Dependence of Concentration of Ammonium Chloride on Solubility of Nickel

Miyamoto, Shinya*; Sato, Mitsuyoshi*; Mihara, Morihiro  

It is planning that radioactive wastes of high alpha concentration generated from reprocessing plant of spent nuclear fuel will be disposed in deep underground repository in Japan. Using the nitrate acid in the reprocessing process, some of radioactive wastes include lots of nitrate salts. The solubility of nitrate salts is very high and they might easily dissolve in groundwater in the repository. In the repository, many steels also will be disposed and nitrate will be reduced to ammonium ion by the interaction of steel. In this study, first the solubility experiments of nickel were performed to evaluate the effect of ammonium ion on solubility. Next the geochemical modeling also was carried out to explain results of solubility experiments using published thermodynamic data of nickel and ammonia. Under conditions of more than 1mol/dm of ammonium chloride, the enhancement of solubility of nickel was observed. It showed 2 or 3 orders magnitude of higher than those of less than 1mol/dm of ammonium chloride. These data were explained by geochemical modeling using data of ammine complex.