Nonlinear Sorption Research Articles

Comparison of percolation to batch and sequential leaching tests: Theory and data

Leaching tests are becoming more relevant in assessing solid waste material, particularly with respect to groundwater risks. In the field, water infiltration is the dominant leaching mechanism, which is simulated in the lab with batch and column tests. In this study, we compared percolation, through analytical solutions of the advection-dispersion equation, to laboratory batch and sequential leaching tests. The analytical solutions are supported with comprehensive data from various field and laboratory leaching of different solutes from waste materials and soils collected in long-term joint research projects funded by the German Federal Ministry for Education and Research and the Federal Environment Agency. The comparison of theory and data is facilitated if concentrations and cumulative release are plotted versus the liquid-solid ratios (LS). Both theory and data indicate that leaching behaviour is independent of duration and physical dimensions of the leaching tests. This holds even if field lysimeters are compared to laboratory columns of different size, different flow velocities as well as different contact times. In general, laboratory batch tests over predict effluent concentrations (for LS<K(d)). Leaching of solutes from solid samples of certain materials (e.g. chloride from incineration ashes or sulphate from demolition waste) in column and lysimeter tests compares very well and agrees with the analytical solutions. Overall, reproducibility and agreement with theory of column tests are better than batch tests, presumably because the latter are prone to artefacts (e.g. in liquid-solid separation steps). Theory and data fit surprisingly well, despite the fact that the theory is based on the local equilibrium assumption; non-linear sorption and chemical reactions in the solid waste materials are not considered.

Modeling Nonlinear Sorption of Alcohol Ethoxylates to Sediment: The Influence of Molecular Structure and Sediment Properties

The nonlinear sorption of individual alcohol ethoxylate (AE) homologues was studied as a function of the chemical structure of AE and properties of six marine sediments and three clay minerals. All sorption data for both sediments and clays are well described by a dual-mode model, combining a Langmuir and linear sorption term. The nonlinear isotherms of a single homologue on different substrates almost overlap when sorbed concentrations are expressed per specific surface area. Below and above the Langmuir maximum capacity, isotherms approach linearity. Accordingly, it is demonstrated for nine individual AE that the two linear sorption coefficients for the clay mineral illite are predictive within a factor of two for a North Sea sediment. The linear sorption term at high concentrations is likely related to bilayer formation on the mineral surfaces, for both clays and sediments. Adsorption and bilayer formation to mineral surfaces dominate the sorption behavior of most AE homologues to the tested marine sediments. The two fitted sorption coefficients correlate well with the polar and nonpolar chain lengths of the AE. The enhanced nonlinearity of isotherms for AE with longer ethoxylate chains is explained by both an increasing adsorption coefficient and a decreasing bilayer formation affinity with additional ethoxylate units.

Evaluation of Organoclays for Use in Landfill Liners

Organoclay obtained from two constituents' coco-dimethyl benzyl ammonium chloride, and bentonite was used in this study to prepare five admixtures, by varying the amount of organoclay, natural soil, and bentonite. Laboratory ex- periments were conducted on these admixtures with the objective of identification and assessment of their potential for use in landfill liners. The admixtures had the organoclay ranging from 10 to 25%, and bentonite in the range of 0 to 20%. The admixtures prepared were evaluated by conducting laboratory sorption tests and permeability tests for the determina- tion of retardation coefficient, and hydraulic conductivity. Permeability tests were conducted using consolidation per- meameter. Total Organic Carbon (TOC) was determined using TOC Analyzer. Admixture with higher percentage of or- ganoclay exhibits higher organic sorption capacity. Retardation coefficient of the admixtures was determined by curve fit- ting the experimental data of sorption tests to fit to Freundlich (nonlinear) sorption isotherm. One-dimensional transport simulations were performed to evaluate completely the effectiveness of these materials for use as landfill liner and to de- velop design charts for determining required liner thickness.

