Effect of storage temperature on the cementitious property of hemihydrate phosphogypsum
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摘要: 半水磷石膏（HPG）长时间堆存状态下会出现固结现象，其胶凝性能也相应下降。以室内HPG结晶水检测和单轴压缩试验为基础，通过设定4种不同堆存温度，分别为20，40，60和80 ℃，探究不同堆存温度作用下HPG试样结晶水质量分数变化和堆存后制备的充填胶凝材料（HCM）抗压强度发展规律，并采用扫描电镜等微观分析手段研究堆存温度对其强度影响机制。结果表明，堆存温度对HPG胶凝性能影响显著，高的堆存温度会加快HPG试样中的自由水转变为结晶水速率，而且会抑制堆存后制备的HCM强度发展。采用数据标准化对不同堆存温度作用后的试样抗压强度作出预测，被证实与实测值较吻合。微观分析发现，堆存温度主要影响体系的过饱和度，而使不同堆存温度作用后制备的HCM微观形态表现差异。Abstract: Whether domestic or foreign, the utilization of phosphogypsum (PG) resources is not satisfactory. A chemical plant in Guizhou produces phosphoric acid through a semi-aqueous process to obtain the byproduct hemihydrate phosphogypsum (HPG), which has a certain gelling activity. If this feature of HPG can be fully utilized, it can replace cement as a cementing material to prepare mine-filling materials. Utilizing HPG for goaf filling can not only reduce the environmental protection problems caused by the surface discharge of PG but also eliminate the hidden safety hazards in the goaf. At present, when HPG is used to prepare mine-filling cementitious materials, HPG will be consolidated into a block and lose its gelling activity when it is stacked for a certain period of time. The gelling performance of the HPG in the storage state appears to decline. Based on the indoor HPG crystal water detection and uniaxial compression test and setting four different storage temperatures (20 ℃, 40 ℃, 60 ℃, and 80 ℃), this study explored the changes in the mass fraction of the crystal water of HPG samples under different storage temperatures. The compressive strength development law of HCM prepared after storage and microscopic analysis methods, such as scanning electron microscopy, were used to study the influence mechanism of the storage temperature on its strength. Results show that the stacking temperature has a significant effect on the gelling performance of HPG. A high stacking temperature will speed up the conversion of free water in the HPG sample to crystal water and inhibit the strength development of the HCM prepared after stacking. Data standardization was used to predict the compressive strength of samples after storage at different temperatures, which is confirmed to be in good agreement with the measured values. The microscopic analysis found that the storage temperature mainly affects the supersaturation of the system, and the microscopic morphology of the HCM prepared after storage at different temperatures is different.
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图 1 HPG的矿物组成和微观形貌分析。（a）HPG的X射线衍射图；（b）HPG的微观结构图
Figure 1. Mineral composition and micromorphology analysis of HPG: (a) X-ray diffraction pattern of HPG; (b) microstructure of HPG
图 4 不同堆存温度HPG结晶水质量分数变化过程
Figure 4. Variation process of the HPG crystal water mass fraction at different storage temperatures
图 5 不同堆存温度HCM试样强度发展过程
Figure 5. Strength development process of HCM specimens at different storage temperatures
图 6 不同堆存温度下HPG胶凝性能标准化。（a）HPG结晶水质量分数标准化；（b）HCM强度标准化
Figure 6. Standardization of HPG properties at different storage temperatures: (a) standardization of HPG crystal water mass fraction; (b) standardization of HCM strength
图 7 试样标准化强度发展曲线斜率与截距误差。（a）斜率误差（3~90 d）；（b）截距误差（3~90 d）
Figure 7. Slope and intercept error of the standardized strength development curve of the specimen: (a) slope error (3–90 d); (b) intercept error (3–90 d)
图 9 不同堆存温度下HCM微观结构图。（a）20 ℃；（b）40 ℃；（c）60 ℃；（d）80 ℃
Figure 9. HCM microstructure of different storage temperatures: (a) 20 ℃; (b) 40 ℃; (c) 60 ℃; (d) 80 ℃
表 1 HPG化学成份及含水率测定结果表（质量分数）
Table 1. Hemihydrate phosphogypsum’s chemical composition and moisture content
% CaO Al2O3 SiO2 P2O5 MgO Fe2O3 SO3 SrO loss Free water Crystal water 37.86 2.46 4.20 1.37 0.28 0.45 44.82 0.36 0.20 22.10 5.40 
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