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Abstract Soil is a heterogeneous porous media that is comprised of a variety of organo-mineral aggregates. Sorption of heavy metals onto these composite solids is a key process that controls heavy metal mobility and fate in the natural environment. Pollution from a combination of heavy metals is common in soil, therefore, understanding the competitive binding behavior of metal ions to organo-mineral composites is important in order to predict metal mobility and fate. In this study, batch experiments were paired with spectroscopic studies to probe the sorption characteristics of ternary Cd Ni Cu sorbates to a binary organo-goethite composite made with Bacillus cereus cells. Scanning electron microscopy shows that goethite nano-sized crystals are closely associated with the bacterial surfaces. Sorption experiments show a larger adsorptivity and affinity for Cu than Cd/Ni on goethite and B. cereus, and the goethite– B. cereus composite. X-ray photoelectron spectroscopy reveals that carboxylate and phosphate functional moieties present on the bacterial cell walls are primarily responsible for metal sorption to the goethite– B. cereus composite. Synchrotron-based X-ray fluorescence shows that Cu and Ni are predominately associated with the bacterial fraction of the goethite– B. cereus composite, whereas Cd is mainly associated with the goethite fraction. The findings of this research have important implications for predicting the mobility and fate of heavy metals in soil multi-component systems. Graphical abstract Image 1 Highlights • Larger adsorptivity & affinity for Cu than Cd and Ni on goethite-bacteria composite. • Competitive sorption among Cu, Cd and Ni is weaker on composite than on goethite. • Cu and Ni are mainly bound to the bacterial fraction of the binary composite. • Cd is sorbed mainly on the goethite fraction of the binary composite. Cd, Ni and Cu ions compete for similar binding sites on the end-member goethite and B. cereus , but due to different binding affinities, Cu and Ni are mainly bound to the bacterial fraction whereas Cd is predominately sorbed on the goethite fraction of the binary bacteria–mineral composite. [ABSTRACT FROM AUTHOR]

Organo-mineral composites formed by the association of iron (hydr)oxides and organic matter are widespread in natural environments and play an important role as scavengers of bioessential elements and contaminants. To better understand the mobility and fate of Cu in natural soils and sediments we precipitated ferrihydrite and goethite organo-mineral composites using humic acid as an analogue for natural organic matter, with organic carbon content in the composites ranging from 2 to 16 wt% C. We then measured the adsorption of Cu to the end-member mineral and organic phases and the composites as a function of pH and Cu concentration. We determined the molecular mechanisms of Cu adsorption to the end-member phases and the composites, and used this information to develop molecularly constrained thermodynamic surface complexation models to quantify Cu adsorption. By combining our work here with previous work on the adsorption of Cu to ferrihydrite-bacteria composites, we provide insight into the predominance of Cu-carboxyl binding for Cu adsorption to iron (hydr)oxide organo-mineral composites, and the nature of Cu adsorption behaviour across a range of iron (hydr)oxide composites composed of different minerals and different types of organic matter. Taken as a whole our results show that Cu adsorption to the carboxyl group present in organic matter coatings on iron (hydr)oxides is likely common to most iron (hydr)oxide composites, such that Cu-carboxyl binding provides a key control on the fate and mobility of Cu in soils and sediments. Our work also suggests there is a universal adsorption behaviour for Cu adsorption to ferrihydrite organo-mineral composites, in which the mineral:organic mass ratio is a crucial parameter for determining Cu uptake. Overall we show that ferrihydrite composites composed of different types of organic matter and containing a wide range of organic mass ratios, but where the mineral is the dominant composite fraction, possess additive Cu adsorption behaviour which can be predicted using a component additivity surface complexation model. [ABSTRACT FROM AUTHOR]

We measured the adsorption of Cu(II) onto goethite (α-FeOOH), hematite (α-Fe2O3) and lepidocrocite (γ-FeOOH) from pH 2–7. EXAFS spectra show that Cu(II) adsorbs as (CuO4Hn)n-6 and binuclear (Cu2O6Hn)n-8 complexes. These form inner-sphere complexes with the iron (hydr)oxide surfaces by corner-sharing with two or three edge-sharing Fe(O,OH)6 polyhedra. Our interpretation of the EXAFS data is supported by ab initio (density functional theory) geometries of analogue Fe2(OH)2(H2O)8Cu(OH)4and Fe3(OH)4(H2O)10Cu2(OH)6 clusters. We find no evidence for surface complexes resulting from either monodentate corner-sharing or bidentate edge-sharing between (CuO4Hn)n-6 and Fe(O,OH)6 polyhedra. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed even though we are supersaturated with respect to CuO and Cu(OH)2. Having identified the bidentate (&z.tbnd6;FeOH)2Cu(OH)20 and tridentate (&z.tbnd6;Fe3O(OH)2)Cu2(OH)30 surface complexes, we are able to fit the experimental copper(II) adsorption data to the reactions and The two stability constants are similar for the three iron (hydr)oxide phases investigated. [Copyright &y& Elsevier]

