Values Of Effective Diffusion Coefficient Research Articles

Mobility of Zinc in the Callovo-Oxfordian Claystone

The diffusion of zinc was studied in the Callovo-Oxfordian claystone, which is a potential host rock for the retrievable disposal of high-level radioactive wastes. Two in-diffusion laboratory experiments were performed with initial zinc concentrations of 4 10−5 mol L−1 and 8 10−6 mol L−1 (resp.) for 35 days. The zinc rock profile was acquired using an original technique, the μLIBS, with a high resolution (10μm), calibrated with the abrasive peeling method.The experimental data, i.e. Zn concentration monitoring in the source reservoir and Zn rock profile, were successfully reproduced using a chemical-transport code. In that code, the sorption of Zn was described by a multisite ion- exchange model, with only the effective diffusion coefficient value being adjusted (De=8 10−11 m2 s−1). This De value, 2 times higher than that of tritiated water, indicates that zinc, like most cations, is also subject to enhanced diffusion in clayrocks.

Effect of calcium in brine on salt diffusion and water distribution of Mozzarella cheese during brining

A soft, pasty, high-moisture surface defect occurs with progressive brining of Mozzarella cheese. Addition of calcium is traditionally used to prevent this defect but the underlying mechanism is not clear. Mozzarella cheese was formed into a cylinder inside brine on its plane surface to ensure semi-infinite, unidirectional mass transfer and placed into brine containing 0, 0.1, or 0.25% (wt/wt) calcium chloride. To monitor the effect on cheese composition of calcium in brine, we measured calcium and water contents of the cheese during brining. The extent of calcium loss from the cheese decreased significantly with the addition of calcium. Addition of calcium to a final concentration of 0.25% decreased the loss of calcium from 94.13 to 18.22% from the outside region of the cheese after 30d, and the water content of the cheese was decreased from 67.8 to 48.8%. To further elucidate the effect of calcium in brine, the Boltzmann method was used to determine the effective diffusion coefficient value, and low-field nuclear magnetic resonance was used to measure the cheese transversal relaxation time. The migration of calcium interfered with salt diffusion. At the end of brining, the amount of water bound to the protein of the cheese significantly increased. Addition of calcium to a final concentration of 0.25% diminished the proportion of bound water by 20.96%. In conclusion, addition of calcium hinders the diffusion of sodium and modifies the distribution of water in Mozzarella cheese during brining.

Inventories and concentration profiles of 137Cs in undisturbed soils in the northeast of Buenos Aires Province, Argentina

Inventories and vertical distribution of 137Cs were determined in La Plata region undisturbed soils, Argentina. A mean inventory value of 891 ± 220 Bq/m2 was established, which is compatible with the values expected from atmospheric weapon tests fallout. The study was complemented with pH, organic carbon fraction, texture and mineralogical soil analyses. Putting together Southern Hemisphere 137Cs inventory data, it is possible to correlate these data with the mean annual precipitations. The large differences in 137Cs concentration profiles were attributed to soil properties, especially the clay content and the pH values.A convection–dispersion model with irreversible retention was used to fit the activity concentration profiles. The obtained effective diffusion coefficient and effective convection velocity parameters values were in the range from 0.2 cm2/y to 0.4 cm2/y and from 0.23 cm/y to 0.43 cm/y, respectively. These data are in agreement with values reported in literature. In general, with the growth of clay content in the soil, there was an increase in the transfer rate from free to bound state. Finally, the highest transfer rate from free to bound state was obtained for soil pH value equal to 8.

