[Show abstract][Hide abstract] ABSTRACT: The effects of “salting out” on the sorption and desorption of polycyclic aromatic hydrocarbons (PAHs) in coastal sediment were investigated. The sorption and desorption isotherms of three PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were linear. The distribution coefficients of sorption (Kd,s) and desorption (Kd,d) increased with salinity and hydrophobicity (log Kow). A three-dimensional model was proposed to explain the combined effects of solubility (S), log Kow and the organic-carbon normalized partition coefficient (log Koc). The sequential desorption of phenanthrene at different salinities of 0–30 ppt from sediment was conducted after sequential sorption at 0 and 30 ppt, respectively. The desorption data was fitted to a biphasic desorption model including linear labile fraction and non-linear desorption-resistant fraction. The linear distribution coefficient (Kdlab) for the labile desorption fraction was affected by the salinity in the previous sequential sorption stage, whereas the desorption-resistance parameters such as the maximum capacity of the desorption-resistant fraction (qmaxres, mg/kg) and the organic carbon-normalized distribution coefficient in the desorption-resistant fraction (Kocres, L/kg-OC), were affected by the salinity in the current desorption stage. In conclusion, the salinity increased the sorbed capacity of PAH as well as the desorption-resistance (as indicated by both qmaxresand Kocres) due to the “salting out effect”.
The Chemical Engineering Journal 06/2013; DOI:10.1016/j.cej.2013.03.069 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Single- and bi-solute sorption and desorption of 2-chlorophenol (2-CP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite
modified with hexadecyltrimethyl-ammonium (HDTMA) were investigated by sequential sorption and desorption. Effect of pH on
the sequential sorption and desorption was investigated. As expected by the magnitude of octanol: water partition coefficient
(Kow), both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2-CP at pH 4.85 and 9.15. For both chlorophenols,
the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated
speciation (about 80% and 99% of 2-chlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption
of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage.
Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or
non-desorbing) fraction was observed in organoclays after several sequential desorptions. This indicates that sorption of
phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption
nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared
to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST)
coupled with the single-solute Freundlich model was positively correlated with the bisolute sequential competitive sorption
and desorption equilibria.
Korean Journal of Chemical Engineering 01/2006; 23(1):63-70. DOI:10.1007/BF02705693 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sorption and desorption kinetics of chlorophenols, 2-chlorophenol (2-ChP), 2,4-dichlorophenol (2,4-DChP) and 2,4,5-trichlorophenol
(2,4,5-TChP), in montmorillonite modified with hexadecyltrimethyl ammonium cations (HDTMA-mont) were investigated by using
laboratory batch adsorbers. To investigate the effect of chemical concentration and sorbent weight on the sorption or desorption
rate constants, the initial chemical concentration and sorbent weight were varied from 50 to 150 mg/L and from 0.2 to 1.0
g, respectively. A one-site mass transfer model (OSMTM) and two compartment first-order kinetic model (TCFOKM) were used to
analyze kinetics. The OSMTM applicable to desorption rate analysis was newly derived. As expected from the number of model
parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM in describing sorption and desorption
kinetics of chlorophenols in HDTMA-mont. The mass transfer coefficient for sorption (ks) in OSMTM generally increased as K
value increases, except for 2,4,5-TChP, while the mass transfer coefficient for desorption (k
) consistently increases as K
value decreases, due to the weaker hydrophobic interaction between the solute and the organoclay. Since most sorption and
desorption complete in an hour and half an hour, respectively, k
values were found to be greater than k
values for all three solutes studied. The fraction of the fast sorption (or desorption) and the first-order sorption (or
desorption) rate constants for the fast and slow compartments in TCFOKM were determined by fitting experimental data to the
TCFOKM. The results of kinetics reveal that the fraction of the fast sorption or desorption and the sorption rate constants
in the fast and slow compartments were in the order 2,4,5-TChP>2,4-DChP>2-ChP, which agrees with the magnitude of the octanol-water
partition coefficient, K
. The first-order sorption rate constants in the fast and slow compartments were found to vary 101–102 hr−1 and 10−3–10−2 hr−1, respectively. However, the desorption rate constants in the fast and slow compartments were not correlated well withK
. The first-order desorption rate constants in the fast compartment (101−102 hr−1) were found to be much larger than those in the slow compartment (10−3–10−4 hr−1). Sorption affinity and desorption resistance of each chlorophenol in 50% HDTMA-mont were found to show the same tendency:
the weakly-sorbed chlorophenol (i.e., 2-ChP) was easily desorbed, while the strongly-sorbed chlorophenol (i.e., 2,4,5-TChP)
was rather resistant to desorption.
