Mechanism study on the generation of oxygen vacancies by ball milling surface modification of siliceous minerals in coal gangue to enhance reactivity

Quartz (Qtz) and kaolinite (Kln) are the main siliceous minerals in coal gangue (CG), which can be converted into effective silica by mechanical activation and improve the utilization efficiency of CG in turn. This study aimed to analyze and reveal the reaction mechanism of siliceous minerals in CG under mechanical activation surface modification by experiments and DFT calculations. We showed that increasing the rotational speed and m(Al 2 O 3 /SiO 2 ) stoichiometric ratio simultaneously boosted the activation ratio of siliceous minerals, up to 3.91 %. Mechanical activation promoted the formation of oxygen vacancy structures on siliceous minerals surfaces, which aligned with the system’s activation capacity. The Exp3P2 polynomial function model best described the relationship between the rotational speed and the activation ratio of different siliceous minerals. The oxygen vacancy, S BET , rotational speed, milling temperature, m(Al 2 O 3 /SiO 2 ) stoichiometric ratio, total pore volume showed significant positive correlations with the activation ratio. First-principles calculations revealed that the oxygen defect formation energy of Kln (5.17 eV) was slightly smaller than Qtz (5.27 eV), Kln was more likely to form oxygen defects than Qtz in mechanically activated reaction. This research contributes to understanding the mechanical activation of CG into effective silica, enhancing its potential for the graded and quality-based utilization.