Precipitation Of Mn Research Articles

Minor and trace element export from a glacierized Alpine headwater catchment (Haut Glacier d'Arolla, Switzerland)

AbstractMajor ion concentrations in meltwaters draining glacial environments have been widely reported. However, concentrations of minor and trace elements have received scant attention. This study presents trace and minor element variations in bulk meltwaters draining Haut Glacier d'Arolla (Switzerland) based on twice‐daily sampling throughout the 1999 ablation season, which represents the most detailed meltwater quality dataset to date. In order to assess the mode of export from the catchment, these elements are partitioned into (i) ‘dissolved’ and (ii) ‘particulate‐associated’ minor and trace element components.A computer‐based speciation model (PHREEQCi) was applied to the bulk meltwater data, suggesting that Ba, Be, Cd, Cu, Li, Rb and Sr exist primarily as mobile monovalent or divalent dissolved cations, which may be involved in interactions with suspended sediment surfaces. Conversely, the model predicts the precipitation of Fe, Al, Mn and Cr (oxi)hydroxides, suggesting these species may be predominantly transported as colloids, which may remove other minor and trace elements from solution by co‐precipitation reactions.Laboratory leaching experiments on suspended sediments and fresh rock powder suggests that minor and trace element concentrations may also be influenced by (oxy)hydroxide precipitation and adsorption–desorption reactions with suspended sediment surfaces. The quantity and transport mode of trace and minor elements may influence their bioavailability downstream of glacierized headwater catchments. Further, the enrichment of many dissolved minor and trace elements in meltwaters compared with world stream‐waters, coupled with the timing of water and sediment delivery during the summer months, may have implications for downstream aquatic environments. Copyright © 2001 John Wiley & Sons, Ltd.

Monitoring the precipitation reactions in a cold-rolled Al–Mn–Mg–Cu alloy using thermoelectric power and electrical resistivity measurements

The aim of the present paper is to monitor multiple precipitation reactions in a normal Al alloy AA 3104 and a Mg- and Cu-rich alloy 3104 during isothermal annealing. Special emphasis is placed on the influence of dislocations on the precipitation kinetics and therefore different cold-rolling reductions are applied prior to the annealing treatment. Using both thermoelectric power (TEP) and electrical resistivity measurements it is possible to split concurrent and sequential precipitation reactions and to reduce the uncertainty about the actual precipitation reactions taking place. It is found that Al 2 CuMg precipitates form at low annealing temperatures, irrespective of the extent of pre-deformation. During annealing at temperatures from 350°C and higher, precipitation of Mn-containing dispersoids is determined as the only process occurring. The rate of this precipitation process is strongly influenced by the degree of cold work prior to the heat treatment. The qualitative information derived from the combined TEP and electrical resistivity experiments is supported by transmission electron microscopy observations. It is also possible to calculate the weight fractions of the elements precipitated semiquantitatively. These calculated fractions are compared with equilibrium thermodynamic data and show good agreement for the precipitation of Al 2 MgCu and the precipitation of Mn at temperatures up to 400 C.

Monitoring the precipitation reactions in a cold-rolled Al–Mn–Mg–Cu alloy using thermoelectric power and electrical resistivity measurements

Abstract The aim of the present paper is to monitor multiple precipitation reactions in a normal Al alloy AA 3104 and a Mg- and Cu-rich alloy 3104 during isothermal annealing. Special emphasis is placed on the influence of dislocations on the precipitation kinetics and therefore different cold-rolling reductions are applied prior to the annealing treatment. Using both thermoelectric power (TEP) and electrical resistivity measurements it is possible to split concurrent and sequential precipitation reactions and to reduce the uncertainty about the actual precipitation reactions taking place. It is found that Al2CuMg precipitates form at low annealing temperatures, irrespective of the extent of pre-deformation. During annealing at temperatures from 350°C and higher, precipitation of Mn-containing dispersoids is determined as the only process occurring. The rate of this precipitation process is strongly influenced by the degree of cold work prior to the heat treatment. The qualitative information derived from the combined TEP and electrical resistivity experiments is supported by transmission electron microscopy observations. It is also possible to calculate the weight fractions of the elements precipitated semiquantitatively. These calculated fractions are compared with equilibrium thermodynamic data and show good agreement for the precipitation of Al2MgCu and the precipitation of Mn at temperatures up to 400°C.

