Coal Preparation » Dewatering
Dewatering of fine coal tailings remains a major operational challenge in the coal industry, limiting effective tailings disposal and water reuse. The presence of ultrafine particles reduces the efficiency of thickeners, centrifuges and filters, resulting in high cake moisture and poor water recovery. While flocculants are traditionally used to enhance particle aggregation, their role in stabilizing micro-nano bubbles (MNBs)-which further entrap water-has been largely overlooked.
Building on outcomes from project C24040, which developed physical deaeration technologies (spinning basket and vacuum deaerator) to break stable froths in flotation concentrates, this project further investigated the formation and stabilization of MNBs in flocculated tailings. It was found that flocculants not only influence solid-liquid separation but also contribute to MNB generation and stabilisation. Low-molecular-weight flocculants facilitate microbubble formation by reducing surface tension, while high-molecular-weight variants stabilize nanobubbles through electrostatic and steric repulsion. This dual behaviour leads to the formation of water-retaining MNB-particle aggregates that resist dewatering.
Excessive flocculant dosages were shown to increase slurry viscosity and promote over-aggregation, reducing centrifuge and filter performance and increasing residual moisture. These MNB-floc aggregates form capillary bridges and trap interstitial water, ultimately diminishing dewatering efficiency.
To address this, a range of physical methods was evaluated to disrupt these stable aggregates.
The project also examined the use of chemical surfactants.
Based on the findings, the integration of a baffle-type static mixer into the tailings circuit is recommended as a practical, low-maintenance solution for improving dewatering performance in coal preparation plants. This technology presents a viable solution to enhance water recovery, thereby reducing pumping energy consumption, mitigating pipeline blockage risks, and optimising the efficiency of downstream processing units. Its passive, in-line design facilitates seamless implementation with a significantly reduced capital expenditure.