Precipitation Of Mn Research Articles

Enzymatic microbial Mn(II) oxidation and Mn biooxide production in the Guaymas Basin deep-sea hydrothermal plume

Microorganisms play important roles in mediating biogeochemical reactions in deep-sea hydrothermal plumes, but little is known regarding the mechanisms that underpin these transformations. At Guaymas Basin (GB) in the Gulf of California, hydrothermal vents inject fluids laden with dissolved Mn(II) (dMn) into the deep waters of the basin where it is oxidized and precipitated as particulate Mn(III/IV) oxides, forming turbid hydrothermal “clouds”. Previous studies have predicted extremely short residence times for dMn at GB and suggested they are the result of microbially-mediated Mn(II) oxidation and precipitation. Here we present biogeochemical results that support a central role for microorganisms in driving Mn(II) oxidation in the GB hydrothermal plume, with enzymes being the primary catalytic agent. dMn removal rates at GB are remarkably fast for a deep-sea hydrothermal plume (up to 2 nM/h). These rapid rates were only observed within the plume, not in background deep-sea water above the GB plume or at GB plume depths (∼1750–2000 m) in the neighboring Carmen Basin, where there is no known venting. dMn removal is dramatically inhibited under anoxic conditions and by the presence of the biological poison, sodium azide. A conspicuous temperature optimum of dMn removal rates (∼40 °C) and a saturation-like (i.e. Michaelis–Menten) response to O 2 concentration were observed, indicating an enzymatic mechanism. dMn removal was resistant to heat treatment used to select for spore-forming organisms, but very sensitive to low concentrations of added Cu, a cofactor required by the putative Mn(II)-oxidizing enzyme. Extended X-ray absorption fine structure spectroscopy (EXAFS) and synchrotron radiation-based X-ray diffraction (SR-XRD) revealed the Mn oxides to have a hexagonal birnessite or δ-MnO 2-like mineral structure, indicating that these freshly formed deep-sea Mn oxides are strikingly similar to primary biogenic Mn oxides produced by laboratory cultures of bacteria. Overall, these results reveal a vigorous Mn biogeochemical cycle in the GB hydrothermal plume, where a distinct microbial community enzymatically catalyzes rapid Mn(II) oxidation and the production of Mn biooxides.

Manganese ore deposits in Koira-Noamundi province of Iron Ore Group, north Orissa, India: In the light of geochemical signature

Several small Mn–Fe oxide and Mn-oxide ore bodies associated with Precambrian Iron Ore Group of rocks are located within Koira-Noamundi province of north Orissa, India. These deposits are classified into in situ (stratiform), remobilized (stratabound) and reworked categories based on their field disposition. Volcaniclastic/terrigenous shale in large geographic extension is associated with these ore bodies. The in situ ore bodies are characterised by cryptomelane-, romanechite- and hematite-dominating minerals, low Mn/Fe ratio (1.1) and relatively lower abundance of trace (1500–2500 ppm) constituents. In such type of deposits the stratigraphic conformity of oxides with the tuffaceous shale suggests precipitation of Mn and Fe at a time of decreased volcaniclastic/terrigenous contribution. The minor and trace elements were removed from solution by adsorption rather than by precipitation. Both Mn and Fe oxides when precipitated adsorb trace elements strongly but the partitioning of elements takes place during diagenesis. The inter-elemental relationship reveals that Cu, Co, Ni, Pb and Zn were adsorbed on precipitating hydrous Mn oxides and form manganates. Some of these elements probably get desorbed from Fe oxide because of their inability to substitute for Fe 3+ in the lattice of its oxide. However, P, V, As and Mo were less partitioned and retained in Fe-oxide phase. Positive correlation between Al 2O 3 and SiO 2, MgO, Na 2O, TiO 2 and some traces like Li, Nb, Sc, Y, Zr, Th and U points to their contribution through volcaniclastic/terrigenous detritus of both mafic and acidic composition. The remobilized ore bodies are developed in a later stage through dissolution, remobilization and reprecipitation of Mn oxides in favorable structural weak planes under supergene environment. Increase in average Mn/Fe ratio (8) and trace content (5000–8500 ppm) by 5–2.5 orders of magnitude, respectively, or more above its abundance in adjoining/underlying protore is characteristic of these deposits. The newly formed Mn ores constituting lithiophorite, cryptomelane/romanechite and goethite get quantitatively enriched in traces like Cu, Co, Ni, Pb and Zn. Positive correlation between Mn, Li, Co and Zn is due to the formation of mineral of lithiophorite–chalcophanite group during redistribution and reconcentration of Mn oxide. P and V, which were present in Fe oxide, also get dissolved and reprecipitate with Fe oxyhydroxide in these ores. Some other elements like Y, Th and U show positive relation with Fe. This is probably due to leaching of these elements during chemical weathering of associated shale and getting re-adsorbed in Fe-oxyhydroxide phase. However, under oxidizing environment selective cations like Ba, K, etc. resorb from Mn-structure, resulting in the development of pyrolusite (Mn/Fe>20). In such transformation, trace metals from pyrolusitic structure expels out, resulting thereby in a considerable reduction in total trace value (<3000 ppm). The reworked ore bodies are allochthonous in nature and developed through a number of stages during terrain evolution and lateritisation. Secondary processes such as reworking of pre-existing crust; solution and remobilization; precipitation and cementation and transport, etc. are responsible for their development. Such deposits are usually very low in Mn/Fe ratio (3) and trace content (<2000 ppm).

