Flotação de metafosforito silicatado de Lagamar/MG

Abstract

The concentration via froth flotation of the metaphosphorite ore, mined at Lagamar/MG, requires careful studies considering that it consists of a complex material from the bottom of the pit. The present bench scale flotation study aimed at investigating the effects of reagents (depressant/dispersant, collector and booster) and pH capable to adequate the concentrate to the targets of P2O5 26% grade and 80% recovery. As preliminary steps, the ore was characterized and dispersion degree determinations were conducted. The P2O5 bearing mineral is fluorapatite and the silicatic gangue contains predominantly quartz, kaolinite, and mica. The natural slimes fraction, material passing 0,038 mm, represents 49% in weight. The silicates are finely disseminated in the apatite grains impairing the concentration due to the lack of liberation. The isoelectric point of the fluorapatite was determined at pH = 2.27. The dispersion degrees of quartz and apatite were low in the presence of sodium metasilicate and sodium tripolyphosphate. In the exploratory step, consisting of rougher flotation at pH = 9, reagents used in direct flotation were sodium oleate as collector and sodium metasilicate as depressant and those employed in reverse flotation were dodecyl amine chloride as collector and sodium tripolyphosphate as depressant, soluble starch and sodium carbonate as depressants. The affinity of the sodium oleate collector with apatite was satisfactory and dodecylamine chloride was selective regarding silicates but the required dosage was high. Concerning the reverse flotation, the decreasing sequence of apatite depression was achieved with sodium carbonate, starch, and sodium tripoliphosphate. Nevertheless, the last acted as gangue depressant, negatively affecting the concentrate grade and recovery. The next stages were planned according to the factorial design of experiments method: (1st) direct flotation (collector sodium oleate, depressant sodium metasilicate); (2nd) direct flotation (same reagents of 1st stage plus booster: emulsion of fuel oil and ethoxylated nonyilphenol); (3rd) reverse flotation (collector dodecylamine chloride, depressant sodium tripolyphosphate); (4th) reverse flotation same reagents of (3rd) stage plus booster: emulsion of fuel oil and ethoxylated nonyilphenol). The performance of the sodium oleate collector used in the rougher flotation was better than that of the dodecylamine chloride employed in the cleaner flotation. The target parameters for the concentrate were achieved with sodium metasilicate as depressant. On the other hand, results obtained with sodium tripolyphosphate were not satisfactory. The emulsion was effective only when added in conjunction with sodium oleate, condition under which the target parameters for the concentrate were achieved and leading to decrease in collector consumption.