Efeitos da reologia de polpa e avaliação de dispersantes como aditivos de moagem na remoagem de um concentrado de minério de ferro

Abstract

This work investigated the effects of the slurrys rheological behavior and use of dispersants on wet ultra-fine grinding of an iron ore concentrate. The influence of the addition of some reagents on the rheological behavior and state of aggregation and dispersion of concentrate slurry was evaluated by determining the degree of dispersion using a settling tube, together with the analysis of flow curves obtained in a concentric cylinder rheometer. These curves were fitted according to models of Herschel-Bulkley and Bingham. The objective was to select reagents that promote a higher slurry thermodynamic stability, at pH 10 (pH used in SAMARCOs regrinding circuit). None of the twenty reagents evaluated in this first stage caused significant increases in the slurrys degree of dispersion. Of the twenty reagents, six reduced the fluid consistency index (k coefficient) and apparent viscosity, with the dosage of 300g/t: three polyacrylic acid, silicone acrylate copolymer, citric acid and sodium hexametaphosphate. The polyacrylic acid of lower molecular weight, together with the other three reagents, were selected for the second stage of this work, aiming at to evaluate the influence of solids content, the addition of reagents (previously selected in step I), pH and the addition of lime in the specific energy consumption in industrial ball mills, through laboratory grinding tests. The reagents selected in step I did not promote reduction in specific energy consumption, since it does not significantly affect the dispersion of slurry at pH 10. However, the addition of these reagents caused a reduction in the generation of Blaine surface per applied energy, being more efficient for sodium hexametaphosphate (26% reduction in the index BSA/kWh/t). The increase of pH from 7.3 to 10.0 increased the slurry dispersion degree, providing lower values of yield stress and apparent viscosity, and a reduction in specific energy consumption by 17.4%. So sodium hydroxide, added to previous steps, has acted as a grinding aid. xvii There were no significant differences in specific energy consumption for the tests performed with 70 and 75% solids, but the specific energy consumption for the test with 80% of solid was 22% higher than the others. The addition of 300 g/t of lime caused an increase of 27% in specific energy consumption, with significant increases in yield stress and consistency index of the fluid, especially for the condition of 18kWh/t.