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Hydration process and microstructure of magnesium potassium phosphate cement with nitrate solution
Yan Tao1, Lai Zhenyu1, Wang Yuanyuan1
1Southwest University of Science and Technology, School of Materials Science and Engineering, State Key Laboratory of Environmental-Friendly Energy Materials, Mianyang 621010, Sichuan, China.
The Science of the Total Environment
|November 16, 2019
Summary
Magnesium phosphate potassium cement (MKPC) shows potential for hazardous waste treatment. High nitrate levels negatively impact MKPC
Area of Science:
- Geochemistry
- Materials Science
- Environmental Engineering
Background:
- Magnesium phosphate potassium cement (MKPC) is a potential solution for hazardous waste solidification/stabilization (S/S).
- Inorganic salts, particularly nitrates, can significantly influence cementitious material performance.
- Assessing MKPC's efficacy in high-nitrate waste treatment requires understanding nitrate's impact on hydration and microstructure.
Purpose of the Study:
- To investigate the hydration process and microstructure of MKPC under varying nitrate concentrations.
- To evaluate the effects of nitrate on MKPC's compressive strength, setting time, pH, and conductivity.
- To determine the threshold of nitrate content that significantly affects MKPC performance.
Main Methods:
- Specimen preparation with varying potassium nitrate (KNO3) concentrations.
- Analysis of hydration products and phase composition using X-ray diffraction (XRD).
- Microstructural characterization via scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS).
- Measurement of physical properties: compressive strength, setting time, pH, and conductivity.
- Pore structure analysis using the Brunauer-Emmett-Teller (BET) method.
Main Results:
- Potassium nitrate (KNO3) did not inhibit struvite-K formation but reduced its crystallization degree, altering microstructure from dense to loose clusters.
- Nitrate addition delayed MKPC setting times and slowed pH development during hydration.
- Nitrate hindered the hydration process, increased porosity, and negatively impacted compressive strength development at concentrations above 5 wt%.
Conclusions:
- MKPC shows promise for S/S of hazardous waste, but nitrate presence requires careful consideration.
- Nitrate ions negatively affect MKPC's hydration, microstructure, and mechanical properties, especially at higher concentrations (>5 wt%).
- Understanding nitrate's influence is crucial for optimizing MKPC performance in real-world waste treatment applications.
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