Mechanistic Analysis of Hydrogen Mineral Phase-Transformed Iron Ore Tailings in Cementitious Materials: A Study on Hydration Kinetics, Mechanical Properties, and Microstructural Characteristics

Abstract

Hydrogen Mineral Phase Transformed (HMPT) represents an efficient separation technology for complex iron ores, facilitating the recovery of valuable elements from iron tailings. However, research on the effective utilization of the resultant iron tailings, termed HMPT-derived Iron Ore Tailings (HMPT-IOTs), remains limited. This study investigates the potential of HMPT-IOTs as supplementary cementitious materials by first examining their fundamental properties and pozzolanic characteristics. Mechanical performance and variation studies of composite cementitious materials containing HMPT-IOTs were conducted with three water-to-binder ratios, three substitution levels, and three curing ages as variables. Additionally, the heat of hydration was measured using isothermal calorimetry, and the hydration reaction was analyzed through fitting with the Krstulovic-Dabic model. SEM-EDS was employed to observe the interfacial transition zone and hydration products, complemented by FTIR to investigate chemical bond changes during hydration. The results indicate that HMPT-IOTs possess a specific surface area and density comparable to cement, measuring 322 m²/kg and 2895 kg/m³, respectively. Unlike traditional iron tailings, HMPT-IOTs exhibit pozzolanic properties and can be directly utilized in cement after drying. When the substitution level of HMPT-IOTs reached 10 wt.%, the compressive strength of the composite cementitious material at 28 d achieved 47.9 MPa. Even at a substitution level of 30 wt.%, the 28-day compressive strength remained substantial at 37.5 MPa. Furthermore, at a reduced water-to-binder ratio of 0.4, the 28-day strength attained 47.5 MPa. Investigating the role of HMPT-IOTs in the hydration mechanism revealed that during the early stages of hydration, the process is controlled by the nucleation growth (NG) phase, with hydration products gradually forming. As the volume of hydration products increases, ion migration slows, transitioning to the interfacial phase boundary reaction (I) phase, characterized by milder reactions, before ultimately being governed by the diffusion (D) phase. Increased substitution levels enhance the nucleation and crystal growth reactions while accelerating the diffusion process. HMPT-IOTs facilitate the hydration extent of the NG phase, with greater substitution levels correlating with increased hydration, though they exhibit a certain inhibitory effect on the I phase. Importantly, HMPT-IOTs do not alter the crystalline geometry or the types of chemical bonds in the hydration products. These properties underscore the promising application of HMPT-IOTs as supplementary cementitious materials.

Keywords: HMPT-IOTs, Supplementary cementitious materials, Pozzolanic property, Hydration kinetics