Functional groups and reactivity of size-fractionated Aldrich humic acid

Tanaka, Tadao 

The interaction affinity of the Aldrich Chemical humic acid (HA) with Co was examined with respect to molecular size of HA. Correlations between the affinity and the structures of HA were studied. At low HA concentration range, Co was interacted with the HA over 100k Da (HA(100)). With increasing HA concentration, the Co was preferentially interacted with the 30k-100k Da of HA (HA(30-100)). HA(100) and HA(30-100) were characterized with respect to their FTIR, 13C-NMR spectral analyses and acid-base titration curves. HA(10) having aliphatic branched structure, smaller amount of COOH group and large proton exchangeable capacity, seem to show low covalent nature and high ion exchangeability. In addition, steric hindrance may effect on the complexation, by winding up like random coils from the branched structure. HA(30-100) is dominated with the aromatic COOH group and OH group and it preferentially coordinates to Co. These presumptions were supported by XPS analysis, in which the biding energy cobalt-humates was discussed.