In order to prepare a selective cation exchanger from brown coal, we try to control an acidity distribution of carboxyl groups. For this purpose, raw coal was pre-exchanged with metal cation such as Ca^<2+>, Co^<2+>, and Ni^<2+>, and then heated at 300℃ for 5h to decompose free carboxyl groups. While the acidity distribution of raw coal was very wide, the treated coal had bimodal distribution, pKa<5.5 and pKa>8. In this way, we could prepare the sample which did not have carboxyl groups with the middle pKa range. Also, from results of cation exchange experiments using this treated coal, it was found that the species of pre-exchanged cation adsorbed more easily than the other species of cation.
