Estudo do processo de calcinação como operação unitária adicional na pelotização de minérios de ferro com altos valores de PPC

Abstract

The mineral resources from the Alegria complex, at the Mariana Ouro Preto/MG region, where Samarco´s deposits (Alegrias Norte, Centro and Sul) are located, present a significant parcel of composition related to low iron grade itabirites (below 50%) and high LOI contents (above 3.5%). The search for producing concentrates from these deposits using the current technology has been indicating yield losses in the beneficiation stage and strong productivity losses in the pelletizing process. Studies on alternative technologies and/or process routes, such as the use of calcining as a complementary unit operation to the pelletizing process, may render feasible the processing of materials with higher LOI contents and value to the business. The objective of this investigation was the study of the use of calcining prior to pelletizing iron ores presenting high LOI contents, aiming at the processing of part of the mineral resources presently classified as marginal ores or wastes. Different analytical techniques and technological essays, at laboratory and pilot scales, were applied to samples of these materials, addressing aspects such as reground concentrates filtration, characterization of low temperatures goethite de-hydroxylation and calcining impact on the productivity and product quality of the pelletizing process. Pelletizing pilot scale studies, with iron ore concentrates samples at LOI contents in the range between 3.83% and 4.45% present significant impacts on productivity and quality at different pelletizing process stages. Preliminary studies searching for adequating the pelletizing process by reducing the coal addition level and using a milder burning profile, indicated significantly improved results. Nevertheless, effects such as drop in the maximum temperature in the kiln lower layer and increase in the standard deviation of burned pellets compression were observed. These pellets phosphorus content did not meet the specifications. The pilot scale results of burning calcined high LOI content materials were worse, under all investigated conditions (burning profile, inputs addition levels, productivities), than those achieved with the low LOI content reference sample or non calcined high LOI content samples