Cobalt pentavalent

The procedure for separating Sb-119 from an alpha-irradiated tin target has been described elsewhere (10,11). The amounts of cobalt and antimony coexisting with the nuclides are estimated to have been about 400 ng/mCi and 300 ng/mCi, respectively, i.e., to have been much smaller than that required for monolayer coverage of 30 mg of the hematite sample. About 10 cm3 of an aqueous solution containing 1 - 2 mCi of divalent Co-57 or 0.1 - 1 mCi of pentavalent Sb-119 was adjusted to an appropriate pH value in a Teflon vessel with a 0.5 mm-thick Teflon window at the bottom, and about 30 mg of hematite powder was added to the solution. The suspension was shaken for 30 min at room temperature. After settling of the powder at the bottom of the vessel, the pH was remeasured. 

Effects of Pentavalent Sb Ions on the Adsorption of Divalent Co-57 on Hematite. Benjamin and Bloom reported that arsenate ions enhance the adsorption of cobaltous ions on amorphous iron oxyhydroxide (J 6). Similarly, when divalent Co-57 ions were adsorbed on hematite together with pentavalent Sb ions, an increase of adsorption in the weakly acidic region was observed. For example, when 30 mg of hematite was shaken with 10 cm3 of 0.1 mol/dm3 KC1 solution at pH 5.5 containing carrier-free Co-57 and about 1 mg of pentavalent Sb ions, 95 % of Co-57 and about 30 % of Sb ions were adsorbed. The emission spectra of the divalent Co-57.ions adsorbed under these conditions are shown in Figure 8 together with the results obtained under different conditions. As seen in Figure 8, the spectra of divalent Co-57 co-adsorbed with pentavalent Sb ions are much different from those of Co-57 adsorbed alone (Figure 3). These observations show a marked effect of the.co-adsorbed pentavalent Sb ions on the chemical structure of adsorbed Co-57. 

Cobalt, as a result of its place in the periodic system, should have a valency of nine. It is, however, mostly divalent and occasionally tervalent. Phosphorus can be tervalent as well as pentavalent sulphur is hexavalent in SOs and tetravalent in S02. At low temperatures the valency is such that the energy is a minimum, and which compounds will be formed can only be predicted when the energy can be calculated accurately. 

The effect of ionic environment on the rate of diffusion controlled e"aq reactions is revealed when one compares the experimental rate constants with the calculated values. In Table I the highly charged bis-pentacyano cobaltic peroxide (I) is much more reactive than expected for a pentavalent anion (1.11). It has been claimed (19) that polyvalent anions exhibit a lower effective charge in their kinetic behavior than expected from their structural formulae. We have checked the salt effect on the reaction of I + e m and compared it with the NOjf e m reaction. The results presented in Table IV and Figure 1 show that nitrate ions possess a normal salt effect, a result previously obtained by competition kinetics (15, 17). On the other hand, the salt effect of the I + e"aq reaction shows that this bis-pentacyano cobaltic peroxide ion has an... 

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