Evaluation of the impacts of mine drainage from a coal waste pile on the surrounding environment at Smolnica, southern Poland

Mine drainage impacts from a coal waste pile at Smolnica, Poland have been monitored. Groundwater in an unconfined aquifer downgradient from the pile has near-neutral pH, but high concentrations of sulfate (up to 3,827 mg/l), chloride (up to 903 mg/l), and sodium (up to 2,606 mg/l). Concentrations of iron and manganese are elevated only locally, and concentrations of other metals are low. The behavior of sulfate seems to be conservative in the downgradient aquifer, and gypsum may only be precipitating locally. Concentrations of iron and manganese seem to be controlled by the precipitation of ferric oxide and hydroxides and rhodochrosite, respectively. Complete neutralization of mine drainage by carbonates is consistent with high concentrations of calcium (up to 470 mg/l) and magnesium (up to 563 mg/l) and also with high strontium concentrations of up to 3.08 mg/l, observed in groundwater downgradient from the pile. Hydraulic head profiles at two sites within the river bottom sediments indicate upward flow toward the river with large local differences in groundwater recharge. Water chemistry profiles in the river bottom sediments and geochemical modeling suggest conservative behavior of Na, Cl, and SO(4) and precipitation of Fe and Mn at the groundwater/river water interface. Mine drainage enters the Bierawka River and causes increasing sulfate concentrations. In contrast, concentrations of sodium and chloride in the Bierawka River decrease downgradient from the pile because water in the river upgradient from the pile is already highly contaminated by these species from the discharge of mining waters. Concentrations of Fe and Mn in the river water are low, as a consequence of the precipitation of Fe and Mn oxide and hydroxides. Direct geochemical modeling was able to reproduce measured concentrations of conservative species (e.g., Na, Cl, and SO(4)), but errors for metals and Ba were relatively large. In addition, calculated P(CO2) values in the river water are very high, suggesting that equilibrium with atmospheric P(CO2) and P(O2) has not been reached, and at least some reactions should be modeled as kinetic processes. High concentrations of Na, Cl, and SO(4) contribute to the contamination of the Odra River, which is joined by the Bierawka River farther downgradient, thus limiting the use of river water for recreation and other purposes.

Genotypic Difference in Resistance to Internal Bark Necrosis in Apple Trees Is Related to Manganese Uptake, the Distribution of Manganese, and Antioxidant Activity

Field investigations and pot culture experiments were performed to elucidate the genotypic differences of two apple cultivars that vary in resistance to internal bark necrosis (IBN). Factors examined were manganese (Mn) uptake, antioxidant activity, as well as the accumulation and distribution of Mn in apple branches. Lesser Mn concentrations were found in the bark and branches of an IBN‐tolerant cultivar (‘Jonagold’) than in those of the sensitive cultivar (‘Fuji’) from both field investigations and pot culture, which is correlated with a reduction in Mn uptake from soil. Histochemical tests and x‐ray microanalyses indicated that Mn is localized in the bark and coincided with the occurrence of necrosis in ‘Fuji,’ whereas a more homogenous distribution of Mn was found in ‘Jonagold,’ possibly resulting in an alleviation of Mn toxicity. Physiological parameters indicated that the occurrence of IBN in apple was related to oxidative stress. Under field conditions, ascorbic acid concentration in the bark or leaves of ‘Fuji,’ which were severely affected by IBN, was less than that of ‘Jonagold.’ Because of greater Mn uptake from soil, an uneven distribution of Mn among tissues, and less reduction activity in the sensitive apple tree, oxidized Mn precipitation occurred in the bark, which ultimately exhibited IBN.

