Page 221 - AJWEP-22-5

Rheological properties of coal gangue slurry

demonstrated significant effectiveness and economic mass ratios (e.g., 7:3 and 3:7) —were systematically
benefits in subsidence control across multiple mining examined to analyze their effects on slurry properties.
areas in China. 2 To improve viscosity, two types of superplasticizers –
The primary objectives of strata separation injection polycarboxylate and sulfamic acid – were analyzed for
are to mitigate ground subsidence, prevent water- their role in reducing viscosity. Finally, the influence of
related hazards in separated strata, and facilitate the injection pressure on the water bleeding rate of the slurry
disposal of mining solid waste. The ideal injection was analyzed to simulate practical injection conditions.
slurry should exhibit low viscosity and high fluidity This study provides valuable insights into the preparation
to ensure effective diffusion to distant areas from the and injection of fly ash–coal gangue mixed slurry.
injection station. Moreover, the slurries should have
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a low water bleeding rate to avoid pipeline clogging 2. Materials and methods
during prolonged grouting operations. The slurries
must be environmentally safe, ensuring non-toxicity 2.1. Raw materials
and minimal environmental impact to protect both The chemical compositions and component contents
geological formations and human health. of fly ash and coal gangue used in this study were
The key performance indicators for strata analyzed using an X-ray fluorescence spectrometer
separation injection slurries include density, water (S8 Tiger, Bruker, Germany) and an X-ray diffraction
bleeding characteristics, and viscosity. In addition, system (D8, Bruker, Germany). The results revealed
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the cost-effectiveness of materials must be taken into that coal gangue was predominantly composed of
consideration during the raw material selection process. silicon dioxide, aluminum oxide, titanium dioxide, and

Fly ash has been proven to be the dominant material in ferric oxide, while fly ash primarily consists of silicon
mining areas for strata separation injection due to its dioxide and ferric oxide (Table 1 and Figure 2). Fly ash
low cost and accessibility, while its increasing demand is typically obtained by collecting fine residues from
– driven by the expanding application of diverse ground coal combustion and has a similar geological
technologies – has led to shortages in some regions. origin to coal gangue. Apart from differences in
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Consequently, coal gangue – a prevalent solid waste component proportions, the two raw materials share
in coal mining areas – is being explored as a potential similar major crystalline phases, including quartz,
alternative raw material for injection slurries. hematite, and anhydrite. Elemental analysis did not
Critical challenges include determining the detect high concentrations of heavy metals in fly ash or
optimal grinding particle size for coal gangue to coal gangue, indicating their environmental safety for
balance economic feasibility and slurry performance. injection into the separated strata space.
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Although extensive research and engineering practices Figure 3 illustrates the results of thermogravimetric-
have focused on preparing slurries with fly ash, the differential scanning calorimetry analysis of coal
development of injection slurries using coal gangue gangue and fly ash. The mass of coal gangue and fly
without cementitious materials remains limited, and ash declined by 6 wt% and 4 wt%, respectively, after
diffusion modeling for such suspensions in fractured heating to 400℃. This mass loss is typically attributed
strata lacks experimental validation. Specifically, to the evaporation of water and the decomposition of
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studies on the fluid properties of slurries prepared organic matter. As the temperature further increased
from fly ash and coal gangue under injection pressure to 900℃, the mass continued to decrease due to the
are relatively scarce. This gap underscores the need decomposition of carbonates and sulfates.
for systematic research to evaluate the compatibility,
rheology, and long-term stability of such complex 2.2. Orthogonal experimental design
systems in practical injection applications. A mixed-level L18 (3 × 5 ) orthogonal array was
2
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This study investigates the rheological performance adopted to systematically evaluate the main effects
of coal gangue and fly ash mixed slurry as a filling of the selected factors (factor A: solid volume
material through orthogonal experiments. The concentration, factor B: coal gangue particle size, and
evaluated performance parameters include water factor C: fly ash-to-coal gangue mass ratio) on slurry
bleeding characteristics, density, and viscosity. Three properties. While orthogonal designs inherently assume
independent factors – solid volume concentrations minimal interaction effects to efficiently screen main
(e.g., 50%, 60%, and 70%), coal gangue particle sizes factors, potential interactions were statistically assessed
(e.g., 50, 100, and 150 mesh), and fly ash-to-coal gangue post-experiment using one-way analysis of variance

Volume 22 Issue 5 (2025) 215 doi: 10.36922/AJWEP025210162