Freundlich Sorption Parameters Research Articles

Predicting phosphorus sorption isotherm parameters in soil using data of routine laboratory tests

Knowledge of phosphorus (P) sorption dynamics across different soil types could direct agronomic and environmental management of P. The objective of this study was to predict P isotherm parameters for a national soil population using data of routine laboratory tests. Langmuir and Freundlich sorption parameters were calculated from two different ranges (0–25 and 0–50 mg P L−1) using an archive of representative agricultural soil types from Ireland. Multiple linear regression (MLR) identified labile forms of aluminium (Al) and iron (Fe), organic matter (OM), cation exchange capacity (CEC), and clay as significant drivers. Langmuir and Freundlich sorption capacities, Freundlich affinity constant, and Langmuir buffer capacity were predicted reliably, with R2 of independent validation > 0.9. Sorption isotherm parameters were predicted from P sorbed at a single concentration of 50 mg P L−1 (S50). An MLR prediction of P sorption maximum in the 0–50 mg P L−1 range was achieved, to an accurate standard, using S50, OM, and Mehlich-3 Fe (R2 of independent calibration and validation being 0.91 and 0.95, respectively). Using Giles’ four shapes of isotherms (C, L, H, and S), L non-strict- and C-shaped isotherm curves accounted for 64% and 27% of the soils, respectively. Hierarchical clustering identified a separation of isotherm curves influenced by two ranges of Mehlich-3 Al. Soils with a low range of Mehlich-3 Al (2.5–698 mg kg−1) had no incidence of rapid sorption (C shape). Single point indices, Al, or available soil data make the regression approach a feasible way of predicting Langmuir parameters that could be included with standard agronomic soil P testing.

The influence of long-term ageing on arsenic ecotoxicity in soil

The ageing of a contaminant in soil influences the bioavailability and toxicity of environmental pollutants. Yet, despite arsenic (As) being an important terrestrial contaminant, the effect of As ageing on phytotoxicity has received relatively little research. Research to date has reported predominantly short term (< 0.5 years) experiments. Here, we studied the influence of ageing over 0.25 and 5 years on the phytotoxicity of As (as arsenate) on Cucumis sativus L. (cucumber). The study showed that increasing ageing time of As from 0.25 to 5 years increased the EC10 and EC50 values by 4.0 and 1.76 fold, respectively. The dependence of ageing on soil properties was also examined, although only Freundlich sorption parameters were correlated to the ageing factor (r = 0.68, P = 0.028). Soils with high adsorption capacity also showed the greatest change in toxicity over 5 years. In addition, data was compiled from relevant literature to develop a model for As ecotoxicity. The combined model (n = 54) showed no relationship with pH but was correlated to the oxalate extractable iron content and %clay. Arsenate ecotoxicity (EC50, mg/kg) in the multivariate model was related to oxalate iron content, %clay and ageing time. Thus, the results of this study have significant implications for risk assessment of long-term As contaminated soils.

Lumped Approach for Reactive Transport of Organic Compound Mixtures through Simulated Aquifer Sands in Lab-Scale Column Tests

The feasibility of the lumped approach for reactive transport of 12 organic compounds in mixtures through simulated aquifer sands with different organic carbon content (foc) within soil columns was evaluated. From direct measurements of effluent samples and temporal and spatial pore-water concentration profiles within soil columns, 12 organic compounds in mixtures were sorbed to different extents due to the different dependence of sorption on foc. Considering the tradeoff between accuracy and simplicity, four, five, and six pseudocompounds were determined for simulated aquifer sands with foc of 0.006%, 0.051%, and 0.221%, respectively, to approximate the reactive transport of 12 organic compounds in mixtures. Each pseudocompound presented obviously different reactive transport behavior in terms of both sorption capacity and nonlinearity, indicating that each pseudocompound contained components with relatively similar sorption capacities and nonlinearity. Similar to the results from batch equilibrium sorption tests, log Koc can be used as the a priori grouping criterion, although the relative contributions of different forces to the overall sorption may differ for different composition of organic mixtures and foc values of aquifer sands. Finally, the assignment of the Freundlich sorption parameters of pseudocompounds using averages of Freundlich sorption parameters of their components led to reasonable prediction for reactive transport of organic compounds in mixtures through the soil columns. Further study is warranted to evaluate the effective coupling between lumped approach and reactive transport model using complex multicomponent mixtures within heterogeneous subsurface systems.

Sequestration effect and mechanism of PCB1 by high-temperature black carbon.