Mn/Ca ratio in planktonic foraminifer from ODP Site 1144, the northern South China Sea: A possible paleoclimate indicator

We report here high-resolution Mn/Ca ratios of planktonic foraminifer, Globigerinoid.es sacculifer from ODP Site 1144 in the northern South China Sea (SCS). The variation pattern of the Mn/Ca ratios of G. sacculifer from the top 170 mcd is very similar to those of the generally used paleoclimate records, such as δO of Globigerinoides ruber and SSTs derived from Mg/Ca ratios of G. sacculifer. Robust Milankovitch periodicities are presented in the power spectrum of the Mn/Ca record, as well as in those of the other paleoclimate records, suggesting orbital forcing for the variation of the Mn/ Ca ratios. Further spectral analysis indicates that the variations of the Mn/Ca ratios lead those of the delta;O of G. ruber at all the orbital periodicities, and are roughly in pace with or slightly lead those of the SSTs at eccentricity and obliquity periodicities, but lag behind that of the SSTs at precession periodicity. This suggests that the driven forcing for the variation of the Mn/Ca ratios mainly associate with those for the SSTs. Comparisons between the Mn/Ca ratios and other geochemical proxies for redox condition in sediments show that higher Mn/Ca ratios of G. sacculifer generally correspond to higher authigenic Mn concentrations and lower contents of total sulfur (TS) and total organic carbon (TOC). Thus, the Mn coatings in the G. sacculifer at ODP Site 1144 are mainly associated with Mn oxides, and the variation of the Mn/Ca ratios of G. sacculifer appears to indicate changes of redox condition in sediments. Exception is observed at the top 10 mcd, in which the Mn/Ca ratios show an upward decreasing trend and low core-top values, while other proxies suggest oxic environment in this section. The low Mn/Ca ratios agree with the general low Mn/Ca ratios in foraminifer tests from core-top sediments in the SCS, and seem to attribute to the fact that authigenic Mn precipitation are mainly generated within sediment column rather than at sediment surface and the oxidation states for them may change from Mn(III) oxyhydroxides to Mn(IV) oxides after burial. However, details are not well known yet. Despite of such uncertainties, the response of the variation of the Mn/Ca ratios of G. sacculifer to paleoclimate changes is significant, indicating that it is an informative paleoclimate indicator.

TEM investigations of MN nitride phases in a 9% chromium ferritic/martensitic steel with normalization conditions for nuclear reactors

The investigations on the precipitate phases in a 9%Cr ferritic/martensitic steel under different normalization conditions have been made by using a transmission electron microscope and an energy-dispersive X-ray spectroscopy. Hot-rolled steel samples were normalized at 1050–1200 °C for 1–2 h followed by an air cooling to room temperature. MN vanadium nitride precipitates with a plate-like morphology and a chemical formula of about (V 0.4Nb 0.4Cr 0.2)N have been observed at triple junctions, grain boundaries and within matrix in the steel samples normalized at 1050–1150 °C for 1–2 h, but they were dissolved out at 1200 °C within 1 h. Vanadium nitride is a stable phase at 1050 °C according to thermocalc prediction of equilibrium phases in the steel. With increasing normalizing temperature and time, there was no a striking change in the chemical composition of metallic elements in the MN phase, but a considerable increase in the size of the MN precipitate.

