Colloidal iron sorption

Figure 4. Sorption of 137Cs and 85Sr by Colloidal Iron Silicates and Na Bentonite at 25°C.

First, it is remarkable that the As concentration was quite high already when injected water was backpumped. It may be that As was sorbed to colloidal iron-oxyhydroxide particles formed during oxidation, but were too small to be removed by filtration over 0.45 pm before analysis. This mechanism was suggested by Rott et al. (1996) who observed similar As peaks during the first cycles of an in situ iron removal system. When samples were analyzed from a later cycle in Schuwacht, the As concentrations had decreased to about 2 pg As/1 and they were similar in unfiltered and 0.1 pm filtered subsamples. Thus, sorption to colloidal iron cannot be mled out as a mechanism and it should be investigated thoroughly in the incipient cycles of another system. 

A sorption colloid flotation method has been developed for the separation of vanadium from sea water. The separation is based on a surfactant-collector inert gas system in which vanadate is sorbed on a positively charged colloidal iron(III) hydroxide collector. The vanadate enriched collector rises to the sea water surface and floats as a separable foam with aid of sodium dodecylsulfate as surfactant and nitrogen as inert gas. The major advantages of this method are the rapid attainment of flotation and the excellent recovery of 86 % vanadium based on spiked sea water samples. Flotation was found to be highly pH sensitive optimal values were found to be 5.00 + 0.02. In effect, at pH 4.90 a slight decline in recovery of vanadium could already be observed, whereas at pH 7 and above there was no vanadium float 53). 

Filer JM, Mojzsis SJ, Arrhenius G (1997) Carbon isotope evidence for early life discussion. Nature 386 665 Emerson D (2000) Microbial oxidation of Ee(II) and Mn(II) at circumneutral pH. In Environmental metal-microbe interactions. Lovley DR (ed) ASM Press, Washington DC, p 31-52 Ewers WE (1983) Chemical factors in the deposition and diagenesis of banded iron-formation. In Iron formations facts and problems. Trendall AF, Morris RC (eds) Elsevier, Amsterdam, p 491-512 Farley KJ, Dzombak DA, Morel FMM (1985) A surface precipitation model for the sorption of cations on metal oxides. J Colloid Interface Sci 106 226-242... 

Actinide and Technetium Sorption on Iron-Silicate and Dispersed Clay Colloids... 

Figure 1. Sorption of 237Pu and 233U by Iron Silicate (top) and Na Bentonite (bottom) Colloids at 25°C.

The results of additional experiments conducted with 85Sr and 137Cs spikes are shown in Figure 4. The well known sorption characteristics of bentonite for Sr and Cs ions is apparent (7). The sorption properties of bentonite are reduced at low pH, which is consistent with an electrostatic concept. 137Cs sorption on the iron silicate colloids is considerably less than that observed with bentonite, even though the colloid zeta potentials are similar, which suggests that mechanisms other than simple electrostatic concepts may be involved. Also, the linear trend of data for Sr in iron silicate systems is considered to represent precipitation rather than sorption. 

Figure 3. Sorption of 95mTc and 235Np on Iron Silicate and Na-Bentonite Colloids at 25°C and Comparison with Possible Tc and Np Speciation.

Davis, C. C., Knocke, W. R., and Edwards, M., 2001, Implications of aqueous silica sorption to iron hydroxide Mobilization of iron colloids and interference with sorption of arsenate and humic substances Environmental Science Technology, v. 35, p. 3158-3162. 

Trivedi, P., and Axe, L. (1999). A comparison of strontium sorption to hydrous aluminum, iron, and manganese oxides. J. Colloid Interface Sci. 218, 554-563. 

Subramaniam, K. et al.. Copper uptake by silica and iron oxide under high surface coverage conditions Surface charge and sorption equilibrium modeling, 7. Colloid Intetf. Sci., 268, 12, 2003. 

Green-Pedersen, H. and Pind, N., Preparation, characterization and sorption properties for Ni(II) of iron oxyhydroxide-montmorillonile. Colloids Surf. A, 168, 133, 2000. 

Hanna, K., Sorption of two aromatic acids onto iron oxides Experimental study and modeling, J. Colloid Inteif. Sci., 309,419, 2007. 

The peptization capabilities of polyphosphates depend on their sorption on aluminosilicates and colloidal particles of hydrated oxides of iron, aluminium and manganese. In practice, this causes problems in water treatment by coagulation when already rather low concentrations of polyphosphates can cause improper agglomeration of colloidal particles into sedimentable floccules. 

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