Efficient Co-Valorization of Phosphogypsum and Red Mud for Synthesis of Alkali-Activated Materials

Phosphogypsum and red mud are bulk industrial solid wastes that trigger local environmental problems. In the present investigation, an efficient valorization process was developed through which phosphogypsum and red mud can be transformed into a precursor for the synthesis of high-strength, alkali-activated materials with a seawater-bearing sodium silicate solution as the alkaline activator. The effects of the activator modulus and liquid-to-solid ratio on the strength evolution of the synthesized AAMs as well as the microstructure and chemistry of the reaction products were investigated. The results showed that mineral reconstruction between PG and RM took place during calcination at 950 ?, forming ye'elimite, anhydrite and gehlenite, which then took part in the alkali-activation process and generated thenardite and C-A-S-H gel. The mechanical properties of the synthesized AAMs, ranging from 12.9 MPa to 40.6 MPa, were determined with the activator modulus and liquid-to-solid ratio. Results from the present investigation contributed to the facile and efficient valorization of phosphogypsum and red mud into cementitious construction materials.

Automated summary

A valorization process was developed to convert phosphogypsum and red mud into a precursor for high-strength, alkali-activated materials using a sodium silicate solution containing seawater as the activator. Mineral reconstruction during calcination resulted in the formation of ye'elimite, anhydrite, and gehlenite, which contributed to the alkali-activation process and the formation of thenardite and C-A-S-H gel. The mechanical properties of the synthesized materials, ranging from 12.9 MPa to 40.6 MPa, were controlled by the activator modulus and liquid-to-solid ratio. This research contributes to the efficient valorization of phosphogypsum and red mud into cementitious construction materials.