Intrinsic Sorption Research Articles

Sorption of Chlorobiphenyls in Sediment—Water Systems Containing Nonionic Surfactants

AbstractNonionic surfactants may aid remediation of contaminated soils and sediments by increasing aqueous concentrations of poorly water‐soluble organic contaminants. In order to explore the effects of nonionic surfactants on the sediment—water distribution of PCBs, a series of batch experiments was performed using four commercial nonionic surfactants (Triton X‐100, Triton X‐405, Triton X‐705, and Tween 80) and Red Cedar River sediment. Sediment—water distributions of 4,4′‐dichlorobiphenyl (Di‐CB), 2,2′,4,4′‐tetrachlorobiphenyl (Tetra‐CB), and 2,2′,4,4′,5,5′‐hexachlorobiphenyl (Hexa‐CB) were studied at aqueous surfactant concentrations ranging from zero to >1.5 times the critical micelle concentration (CMC) of each surfactant. The results show decreases in apparent soil—water distribution coefficients (K*) of PCB congeners at all surfactant concentrations as compared to the intrinsic sorption coefficient (K) in the absence of surfactant, unlike that previously reported. A new model incorporating a surface micellization concept for the sorbed surfactant phase was successfully applied to experimental data presented here and in a previous study.

Hydrophobicity and sorption of chlorophenolates to lipid membranes

We have studied sorption of ionized species of chlorophenols and pentahalophenols to lipid membranes using egg-phosphatidylcholine (egg-PC) vesicles and measuring their zeta-potential as a function of aqueous concentration of the phenolates. The zeta-potential isotherms can be understood in terms of a sorption model that is a combination of the Gouy-Chapman model of the electrical double layer at the membrane-water interface and the Langmuir model for sorption. Two intrinsic sorption parameters were determined: the linear partition coefficient, β m , which relates the membrane surface density of the phenolates to their aqueous concentration and the area of the adsorption site, P s. The linear partition coefficient is the measure of the affinity of phenolates to the lipid membrane. It depends strongly on the molecular structure: 2,6-dichlorophenolate β im=(0.45±0.08)×10 −7m; 3,5-dichlorophenolate β m=(0.22±0.02)×10 m; 2,4,6-trichlorophenolate β m=(0.63±0.06)×10 −6 m; 2,4,5-trichlorophenolate β m=(0.11±0.01)×10 −5 m; 2,3,5,6-tetrachlorophenolate β m=(0.56±0.07)×10 −5 m; 2,3,4,5-tetrachlorophenolate β m=(0.55±0.06)×10 −5 m; pentachlorophenolate β m=0.34±0.05)×10 −4 m; pentachorophenolate β m=(1.00±0.13)×10 −7 m and pentabromophenolate β m=(0.19±0.04)×10 −3 m. P s was found to be independent of phenolate structure, P s= 3.3±0.1 nm 2. The membrane affinity of chlorophenolates was compared with the octanol-water partition coefficients of un-ionized chlorophenols. It was shown that the free energy of transfer of chlorophenolates from water into the lipid membrane can be divided into non-electrostatic and electrostatic contributions. The no-nelectrostatic contribution corresponds to the hydrophobicity parameter α=−3.94±0.0.08 kcal per nm 2 of molecular surface area. The electrostatic contribution contains a term inversely proportional to the molecular radius of the phenolate ion which has the physical meaning of the work of transfer of the phenolate ion from water into the membrane. The polarity of the sorption region of egg-PC membranes is given in terms of the dielectric constant and was estimated to be 12.4 (range 10.5–13.4).

Intrinsic sorption potential of aluminum-substituted calcium silicate hydroxy hydrate for cesium-137

The sorption capacity of synthetic calcium silicate hydrate Ca 5 Al x Si 6− x O 18 H 24 ·nH 2 O (where x = 0.025) for Cs 137 has been investigated at 25°C using the radiometric method. Cs 137 uptake at different concentrations has been investigated under uniform conditions at various time intervals. The material exhibits the capacity to uptake Cs 137 from tracer solutions. Cs sorption has been studied with pure Cs solution and at 1000 to 5000 times concentration of sodium ions as the competing cation. spAdvanced Cement Based Materials 1995, 2, 80–83

Sorption Kinetics of p-Ethyltoluene in NaH-ZSM-5 Crystals-Simultaneous Effect of Intracrystalline Diffusion and a Mass Transport Resistance within the Crystal Surface

Adsorption equilibrium and sorption uptake data have been measured for the system p-ethyltoluene/NaH-ZSM-5 zeolite under constant volume/variable pressure condition at elevated ambient temperature of 343 K. The equilibrium data are described by a superposition of two Langmuir isotherms. The uptake curves observed in the present paper revealed devations from the second Fick law behaviour. The experimental uptake curves are compatible with rate mechanism involving Fickian diffusion superimposed by a surface barrier. The evaluation of the model parameters was carried out by simulation of the kinetic curves that include both the interactions of the system with the apparatus and the intrinsic sorption kinetics. The dependence of the fitted model parameters on sorbent amount and pressure, respectively, is consistent with Langmuir sorption kinetics at crystal surface on one side and with the concept of molecule jumps on a system of fixed positions in the crystal bulk on the other.

A Nonequilibrium Surface Barrier for Sorption Kinetics of p-Ethyltoluene on ZSM-5 Molecular Sieves

Adsorption equilibrium and kinetic data were measured for the system p-ethyltoluene/Na,H-ZSM-5 zeolite at 343 K. The equilibrium data can be described by the superposition of two Langmuir isotherms. The kinetic data follow a complex mechanism of Fickian diffusion superimposed on the penetration of a surface barrier. The evaluation of the model parameters was carried out by simulation of sorption uptake curves including interactions of the system with both the apparatus and the intrinsic sorption kinetics. The dependence of fitted model parameters with respect to loading and pressure, respectively, is consistent with mechanistic understanding of the mobility within the crystal interface layer and in the crystal bulk

Theory of zero length column chromatography with the condition of a well-stirred sorbing zone

In this paper, a complete solution of the mathematical model of ZLC chromatography using a Volterra integral technique is described. The model includes the effects of isotherm non-linearity, extracolumn broadening and various types of intrinsic sorption kinetics. Another attribute of the model is that it describes exactly the initial stage of the ZLC chromatographic experiment. The above effects (influence of the diffusivity, of the carrier gas flow rate and of the isotherm non-linearity) on the shape of the system response is demonstrated. The effectiveness of the model is illustrated by experimental curve fitting.