<p>The implementation of porous, chemically stable geopolymers offers a viable solution for enhancing wastewater treatment efficiency and sustainability. This study evaluates modified metakaolin/ground granulated blast furnace slag (80% MK: 20% GGBFS) geopolymers as effective adsorbents for heavy metal removal. Both foamed (FMSG) and non-foamed (NMSG) structures were systematically characterized and tested. Experimental results indicate that FMSG achieves a notable maximum adsorption capacity of 72.11 mg/g for Cd⁺² ions and 38.46 mg/g for Mn²⁺ ions, significantly outperforming NMSG. The incorporation of H₂O₂ enhanced the adsorption capacity of FMSG. The Freundlich and Langmuir isothermal adsorption models were used to analyze the adsorption process, revealing that the adsorption of Mn²⁺ aligns better with the Freundlich model, while the Langmuir model is superior for Cd²⁺. Furthermore, the pseudo-second-order kinetic model accurately represented the adsorption kinetics. These findings underscore the potential of modified geopolymers for effective heavy metal remediation, contributing to cleaner water resources.</p> Graphical abstract <p></p>