Phosphoric acid activation of Ouixane iron ore tailing assisted with volumetric irradiation in the synthesis of high performance geopolymers: Microstructural and mechanical properties

This study investigates the synthesis and multi-scale characterization of phosphoric-acid-activated geopolymers derived from iron ore tailings (IOTs) and cured through volumetric microwave irradiation. This coupled approach, applied for the first time to IOT activation, significantly accelerates geopolymerization, reduces the overall processing time to just a few minutes, while simultaneously offering an effective response to the problem of excessive energy consumption, which has been highlighted as a key research gap in recent studies on geopolymer curing. The raw IOTs contain (16 wt% of SiO₂, 5 wt% of Al₂O₃ with (SiO₂/Al₂O₃ = 3.6), and 60 wt% of Fe₂O₃, a structure stabilizer, confirming their suitability as aluminosilicate precursors. Mechanical testing, SEM–EDS mapping, FTIR, XRD, and thermal analyses were performed to evaluate the evolution of the technological properties related to the resulting materials. Phosphoric acid concentration, microwave power, and irradiation duration were varied to determine optimal synthesis conditions. The geopolymers exhibited pronounced structural densification and the formation of Al–O–Si, Al–O–P, and mixed Al–O–Si–O–P linkages, along with the crystallization of characteristic aluminophosphate phases at optimal conditions (14 M H₃PO₄, 700 W, 10 min). Mechanical strength improved substantially with parameter optimization, increased from 5.0 MPa reaching up to 23 MPa before decreasing at prolonged irradiation (20 min). The geopolymers also demonstrated excellent resistance to aggressive environments with only 1,5% loss in compressive strength, highlighting the effectiveness of acidic activation combined with microwave curing in improving durability. Water absorption tests corroborated these findings, with values decreasing from 12.23% to as low as 3.59% under optimized microwave power and acid concentration, confirming a marked reduction in open porosity and improved matrix compactness confirmed by resistance to aggressive environments attacks with limited strength losses, generally below 1–1.7%. Overall, this pioneering route represents a sustainable, energy-efficient alternative to conventional thermal curing and produces high-performance IOT-based geopolymers suitable for green construction, metal immobilization, wastewater remediation, and photocatalytic applications.