Phenanthrene sorption to humic acids, humin, and black carbon in sediments from typical water systems in China

Humic acid (HA) and humin (HM) were extracted with 0.1 M NaOH and black carbon (BC) was isolated using a combustion method at 375 degrees C from six sediments in different areas in China and their sorption isotherms for phenanthrene (Phen) were determined. All sorption isotherms were nonlinear and fitted well with the Freundlich model. Among the SOM, HM and BC with more aromatic carbon controlled the sorption nonlinearity and capacity. Compared to HM, higher K (oc) values were observed for BC due to the combustion of organic matter and native sorbates in HM. For HAs isotherms, a positive relation was observed between the K (oc) values and aliphaticity or H/C ratios, but a negative relation was shown between the n values and polarity of HAs. HA, HM, and BC were responsible for 0.4-9.3%, 46-97%, and 65-96% of the total sorption, respectively, indicating the dominance of HM and BC fractions in overall sorption of Phen by the sediments.

Predicted models for phenanthrene sorption nonlinearity and capacity based on different HA/BC ratios in sediments

Phenanthrene (Phen) sorption isotherms for synthetic sediment organic matter samples with nine different humic acid/black carbon (HA/BC) ratios were determined to provide predicted models for Phen sorption nonlinearity and affinity by sediments. The sorption data were fitted well by the Freundlich model. The nonlinear sorption of Phen was dominated by BC particles. According to BC/TOC content, Phen sorption nonlinearity can be predicted using the exponential model: n = 0.410 + 0.454 ∗ exp(−0.028 BC/TOC). As sorption is a combination of absorption into soft carbon and adsorption onto hard carbon, based on published K HA, K FBC, and n bc values and measured f BC and f oc values, Phen sorption affinity-related parameter K oc values can be predicted from the simplified dual sorption model: f oc K oc = ( f oc - f BC ) K HA + f BC K FBC C e n bc - 1 . For sediments from the Song–Liao watershed (China), the exponential model and dual sorption model gave good predictions for n and K oc values, which support the availability of the two predicted models.

Nonlinear sorption of nonreactive components during polluted-groundwater flow in soils

When polluted groundwater flows in soils, some components are sorbed by the solid phase. A mathematical model of sorption incorporates the description of equilibrium between the mobile and sorbing phases (isotherm) and the kinetics of mass transport, which controls the tailing of the pollution front. In the case of nonlinear isotherms, the sorption and desorption are governed by different types of isotherms, resulting in histeresis effects or essential difference between the shapes of pollutant fronts. Moreover, the sorption has a damping effect, i.e., it smoothes concentration variations on the soil surface caused by seasonal variations and other factors.

Simulation of nonlinear sorption of N-heterocyclic organic contaminates in soil columns

The transport of organic contaminants in porous media is frequently influenced by nonequilibrium sorption and/or nonlinear sorption. In this study, sorption of coal tar related contaminants with different sorption properties, i.e., toluene, quinoline, quinaldine, and benzotriazole, was studied in column experiments using a European reference soil and compared with batch sorption results in order to quantify the governing sorption features. The breakthrough curves (BTCs) were simulated with a versatile 1-D reactive transport model using a one-site first-order sorption approach. Some differences in fitted parameters from batch and column experiments were found and discussed in terms of different sorption mechanisms in different aqueous concentration ranges, effects of solution properties (e.g., pH) and differences in solid-to-solution ratio and accessible sorption sites. The modeling results show that the fitting results were not sensitive to mass transfer coefficients and that a local equilibrium assumption provides excellent agreement with BTCs in our designed column when Damkohler numbers were greater than 20. Nonequilibrium sorption resulting from intraparticle diffusion thus was negligible in the column experiments. Tailing of BTCs nevertheless occurred and was primarily attributed to nonlinear sorption due to specific interactions in the sorption processes rather than to sorption nonequilibrium. Our study demonstrates how column experiments with different concentrations and flow velocities can be designed to obtain reliable sorption parameters for polar solutes with nonlinear sorption isotherms from modeling.

