Molecular models of hematite, goethite, kaolinite, and quartz: Surface terminations, ionic interactions, nano topography, and water coordination

LO Filippov and LA Silva and AM Pereira and LC Bastos and JCG Correia and K Silva and A Picarra and Y Foucaud, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 650, 129585 (2022).

DOI: 10.1016/j.colsurfa.2022.129585

In light of the modern needs in mineral processing and extractive metallurgy, advanced knowledge about the surface chemistry of minerals is essential, especially their interactions with water. These interactions are intimately related to several processes in mineral technology, such as flotation, wet grinding, dewatering, and leaching. Hematite, goethite, quartz, and kaolinite are the main minerals in iron ore processing circuits. Thus, understanding their differences is fundamental to making lower-grade iron ores processing worthwhile. In this work, we studied the surface physical chemistry of these minerals by molecular modeling and simulation, focusing on surface terminations, protonation degrees, ionic interactions, nano topography, and water coordination. We demonstrate that fundamental differences exist between the terminations of the same mineral, particularly for quartz (100) and hematite (001) surfaces. Iron minerals exhibit strong interactions with water, mainly due to the coordination of surface iron atoms by aquo ligands and their relatively low molecular-scale roughness, in most cases. Such characteristics help explain the behavior of adsorption of reagents and the difficulties in dewatering and drying iron ore. In contrast, the silicate minerals present lower water structuring. We also show how neutral surfaces behave towards ions, cases of both attraction and repulsion were observed and attributed to the surfaces' topmost atomic layering. This work provides novel insights which can connect the fundamentals of surface phenomena with process engineering. Additionally, we provide molecular models to help in related computational studies.

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