DXRD STUDIES OF SODIUM NICKEL FERROCYANIDE REACTIONS WITH EQUIMOLAR NITRATE NITRITE SALTS

Dynamic X-ray diffraction (DXRD) has been used to identify and quantif y the solid-state reactions that take place between sodium nickel ferr ocyanide, Na2NiFe(CN)6, and equimolar concentrations of sodium nitrate /nitrite, reactions of interest to the continued environmental safety of certain waste storage tanks at the Hanford site in eastern Washingt on. The results are supportive of previous work that indicated that en dothermic dehydration and melting of the nitrates take place prior to the occurrence of exothermic reactions, which begin about 300-degrees- C. The DXRD results show that a major reaction set at these temperatur es is the occurrence of a series reaction which produces sodium cyanat e, NaCNO, as an intermediate in a mildly exothermic first step. In the presence of gaseous oxygen, NaCNO subsequently reacts exothermally an d at a faster rate to form metal oxides. Measurements of the rate of t his reaction are used to estimate the heat release, and comparisons of this with heat-transfer rates from a hypothetical ''hot spot'' show t hat, even in a worse case scenario, the heat-transfer rates are approx imately eight times higher than the rate of energy release from the ex othermic reactions.