LFERs for Soil Organic Carbon−Water Distribution Coefficients (KOC) at Environmentally Relevant Sorbate Concentrations

Organic carbon-water distribution coefficients, Koc, for organic compounds at environmentally relevant, low sorbate concentrations may substantially differ from those at higher concentrations due to nonlinear sorption to soil organic matter. However, prediction methods for Koc such as linear free energy relationships (LFERs) are currently only available for high sorbate concentrations (i.e., near solubility limits), reflecting the lack of a set of consistent experimental data in an environmentally more relevant concentration range (i.e., orders of magnitude lower than solubilities). In this study, we determined Koc for two model sorbents of soil organic matter, peat and lignite, at sorbate concentrations of 4.3 and 19 mg/kg-organic-carbon, respectively, in batch suspensions. The measured Koc values for organic sorbates (51 for peat, 58 for lignite) of varying sizes and polarities were modeled successfully with polyparameter linear free energy relationships (PP-LFERs). The resulting PP-LFER for peat was significantly different from the PP-LFERs in the literature determined at near aqueous solubility limits of sorbates. The literature PP-LFERs were found to underestimate the measured Koc values for peat at the low concentration by up to 1 order of magnitude. The extent of underestimation highly depends on the sorbate properties and can be explained by differing sorption nonlinearities of the sorbates as predicted by a reported empirical relationship between the nonlinearity in peat and the sorbate dipolarity/polarizability parameter S. Lignite appearsto be a stronger sorbent toward many sorbates than typical soil organic matter irrespective of the concentration range and thus may not be representative for organic matter with regard to the magnitude of Koc. The present study offers the first PP-LFER equation for log Koc in soil organic matter at typical environmental sorbate concentrations.

Effects of sorption competition on caesium diffusion through compacted argillaceous rock

We carried out a small-scale laboratory diffusion experiment on a disk-like sample of Opalinus clay from the Mont Terri underground laboratory (Switzerland) using 134Cs as tracer. A through-diffusion phase was followed by an out-diffusion phase where the tracer taken up by the sample was released again. Since the tracer concentration at both boundaries was monitored, careful mass-balance considerations were feasible. A first analysis of the experimental data was done in the frame of a single-species model accounting only for transport and non-linear sorption of caesium. The model could match the data of the through-diffusion phase, however only, when strongly reducing the sorption data based on batch sorption experiments. Yet, such a procedure was in strong contradiction with sorption measurements performed on dispersed and compacted systems. In addition, predictions concerning tracer out-diffusion and mass-balance considerations clearly revealed the shortcomings of this type of model. In a second attempt we applied a multi-species transport model where now the whole water chemistry and a sorption model for caesium were considered. First, the value for the diffusion coefficient was fixed to the best-fit value of the single-species model. But again, the sorption site densities had to be reduced strongly albeit the reduction factor was smaller. Only when fixing the sorption site densities to those values of the sorption model and letting the effective diffusion coefficient D e free for the adjustment, could through-diffusion data be reasonably well fitted and out-diffusion as well as mass-balances be predicted in a satisfying manner. The main results are: (1) The best-fit could be achieved with a value for D e of 1.8 × 10 −10 m 2 s −1 which is rather high but corroborated by results of a molecular modelling study. (2) If caesium arrives in the Opalinus clay sample potassium and sodium (calcium etc.) ions are released and caesium ions are sorbed. The released cations diffuse to lower concentration regions according to their individual concentration gradients. Since locally the cation concentration for potassium, (sodium and calcium) is increased, sorption of these cations is also locally enhanced, affecting in return the sorption behaviour of migrating caesium. Consequently, the sorption process of caesium in such diffusion experiments cannot be addressed by a non-linear isotherm formalism any longer. (3) A reasonable analysis of such single tracer diffusion experiments therefore requires the combined description of transport (diffusion) and sorption of many cations and the whole complex water chemistry of the system. Thus, single-species models can only be applied with care in the considered concentration ranges.

