The thermal decomposition of neptunium carbonate and sulfate complexes with hexammine Co(III) cation

Thermal decompositions of the Np(IV), (V) and (VI) carbonate and sulfate complexes of the compositions [Co(NH3)6]2 [NpL5].nH2O,[Co(NH3)6][NpO2L2].α[Co(NH3)6]2 L3.nH2O and [[Co(NH3)6]X]2[NpO2L3].nH2O, where L = CO3 or SO4, X = NO3 for L = CO3 and X = HSO4 for L = SO4, were studied using DTA and TGA apparatus. DTA and TG curves were measured in the air from room temperature to 9000C, for each complex. Decomposition of the carbonates begins at about 500C, and major weight loss starts at about 1100C which is caused by the transition of Co(III) ammine complex to CoCO3. Final product, NpO2 + Co3O4, is formed at about 4000C. Sulfate complexes in any oxidation states decompose through four steps, at about 170, 280, 450 and 6800C. NpO2 is formed at 6000C, which is identified by X-ray diffraction. A relation between composition of the complexes and decomposition temperature is discussed. (author)