Reductive acid leaching of spent zinc–carbon batteries and oxidative precipitation of Mn–Zn ferrite nanoparticles

The non-magnetic 8-mesh undersize material obtained by crushing, magnetic separation and sieving of spent zinc-carbon batteries assayed 23.9% Mn, 14.9% Zn, and 4% Fe. Reductive acid leaching of this material at a solid/liquid ratio of 1:10, and 60 °C with 2 mol dm − 3 H 2SO 4 and 0.39 mol H 2O 2 extracted 97.9% Mn, 98.0% Zn and 55.2% Fe after 60 min. The leach liquor composition was then adjusted to a Mn:Zn:Fe molar ratio of 1:1:4 suitable for producing MnZnFe 4O 8 ferrite powder by adding Mn(II), Zn(II) and Fe(II) sulfates. The effect of pH in the range pH 5–12 on the precipitation of Mn–Zn ferrite powder was investigated over 60 min using O 2 gas flow rate of 1.3 dm 3 min − 1 at 80 °C. The precipitated Mn–Zn ferrite at pH 12 were 20 nm particles that had a spinel structure. The saturation magnetizations of Mn–Zn ferrite powder (Mn 1 − x Zn x Fe 2O 4) were determined to be 39–91 emu/g with various zinc contents ( x = 0.2–0.8).

Homogenization of a twin-roll cast thin Al–Mn strip

A sound homogenization practice was investigated for thin Al–Mn strips. The structure in the as-cast state reveals features typical of rapid solidification. The impact of subsequent hot rolling of the just solidified strip in the caster roll gap is also evident. A homogenization treatment makes a critical contribution by allowing the precipitation of excess Mn in solution. However, homogenized thin Al–Mn strips suffer coarse surface grains owing to the pinning of low and/or high angle grain boundaries by the fine dispersoids. However, homogenization improves the response to a subsequent annealing treatment in a profound way. The strip sample processed without a homogenization treatment softens very slowly, retaining high strength levels even after 3 h at 375 °C. In contrast, the homogenized strip samples soften fully when annealed at temperatures below 350 °C. Homogenization at the cast gauge is identified as the best practice, as prior cold rolling does not improve the grain structure or accelerate the softening behaviour of thin Al–Mn strip.

Structure and composition of the consolidated mud tube of Maldane sarsi (Polychaeta: Maldanidae)

Maldanid polychaetes can be important components of marine benthic communities, playing significant roles in particle subduction or sediment irrigation. Many maldanids are known to inhabit tubes consisting of sediments consolidated by mucus; the structure and composition of these tubes, and their potential impact on benthic environments, are poorly known. We examined the three-dimensional organization of Maldane sarsi tubes, using CT scanning together with analyses of sediment grain size and concentrations of Fe, Mn, organic carbon and bacteria in tube material. M. sarsi tubes consist of stacks of individual consolidated mud disks, surrounding a dense, continuous, inner tube. The tubes of M. sarsi contained fewer fine particles than surrounding sediments, and greater concentrations of Fe, Mn, organic carbon and bacteria, especially in the inner zone. These distributions suggest that tube irrigation affects Fe and Mn oxidation and precipitation in a narrow zone surrounding M. sarsi, and that mucous secretion and potential feeding activities (the hoeing of surface sediments) lead to increases in organic carbon and bacteria in the inner, and deepest parts of the tube. The finding of relict tubes, buried at up to 15 cm depth, indicates a relatively high longevity for these structures and suggests a potential importance in biogeochemical cycling.

Manganese metalliferous sediments of the Deryugin Basin (Sea of Okhotsk): Chemical composition and geological setting

This paper reports the results of an investigation of the chemical composition and distribution of manganese-rich metalliferous sediments in the Deryugin Basin. They compose an upper sedimentary layer up to 30 cm thick within a strip up to 40 km wide and 180 km long in the central part of the basin along the East Deryugin suture zone bounding the Deryugin sedimentary basin to the east. The sediments are enriched relative to the regional background composition in Mn (by a factor of 35); Au; Ni; Zn; Co (by a factor of 3–5); and, locally, in Mo, V, Ba, Cu, Pb, and Hg. It was supposed that their formation was controlled by several processes: precipitation of Mn and some other trace elements from hydrothermal plumes of seawater that occasionally form above submarine hot vents in the northern part of the basin, precipitation from anoxic bottom waters at the eastern boundary of the Deryugin sedimentary basin, and early diagenetic migration of Mn into the surface sediments.

