Efflorescence and mitigation of red mud–fly ash–phosphogypsum multicomponent geopolymer

In this study, the efflorescence formation of geopolymers synthesized from red mud (RM), fly ash (FA) and phosphogypsum (PG) was evaluated to investigate the influence of different proportions. The mechanical properties, leaching properties and microstructure of the geopolymers were studied through compressive strength test, visual observation of efflorescence, leach properties and a series of microscopic tests by changing PG content (0–25 %), reducing precursor alkali concentration (4–10 %) and changing FA content (0–300 g). The results show that PG rich in SO42- lead to the formation of a new efflorescence product Na2SO4, the presence of Aluminum (Al) in FA is beneficial to the polymerization degree and chemical stability of the geopolymer gel, and excessive or insufficient alkali content will affect the polymerization reaction and the efflorescence resistance of the geopolymer. The geopolymers are synthesized with 55 % RM, 25 % FA and 20 % PG as precursors and activated with 10 wt% Na2O, which shows good strength and resistance to efflorescence. Proper alkali content is conducive to the formation of geopolymer strength phase. The initial pH value required for the suitable effective strength and strength development of the multicomponent geopolymers in this study is about 10.5–11.3, which can provide a reference for the synergistic utilization of RM-FA-PG. •Efflorescence mechanism of geopolymers with SO42−-rich phosphogypsum was analyzed.•Phosphogypsum accelerates the geopolymerization and promotes strength development.•Insufficient or excessive Na2O% will aggravate the efflorescence of geopolymers.•The initial pH value can be used to speculate the strength development of geopolymers.•Efflorescence can be alleviated by increasing the degree of geopolymerization of the gel.