Linear Adsorption of Nonionic Organic Compounds from Water onto Hydrophilic Minerals:  Silica and Alumina

Abstract

To characterize the linear adsorption phenomena in aqueous nonionic organic solute-mineral systems, the adsorption isotherms of some low-molecular-weight nonpolar nonionic solutes (1,2,3-trichlorobenzene, lindane, phenanthrene, and pyrene) and polar nonionic solutes (1,3-dinitrobenzene and 2,4-dinitrotoluene) from single-and binarysolute solutions on hydrophilic silica and alumina were established. Toward this objective, the influences of temperature, ionic strength, and pH on adsorption were also determined. It is found that linear adsorption exhibits low exothermic heats and practically no adsorptive competition. The solute-solid configuration and the adsorptive force consistent with these effects were hypothesized. For nonpolar solutes, the adsorption occurs presumably by London (dispersion) forces onto a water film above the mineral surface. For polar solutes, the adsorption is also assisted by polar-group interactions. The reduced adsorptive forces of solutes with hydrophilic minerals due to physical separation by the water film and the low fractions of the water-film surface covered by solutes offer a theoretical basis for linear solute adsorption, low exothermic heats, and no adsorptive competition. The postulated adsorptive forces are supported by observations that ionic strength or pH poses no effect on the adsorption of nonpolar solutes while it exhibits a significant effect on the uptake of polar solutes.

Effect of sorbed nonylphenol on sorption of phenanthrene onto mineral surface

“…Linear sorption of phenanthrene (R 2 = 0.99) were observed on the mineral surface, whereas the K d values were much lower, which was 28.44 L/kg on organic-removed sediment and 30.10 L/kg on kaolinite, respectively. High-isotherm linearity of phenanthrene onto hydrophilic minerals was also reported in other studies [3], and the sorption mechanism was explained by London forces between the HOCs solute and the water film above the mineral surface.…”

“…However, for sorbents containing only very small amount of organic carbon (OC), the mineral phase was found to contribute significantly to the sorption of HOCs [1,2]. The sorption of HOCs onto mineral surface is considered to occur presumably by dispersion force onto a water film above the minerals [3]. Even if the interaction is usually weak and non-special, difference of HOCs sorption on different mineral surfaces has also been found [4][5][6].…”

Thermodynamics of naphthalene sorption to organoclays: Role of surfactant packing density

“…Sorption of HOCs from water to the sorbents includes water-motivated sorption and sorbent-motivated sorption [38,39]. Since the solution conditions were similar for naphthalene sorption to the four organoclays, the variation of thermodynamics should arise from the differences of sorbent-motivated sorption thermodynamics.…”

Sorption of aromatic hydrocarbons onto montmorillonite as affected by norfloxacin

“…The sorption mechanisms of PAHs on clay minerals were controversial. Several models have been outlined to describe the driving forces for sorption of PAHs by mineral surfaces: (1) hydrophobic interaction, which was driven by a substantial thermodynamic gradient due to a combination of relatively small van der Waals forces and large entropy differences [18,19]; (2) partition from bulk aqueous phase to vicinal water film on montmorillonite surface [20,21]; (3) cation-interaction between the accumulated "soft" cations on clay mineral surface and aromatic ring [22]; (4) capillary condensation into interlayer nano or micropores of montmorillonite [17].…”