In order to obtain regenerated humic acids from bituminous coals, six kinds of coals-Takamatsu (C: 75.7%), Onoura (C: 80.1%), Miike (C: 82.3%), Hashima (C: 85.0%), Shin-omine (C: 87.1%) and Nishikawachi (C: 89.5%) were oxidized with nitric acid under various conditions. In the case of Miike coal, a maximal yield of humic acid (based on original coal) was obtained at the oxidation time about 14 hours with 1 normal nitric acid and about 6 hours with 2 normal nitric acid at 100°C. On the oxidation of bituminous coals with 2 normal nitric acid in 5 hours at 100°C, the yield of humic acids depended upon the rank of coals. Under these conditions coal containing about 84% carbon gave a maximal yield of humic acid. To prepare humic acids in good yiels from coals of the higher rank, it was necessary to employ the more drastic oxidation conditions.
Carbon, hydrogen and nitrogen contents, neutralization equivalent weights and cadmium ion uptakes of humic acids that regenerated from bituminous coals were determined.