Characteristics of Soil Organic Matter and Sorption of Phenanthrene, Naphthalene 1,3,5-TCB and o-Xylene

Nonlinear isotherm behavior has been reported for the sorption of hydrophobic organic compounds (HOCs) in soil/water systems, but the mechanisms are unclear. The model of “soft” and “hard” carbon domains has been extensively cited in the sorption literature to account for nonlinear sorption behaviors, but the structural compositions of soil organic matter (SOM) are not well understood. The objective of this study was to examine the characteristics of SOM and the effect of SOM heterogeneity on sorption isotherm by elemental analysis, organic petrographic examination, scanning electron microscopy, 13C nuclear magnetic resonance and studying the sorption behaviors of phenanthrene, naphthalene, 1,3,5-trichlorobenzene and o-xylene in soil and its isolated fractions, humic acid (HA) and humin (denser particulates and lighter particulates). DP mainly contained low maturation and high paraffinic carbon huminite. LP was composed of inertinite, huminite, vitrinite and exinite, with smaller particle size and higher maturation than DP. Humic acid approached the lignite coal rank. All isotherms were nonlinear, and nonlinearity increased in the following order: HA > DP > soil > BE > LP. The sorption of HOCs in soil was primarily regulated by SOM. Humic acid seemed to be the soft carbon domain and insoluble condensed organic matter (humin) the hard carbon domain. Isotherm nonlinearity was negatively correlated with hydrophobicity and molecular size, while sorption capacity increased with increase of these parameters. Aliphatic structures of SOM, as observed for LP, could also contribute to both isotherm nonlinearity and large sorption capacity.

Mass removal and low-concentration tailing of trichloroethene in freshly-amended, synthetically-aged, and field-contaminated aquifer material

This study investigates the effect of contaminant aging on the sorption/desorption and transport of trichloroethene in a low organic-carbon content aquifer material, comparing mass removal and long-term, low-concentration elution tailing for field-contaminated, synthetically-aged (contact times of approximately four years), and freshly-amended aquifer material. Elution of trichloroethene exhibited extensive low-concentration tailing, despite minimal retention of trichloroethene by the aquifer material. The observed nonideal transport behavior of trichloroethene is attributed primarily to rate-limited sorption/desorption, with a smaller contribution from nonlinear sorption. It is hypothesized that interaction with physically condensed carbonaceous material, comprising 61% of the aquifer material’s organic-carbon content, mediates the retention behavior of trichloroethene. The elution behavior of trichloroethene for the field-contaminated and aged treatments was essentially identical to that observed for the fresh treatments. In addition, the results of three independent mass-balance analyses, total mass eluted, solvent-extraction analysis of residual sorbed mass, and aqueous-phase concentration rebounds following stop-flow experiments, showed equivalent recoveries for the aged and fresh treatments. These results indicate that long-term contaminant aging did not significantly influence the retention and transport of trichloroethene in this low organic-carbon aquifer material.

Influence of Sorption Intensity on Solute Mobility in a Fractured Formation

Diffusive mass transfer between fracture and matrix accompanied with sorption significantly influences the efficiency of natural attenuation in hard rocks. While these processes have extensively been studied in a fractured formation, limited information exists on the sorption nonlinearity. For this purpose, a numerical model is developed that couples matrix diffusion and nonlinear sorption at the scale of a single fracture using the dual-porosity concept. The study is limited to a constant continuous solute source boundary condition. The influence of both favorable and unfavorable sorption intensities on solute mobility is investigated using the method of spatial moments. The differing capacities of available sorption sites between fracture surfaces at the fracture-matrix interface and the solid grain surfaces within the rock matrix result in a slower migration of solutes along the fracture, and a larger amount of diffusive mass transfer away from the high permeability fracture.

