Mechanism of enhanced rubidium extraction from biotite via magnesium nitrate-assisted acid leaching: Experimental and DFT theoretical insights

This study explored the mechanism and optimization of technical condition for enhanced rubidium extraction by utilizing magnesium nitrate in the sulfuric acid leaching process of biotite. The extraction efficiency of rubidium was significantly improved with the addition of magnesium nitrate. Under optimized conditions, the Rb leaching efficiency achieved 95.9 %. Concurrently, the leaching efficiency of impurity ions such as iron and aluminum were effectively reduced. Compared with the sulfuric acid leaching process, the iron leaching efficiency decreased from 90.3 % to 67.9 %, and the aluminum leaching efficiency decreased from 64.8 % to 17.0 % in enhanced process. The crystal structure transformation of biotite was systematically investigated using SEM-EDS, XRD, FTIR, FIR, and Mossbauer techniques. These analyses revealed significant modifications in the interlayer spacing, tetrahedral coordination, and octahedral structure. The DFT calculations have confirmed that the ion exchange process involves the participation of Mg^2 + and H⁺, which play a critical role in facilitating the rubidium extraction. This interaction resulting in an increase in the (001) interplanar crystal spacing of biotite from 0.993 nm to 1.00 nm. The results demonstrated that magnesium nitrate functions as an exceptional enhancer for the acid leaching of rubidium from biotite. This process provides a novel strategy for the development of more efficient and environmentally sustainable processes for the recovery of valuable metals from micas.