A molecular dynamics simulation study of water structure and adsorption states at talc surfaces

A preliminary molecular dynamics simulation (MDS) study regarding interfacial phenomena at talc surfaces is reported. The use of computer methodology in the development of mineral processing technology has long been of interest to Professor R. P. King and, in this regard, it is appropriate that such a computer study of flotation chemistry be included in this special IJMP volume. Simulation results show that due to the absence of hydrogen bonding sites, the hydrophobic talc basal plane is not in close contact with water molecules, thus leaving a 3 A void space at the basal plane. As expected from the previous laboratory studies the hydrophobic chains of the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) preferentially adsorb at the talc basal plane surface through hydrophobic interactions. On the other hand, the breakage of Si-O and Mg-O bonds provides the talc edge surface with many hydrogen bonding sites which facilitates the formation of strong, hydrogen bonds with water dipoles. Thus, water wets the hydrophilic edges, and, in contrast to the face surface, simulation results reveal that the DTAB cationic surfactant adsorbs at the talc edge surface through electrostatic interactions. Finally, when a model dextrin molecule is considered, the simulation results suggest that the hydrophobic interaction between the talc basal plane surface and the hydrophobic moieties in the dextrin molecule plays a significant role in dextrin adsorption at talc surfaces. Whereas, at the talc edge surface the dextrin molecule is not able to displace water molecules at the edge surface. (c) 2006 Elsevier B.V. All rights reserved.