Dong-Ik Song

A simple mathematical analysis on the effect of sand in Cr(VI) reduction using zero valent iron

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.

pH-DEPENDENT SORPTIONS OF PHENOLIC COMPOUNDS ONTO MONTMORILLONITE MODIFIED WITH HEXADECYLTRIMETHYLAMMONIUM CATION

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.

Sequential competitive sorption and desorption of chlorophenols in organoclay

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.

Sorption and desorption kinetics of chlorophenols in hexadecyltrimethyl ammonium-montmorillonites and their model analysis

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 Kow value increases, except for 2,4,5-TChP, while the mass transfer coefficient for desorption (kd) consistently increases as Kow 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, kd values were found to be greater than ks 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, Kow. 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 withKow. 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.

Dual-Mode Sorption Model for Single-and Multisolute Sorption onto Organoclays

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...

Sorption and desorption kinetics of PAHs in coastal sediment

Sorption and desorption kinetics of PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were investigated. Several kinetic models were used to analyze the kinetics: one-site mass transfer model (OSMTM), pseudo-first-order kinetic model (PFOKM), pseudo-second-order kinetic model (PSOKM), two compartment firstorder kinetic model (TCFOKM) and modified two compartment first-order kinetic model (MTCFOKM). Among the models, the MTCFOKM was the best in fitting both sorption and desorption kinetic data, and therefore could predict the most accurately. In MTCFOKM, the fast sorption fraction (f′1, s) increased with the hydrophobicity (Kow) of the PAHs, whereas the fast desorption fraction (f′1, d) decreased. The fast sorption rate constant (k′1, s) was much greater than the slow sorption rate constant (k′2, s). Effect of aging on the desorption kinetics was also analyzed. The f′1, d in MTCFOKM decreased but the slow desorption fraction (f′2, d) increased with aging, indicating that slow desorption is directly related to aging.

Solubility-normalized Freundlich isotherm for the prediction of sorption of phenols in HDTMA modified montmorillonite

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 (Kow). 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 (Henrys law resion) and at high concentration (Ralouts law region).

Sorption and Desorption Kinetics of Naphthalene and Phenanthrene on Black Carbon in Sediment

Black carbon (BC), a kind of high surface area carbonaceous material (HSACM), was isolated from Andong lake sediment. Sorption and desorption kinetics of naphthalene (Naph) and phenanthrene (Phen) in organic carbon (OC) and BC in the Andong lake sediment were investigated. Several kinetic models such as one-site mass transfer model (OSMTM), two-compartment first-order kinetic model (TCFOKM), and a newly proposed modified two-compartment first-order kinetic model (MTCFOKM) were used to describe the sorption and desorption kinetics. The MTCFOKM was the best fitting model. The MTCFOKM for sorption kinetics showed that i) the sorbed amounts of PAHs onto BC were higher than those onto OC, consistent with BET surface area; ii) the equilibration time for sorption onto BC was longer than those onto OC due to smaller size of micropore () of BC than OC (); iii) initial sorption velocity of BC was higher than OC; and iv) the slow sorption velocity in BC caused the later equilibrium time than OC even though the fast sorption velocity was early completed in both BC and OC. The MTCFOKM also described the desorption of PAHs from the OC and BC well. After desorption, the remaining fractions of PAHs in BC were higher than those in OC due to stronger PAHs-BC binding. The remaining fractions increased with aging for both BC and OC.

THE SECOND VS. THE THIRD MOMENT MATCHING BETWEEN DIFFUSION MODELS FOR DYNAMIC ADSORBER

Four diffusion models for the dynamic adsorber, i.e. LDF model, single diffusivity diffusion model, two diffusivity diffusion model for beds packed with bidisperse and/or zeolite-type particles, were considered. The third moments for the four diffusion models were obtained. Relations between the system parameters involved in each model were derived by matching mean, vanance or the third moment between diffusion models. The two relations from either variance or the third moment matching were examined to investigate which one is superior when model simplification is required, by comparing the time domain elution curves for the single and the two diffusivity diffusion models. For the symmetric elution curves, relation from the variance matching is much better as expected, than the relation matching the third moment which measures skewness about mean. As the elution curves become highly asymmetric, eluting shortly after injection and exhibiting long tailing due to both the small intraparticle diffusivities and small space time in the adsorber, either relation failed to satisfactorily simplify the two diffusivity diffusion model. Contrary to the expectation that the third moment matching would work better in the asymmetric curves due to the nature of the third moment, variance matching still gives slightly better results. Relation from the variance, instead of the third moment, matching is strongly recommended for model simplification due to its simplicity in formula.

Removal of Sorbed Naphthalene from Soils Using Nonionic Surfactant

The environmental behaviors of polycyclic aromatic hydrocarbons (PAHs) are mainly governed by their solubility and partitioning properties on soil media in a subsurface system. In surfactant-enhanced remediation (SER) systems, surfactant plays a critical role in remediation. In this study, sorptive behaviors and partitioning of naphthalene in soils in the presence of surfactants were investigated. Silica and kaolin with low organic carbon contents and a natural soil with relatively higher organic carbon content were used as model sorbents. A nonionic surfactant, Triton X-100, was used to enhance dissolution of naphthalene. Sorption kinetics of naphthalene onto silica, kaolin and natural soil were investigated and analyzed using several kinetic models. The two compartment first-order kinetic model (TCFOKM) was fitted better than the other models. From the results of TCFOKM, the fast sorption coefficient of naphthalene (k1) was in the order of silica > kaolin > natural soil, whereas the slow sorbing fraction (k2) was in the reverse order. Sorption isotherms of naphthalene were linear with organic carbon content (foc) in soils, while those of Triton X-100 were nonlinear and correlated with CEC and BET surface area. Sorption of Triton X-100 was higher than that of naphthalene in all soils. The effectiveness of a SER system depends on the distribution coefficient (KD) of naphthalene between mobile and immobile phases. In surfactant-sorbed soils, naphthalene was adsorbed onto the soil surface and also partitioned onto the sorbed surfactant. The partition coefficient (KD) of naphthalene increased with surfactant concentration. However, the KD decreased as the surfactant concentration increased above CMC in all soils. This indicates that naphthalene was partitioned competitively onto both sorbed surfactants (immobile phase) and micelles (mobile phase). For the mineral soils such as silica and kaolin, naphthalene removal by mobile phase would be better than that by immobile phase because the distribution of naphthalene onto the micelles (Kmic) increased with the nonionic surfactant concentration (Triton X-100). For the natural soil with relatively higher organic carbon content, however, the naphthalene removal by immobile phase would be better than that by mobile phase, because a high amount of Triton X-100 could be sorbed onto the natural soil and the sorbed surfactant also could sorb the relatively higher amount of naphthalene.