title: Monte Carlo molecular simulation of the hydration of K-montmorillonite at 353 K and 625 bar.
abstract: Monte Carlo molecular simulations of the hydration of K-saturated Wyoming-type montmorillonite at constant stress in the NPzzT ensemble and at constant chemical potential in the grand canonical muVT ensemble, under basin-like conditions of 353 K and 625 bar, show a strong tendency of the K+ ions to adhere to the siloxane surface, forming predominant inner-sphere complexes with tetrahedral oxygen atoms and adsorbed water molecules. Simulations in the grand canonical ensemble predict that none of the K-montmorillonite hydrates, the one-, two-, and three-layer hydrates, are stable in this environment of high depth, temperature, and pressure. The most nearly stable configuration corresponds to the one-layer hydrate, characterized by a d001 spacing of 12.75 A, the adsorbed water being 60 molecules/layer or 180.83 mg of H2O/g of clay, an internal energy of -22.73 kcal/mol, an interlayer density of 0.365 g/mL, and a pressure tensor, Pzz, of 1999.9 bar. The interlayer structure consists of two close layers of water molecules 0.50 A from the midplane, with broad shoulders on the sides, the protons oriented toward the midplane and the siloxane surfaces, and the K+ ions close to the clay surfaces and on the interlayer midplane.
authors.affiliation: Facultad de Química, Universidad Nacional Autónoma de México, 04510 México, D. F., Mexico.
authors.forename: M de Lourdes
authors.initials: Mde L
authors.lastname: Chávez
authors.forename: Liberto
authors.initials: L
authors.lastname: de Pablo
authors.forename: Juan J
authors.initials: JJ
authors.lastname: de Pablo
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D008958:Models, Molecular; D009010:Monte Carlo Method; D011188:Potassium / Q000737:chemistry*; D011312:Pressure; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D001546:Bentonite; D011188:Potassium