Steel slag base geopolymer for efficient removal of Zn and Ni ions from aqueous solutions: Preparation and characterization

•The solid waste steel slag is recycled for the preparation of steel slag base geopolymer (SSGP).•Alkali activation effectively increases the specific surface area of the SSGP, which is about 4 times that of steel slag.•Adsorption may explain for the removal Zn and Ni ions.•SSGP achieved the maximum adsorption capacity of Zn and Ni ions was 145.43 and 69.97 mg/g, respectively. Geopolymer was successfully prepared by using the steel slag and sodium hydroxide. The changes in morphology, functional groups, specific surface area and crystal structure during geopolymerization were observed by SEM-EDS, FTIR, BET, XRD, VSM and other techniques. The results showed that the specific surface area of the geopolymer is nearly 3 times higher than that of the steel slag, which enhanced the adsorption capacity of the geopolymer. Steel slag base geopolymer easily achieved the maximum adsorption capacities of Zn (145.43 mg/g) and Ni ions (69.97 mg/g). These findings imply that the steel slag base geopolymer is a promising material for removing Zn and Ni.