Cation exchange properties of several kinds of humic acid were studied in the range of 1/10N-1/2, 000N of metal salts in aqueous solution.
In high concentration of metal salts in aqueous solution, humic acid extracted from HNO3-oxidized coals has more exchange capacity than that obtained from O2-oxidized coal, however, in low concentration of their aqueous solutions, later has more exchange capacity than the former. Variation of KNiH with the concentration of NiCl2 showed that the cation exchange property of humic acids extracted from oxidized coals was different from that of cation exchange resin Amberlite IRC-50. It was found that in low concentration of metal salts in aqueous solutions, the exchange capacity of humic acid obtained from oxidized coals was in order of transition metal<alkaline earth metals< alkaline metal. Carboxyl acidity of O2-oxidized coals was in linear relation with their Ni uptake in 1/1, 000 N NiCl2 in aqueous solution. This result seemes to show that carboxyl groups take part in Ni uptake reaction in ever low concentration of NiCl2 aqueous solution.
These results suggest that coal oxidation products have carboxyl groups to be able to form chelates and exchange cation. As O2-humic acid is better than the other samples in this capacity, it has more metal uptake in low concentration of metal salts in aqueous solution.