Modeling calcium and water intake in threshed corn grain during thermo-alkaline treatment

A mathematical model describing simultaneous solvent diffusion and gelatinization of starch was used to explain the water and calcium absorption in threshed corn grains during the thermo-alkaline treatment. A computer-aided nonlinear optimization technique was used to find the effective diffusion coefficients and the reaction rate constants of water and calcium in threshed corn grains at boiling temperature (92.5±0.3°C). The mathematical model shows good correlation between measured and predicted values of water and calcium intake. It is concluded that the cooking process is limited by the reaction of starch components with water and calcium. The effective diffusion coefficient for water varied between 1.18×10−10 and 1.45×10−10m2/s and for calcium between 8.55×10−10and 16.77×10−10m2/s. The diffusion of water and calcium in threshed corn was produced with a reaction rate constants in the range of 6.83×10−4 to 10.4×10−4s−1 for water and 2.7×10−5–7.6×10−5s−1 for calcium. According to these effective diffusion coefficient values the diffusive process seems to be slower for water than for calcium. However, the reaction rate constant values are approximately 10 times higher for water than for calcium which may indicate that a higher amount of solvent was linked in the water diffusion process due to the gelatinization. Low concentration of Ca(OH)2 such as 0.10% did not significantly affect the water diffusion of threshed corn during the cooking process.

DRYING KINETICS OF WEST INDIAN CHERRY: INFLUENCE OF OSMOTIC PRETREATMENT

The purpose of this work was to study the influence of osmotic pretreatment on the convective drying kinetics of the West Indian cherry (Malpighia emarginata DC). Osmotic dehydration was performed with a 65ºBrix sucrose solution at room temperature, having the fruits immersed for 4 or 12 hours, using a 1:10 proportion of fruit:solution (w:w). After the osmotic dehydration, the fruits were convectively-dried at 50ºC on a tray dryer. The convection drying was modeled based on Fick’s second law, while the effective mass diffusion (Def) was determined using Levenberg-Marquardt’s minimization algorithm by means of the paradigm of inverse methods. The values of effective mass diffusion coefficients observed were in the same order of magnitude as those reported in the literature. The condition that promoted the highest value of diffusivity was convective drying preceded by 4 hours of osmotic dehydration. This condition was also the one with the best fit agreement of the tested model.

Diffusion of HTO, 36Cl− and 125I− in Upper Toarcian argillite samples from Tournemire: Effects of initial iodide concentration and ionic strength

Diffusion parameters for HTO, 36Cl−, and 125I− were determined on Upper Toarcian argillite samples from the Tournemire Underground Research Laboratory (Aveyron, France) using the through diffusion technique. The direction of diffusion was parallel to the bedding plane. The purpose of the present study was 3-fold; it was intended (i) to confirm the I− interaction with Upper Toarcian argillite and to verify the effects of initial I− concentration on this affinity, as previously observed by means of radial diffusion experiments, (ii) to highlight any discrepancy between Cl− and I− diffusivity, and (iii) to investigate the effect of an increase of the ionic strength of the solution on the anionic tracers’ diffusive behaviour. The results show that the effective diffusion coefficient (De) and diffusion accessible porosity (εa) values obtained with an ionic strength (I.S.) synthetic pore water of 0.01 eq L−1 are: De = 2.35–2.50 × 10−11 m2 s−1 and εa = 12.0–15.0% for HTO, and De = 14.5–15.5 × 10−13 m2 s−1 and εa = 2.5–2.9% for 36Cl−. Because of anionic exclusion effects, anions diffuse slower and exhibit smaller diffusion accessible porosities than HTO, taken as a water tracer. The associated effective diffusion coefficient (De) and rock capacity factor (α) obtained for 125I are: De = 7.00–8.60 × 10−13 m2 s−1 and α = 4.3–7.2%. Such values make it possible to calculate low 125I distribution ratios (0.0057 < RD < 0.0192 mL g−1) which confirm the trend indicating that the 125I rock capacity factor increases with the decrease of the initial I− concentration. Additional through-diffusion experiments were carried out with a higher ionic strength synthetic pore water (I.S. = 0.11 eq L−1). No evolution of HTO diffusion parameters was observed. The anionic tracers’ effective diffusion coefficient increased by a factor of two but no clear evolution of their accessible porosity was observed. Such a paradox could be related to the particularly small mean pore size of the Upper Toarcian argillite of Tournemire. The most significant finding of this study is the large discrepancy (factor of two) between the values of the effective diffusion coefficient for 125I and 36Cl. Whatever the ionic strength of the synthetic solution used, 125I exhibited De values two times lower than those of 36Cl. A detailed explanation for this difference cannot be given at present even if a hypothesis based on ion-pairing or on steric-exclusion cannot be excluded. This makes questionable the assumption usually made for quantifying 125I sorption and postulating that 36Cl and 125I would diffuse in the same porosity. In other terms, at Tournemire, 125I sorption could be more pronounced than previously indicated.