Black carbon (BC) is a substance that significantly affects the migration and transformation of hydrophobic organic compounds (HOCs) in soil/sediment. High-temperature BC is an important form of BC in the environment, and, currently, there is relatively little research on the influence of high-temperature BC on the sorption and the desorption behavior of HOCs and its mechanism. In this study, the sorption isotherms and TENAX-aided desorption kinetics of PCB1 by three typical high-temperature BCs (fly ash (FC), soot (SC), and high-temperature biochar (BC 900)) and a low-temperature biochar (BC 400) were compared. In addition, the sorption-desorption mechanism was clarified through its correlation with the physicochemical properties of BC. The results indicated that the Freundlich sorption parameters of FC, SC, BC 900, and BC 400 were 9947.90, 5417.57, 77690.16, and 2804.54 (mg kg-1)/(mg L-1), respectively, indicating that these high-temperature BCs had stronger sorption capacity. The desorption rate of PCB1 on BC 900 was slow, and the ratio of the difficult desorption fraction (Fr) was as high as 96.2%, while those of FC, SC, and BC 400 were only 35.3%, 19.1%, and 54.7%, respectively. The sorption and desorption mechanisms of the three high-temperature BCs were similar to those of BC 400. They exhibited nonlinear adsorption at low PCB1 concentrations and linear partition at high PCB1 concentrations. Moreover, the results demonstrated that different types of high-temperature BCs in the environment have different sequestration effects on HOCs. Frap, the part that can be quickly desorbed, was predominantly PCB1 sorbed onto BC through a linear partition mechanism, but the surface acidic functional groups and larger pores would also increase the Frap. Meanwhile, the slow desorption ratio (Fslow) was mainly affected by the degree of surface aromatization; the difficult-to-desorb PCB1 (Fr) was combined with BC through a nonlinear adsorption mechanism and was mainly related to the micropore volume. Graphical abstract.

Effects of Random and Systematic Errors on Freundlich Parameters for Pesticide Sorption

Assessment of the Freundlich sorption parameters of pesticides is an important element of their environmental risk assessment (especially leaching to groundwater), and therefore these parameters must be accurately assessed. In this work, the effect of random and systematic errors on the accuracy of the Freundlich sorption parameters was assessed for pesticide–soil sorption studies using Monte Carlo simulations and analytical approximations. This assessment was performed for the so-called indirect method, which assumes that the mass in the system at the end of the study is equal to the added mass. The errors in these parameters appeared to depend strongly on the percentage decrease in the concentration in the liquid phase. The effects of random errors on these parameters was shown to be limited if the recommendations of the current Organisation for Economic Cooperation and Development (OECD) guideline were followed. However, the effect of the systematic error resulting from the loss of substance during the study might lead to observed Freundlich sorption coefficients that are approximately two times too high and Freundlich exponents that are 10% too high. Therefore, it is recommended that the possible effect of loss on the Freundlich sorption parameters should be assessed. This effect can be relatively simply calculated by combining the observed percentage decrease in the liquid phase with an upper limit of the percentage loss during the study. It is further recommended that the highest possible solid/liquid ratio should be used in pesticide–soil sorption studies. These recommendations are especially relevant for pesticides with low sorption for which the leaching assessment is most critical.

Ability of natural, acid-activated, and surfactant-modified Terra Rossa soils to sorb triazine herbicides and their degradation products

Two Terra Rossa soils that were collected in the Mediterranean region of Croatia and Turkey were tested in their natural, acid-activated, and surfactant-modified forms as sorbents for hydrophobic triazine groundwater pollutants in terms of their potential application to the multi-mineral landfill barriers. The soils were predominantly composed of kaolinite, followed by quartz, calcite, iron-bearing oxides/oxyhydroxides, and several other types of clay. The natural soils were poor in organic carbon (OC ≤2%), were similar in chemical composition, and were significantly different in their cation-exchange capacity (CEC). Sorption experiments were conducted with hydrophobic, weakly basic and ionisable triazine herbicides (atratone, ametryn, and atrazine) and three atrazine dealkylated degradation products. The Freundlich sorption parameters were evaluated and compared with respect to the physicochemical properties of the sorbates and sorbents. The low affinities of the natural soils for the sorption of all of the tested triazines were significantly enhanced by soil acid activation. The highest fractions of sorbed triazines were observed in the acid-activated soil with the higher CEC: 90% for the most basic and partially protonated atratone and ametryn and 78% and 61% for the more polar degradation products deisopropylatrazine and didealkylated atrazine, respectively. The enrichment of natural soils with OC by the sorption of the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) was more efficient in soil with higher CEC. The sorption intensities of all of the triazines except the most polar didealkylated atrazine increased significantly with increasing soil OC and correlated positively with the hydrophobicity of the compound. The sorption capacities of the HDTMA-modified soils were greater for most compounds than the capacities of the acid-activated soils. Based on the calculated sorbate fractions that were resistant to desorption, atratone and ametryn would be expected to be retained longest in the acid-activated soils, while the soil modification with HDTMA primarily prolonged the retention of ametryn and atrazine. The results indicated that, unlike natural Terra Rossa soils, their acid-activated or surfactant-modified forms could be applicable as components of an organophilic layer in multi-mineral barriers for retention of triazines and similar chemicals.

