竹炭における硝酸イオン吸着能とその機構

Bamboo charcoal was examined to assess its nitrate ion adsorption capacity and mechanism in aqueous solutions. Three types of bamboo charcoal were prepared from Moso bamboo at different carbonization temperatures, namely, 400, 600 and 800°C (i.e., BC400, BC600, BC800). Although BC600 had the largest BET surface area and micropore volume (245.4m² · g^-1 and 0.162cm³ · g^-1, respectively), the batch adsorption experiment showed that BC800 had the highest nitrate ion adsorption capacity (3mg-N · g^-1 at about 80mg-N · <I>l</I>^-1). In addition, at the initial pH of the aqueous solutions of 2, the adsorption capacity was larger than that at about pH 6. Furthermore, the effects of acid and alkali treatments were examined. BC800_NaOH-HCl treated with acid following alkali treatment had a higher adsorption capacity than BC800_HCl-NaoH treated with alkali following acid treatment. This suggested that some hydroxide ions adsorbed onto BC800_NaOH-HCl were replaced with chlorine ions with the last acid treatment, although all of the anion exchange groups on BC800_HCl-NaOH adsorbed only hydroxide ions with the last alkali treatment. In other words, bamboo charcoal with partial substitution of chlorine ions for hydroxide ions can adsorb ions better. Therefore, it was concluded that the mechanism of nitrate ion adsorption onto bamboo charcoal is through ion exchange chemical adsorption.