Refractory Challenges in Lead and Zinc Furnaces
25
Fig. 4 Magnesia-chromite
brick. Mineralogical
investigation. Corrosion of
the magnesia (MgO) by
sulfur attack. Idiomorphic
periclase crystals at
magnesia rims (arrows).
Idiomorphic forsterite
crystals (Fo). Chromite (Cr).
Lead oxide (PbO)
The penetration of gaseous SO 2 caused by oxidation of sulfidic ore leads to the
formation of SO 3 , which below temperatures of approximately 1100 °C reacts with
the basic oxide of the magnesia-chromite brick leading to the formation of magnesium
sulfate (MgSO 4 ) [13].
In case of magnesia-chromite bricks with high CaO/SiO 2 ratio, also the interstitial
phase in the magnesia such as dicalcium-silicate (Ca 2 SiO 4 ) is massively corroded.
The latter results in formation of Ca-sulfate (CaSO 4 ). Due to a severe corrosion of the
brick bonding phase, the initially high CaO/SiO 2 ratio is decreased into the stability
area of forsterite. Therefore, numerous single forsterite crystals could additionally
form in such a melt (Fig. 4). This is mainly caused by sulfate melt condensated close
to the brick cold face. The possible reaction is schematically represented as follows:
SO 3 + 2Ca 2 SiO 4 + MgO → Ca 3 MgSi 2 O 8 + CaSO 4
This means that the CaO/SiO 2 ratio of the silicate phases is shifted to a lower
value, and this similarly continues until forsterite is formed. As indicated by the
above equation, this reaction takes place only if CaSO 4 , which is a component of the
sulfate melt and not a solid phase, is penetrating to regions more distant from the hot
face.
At temperatures above 1100 °C, MgSO 4 will dissociate and form fine crystalline
MgO at magnesia rims (Fig. 4) [14]. This takes place without adequate rebuilding
of the original ceramic bonding of the brick.
Iron Oxide Attack
Either at the interface between the slag coating and the brick hot face or in the first
few mm from the hot face the magnesia-chromite brick becomes highly enriched
25
Fig. 4 Magnesia-chromite
brick. Mineralogical
investigation. Corrosion of
the magnesia (MgO) by
sulfur attack. Idiomorphic
periclase crystals at
magnesia rims (arrows).
Idiomorphic forsterite
crystals (Fo). Chromite (Cr).
Lead oxide (PbO)
The penetration of gaseous SO 2 caused by oxidation of sulfidic ore leads to the
formation of SO 3 , which below temperatures of approximately 1100 °C reacts with
the basic oxide of the magnesia-chromite brick leading to the formation of magnesium
sulfate (MgSO 4 ) [13].
In case of magnesia-chromite bricks with high CaO/SiO 2 ratio, also the interstitial
phase in the magnesia such as dicalcium-silicate (Ca 2 SiO 4 ) is massively corroded.
The latter results in formation of Ca-sulfate (CaSO 4 ). Due to a severe corrosion of the
brick bonding phase, the initially high CaO/SiO 2 ratio is decreased into the stability
area of forsterite. Therefore, numerous single forsterite crystals could additionally
form in such a melt (Fig. 4). This is mainly caused by sulfate melt condensated close
to the brick cold face. The possible reaction is schematically represented as follows:
SO 3 + 2Ca 2 SiO 4 + MgO → Ca 3 MgSi 2 O 8 + CaSO 4
This means that the CaO/SiO 2 ratio of the silicate phases is shifted to a lower
value, and this similarly continues until forsterite is formed. As indicated by the
above equation, this reaction takes place only if CaSO 4 , which is a component of the
sulfate melt and not a solid phase, is penetrating to regions more distant from the hot
face.
At temperatures above 1100 °C, MgSO 4 will dissociate and form fine crystalline
MgO at magnesia rims (Fig. 4) [14]. This takes place without adequate rebuilding
of the original ceramic bonding of the brick.
Iron Oxide Attack
Either at the interface between the slag coating and the brick hot face or in the first
few mm from the hot face the magnesia-chromite brick becomes highly enriched