Dewatering of coal plant tailings: Flocculation followed by filtration

Naureen Alam, Orhan Ozdemir, Marc A. Hampton, Anh V. Nguyen

Research output: Contribution to journalArticlepeer-review

107 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)26-35
Number of pages10
JournalFuel
Volume90
Issue number1
DOIs
Publication statusPublished - Jan 2011
Externally publishedYes

Funding

The authors gratefully acknowledge the Australian Research Council for financial support through a Discovery grant, BMA for the support of the BMA Chair of Minerals Processing at the University of Queensland and the coal samples, and Ciba Specialty Chemicals Pty Ltd. (USA) for the flocculant samples.

FundersFunder number
Ciba Specialty Chemicals Pty Ltd.
British Medical Association
Australian Research Council
University of Queensland

    Keywords

    • Coal tailings
    • Dewatering
    • Filtration analysis
    • Flocculation
    • Fractal dimension

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