Late Paleoproterozoic Mn-rich oncoids: Earliest evidence for microbially mediated Mn precipitation

Research Article| September 01, 2001 Late Paleoproterozoic Mn-rich oncoids: Earliest evidence for microbially mediated Mn precipitation Markus O. Schaefer; Markus O. Schaefer 1Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park 2006, South Africa Search for other works by this author on: GSW Google Scholar Jens Gutzmer; Jens Gutzmer 1Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park 2006, South Africa Search for other works by this author on: GSW Google Scholar Nicolas J. Beukes Nicolas J. Beukes 1Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park 2006, South Africa Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (9): 835–838. https://doi.org/10.1130/0091-7613(2001)029<0835:LPMROE>2.0.CO;2 Article history received: 06 Dec 2000 rev-recd: 07 May 2001 accepted: 21 May 2001 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Markus O. Schaefer, Jens Gutzmer, Nicolas J. Beukes; Late Paleoproterozoic Mn-rich oncoids: Earliest evidence for microbially mediated Mn precipitation. Geology 2001;; 29 (9): 835–838. doi: https://doi.org/10.1130/0091-7613(2001)029<0835:LPMROE>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Well-preserved Mn-rich oncoids are described from late Paleoproterozoic (ca. 1.9 Ga) shallow-water manganese ores at the Bronkhorstfontein deposit in the Northern Province of South Africa. A close examination reveals obvious similarities of these ancient oncoids to modern biogenic oncoids in terms of internal structure and porosity. The occurrence of Mn in the oncoids suggests that Mn precipitation was biogenically controlled, providing the earliest textural evidence for microbially mediated Mn precipitation in the geologic record. The late Paleoproterozoic appearance of Mn-rich oncoids is not restricted to the occurrence described, but has been noted in at least three other sedimentary successions. Their appearance coincides with the formation of the first shallow-water Mn deposits, and the corresponding demise of deep-water Mn formations. This change in Mn metallogenesis is tentatively attributed to the depletion of the primary deep-ocean Mn reservoir in the late Paleoproterozoic. This environmental pressure may have forced Mn-oxidizing microorganisms to adapt to the shallow sedimentary environment that was more proximal to the Mn supply from continental runoff. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Magnetic Properties of Fe- and Mn-Implanted SiC

under conditions that avoided amor-phization ~substrate temperature ;350°C!. After annealing at 700°C, the magnetic properties of the samples were examined bysuperconducting quantum interference device magnetometry. Both the Fe- and Mn-implanted samples showed ferromagneticproperties up to approximately 250 K for the highest doses employed. The origin of the ferromagnetism is not the formation ofsecondary phases involving precipitation of Fe or Mn.© 2001 The Electrochemical Society. @DOI: 10.1149/1.1414945# All rights reserved.Manuscript submitted June 14, 2001; revised manuscript received August 24, 2001. Available electronically October 15, 2001.

Low temperature synthesis of γ-LixMnO2 powders in ethylene glycol

The reaction of Electrolytic Manganese Dioxide (EMD γ-MnO2) with anhydrous LiOH in ethylene glycol (EG) was studied. It was found that this reaction proceeds in three steps while the reaction temperature increases: (1) chemical insertion of lithium in γ-MnO2 structure leading to γ-LixMnO2 phase, (2) progressive dissolution of this reduced phase and (3) precipitation of a Li-free organo-metallic compound Mn(OCH2CH2O) with lamellar structure (Mn-EG). If the reaction is performed at moderate temperature (T<120°C), we can limit the dissolution reaction and completely avoid the precipitation of the organo-metallic phase. The x value in the resulting LixMnO2 phases is found to be mainly linked to the temperature of the reaction medium. Although a maximum value of x=0.35 can be obtained at 30°C, Li0.84MnO2 can be prepared at 120°C. We showed that the LixMnO2 formation mechanism consists of a direct lithium insertion in the structure of MnO2 concomitant with Mn reduction by the organic medium. By changing the medium cationic content of the medium, we were able to prepare various reduced MnO2 compositions, such as HxMnO2, (Li,H)xMnO2, (Na,H)xMnO2, (K,H)xMnO2. These LixMnO2 phases, when tested in half Li-cells, show poor cyclability but large first charge capacity (260 mAh/g for x=0.84) that takes place at significantly higher voltage than observed for electrochemically inserted EMD. This finding was related to the presence of chemically inserted protons besides lithium ions.

