Wyniki wyszukiwania - Biblioteka Nauki

1

Sorption of organic compounds by organo-zeolites

100%

Wołowiec M. , Muir B. , Bajda T.

|

tom Vol. 42, no. 1

139--140

EN

Organic compounds such as BTEX and PAHs are one of the most common contaminants in water system. These contaminants would take decades to degrade and they have harmful effects on human health (Qin et al. 2008). Several treatment methods have been developed to remove those contaminants from industrial wastewater. They include ion-exchange, filtration, adsorption and the use of various types of sorbents for example zeolites (Kibazohi et al. 2004, Mathur et al. 2007, Aivaliotiet al. 2012, Almeida et al. 2012). Natural clinoptilolite (Cp) from the Bystré deposit in Slovakia and zeolite Na-X synthesized from fly ash has been modified with a hexadecyltrimethyl ammonium bromide (HDTMA) in amounts of 1.0 and 2.0 of external cation exchange capacity (ECEC) of the zeolites (Szala et al. 2013). The sorption properties of unmodified zeolites and organo-zeolites in terms of aqueous solutions of benzene, ethylobenzene, toluene, p-xylene (BTEX) and their mixtures as well as anthracene, naphthalene, benzo[a]pyrene, dibenzo[a,h]anthracene (PAHs) and their mixtures at different concentrations were evaluated. The results showed that the modification of the zeolite Na-X and Cp with HDTMA improves the sorption properties. Modification in the amount of 1.0 ECEC proved to be the best in terms of p-xylene, anthracene, naphthalene, benzo[a]pyrene, dibenzo[a,h]anthracene. On the other hand benzene, ethylobenzene and toluene were adsorbed the most effectively by 2.0 ECEC modification of Na-X and Cp. Based on experimental data, the removal efficiencies for BTEX follows the order: p-xylene > toluene > benzene > ethylobenzene, for POHs: dibenzo[a,h]anthracene > benzo[a] pyrene > anthracene > naphthalene. P-xylene and naphtalene were adsorbed in the greatest quantity and benzene and anthracene in the lowest quantity from the mixtures of BTEX and PAHs, respectively. The sorption efficiency depends on the physicochemical properties of the organic compounds (dipole moment, molar mass, molecule structure and the time of the sorption process) as well as natural Cp and synthetic zeolite Na-X properties, such as Si/Al ratio, texture parameters and external cation exchange capacity. With an increasing concentration of the hydrocarbons in the solution the sorption capacity increases (Szala et al. 2015). Natural Cp is a better sorbent than synthetic zeolite Na-X in case of BTEX sorption, while PAHs are adsorbed more effectively by zeolite Na-X and its modifications. The mechanism of the sorption consists on the dissolving of the organic compounds into the organic layer of the surfactant (on the zeolites’ surface) as well as on the organic compounds’ penetration into the mesopores.

2

Molybdates and tungstates sorption on organo-smectites as a process controlled by the type and amount of surfactant

100%

Muir B. , Andrunik D. , Bajda T.

|

tom Vol. 42, no. 1

102--103

EN

Modification of a smectite with organic surfactants leads to the formation of an organo-mineral complex characterized by a positive charged (Baj da et al. 2015). The process involves the exchange of naturally occurring cations, e.g. Ca 2+, Mg 2+, Na +, K + by large organic cations of surfactants. This alteration makes it possible to use organo-smectites as sorbents to remove anionic forms of Mo(VI) and W(VI) from aqueous solutions. The concentration of molybdenum in the environment is significantly enhanced by anthropogenic inputs from coal-resource development, fly ash, sewage sludge and hard-rock mining activity (Kalembkiewicz & Sočo 2009). W(VI) is released to the environment through its use in winter tires or by its applications in industry e.g. enriches alloys or electrotechnics (Gustafsson 2003). The environmental behavior of molybdenum and tungsten becomes very complex once they dissolve as Mo(VI) and W(VI) anions occur as a monomer only in alkaline or neutral solutions. Bentonite from the Jelšovy Potok in Slovakia, rich in montmorillonite phase, was used in the sorption experiments (Bajda et al. 2015). Through the preparation of a series of experiments it was possible to define the impact of various surfactants, their amount and organo-smectites’ properties order on the sorption capacity and pH effect. Smectite has been modified with dodecyltrimethylammonium bromide (DDTMA), didodecyldimethylammonium bromide (DDDDMA), hexadecyltrimethylammonium bromide (HDTMA) and dihexadecyldimethylammonium bromide (DHDDMA) in amounts of: 0.5, 1.0 and 2.0 of cation exchange capacity (CEC). Experiments of Mo(VI) and W(VI) sorption on organo-smectites were conducted under various concentrations of Mo(VI) and W(VI) (0–20 mM) and in wide range of pH’s (1–13). The effectiveness of modifications follows the order DDTMA-smectite > HDTMA-smectite > DDDDMA-smectite > DHDDMA-smectite. The unmodified smectite did not remove Mo(VI) and W(VI) anions from the aqueous solution at all. In the removal of Mo(VI), sorption efficiency follows the order: DDTMA-smectite > DDDDMA-smectite > HDTMA-smectite > DHDDMA-smectite. In case of W(VI) the efficiency of the removal can be place: DDDDMA-smectite > DDTMA- -smectite > HDTMA-smectite > DHDDMA- -smectite. With an increasing concentration of Mo(VI) or W(VI) in the solutions, the sorption increases. The maximum sorption capacity in the removal of Mo(VI) was 1710 mmol Mo(VI)/kg in case of smectite modified with DDTMA at 0.5 CEC. The best result of tungsten sorption was 5882 mmol W(VI)/kg and it was obtained for DDDDMA-smectite (0.5 CEC). Results showed that the sorption is more effective at a lower pH, in both Mo(VI) and W(VI) removal. The smectite modified with surfactant with double carbon chain (DDDDMA, DHDDMA) proved to be a better sorbent. With an increasing amount of surfactant attached to the smectite, the sorption efficiency increases.

3

The removal of organic compounds by natural and synthetic surface-functionalized zeolites: a mini-review

88%

Muir B. , Wołowiec M. , Bajda T. , Nowak P. , Czupryński P.

|

tom Vol. 48, iss. 1/4

145--156

EN

The use of zeolites as sorbents has been investigated as a replacement for existing costly methods of removing organic contaminants from water solutions. Zeolites can be modified by inorganic salts, organic surfactants, metals or metal oxides in order to increase their adsorption capacity. The unique ion exchange and adsorption properties of zeolites make them very suitable for application in the removal of organic compounds such as volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), phenols and other complex petrochemicals. Many different studies have demonstrated their effectiveness in reducing the concentrations of organic contaminants as well as petroleum derivatives in water, which has been summarized in this paper.