Cobalt sorption

Since NaOH and NaA102 had no apparent effect on cobalt solubility, it seemed likely that cobalt sorption was increased by these components due to effects they had on the sediment minerals. Studies of the effects of NaOH and NaA102 on the sediment minerals are required to identify possible new mineral phases which might cause increased cobalt sorption. 

The increased cobalt sorption caused by EDTA was unexpected in light of cobalt s increased solubility with EDTA present and was opposite the sorption behavior found with HEDTA present. Further studies are required to explain the effect of EDTA on cobalt sorption. 

The solubility results were reflected in the sorption behaviors observed for the five radioelements. Sorption of strontium and americium was decreased by HEDTA and EDTA. Cobalt sorption also decreased in the presence of HEDTA. Sorption of both cobalt and strontium was decreased by increasing sodium ion concentration in the HLW due to competition of the cations for sorption sites. 

The possible role of amorphous aluminum and silicon oxides as controls. These merit further investigation since Elgabaly (66) foimd increased zinc fixation by kaolinite after nine days of grinding even though Tiller et al. (239) found little effect of sodium hydroxide extractions on cobalt sorption by soil clays. Tiller (237) has recently found that zinc sorption by montmorillonite is enhanced by the addition of soluble silicon. 

Model Ml monomeric complexes and precipitation alone. Our first cobalt sorption model ( Ml in Table I) was constructed to test the necessity of multinuclear complexes, so assumed that mononuclear complexes and precipitation of Co(OH)2 alone contribute to sorption. Equilibrium constants were optimized by trial and error. The best fit achieved with this model underestimates uptake for 7.5mononuclear complexes and precipitation alone. 

Brooks, S.C., and J.S. Herman. 1998. Rate and extent of cobalt sorption to representative aquifer minerals in the presence of a moderately strong organic ligand. Appl. Geochem. 13 77-88. 

Cobalt is strongly adsorbed by Mn oxides. There are close relationships between Co and the easily reducible fraction of Mn (Mn oxides) in soils (Jarvis, 1984) and will be in detail discussed in next chapter. Cobalt is frequently accumulated in Mn nodules in soils (Mckenzie, 1975). It was suggested that the Co2+ ion was first sorbed, then slowly oxidized to Co3+ and became incorporated into the surface layers of the crystal lattice, releasing the Mn2+ ion into the solution (Bums, 1976 Mckenzie, 1975). X-ray photoelectron spectroscopy showed that Co3+ was present on the surface of bimessite after the sorption of the Co2+ ions took place (Murray and Dillard, 1979). Traina and Donor (1985) suggested that the Mn release during Co2+ sorption resulted not only from the oxidation of Co2+ to Co3+, but also... 

Cobalt is capable of substitution for Fe2+ and other transition metals in the phyllosilicates due to the similarity of ionic radii. On the other hand, cobalt (Co2+) is specifically adsorbed by Mn and Fe oxides, and concentrations of Co sorbed by Mn oxides are much greater than those by Fe oxides (Backes, et al., 1995). Traina and Donor (1985) suggested that the Mn release during Co2+ ion sorption resulted not only from the oxidation of... 

Ainsworth C.C., Pilon J.L., Gassman P.L., Van Der Sluys W.G. Cobalt, cadmium, and lead sorption to hydrous iron oxide Residence time effect. Soil Sci Soc Am J 1994 58 ... 

McLaren R.G., Lawson D.M., Swift R.S. Sorption and desorption of cobalt by soils and soil components. J Soil Sci 1986b 37 413 126. 

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). 

Isshiki and Nakayama [234] have discussed the selective concentration of cobalt in seawater by complexation with various ligands or sorption on macro-porous X AD resins. Complexed cobalt is collected after passage through a small XAD resin-packed column. 

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. 

XPS results are very similar. The Co 2p splitting values 15.5 0.1 eV are equal within experimental error, the N(amine)/Co atomic ratios are 1.7 and 1.3, respectively, and the individual Co/Mn surface and bulk ratios are approximately equal at each pH. This latter result indicates that the sorption process occurs predominately on the surface at pH 6 and 7. The Co 2p splitting results are intermediate between values measured for Co(III) and Co(II)-containing compounds. To account for the Co 2p splitting result, a cobalt material with such an intermediate splitting or a mixture of the two cobalt oxidation states must be present. A survey of representative cobalt-containing materials (19,24,26) reveals that Co 2p splittings at about 15.5 eV are not common. 

If hydrolysis plays a role in the sorption process, the slight differences for the Co/Mn ratio at the higher pH could be related to the relatively lower rates for hydrolysis of the cobalt ethylenediamine complex at low pH (27). 

The XPS results do not indicate significant cobalt(II) hydroxide formation following complex sorption at pH 8 or 10 for... 

Surface characterization of birnessite following the sorption of Co(II) indicates the presence of oxidized cobalt (CoOOH) at pH values, 4-6, where precipitation of Co(0H>2 does not occur, and a... 

Sorption of small amounts of cobalt(II) on ir-on(III) oxide. Microdiim. Acta 1 105-112 Music, S. Gessner, M. Wolf, R.H.H. (1979a) Sorption of small amounts of europium(III) on iron(III) hydroxide and oxide. J. Radioanal. Chem. 50 91-100... 

Tiller, K.G., Hodgson, 3.F. and Peech, M., 1963. Specific sorption of Cobalt by soil clays. Soil Science, 95 392-399. 

It has been shown that cesium diffuses into the lattice of micaceous minerals, resulting in its entrapment (12) The 35 to 40% "fixed" cesium (Figure 4) is, therefore, likely bound internally at lattice sites, which would have to be destroyed in order to release the cesium. The extraction of cesium by KTOX in these experiments is likely due to dissolution of iroir-bearing minerals, such as biotite and horneblende rather than oxyhydroxides. If sorption by oxyhydroxides had been involved, a trend of increasing sorption with granite alteration, similar to that exhibited by cobalt and selenium, should have been observed. 

Effects of Hanford High-Level Waste Components on the Solubility and Sorption of Cobalt, Strontium, Neptunium, Plutonium, and Americium... 

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