Combining Transport of Pendular Water with Wind-Assisted Interfacial Evaporation for Dewatering of Concentrated Slurry Waste

TL;DR

The paper tackles the challenge of dewatering highly concentrated slurry wastes, such as tailings, by employing wind-driven interfacial evaporation with a sailboat evaporator that uses root-like dendritic structures to access pendular water pockets. It demonstrates that dendritic roots, spatial replantation, and hydrodynamic flushing synergistically enhance water conduction and evaporation in high-solid regimes, achieving up to $4 kg/(m^2 h)$ at around $80 wt\%$ solids and substantially improving performance over non-replanted or non-flushed setups. Outdoor and large-scale tests validate scalability and robustness under real wind conditions, including tailings ponds, while vibrations tend to neither improve nor significantly hinder performance. Overall, the approach offers a renewable-energy-based, scalable pathway for industrial wastewater dewatering, particularly for challenging sludge-like slurries in tailings ponds.

Abstract

Drying concentrated slurry waste is slow, particularly due to the entrapment and limited accessibility of water entrained between the particles in the slurry. A sailboat evaporator with a root-like structure is a new system that enables wind-assisted interfacial evaporation of concentrated particle slurries. In this work, we create access to the disconnected water pockets in concentrated slurry waste, facilitating faster water conduction and efficient evaporation at extremely high solid concentration. The evaporator's long roots effectively extracted water beneath 150 cm deep supernatant water layer. Through replantation of the evaporator to a separate location, an impressive evaporation rate (ER) of 4 kg/(m^2*h) close to 80 wt% solid concentration, a 25% increase to a non-replanted sample. Furthermore, long periods of efficient of evaporation was achieved even at high solid concentration through hydrodynamic flushing of roots. Outdoor experiments achieved substantial volumetric reduction, yielding dried residues with over 75 wt% solid concentration. These results underscore the system's reliable performance against highly concentrated slurries, yet to be by conventional industrial methods, including flocculation and tail-lift drying. The integration of renewable energy coupled with efficient enhancement techniques makes the sailboat evaporator a scalable and sustainable pathway for industrial wastewater dewatering.

Figures (8)

• Figure 1: A) Sketch of the wind tunnel for the wind evaporation experiments; B) Schematic of the sailboat evaporator (SE) setup, with illustration of the various physical processes; C) Image of the SE setup; Schematic diagram of evaporation enhancement through D) sailboat replantation to a new location and E) hydrodynamic flushing.
• Figure 2: A) Viscosity vs shear rate of different particle-laden suspensions; B) ER comparison between water, silica and tailing suspensions; C) Image of the dendritic root structure; D) ER vs the root structure beyond 65 wt% and 75 wt% solid concentration; E) ER vs solid concentration of tap and dendritic roots setup beyond 77 wt%.
• Figure 3: a) ER vs A) time and B) solid concentration exhibiting the effect of replanting the SE setup into a new location against 60 wt% silica slurry (blue zone: replantation induced); C) ER vs solid concentration of tailing suspension exhibiting the effect of replanting the SE setup; D) ER vs time displaying the effect of replanting for a stratified 60 wt% tailing setup; E) Shear stress vs shear rate for a 50 wt% silica slurry; F) ER vs time exhibiting the influence of stirring on the replantation process (blue zone: stirring induced).
• Figure 4: Spatial moisture distribution within the silica slurry after 45 hours A) without and B) with replanting the SE setup.
• Figure 5: FTIR spectrum of water on the cotton sail surface with and without replanting for evaporating a A) silica and a B) tailing suspension; C) Image of the Hele-Shaw apparatus; D) X-Ray imaging of moisture distribution within the silica slurry though a Hele-Shaw setup; E) Moisture content % as a function of horizontal distance away from the root in the Hele-Shaw setup.