Efeito de gases não-convencionais na flotação da apatita

Abstract

Three major classes of ores or minerals are generally considered in the mineral industry: metallic, non-metallic and energetic. There is a subdivision in the non-metallic class into: rocks and industrial minerals, gems and mineral waters. Among the rocks and industrial minerals, in the group of agrominerals, which are minerals and rocks used in agriculture, is phosphate. In Brazil, phosphate deposits are of igneous origin and have a particularity: carbonate gangue associated with apatite. In commerce, industry, technical and scientific means, it is common to analyze phosphate concentrates according to their phosphorus pentoxide (P2O5) content, being the phosphate rock considered the only viable source to obtain phosphorus. Apatite, considered na ore mineral of phosphorus, has 5 to 15% of P2O5, and is used, essentially, in the manufacture of phosphoric acid, raw material for the production of fertilizers. The separation between apatite and carbonate gangue is performed by flotation, a physical-chemical process of separation of minerals performed in a suspension in water, based on the differences in the surface characteristics of the mineral species, more specifically, in the capacity of adhesion, or not, of the particles to the gas bubbles. The commonly used gas is air, presenting the advantages of being totally free and widely available, however, in the present work it was decided to evaluate if the gases oxygen, nitrogen and carbon dioxide could bring some benefit in the flotation of apatite, so as to result in greater flotability, which would justify even the cost. It is also important to mention that pure oxygen can be obtained by the alkaline electrolysis of water using photovoltaic energy (renewable and technologically available) while carbon dioxide is a very common by-product in industrial processes (combustion, decarbonation and fermentation) almost always unused and discarded directly into the environment. For this, initially drag tests were conducted, in which CO2 presented the highest percentage of drag, and later flotation tests in Hallimond tube, with the collectors Flotigam 5806 and saponified rice oil, with variations in concentration, 8, 10 and 12 mg/L, and pH, 8, 9 and 10. All tests were performed in triplicate, and statistical analysis was performed for a significance level of 5%, resulting in recoveries significantly equal or lower than those obtained with air for most experimental conditions, and in two situations, significantly higher results were observed with alternative gases compared to air. In a second phase of the work some surfactants were evaluated as potential collectors in the apatite flotation, which did not present satisfactory results for the conditions initially worked, pH 8, 9 and 10, concentration 8, 10 and 12 mg/L; however, in tests performed with a higher concentration of 60 mg/L at pHs 5 and 9, the flotability increased, indicating that for such surfactants it would be necessary to use higher concentrations than those applied for traditional collectors.