Sorption of Nonpolar Organic Compounds, Inorganic Cations, and Inorganic Oxyanions by Surfactant-Modified Zeolites

Abstract

Treatment of natural zeolites with cationic surfactants yielded sorbents with a strong affinity for nonpolar organics and for inorganic oxyanions, and caused little decrease in the zeolite's sorption of transition metal cations. Two zeolites modified with hexadecyltrimethylammonium or methyl-4-phenylpyridinium remained chemically stable in aggressive aqueous solutions and organic solvents. The modified zeolites sorbed benzene, toluene, p-xylene, ethylbenzene, 1,1,1-trichloroethane, and perchloroethylene from aqueous solution via a partitioning mechanism; sorption affinity was in the order of the sorbates' octanol-water partition coefficients. Zeolites with or without surfactant treatment strongly sorbed Pb 2+ from solution. Surfactant-modified zeolite also sorbed chromate, selenate, and sulfate from solution; the mechanism appears to be surface precipitation of a surfactant-oxyanion complex.Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers, molecular sieves, and catalysts. Clinoptilolite is the most abundant naturally occurring zeolite. It has a two-dimensional 8-ring and lu ring channel structure with the largest aperture measuring 4.4 by 7.2 Λ (7). The unit cell formula is (Ca,Na2,K 2 ) 3 [Al 6 Si3o072] e 24H 2 0. Most zeolites used in the water treatment field are not true zeolites but are amorphous sodium aluminosilicates with limited cation exchange capacities. The low cost of natural zeolites ($60-$100/ton) makes their use attractive in pollution abatement applications.Zeolite chemistry resembles that of smectite clays. In contrast to clays, however, natural zeolites can occur as mm-or greater-sized particles and are free of shrink/swell behavior. As a result, zeolites exhibit superior hydraulic characteristics and are suitable for use in filtration systems (2) and potentially as 0097-6156/95/0594-0054$12.00A)

Field Demonstration and Validation of a New Device for Measuring Groundwater and Perchlorate Fluxes at IHDIV-NSWC, Indian Head, MD

“…Also, note the order of selectivity for the three ions: perchlorate > chromate > selenate; note that the same selectivity sequence was found for SM-SI-GAC. Bowman et al, 1995;Haggerty and Bowman, 1994). Bowman et al (1995) and Neel and Bowman (1992) also examined the sorption of several nonpolar organic contaminants on surfactant modified zeolite.…”

“…Bowman et al, 1995;Haggerty and Bowman, 1994). Bowman et al (1995) and Neel and Bowman (1992) also examined the sorption of several nonpolar organic contaminants on surfactant modified zeolite. Their sorption data ( Figure 4-8) show that 1) significant capacity for hydrophobic sorption can be generated by surfactant modification of the zeolite; and 2) the carbon-normalized sorption isotherm coefficients (K oc ) are proportional to the octanol-water partition coefficient (K ow ) values.…”

“…This suggests that the mechanism responsible for nonpolar contaminant sorption by the SMZ is dominantly within the hydrophobic (partitioning) domains created by the surfactant bilayer on the modified zeolite. Bowman et al, 1995;Neel and Bowman, 1992).…”

In Situ Clay Formation: Evaluation of a Proposed New Technology for Stable Containment Barriers

“…Materials in the forefront for use in reactive barriers include zero-valent metals, especially Fe, that reduce and adsorb toxic metals such as Cr(VI) (EPA, 1995). Other materials, including lime, fly ash, Fe-oxyhydroxides, calcium phosphate, Fe-sulfate, and surfactant-coated zeolites have also been shown to sorb various contaminants to differing degrees under prescribed environmental conditions (EPA, 1995;Davidovits, 1993;Bowman et al, 1995). While many of these materials have narrow windows of geochemical stability that may or may not be found in nature, fewer exhibit any geomechanical stability.…”

Technologic Tests of Turkey-Gordes Zeolite Minerals

“…The amount of clearance is between 20% and 50% of the total volume. These channels and cages are adequate for adsorbing molecules smaller than these channels and/or tunnels, so in this regard, zeolites are known as "molecular sieves" [1] [2] [3].…”