Browsing by Subject "desorption"
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Item Adsorption and desorption of atrazine on a melamine-based soil amendment(Texas A&M University, 2004-09-30) Neitsch, Susan LynnAdsorption kinetics and adsorption-desorption of atrazine on organoclay composites prepared with the surfactant 6-piperazin-1-yl-N,N'-bis-(1,1,3,3-tetramethyl-butyl)-(1,3,5)triazine-2,4-diamine and Houston Black clay were studied using the indirect batch equilibration procedure. The organoclay composites sorbed significantly more atrazine than the Houston Black clay. Adsorption equilibrium was reached after 72 h for the organoclay composites. Atrazine adsorption isotherms were described by linear partitioning. The Koc values ranged from 605 to 5271 L kg-1 for the organoclay composites compared to a value of 41 L kg-1 for the Houston Black clay. The organoclay composite containing 20% surfactant on a total weight basis provided the most efficient adsorption of atrazine, although organoclay composites containing much lower amounts of surfactant also adsorbed significant amounts of atrazine. An average of 11% of sorbed atrazine was released during desorption. Characterization of desorption products showed only atrazine molecules being released from the organoclay composites.Item Methyl arsenic adsorption and desorption behavior on iron oxides(Texas A&M University, 2005-08-29) Lafferty, Brandon JamesArsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.Item Regeneration of Carbon Aerogel Exhausted in Water Purification(2012-02-14) Tewari, SanjayCarbon has been used electrochemically in various forms for water treatment and the carbon aerogel is one of them. Carbon Aerogels (CA) are used as electrodes due to their high surface capacity and high electrical conductivity. They are also known as Carbon Nanofoams (CNF). CA electrodes attract oppositely charged ions that are nearby. This concept is known as Capacitive De-Ionization (CDI). The use of CA in CDI for water purification is well documented, but not much work has been done on regeneration of CA electrodes. Once saturated, these electrodes lose their ability to adsorb additional ions and it must be restored by regeneration. If they cannot be regenerated, they would need to be replaced, which would greatly increase the cost of the treatment they are expensive. The goal of this study is to obtain data to define optimal regeneration conditions and to develop predictive capability by examining desorption behavior of adsorbed ions on CA electrodes. This study focuses on desorption of adsorbed ions and regeneration of CA. Various experiments were conducted to explore the effects on regeneration of CA of shorting of electrodes, change of polarity of electrodes, flow speed of water over CA electrodes, and temperature of regeneration water. The optimal combination of experimental variables was identified and was used for remaining experiments that tested the effect of size, charge and mass of adsorbed ions on regeneration of CA. Also, the effect of thickness of CA and its pore size on regeneration of CA was studied. Results indicated that application of reverse potential for the first few minutes of the total regeneration time provided the greatest regeneration. Longer application of reverse potential did not result in higher regeneration. The regeneration behavior when no potential applied with and without shorting was as expected. Application of reverse potential with variable temperature or variable flow speed of water over CA surfaces provided results that were different from the ones that were obtained with no potential being applied with or without shorting of electrodes.