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Permanent link (DOI): https://doi.org/10.7939/R35C87

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Alternating current electrocoagulation (AC/EC) of fine particulate suspensions Open Access

Descriptions

Other title
Subject/Keyword
Floc growth
Fine tailings
Bentonite
Coagulation
Silica
Suspension
Hydroxoaluminum
Adsorption
Colloid
Alternating current electrocoagulation
Settling behaviour
Electrical double layer
MFT
Aqueous aluminum chemistry
Floc fragmentation
Electrocoagulation
AC/EC
Aluminum speciation
Coal
Zeta potential
Indirect
Direct
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Ifill, Roy O.
Supervisor and department
Etsell, Thomas H. (Chemical and Materials Engineering)
Examining committee member and department
Liu, Qi (Chemical and Materials Engineering)
Kessick, Michael A. (RJ Oil Sands Inc.)
El-Din, Mohamed Gamal (Civil and Environmental Engineering)
Etsell, Thomas H. (Chemical and Materials Engineering)
Plitt, L.R. (Civil and Environmental Engineering)
Department
Department of Chemical and Materials Engineering
Specialization

Date accepted
2010-01-29T21:29:36Z
Graduation date
2010-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 µm), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 µm) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23° to 85°C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the company’s own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT.
Language
English
DOI
doi:10.7939/R35C87
Rights
License granted by Roy Ifill (ifill@ualberta.ca) on 2010-01-29T19:40:44Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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