Effect of temperature on the containment properties of argillaceous rocks: The case study of Callovo–Oxfordian claystones

Heat generated by high level radioactive wastes could alter the performance of a clay repository. It was intended to investigate the effect of such a thermal period on the diffusive properties of Callovo–Oxfordian claystones. Thus, through-diffusion experiments with HTO, Cl-36, Na-22 and Cs-137 were performed before, during and after stages of heating at 80 °C that lasted for up to one year. A special attention was paid to limit the occurrence of any chemical disturbance. Therefore (i) the temperature was raised to 80 °C, then progressively brought back to 21 °C, thanks to three intermediate temperature stages, and (ii) specific synthetic solutions were used for each temperature, chemistry of which being close to the equilibrium state, especially with respect to the carbonate and sulphate minerals. It was found that experiments carried out at 80 °C showed a clear increase of the effective diffusion coefficient values for the four tracers with respect to those obtained at 21 °C (by a factor of 3 for HTO and Cl-36, 5 for Na-22 and 2 for Cs-137). On the other hand, the porosity and rock capacity values did not exhibit any significant discrepancy between 21 °C and 80 °C, indicating no observable damage of both the pore conducing network and the sorption properties of clay minerals. The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could be used to describe the temperature dependence of the diffusion of HTO and Cl-36 but failed to describe the diffusive evolution of the two sorbing cations, Na-22 and Cs-137. Furthermore, experiments performed after the thermal period led to diffusive properties well matching those obtained before heating. All these results suggest that at the lab scale the heating of rock samples would not alter the claystone containment properties.

Ag2O를 첨가한 압축 벤토나이트에 대한 요오드 이온의 확산 특성 관찰

[ <TEX>$Ag_2O$</TEX> ] 첨가한 압축 벤토나이트에 대하여 관통 확산법으로 요오드 이온의 이동 특성을 관찰하였다. <TEX>$Ag_2O$</TEX>를 첨가하지 않은 압축 벤토나이트와 마찬가지로 <TEX>$Ag_2O$</TEX>를 첨가한 압축 벤토나이트에서도 요오드 이온은 확산에 의하여 이동하는데, <TEX>$Ag_2O$</TEX>를 첨가한 압축 벤토나이트는 <TEX>$Ag_2O$</TEX>를 첨가하지 않은 압축 벤토나이트에 비하여 요오드 이온의 초기 누출 시간이 지연되는 것으로 나타났다. <TEX>$Ag_2O$</TEX>를 첨가한 압축 벤토나이트에서 요오드 이온의 초기 누출 시간 지연은 확산 용액으로 순수 요오드 이온 수용액을 사용하였을 때 뿐만 아니라 0.1 M NaCl-요오드 이온 수용액을 사용하였을 때에도 관찰되었다. 또한 <TEX>$Ag_2O$</TEX>를 첨가한 압축 벤토나이트의 겉보기 확산 계수는 <TEX>$Ag_2O$</TEX>를 첨가하지 않은 압축 벤토나이트의 겉보기 확산 계수보다 낮은 값을 나타내었다. <TEX>$Ag_2O$</TEX>를 첨가하지 않은 압축 벤토나이트의 유효 확산 계수는 기존 문헌에 보고된 값과 거의 일치하는 결과를 얻었으며, <TEX>$Ag_2O$</TEX>를 첨가한 압축 벤토나이트에서 요오드 이온의 유효 확산 계수는 <TEX>$Ag_2O$</TEX> 첨가에 따라 대체적으로 감소하는 경향을 나타내었다. In the compacted bentonite containing <TEX>$Ag_2O$</TEX>, the transport of iodide ion was investigated by Through-diffusion method. It is confirmed that Iodide ion is transported by diffusion process in the compacted bentonite containing <TEX>$Ag_2O$</TEX> as well as in the compacted bentonite without <TEX>$Ag_2O$</TEX>. However, the lag-time of iodide ion in the compacted bentonite containing <TEX>$Ag_2O$</TEX> is larger than that in the compacted bentonite without <TEX>$Ag_2O$</TEX>. The increase of the lag-time was observed in pure iodide ion solution and also in 0.1M NaCl-iodide ion solution. The apparent diffusion coefficient of iodide ion in the compacted bentonite containing <TEX>$Ag_2O$</TEX> has lower value than that in the compacted bentonite without <TEX>$Ag_2O$</TEX>. The effect of <TEX>$Ag_2O$</TEX> on the effective diffusion coefficient was not clearly investigated in the compacted bentonite containing <TEX>$Ag_2O$</TEX> while the values of effective diffusion coefficient of iodide ion in the compacted bentonite without <TEX>$Ag_2O$</TEX> obtained in this study were similar to those in the compacted bentonite reported in the literature.

