Adsorption of water and fatty acids at magnesium hydroxide surface from an MDS perspective

The adsorption characteristics of fatty acids at the magnesium hydroxide (Mg(OH)₂) surface are crucial in the wet surface modification process for the preparation of apyrous high-polymer materials and the concentration of brucite by flotation. In this regard, the interfacial water structures at the magnesium hydroxide (001), (101), (102) and (110) surfaces were examined and compared. The adsorption of fatty acids – namely, undecylenic acid (C₁₁H₂₀O₂), lauric acid (C₁₂H₂₄O₂), oleic acid (C₁₈H₃₄O₂) and stearic acid (C₁₈H₃₆O₂) – and their hydrophobicity at the magnesium hydroxide (001) surface were investigated by molecular dynamics simulation (MDS). The results indicate that the magnesium hydroxide (101) and (001) surfaces have the greatest and least effect on the interfacial water structure, respectively. The fatty acids overall have similar adsorption affinity at the magnesium hydroxide (001) cleavage surface, while the chemical reaction mainly contributes to the fatty acid adsorption at the magnesium hydroxide (001) surface. The hydrophobicity of the magnesium hydroxide surface increases as a function of the carbon (C) chain length with the adsorption of fatty acids. The presented results improve the fundamental understanding of fatty acid adsorption at the magnesium hydroxide surface, which will help enhance and/or support the robust performance of magnesium hydroxide wet surface modification and brucite flotation.