Modified samples of a coal based activated carbon, Chemviron F400, were oxidized by nitric acid and air. Nitric acid oxidized samples were treated to remove humic type by-products of the oxidation process either by washing with sodium hydroxide solution or heating under vacuum. All samples were characterized to investigate the effect of the treatment and the chemical as well as the physical characteristics of these materials. The characterization included scanning electron micrographs (SEM), Brunauer-Emmett-Teller (BET) and Langmuir surface area measurements, Fourier Transform Infra Red spectroscopy (FTIR) analysis, sodium capacity measurement, pH titration and zeta potential measurements. The results indicated that there was a significant change in the structure of the precursor by oxidation and subsequent treatments. The ion exchange capacity of the carbon was markedly enhanced by the addition of oxygen containing weakly acidic surface groups.