Changes in containment properties of claystone caprocks induced by dissolved CO2 seepage

Abstract The capture and the storage of CO2 in deep geological media are proposed to reduce the emission of CO2 to the atmosphere. While the argillaceous formations have been extensively studied since more than two decades as potential host-rocks for nuclear waste disposal, only few studies have dealt with the potential degradation of their containment properties as caprocks induced by a CO2 attack. This paper focuses on the impact of a CO2-enriched fluid on the diffusive transport parameters of indurated argillaceous samples originating from the massif of Tournemire (Aveyron, France). Two through-diffusion experiments were carried out, the first one with a CO2-enriched fluid and the second one with an equilibrated fluid, chemistry of which is very close to that measured in-situ. Non-radioactive (deuterium and bromide) and radioactive tracers (tritium and Cl-36) were successively used. Throughout the duration of the experiments, the evolution of water chemistry was monitored by measuring pH, Ca, Na, Mg, K, Cl, SO4, TOC and alkalinity. The effect of the CO2 stress has been clearly evidenced. On the one hand, the tracer fluxes in the downstream reservoir of the cell having undergone CO2 attack were up to 3 times higher than in the reference cell, indicating a significant increase of the porosity and effective diffusion coefficient values (up to 100% for Cl-36 porosity and up to 300% for Cl-36 effective diffusion coefficient). On the other hand, the chemical monitoring showed that magnesium, calcium and carbonate concentrations in the collection reservoirs increased up to one order of magnitude, suggesting a possible dissolution of some carbonate minerals such as calcite, reacting with the acid fluid.

Water absorption behavior of carpet waste jute-reinforced polymer composites

This article deals with the water absorption behavior of low-cost polymer composite composed of carpet waste jute yarns and thermoset matrices (i.e., epoxy and polyester). The water absorption behavior of the composites and deviation of their flexural and impact properties after aging in distilled water were investigated. The magnitude of diffusion parameters such as n and K were evaluated to assess the mode of water transport. It was found that the composites follow Fickian diffusion behavior. Both maximum water content (Mmax) and effective diffusion coefficient (Deff) values increased with increasing fiber content. Epoxy matrix composites showed higher Mmax and D eff values when compared to those of polyester matrix composites. D eff value increased remarkably with an increase in immersion temperature, whereas temperature had relatively little impact on Mmax value. Thermodynamics of diffusion process was investigated using Arrhenius plots and the magnitude of the activation energy for the process of diffusion (E a) was evaluated. Ea increased with temperature increment, suggesting fast access of water into polymer segments at elevated immersion temperatures. NaOH treatment of jute yarns was also investigated in terms of the water absorption behavior of the composites. It was shown that alkali treatment reduces water absorption of the composites remarkably, which was attributed to interface improvement. Flexural strength and modulus of the composites decreased up to 40% and 60%, respectively, whereas Charpy impact strength increased up to 30% after 168 h of water immersion.

