Ordinary Portland Cement is the most widely used binder in the construction sector; however, a very high carbon footprint is associated with its production process. Consequently, more sustainable alternative construction materials are being investigated, namely, one-part alkali activated materials (AAMs). In this work, waste-based one-part AAMs binders were developed using only a blast furnace slag, as the solid precursor, and sodium metasilicate, as the solid activator. For the first time, mortars in which the commercial sand was replaced by two exhausted sands from biomass boilers (CA and CT) were developed. Firstly, the characterization of the slag and sands (aggregates) was performed. After, the AAMs fresh and hardened state properties were evaluated, being the characterization complemented by FTIR and microstructural analysis. The binder and the mortars prepared with commercial sand presented high compressive strength values after 28 days of curing-56 MPa and 79 MPa, respectively. The mortars developed with exhausted sands exhibit outstanding compressive strength values, 86 and 70 MPa for CT and CA, respectively, and the other material’s properties were not affected. Consequently, this work proved that high compressive strength waste-based one-part AAMs mortars can be produced and that it is feasible to use another waste as aggregate in the mortar’s formulations: the exhausted sands from biomass boilers.

In this work, alkali-activated fly ash-derived foams were produced at room temperature by direct foaming using aluminum powder. The 1 cm³ foams (cubes) were then evaluated as adsorbents to extract heavy metals from aqueous solutions. The foams’ selectivity towards lead, cadmium, zinc, and copper ions was evaluated in single, binary, and multicomponent ionic solutions. In the single ion assays, the foams showed much higher affinity towards lead, compared to the other heavy metals; at 10 ppm, the removal efficiency reached 91.9% for lead, 83.2% for cadmium, 74.6% for copper, and 64.6% for zinc. The greater selectivity for lead was also seen in the binary tests. The results showed that the presence of zinc is detrimental to cadmium and copper sorption, while for lead it mainly affects the sorption rate, but not the ultimate removal efficiency. In the multicomponent assays, the removal efficiency for all the heavy metals was lower than the values seen in the single ion tests. However, the superior affinity for lead was preserved. This study decreases the existing knowledge gap regarding the potential of alkali-activated materials to act as heavy metals adsorbents under different scenarios.

Additive manufacturing allows the fabrication of complex geopolymer geometries for water and environmental applications, but 3D-printed bulk structures often have lower specific surface area (SSA) than powders, limiting their adsorption performance in advanced water treatment technologies processes. Herein, we report a post-processing strategy to overcome this limitation by using ethylenediaminetetraacetic acid (EDTA) dealumination on metakaolin-based 3D-printed geopolymers. This approach supports pollution mitigation by enhancing the adsorption performance of 3D-printed geopolymer structures. The effects of EDTA concentration and contact time on lattice physicochemical properties were systematically studied. Successful dealumination was confirmed by aluminum leaching and increased Si/Al ratios. The optimized lattice, treated with 0.1 M EDTA for 8 h, achieved a SSA of 137 m²/g - a 41% increase over the pristine structure - among the highest for 3D-printed geopolymers. Although mechanical strength decreased, the lattice retained sufficient structural integrity (2.4 MPa) for practical operation in water treatment systems. In methylene blue adsorption tests, the modified material reached a maximum uptake of 30.86 mg/g and removal efficiencies above 98% at pH 10.5 (C₀ = 165 ppm). The lattices were successfully regenerated, maintaining >93% removal after 10 adsorption-desorption cycles. These results demonstrate that EDTA dealumination is an effective surface-engineering approach to enhance SSA and adsorption in 3D-printed geopolymer structures, supporting improved mitigation of water pollution and sustainable use of environmental resources.

Acacia dealbata, an invasive species in Portugal, produces large amounts of residual biomass during control operations, thereby presenting challenges and opportunities for sustainable valorization. Heavy metal contamination, including zinc (Zn), remains a critical environmental challenge due to its widespread industrial release and potential ecotoxicological impacts. This study explores the potential use of A. dealbata biomass as a biosorbent for zinc removal from aqueous solutions, comparing the performance of natural biomass and A. dealbata charcoal fines. Adsorption isotherms, kinetics, and surface characterizations were conducted to evaluate their physicochemical properties and sorption efficiency. The A. dealbata charcoal fines exhibited a significantly higher specific surface area (33 m² g⁻¹) and total pore volume (0.030 cm³ g⁻¹) compared with the untreated biomass (1.4 m² g⁻¹ and 0.004 cm³ g⁻¹, respectively). Despite these structural differences, both materials demonstrated similar maximum adsorption capacities (23.36 and 23.79 mg g⁻¹ for natural and charcoal fines, respectively). These results indicate that untreated A. dealbata biomass can perform as a biosorbent comparably to its carbonized form, representing a simple, low-cost, and sustainable alternative for heavy metal removal, offering a low-energy and sustainable alternative for Zn remediation.