The finished products processed by it
include thermal insulation products (board, felt, and tube), sound absorption products
(board, felt, strip, and belt), and fireproofing products (board and fiber).
Slag wool is widely used in metallurgy,
machinery, construction, chemistry, and transportation sectors.
Slag glass-ceramics
Glass-ceramics is a new type of inorganic
material that has been developed in recent decades. Various rocks and stones
can be used as the raw materials of glass-ceramics, which are extremely rich.
And blast furnace slag can also be used to produce slag glass-ceramics.
The slag glass-ceramics are composed of 62%-78%
of blast furnace slag, and 22%-38% of silica or other non-ferrous metallurgical
slags.
Slag glass-ceramics mainly consists of the
following chemical elements:
2
Al203
CaO
MgO
Na20
Nucleation agent
Proportion
40%-70%
5%-15%
15%-35%
2%-12%
2%-12%
5%-10%
Slag glass-ceramic products are harder than
high-carbon steel and lighter than aluminum. Its mechanical properties are
better than ordinary glass, and its wear resistance is better than that of cast
stone. It has good thermal stability, and its electrical insulation performance
is close to that of high-frequency porcelain.
The slag glass-ceramics are used in the
anti-corrosion layer of various container equipment in the metallurgy, chemical
industry, coal, machinery, and other industrial sectors.
The production process of glass-ceramics
Slag silicon calcium magnesium fertilizer
Slag silicon calcium magnesium fertilizer
is made of blast furnace slag, vertical kiln ash, waste residue, and silicon residue.
The above materials are melted at high temperatures in a blast furnace or
electric furnace. The finished product is cheap in price and rich in composition.
The production process of slag fertilizer
At present, France and Luxembourg produce
the silicon calcium magnesium fertilizer by combining the characteristics of
their own iron ore and steel-making methods. Japan and North Korea also use
slag to make silicon fertilizer.
Conclusion
Slag has many other applications. For
example, slag can be used to produce permeable bricks, imitation stone and
artificial stone.
The characteristics of slag products such
as strength, water resistance, fireproofing, sound insulation, anti-corrosion,
shock resistance, and others also bring it a broader market prospect.
