Rate-limited cation exchange in thin bentonitic barrier layers

2006 ◽  
Vol 43 (4) ◽  
pp. 370-391 ◽  
Author(s):  
Ho Young Jo ◽  
Craig H Benson ◽  
Tuncer B Edil
Keyword(s):  
Cation Exchange ◽  
Chemical Equilibrium ◽  
Pore Space ◽  
Compartment Model ◽  
Monovalent Cation ◽  
Thin Layers ◽  
Dry Density ◽  
Factors Affecting ◽  
Barrier Layers ◽  
Time Required

A three-compartment model was developed for simulating cation transport in bentonitic barrier layers that incorporates diffusion-controlled cation exchange among the mobile intergranular water (bulk pore water), immobile interparticle and interlayer water, and the montmorillonite mineral solid. Exchange on the external surfaces and interlayer region of montmorillonite is included. The model was evaluated for divalent-for-monovalent cation exchange in bentonite with experiments. A parametric study was conducted using the model to investigate factors affecting the time required to establish chemical equilibrium (i.e., completion of cation exchange) between the permeant liquid and thin layers of bentonite simulating geosynthetic clay liners (GCLs). Predictions obtained with the model were in general agreement with the data without calibration, except for Na concentrations in the effluent at very long times. Parametric simulations conducted with the model show that the time required to establish chemical equilibrium in GCLs is affected by the rate at which adsorbing cations are delivered to the pore space (affected by seepage velocity or influent concentration), the rate of mass transfer between the mobile and immobile liquid phases (controlled primarily by granule size of the bentonite), and the number of sites available for sorption (controlled by CEC and the dry density of the bentonite).Key words: bentonite, montmorillonite, exchange complex, diffusion, immobile liquid, interlayer.

scholarly journals Adsorption and Separation of Crystal Violet, Cerium(III) and Lead(II) by Means of a Multi-Step Strategy Based on K10-Montmorillonite

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 466 ◽  
Author(s):  
Filippo Parisi
Keyword(s):  
Metal Ions ◽  
Cation Exchange ◽  
Crystal Violet ◽  
Metal Ion ◽  
Complete Removal ◽  
Experimental Conditions ◽  
Factors Affecting ◽  
Adsorption Processes ◽  
Removal Of Metal Ions ◽  
Time Required

A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common contaminants, i.e., crystal violet dye (CV), Ce(III) and Pb(II) were chosen as “model” pollutants. The main factors affecting the pollutants’ sorption were investigated. The experimental data were correlated with adsorption isotherms and kinetic models to obtain a deeper insight into the adsorption processes. The affinity of the clay toward the pollutants is favored by an increasing pH and follows the order CV > Pb(II) > Ce(III). Whereas Ce(III) metal ions do not adsorb onto clay under strongly acidic conditions, both Pb(II) and CV can adsorb under all the investigated pH conditions. The analysis of isotherms and kinetic profiles revealed that CV adsorbs onto clay through a mechanism consisting of two parallel processes, namely cation exchange on the external mineral surface and in the interlayer and surface complexation at the edge sites, while metal ion uptake is due solely to cation exchange processes involving mineral surfaces. The time required for the complete removal of pollutants follows the order CV > Ce(III) >> Pb(II). The possibility to modulate the adsorption features by changing experimental conditions was successfully employed to propose the best strategy for the progressive removal of different components from aqueous solutions.

scholarly journals Various factors affecting the bacterial corneal ulcer healing: a 4-years study in referral tertiary eye hospital in Indonesia

2015 ◽  
Vol 24 (3) ◽  
pp. 150-5 ◽  
Author(s):  
Muhammad Asroruddin ◽  
Rina L.D. Nora ◽  
Lukman Edwar ◽  
Soedarman Sjamsoe ◽  
Made Susiyanti
Keyword(s):  
Corneal Ulcer ◽  
Ocular Trauma ◽  
Antibiotic Sensitivity ◽  
Pseudomonas Sp ◽  
Chi Square ◽  
Factors Affecting ◽  
Corneal Ulcers ◽  
Time Required ◽  
Mean Time ◽  
Epithelial Healing

