Hydration mechanism of amorphous layer on the surface of ultrafine iron tailings particles in clinker-free cement system

Due to the fact that the mineral composition in metal tailings is inert under normal conditions, and the fineness modulus of fine-grained tailings is much smaller than that of construction sand. Meanwhile, the source of activity of fine-grained tailings under non calcination conditions is not yet clear. Therefore, it cannot be widely consumed in civil engineering. To explore the active source of fine-grained tailings under non calcination conditions and improve their utilization ratio, this study attempted to determine the change in surface hydration activity of ultrafine particles of metal tailings during fine mechanical grinding. Unlike previous research methods conducted by most scholars in rich cement systems, this paper chooses to investigate the activity source of fine-grained iron tailings in a clinker-free system of lime and gypsum to avoid the hydration process of clinker masking the activity behaviour of fine-grained iron tailings. The influence of median particle size (D50) on the surface structure and activity of iron tailings powder (ITP) was studied by testing and analysing particle size distribution, XRD, FTIR, XPS, TEM and alkali dissolution characteristics, and the consolidation effect of ITP in CaO-CaSO 4 -H 2 O system was verified. Results show that superfine grinding has a selective grinding tendency to the aluminium-containing minerals in the iron tailings, the amorphous components formed on the surface of the superfine particles have hydration activity, and the ultrafine ITP with D50 of 5.68 μm can produce a clinker-free consolidation strength with 36.79 MPa for 28 d. Combined with the scanning electron microscope (SEM) test results, this study confirmed that the amorphous components on the surface of ultrafine iron tailings could undergo hydration reaction in a CaO-CaSO 4 -H 2 O system to generate AFt and C-(A)-S-H and produce consolidation strength. The micro-nano iron tailings particles were the 'active' units in the consolidated body. This article represents a popular research topic, aimed at promoting high value application of mining solid waste and green, low-carbon development of cementitious materials. ● The morphology of the amorphous layer on the surface of iron tailings was characterized for the first time. ● The control parameters for significant activity generated by iron tailings have been determined. ● Confirmed that lattice distortion induced activity is the origin of iron tailings activity.