Abstract: Taking the lateritic soil collected from Miaoling town, Ezhou city, Hubei province as the study object, the free iron oxide in the undisturbed clay was removed by chemical selective dissolution combined with leaching as the treatment method in gradient, and the relationship between the drenching time of dithionite-citrate-bicarbonate (DCB) solution and the iron removal rate was achieved, and the effects of different leaching times on the physical, mechanical properties and the microscopic pore structure of the lateritic soil were analyzed. The experimental results show that the leaching time of DCB solution has a strong correlation with the iron removal rate, and the iron removal rate first increases rapidly and then gradually stabilizes with the time. Since the free iron oxide primarily plays the role of cementation between lateritic soil, the drenching time has a great influence on the physical and mechanical properties of lateritic soil. With the increase of drenching time, the contents of clay particles and colloidal particles gradually increase, the heat resistance increases marginally, and the unconfined compressive strength decreases significantly, while the overall trend of unconfined compressive strength decreases sharply in the early stage and tends to be stable in the later stage. Results of nuclear magnetic resonance (NMR), differential thermal analysis (DTA) and scanning electron microscopy (SEM) reveal that as the leaching time increases, the internal pores of the Miaoling lateritic soil enlarge, the free water diminishes, the bound water increases, the microscopic morphology of the agglomerate structure is destroyed, the cemented material is significantly reduced, and the structural form gradually converts from a compact granule stacking structure to an aggregate-loose granular structure.

Key words: free iron oxide, lateritic soil, iron removal rate, physical and mechanical characteristics, leaching