Background: Corneal ulcer is one of the most common causes of visual acuity impairment and blindness all over the world. The aim of the study was to evaluate various factors affecting the bacterial corneal ulcers healing, including the predisposing factors, causative organisms, antibiotic sensitivity, as well as the treatment outcomes.Methods: All data were taken retrospectively from medical records of patients who underwent corneal scraping for Gram examination and/or culture over a-4-year period (2008-2011) at the Cipto Mangunkusumo Hospital Jakarta. Treatment outcome were analyzed using Chi-square test, one-way ANOVA, and post-hoc analysis. Mean time required for complete epithelial healing was also investigated.Results: 220 cases of bacterial corneal ulcers in 216 patients were included. The most common risk factors were ocular trauma (45.8%). Gram-positive coccus were found in 65.7% cases other than other microbes. Pseudomonas sp. (25,0%) and Staphylococcus epidermidis (18.4%) were the most common isolates, sensitive to almost all kinds of antibiotics. About 83.0% (106 cases) were improved with antibiotics only, the rest were not improved and worsened. Mean time for complete epithelial healing was 17.5 ± 8.9 days with mild ulcer had the most rapid recovery. Eyes treated with fluoroquinolone eyedrops were healed in 14 days, faster than other regiments.Conclusion: Ocular trauma was the most common risk factor for corneal ulcer, and the most commonly isolated organism was Pseudomonas sp. Most cases were improved with antibiotics, and fluoroquinolone showed faster healing. Complete epithelial healing occurred in about 17.5 days.

A modified fractionation procedure for avian erythrocyte histones

1969 ◽  
Vol 47 (12) ◽  
pp. 1121-1123 ◽  
Author(s):  
G. H. M. Adams ◽  
J. M. Neelin
Keyword(s):  
Cation Exchange ◽  
Exchange Chromatography ◽  
Cation Exchange Chromatography ◽  
Fractionation Procedure ◽  
Exclusion Chromatography ◽  
One Step ◽  
Avian Erythrocyte ◽  
Fractionation Method ◽  
Time Required

The fractionation method of Vidali and Neelin for avian erythrocyte histones was modified to reduce the time required to obtain clean fractions of serine-rich and arginine-rich histones. Histones were extracted from washed nuclei in one step with 0.20 M HCl. The lysine-rich and the moderately lysine-rich histones were fractionated by cation-exchange chromatography but the serine-rich and arginine-rich histones were eluted together. These histones were separated by subsequent exclusion chromatography.

Temporal Estimation in the Perception of Occluded Motion

1968 ◽  
Vol 26 (2) ◽  
pp. 407-416 ◽  
Author(s):  
Horace N. Reynolds
Keyword(s):  
Moving Object ◽  
Field Of View ◽  
Stimulus Information ◽  
Opaque Screen ◽  
Factors Affecting ◽  
Background Structure ◽  
Temporal Estimation ◽  
Time Required ◽  
Perceived Speed ◽  
Occluded Motion

Ss were shown a rectangular object which moved transversely across their field of view and passed behind an opaque screen. The purpose was to investigate some of the factors affecting estimates of the time required for the occluded moving object to travel a given distance behind the screen. The factors selected for study were (1) method of viewing the moving object (pursuit, static fixation), (2) background structure (homogeneous, textured), and (3) object size. According to previous studies, these variables affect the perceived speed of a moving object and might therefore be expected to affect estimates of the duration of occluded traversal. The results did not show statistically significant differences among experimental groups, although data trends are discussed. An additional finding was that Ss significantly overestimated the duration of occluded traversal, consistent with a tendency to overestimate traversal distance. The experiment is related to Michotte's studies of “amodal perception” and discussed in terms of Gibson's stimulus information approach to perception.

