Caracterização dos minerais micáceos e da apatita presentes nos minérios fosfáticos do Centro-Sudeste do Brasil – implicações no processamento

Abstract

The objective of this research was to study phosphate ores having apatite as an economic mineral and phyllosilicates, mainly as gangue minerals. In the first stage, a synthetic sample was studied, composed of apatite and the phlogopite and biotite micas, with emphasis on the adsorption of a soap derived from an oil from the Amazonian patauá palm. The chemical and mineralogical composition, electrokinetic properties and floatability of apatite, biotite and phlogopite in the presence of patauá fatty acid soaps, as well as the reagent synthesis and adsorption mechanism were investigated in this work. The collector was successfully synthesized and showed a 90% selectivity gap between apatite and micaceous minerals in microflotation tests, at neutral and alkaline pH. The formation of calcium dicarboxylate was indicated to be the collector adsorption mechanism for apatite, whereas a less significant interaction with interlayer cations exposed during comminution was pointed as the adsorption mechanism for biotite and phlogopite. In the second stage, three samples of real apatitic ores, from mines located in western Minas Gerais State, were characterized, with an emphasis on micaceous phyllosilicates. The techniques of quantitative chemical analysis, X-ray diffractometry (XRD), thermogravimetric analysis and scanning electron microscopy with the support of microanalysis with energy-dispersive X-ray spectrometry were used. The mineralogical compositions, to date, are Mosaic: apatite, dolomite, ilmenite, quartz, vermiculite, interstratified phyllosilicates; Rocha Alterada: apatite, diopside, ilmenite, magnetite, vermiculite, interstratified phyllosilicates; mica base 1: apatite, diopside, magnetite, vermiculite, interstratified phyllosilicates. The specific analyzes by XRD allowed to determine the specific stratification, that is, the stacking sequence of the mica and vermiculite layers, in the 3 types of mixed layer phyllosilicates identified in the samples, according to the Reynolds model (1980). Potassium content, reported as K2O, is the only microchemical parameter to distinguish the specific phyllosilicate in EDS microanalyses. a) when the % of K2O is very low or tends to zero, it is vermiculite; b) when this content is between 1.0 and 8.5%, this characterizes the mixed layer or interstratified phyllosilicate; c) the original or even slightly altered mica would have K2O contents ranging from 9.2 to 11.8%.