Abstract: In order to improve the pozzolanic activity of iron tailings， the effects of different activation time and ball to material ratios on the activity index of iron tailing mortar were studied by means of PSD， XRD and SEM. The test results showed that the mechanically activated iron tailings have potential cementitious property， and its activity index is greatly affected by the activation time and ball to material ratio. The activity index of iron tailings with mechanical activation for 40min， ball to material ratio of 9∶4 and mechanical activation for 30min， and ball to material ratio of 2∶1 can meet the application requirements of pozzolanic mixtures. The cementitious property of mechanically activated iron tailings is greater than its micro-filling effect， and the micro-grading uniformity of activated iron tailings is less than that of non-activated iron tailings. The addition of iron tailings changes the alkalinity of cement systems and the pore structure of hydration products， and makes more CO₂ enter the mortar， resulting in more carbonate products.

Key words: iron tailing; activity index; hydration product; pore structure; micro-grading