Fluidización

FLUID DYNAMICS STUDY OF THE ROASTING OF ZINC
SULFIDE CONCENTRATE IN A FLUIDIZED BED REACTOR


O. A. Cortez1, F. J. Moura1, R. J. de Carvalho1* and T. Takayama Filho2

1Departmento de Ciência dos Materiais e Metalurgia – Pontifícia Universidade Católica do Rio de Janeiro
2Companhia Paraibuna de Metais – Grupo Votorantim



Keywords: Fluid Dynamics, Zinc Sulfide and Fluidized Bed.Abstract. Oxidizing roasting is a unit operation used in the metallurgical industry to convert metal sulfides into oxides, sulfates or oxy-sulfates. In the hydrometallurgical routes to obtain the metals, the oxides and sulfates are easily dissolved in solutions but the sulfides are very difficult to dissolve. The sulfide concentrates are usually roasted in industrial reactors using air attemperatures varying from 600 to 1000°C. A commonly used reactor is the fluidized bed reactor, which presents a simple design, good thermal recovery, easy temperature control and high conversion when compared to other rectors. In an industrial plant in Brazil, zinc sulfide concentrates are roasted in a fluidized bed reactor at temperatures around 950°C in the presence of air. According tothermodynamic studies, the use of temperatures above 950°C would improve the sulfide to oxide conversion. However, the concentrates also contain iron, lead and copper sulfides among others. The presence of these compounds leads to some reactions that form low melting point phases causing agglomeration and sintering of the particles in the bed, thus restricting the operating temperature. Another way ofimproving the conversion is to use air enriched with oxygen. This work presents a detailed study of the fluid dynamics of the roasting reaction of zinc sulfide concentrates at 950oC. The data were collected from experiments carried out in an industrial fluidized bed reactor. The theoretical and experimental characterization was performed using the operating variables of the industrial reactor. Fluiddynamics diagrams (Geldart, Schytill and Grace) were drawn for the industrial practice at certain conditions. From the analysis of these diagrams, it is suggested that superficial gas velocities in the range 0.2 - 0.6 m/s should be used.






Introduction

Oxidizing roasting is a unit operation used in the metallurgical industry to convert the sulfides into oxides, sulfates oroxy-sulfates to be sent to further treatments to recover the metals of concern. In the hydrometallurgical routes to obtain the metals, the oxides and sulfates are easily dissolved in solutions but the sulfides are very difficult to dissolve.
The sulfide concentrates are usually roasted in industrial reactors using air at temperatures varying from 600 to 1000°C. Among the available reactors, thefluidized bed reactor presents a simple design, good thermal recovery, easy temperature control and high conversion when compared to the others.
The zinc sulfide concentrates are roasted in a fluidized bed reactor at temperatures around 950°C in the presence of air. According to thermodynamic studies, the use of temperatures above 950°C would improve the sulfide to oxide conversion. However, the zincsulfide concentrates also contain iron, lead and copper sulfides among others. The presence of these sulfides leads to some reactions that form low melting point phases causing agglomeration and sintering of the particles in the bed, thus restricting the operating temperature (Ozga and Riesenkampf, 1996). Another way for improving the conversion is to use air enriched with oxygen. Studies showthat an air enrichment of 3% of O2 increases the conversion in 21% (Shu et al., 1999).
The objective of this work is to study the fluid dynamics behavior of the roasting reaction of zinc sulfide concentrates in an industrial fluidized bed reactor. This is accomplished by fluid dynamics calculations performed with the operating data from an industrial fluidized bed reactor.

Natural Occurrence...