Physicochemical and ion-binding properties of highly aliphatic humic substances extracted from deep sedimentary groundwater

Saito, Takumi; Terashima, Motoki  ; Aoyagi, Noboru   ; Nagao, Seiya*; Fujitake, Nobuhide*; Onuki, Toshihiko

The deep groundwater HSs were different from surface HSs, having high aliphaticities, sulfur contents, and small molecular sizes. The amounts of their acidic functional groups were comparable to or slightly larger than those of surface HSs; however, the magnitude of Cu binding to the deep groundwater HSs was smaller. The NICA-Donnan model attributed this to the binding of Cu to chemically homogeneous carboxylic-type sites via mono-dentate coordination at relatively low pH. The binding mode tended to shift to multi-dentate coordination with carboxylic-type and probably more heterogeneous alcoholic hydroxide-type groups at higher pH. This study shows the particularity of the deep groundwater HSs in terms of their physicochemical and ion-binding properties, compared with surface HSs.