Effect of Lead Slag Origin on the Compressive Strength and Immobilization Capacity of Metakaolin-Based Geopolymers

The use of industrial waste in cementitious materials has been extensively studied as a sustainable alternative to reduce environmental impact and valorize by-products. The aim of this study was to evaluate the effects of the incorporation of secondary lead slag (<200 mesh) from two different sources on the mechanical, microstructural and environmental properties of metakaolin-based geopolymers. After 28 days of curing, analyses of compressive strength, X-ray diffraction, scanning electron microscopy, porosimetry, specific surface area and leaching of potentially toxic elements (PTEs) were performed. The addition of 20% slag led to a reduction in compressive strength of 25.3% (slag A) and 16.7% (slag B) compared to the reference sample. Despite the formation of damaging pores and cracks, both formulations showed effective immobilization of PTEs, with leachate concentrations below the limits specified in NBR 10004 (2004). The results show that the chemical composition of the slag significantly influences the final properties of the material. This study highlights the potential of geopolymers as a solution for the recycling of hazardous waste and the reduction in emissions associated with the cement industry.