Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation
Graphical abstract
Introduction
Quantification of redox sensitive metals such as Cr(VI) in soils at contaminated sites is necessary for preventing and handling additional pollution [1], [2], [3]. The environmental, toxicological, and health risks associated with Cr(VI) are closely linked to its speciation and behavior in the environment [4], [5], [6]. Therefore, there is a need for understanding the adsorption of Cr(VI) at the solid-soil solution interface, which is a major factor in determining its distribution [7], [8]. In order to describe the adsorption of Cr onto different soil minerals, various robust and complex mechanistic models are used [9], [10], [11]. In contrast to (semi)empirical adsorption models, thermodynamically based surface complexation models (SCMs) have the greatest predictive power for real natural soil systems [9], [11], [12]. SCMs differ mainly in their treatment of the electrical layers. The two-pK models such as the constant capacitance model (CCM) and the diffuse-layer model (DLM) capture only the formation of inner-sphere complexes, which are located in a single surface plane. The triple layer model (TLM) can describe the formation of outer-sphere complexes adsorbed in a β-plane, in addition to the formation of inner-sphere complexes. One pK model based on the Stern model describes the formation of inner-sphere surface complexes of H+ and OH− and the formation of outer-sphere complexes of other ions in the d-plane [13], [14].
Although SCMs have been extensively used during the last decades by many researchers [10], [15], [16], [17], [18], [19], [20], accurate datasets for SCMs have not been fully developed due to the complexity of natural systems. There have been some studies related to the development of SCMs for modeling Cr(VI) adsorption mainly on Fe oxyhydroxides. However, such robust SCMs for Cr have not been developed for other important soil minerals, such as clay minerals [21]. On the other hand, the predictions obtained from SCMs need to be confirmed by direct spectroscopic analyses. Different techniques have been previously tested for the identification of Cr(VI) complexes on Fe or Al oxyhydroxide surfaces [22], [23], [24], [25]. In addition, the redox transformation of Cr(VI) during adsorption onto environmentally relevant surfaces, including oxides and clay minerals have been investigated using X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), and X-ray absorption spectroscopy (XAS) [22], [26], [27], [28]. Therefore, studies using coupled modeling and spectroscopic approaches to soil mineral surfaces would provide valuable information. For this reason, a combination of SCMs and spectroscopic analyses was used in this study to better understand Cr(VI) adsorption onto synthetic ferrihydrite and birnessite, as well as natural kaolinite and illite. The speciation changes of Cr during adsorption were also examined. Although few recent studies have combined surface complexation modeling with a spectroscopic approach [16], [18], [19], [29], such studies for Cr and other soil sorbents remain scarce.
Therefore, the main objective of this study is to develop DLM and TLM based on data from batch experiments and to simulate the adsorption of Cr onto selected mineral phases. Spectroscopic measurements, including XPS, FTIR, and XAS, are performed to obtain a more detailed insight into the mechanisms of Cr(VI) adsorption and the accompanied redox processes. The results from the coupled SCM and spectroscopic approach will be useful for further investigations of complex mineral mixtures in real soils.
Section snippets
Characterization of solid phases
2-Line ferrihydrite was synthesized by rapid hydrolysis of 0.2 M Fe(NO3)3·9H2O solution at 25 °C by titrating the solution with 1 M KOH to pH = 8 under vigorous stirring [30]. Birnessite was synthesized by adding 35% HCl dropwise to a boiling solution of 0.4 M KMnO4 under vigorous stirring [31]. Ferrihydrite and birnessite were filtered, washed with 300 mL of distilled water 4–5 times, air-dried, and then ground and stored for further analyses. The natural clay minerals, namely kaolinite (KGa-2) and
Development of surface ionization reactions
Ferrihydrite, birnessite, kaolinite, and illite have been chosen as representatives of soil minerals responsible for regulating Cr(VI) mobility, transportation, and bioavailability in natural systems [7], [45]. The basic characteristics of selected soil minerals are summarized in Table 2 and Fig. S2.
One of the main aims of this study is to find the simplest surface complexation model which provides a good fit to experimental data. Therefore, the DLM, which requires only surface protonation
Conclusions
In order to gain an insight into the mechanisms of Cr(VI) adsorption onto selected soil minerals, a combination of spectroscopic investigation and modeling with DLM and TLM was performed. All the adjustable model parameters were optimized for the studied adsorbents using the software FITEQL 4.0 and ProtoFit. The DLM provides a reasonable prediction for Cr(VI) adsorption onto ferrihydrite at pH <7, capturing the formation of spectroscopically confirmed single monodentate inner-sphere complexes.
Supplementary material
Details about SCM, characteristics of soil minerals and their dissolution, XAS and XPS measurements are available as supporting information.
Acknowledgements
This research was funded by the Czech Science Foundation, Grant No. P210/15-17224Y and Internal Grant Agency of the Faculty of Environmental Sciences, CULS Prague (project 4240013123159). We are grateful to Petr Drahota for the help with the powder XRD analyses and Hana Šnajdaufová for the N2 BET analyses. We also thank Benjamin F. Turner for advices and help with Protofit modeling. Marie Králová, Quentin Lorenzo Chevalier, Edita Pehová and Barbora Hudcová are thanked for their assistance
References (77)
- et al.
Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: a review
J. Hazard. Mater.
(2013) - et al.
Phytoremediation of contaminated soil with cobalt and chromium
J. Geochem. Explor.
(2014) - et al.
Comparison of the spectroscopic speciation and chemical fractionation of chromium in contaminated paddy soils
J. Hazard. Mater.
(2015) - et al.
Chromium occurrence in the environment and methods of its speciation
Environ. Pollut.
(2000) - et al.
Assessment of health risks with reference to oxidative stress and DNA damage in chromium exposed population
Sci. Total Environ.
(2012) - et al.
Evaluation of toxicological risk of foodstuffs contaminated with heavy metals in Swat Pakistan
Ecotox. Environ. Safe.
(2014) Surface reactions of chromium in soils and waters
Geoderma
(1995)Adsorption of heavy metal ions on soils and soils constituents
J. Colloid Interface Sci.
(2004)The significance of surface complexation reactions in hydrologic systems: a geochemist's perspective
J. Hydrol.
(2000)- et al.
Surface complexation modeling of Pb (II) adsorption on mixtures of hydrous ferric oxide, quartz and kaolinite
Chem. Geol.
(2010)
Adsorption of Cr (VI) on (-alumina in the presence and absence of CO2: Comparison of three surface complexation models
Geochim. Cosmochim. Acta
Modeling sorption of divalent metal cations on hydrous manganese oxide using the diffuse double layer model
Appl. Geochem.
Surface complexation models: an evaluation of model parameter estimation using FITEQL and oxide mineral titration data
J. Colloid Interface Sci.
Use of surface complexation models in soil chemical systems
Adv. Agron.
Cadmium adsorption to mixtures of soil components: testing the component additivity approach
Chem. Geol.
Adsorption of mercury on lignin: combined surface complexation modeling and X-ray absorption spectroscopy studies
Environ. Pollut.
Surface complexation modeling and spectroscopic evidence of antimony adsorption on iron-oxide-rich red earth soils
J. Colloid Interface Sci.
Surface complexation modeling of Cr (VI) adsorption at the goethite–water interface
J. Colloid Interface Sci.
Mechanisms of chromate adsorption on boehmite
J. Hazard. Mater.
Chemical and spectroscopic evidence for specific adsorption of chromate on hydrous iron oxide
Chemosphere
Differential redox and sorption of Cr (III/VI) on natural silicate and oxide minerals: EXAFS and XANES results
Geochim. Cosmochim. Acta
Gallium (III) adsorption on carbonates and oxides: X-ray absorption fine structure spectroscopy study and surface complexation modeling
J. Colloid Interface Sci.
Adsorption and surface complex modeling of silicates on maghemite in aqueous suspensions
J. Colloid Interface Sci.
Protofit: a program for determining surface protonation constants from titration data
Comput. Geosci.
Sorption and speciation of heavy metals on hydrous Fe and Mn oxides. From microscopic to macroscopic
Appl. Clay Sci.
Surface ionization and complexation at the oxide/water interface II. Surface properties of amorphous iron oxyhydroxide and adsorption of metal ions
J. Colloid Interface Sci.
Coprecipitation of chromate with calcite: batch experiments and X-ray absorption spectroscopy
Geochim. Cosmochim. Acta
Modeling anion adsorption on kaolinite
J. Colloid Interface Sci.
Dissolution kinetics of soil clays in sulfuric acid solutions: ionic strength and temperature effects
Appl. Geochem.
Dissolution behavior of Jordanian clay-rich materials in alkaline solutions for alkali activation purpose. Part I
Appl. Clay Sci.
The mechanism of dissolution of minerals in acidic and alkaline solutions: part IV equilibrium and near-equilibrium behaviour
Hydrometallurgy
Evaluation of synthetic Birnessite utilization as a sorbent for cobalt and strontium removal from aqueous solution
Chem. Eng. J.
Spectroscopic study of the reaction of aqueous Cr(VI) with Fe3O4 (111) surfaces
Surf. Sci.
Heterogeneous Fe (II) oxidation and zeta potential
J. Geochem. Explor.
Adsorption and heterogeneous oxidation of As (III) on ferrihydrite
Water Res.
Development of a technique to prevent radiation damage of chromate conversion coatings during X-ray photoelectron spectroscopic analysis
Appl. Surf. Sci.
Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: cr, Mn, Fe, Co and Ni
Appl. Surf. Sci.
Modeling selenite adsorption envelopes on oxides clay minerals, and soils using the triple layer model
Soil Sci. Soc. Am. J.
Cited by (55)
A multi-scale assessment of the impact of salinity on the desorption of chromate from hematite: Sea level rise implications
2024, Journal of Hazardous MaterialsCharacteristics of iron (hydr)oxides and Cr(VI) retention mechanisms in soils from tropical and subtropical areas of China
2024, Journal of Hazardous MaterialsMigration and transformation pathways of Cr(Ⅵ) in ferrihydrite-humic acid-Cr(Ⅵ) coprecipitation induced by Shewanella putrefaciens: Combination of adsorption and reduction
2024, Colloids and Surfaces A: Physicochemical and Engineering AspectsApplication of community data to surface complexation modeling framework development: Iron oxide protolysis
2023, Journal of Colloid and Interface Science