Naphthalene and phenanthrene sorption to very low organic content diatomaceous earth: Modeling implications for microbial bioavailability

Naphthalene and phenanthrene sorption was investigated on microporous/high surface area and low-microporous/low surface area particles with very low organic ( f oc ) content. Partitioning coefficients ( K p ) for naphthalene were similar to those predicted from the Karickhoff equation in both competitive and non-competitive sorption isotherms, even given the very low f oc . In contrast, phenanthrene K p values in competitive isotherms were 10-fold higher than predicted by Karickhoff, suggesting phenanthrene out-competes naphthalene for sorption sites. Naphthalene exhibited greater non-competitive K p at higher concentrations on the microporous particles, as evidenced by a Freundlich n = 0.74. Both compounds had 100-fold lower adsorption and desorption mass flux on the microporous particles. Adsorption followed first order kinetics, with phenanthrene adsorbing at 1.5 and 3 times the rate of naphthalene on the low surface area and high surface area particles, respectively. Naphthalene and phenanthrene desorption kinetics were well-described by a Fickian diffusion model with observed diffusivities ( D obs ) of 1.7–1.9 × 10 −8 and 0.93–1.9 × 10 −8 cm 2 s −1 for naphthalene and phenanthrene, respectively. Phenanthrene D obs were 3–5 orders of magnitude faster than those reported in organic-rich sediments. Naphthalene D obs were 100-fold lower than fast-domain diffusivities, indicating access to micropores. Naphthalene sorption non-linearity was investigated via simulations with two coupled desorption–biodegradation models. Results indicate that non-linearity would not significantly affect bioavailability in low f oc geosorbents. In contrast, sorption non-linearity would result in greatly decreased bioavailability in organic-rich geosorbents, indicating that desorption non-linearity should be considered for surface soils and sediments but may not be critical for low f oc aquifer material.

Contribution of black carbon to nonlinearity of sorption and desorption of acetochlor on sediment

In order to investigate the contribution of various black carbon (BC) contents to nonlinearity of sorption and desorption isotherms for acetochlor on sediment, equilibrium sorption and desorption isotherms were determined to measure sorption and desorption of acetochlor in sediment amended with various amounts of BC. In this paper, two types of BC referred to as BC400 and BC500 were prepared at 400°C and 500°C, respectively. Higher preparation temperature facilitated the formation of micropores on BC to enhance its sorption capacity. Increase of the BC content obviously increased the sorption amount and reduced the desorption amount for acetochlor. When the BC500 contents in total organic carbon (TOC) increased from 0 to 60%, Freundlich sorption coefficient (Kf) increased from 4.07 to 35.74, and desorption hysteresis became gradually obvious.When the content of BC in TOC was lower than 23%, the sorption isotherm had a significant linear correlation (p = 50.05). In case of desorption, a significant nonlinear change could be observed when the content of BC was up to 13%. Increase of BC content in the sediment would result in shifting the sorption-desorption isotherms from linearity to nonlinearity, which indicated that contribution of BC to nonlinear adsorption fraction became gradually remarkable.

Modeling the effects of methanol on iron dechlorination of a complex chlorinated NAPL

Research was conducted to examine the effects of various fractions of cosolvent solutions on dechlorination of toxaphene by zero-valent iron (Fe 0). Experimental results showed that toxaphene degradation in solution was found to be the result of dechlorination at the Fe 0 surface. The rate of toxaphene dechlorination was also found to reduce with the increase of cosolvent in solution, as the cosolvent presence caused a reduction in toxaphene adsorption to Fe 0 surfaces. Toxaphene sorption to Fe 0 was found to correspond to a Freundlich nonlinear sorption equation and indicated that the linearity of this isotherm in the presence of cosolvent was related to the saturation of solution, which was the ratio of aqueous concentration to the solubility ( C a/ S c). When C a/ S c > 0.2, the sorption isotherm was almost linear and the concept of cosolvency power can be applied mathematically to describe this process. A mathematical model detailing the sorption and dechlorination of toxaphene by Fe 0 was developed, and showed that experimental data agreed with the theoretically derived data. Overall, results indicated that dechlorination of complex chlorinated substances, such as toxaphene, by Fe 0 can be greatly dependent upon adsorption to the iron surface.