The adsorption of extracellular polymeric substances (EPS) onto soil minerals is an important process for understanding bacterial adhesion to mineral surfaces and environmental cycling of nutrients and contaminants. To clarify the molecular level mechanisms and processes of EPS adsorption, the interaction mechanisms between EPS and goethite was explored using two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (CoS) assisted by C 1s near edge X-ray absorption fine structure spectroscopy (NEXAFS). Results show that the amide functional groups of EPS play an important role in its adsorption on goethite, and the adsorption of EPS-proteins on goethite is a function of electrolyte concentration, with increasing adsorption at a higher electrolyte concentration. Results also show that the order in which the EPS functional groups interact and bind with goethite is dependent on electrolyte concentration, where carboxyl and phosphoryl functional groups are the first to adsorb at low electrolyte concentration, while amide groups are the first to adsorb at higher electrolyte concentration. Deconvolution and curve fitting of the amide I band at the end of the adsorption process (~300 min) shows that the secondary structure of proteins is converted from a random coil conformation to aggregated strands, α-helices and turns. This conversion leads to increased adsorption of EPS-proteins and explains the overall adsorption increase of EPS on goethite surfaces with an increasing concentration of electrolyte. Furthermore, the adsorption of the carboxyl functional groups of EPS decreases with increasing electrolyte concentration, likely due to more effective screening of the goethite surface charge with increasing concentration of electrolyte. The integrated results from ATR-FTIR and 2D-CoS allow us to construct a comprehensive overview of EPS-goethite interaction processes at the molecular level, which can be used to improve our understanding of EPS-mineral interactions in the natural environment. These results also provide fundamental information for a better understanding of bacterial biofilm formation on soil and sediment minerals, and facilitate research on the subsequent interaction of nutrients and contaminants with the reactive constituents of biofilms in natural and contaminated environments. [ABSTRACT FROM AUTHOR]

Marine ferromanganese crusts and nodules are highly enriched in transition metals such as Ni and Co, yet the crystal chemistry and mode of incorporation of these metals is poorly known. We characterized the crystal chemistry of Ni in two hydrogenetic Pacific ocean ferromanganese crust samples and a hydrogenetic nodule from the Madeira abyssal plain. Energy dispersive spectrometry shows that Ni is associated with the manganese oxide phases, in agreement with previous work. X-ray diffraction patterns show that the dominant Mn3+/4+ oxide is a phyllomanganate similar to hexagonal birnessite or δ-MnO2. Extended X-ray absorption fine-structure spectroscopy shows that the coordination environment of Ni results from structural incorporation into the phyllomanganate phase by replacement of Mn3+/4+. In contrast, Ni initially sorbs to freshly prepared synthetic birnessite by surface complexation over vacancy sites in the MnO2 layer. We propose that the transformation of Ni sorption from surface complexation to structural incorporation provides a potentially irreversible sink for Ni in seawater. [ABSTRACT FROM AUTHOR]

Strontium is an important contaminant radionuclide at many former nuclear sites. This paper investigates the effect of changing pH and ionic strength on the sorption of Sr to a range of common soil minerals. Specifically it focuses on the sorption of Sr onto illite, chlorite, goethite, and a mixed sediment. The interplay between ionic strength and pH was determined by varying the background ionic strength of the system using both NaCl (for a constant pH) and NaOH (to also vary pH). Under conditions of moderate pH, Sr sorption decreased with increasing ionic strength, due to competition between the Na and Sr atoms for the outer-sphere complexes. However, where increasing ionic strength was accompanied by increasing pH, Sr sorption remained high. This suggested that Sr was sorbed to the minerals without competition from background Na ions. Extended X-ray absorption fine structure (EXAFS) spectra confirmed that at highly alkaline pH (>12.5) Sr was forming inner-sphere complexes on the surfaces of all minerals. This specific adsorption of the Sr (as SrOH+) explains why it was still adsorbed to the minerals under very high ionic strength conditions and was not out-competed by Na. [ABSTRACT FROM AUTHOR]

