Study on the Crystal Structure of Coal Kaolinite and Non-Coal Kaolinite: Insights from Experiments and DFT Simulations
Abstract
Coal is often coated by kaolinite in flotation, leading to a decrease in the quality of clean coal. The structure of the mineral determines its properties and flotation behavior. Therefore, to remove the kaolinite from coal efficiently, the difference in mineralogical characteristics between non-coal and coal kaolinite were analyzed using advanced instruments. The experiment results showed that, due to the substitution of the C atom for Si atom, the interplanar spacing of the kaolinite (001) surface became small with C-O-C, Al-O-C, and C-O-Si covalent bonds formed instead of Al-O-Si and Si-O-Si bond. Based on this, the models of monolayer and bilayer coal kaolinite (001) surfaces were built and the structure difference was compared through DFT calculation. The calculation results showed that the silicon atom of the kaolinite Si-O-(001) surface was easier to be doped by carbon atoms with external energy as the interplanar spacing of the kaolinite (001) surface decreased with the increase in doped carbon atoms (7.15440 Å→7.11859 Å→7.10902 Å→7.10105 Å). The structural difference between non-coal kaolinite and coal kaolinite were compared from the view of the experiment and quantum chemistry, which provides an important theory for subsequent research on the properties of coal kaolinite and its further processing and utilization.