Adsorption and transport of arsenate in carbonate-rich soils: Coupled effects of nonlinear and rate-limited sorption

The transport and fate of arsenate in carbonate-rich soil under alkaline conditions was investigated with multiple approaches combining batch, sequential extraction and column experiments as well as transport modeling studies. Batch experiments indicated that sorption isotherm was nonlinear over a wide range of concentration (0.1–200 mg L −1) examined. As(V) adsorption to the calcareous soil was initially fast but then continued at a slower rate, indicating the potential effect of rate-limited sorption on transport. Column experiments illustrated that transport of As(V) was significantly retarded compared to a non-reactive tracer. The degree of retardation decreased with increasing As(V) concentration. As(V) breakthrough curves exhibited nonideal transport behavior due to the coupled effects of nonlinear and rate-limited sorption on arsenate transport, which is consistent with the results of modeling studies. The contribution of nonlinear sorption to the arsenate retardation was negligible at low concentration but increased with increasing As(V) concentration. Sequential extraction results showed that nonspecifically sorbed (easily exchangeable, outer sphere complexes) fraction of arsenate is dominant with respect to the inner-sphere surface bound complexes of arsenate in the carbonate soil fraction, indicating high bioavailability and transport for arsenate in the carbonate-rich soils of which Fe and Al oxyhydroxide fractions are limited.

Compound-Specific Factors Influencing Sorption Nonlinearity in Natural Organic Matter

Nonlinear sorption by natural organic matter may have a significant impact on the behavior of organic contaminants in soils and sediments. This study presents a molecular probe approach based on linear solvation energy relationships (LSERs) to identify and quantify the molecular interactions causing concentration-dependent sorption and proposes estimation methods for sorption nonlinearities. Sorption isotherms ranging over concentrations of more than 4 orders of magnitude were determined in batch systems for 23 and 16 chemically diverse probe compounds in a lignite sample and a peat soil, respectively. Each sorbent showed characteristic nonlinear sorption with Freundlich exponents (1/n) being 0.7-1. The LSER-based analysis revealed that the strength of nonspecific interactions did not vary with concentration for both sorbents. In lignite, specific interactions did not affect sorption nonlinearity either, suggesting that compound-independent factors of lignite were responsible for the nonlinear sorption. In the peat soil, by contrast, the specific interactions related to the solute polarizability/dipolarity parameter (S) decreased with increasing concentration. Consequently, compounds of higher S values were more susceptible to nonlinear sorption in the peat soil. Phenol probes have shown that hydrogen bond donating properties of sorbate compounds have a substantial impact on the overall strength of sorption with organic matter, but no significant influence on sorption nonlinearity. Heterocyclic aromatic compounds appear to undergo additional interactions that are not accounted for by the LSER. These additional interactions considerably enhance both sorption capacity and nonlinearity.