Lumping Analysis for Sorption of Neutral Organic Compounds in Mixtures to Simulated Aquifer Sorbents

The concept of using lumping analysis to reduce the complexity associated with the sorption of 12 neutral organic compounds (NOCs) comprising complex mixtures to simulated aquifer sorbents was evaluated. The sorbates covered a wide range of octanol-water partitioning coefficients, Kow (i.e., � 0:24 ≤ logKow ≤ 4:23), and the sorbents included different types of mineral surfaces and humic acid- mineral complexes with different fractions of organic carbon, f oc (i.e., 0:006% ≤ f oc ≤ 0:221%). Both a priori lumping criteria (i.e., the aqueous activity coefficient at saturation γ sat , and the organic carbon partitioning coefficient, Koc) and experimentally derived lumping criteria (i.e., Freundlich sorption parameters) were evaluated as potential lumping criteria. The results indicated that the sorption behavior of the 12 NOCs contained in mixtures could be approximated reasonably well by lumping them into a fewer number of pseudocompounds (four to six) with similar sorption behaviors based on Freundlich sorption parameters, and that both γ sat and Koc could be used as viable a priori lumping criteria. However, the number and compositions of the pseudocompounds were a complex function of the hydrophobicity (i.e., γ sat and Koc) of the NOCs and varied as a function of the type of mineral surface (e.g., uncoated, α-FeOOH-coated, and Al2O3-coated sands) and the f oc of the sorbent. DOI: 10.1061/(ASCE)EE.1943-7870.0000498. © 2012 American Society of Civil Engineers. CE Database subject headings: Organic carbon; Organic compounds; Organic matter; Pollutants; Soil pollution; Sorption; Subsurface environment. Author keywords: Lumping analysis; Mixtures; Neutral organic compounds; Pseudocompounds; Simulated aquifer sorbent; Sorption.

Experimental Study of Factors Controlling Sorption of Heavy Metals on Ariake Clay and Implication for Practice

A series of batch tests have been presented to investigate the effects of solid-solution contact time, solid:solution ratio, and pH of solution on sorption of Cd2+ and Pb2+ on Ariake clay from Kyushu region of Japan. The results show that, among the three investigated factors, solid:solution ratio (SD/SN) seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests were applied to a typical field landfill in which the Ariake clay was used as soil barrier. The impacts of the landfill were assessed by numerical analysis. Based on the analysis result, the significance of selecting proper solid:solution ratio for determining sorption parameters from batch test has been discussed.

A study on sorption properties of Cd 2+ on Ariake clay for evaluating its potential use as a landfill barrier material

To assess the potential use of Ariake clay from Kyushu region of Japan as a landfill barrier material, the results of a series of batch tests are presented to investigate on the effects of solid–solution contact time, solid : solution ratio and pH of solution on sorption of Cd 2+ and Pb 2+ on the Ariake clay. The results show that in addition to the three investigated factors, solid : solution ratio seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests are applied to a typical landfill site in which the Ariake clay is used as a soil barrier. The impacts of the landfill on the underlying aquifer are assessed through numerical analysis. Based on the analysis results, the significance of selecting proper solid : solution ratio for determining sorption parameters from batch tests is discussed.

Modeling the vertical distribution of carbendazim in sediments

AbstractThe sorption, fate, and vertical distribution of the fungicide Derosal ® with active ingredient carbendazim in sediments were investigated in indoor freshwater microcosms. Carbendazim penetration in the sediment was measured as a function of time and depth. Freundlich sorption parameters were determined by batchwise equilibration of carbendazim in a sediment suspension. Freundlich parameters were Kf = 258 μg(1‐n)Ln/kg and n = 0.78. Analysis of different layers of sediment cores showed a slow penetration of carbendazim in the first 6 cm of the sediment in 60 d. The penetration was successfully simulated with a multilayer model accounting for sorption to organic matter (using the measured isotherm), molecular diffusion, biodegradation, and bioturbation. The calibrated model was most sensitive to the parameters for molecular diffusion and sorption in the sediment. Bioturbation did not affect the carbendazim profiles because of carbendazim toxicity for bioturbators. So there was a direct feedback between carbendazim toxicity and fate. The calibrated model was validated using a dataset obtained from another freshwater microcosm.

Removing 2,4-D from water by organo-clays

Decylammonium-montmorillonite (C10M) and decylammonium-vermiculite (C10V) were assayed as sorbent for the weak acid herbicide 2,4-D (2,4-dichlorophenoxy acetic acid) and were compared with untreated clays and activated carbon. Langmuir and Freundlich sorption parameters were calculated from the sorption isotherms. These indicated an increase of sorption capacity for 2,4-D of clays after decylammonium exchange. The sorption at different pH showed that molecular forms were preferentially adsorbed on C10M whereas anionic forms were on C10V. The C10V sample showed much higher and stronger sorption capacity than C10M. The different behaviour of both organic sorbents was related to the different arrangement of decylammonium cations in the interlayer of both minerals, as a consequence of their different layer charge.