Degradação mecânica de pelotas verdes de minério de ferro

Abstract

Handling and transporting of green pellets inside the pelletizing unit may cause mechanical degradation. When this occurs, the degradation may lead to greater recycling and rework in the circuit, and may even have deleterious effect on the quality of the final product after firing. The mechanical strength of green pellets should be high enough to withstand this handling step. The present work dealt with the production of green pellets on a laboratory scale, aiming to study the influence of bentonite content on the mechanical characteristics of green pellets, as well as the effect of handling variables on mechanical strength: pellet size, drop height, impact surface, angle of impact, mode of application of forces and loading speed when breaking green pellets. Increasing the bentonite content resulted in increased pellet resistance to impact. Smaller sized pellets also showed higher compressive strength and low magnitude impacts. Pellets showed higher resistance when subjected to loading at higher rates, as well as to single loading (drop test) than to double loading (compression). Increased impact energy as well as drop height resulted in increased pellet degradation. However, it is observed that, for impacts with heights greater than 25 cm, that the total fall height was the variable that defined the proportion of fragmented pellets, not the height used in each impact. In order to evidence the effect of damage to green pellets by impacts, intact and previously damaged pellets were fired, and it was shown that the resistance of damaged pellets was much lower than that of intact pellets.