Estudos eletrocinéticos e de flotabilidade de Wavellita, Turquesa, Senegalita e Apatita

Abstract

Wavellite, turquoise and senegalite are examples of the most common secondary phosphates which occur in the iron ores of sedimentary deposits, while apatite occurs in magmatic deposits. Phosphorus is an extremely harmful element in steel making, causing increased hardness and brittleness and decreased ductility. The beneficiation of iron ores with apatite as phosphorus source has been made by reverse anionic flotation with fatty acids. However, this route has not been successfully used in the case of iron ores of sedimentary deposits. Floatability studies in a modified Hallimond tube, with anionic and cationic collectors, and zeta potential measurements by electrophoresis technique were carried out for wavellite, turquoise, senegalite and apatite. The aim was to define the best conditions of separability by froth flotation between secondary phosphates and iron oxides and hydroxides. Apatite consists primarily of fluorapatite and showed negative zeta potential in the examined pH range. The wavellites pHPIE was achieved at pH 5.2, while the pHPIE for turquoise and senegalite were pH 7,2 and pH 6,2, respectively. The addition of phosphate ions rendered the zeta potential more negative for the three minerals, while the addition of aluminum ions caused reversal of zeta potential up to approximately pH 10. The floatability levels with dodecylamine were higher than those achieved with octylamine. This collector was able to reverse the zeta potential of all minerals and makes them more positive in the full examined pH range. Between pH 3 and pH 10, the floatabilities values obtained for apatite, wavellite and turquoise with sodium oleate at the concentration 1x10-3M were near 100%. Apatite presented almost 100% of floatability with sodium dodecylsulphonate at the concentration 1x10-3M in the full examined pH range, while wavellite and turquoise presented 100% of floatability until approximately their pHPIE values. Bench scale flotation tests showed that it is possible to reduce the phosphorus content through the reverse cationic flotation of phosphate, using starch as depressant for iron oxides. The residual content, from which the flotation loses its efficiency, appears to be mainly due to nanometric phosphates or the anionic form as substitutions in iron oxides and hydroxides.