Interlayer formation of humin in smectites

Abstract

The stability of humin, the alkali-resistant part of humic matter in soil^1–4, is usually accounted for by its intimate association with inorganic soil colloids, especially swelling clays and iron compounds. Although the stability of these organo-clay complexes has been explained by interlamellar intercalation, there is evidence^2–4 that large-sized humic acid nuclei are unlikely to penetrate layer silicates in normal soil conditions. The ability of clay minerals to promote polymerization of organic monomers has long been recognized⁵, and has been confirmed recently^6–8; however, the conditions in which these catalytic properties were exhibited were unlike those existing in natural soils. We now report the results of preliminary investigations suggesting that humin-like substances may form between layers of silicate clays from smaller aromatic molecules in conditions that resemble those occurring naturally.