Adsorption Of Sulfate And Phosphate At The Mineral Water Interface

The transport and bioavailability of sulfate and phosphate are significantly affected by adsorption reactions with soil minerals. Elucidating the adsorption mechanisms and kinetics is critical to improving surface complexation models, which are used to simulate the reactive transport of nutrients in soils. The objective of this investigation was to utilize computational DFT methods to improve our understanding of sulfate and phosphate adsorption at the mineral-water interface. The effect of dehydration on sulfate adsorption at the hematite-water interface was investigated, using ATR-FTIR spectroscopy and DFT calculations. The DFT calculations were performed with edge-sharing dioctahedral Fe(III) cluster models of sulfate and bisulfate complexes. The DFT calculations suggested that sulfate formed a monodentate or bidentate bridging complex under hydrated conditions, but that bisulfate formed under dehydrated conditions (i.e., speciation change). A QMD simulation of monodentate bisulfate at the (101) goethite-water interface, however, suggested that a speciation change is probably reversible. The energies of sulfate adsorption pathways on edge-sharing dioctahedral Al(III) and Fe(III) cluster models were estimated with DFT calculations. The DFT-calculated adsorption energies were directly related to the proton/sulfate stoichiometry and the overall charge of the Al(III) and Fe(III) clusters. DFT-calculated adsorption energies for bidentate bridging and monodentate sulfate on a +1 charged Fe(III) cluster agreed reasonably well with experimental measurements of sulfate adsorption on goethite. The binding geometries of bidentate bridging and monodentate sulfate complexes at the Fe-(hydr)oxide-water interface were investigated, using cluster and periodic slab DFT calculations. The DFT cluster calculations were performed with edge-sharing dioctahedral Fe(III) models. The periodic DFT calculations were performed with a slab model of the (100) goethite surface. The cluster model predictions of the interatomic distances and angles of monodentate and bidentate bridging sulfate were in good agreement with the periodic slab model predictions. QMD simulations were performed to better understand the dynamical behavior of sulfate and phosphate complexes at the (101) goethite-water interface. The H-bonding interactions of sulfate and phosphate with goethite surface OH functional groups and with solvent water molecules were investigated. To explain why phosphate is a stronger competitor than sulfate for goethite surface sites, a proton-assisted ligand exchange mechanism was proposed.

The biogeochemical cycling of iron and manganese involves the reductive dissolution and oxidative precipitation of Fe(III) and Mn(IV/III) oxides. Biogenic Fe(III) and Mn(IV/III) oxides are often characterized by high surface areas and therefore high sorptive capacities. As a result, these minerals can substantially alter the chemistry of natural waters and the availability of micronutrients in soils and sediments by scavenging trace metals. Recent research indicates that the adsorption of aqueous Fe(II) onto Fe(III) oxides involves oxidative adsorption, electron transfer, and subsequent reductive dissolution at another surface site [a process collectively referred to as 'electron transfer-atom exchange' (ET-AE)]. Aqueous Mn(II) adsorption onto Mn(IV/III) oxides likely also involves oxidation, but because of the potential for Mn(II) Mn(IV) comproportionation reactions and the accessibility of nearly all atoms in Mn(IV/III) oxide sheets to reaction with aqueous solution, aqueous Mn(II)-solid Mn(IV/III) interactions are expected to differ substantially from the analogous Fe system. These complex interactions between reduced and oxidized forms of Fe (and Mn) occur at redox interfaces and can exert substantial effects on trace metal fate. These processes may, in turn, be affected by ions common in natural systems. The main objective of this dissertation is to determine how interactions between ions commonly present during biogeochemical Fe or Mn cycling in natural systems [e.g., phosphate, sulfate, Ni, Zn, Fe(II), or Mn(II)] alter one another's interactions with Fe and Mn oxide surfaces. This research specifically seeks to (1) identify the mechanisms through which the oxoanions phosphate and sulfate alter Fe(II) adsorption onto Fe oxides; (2) determine how oxoanion-Fe(II) interactions alter trace metal partitioning between the mineral surface, bulk mineral structure, and aqueous phase; (3) characterize the effect of Mn(II) on phyllomanganate sheet structures; and (4) examine the effect of Mn(II) on trace metal sorption on phyllomanganates. Macroscopic adsorption edges show that Fe(II) cooperatively co-adsorbs with sulfate and phosphate on Fe(III) oxide surfaces. Both attenuated total reflectance Fourier transform infrared spectroscopy and surface complexation modeling indicate that this cooperative adsorption behavior arises from a combination of ternary complexation and electrostatic interactions. The formation Fe(II)-oxoanion ternary complexes suggests that processes associated with Fe(II) Fe(III) ET-AE reactions may be altered in the presence of oxoanions, depending on the stability and identity of the ternary complex that forms. The effect of these oxoanions on one such process, trace metal repartitioning, was investigated in detail. Sulfate and, to a larger degree, phosphate suppress Ni cycling through hematite during Fe(II)-catalyzed recrystallization by altering Ni adsorption, structural incorporation, and release back into solution. Conversely, Ni cycling through goethite is unaffected or enhanced by phosphate and sulfate. This dissertation also investigated Mn(II) effects on phyllomanganate structure and the fate of associated trace metals. Powder X-ray diffraction and X-ray absorption fine structure spectroscopic measurements indicate that Mn(II) causes distortion of the sheet structure of Mn(IV/III) oxides and alters sheet stacking at low pH, but has a minimal effect on phyllomanganate structures at circumneutral pH. As a result, Ni and Zn adsorption mechanisms on phyllomanganates are altered in the presence of aqueous Mn(II) at pH 4, but exhibit few changes at pH 7. The Ni and Zn adsorption behaviors with aqueous Mn(II) suggests that Mn(II) alters phyllomanganate reactivities by decreasing phyllomanganate vacancy content. These results emphasize the importance of understanding adsorbate interactions in systems with coexisting reduced and oxidized Fe or Mn, as under such conditions Fe and Mn oxide minerals undergo dynamic structural transformations. Trace metal uptake and partitioning between Fe oxide surfaces can be altered in systems with appreciable amounts of phosphate or sulfate (e.g., riparian zones, estuaries, or marine sediments). The complex interactions at iron oxide surfaces must be considered when evaluating trace metal fate at redox interfaces or interpreting trace metal proxies in the rock record to reconstruct ancient water compositions. The Mn(II)-induced phyllomanganate structural changes observed here suggest a relationship between water composition and the reactivity of Mn oxides as adsorbent materials. The identified phyllomanganate restructuring may also modify the capacity of Mn oxides to serve as oxidants of inorganic and organic compounds in aquatic systems. This dissertation highlights the complex structural and chemical processes that occur via cooperative and competitive interactions of ion at iron and manganese oxide surfaces.

