Chemical evaluation of immobilization of wastes containing Pb, Cd, Cu and Zn in alkali-activated materials: a critical review

•Insoluble M(OH)2, MCO3, MSiO3, MO and MS (M = Pb, Cd, Cu and Zn) exist in geopolymer.•M(OH)2 could be transformed within geopolymer into soluble M(OH)3− and M(OH)4−.•Metal species have water solubilities that are lower than the accepted limits.•Metal sulfides are the most resistance to leaching from geopolymer.•Pb-O, Cu-O and Si-O bonds have similar ionic character.