Jihene Nouairi

The increasing accumulation of mine waste and the associated release of toxic elements represent a major environmental challenge, particularly in regions impacted by Pb–Zn mining activities. In this context, this study aims to investigate the valorization of mine waste from Lakhouat, an abandoned Pb–Zn site in Northern Tunisia, as a sustainable additive in metakaolin-based geopolymers. This approach contributes to circular economy strategies by transforming hazardous waste into value-added materials for environmental and construction applications. Geopolymer formulations were synthesized by incorporating mine waste at different proportions (0, 5, 10, 20, and 30 wt.%) with metakaolin, while maintaining constant SiO₂/Al₂O₃ and Na₂O/Al₂O₃ molar ratios. The materials were prepared through alkali activation using sodium silicate and sodium hydroxide, followed by curing. Comprehensive characterization was carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, adsorption experiments using methylene blue (MB) were conducted to evaluate the environmental performance of the synthesized geopolymers. The results revealed that the mine waste contains high concentrations of potentially toxic elements (up to 2.23 wt.% Pb and 8.2 wt.% Zn), highlighting the need for effective stabilization. Microstructural analysis confirmed the formation of predominantly amorphous geopolymer matrices with varying degrees of reaction depending on MW content. The highest compressive strengths (25–30 MPa) were achieved for formulations containing 5–10 wt.% MW after 28 days of curing. Furthermore, the geopolymers demonstrated efficient methylene blue removal, following pseudo-second-order kinetics and fitting the Langmuir isotherm model, with enhanced adsorption performance observed at higher MW contents. These findings indicate that MW-based geopolymers are promising materials for mine waste valorization and methylene blue removal. However, standardized leaching tests are required to confirm the long-term immobilization of Pb, Zn, Cd, As, and other potentially toxic elements within the geopolymer matrix. The study highlights their potential as sustainable, low-impact materials, supporting waste valorization and contributing to the development of environmentally resilient systems within a circular economy framework.

Geopolymers, characterized by their sustainable composition, are increasingly recognized as viable alternatives in construction materials. This paper examines the prospects of geopolymers within the sustainable blue economy, as a context emphasizing blue growth in smart, inclusive and above all sustainable development in the marine and maritime sectors. A synthesis of existing knowledge, emphasizing geopolymers’ potential contribution to sustainable practices within the blue economy is presented, delving into specific but innovative applications such as the use of alternative and non-conventional materials for marine infrastructures and offshore construction, and assessing the performance and the many advantages of geopolymers in challenging marine environments through a number of studies. Sustainability considerations and environmental impact are analysed, comparing geopolymers with conventional materials. The paper also identifies challenges related to the applications for marine infrastructures and offshore construction, proposing research directions and solutions. Finally, regulatory aspects are explored outlining current guidelines and advocating for a regulatory framework supportive of geopolymer integration in the Blue Economy sectors, and future trends and innovations are discussed, providing insights into ongoing research. The aim of the present review is to inform researchers, practitioners and policymakers involved in the intersection of geopolymer materials, marine ecosystems and circular economy.