Page 190 - AJWEP-22-5

Hou, et al.

A B

Figure 2. The X‑ray diffraction profiles of (A) coal gangue and (B) fly ash

exist predominantly in crystalline silicates that require
mechanochemical activation. In contrast, about 30% of
the Si/Al in fly ash exists as amorphous glass, readily
available for hydration reactions. After ball-milling,
fresh coal-gangue surfaces dissolve in an alkaline
medium to release [SiO ]⁻ and [AlO ]⁻ units, which
44
45
react with the active silica–alumina in fly-ash glass to
form a three-dimensional C(A)SH gel network. Gypsum
in fly ash can also react with Ca ⁺ and Al ⁺ released from
2
3
gangue to form ettringite (AFt), further densifying
26
the matrix. Moreover, Fe O ’s oxidative inertness and
2
3
the electrostatic adsorption of surface hydroxyl groups
(–OH) help immobilize heavy-metal ions (e.g., As ⁺,
3
Pb ⁺). This mineral-chemical synergy not only enhances
2
the rheological stability and environmental safety but
also demonstrates the engineering feasibility of using Figure 3. Bingham model fitting curves of coal
coal gangue-fly ash slurry for mine backfilling. gangue‑fly ash slurry at different solid mass
concentrations. All lines indicate linear relationship
2
3.2. Bingham rheological properties and (R > 0.99)
concentration effects
The Bingham model fits for slurries with solid mass in stronger interparticle friction and a denser particle
concentrations of 68%, 70%, 72%, 74%, and 76% are network. Consequently, the internal resistance to shear
shown in Figure 3. In each case, the shear stress exhibits deformation increases, making the slurry more resistant
a strong linear relationship with the shear rate (R >0.99), to flow. Moreover, the intercept (yield stress) increases
2
confirming well with the Bingham fluid behavior. This as well, suggesting that slurries with higher solid
concentration range was selected because earlier studies content require greater initial shear stress to initiate
reported poor flowability above 76wt% and inadequate movement. 29,30 This phenomenon reflects structural
stability below 68 wt%. 23,24 In this model, the slope of densification and stronger interparticle bonds, which
the fitted line represents plastic viscosity – the internal produce a more rigid and cohesive slurry matrix.
resistance to flow – while the intercept represents yield At lower concentrations (68 – 70%), the slurry
stress, which is the minimum shear stress required to exhibits relatively low plastic viscosity and yield stress,
initiate flow. 27,28 A concentration increase from 68% to indicating higher flowability and lower resistance
76%, the slope progressively rises, signifying an increase to shear. This makes the slurry more suitable for
in plastic viscosity. This behavior is primarily attributed applications requiring easy pumpability and smooth
to the higher solid content at elevated concentrations, pipeline transport. However, as the concentration
which enhances particle-particle interactions, resulting exceeds 72%, both yield stress and plastic viscosity rise

Volume 22 Issue 5 (2025) 184 doi: 10.36922/AJWEP025200154