Abstract:
The sorption kinetic and isothermal behaviors of BDE-47 on three natural soils with different soil organic matter fractions(fOC) were studied. The results demonstrated that a two(fast and slow)-compartment first-order model was more appropriate for describing the sorption kinetic data, compared to a one-compartment first-order model, especially in the initial sorption stage within 49 h. The fast sorption was dominant during the whole sorption process from beginning to the apparent sorption equilibrium; while the contribution of the slow sorption to the total sorption amount gradually increased over time and then attained to a plateau at 97 h. The achieving time to the individual sorption capacity for the fast sorption was much shorter than that for the slow sorption. The contribution of the fast sorption to the increase in the total sorption amount of BDE-47 was prevailing at the start of sorption process from 3 h to 5 h; while the fraction of the slow sorption became principal in the subsequent stage of sorption process. Within the narrow equilibrium concentration range due to the fairly low aqueous solubility of BDE-47, the fitting results by the linear partitioning model were comparable with the linear portion by the nonlinear Freundlich model in this study. As for the Freundlich model, the nonlinear exponent(n) values of BDE-47 for the two samples with lower fOC(0.72%) or higher fOC(7.90%) were obviously lower than 1.0(0.75±0.03 and 0.74±0.02, respectively), suggesting somewhat nonlinear sorption characteristics in the studied range of apparent equilibrium concentrations of BDE-47; whereas the linear behavior of BDE-47 for the left sample with medium fOC(2.86%) was indicated by its n value much closed to 1.0(1.03±0.03).Keywords:
Isothermal process
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Long-term sorption/desorption behavior of pyrene in six types of soils are investigated. The results show that long-term sorption and desorption entail two phases, including initially rapid process followed by a slow sorption/desorption. When soil organic matter (SOM) content was below 1%, the constant of sorption Kd of dissimilar soils increased with SOM content under different equilibrium time. While clay content played an important role in sorption capacity of the soils as SOM content was below 1%. In long-term sorption experiment, the Kd values of the six soils increased from 35.1% to 557.9%, respectively, with the sorption equilibrium time increased from 2 d to 180 d. Clay influenced significantly on Kd, while the effect of SOM was different, which suggested that the effect of sorption time on Kd of some soils could not be ignored. In long-term desorption experiment, the slow desorption percentages of pyrene from the six soils were in the range of 12.05% - 41.00%, with the tendency that the attribution of slow desorption fraction to desorption process increased with SOM. Ignoring the influence of aging on the sorption/desorption, it indicates that the attribution of SOM to the capacity of irreversible sorption compartment is distinctly higher than that of clay, which is consistent to the attribution of SOM to slow desorption process.
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A comparison of the kinetics of the sorption of copper(II) on to peat from aqueous solution at various initial copper(II) concentrations and peat doses was made. The Elovich model and the pseudo-second order model both provided a high degree of correlation with the experimental data for most of the sorption process. There was a small discrepancy at the initial stages of sorption which suggested that film diffusion or wetting of the peat may be involved in the early part of the sorption process. Models evaluated included the fractional power equation, the Elovich equation, the pseudo-first order equation and the pseudo-second order equation. The kinetics of sorption were followed based on the sorption capacity of copper(II) on peat at various time intervals. Results show that chemical sorption processes may be rate-limiting in the sorption of copper(II) on to peat during agitated batch contact time experiments. The rate constant, the equilibrium sorption capacity and the initial sorption rate were calculated. From these parameters, an empirical model for predicting the concentrations of metal ions sorbed was derived.
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Granule (geology)
Palygorskite
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The time-dependent sorption behaviors of phenanthrene on 8 soils with different organic carbon contents were investigated, and the phase distribution relationships at different contacting time of 1 h, 48 h and 720 h were described using Freundlich equation. The experimental data demonstrated that, at different contacting time studied, a significantly linear correlation occurred between the values of the sorption capacity KF and the soil organic carbon contents, the nonlinearity index n gradually decreased, whereas the organic carbon content normalized single-point Koc* values increased for all the soil samples. These results indicate that soil organic matters are the main sink of organic contaminants in soil, and the potential energy of sorption sites in soil organic matters is heterogeneously distributed, and the site capacity of the organic matters inside the soil particles is larger than that outside the soil particles. In addition, by subtracting approach to sorption isotherms, the phase distribution nonlinearity of the slow sorption in the latter section of sorption procedure was significantly higher than that of the fast sorption in the former section of the sorption procedure, which implies that the influence of the condensed organic carbon fractions is much stronger in the slow sorption section, and the diffusion of hydrophobic organic compounds in the condensed organic carbon fractions is probably the main rate-dependent step of the slow sorption.
Soil carbon
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Abstract The time dependency of phosphate sorption‐desorption in fertilized soil is particularly important to the efficiency with which plant roots absorb applied phosphorus from the soil solution. In this study, phosphorus sorption by two acid, sandy soils was measured with time using a laboratory batch technique for a range of initial phosphorus concentrations in solution. A comparison of experimental data with results calculated using a two‐site sorption‐desorption model showed that for contactimes > 1 hour the observed phosphorus sorption in both these sandy soils could be described by assuming rapid and slow reversible reactions to occur simultaneously at two separate types of sorption sites. However, for shorter contact times (< 1 hour) the 2‐site model did not describe the P sorption adequately. The orders of the forward reactions at the rapid and slow sorption sites were fractional and first‐order, respectively, with regard to the P concentration in solution. For a given soil, one set of rate coefficient values was sufficient to describe the solution phase concentration of P for several different initial concentrations.
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Hysteresis
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Langmuir adsorption model
Caesium
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Caesium
Langmuir adsorption model
Chemisorption
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