Design Criteria and Required Chemistry for Removing Manganese in Acid Mine Drainage Using Subsurface Flow Wetlands

Manganese (Mn) is a difficult metal to remove in acid mine drainage because of high pH requirements for oxidation of Mn to form Mn oxide precipitates. However, Mn removal can be quickened in a gravel system providing a large surface area and high pH for Mn oxidation to occur with microbiological mediation. An experiment was designed with 12 gravel bed mesocosms that were 9.8 m3 × 6.7 m3 × 0.6 m3 to determine the best design criteria for optimizing Mn removal. Treatments consisted of two Mn loading rates (1.1 and 2.7 g/m2·d) and two gravel types (limestone and river gravel) and were replicated three times. Water flowed through the experimental wetlands for 734 days. Manganese removal was more effective in limestone than in river gravel. Manganese removal was not affected by water temperature ranging from 5 to 30 °C in either rock material. Manganese removal rates ranged from 100 to 600 m/a in the limestone wetlands and 10 to 60 m/a in the river gravel wetlands. Greater pH in limestone (approximately 6.9) compared with river gravel (approximately 5.5) favored Mn oxide precipitation. Greater pH, coupled with oxidation–reduction potential (redox) values greater than 430 mV in the limestone, resulted in water chemistry near conditions predicting manganite to be the dominant Mn phase. Ideal pH and redox conditions for Mn removal are pH from 6.8 to 7.2 and redox greater than 500 mV. The range of dissolved oxygen (DO) required to remove Mn in the various wetlands ranged from 3 to 5 mg/L, with approximately one‐half of the DO loss caused by Mn hydroxide formation and one‐half ascribed to biological consumption. The influent DO should be at least 0.35 mg/L for every 1 mg/L Mn removed. Removal rates for Mn ranged from 1 to 17 g/m2·d in limestone and from 1 to 2 g/m2·d in river gravel. Limestone is the material of choice for subsurface flow wetlands for Mn removal. Removal rates and required chemistry determined in this study can be used to design subsurface flow wetlands for optimum Mn removal.

In situ characterization of Mn(II) oxidation by spores of the marine Bacillus sp. strain SG-1

Microbial oxidation of Mn(II) and subsequent precipitation of insoluble, reactive Mn(IV) oxides are primary sources of these solid phases in the environment and key controls on Mn cycling in natural waters. We have performed in situ x-ray absorption near-edge structure (XANES) spectroscopic measurements of Mn(II) oxidation by spores of the marine Bacillus sp. strain SG-1 to characterize the intermediates and products of the oxidation reactions. Mn(IV)-oxides resembling δ-MnO 2 were observed to form at a rapid rate (within 14 min of reaction onset). Mn(III) intermediates did not occur above detection limit (5 to 10% of total Mn), even though Mn(III)/(II,III) oxides (MnOOH or Mn 3O 4) should have been more stable than MnO 2 under the conditions of the experiments. These results suggest that Mn(IV) is the primary product of bacterial Mn(II) oxidation by Bacillus strain SG-1. Given that SG-1 is a good model for Mn(II)-oxidizing bacteria, these findings help to explain the predominance of Mn(IV)-oxides in aquatic environments.

Monitoring the Precipitation Reactions in a Cold Rolled Al-Mn-Mg-Cu Alloy using Thermoelectric Power and Resistivity Measurements

Precipitation processes in an industrial Al-Mn-Mg-Cu alloy have been monitored using thermoelectric power and resistivity measurements. Using both techniques it is possible to separate effects due to Mg/Cu and Mn/Fe precipitation, and to calculate the weight percentage precipitated during each process. It is found that Al 2 MgCu precipitates form at annealing temperatures below 225°C. At these temperatures a maximum of 0.25 wt% of each element precipitates. For this type of precipitation the dislocation density prior to annealing has no significant effect on the precipitation kinetics. Precipitation of Mn occurs at temperatures above 225°C and a maximum of 0.48 wt% precipitates. In contrast to Mg/Cu precipitation, the dislocation density and annealing temperature both exert a significant influence on the Mn/Fe precipitation kinetics. Only a very small amount of Mg 2 Si phase was found to precipitate. Based on the experimental evidence it is likely that Al 2 MgCu precipitation on dislocations is favored by annealing at temperatures below 300°C whilst Mn bearing precipitates form at dislocations after short annealing times at 500°C.

Toxicity of manganese to Ceriodaphnia dubia and Hyalella azteca.

