The rubidium leaching process from biotite generates a large amount of waste materials that should ideally be reused for heavy metal ion adsorption so as not to create environmental problems. Ferric oxide/mesoporous silica (FO/MS) is a novel adsorbent used for heavy metal ion removal with a high removal capacity of Pb2+ (143.47 mg/g within 60 min) that was prepared for the first time by comprehensively utilizing both rubidium-containing biotite leaching residues and wastewater. The incorporation of mesoporous silica prepared by leaching residues could provide a porous framework and channel for depositing ferric oxide. Mesoporous channels have a high specific surface area that improves the adsorption activity and capacity of the material. Additionally, in a pH study, the adsorptive thermodynamic and dynamic analyses, as well as XPS and FTIR analyses, verified the adsorption properties involved in surface complexing and electrostatic binding. The surface complexation process mainly was the interaction of Pb2+ with surface hydroxyl groups. This work provided a novel and effective strategy for preparing waste solid-based heavy metal ion adsorption and expanded technologies for treating acid leaching wastewater. The adsorbents of FO/MS with a high Pb2+ adsorption capacity suggested that, compared with other materials, it is a suitable remediation material for Pb2+ contaminated water.

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Lithium is an important strategic metal, but the supply of lithium ore is growing slowly, which is in sharp contradiction with the rapidly growing demand. Therefore, it is urgent to find new lithium resources. Recently, it has been found that coal-based lithium ore is expected to become a new type of lithium resource to meet the rapidly growing demand for lithium. However, the traditional Li extraction process using inorganic acids (i.e., H 2 SO 4 ) is facing serious environmental issues, and the excess acid needs to be neutralized before the subsequent purification process. Herein, for the first time, we proposed a novel recycling strategy for the efficient and scalable Li leaching from coal-based Li ores with a reusable solid acid (oxalic acid), in which oxalic acid can be easily recovered after the leaching process with facile solubility engineering. The influences of the leaching conditions and oxalic acid concentration on the Li leaching and recycling rates of oxalic acid were explored in detail. Under the optimal conditions, the Li leaching rate (89.12%) and recovery rate (88.12%) of oxalic acid reached nearly 90%. In addition, the results of X-ray diffraction and Fourier-transform infrared clearly proved the high purity of the recovered oxalic acid after Li leaching, and the recovered oxalic acid also possessed excellent leaching performance after five times of recycling experiments. Moreover, the leaching kinetic analysis showed that the Li extraction from coal-based Li ore with oxalic acid was a chemical-controlled process with an activation energy (E a ) of 74.42 kJ/mol. Therefore, with solubility engineering, the recycling of oxalic acid after Li leaching could be easily realized, which is possible for other solid acids and provides a promising strategy for the simultaneous realization of green Li extraction and leaching acid recovery.

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