Abstract
The properties of carboxyl groups in the oxidized coals obtained from Tenpoku-Fujita (C: 70.9%a.m.f.) and Sumiyoshi (C: 76.2%a.m.f.) coals by HNO3 treatment were studied by using the methods of ion exchange with Ca (CH3COO) 2 aq.sol.and infrared absorption spectra.
Carboxyl groups in oxidized Fujita coals were subjected to Ca (CH3COO) 2 aq.sol.exchange completely under N2 atmosphere 18°C, 20hrs. While oxidized Sumiyoshi coals had later exchange rate than Fujita's, and yet exchange reaction proceeded after 7 days. But the exchange rate of the humic acid extracted from oxidized Sumiyoshi coal did not vary significantly from Fujita humic acid.
These results were accessible by assuming a rate-determing diffusion of Ca++ ion into oxidized coals. In the case of treating the oxidized coals in much amount of Ca (CH3COO) 2 aq. sol., it could be seen that other acidic groups (probably phenolic) exchanged with Ca (CH3COO) 2. When the oxidized coals were heated in Ca (CH3COO) 2 aq. sol., a remarkable increase of exchange capacities was seen. These increase may be reduced to the action of CO2 given by decarboxylation and newly produced carboxyl groups.