Korean Journal of Chemical Engineering 11/2005; 22(6):857-864. DOI:10.1007/BF02705665 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Single- and bisolute competitive sorption of phenols (2-chlorophenol, 3-cyanophenol and 4-nitrophenol) onto montmorillonite
modified with cationic surfactant (hexadecyltrimethylammonium, HDTMA cation) was investigated. In single-solute sorption,
sorption affinity increased in the order of 2-chlorophenol>4-nitrophenol>3-cyanophenol, as expected from the magnitude of
the octanol-water partition coefficient (K
ow). The difference in affinity is mainly attributed to the hydrogen bonding with the water molecules incorporated in the sorbed
phase. The sorption affinity of the phenolic compounds onto the HDTMA-montmorillonite was in the order of pH 7>pH 3≫pH 11.5.
Compared to uptake at pH 3 and 7, the uptake at pH 11.5 was quite low. The reduced uptake at pH 11.5 is attributed to lower
solubility of anions in the core of the organic medium due to the unfavorable hydrophobic interaction between hydrated anions
and nonpolar organic medium and thus anions adsorbing near the surface of the nonpolar organic medium. Solubility-normalized
Freundlich model fitted the single-solute sorption data well. Competition between the solutes in bisolute sorption reduced
the sorbed amount of each solute compared with that in the single-solute system. The ideal adsorbed solution theory (IAST)
coupled with the solubility-normalized Freundlich model predicted the bisolute competitive sorption data successfully. The
solubility-normalized model was analyzed to characterize sorption mechanism of phenols onto HDTMA-montmorillonite at very
low (Henry's law resion) and at high concentration (Ralout's law region).
[Show abstract][Hide abstract] ABSTRACT: A new three-parameter empirical isotherm model (the Song isotherm model, hereinafter) is proposed. This model satisfies the Henry's law and the Freundlich isotherm model in the low and high concentration ranges, respectively. We applied this model to the single-solute sorption of 2-chloro-, 3-cyano-, and 4-nitrophenol from water to montmorillonites organically modified with either hexadecyltrimethylammonium (HDTMA) cation or both HDTMA and tetramethylammonium (TMA) dual cations. Sorption to organoclays (i.e., organically modified clays) modified with the long-hydrocarbon chain organic cations or the short- and long-hydrocarbon chain dual organic cations usually occurs by a partition mechanism. Sorption of polar organic compounds to organoclays, however, becomes nonlinear when the solution-phase concentration covered is more than 3 orders of magnitude. The three parameters contained in the presently proposed model could be estimated from the plot, log(q/c) versus log c. The partition coefficient in the Henry's law region (K) can be estimated from the ordinate value of the asymptote in the low concentration region, the Freundlich index (n) can be estimated from the slope of the asymptote in the high concentration region, and the parameter (beta) corresponding to the crossover point can be estimated from the intersection point of the two asymptotes. By performing nonlinear curve fitting to the raw data, q versus c, using the initial guesses estimated from the manipulated data, log-(q/c) versus log c, the optimum set of parameters could be determined without worrying much over the annoying local minima. The Song model was compared with other existing two- and three-parameter isotherm models. The Song model fitted our experimental data better than the Langmuir and Freundlich models and showed nearly the same goodness-of-fit as the Redlich-Peterson and dual-mode models. The obvious merit of the Song model is that it provides us with the partition coefficient in the Henry's law region. The organic carbon-normalized partition coefficients in the Henry's law region were found to be about 1 order of magnitude higher than the corresponding octanol-water partition coefficients, at least for the phenolic compounds covered in this study.
[Show abstract][Hide abstract] ABSTRACT: Single- and bi-solute sorption and desorption of 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite modified with hexadecyltrimethylammonium (HDTMA) were investigated using multi-step sorption and desorption procedure. Effect of pH on the multi-step sorption and desorption was investigated. As expected by the magnitude of octanol-water partition coefficient, K
, both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2,4-DCP at pH 4.85 and 9.15. For both chlorophenols, the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated speciation (about 95% and 99% of 2,4-dichlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage. Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or non-desorbing) fraction was observed in organoclays after several multi-step desorptions. This indicates that sorption of phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST) coupled to the single-solute Freundlich model successfully predicted bisolute multi-step competitive sorption and desorption equilibria.