Manganese is a toxic element frequently overlooked when assessing toxicity of effluents, sediments, and pore waters. Manganese can be present at toxic levels in anoxic solutions due to increased solubility under chemically reducing conditions, and it can remain at those levels for days in aerated test waters due to slow precipitation kinetics. Ceriodaphnia dubia and Hyalella azteca are freshwater organisms often used for toxicity testing and recommended for assessments of effluents and pore waters. Lethal and reproductive-inhibition concentrations of Mn were determined for C. dubia in acute 48-h tests and chronic three-brood tests using animals <24 h old and between 24 and 48 h old. Sensitivity of H. azteca to Mn was determined with 7-day-old animals in acute 96-h tests. Tests were run at three levels of water hardness to assess the amelioratory effect, which was often significant. Manganese concentrations were measured analytically at test initiation and after 96 h for calculation of toxicity and determination of Mn precipitation during the tests. Minimal amounts of Mn (</=3%) precipitated within 96 h. LC(50)s determined for H. azteca progressively increased from 3.0 to 8.6 to 13.7 mg Mn/L in soft, moderately hard, and hard waters, respectively. The tolerance of C. dubia to Mn was not significantly different between moderately hard and hard waters, but was significantly lower in soft water. Manganese sensitivity of C. dubia was not significantly different between the ages tested. Acute LC(50) values for C. dubia averaged 6. 2, 14.5 and 15.2 mg Mn/L and chronic IC(50) values averaged 3.9, 8.5 and 11.5 mg Mn/L for soft, moderately-hard and hard waters, respectively. Manganese toxicity should be considered when assessing solutions with concentrations approaching these levels.

Reduction of Mn-oxides by ferrous iron in a flow system: column experiment and reactive transport modeling

The reduction of Mn-oxide by Fe2+ was studied in column experiments, using a column filled with natural Mn-oxide coated sand. Analysis of the Mn-oxide indicated the presence of both Mn(III) and Mn(IV) in the Mn-oxide. The initial exchange capacity of the column was determined by displacement of adsorbed Ca2+ with Mg2+. Subsequently a FeCl2 solution was injected into the column causing the reduction of the Mn-oxide and the precipitation of Fe(OH)3. Finally the exchange capacity of the column containing newly formed Fe(OH)3 was determined by injection of a KBr solution. During injection of the FeCl2 solution into the column, an ion distribution pattern was observed in the effluent that suggests the formation of separate reaction fronts for Mn(III)-oxide and Mn(IV)-oxide travelling at different velocities through the column. At the proximal reaction front, Fe2+ reacts with MnO2 producing Fe(OH)3, Mn2+ and H+. The protons are transported downstream and cause the disproportionation of MnOOH at a separate reaction front. Between the two Mn reaction fronts, the dissolution and precipitation of Fe(OH)3 and Al(OH)3 act as proton buffers. Reactive transport modeling, using the code PHREEQC 2.0, was done to quantify and analyze the reaction controls and the coupling between transport and chemical processes. A model containing only mineral equilibria constraints for birnessite, manganite, gibbsite, and ferrihydrite, was able to explain the overall reaction pattern with the sequential appearance of Mn2+, Al3+, Fe3+, and Fe2+ in the column outlet solution. However, the initial breakthrough of a peak of Ca2+ and the observed pH buffering indicated that exchange processes were of importance as well. The amount of potential exchangers, such as birnessite and ferrihydrite, did vary in the course of the experiment. A model containing surface complexation coupled to varying concentrations of birnessite and ferrihydrite and a constant charge exchanger in addition to mineral equilibria provided a satisfactory description of the distribution of all solutes in time and space. However, the observed concentration profiles are more gradual than indicated by the equilibrium model. Reaction kinetics for the dissolution of MnO2 and MnOOH and dissolution of Al(OH)3 were incorporated in the model, which explained the shape of the breakthrough curves satisfactorily. The results of this study emphasize the importance of understanding the interplay between chemical reactions and transport in addition to interactions between redox, proton buffering, and adsorption processes when dealing with natural sediments. Reactive transport modeling is a powerful tool to analyze and quantify such interactions.

