AbstractMine tailings‐based geopolymers were prepared at ambient temperature. The evolution of their microstructure and the immobilization of lead were studied. Characterizations include measurements in compressive strength, scanning electron microscope (SEM), Fourier‐transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and toxicity characteristic leaching procedure (TCLP) tests. With increasing the ratio of metakaolin from 0% to 50%, geopolymer gel in the mine tailings‐based geopolymers increased from 33.92% to 79.45%, leading to the compressive strength that increased from 2 to 15.5 MPa. With addition of Pb(NO3)2, a three‐stepped changes in the compressive strength and microstructure of the geopolymers were observed. As increasing Pb(NO3)2 dosage from 0% to 6%, geopolymer gel was kept constant, while lead silicate glass increased from 0% to 10.51%, and Si sites in calcium silicate hydrate (CSH) gel decreased from 20.55% to 11.3%. Pb2+ was effectively immobilized in the geopolymers. This study first presents the evolution of geopolymer gel, belite, lead silicate glass, and CSH gel in mine tailings‐based geopolymers as the functions of metakaolin and Pb(NO3)2 additions.