Estudo de flotação de grafita em escala de laboratório

Abstract

Flotation is the most commonly used ore concentration technique in industry. It is based on natural or induced differences in the surface properties of mineral species to be separate. An example of mineral that responds very well to flotation, for being a naturally hydrophobic solid, is the graphite, one of the allotropic forms of carbon, which has good refractory properties, lubricant characteristics and high thermal and electrical conductivity, being widely used in the production of refractory bricks, crucibles, lubricants, pencils, etc. In the present work, a sample of graphite ore was analyzed in a concentration study, using a laboratory bench flotation test machine. Firstly, the 32.7 kg sample was crushed until the particle size was lower than 3.35 mm, homogenized in a longitudinal pile and divided into smaller samples of 1.0 kg for the tests. Then, the particle size distribution, semiquantitative mineralogical analysis and chemical characterization of one of these samples were performed, indicating that the ore is mostly composed by graphite (C) and quartz (SiO2), with a graphitic carbon content of approximately 17.8% and that 61.9% of the ore and 71.3% of the carbon content are retained on 80 mesh. Furthermore, tests to study the effects of grinding time and the kerosene and Flotanol D-25 frother dosages on rougher flotation were carried out. Therefore, it was observed an ideal grinding time of 7.5 minutes and a 200 g/t kerosene and 100 g/t frother dosages. Under these conditions, a concentrate with a 55.6% carbon content and a 95.3% recovery were obtained, indicating the need for additional steps of grinding and cleaner flotation in order to increase the graphitic carbon content in the final concentrate. Thus, three successive steps of grinding and cleaner flotation were carried out, being the first two grindings performed with ball charges and the last one with steel shots. Finally, a final concentrate was obtained presenting a carbon content of approximately 91.6% and 78.8% recovery. In conclusion, it was possible to obtain, in laboratory tests, a final concentrate with a high carbon content (above 90%) but a low recovery, which means that a significant amount of graphite has not floated, remaining in the flotation tailings, with the gangue minerals of the flotation tests.