The character of the suspended and dissolved phases in the water cover of the flooded mine tailings at Stekenjokk, northern Sweden

Studies of the suspended and dissolved phases of the pond water, material collected from sediment traps, and surficial sediments/tailings from the flooded tailings pond at Stekenjokk have been performed. The aim was to characterise the material, to study the seasonal variations and to quantify possible resuspension of the tailings in the pond. The element concentrations in the pond at Stekenjokk seem to be largely controlled by processes controlling the precipitation and dissolution of Mn- and Fe-oxyhydroxides in both the water column and in the surficial tailings. Physiochemical processes such as weathering of silicates on the surrounding mountain slopes or dykes contributes both dissolved elements and detrital particles. The suspended phase consists of detrital silicate material as well as Fe- and Mn-oxyhydroxides. The average heavy metal concentrations are high, e.g. 0.42% Cu, 0.15% Pb and 3.1% Zn, which is probably due to sorption onto Fe- and Mn-oxyhydroxides. The suspended phase is richer in Fe, and particularly Mn, during the winter. The suspended phase resembles the material collected in sediment traps and the material in the surficial sediments. The pond water is well mixed during the ice-free season. The dissolved heavy metal concentrations are generally rather low with, e.g. maximum concentrations of 2.03 μg/l Cu, 0.23 μg/l Pb and 268 μg/l Zn during the winter. Higher dissolved concentrations are found below the ice-cover above the sediment surface during the winter, caused by diffusion of elements from the sediment–water interface up into the pond water. Most of the metals occurring in the pond are dissolved and resuspension of tailings is negligible.

Orientation relationship between Al6Mn precipitates and the Al matrix during continuous recrystallization in Al–1.3%Mn

Annealing of cold-rolled supersaturated Al–1.3 wt% Mn leads to heavy precipitation of fine particles on the as-deformed microstructure. Depending on the crystallographic orientation of the deformed matrix grains, particles with different morphologies, namely spherical, rhomboidal and plate-like, have been observed. This variation in morphology could be traced back to differences in local misorientation caused by different dislocation substructures in different matrix orientations. Microstructural investigations and selected-area diffraction (SAD) analysis in a transmission electron microscopy (TEM) study were employed to characterize the various particles and to determine their orientation relationship to the Al matrix. Independent of the particle morphology, most Mn precipitates were identified as Al6Mn; only occasionally was Al12Mn observed. Upon consideration of the various crystal symmetries, two different orientation relationships were discerned, which can be written as (110)m||(111)p, [001]m||[2¯11]pand (110)m||(111)p, [11¯2]m||[12¯1]p. These orientation relationships are discussed with respect to the existence of several low misfits of lattice spacings and compared to literature data.

Sediment content of metals before and after lake water liming

Long-term liming (1980–1991) of an acidified lake (Lake Terjevann) in the southernmost part of Norway, show an increased accumulation of Al, Fe, Mn, Cd, Cu, Ni, Zn in the sediments which clearly corresponds with the liming history. The increased precipitation of Al, Fe and Mn are ascribed to extended formation of oxyhydroxides due to increased pH after introduction of the lime. Statistically significant correlations indicate that Cu, Ni and Zn are coprecipitated with both Al and Fe oxyhydroxides while Cd is coprecipitated primarily with Fe oxyhydroxides both previous to and after lake water liming.

Preparation and characterization of nanosize Mn–Zn ferrite

Synthesis of nanosize (9–12 nm) Mn 0.65Zn 0.35Fe 2O 4 particles from metal chloride solution through a hydrothermal precipitation route using aqueous ammonia, and their characterization by XRD, TEM and VSM are reported. Chloride ion concentration in the solution and the pH of precipitation are shown to play a crucial role in retaining the initial stoichiometry of the solution in the nanoparticles. While at lower pH, precipitation of Mn was incomplete, higher pH of precipitation led to Zn loss in the particles. The optimum pH for stoichiometric precipitation was found to lie around 10. The coercive force, H c and the transition temperature, T c (from ferrimagnetic to paramagnetic state) were high as compared to reported bulk values and confirm the nanosize nature of the particles. The M versus T curve, instead of showing a monotonic drop of magnetization, showed a cusp before T c. This cusp-like feature is shown to arise due to an irreversible phase transition involving cationic redistribution in the unit cell of the nanoparticles.

Apparent bioaccumulation of Mn derived from paper-mill effluent by the freshwater crayfish Cherax destructor — the role of Mn oxidising bacteria

Bioaccumulation studies of wastewater from a thermo-mechanical paper mill using the freshwater crayfish (Cherax destructor) consistently demonstrated elevated levels of manganese. Most of the Mn appeared to be associated with the carapace of the animals. It is suggested that the elevated Mn levels are the result of Mn-oxidising bacteria forming biofilms on the carapace of the crayfish followed by Mn oxide precipitation rather than active uptake of Mn by the crayfish.

