Refractory Challenges in Lead and Zinc Furnaces
29
High Soda Supply
The high alkali supply in secondary lead production vessels results under oxidizing
atmospheric conditions in a formation of chromium (VI) salts. The chromate formation is caused by the key agents like potassium and sodium contained in the furnace
feed. According to thermodynamic calculations by FactSage
TM , the formation of the
chromate phases occurs in a temperature range between 900 and 1000 °C. By the use
of the X-ray diffraction, alkali-bearing chromates such as K 3 NaCr 2 O 8 and K 2 CrO 4
(tarapacaite) were identified. Both mentioned salts contain toxic chromium (VI).
Conclusion
Post-mortem studies clearly highlight which specific stresses affect the refractory
product performance in the lead and zinc processing furnaces. Even though the
various wear phenomena in the individual production vessels differ in their nature
and cause, their final effect is the same, namely a significant refractory destruction
by degeneration of the brick microstructure.
Furthermore, post-mortem studies demonstrated clearly that as consequence of
chemical attack (by acidic slag, high supply on SiO 2 , sulfur, soda, iron oxide), the
infiltration and corrosion of the brick’s inherent components lead to a weakening of
the refractory microstructure, loss of flexibility, and brick strength. Such weakened
microstructure is highly susceptible to continuous wear by hot erosion. Additionally,
due to changed (thermo-)mechanical properties, crack formation, primarily at the
interface between the infiltrated and non-infiltrated brick microstructure, occurs.
Discontinuous wear by spalling is then the final consequence.
Also reduction and Red-Ox phenomena will result in permanent defects. Once
the bond between particles and matrix is loosened, the brick microstructure will not
reform. This reduces the strength of the brick and increases the susceptibility of the
microstructure to further infiltration/corrosion.
The precise knowledge of the wear phenomena and the metallurgical process is
an absolutely necessary prerequisite for the refractory producer for providing appropriate brick lining solutions. RHI Magnesita enhances this refractory optimization
process through active collaborations with its customers. The post-mortem studies
additionally provide an important base for the focused product development, leading
to new refractory products for the lead and zinc industry.
29
High Soda Supply
The high alkali supply in secondary lead production vessels results under oxidizing
atmospheric conditions in a formation of chromium (VI) salts. The chromate formation is caused by the key agents like potassium and sodium contained in the furnace
feed. According to thermodynamic calculations by FactSage
TM , the formation of the
chromate phases occurs in a temperature range between 900 and 1000 °C. By the use
of the X-ray diffraction, alkali-bearing chromates such as K 3 NaCr 2 O 8 and K 2 CrO 4
(tarapacaite) were identified. Both mentioned salts contain toxic chromium (VI).
Conclusion
Post-mortem studies clearly highlight which specific stresses affect the refractory
product performance in the lead and zinc processing furnaces. Even though the
various wear phenomena in the individual production vessels differ in their nature
and cause, their final effect is the same, namely a significant refractory destruction
by degeneration of the brick microstructure.
Furthermore, post-mortem studies demonstrated clearly that as consequence of
chemical attack (by acidic slag, high supply on SiO 2 , sulfur, soda, iron oxide), the
infiltration and corrosion of the brick’s inherent components lead to a weakening of
the refractory microstructure, loss of flexibility, and brick strength. Such weakened
microstructure is highly susceptible to continuous wear by hot erosion. Additionally,
due to changed (thermo-)mechanical properties, crack formation, primarily at the
interface between the infiltrated and non-infiltrated brick microstructure, occurs.
Discontinuous wear by spalling is then the final consequence.
Also reduction and Red-Ox phenomena will result in permanent defects. Once
the bond between particles and matrix is loosened, the brick microstructure will not
reform. This reduces the strength of the brick and increases the susceptibility of the
microstructure to further infiltration/corrosion.
The precise knowledge of the wear phenomena and the metallurgical process is
an absolutely necessary prerequisite for the refractory producer for providing appropriate brick lining solutions. RHI Magnesita enhances this refractory optimization
process through active collaborations with its customers. The post-mortem studies
additionally provide an important base for the focused product development, leading
to new refractory products for the lead and zinc industry.