Fractional Extraction of Humic Substance Involved in Kibushi-clay

Abstract

Motoyama-, Hara-, and Iga-kibushi clays were subjected to fractional extraction by using NaOH and Na₄P₂O₇ to characterize the humic substance involved in the clay. Cation exchange capacity (CEC) was also measured for the untreated and H₂O₂-treated clays. Followings were verified:
1) The humic substance involved in Motoyama-and Hara-kibushi was mainly composed of a humin-type, which was hardly extracted with NaOH and Na₄P₂O₇, while the humic substance was extracted readily from Iga-kibushi.
2) The humic substance extracted was considered to be bound with clay via Al-ions.
3) While CEC was larger for untreated clay than for H₂O₂-treated one in an alkali region, there was not much difference in CEC between both treatments in the neutral and acidic regions except Iga-kibushi.
The contribution of the humic substance to the negative charge of the clay surface was discussed on the basis of the CEC mesured.