Water Air and Soil Pollution 01/2005; 166(1):367-380. DOI:10.1007/s11270-005-6329-5 · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple mathematical model was proposed to analyze the enhancement of Cr(VI) reduction when sand materials are added to the
zero valent iron (ZVI). Natural decay of Cr(VI) in a control experiment was analyzed by using a zero-order decay reaction.
Adsorption kinetics of Cr(VI) to sand was modeled as a first-order reversible process, and the reduction rate by ZVI was treated
as a first-order reaction. Natural decay of Cr(VI) was also included in other experiments, i.e., the adsorption to sand, the
reduction by ZVI, and both adsorption and reduction when sand and ZVI are present together. The model parameters were estimated
by fitting the solution of each model to the corresponding experimental data. To observe the effect of sand addition to ZVI,
both adsorption and reduction rate models were considered simultaneously including the natural decay. The solution of the
combined model was fitted to the experimental data to determine the first-order adsorption and reduction rate constants when
sand as well as ZVI is present. The first-order reduction rate constant in the presence of sand was about 35 times higher
than that with ZVI only.
Korean Journal of Chemical Engineering 01/2005; 22(1):67-69. DOI:10.1007/BF02701464 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Single-solute sorptions onto the organically modified montmorillonite were completed at 2 different pH conditions, 7 and 11.5, in a batch reactor to investigate the pH-dependent uptake of 2-chlorophenol (ChP), 3-cyanophenol (CyP), and 4-nitrophenol (NiP) dissolved in water at 25°C. During the preparation of HDTMA-clay, hexadecyltrimethylammonium (HDTMA) cation was exchanged for metal cations on the montmorillonite at the cation exchange capacity of the montmorillonite. During the process, the montmorillonite changed from having a hydrophilic to an organophilic surface. Experimental results show that the sorption affinity on HDTMA-clay was in the order of 2-ChP > 4-NiP > 3-CyP for the 2 pH conditions. The Langmuir and the Redlich-Peterson (RP) models were used to fit the single-solute sorption equilibria data graphically. The ideal adsorbed solution theory (IAST) coupled with a single-solute model (i.e., either Langmuir or RP model) was used to predict the multisolute competitive-sorption equilibria. Predictions from the IAST at each pH condition yielded favorable representations of multisolute competitive sorption of the phenolic compounds onto HDTMA-clay.
[Show abstract][Hide abstract] ABSTRACT: Single- and multisolute competitive sorptions were carried out in a batch reactor to investigate the uptake of phenol, 4-methylphenol (MeP), 2,4-dimethylphenol (DMeP), and 4-ethylphenol (EtP) dissolved in water at 25°C onto organically modified montmorillonite. Hexadecyltrimethylammonium (HDTMA) cation was exchanged for metal cations on the montmorillonite to the extent of the cation-exchange capacity (CEC) of the montmorillonite to prepare HDTMA–montmorillonite, changing its surface property from hydrophilic to organophilic. It was observed from the experimental results that the adsorption affinity on HDTMA–montmorillonite was in the order 4-EtP ≈ 2,4-DMeP 4-MeP phenol. The Langmuir, dual-mode sorption (DS), and Redlich–Peterson (RP) models were used to analyze the single-solute sorption equilibria. The competitive Langmuir model (CLM), competitive dual-mode sorption model (CDSM), and ideal adsorbed solution theory (IAST), coupled with the single-solute models (i.e., Langmuir, DS, and RP models), were used to predict the multisolute competitive sorption equilibria. All the models considered in this work yielded favorable representations of both single- and multisolute sorption behaviors. DSM, CDSM, and IAST coupled with the DSM were found to be other satisfactory models to describe the single- and multisolute sorption of the phenolic compounds onto HDTMA–montmorillonite.
[Show abstract][Hide abstract] ABSTRACT: The dual-mode sorption model (DSM) was applied to the single-solute sorption of 2-chlorophenol, 3-cyanophenol, and 4-nitrophenol from water onto organoclays. The three parameters contained in the DSM were determined for each solute by fitting to the single-solute isotherm data and subsequently utilized in competitive multisolute sorptions. A systematic method to determine the parameters for each solute was also suggested. The ideal adsorbed solution theory (IAST) coupled with the single-solute DSM and the competitive dual-mode sorption model (CDSM) extended to describe multisolute sorption were used to predict multisolute sorption onto organoclays and compared with the data to determine the predictive capabilities. The DSM was found to describe well single-solute sorption from water onto organoclays. The predictions from the CDSM and the IAST based on the DSM, though rather poor for some solutes, were generally in agreement with the multisolute sorption data. However, we could not tell at this stage which of the two competitive models is better.