This book introduces the latest research regarding the adsorption of heavy metals, toxic ions, and organic compounds at the interfaces of water/minerals, such as mineralogical characterizations, surface chemistry, and modification of natural minerals as adsorbents, as well as the adsorption of cations, anions, and organic compounds in water. Presenting findings by the authors and their co-workers, the book helps readers grasp the principals and benefits of using minerals for water treatment, as well as the advanced technologies in the area developed over last 30 years, especially the last 10 years.

Electronic reproduction.

Volume 23 of Reviews in Mineralogy and accompanying MSA short course covers chemical reactions that take place at mineral-water interfaces. We believe that this book describes most of the important concepts and contributions that have driven mineral-water interface geochemistry to its present state. We begin in Chapter 1 with examples of the global importance of mineral-water interface reactions and a brief review of the contents of the entire book. Thereafter, we have divided the book into four sections, including atomistic approaches (Chapters 2- 3), adsorption (Chapters 4-8), precipitation and dissolution (Chapters 9-11), and oxidation-reduction reactions (Chapters 11-14).

Reagents in Mineral Technology provides comprehensive coverage of both basic as well asapplied aspects of reagents utilized in the minerals industry.This outstanding, single-source reference opens with an explicit account of flotation fundamentals,including coverage of wetting phenomena, mineral/water interfacial phenomena, flo tationchemistry, and flocculation and dispersion of mineral suspensions.It then discusses flotation of sulfide and nonsulfide minerals, with attention to formation ofclithiolates, formation of metal thiol compounds, application of fatty acids, sulfosuccinic acids,amines, and other collectors.Reagents in Mineral Technology also reviews adsorption of surfactants on minerals .. .details adsorption of polymers .. . and considers the chemistry and application of chelation agentsin minerals separations.Additional chapters consider grinding aids, frothers, inorganic and polymeric depressants,dewatering and filtering aids, analytical techniques, and much more.Unique in its depth of coverage, Reagents in Mineral Technology will prove an invaluablereference for mineral engineers and processors; analytical, surface, colloid, and physical chemists;petroleum, petrochemical, metallurgical, and mining engineers; and for use in advancedundergraduate- and graduate-level courses in these and related fields.

Clearly explains how to more effectively decipher and predict contaminant fate in the environment by combining kinetic methods and molecular-scale spectroscopic and microscopic techniques to analyze mineral/water interfacial reactions in situ. The book begins with a broad overview, then continues with three sections written by internationally known expert. The first deals specifically with spectroscopic/microscopic techniques that can be used in combination with macroscopic approaches to glean mechanistic information on mineral/water reactions and processes. The second section emphasizes computer models that are used to elucidate surface mediated reaction mechanisms. The remainder of the volume is organized around reaction type, including sorption/desorption of inorganic species, sorption/desorption of organic species, precipitation/dissolution processes, heterogeneous electron transfer reactions, photochemically driven reactions, and microbially mediated reactions. Mineral-Water Interfacial Reactions will be a valuable resource for environmental scientists, geochemists, soil chemists, microbiologists, and marine engineers who need to be familiar with the most current and effective methods for testing and controlling the mobility, speciation, and bioavailability of contaminants in the environment.

Over the past 20 years, synchrotron-based research applications have provided important insight into the geochemical cycling of ions and the chemical and crystallographic properties of minerals in soils and sediments. Of particular significance is the understanding of local coordination environments with the use of X-ray absorption spectroscopy. The high flux and brightness of the X-ray beams have allowed researchers to work at environmentally relevant concentrations. The use of focusing mirrors and apertures which allow for mapping and trace particle surfaces, microbes, roots, channels and elements at the micron and at a nano-meter scale in 2 and 3D have also been a great enhancement to science. This book provides the most up-to-date information on synchrotron-based research applications in the field of soil, sediment and earth sciences. Invited authors provide chapters on a wide range of research topics including multiphase flow and transport processes (physical aspects), rhizosphere and microbial life (biological aspects), and dynamics of C, N, S, P and heavy metals and metalloids (chemical aspects). In addition, perspectives on the impact of synchrotron based applications, particularly X-ray absorption spectroscopy, and the role of synchrotron applications in remediation, regulatory, and decision making processes are considered. Up-to-date, with the latest research results and techniques in synchrotron-based techniques Information on specific techniques, elements and minerals, regulatory and remediation decision making, contaminants and the impact of X-ray absorption spectroscopy on soil science Internationally recognized leaders in their fields of expertise from Europe, North America, Asia and Australia