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.
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