Abstract: To solve the problems of low comprehensive utilization rate and insufficient cementitious activity of iron ore tailings,and clarify the influence mechanism of mechanical activation on the particle characteristics and cementitious activity of iron ore tailings,four typical iron ore tailings (Type A,B,C,D) from Hebei Province were taken as the research objects.Me chanical activation was carried out with a planetary ball mill for different times (0~4.0 h).Combined with laser particle size analysis,XRD,SEM and mortar strength test methods,the influence laws of mechanical activation on the particle size,micro morphology,phase composition and cementitious activity of iron ore tailings were systematically explored,and the particle distri bution uniformity was analyzed by Rosin-Rammler (R-R) model fitting.The results show that the mechanical activation is dominated by particle crushing and refinement in the early stage.For all four types of iron tailings,there exists an optimal inter val characterized by the competition between particle refinement and agglomeration,with the ideal particle size distribution a chieved at activation times between 1.5 and 2.5 h.The R-R model has a good fitting effect (correlation coefficient COD is greater than 0.96),and both the characteristic particle size De and the uniformity constant n show a trend of "rapid decrease, tendency to fluctuate" with the increase of activation time.Mechanical activation is likely to lead to the lack of intermediate particle size and reduce the distribution uniformity.Mechanical activation can promote the transformation of the main phases of iron ore tailings to amorphous state,and an amorphous "diffuse package" appears in the XRD pattern.The optimal phase modi fication time is 2 h for Type A and D iron ore tailings (containing high-hardness minerals such as quartz and pyroxene),and 1.5 h for Type B and C iron ore tailings.After 0.5 h of mechanical activation,the activity indexes of the four types of iron ore tailings all meet the requirements of GB/T 2847—2005 (≥65%).The synergistic effect of particle refinement and crystal amorphization significantly improves their pozzolanic activity,among which the maximum activity index of Type B iron ore tail ings reaches 84.6%,and that of Type A iron ore tailings (high-silicon type) is the lowest at 74.2%.Considering the activation effect and process economy,it is suggested that the mechanical activation time of the four types of iron ore tailings should be controlled within 1.5~2.5 h.Introducing classification grinding process and adding grinding aids after 1 h of activation can op timize the activation effect.The research results can provide data support and theoretical guidance for the high-value resource utilization of iron ore tailings.

Key words: iron ore tailings,mechanical activation,particle characteristics,characteristic particle size,refinement index, cementitious activity,microscopic mechanism