Effects of water content on reactive transport of 85Sr in Chernobyl sand columns

It is known that under unsaturated conditions, the transport of solutes can deviate from ideal advective–dispersive behaviour even for macroscopically homogeneous porous materials. Causes may include physical non-equilibrium, sorption kinetics, non-linear sorption, and the irregular distribution of sorption sites. We have performed laboratory experiments designed to identify the processes responsible for the non-ideality of radioactive Sr transport observed under unsaturated flow conditions in an Aeolian sandy deposit from the Chernobyl exclusion zone. Miscible displacement experiments were carried out at various water contents and corresponding flow rates in a laboratory model system. Results of our experiments have shown that breakthrough curves of a conservative tracer exhibit a higher degree of asymmetry when the water content decreases than at saturated water content and same Darcy velocity. It is possible that velocity variations caused by heterogeneities at the macroscopic scale are responsible for this situation. Another explanation is that molecular diffusion drives the solute mass transfer between mobile and immobile water regions, but the surface of contact between these water regions is small. At very low concentrations, representative of a radioactive Sr contamination of the pore water, sorption and physical disequilibrium dominate the radioactive Sr transport under unsaturated flow conditions. A sorption reaction is described by a cation exchange mechanism calibrated under fully saturated conditions. The sorption capacity, as well as the exchange coefficients are not affected by desaturation. The number of accessible exchange sites was calculated on the basis that the solid remained in contact with water and that the fraction of solid phase in contact with mobile water is numerically equal to the proportion of mobile water to total water content. That means that for this type of sandy soil, the nature of mineral phases is the same in advective and non-advective domains. So sorption reaction parameters can be estimated from more easily conducted saturated experiments, but hydrodynamic behaviour must be characterized by conservative tracer experiments under unsaturated flow conditions.

Analysis and Sorption of Psychoactive Drugs onto Sediment

An analytical method was developed to analyze eight psychoactive pharmaceuticals--including the antiepileptic carbamazepine, the opiates morphine, codeine, dihydrocodeine, the opiode tramadol, and the tranquilizers diazepam, oxazepam, temazepam--and the antibiotic sulfamethoxazole as well as three metabolites (10,11-dihydrocarbamazepine (DHC), 10,11-dihydroxy-10, 11-dihydrocarbamazepine, and N4-acetylsulfamethoxazole) in river sediments. Relative recoveries of all analytes exceeded 97% using either deuterated or 13C15N-labeled surrogate standards. Sorption isotherms of all analytes were constructed at pH 6.5-6.6 on two natural river sediments (Burgen and Dausenau) that differed in organic carbon contents and particle size distributions. Affinities of all analytes were up to an order of magnitude higher for the Dausenau sediment in comparison to the Burgen sediment. Isotherms were well described by the Freundlich model. Sorption of all analytes was linear on the Burgen sediment except for structurally similar carbamazepine (n = 0.90) and DHC (n = 0.88). Conversely, most analytes showed pronounced nonlinear sorption to the Dausenau sediment (n = 0.77-0.92) except for positively charged codeine, dihydrocodeine, and tramadol. Linear sorption of the latter was taken to arise from concentration-independent electrostatic interactions of the organocations with negatively charged surfaces on clay minerals or in the sediment organic matter. Desorption gave rise to hysteresis in 13 out of 16 investigated analyte-sorbent systems. Hysteresis was likely due to slow desorption kinetics beyond 24 h used in the experiment.

Sorption behavior of tetrabromobisphenol A in two soils with different characteristics

Sorption of tetrabromobisphenol A (TBBPA) in soil influences its fate and transport in the environment. The sorption behaviors of TBBPA in two soils with different characteristics were investigated using batch equilibration experiments in the study, and the impacts of ionic strength and pH on the sorption were also evaluated. The results showed that the fast sorption rather than the slow sorption played a main role in the sorption process. The nonlinear sorption isotherms of TBBPA in the soils were observed and the Freundlich model could describe the sorption behavior of TBBPA well. The calculated K F were 78.5 and 364.6 (mg/kg)(mg/L) − n for LN soil (loamy clay) and GX soil (silt loam), respectively. Soil organic matter (SOM) played a main role in the sorption of TBBPA, which contributed about 90% to the sorption in the soils. The desorption hysteresis of TBBPA was revealed in the single-cycle sorption and desorption experiments. The sorbed amount of TBBPA decreased with the increase in solution pH and increased with the increase in ionic strength. It was found that the effects of ionic strength on the sorption were mainly caused by the change of solution pH.