Persistent Link:
http://hdl.handle.net/10150/289088
Title:
Electrokinetic and bouyancy effects in colloidal suspensions
Author:
Belongia, Brett Matthew
Issue Date:
1999
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Dewatering of silica and alumina suspensions was accomplished using electrodecantation and electrocoagulation. Electrocoagulation was found to occur in high-conductivity alumina suspensions (250-1300 μS/cm), while electrodecantation was found to be the separation mechanism in low-conductivity suspensions of alumina and silica ( < 20 μS/cm). With these low-conductivity suspensions, a clear fluid layer developed on the surface of the suspension. A clear fluid layer did not develop in high conductivity silica suspensions, 250 μS/cm, even though electrodecantation was found to dominate the separation. Spatial variations in the pH and conductivity were measured at the completion of electrodecantation experiments. A boundary-layer model was developed to quantitatively establish the principles of electrodecantation. This model provides an explanation for the formation of the clear fluid layer on the surface of colloidally stable suspensions and provides an understanding of how buoyancy driven motion redistributes ions produced/consumed at the electrodes, which results in the formation of pH and conductivity gradients. The growth rate of the clear layer at the top of the chamber is initially slower than that predicted by the model; at later stages the theory and experiments are in agreement. Numerical simulations were performed to support the boundary-layer model and were used to incorporate important features such as electrode reactions, ion gradients, and cell geometry omitted from the model. Two-dimensional simulations were performed to study the effects of buoyancy driven motion in the absence of any ion gradients. Due to limited computer resources, one-dimensional simulations were used to show that a clear fluid layer would not necessarily be expected in high-conductivity suspensions and to study the effects of electrode reactions in the absence of any fluid motion. To characterize properties important to electrodecantation, two techniques were developed to measure particle diffusion coefficients, size, and electrophoretic mobility. Taylor-Aris dispersion measurements are shown to provide accurate diffusion coefficient measurements for colloidal particles up to about 0.3 μm in diameter and capillary electrophoresis is used to establish a novel method for measuring electrophoretic mobilities of colloids that compares favorably with existing methods.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Engineering, Chemical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemical and Environmental Engineering
Degree Grantor:
University of Arizona
Advisor:
Baygents, James C.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleElectrokinetic and bouyancy effects in colloidal suspensionsen_US
dc.creatorBelongia, Brett Matthewen_US
dc.contributor.authorBelongia, Brett Matthewen_US
dc.date.issued1999en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractDewatering of silica and alumina suspensions was accomplished using electrodecantation and electrocoagulation. Electrocoagulation was found to occur in high-conductivity alumina suspensions (250-1300 μS/cm), while electrodecantation was found to be the separation mechanism in low-conductivity suspensions of alumina and silica ( < 20 μS/cm). With these low-conductivity suspensions, a clear fluid layer developed on the surface of the suspension. A clear fluid layer did not develop in high conductivity silica suspensions, 250 μS/cm, even though electrodecantation was found to dominate the separation. Spatial variations in the pH and conductivity were measured at the completion of electrodecantation experiments. A boundary-layer model was developed to quantitatively establish the principles of electrodecantation. This model provides an explanation for the formation of the clear fluid layer on the surface of colloidally stable suspensions and provides an understanding of how buoyancy driven motion redistributes ions produced/consumed at the electrodes, which results in the formation of pH and conductivity gradients. The growth rate of the clear layer at the top of the chamber is initially slower than that predicted by the model; at later stages the theory and experiments are in agreement. Numerical simulations were performed to support the boundary-layer model and were used to incorporate important features such as electrode reactions, ion gradients, and cell geometry omitted from the model. Two-dimensional simulations were performed to study the effects of buoyancy driven motion in the absence of any ion gradients. Due to limited computer resources, one-dimensional simulations were used to show that a clear fluid layer would not necessarily be expected in high-conductivity suspensions and to study the effects of electrode reactions in the absence of any fluid motion. To characterize properties important to electrodecantation, two techniques were developed to measure particle diffusion coefficients, size, and electrophoretic mobility. Taylor-Aris dispersion measurements are shown to provide accurate diffusion coefficient measurements for colloidal particles up to about 0.3 μm in diameter and capillary electrophoresis is used to establish a novel method for measuring electrophoretic mobilities of colloids that compares favorably with existing methods.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectEngineering, Chemical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemical and Environmental Engineeringen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBaygents, James C.en_US
dc.identifier.proquest9960292en_US
dc.identifier.bibrecord.b40273891en_US
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