Study of organic-matter intercalated vermiculitic phases in the hydromorphic red earth sediments

• Published in: Applied clay science Vol. 196; p. 105744
• Main Authors: Hong, Hanlie, Fang, Qian, Churchman, Gordon Jock, Zhao, Lulu, Ji, Kaipeng, Jin, Xiaoxue, Yin, Ke, Wang, Chaowen, Liu, Chen
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2020
• Subjects: Hydromorphic soil; Hydroxy-interlayered vermiculite; Mixed-layer illite-vermiculite; Organic matter intercalation; Pedogenesis; Red earth; Pedogenesis; Hydromorphic soil; Red earth; Mixed-layer illite-vermiculite; Hydroxy-interlayered vermiculite; Organic matter intercalation
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2020.105744

Al-hydroxy intercalated vermiculitic phases have been widely observed in pedogenic environment, but soil organic intercalations have rarely been reported. In the present study, mixed-layer illite–vermiculite (I/V) with organic matter (OM) intercalation under hydromorphic conditions in the Xuancheng red earth sediments was investigated in order to better understand the interlayer components occurring in mixed-layered clay minerals and the formation of this unusual OM interlayered mixed-layer clay species. Selective extraction of organic fillings by ammonium ethylene diamine tetraacetic acid (EDTA) and acid ammonium oxalate (NH4OX) showed that the components associated with organic complexes in the interlayer space of the 2:1 clays are mainly Fe- and A1-(oxy)hydroxides, which block substantial swelling after ethylene glycol solvation and complete collapse after heating. The OM interlayer filling contains CH3(CH2), CO, COO-, and NH functional groups and are resistant to H2O2 extraction although the binding intensity to the interlayer surface may change. Upon heating to ~300 °C the OM filling escapes from the interlayer space which causes the collapse of the 2:1 clay species. Alteration of primary illite during pedogenesis causes release of K and intercalation of hydrated cations in the interlayer space, and also leaching of Al and Fe. There is accumulation of exchangeable cations and Al and Fe oligomers in the interlayer region, which affects the behavior of I/V clays on glycolation and heating. Hydromorphic conditions favor the transformation of organic polymers into small size organic acids, and thus, favor the intercalation of interlayer OM filling into the 2:1 clays. Pedogenesis processes involves both the weathering of clay minerals and the decomposition of OM, leading to formation of interlayer clay-organic complexes in a hydromorphic soil. •Organic matter (OM) is present in interlayer spaces of soil-derived vermiculitic phases.•Interlayer filling occurs as organo-Fe-Al complexes.•The OM filling is resistant to H2O2 extraction and escapes upon heating to ~300 °C.•Hydromorphic conditions favor organic matter filling in soil-derived 2:1 clays.