Deep-sea REY (lanthanides and yttrium) can be initially scavenged by nano ferromanganese (oxyhydr)oxides via ion adsorption and lattice substitution, while subsequent aging and partial recrystallization induced by reduction during diagenesis usually cause release and redistribution of REY. Previous studies find positive correlations among REY, goethite (α-FeOOH) and phosphorus/phosphate in some marine (micro)nodules, but the mechanism responsible for these correlations is yet unclear. The interaction between iron oxyhydroxides and metal oxyanions has been studied extensively, but no study focuses on interactions between iron oxyhydroxides, REY, and phosphate. This study investigates the immobilization and release mechanisms of REY by synthetic goethite at macro- and molecular scales by comprehensive usage of ad/desorption experiments, inductively coupled plasma mass spectrometry, X-ray absorption fine structure (XAFS) spectroscopy, and density functional theory calculations. The results indicate that goethite exhibits an adsorption preference for heavy REY, displaying obvious lanthanide tetrad effects. Phosphate (0.02 mM ≤ C P ≤ 0.2 mM) however, greatly enhances REY adsorption by forming ternary complexes, particularly light REY. EXAFS interpretations further confirm the formation of ternary complexes in La-adsorbed samples, and that phosphate can link trivalent REY and goethite on the surface. Moreover, some CeIII is further oxidized to CeIV with the help of dissolved oxygen. These observations illuminate how phosphate contributes to rare earth enrichment during early diagenesis. As goethite recrystallization is common in hypoxic environment, we further monitored REY behavior during recrystallization and find that previously adsorbed La/Ce and phosphate are released and combined to form LaPO 4 /CePO 4 precipitates. Importantly, the CeIV reduced during recrystallization indicates that the positive Ce anomaly is likely to pass down, potentially explaining why a positive Ce anomaly is observed in diagenetic nodules and apatite at lower depth. Our study provides insights into the role of phosphate in REY-adsorption on goethite and possible mechanisms of REY enrichment, and desorption during early diagenesis, corresponding with REY patterns observed in marine iron oxyhydroxides. [Display omitted] • Adsorption of ΣREY on goethite reaches up to ∼3000 ppm with the help of phosphate. • Goethite contributes to positive Ce anomaly by CeIII oxidized on its surface by DO. • Goethite recrystallization causes REY redistribution and Ce reduction in sediment. [ABSTRACT FROM AUTHOR]

The outer membrane c-type cytochromes (c-Cyts) OmcA and MtrC in Shewanella are key terminal reductases that bind and transfer electrons directly to iron (hydr)oxides. Although the amounts of OmcA and MtrC at the cell surface and their molecular structures are largely comparable, MtrC is known to play a more important role in dissimilatory iron reduction. To explore the roles of these outer membrane c-Cyts in the interaction of Shewanella oneidensis MR-1 with iron oxides, the processes of attachment of S. oneidensis MR-1 wild type and c-type cytochromedeficient mutants (the omcA, mtrC, and omcA mtrC mutants) to goethite are compared via quartz crystal microbalance with dissipation monitoring (QCM-D). Strains with OmcA exhibit a rapid initial attachment. The quantitative model for QCM-D responses reveals that MtrC enhances the contact area and contact elasticity of cells with goethite by more than one and two times, respectively. In situ attenuated total reflectance Fourier transform infrared two-dimensional correlation spectroscopic (ATR-FTIR 2D-CoS) analysis shows that MtrC promotes the initial interfacial reaction via an inner-sphere coordination. Atomic force microscopy (AFM) analysis demonstrates that OmcA enhances the attractive force between cells and goethite by about 60%. As a result, OmcA contributes to a higher attractive force with goethite and induces a rapid short-term attachment, while MtrC is more important in the longer-term interaction through an enhanced contact area, which promotes interfacial reactions. These results reveal that c-Cyts OmcA and MtrC adopt different mechanisms for enhancing the attachment of S. oneidensis MR-1 cells to goethite. It improves our understanding of the function of outer membrane c-Cyts and the influence of cell surface macromolecules in cell-mineral interactions. [ABSTRACT FROM AUTHOR]