It is known that PO4 is retained by soils through ligand exchange, i.e., inner sphere complexation, but the mechanism for SO4 adsorption at the mineral‐water interface has been in debate. By studying the effects of ionic strength on ion adsorption, it is possible to distinguish between inner and outer sphere ion surface complexes. This study was conducted to evaluate ionic strength effects on SO4 and PO4 adsorption on γ‐Al2O3 and kaolinite at varying solution pH (3–11), and to infer SO4 and PO4 adsorption mechanisms at the mineral‐water interface. The adsorption of SO4 on γ‐Al2O3 and kaolinite decreased monotonically with increasing solution pH and was markedly reduced by increasing the concentration of background electrolyte. On the other hand, PO4 adsorption on γ‐Al2O3 and kaolinite increased from pH 3 to 4 and decreased from pH 6 to 11, with an adsorption plateau between pH 4 and 6. Effects of change in ionic strength on PO4 adsorption varied with pH. At low pH, PO4 adsorption demonstrated a slight decrease with increasing ionic strength, whereas at high pH, PO4 adsorption increased slightly with increasing ionic strength, resulting in a crossover point where there was no ionic strength effect. The triple‐layer model (TLM) was applied to model the adsorption of SO4 and PO4 with both inner and outer sphere complexes using the FITEQL 3.1 computer program. Sulfate adsorption was better modeled by assuming outer sphere complex formation, while PO4 adsorption was better modeled by assuming inner sphere complex formation.

Complexation by microbially produced exopolymers may significantly impact the environmental mobility and toxicity of metals. This study focused on the conformational structure of the bacterial exopolymer, γ-D-poly(glutamic acid) and its interactions with U(VI) examined using ATR-FTIR spectroscopy. Solution pH, polymer concentration, and ionic strength affected the conformation of the exopolymer, and U(VI) binding was monitored. At low pH, low concentration, or low ionic strength, this exopolymer exists in an R-helical conformation, while at high pH, concentration, or ionic strength the exopolymer exhibits a β-sheet structure. The change in exopolymer conformation is likely to influence the number and nature of exposed surface functional groups, sites most responsible for metal complexation. We found the polyglutamate capsule binds U(VI) in a binuclear, bidentate fashion; in contrast the glutamate monomer forms a mononuclear, bidentate complex with U(VI). The apparent polynuclear binding of U(VI) may induce β-sheet structure formation provided the U(VI) concentration is sufficiently high.

Spores of marine Bacillus sp. strain SG-1 are capable of oxidizing Mn(II) and Co(II), which results in the precipitation of Mn(III, IV) and Co(III) oxides and hydroxides on the spore surface. The spores also bind other heavy metals; however, little is known about the mechanism and capacity of this metal binding. In this study the characteristics of the spore surface and Cu(II) adsorption to this surface were investigated. The specific surface area of wet SG-1 spores was 74.7 m2 per g of dry weight as measured by the methylene blue adsorption method. This surface area is 11-fold greater than the surface area of dried spores, as determined with an N2 adsorption surface area analyzer or as calculated from the spore dimensions, suggesting that the spore surface is porous. The surface exchange capacity as measured by the proton exchange method was found to be 30.6 μmol m−2, which is equal to a surface site density of 18.3 sites nm−2. The SG-1 spore surface charge characteristics were obtained from acid-base titration data. The surface charge density varied with pH, and the zero point of charge was pH 4.5. The titration curves suggest that the spore surface is dominated by negatively charged sites that are largely carboxylate groups but also phosphate groups. Copper adsorption by SG-1 spores was rapid and complete within minutes. The spores exhibited a high affinity for Cu(II). The amounts of copper adsorbed increased from negligible at pH 3 to maximum levels at pH >6. Their great surface area, site density, and affinity give SG-1 spores a high capability for binding metals on their surfaces, as demonstrated by our experiments with Cu(II).

The oxidation of iron(II) and manganese(II) usually leads to the formation of insoluble metal oxides, hydroxides, and oxyhydroxides which are of wide-ranging environmental importance. Microorganisms catalyze the oxidation of Fe(II) and Mn(II), however, the mechanisms of metal oxidation, particularly in the case of Mn(II) oxidation, and the effect microorganisms have on the properties of the solid phases, are not well known. The state of knowledge concerning Fe and Mn biomineralization is briefly reviewed. Considerable progress has been made in recent years in understanding the mechanisms and products of Μn(II) oxidation by bacteria. Results obtained using classical and modern approaches, including biochemical, molecular biological, mineralogical and stable oxygen isotopes have provided new insights into bacterial Μn(II) oxidation.Iron (Fe) and manganese (Mn) oxides (a collective term meant here to include oxides, hydroxides, and oxyhydroxides) are recognized as reactive mineral components in soils, sediments, and aquatic systems. They adsorb a variety of ions and participate in oxidation and reduction reactions with inorganic and organic species and compounds. Microorganisms, especially bacteria, are known to participate in Fe and Mn mineralization processes, however, the importance of these "iron bacteria" and "manganese bacteria" in environmental processes is often overlooked. In addition, because of the difficulty in working with many of these organisms (many of them have never been cultured or some grow only very slowly in culture) and the complex chemistry of Fe and Mn, there is a lack of knowledge concerning the physiology and biochemistry of these microbes. Recently, new insights into bacterial Mn(II) oxidation have been realized through modern approaches using molecular biological and stable isotopic methods. This paper presents general background information on Fe and Mn chemistry and microbiology and a more detailed focused description of recent results concerning a model Mn(II)-oxidizing bacterium, the marine Bacillus sp. strain SG-1.

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