Potassium Recovery from Biotite-Rich Rock by Thermal Activation and Sulfuric Acid Leaching

Abstract

Potassium-bearing silicate minerals have emerged as potential alternative resources for fertilizer production due to increasing concerns regarding the sustainability, geographic concentration, and economic vulnerability of conventional potash reserves. Among these minerals, biotite is particularly attractive because of its relatively high potassium content and widespread occurrence in mineral deposits and mining residues. However, the strong incorporation of potassium within the mica structure limits its direct agronomic use and requires mineral activation to enhance potassium availability. This study evaluated the effect of thermal activation using chloride- and sulfate-based additives on potassium recovery from a biotite-rich rock from the Carajás Mineral Province, Brazil. The material contained approximately 69 wt.% biotite and 9.6 wt.% K₂O. Two activation systems, CaCO₃–MgCl₂·6H₂O and CaSO₄·2H₂O–Na₂CO₃, were investigated at 800 and 900 °C for 6 h, followed by sulfuric acid leaching at pH 2–3, 85 °C, and 60 min. The chloride-based route achieved potassium recoveries of up to 63%, whereas the sulfate-based system reached 41%. Thermodynamic simulations indicated the formation of soluble potassium-bearing phases, including KCl and KCaCl₃ in the chloride system and aphthitalite-type compounds in the sulfate system. Iron and aluminum dissolution remained below 5%, demonstrating selective potassium extraction. The results show that chloride-assisted thermal activation effectively promotes structural modification of biotite and enhances potassium release, generating potassium-rich sulfate liquors suitable for subsequent fertilizer production and supporting the valorization of potassium-bearing mineral resources and mining residues.