Rock containing biotite as an alternative source of potassium for fertilizer by thermal processing with additives

Abstract

Biotite is a ferromagnesian phyllosilicate that contains potassium. It is very abundant and scattered all over the world. Usually formed as a secondary product in metamorphic processes, it is considered to be an impurity in many mineral processing. Even though it is an alternative source of potassium, it is still not extracted commercially on a large scale due to the lack of commercial technology that makes the business viable economically. The objective of this work was to investigate the effect of thermal processing, using additives, in the solubilization of potassium and impurities in dilute mineral acid, of rock contains biotite. A rock from the Carajás-Pará-Brazil mineral province, with a content of 9.7% K₂O and 70% biotite was selected. Thermal processing was performed at two temperatures, 800°C and 900°C, for 6h using two systems: (biotite + CaCO₃ + MgCl₂.6H₂O) and (biotite + gypsum + Na₂CO₃). The sulfuric acid leaching step was performed at pH maintained between 2.0 and 3.0, at 85 ℃ for 1h. The extraction in the system with magnesium chloride (800°C) reached 63% of the potassium and with solubilization maximum of 5% of Fe and Al. The extractions of potassium with gypsum were smaller, 41%, showing a trend of better efficiency at higher temperatures than those chosen for this study, however, with effluent liquor from aluminum-free leaching and 1.2% maximum iron extraction.