Quantifying gel properties of industrial waste-based geopolymers and their application in Pb2+ and Cu2+ removal

In this study, novel geopolymers based on solid wastes (coal gangue and red mud) were used in the adsorption of heavy metals (Pb2+ and Cu2+) from solution. The correlations between the composition and quantity of the geopolymer gels and heavy metal adsorption were investigated under various conditions using hydrochloric acid dissolution and spectroscopic techniques. The results showed that the geopolymer gel positively correlated with the Pb2+ and Cu2+ adsorption capacities in the absence of external silica and aluminum. Moreover, external silica and aluminum sources promoted Al2O3 and SiO2 dissolution in the raw materials, which increased and decreased the specific surface areas, respectively. All of the tested geopolymers exhibited Pb2+ and Cu2+ adsorption based on the Langmuir isotherm and the pseudo-second-order kinetic model, with adsorption maxima of 137.7 and 90 mg g−1, respectively. This research first determined the correlation between the geopolymer gel and its heavy metal adsorption performance, and demonstrated industrial waste-based geopolymers could be effectively applied for the removal of heavy metal which can help reduce the burden of waste management and provide new insights about the resource recovery of solid wastes.