Real-time measurement of oxygen transport across an oil–water emulsion interface

A method for real-time, in situ measurement of oxygen transport across oil-in-water emulsion interface was developed. This method is based on reversible fluorescence quenching of tris ruthenium (II) bis (hexafluorophosphate) complex dye encapsulated in the oil phase of an emulsion upon interaction with oxygen. Oxygen transport across the oil–water interface for four different emulsions (whey protein isolate (WPI), sodium-dodecyl sulphate (SDS), cross-linked WPI and SDS–chitosan emulsions) was measured and effective diffusion coefficients were calculated. Results show that cross-linking of WPI did not alter the oxygen transport rate ( p > 0.01), while addition of a chitosan layer to the SDS emulsion significantly reduced the oxygen transport rate ( p < 0.01). An increase in temperature from 25 to 40 °C reduced the oxygen transport rate in WPI and cross-linked WPI emulsions ( p < 0.01). Effective diffusion coefficient values for transport of oxygen based on fluorescence data were 0.14–1.15 × 10 −12 cm 2/s for the tested emulsions. Regardless of relatively low effective diffusion coefficients, the selected emulsions exhibited poor barrier properties in limiting oxygen transport across an emulsion interface. In summary, this rapid method is sensitive to detect changes in rate of oxygen transport due to changes in temperature and chemical composition of emulsion interface. This method can be used to screen and evaluate the barrier properties of encapsulation matrices leading to rational design of encapsulated structures.

Nanocrystallization of Al‐based glasses via nucleation and growth under “soft impingement” conditions

AbstractThe nanocrystallization behaviour of Al86Ni6Co2Gd3Y2Tb1 amorphous alloy has been studied by X‐ray diffraction methods involving small angle scattering, resistance measurements and differential scanning calorimetry. It has been established that the transformation in amorphous alloy investigated occurs mainly by the growth process at initial state of transformation while at final stage nucleation contributes into formation of nanocomposite structure. In order to describe the nanocrystallization kinetics of the Al‐based glasses the analytical kinetic equations in the frames of Kolmogorov‐Johnson‐Mehl‐Avrami model have been proposed and the effective volume diffusion coefficient values which govern the diffusion‐limited growth nanocrystals have been determined. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Determination of the diffusion coefficients of small solutes in cheese: A review

In cheese technology, the mass transfer of small solutes, such as salt, moisture and metabolites during brining and ripening, is very important for the final quality of the cheese. This paper has the following objectives: (i) to review the data concerning the diffusion coefficients of solutes in different cheese types; (ii) to review the experimental methods available to model the mass transfer properties of small solutes in complex matrices such as cheese; and (iii) to consider some potential alternative approaches. Numerous studies have reported the transfer of salt in cheese during brining and ripening. Regardless of the type of cheese and its composition, the effective diffusion coefficients of salt have been reported to be between 1 and 5.3 × 10−10 m2·s−1 at 10–15 °C. However, few papers have dealt with the mass transfer properties of other small solutes in cheese. Most of the reported effective diffusion coefficient values have been obtained by macroscopic and destructive concentration profile methods. More recently, some other promising techniques, such as nuclear magnetic resonance, magnetic resonance imaging or fluorescence recovery after photobleaching, are currently being developed to measure the mass transfer properties of solutes in heterogeneous media at microscopic scales. However, these methods are still difficult to apply to complex matrices such as cheese. Further research needs to focus on: (i) the development of nondestructive techniques to determine the mass transfer properties of small solutes at a microscopic level in complex matrices such as cheese; and (ii) the determination of the mass transfer properties of metabolites that are involved in enzymatic reactions during cheese ripening.

