Efeito do dispersante silicato de sódio alcalino na aglomeração de partículas ultrafinas de minério de ferro para o processo de sinterização em escala piloto

Abstract

The Brazilian sintering perspective on the quality of the sinter feeds from the ‘Quadrilátero Ferrífero’ indicates a drastic deterioration of its chemical and physical composition. As a solution, the use of pellet feed in the sintering has been the alternative adopted for raising the iron content in the sinter feed, but with significant losses in the productivity of this process. Given this scenario, projects have been evaluated that allow the use of pellet feed without any productive damage. Among them, the alteration in the cold agglomeration stage, exemplified by studies involving binders, equipment (horizontal and vertical intensive mixer, pelletizing disc and drum elongation) and its configurations (HPS, MEBIOS and selective granulation). In a still incipient way, there are few studies about application of dispersants in the sintering. The objective of this study was to evaluate the effect of alkaline sodium silicate on the dispersion of ultrafine particles in cold granulation process on a pilot scale, for the iron ore sintering process. First, it was necessary to investigate the effect of pH, solids content and amount of dispersant in the dispersion of the system composed by limestone, water and sodium silicate. For this, the dispersion test on a bench scale was used. This was necessary to ensure that the pulp had the maximum of ultrafine particles of the calcitic limestone dispersed by the sodium silicate. At the pilot scale, this pulp replaced the water in the cold agglomerates, using two types of iron ore mixtures, named Coarse Blend (24.7% <0.15mm) and Fine Blend (42.8% <0.15mm). Cold agglomerates were produced on three cold agglomeration technological routes. In the first route, the drum was used to homogenize and granulate. At that moment the moisture effect was evaluated which the value that provided the best granulation condition was proceeding to further agglomeration routes. In the second route, the intensive mixer was used to homogenize, keeping the drum as a granulator. In the third route, the intensive mixer was used to homogenize and granulate. To measure the performance of the cold agglomerates produced with and without pulp, the granulation index was determined to quantify the particles <0.25mm adhered to the agglomerates. In addition, the microstructure of these agglomerates was evaluated by light microscopy. The results of the dispersion test evidenced the strong influence of the investigated factors (pH, solids content and amount of sodium silicate). The pulp with maximum dispersion was produced with 1.23% of calcitic limestone, pH equal to 11 and liquid alkali sodium silicate (0.2mL for each 1g of calcitic limestone). In the manufacturing stage of the cold agglomerates it was verified that 8% was the moisture that provided the best performance of the agglomerates for the two types of sintering mixtures. The effect of the limestone pulp with sodium silicate was conditioned to the type of mixture and the technological route. In the drum route, this pulp negatively affected the granulation index and reduced the average size of the agglomerates, regardless of the mixture type. In the intensive mixer routes using the Fine blend (42.8% <0.15mm), the pulp also reduced the granulation index and the average size of the agglomerates. However, in those made from the Coarse Blend (24.7% <0.15 mm) with intensive mixer and drum or with only intensive mixer, the limestone pulp with sodium silicate improved the average size and the granulation index of cold aggregates.