Role of free iron oxides in the physicochemical and mechanical properties of natural clay

• Published in: Engineering geology Vol. 303; p. 106665
• Main Authors: Zhang, Xianwei, Liu, Xinyu, Kong, Lingwei, Chen, Cheng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20-06-2022
• Subjects: Cementation; Iron oxides; Mechanical characteristics; Microstructure; Natural clay; Occurrence; Mechanical characteristics; Iron oxides; Microstructure; Natural clay; Occurrence; Cementation
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2022.106665

While it is widely acknowledged that interparticle bonding due to free iron oxide (FIO) dramatically affects the behavior of natural clay, the exact role of FIO in determining soil physicochemical and mechanical properties and the underlying mechanism remain unknown. In response, this study removes FIO from natural Zhanjiang clay, a structured marine clay with cementation, to investigate how FIO affects the physicochemical and mechanical behaviors of soil. The immersion method and leaching method (with dithionite-citrate-bicarbonate solution) are used for FIO removal. The test results indicate that the removal of FIO significantly changes the soil physical indices and degrades the mechanical properties. The effects of FIO removal are explained from the perspective of microstructural alterations as revealed by scanning electron microscopy (SEM) observations, mercury intrusion porosimetry (MIP) tests, energy-dispersive X-ray spectroscopy (EDS), and zeta potential measurements. FIO is distributed at the contacts between soil particles and exists in the bridging form. Due to the attraction between the positively-charged FIO and the negatively-charged clay mineral surfaces, soil particles are bounden to form larger soil aggregates with enhanced stability. The removal of FIO leads to the breakdown of soil aggregates and the generation of large pores, thereby increasing soil compressibility and decreasing the shear strength. This study provides some new micro-level understandings of how FIO affects the behavior of natural clay.
•Effects of free iron oxide on engineering geology of natural clay is studied.•Free iron oxide is removed from natural clay.•Removal of free iron oxide leads to degradation of mechanical features.•Role of free iron oxide is explained considering its occurrence.