Morphology of slags components

by scanning microscopy

Glaze

Al As Bi Ca Cd Cu Fe K Mg Na Ni6,82 0,62 0,01 0,01 0,09 0,02 2,26 7,27 0,15 2,74 0,01

O P Pb S Se Si Te Ti V Zn

47,37 2,30 0,03 4,12 0,53 25,4

0 0,04 0,13 0,01 0,07 100,00

Glaze is the main component of slags.

Slags originating from the direct production of a metallurgical furnace are rich in isotropic glaze with a smooth, uncracked surface.

As a result of a devitrification process, glaze is covered with a lattice of cracks, which with the flow of time become larger causing its disintegration and occurrence of an amorphic substance.

Concentration of elements [Mass%] – example

Isotropic glaze surrounded by iron oxidesTransmitted light, magnification 100x,

crossed nicols

Glaze

Fot. XN, 100x

Glaze with hematite and magnetiteTransmitted light, magnification 100x,

crossed nicols

Glaze

Fot. XN, 100x

In the glaze there are metallic precipitations and crystalline nuclei of non-metallic phases.

Crystalline nuclei of melilitesTransmitted light, magnification 100x, one

nicol

Glaze surrounded by metallic precipitations

Reflected light, magnification 100x, one nicol

Drops of metalMetallic precipitations form individual drops of pure metal or

they appear in the form of polymetallic aggregates. In slags after the production of iron and steel they are first of all connected with iron concentrations, in slags after zinc and lead metallurgy metallic precipitations are rich in Zn and Pb, only sporadically silver drops can be found in them.

Drops of ironSEM microphotography, scanning

microscopy

Drops of zincBSE microphotography, scanning microscopy

Metals are present in glaze, they form: inclusions in the other minerals, their own minerals (magnetite, hematite) and metallic aggregates and they are also present in the structure of other minerals (augite, mellite).

Pyroxenes with inclusions of metalsTransmitted light, magnification 200x, one

nicol

Quartz with cracks filled by metalic precipitations

Transmitted light, magnification 100x, crossed nicols

Oxide phases identified in steelmaking slags include principally a number of iron oxides from

wustite FeO, through magnetite Fe3O4 to hematite Fe2O3 and sporadic occurrence of goethite FeOOH.

Iron oxides

Magnetite

Hematite

Wustite

Wustite creates globular forms. Such a form of wustite is created through the oxidation of iron and by assuming by this phase morphological forms characteristic for the liberation of metals.

Transmitted light, magnification 200x, one nicol

SEM microphotography, scanning microscopy

Magnetite

In the waste material we can distinguish two generations of magnetite.

First generation is represented by the sharp grains characterized by the square section. Its were crystallized with the other minerals during the alloy self cooling .

Second generation is represented by fine grains often mixed with the other compounds of the wastes. This generation was formed as a result of devitrification of glaze or silicate phases.

Transmitted light, magnification 100x, one nicol

Hematite can form several generations, from very fine grains dispersed among other phase components to larger, sharp-edged crystals. Yet, they are always characteristic of red-brown colouring, fine grains form pigment providing the glaze with red colouring.

Transmitted light, magnification 100x, one nicol