Factors affecting the detection of possums by spotlighting in Western Australia

2005 ◽  
Vol 32 (8) ◽  
pp. 689 ◽  
Author(s):  
A. F. Wayne ◽  
A. Cowling ◽  
J. F. Rooney ◽  
C. G. Ward ◽  
I. B. Wheeler ◽  
...  
Keyword(s):  
Detection Efficiency ◽  
Lunar Cycle ◽  
Survey Method ◽  
Brushtail Possum ◽  
Start Time ◽  
Detection Rates ◽  
Eucalyptus Marginata ◽  
Factors Affecting ◽  
Abundance Estimates ◽  
Time Required

This paper describes how environmental factors, survey method procedures and differences in forest structure resulting from logging relate to the detection of koomal (common brushtail possum, Trichosurus vulpecula hypoleucus) and ngwayir (western ringtail possum, Pseudocheirus occidentalis). A total of 169 vehicle-based spotlight surveys of possums within native jarrah (Eucalyptus marginata) forest was conducted on three transects over eight years (1996–2003). Up to 5.7 koomal and up to 3.3 ngwayir were detected per kilometre per transect side. Only one ngwayir was detected during the eight surveys conducted between 2001 and 2003. More koomal were seen in spring and autumn (i.e. September–November and March–May respectively) and more ngwayir were seen between October and April. Although surveys were not conducted on very rainy or excessively windy nights, fewer possums were nonetheless seen on nights following rainy days and on cold nights. Cloud cover also affected sightings of koomal. The time taken to complete the surveys increased in conjunction with the number of possums detected, on account of the time required to record data. The importance of standardising travelling speed also is emphasised. Possum spotlight counts differed between recently logged and unlogged areas. However, these findings were not supported by complementary koomal abundance estimates derived from trapping, suggesting that vegetation structure may affect detectability. Factors such as the lunar cycle, wind speed and survey start time after sunset did not significantly affect detection rates of either species. On the basis of these findings, specific survey conditions can be selected to improve spotlight detection efficiency.

Effects of high pH solutions with large monovalent cation concentrations on cation exchange properties

Soil Research ◽  
1996 ◽  
Vol 34 (2) ◽  
pp. 229 ◽  
Author(s):  
RE Liefering ◽  
CDA Mclay
Keyword(s):  
Organic Matter ◽  
Cation Exchange ◽  
Negative Charge ◽  
Monovalent Cation ◽  
Exchange Capacity ◽  
Exchangeable Cations ◽  
Ion Concentration ◽  
Exchangeable Sodium ◽  
High Ph ◽  
Exchange Properties

Disposal of strongly alkaline industrial liquid wastes, which contain large monovalent cation concentrations, by means of land treatment systems is becoming increasingly common. This study investigated the effects of solutions with large monovalent cation concentrations and high pH on cation exchange properties in four New Zealand soils with different clay mineralogies. The soils were shaken with a range of concentrations (0–0.3 M) of NaOH, KOH, NaCl, and KCl. Cation exchange capacity (CEC) and exchangeable cations (Ca2+, Mg2+, K+, and Na+) were measured following shaking and washing procedures. Although the hydroxide solutions dissolved significant amounts of organic matter from all soils, there was still a net increase in CEC measured at all hydroxide concentrations. The magnitude of the CEC increase was dependent on hydroxide concentration. The increase in CEC is attributed to newly generated negative charge on surfaces which possess variable charge (i.e. pH dependent) characteristics such as edge sites of clay minerals, sesquioxides, and the undissolved organic matter remaining in the soil. In contrast to hydroxide solutions, no increase in CEC was measured in chloride-treated samples. Increases in the concentration of all treatment solutions resulted in increases in the exchangeable ion concentration of the index cation used in the treatment solution (either Na+ or K+) and decreases in concentration of the other three exchangeable cations. In general, higher exchangeable sodium percentage (ESP) values were measured in samples treated with NaOH than samples treated with NaCl at all concentrations. Similarly, higher exchangeable potassium percentage (EPP) was measured in samples treated with KOH than samples treated with KCl at all concentrations. The higher ESP and EPP values recorded when hydroxide solutions were used as treatments are attributed to the newly generated negative charges being counter-balanced by the monovalent index cation present in the treatment solution. It is suggested that existing equations commonly used to predict ESP and EPP values are unsuccessful for accurately predicting changes when soils are treated with hydroxide solutions, due to their inability to account for the newly generated exchange sites. The equations did, however, adequately predict the effects of both chloride solutions on ESP and EPP.

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