Thermodynamics of cationic surfactant sorption onto natural clinoptilolite
- New Mexico Inst. of Mining and Technology, Socorro, NM (United States)
- Los Alamos National Lab., NM (United States)
Sorption enthalpies of hexadecyltrimethylammonium bromide (HDTMA) as monomers and micelles and tetraethylammonium bromide (TEA) were used with surfactant, counterion, and co-ion sorption isotherms to infer the conformation, sorption mechanism, and relative stability of the sorbed surfactants on natural clinoptilolite. The average value of the sorption enthalpy was {minus}10.38 kJ/mol for monomers, {minus}11.98 kJ/mol for micelles, and +3.03 kJ/mol for TEA. Sorption of monomers produced a lower sorption plateau than equivalent micelle sorption (maxima 145 mmol/kg, 225 mmol/kg). Analysis of the sorption data demonstrated a change in the sorption mechanism at the external cation exchange capacity (ECEC) of clinoptilolite. Sorption data from below and above the ECEC were fit to a simple polynomial model and the Gibbs free energy of sorption ({Delta} G{sub m}{sup 0}) and sorption entropies were calculated. Resultant values of {Delta} G{sub m}{sup 0} were {minus}9.27 and {minus}14.38 kJ/mol for HDTMA monomers and micelles, respectively, for sorption below the ECEC, and {minus}16.11 and {minus}23.10 kJ/mol, respectively, for sorption above the ECEC. The value for TEA was {minus}1.04 kJ/mol, indicating weaker sorption than for HDTMA. Monomer sorption to clinoptilolite exceeded the ECEC, even when the solution concentration was below the critical micelle concentration. Hydrophobic (tail-tail) components of {Delta} G{sub m}{sup 0} were the driving force for sorption of HDTMA, both below and above the ECEC. A significant kinetic effect was observed in the sorption isotherms with a period of rapid sorption followed by slow equilibration requiring 7 days to achieve steady state for HDTMA; TEA equilibration occurred within 24 h.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AR21-95MC32108
- OSTI ID:
- 672482
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 206, Issue 2; Other Information: PBD: 15 Oct 1998
- Country of Publication:
- United States
- Language:
- English
Similar Records
Sorption kinetics of hexadecyltrimethylammonium on natural clinoptilolite
Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: Effects of sorption, surfactants, and natural organic matter