Hydroxide precipitation and co-precipitation with samarium hydroxide of Mg, Ca, Sr, and Ba toward chemical study of nobelium

Abstract The hydroxide precipitation behavior and co-precipitation behavior with samarium hydroxide were investigated for group 2 elements to clarify the reason for the difference in precipitation and co-precipitation behavior and to obtain comparative data for chemical study of element 102, nobelium. Although hydroxide precipitation behavior qualitatively agreed with the tendency of the solubility products of M(OH) 2 , co-precipitation behavior did not. The dependence of the precipitation behavior on the amounts of metal (Sr and Ba) did not show a simple tendency. Sr dimer species were observed in the filtrate samples of precipitation experiments using electrospray ionization mass spectrometry (ESI-MS). X-ray absorption fine structure (XAFS) spectra of Sr hydroxide precipitate samples revealed that Sr atoms exist in the second coordination sphere of Sr in the precipitate samples, which is different from that in strontium hydroxide octahydrate. From these, it was suggested that Sr formed dimers at large amounts of metal in both filtrate and precipitate samples under the present conditions. From the dependence of the precipitation yields on the amount of metal, precipitation involving dimers is dominant at > 1 mg for Sr and > 10 mg for Ba. In the range of lower metal amount, precipitation behavior is expected to become complicated due to the involvement of monomers. The co-precipitation yields of group 2 elements can be appropriately used for comparison of the co-precipitation yields of nobelium with samarium hydroxide, because nobelium exists as several atoms at a time and would not form dimer molecules under such conditions.