Mathematical modeling of thin-layer drying of fermented and non-fermented sugarcane bagasse

This work reports hot-air convective drying of thin-layer fermented and non-fermented sugarcane bagasse. For this purpose, experiments were carried out in a laboratory-scale dryer assessing the effects of solid-state fermentation (SSF) on the drying kinetics of the processing material. The fermented sugarcane bagasse in SSF was obtained with the use of Kluyveromyces marxianus NRRL Y-7571. Drying experiments were carried out at 30, 35, 40 and 45 °C, at volumetric air flow rates of 2 and 3 m3 h−1. The ability of ten different thin-layer mathematical models was evaluated towards representing the experimental drying profiles obtained. Results showed that the fermented sugarcane bagasse presents a distinct, faster drying, behavior from that verified for the non-fermented material at the same conditions of temperature and volumetric air flow rate. It is shown that the fermented sugarcane bagasse presented effective diffusion coefficient values of about 1.3 times higher than the non-fermented material. A satisfactory agreement between experimental data and model results of the thin-layer drying of fermented and non-fermented sugarcane bagasse was achieved at the evaluated experimental conditions.

Adsorptive removal of Cd(II) ions from aqueous solutions by rice husk ash

AbstractThis study deals with the adsorption characteristics of Cd(II) onto rice husk ash, low valued agricultural by‐product obtained during the rice processing from rice mill. The influences of pH, contact time, initial metal ion concentration, adsorbent concentration on the selectivity and sensitivity of the removal process were investigated. The optimum pH for adsorption was found to be 5 for Cd(II), and equilibrium was achieved within 2 h of contact time. Maximum adsorption of Cd(II) was obtained at an adsorbent dosage of 7.5 g/L, which may be considered as optimum adsorbent dosage level. Kinetics data were best described by pseudo‐second order model. The value of effective diffusion coefficient was of the order of 10−10 m2/s. The equilibrium adsorption data were better fitted to Freundlich isotherm models. The adsorption capacity (qmax) of rice husk ash for Cd(II) ions in terms of monolayer adsorption was 35.84 mg/g. The thermodynamic equilibrium constant and the Gibbs free energy were determined for and results indicated the spontaneous nature of the adsorption process. The adsorption energy calculated using Dubinin‐Radushkevich isotherm shows that adsorption of Cd(II) is chemical in nature. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Removal of Brill Red 5B from an aqueous solution using Cicca acida biomass

AbstractThe biosorption of Brill Red 5B from an aqueous solution, using Cicca acida plant's leaves was investigated in a batch system with the influence of pH (1–6), temperature (25–35°C) and initial dye concentration (10–100 mg/L). Maximum biosorption was observed at initial pH of 2.0, temperature of 30°C and at the initial dye concentration of 100 mg/L. Batch biosorption kinetic was studied using the pseudo first and pseudo‐second‐order rate equations. From the result, it was observed that pseudo‐second‐order rate expression fitted the experimental data well when compared to pseudo first order kinetic model. The intra‐particle diffusion coefficient (Ki) and effective diffusion coefficient (Di) values obtained for the sorption of Brill Red 5B using C. acida plant's leaves were found to be increased with increase in initial dye concentration.

Water Diffusivity and Drying Kinetics of Air Drying of Figs

The aim of this study is to evaluate experimentally the effective diffusion coefficient and the drying kinetics of whole unpeeled figs (Ficus carica L. var. tsapela) in terms of drying conditions. Estimation of the effective diffusion coefficient was carried out employing Fick's law for unsteady diffusion, which was solved analytically and numerically. In both methods, shrinkage effect was considered. The results from the two methods were compared and presented together with the limited results from the literature. The estimated effective diffusion coefficient values by both methods were fitted to a modified Arrhenius equation. Finally, a model predicting drying kinetics was developed. The model's coefficients were associated to the experimental conditions.

