Adsorption of Strontium onto Synthetic Iron(III) Oxide up to High Ionic Strength Systems

Abstract

In this work, the adsorption behavior of Sr onto a synthetic iron(III) oxide (hematite with traces of goethite) has been studied. This solid, which might be considered a representative of Fe3+ solid phases (iron corrosion products), was characterized by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS), and its specific surface area was determined. Both XRD and XPS data are consistent with a mixed solid containing more than 90% hematite and 10% goethite. The solid was further characterized by fast acid-base titrations at different NaCl concentrations (from 0.1 to 5 M). Subsequently, for each background NaCl concentration used for the acid-base titrations, Sr-uptake experiments were carried out involving two different levels of Sr concentration (1·10−5 and 5·10−5 M, respectively) at constant solid concentration (7.3 g/L) as a function of −log([H+]/M). A Surface Complexation Model (SCM) was fitted to the experimental data, following a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-specific pair-formation constants, whereas the Pitzer-approach involves ion-interaction parameters that enter the model through activity coefficients for aqueous species. A simple 1-pK model was applied (generic surface species, denoted as >XOH−1/2). Parameter fitting was carried out using the general parameter estimation software UCODE, coupled to a modified version of FITEQL2. The combined approach describes the full set of data reasonably well and involves two Sr-surface complexes, one of them including chloride. Monodentate and bidentate models were tested and were found to perform equally well. The SCM is particularly able to account for the incomplete uptake of Sr at higher salt levels, supporting the idea that adsorption models conventionally used in salt concentrations below 1 M are applicable to high salt concentrations if the correct activity corrections for the aqueous species are applied. This generates a self-consistent model framework involving a practical approach for semi-mechanistic SCMs. The model framework of coupling conventional electrostatic double layer models for the surface with a Pitzer approach for the bulk solution earlier tested with strongly adsorbing solutes is here shown to be successful for more weakly adsorbing solutes.

Chitosan- and Alginate-Based Hydrogels for the Adsorption of Anionic and Cationic Dyes from Water

“…One reason for this is that as the ionic strength increases, MB and MO adsorption sites decrease, and thus the MB adsorption capacity decreases. Since Ca 2+ makes a greater contribution to ionic strength and has more positive charge than Na + , the effect of Ca 2+ on adsorption is stronger than that of Na + [95][96][97][98]. The effect of salt on reducing the adsorption capacity appeared to be due to both the steric hindrance effect and the obstruction of aggregation of particles exerted by the salts, which prevented the formation of adsorption layers and reduced their overall adsorption capacity [98].…”

“…Since Ca 2+ makes a greater contribution to ionic strength and has more positive charge than Na + , the effect of Ca 2+ on adsorption is stronger than that of Na + [95][96][97][98]. The effect of salt on reducing the adsorption capacity appeared to be due to both the steric hindrance effect and the obstruction of aggregation of particles exerted by the salts, which prevented the formation of adsorption layers and reduced their overall adsorption capacity [98]. The ionic strength present in the solution affected the adsorption of MO or MB on the gels.…”

Cation Adsorption in TiO2 Nanotubes: Implication for Water Decontamination

“…The heterogeneity of the TiO 2 NTs samples in terms of the presence of amorphous solid, different exposed atoms, the polydispersity of sizes, etc . mandates simplification of the model, which reduces the number of adjusted parameters . We focused on the preferential cation adsorption between the exposed surfaces, for which we considered a single adsorption site along with multiple equilibria model for successive protonations and Cs + associations onto the exposed oxygen atom .…”

“…mandates simplification of the model, which reduces the number of adjusted parameters. 37 We focused on the preferential cation adsorption between the exposed surfaces, for which we considered a single adsorption site along with multiple equilibria model for successive protonations and Cs + associations onto the exposed oxygen atom. 38 We obtained the following set of equilibria, expressed as site-ion association constants: where [H + ] loc, j and [Cs + ] loc, j are local (surface) ions concentrations.…”

In situ (bio)remediation treatment options for U and Sr contaminated land: a comparison of radionuclide retention and remobilisation

“…54 At low ionic strengths and at circumneutral to basic conditions, Sr(II) can sorb to mineral surfaces including Fe-(oxy)hydroxides and clays due to their large cation exchange capacity and surface area. [55][56][57][58][59][60] Here, Sr(II) typically forms outer-sphere complexes in competition with other cations (such as H + , Na + , K + , Mg 2+ ), [61][62][63][64][65] and Sr(II) bound via outer sphere sorption is considered susceptible to desorption and remobilisation with changes in pH and ionic strength. [65][66][67] Simple electron donors (such as acetate, lactate or glycerol) which promote bioreduction processes typically do not impact Sr(II) removal from solution 64,68,69 unless other biogeochemical processes impact on pH and lead to alkaline conditions.…”