Cobalt sorption reactions

Chemical components in the waste solutions potentially could affect radioelement solubility and sorption reactions, and thus enhance or reduce radionuclide transport. The effects of 12 chemical components on the solubility and sorption of cobalt, strontium, neptunium, plutonium, and americium were studied to... 

In summary, the solubility and sorption reactions of cobalt, strontium, neptunium, plutonium, and americium were found to be dependent on HLW compositions. Evidence revealed the formation in HLW of organic complexes of cobalt, strontium, and americium, and of hydroxide complexes of neptunium(V) and plutonium(V). Sorption reactions were dependent on radioelement complex formation and suspected waste/sediment reactions. These data can aid in assessing effects of future HLW processing operations as well as in judging the feasibility of continued storage of HLW in existing tanks. 

It was reported that cobalt (Co2+) was specifically adsorbed by Mn and Fe oxides, and the concentration of Co sorbed by Mn oxides was much greater than those by Fe oxides (Backes et al., 1995). Cobalt can replace the Mn ion in Mn oxides. Furthermore, it was suggested by Mckenzie (1975) that Co only replaces the low-valence Mn (Mn3+) ion in Mn oxides. Traina and Donor (1985) suggested that the Mn release during Co2+ sorption resulted not only from the oxidation of Co2+ to Co3+, but also from a direct exchange of Co2+ for Mn2+ produced during the redox reaction. Cobalt in the ERO fraction may be, therefore, in part, as Co3+ ion, while in the CARB fraction it is present as Co2+. 

The present study concerns the interaction of propene molecules with cobalt sites in CoZSM-5. The experiments of CO and NO sorption evidenced that this zeolite contained practically only Co2+ in exchange position and Co3+ in oxide form. Propene is a reactant in several reactions catalyzed by cobalt containing zeolites (like reduction of NO, amonoxidation of propene and others). 

The sorption processes for cobalt complexes can be complicated by hydrolysis reactions of the complex in solution, surface induced ligand loss processes, sorption of hydrolysis products of either amine, protonated amine, or mixed amine/aquo cobalt complexes, and oxidation/reduction processes associated with cobalt. The principal objective of the XPS studies was to evaluate, the chemical state of cobalt and amine ligands, the surface concentration of the respective elements, and the ligand to cobalt ratio as indicated by the surface nitrogen to cobalt atomic ratio. 

Katz, L.E. 1993. Surface complexation modeling of cobalt ion sorption at the a-Al203-water interface Monomer, polymer and precipitation reactions. Ph.D. diss. Univ. Michigan, Ann Arbor, MI. 

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