Green and high-efficiency sulfuric acid leaching strategy for enhanced recovery of rubidium and potassium from biotite

The extraction of rubidium (Rb) and potassium (K) from biotite faces challenges due to the mineral's structural stability and high energy consumption in conventional methods. Herein, an environmentally friendly ion-exchange synergistic oxidation process was developed to enhance sulfuric acid leaching efficiency. By introducing sodium ions and magnesium ions as exchange agents and hydrogen peroxide as an oxidant, the layered structure of biotite was preserved while facilitating rubidium ion release. Key parameters, including sulfuric acid concentration, additive dosage, oxidant concentration, liquid-to-solid ratio, and temperature, were systematically optimized. Under optimal conditions (1.5 mol/L H₂SO₄, 0.4 g/g MgSO₄, 0.2 g/g Na₂SO₄, 1 mol/L H₂O₂, L/S ratio 5 mL/g, 90 °C), a maximum Rb extraction efficiency of 95.2 % was achieved. By employing a 4-stage countercurrent leaching sequence followed by 3-stage countercurrent washing, the Rb⁺ concentration was ultimately increased to 1250 mg/L. Kinetic analysis revealed a two-stage mechanism: the initial 0–2 h phase was chemically controlled with an activation energy of 17.5 kJ/mol, while the subsequent 2–7 h phase transitioned to diffusion control with an activation energy of 16.5 kJ/mol. Multi-stage countercurrent leaching further concentrated rubidium ions to 1250 mg/L. DFT Calculations and structural analyses (XRD, FTIR, FIR, SEM-EDS, XPS) confirmed intact silicate frameworks and successful Na⁺/Mg²⁺ interlayer exchange, avoiding mineral decomposition. This strategy significantly reduces acid consumption, eliminates nitrate pollution, and demonstrates a promising and sustainable approach for the extraction of Rb and K from biotite.