Fluidized bed roasting of micro-pelletized zinc concentrate : Part I-Pellet strength and roasting kinetics

Abstract

Zincor, a zinc refinery in South Africa, uses oxygen enrichment of up to 26% O2 in its fluidizing air to increase concentrate-throughput in its fluidized bed roasters. The aim of the study is to determine whether O2 enrichment can be reduced by introducing micropelletized concentrate into the feed blend, while maintaining concentrate throughput rates and calcine quality. A laboratory scale fluidized roaster was used to determine the strength and oxidation kinetics of suitable micro-pellets. The strength of the pellets was determined by the extent of attrition during roasting. It was found that micro-pelletization decreases the fines in the feed to the roasters; the –500 μm fraction decreased from 87% to 10%. The micro-pelletized particles do break down during roasting, which increases the -500 μm fraction to 31%. The general morphologies of the roasted particles are similar to those found by previous workers. Micro-pelletized concentrate particles require more time than nonpelletized concentrate particles to oxidize in the roasting step, although this is less than the mean residence time of the Zincor roasters. Roasting micro-pellets in O2-enriched fluidizing air increased the reaction rate.