Effect of Foaming Agent on Physical and Mechanical Properties of Foamed Phosphogypsum

Foamed phosphogypsum (FPG) has recently attracted extensive interest owing to its potential consumption of phosphogypsum and its substitution for traditional gypsum building materials. However, as an important component in the preparation of FPG, the effect of foaming agent on the performance of FPG is still unclear. Herein, Legao 3210 (LG), sodium alpha-olefin sulfonate (AOS), animal protein compound (APC), cocoamidopropyl hydroxy sulfobetaine (CHSB), and tea saponin (TS) were chosen as the foaming agents for FPG. The foam stability and foam structure were studied, and the results showed that the foams produced by TS and APC were more stable. The effects of different foaming agents on FPG's fluidity, density, strength, water absorption, and thermal conductivity were also studied. The results showed that FPG prepared with TS exhibited the highest compressive strength, measuring up to 1.34 MPa, which represented a 97% increase compared with that of APC. Moreover, the dry density and thermal conductivity of FPG prepared with TS were 517 kg/m3 and 0.109 W/(m·K). The digital microscope analysis indicated that the keys to the simultaneous realization of high strength and light weight in the FPG were uniform pore size distribution, small pore size, and thicker pore gaps. Furthermore, through scanning electron microscope (SEM) analysis, it was suggested that the formation of strong interlocking structure by hydration products was the microstructural mechanism for improving the strength of FPG. This study suggested that FPG has the possibility to compete with traditional gypsum materials and it is also expected to solve the problem of phosphogypsum utilization.