N2O catalytic decomposition — effect of pelleting pressure on activity of Co-Mn-Al mixed oxide catalysts

AbstractThe effect of pelleting pressure (0–10 MPa) during the preparation of Co-Mn-Al mixed oxide catalyst on its texture and activity for N2O catalytic decomposition was examined for small grain sizes used in laboratory experiments, and for model industry catalyst particles. Adsorption/desorption measurements of nitrogen, mercury porosimetry and helium pycnometry were used for detail characterization of porous structure. A volume of micropores of about 20 mm3 g−1 was evaluated using modified BET equation. This value did practically not change with the increasing pelletization pressure except that of the sample formed at the pressure of 10 MPa. Although an increase of pelleting pressure caused an increase in bulk density and a decrease in pore size and pore volume of the prepared catalyst (resulting in lower values of N2O effective diffusion coefficient), no direct correlation between pelleting pressure used and catalyst activity has been found. In contrary, estimation of the internal diffusion limitation according to the Weisz-Prater criterion indicated that even laboratory experimental data obtained for catalyst grains with particle size lower than 0.315 mm pelletized at higher pressures could be influenced by internal diffusion. Estimation of the internal mass transfer limitation in industrial catalyst particles described by the effectiveness factor showed that effectiveness factor of about 0.07 and 0.2 can be obtained for spheres with the radius of 1.5 mm and 0.5 mm, respectively, if pelleting pressure of about 6 MPa was used for the catalyst preparation.

Rotational Hydrodynamic Diffusion System To Study Mass Transport Across Boundaries

The design and operation of a new mass transport technique is presented. Rotational hydrodynamic diffusion system (RHDS) is a method that can be adapted for analytical laboratory analysis as well as industrial-scale separation and purification. Although RHDS is not an electrochemical technique, its concept is derived from hydrodynamic rotating disk electrode voltammetry. A diffusion advantage gained using the RHDS is higher flux of probe molecules across the boundary (e.g., membrane or porous media) with increased rotation rate compared to the static two-half-cell (THC) method. The separation concept of RHDS differs from pressurized, agitated, electrodialysis, and reversed osmosis systems in design and theory. The detection mechanism of the RHDS opens the possibility to study mass transport properties of a large variety of molecules using different types of ultrathin membranes. Therefore, the RHDS is a potential alternative to classical mass transport detection methods such as THC, impedance spectroscopy, and cyclic and rotating disk electrode voltammetry. Theoretical analysis on the rotational hydrodynamic flux is derived and compared to experimental flux measured using HCl, KCl, KNO 3, Ni(NO 3) 2, LiCl, camphor sulfonic acid, and K 3Fe(CN) 6 ionic solutions. Values of effective diffusion coefficients of salts across Nucleopore membranes of thickness 6.0 and 10 mum with pore size 0.1 and 0.2 mum, respectively, are presented and discussed.

Removal of Reactive Orange 4 from Aqueous Solution by Waste Eichhornia crassipes Biomass

Biosorption of Reactive Orange 4 dye, from an aqueous solution was evaluated by Eichhornia crassipes in a batch system. The influence of pH (1-6), temperature (20-30°C) and initial dye concentration (20 to 120 mg/L) on the biosorption process was studied. Maximum biosorption was observed at initial pH of 2.0, temperature of 30°C and at the initial dye concentration of 120 mg/L. Batch biosorption kinetics was studied with different initial dye concentrations and rate of biosorption was determined using the pseudo first and pseudo second order rate equations. From the result it was observed that pseudo second order rate expression fit the experimental data well for Reactive Orange 4 when compared to pseudo first order kinetic model. The intra particle diffusion coefficient (Ki) and effective diffusion coefficient (Di) values obtained for the sorption of Reactive Orange 4 using E. crassipes was found to be increased with increase in initial dye concentrations.