Heterogeneous Oxidation and Precipitation of Aqueous Mn(II) at the Goethite Surface: A SPM Study

Abstract Since its invention inl982 scanning probe microscopy (SPM) has become an important analytical tool in every branch of physical science. The two most widely used types of SPM are atomic force Microscopy (AFM) and scanning tunneling microscopy (STM). Both AFM and STM allow measurement of the microtopography of a surface down to the atomic scale. Many spin-off applications such as lateral force and magnetic force allow measurement of a variety of the physical properties of a surface while imaging its microtopography. SPM can be done in both air and liquid and hence can be used to observe the interactions that take place at a solid-solution interface. SPM has been used in mineralogy and geochemistry since 1989. Here as in other applications the great strength of SPM is in the characterization of the heterogeneous nature of mineral surfaces and the ability to observe many geochemical processes in real time.

Formation of root plaques and their influence on tissue phosphorus content in Lobelia dortmanna

Oxygen release from the roots of the freshwater isoetid, Lobelia dortmanna L., influences redox related processes of iron (Fe) and manganese (Mn) in the sediments. Because oxidized species of Fe and Mn have high capacity for phosphorus (P) binding, the availability of sediment P to aquatic plants is influenced by root oxygen release. We investigated 30 sediment cores vegetated with L. dortmanna from oligotrophic Mirror Lake to analyse sediment variables responsible for precipitation of Fe and Mn on root surfaces (plaques), and P content of plant tissue. Close negative correlations between redox potential and concentrations of Fe ( r=−0.924) and Mn plaques ( r=−0.897) were found. Also, correlations between exchangeable Fe and Fe plaques ( r=0.716) and between exchangeable Mn and Mn plaques ( r=0.783) were found indicating that plaques are formed in reduced sediments with high concentrations of reduced Fe and Mn. For plants with Fe plaque concentrations lower than 30 μmol g −1 there were significant positive correlations between the tissue P content and the concentration of the less-plant-available P fractions in the sediment. In contrast, plants with Fe plaque concentrations higher than 30 μmol g −1 showed low tissue-P content (about 20 μmol g −1) independent of the P concentration in the sediment indicating that P uptake by L. dortmanna is reduced by Fe plaques. L. dortmanna with low tissue P content (<30 μmol g −1) showed significantly higher mycorrhizal infection than plants with high tissue P content (>30 μmol g −1) indicating that fungal association may be important in P assimilation by rooted aquatic plants in habitats with low P availability.

Mn- and Fe-rich black travertine shrubs; bacterially (and nanobacterially) induced precipitates

ABSTRACT Black shrubs (i.e., arborescent forms) are present within hot-water travertine deposits from Morocco. The shrubs are commonly a few centimeters high and laterally grouped along individual laminae. Other than in mineral composition, the black shrubs closely resemble the calcite shrubs from other hot-water travertine deposits (e.g., Bagni di Tivoli, Italy, and Mammoth Hot Springs, Yellowstone National Park). They are composed of a variety of minerals that are Mn-rich and also have a significant Fe-oxide component. Similar Mn- and Fe-rich shrub-like forms have been described from desert varnish, deep-sea Mn nodules, and marine carbonates (Frutexites). SEM analyses show that bacterial bodies are densely packed within the Mn-rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae. The bacterial bodies range in shape and size from rods (commonly 0.8 m long by 0.1 m in diameter), to spherical forms (commonly 0.3 m in diameter) that form chains up to 1 m long, to nanobacterial spheres (150 to 200 nm in diameter) that make up densely packed chains commonly 15 m in length. It is well documented within the microbiological literature that, not only do bacteria have the ability to induce the precipitation of Mn and Fe, they can concentrate Mn in mineral precipitates from waters with very low to essentially undetectable concentrations of Mn. The black Mn-rich shrubs within the Moroccan travertines, other hot-water travertines, and related features such as desert varnish, deep-sea Mn nodules, and Frutexites are postulated to also be the result of bacterially induced precipitation.

Surface Charge Properties of and Cu(II) Adsorption by Spores of the Marine Bacillus sp. Strain SG-1

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 m 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 N(2) 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 mumol m, which is equal to a surface site density of 18.3 sites nm. 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).