Dewatering of coal plant tailings: Flocculation followed by filtration

Alam, Naureen, Ozdemir, Orhan, Hampton, Marc A. and Nguyen, Anh V. (2011) Dewatering of coal plant tailings: Flocculation followed by filtration. Fuel, 90 1: 26-35. doi:10.1016/j.fuel.2010.08.006


Author Alam, Naureen
Ozdemir, Orhan
Hampton, Marc A.
Nguyen, Anh V.
Title Dewatering of coal plant tailings: Flocculation followed by filtration
Journal name Fuel   Check publisher's open access policy
ISSN 0016-2361
1873-7153
Publication date 2011-01-01
Year available 2010
Sub-type Article (original research)
DOI 10.1016/j.fuel.2010.08.006
Open Access Status Not yet assessed
Volume 90
Issue 1
Start page 26
End page 35
Total pages 10
Place of publication Kidlington, Oxford, United Kingdom
Publisher Elsevier
Language eng
Subject 2103 Fuel Technology
2102 Energy Engineering and Power Technology
1500 Chemical Engineering
1605 Organic Chemistry
Abstract A sustainable alternative to tailings dam disposal of coal refuse is mechanical dewatering of tailings, which provides fast production of dry solids and water reuse. In this study, flocculation followed by filtration of coal plant tailings, a new concept in tailings dewatering is investigated in detail. This paper focuses on the effect of preconditioning tailings with varying flocculants and dosages on filtration kinetics and the resultant moisture content of the filter cake. The results show that the cationic flocculant, MAGNAFLOC LT 425, requires a high dosage to produce a low moisture content filter cake and clear filtrate. Optimal sized flocs were produced with the anionic flocculant, MAGNAFLOC 5250, even though the particles are negatively charged. The kinetics of the filtration was dependent on the composition of process water as indicated by supporting sedimentation tests. The concentration of divalent alkali earth metals such as Ca(2+) and Mg(2+) allow for large floc growth by a bridging mechanism, which involves binding of the polymer and the negativity charged particle. Filtration and settling curves at this dosage were also supported by filter cake analysis using Darcy plots. It was found that the large floc size significantly increases the permeability of the filter cake. Floc size measurements and fractal dimension showed that while the large flocs were produced with anionic flocculant, the flocs produced with the cationic flocculant were small and weak. The results indicate that the optimum dosage and flocculant type for effective and efficient filtration of coal plant tailings is approximately 350 g/t of anionic flocculant at a 35% solids content and 40 kPa filtration pressure. (C) 2010 Elsevier Ltd. All rights reserved.
Formatted abstract
A sustainable alternative to tailings dam disposal of coal refuse is mechanical dewatering of tailings,
which provides fast production of dry solids and water reuse. In this study, flocculation followed by filtration
of coal plant tailings, a new concept in tailings dewatering is investigated in detail. This paper
focuses on the effect of preconditioning tailings with varying flocculants and dosages on filtration kinetics
and the resultant moisture content of the filter cake. The results show that the cationic flocculant, MAGNAFLOC
LT 425, requires a high dosage to produce a low moisture content filter cake and clear filtrate.
Optimal sized flocs were produced with the anionic flocculant, MAGNAFLOC 5250, even though the particles
are negatively charged. The kinetics of the filtration was dependent on the composition of process
water as indicated by supporting sedimentation tests. The concentration of divalent alkali earth metals
such as Ca2+ and Mg2+ allow for large floc growth by a bridging mechanism, which involves binding of
the polymer and the negativity charged particle. Filtration and settling curves at this dosage were also
supported by filter cake analysis using Darcy plots. It was found that the large floc size significantly
increases the permeability of the filter cake. Floc size measurements and fractal dimension showed that
while the large flocs were produced with anionic flocculant, the flocs produced with the cationic flocculant
were small and weak. The results indicate that the optimum dosage and flocculant type for effective
and efficient filtration of coal plant tailings is approximately 350 g/t of anionic flocculant at a 35% solids
content and 40 kPa filtration pressure.
2010 Elsevier Ltd. All rights reserved.
Keyword Coal tailings
Dewatering
Flocculation
Fractal dimension
Filtration analysis
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online 24 August 2010

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2011 Collection
 
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Created: Sun, 12 Dec 2010, 10:07:47 EST