Surface charge, hematite, effect adsorption

Effects of Pentavalent Sb on the Adsorption of Divalent Co-57. The emission Mossbauer spectra of divalent Co-57 adsorbed on hematite with pentavalent Sb ions (Figure 8) are complex and we have not yet succeeded in their analysis. It is certain, however, from the spectra that trivalent Fe-57 ions produced by the EC decay of Co-57 are interacting magnetically with the ferric ions of the substrate. This means that the divalent Co-57 are not adsorbed on the pentavalent Sb ions, but on hematite directly. The [Sb(OH)g]- anions are considered to facilitate direct adsorption of divalent Co-57 ions on the positively charged surfaces of hematite in the acidic region. 

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. 

Hesleitner, P. Babic, D. Kallay, N. Matijevic, E. (1987) Adsorption at solid/solution interfaces. 3. Surface charge and potential of colloidal hematite. Langmuir 3 815-820 Hesleitner, P. Kallay, N. Matijevic, E. (1991) Adsorption at solid/liquid interface. 6. The effect of methanol and ethanol on the ionic equilibrium at the hematite/water interface. Langmuir 7 178-184... 

At equilibrium surfactant concentrations of less than 0.0003 M SDS where the hematite surface is still positively charged, adsorption of surfactant follows its normal pattern due to the electrostatic forces which provide the driving force for adsorption. Sufficient effective surface area must be available for this level of SDS adsorption density. As surfactant adsorption... 

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