Research on the Hydrophilicity of Non-Coal Kaolinite and Coal Kaolinite from the Viewpoint of Experiments and DFT Simulations

Peng Xi,Wenli Liu,Ruixin Ma

doi:10.3390/sym12071199

Peng Xi, Wenli Liu + Show 1 more

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https://doi.org/10.3390/sym12071199

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Abstract

Coal is often coated by coal kaolinite in flotation, resulting in an increase in concentrate ash. The natural hydrophilicity of minerals is the key factor to determining its flotation behavior. The results of studies on the contact angle of non-coal kaolinite and coal kaolinite samples found that the contact angle of coal kaolinite was bigger than that of non-coal kaolinite and the hydrophilicity of the latter was stronger. To investigate the mechanism of the hydrophilic difference between non-coal kaolinite and coal kaolinite, the adsorption of a single water molecule on non-coal kaolinite and coal kaolinite (100) and (00 1 ¯ ) surfaces was calculated with the first principle method of the density functional theory (DFT). The calculation results showed that hydrogen bonds were formed between the hydrogen atom and the oxygen atom of the surface and the hydrogen atom and the oxygen atom of the water molecule after the water molecule was adsorbed on the kaolinite (100) and (00 1 ¯ ) surface. The adsorption process of water molecules on the kaolinite surface was physical adsorption with Van der Waals force existing between them. Regardless of whether the kaolinite (001) surface or the kaolinite (00 1 ¯ ) surface was doped with a carbon atom, the adsorption of a single water molecule was weakened, with a weaker hydrogen bond formed. The calculated results explained the difference of hydrophilicity between non-coal kaolinite and coal kaolinite samples from the molecular and atomic viewpoint.

Highlights

Flotation is a separation method to separate one mineral from another based on the differences in their hydrophilicity within an ore [1]
Based on the previously built models of non-coal kaolinite and coal kaolinite [8], the adsorption of a single water molecule on an undoped kaolinite surface and a kaolinite surface doped by carbon atoms is compared by analysis of the adsorption energy, bond, charge transfer, and DOS with the first principle method of density functional theory (DFT)
TheThe contact angles of non-coal kaolinite andand coalcoal kaolinite were measured, withwith the the results shown in Table results shown in Table

Summary

Introduction

Flotation is a separation method to separate one mineral from another based on the differences in their hydrophilicity within an ore [1]. With the depth of coal and mechanized mining, the increase of high-ash slime resulted in the increase of concentrate ash in the flotation process. The coal kaolinites are argillized to form fine particles when they interact with water molecules in water. They agglomerate with the target minerals (coal) in the flotation process and cover the latter. They enter into the concentrate with the mechanical entrainment of the foam water and the entrainment of the concentrate so that the selectivity of the separation process is affected and the quality of the flotation concentrate is reduced. The gangue minerals mainly entered the froth layer through entrainment, and the dissociated fine particles were recovered in the concentrate tank with a thin water layer between the Symmetry 2020, 12, 1199; doi:10.3390/sym12071199 www.mdpi.com/journal/symmetry

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