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| Mechanism of bentonite in regulating the drying-solidification of fluid sludge using phosphogypsum-based powder |
| TAN Yunzhi1, 2, XIE Jinyong1, CHEN Hongfeng1, 3*, LUO Zengyan1, 2, MING Huajun1, 3, WANG Chong1, 2, WU Jun1, 2 |
| (1. Yichang Key Laboratory of the Resources Utilization for Problematic Soils, China Three Gorges University, Yichang, Hubei 443002, China; 2. Hubei Key Laboratory of Disaster Prevention and Mitigation, China Three Gorges University, Yichang, Hubei 443002, China; 3. College of Hydraulic and Environmental Engineering, China Three Gorges University, Yichang, Hubei 443002, China) |
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Abstract The phosphogypsum-based material, composed of phosphogypsum, slag, and lime, used for solidifying sludge has been extensively studied. However, it still encounters challenges such as slow early-stage hydration and low long-term strength due to the high water content of sludge, which weakens stabilization efficiency. This paper employs phosphogypsum-based powder combined with bentonite as a regulating agent, capitalizing on the unique water conversion and expansion properties of ettringite. A combination of macro-performance tests and micro-characterization techniques was utilized to investigate the hydro-mechanical properties of the stabilized sludge and to evaluate the effectiveness of bentonite. The results demonstrate that bentonite significantly reduces the free water content in the solidified sludge, achieving a 10% reduction after both 28 and 90 days of curing. Additionally, bentonite enhances the mechanical properties of the solidified sludge during the curing process. The strength of the solidified sludge after 90 days of curing reaches 3.8 MPa, which is double that achieved after curing14 days (1.9 MPa). Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) results indicate the formation of a dense, interwoven network of needle-like ettringite alongside cementitious hydration products (e.g., calcium silicate hydrate, calcium aluminate hydrate) in the samples cured for 90 days. Mercury Intrusion Porosimetry (MIP) results further confirm the near disappearance of large pores (＞10 μm), suggesting that the expansive filling effect of ettringite significantly reduces macroporosity. The water conversion and expansion driven by ettringite accelerate early-stage cementitious formation and enhance long-term strength. Moreover, the comprehensive cost index of bentonite-solidified sludge is only 6.51% of that of tricalcium aluminate. Therefore, utilizing low-cost, readily soluble bentonite as a regulating agent in phosphogypsum-based sludge stabilization is a viable option. This study provides a sustainable strategy for the synergistic utilization of dredged sludge and phosphogypsum, thereby broadening the application scope of special soils.
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2026, Vol. 45 
