Effect of storage temperature on the cementitious property of hemihydrate phosphogypsum

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.