98
CRUCIBLE CORROSION TEST TO EVALUATE THE PERFORMANCE OF
Al
2
O
3
-Cr
2
O
3
CASTABLE REFRACTORY FOR USE IN SHORT ROTARY
FURNACE OF LEAD RECYCLING
Prestes, E.
1,*
; Chinelatto, A. S. A.
1
; Resende, W. S.
2
1
2
Indústrias Brasileiras de Artigos Refratários - IBAR
The recycled lead obtained mainly from the recovery of lead from lead-acid batteries is named
secondary lead [1]. The process of smelting and reduction is carried out in a short rotary
furnaces where the lead metallic scrap composed of Pb, PbO
2
and PbSO
4
is added together
with C and Fe as reductant agents and Na
2
CO
3
as flux [2]. The oxi-reduction reactions happen
at temperatures above 1000
o
C and the slag produced in the process presents high content of
FeO component. The corrosion by slag attack is the main wear mechanism in furnaces of the
lead industry. Burned magnesia chromite bricks are the standard product for the lining since
MgO shows good resistance to solvent action of FeO and the Cr
2
O
3
improve the hot mechanical
resistance [3,4]. The employment of castable refractory in short rotary furnace of secondary
lead smelting is not found in the literature. In some waste melting furnaces the material for the
working lining are Al
2
O
3
-Cr
2
O
3
castable refractories, which have greatly extended the lining life
[5]. Therefore, with the purpose of examining the use of castable refractory in short rotary
furnace of secondary lead smelting, one commercial castable based on 81% Al
2
O
3
-3,5% Cr
2
O
3
was selected for the evaluation of slag infiltration potential in refractory material by static slag
attack “crucible corrosion test”. The sample test was molded following the technical data
supplied by the manufacturer and it was burned at a rate of 2
o
C/min to 1000
o
C and held at this
temperature for 5 hours. In the crucible corrosion test the hole is filled with slag and exposed to
high temperature to promote slag-refractory interaction. For this test the sample was filled with
170 grams of secondary lead slag and heated at a rate of 2
o
C/min to 1400
o
C and held at this
temperature for 5 hours. The slag chemical composition was 51,9% FeO; 15,9% SO
3
; 13,2%
Na
2
O; 10,4% SiO
2
; 2,09% Al
2
O
3
; 1,96% CaO; 1,56% PbO and 2,99% others. After the slag
attack test the cross section of the sample was obtained with a photographic digital camera as
seen in picture 1. The low slag infiltration shows the good performance of castable refractory.
Picture 2 shows the backscattered electron image of refractory-slag interface and picture 3
shows the EDS mapping image for the main elements of the slag (Fe, S, Na and Si). As seen
the FeO is the main corrosive agent of secondary lead slag due to its reaction with refractory
components (matrix and aggregate) and the formation of low melting compounds. EDS mapping
image of refractory slag interface (Picture 3) shows that there was no diffusion of the Fe
element inside of the refractory microstructure. This behavior is due to the presence of Cr
2
O
3
in
the refractory composition which has low solubility saturation in FeO rich slag and also the
indirect dissolution of Cr
2
O
3
in the slag due to formation of FeO.Cr
2
O
3
and consequently
retarding the corrosion process [6]. The slag attack result obtained by the tested product shows
the possibility of using of refractories castable in a short rotary furnace of secondary lead
smelting. Also the use of monolithic materials can increase the life of refractory lining.
References:
[1] R. Jolly and C. Rhin, Resources, Conservations and Recycling 10 (1994) 137-143.
[2] F. Chavez, R.D. Morales, A. Romero and A. Guerrero, Third International Symposium on
Recycling of Metals and Engineered Materials (1995) 337-347.
[3] T. Taschler and M. Köffel, European Metallurgical Conference (2005) 1045-1067.
[4] Poirier and M. Bouchetou, Refractories Applications Transactions 2 (2006) 1-8.
[5] K. Okamoto, T. Miyaji and Y. Miyagishi, J. Tech. Assoc. Refrac. Japan 24 (2004) 9-13.
[6] H-Y. Yang and C.F. Chan, J. Am. Ceram. Soc. 73 (1990) 1074-1077.