Metal mobility in the groundwater of a paddy field in Camargue (South eastern France)

Waterlogged soils are submitted to temporal variations of aeration and aerobic–anaerobic conditions which influence redox conditions and thus element mobility. Cultivated paddy soils, that are an accurate redox-dynamic environment, can be found in Camargue (Rhône deltaic plain, SE France). In order to monitor fast physical and chemical variations in the waterlogged soil, a multiparametric probe was chosen to acquire continuous and in situ data. It can be showed that (i) Eh variations happen at quasi-constant pH during Mediterranean storms in non-irrigated seasons, and induce sharp variations of Fe(II) and Mn concentrations, and (ii) the soil is saturated with water under anaerobic conditions during long periods, where sharp pH fluctuations controlled by pCO 2 evolution affect redox processes. During irrigation periods, Fe and Mn precipitate as oxides or co-precipitate with Al, Mg and Si at depth. These neoformed phases however can be dissolved when irrigation stops. The understanding of the reactions of the system, under varying conditions, is important in order to better assess its durability and anticipate the consequences of soil use or agricultural practices changes.

Mobilization and re-distribution of major and trace elements during extreme weathering of basalt in Hainan Island, South China

Major, trace and organic elements of a laterite profile developed on Neogene basalts in northern Hainan Island, South China were reported in this paper, the aim of which was to investigate element mobilization and re-distribution during extreme weathering. The results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution. Organic matter (OM) can significantly improve the transport of insoluble elements. Among all the elements, Th is the least mobile. As for the general conservative elements during incipient chemical weathering, such as Fe, Ti, Zr, Hf, Nb and Ta, the removals are up to 20–40% in the upper profile. However, these elements behave as conservatively as Th in the lower profile. In the middle profile, oxic environment occurs, accompanied with significant OM decomposition. The Mn and Ce transferred downward are readily oxidized into insoluble Mn(IV) and Ce(IV) and precipitate in the oxic front. Important OM decomposition decreases the capacity of transfer of insoluble elements in aqueous solution. Consequently, Al significantly precipitates in the oxic front, and REEs, with the exception of Ce, precipitate largely in the OM-depleted layers. Co and U are also concentrated in the oxic front in association with Mn and Ce, respectively. However, Cr shows a negative correlation with Mn because its response to redox condition changes is reversed from that of Mn. Mn oxides/hydroxides, Fe oxides/hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for REEs except for Ce in the profile; REEs with high concentrations in the profile seem closely associated with Mn oxides/hydroxides. Remarkable, highly correlated, Ce and Gd anomalies are observed in the profile. Ce anomalies are caused by Ce precipitation in the oxic environment and successive decomposition of organic matter. Gd anomalies are likely to have resulted from lower stability constants of Gd–OM complexes compared to those of neighboring REEs. The overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re-distribution of the elements during extreme weathering.

Magnetic and structural properties ofGexMn1−xfilms: Precipitation of intermetallic nanomagnets

We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05 films to their magnetic properties. The formation of ferromagnetic nanometer sized inclusions in a defect free Ge matrix fabricated by low temperature molecular beam epitaxy is observed down to substrate temperatures T_S as low as 70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount of these precipitates decreases with decreasing T_S. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn_5Ge_3 at approximately room temperature and a lower, T_S dependent blocking temperature T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3 precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates with blocked magnetic moments is observed. At the lowest temperatures, the films show features characteristic for a metastable state.

Manganese removal from mine waters – investigating the occurrence and importance of manganese carbonates

Manganese is a common contaminant of mine water and other waste waters. Due to its high solubility over a wide pH range, it is notoriously difficult to remove from contaminated waters. Previous systems that effectively remove Mn from mine waters have involved oxidising the soluble Mn(II) species at an elevated pH using substrates such as limestone and dolomites. However it is currently unclear what effect the substrate type has upon abiotic Mn removal compared to biotic removal by in situ micro-organisms (biofilms). In order to investigate the relationship between substrate type, Mn precipitation and the biofilm community, net-alkaline Mn-contaminated mine water was treated in reactors containing one of the pure materials: dolomite, limestone, magnesite and quartzite. Mine water chemistry and Mn removal rates were monitored over a 3-month period in continuous-flow reactors. For all substrates except quartzite, Mn was removed from the mine water during this period, and Mn minerals precipitated in all cases. In addition, the plastic from which the reactor was made played a role in Mn removal. Manganese oxyhydroxides were formed in all the reactors; however, Mn carbonates (specifically kutnahorite) were only identified in the reactors containing quartzite and on the reactor plastic. Magnesium-rich calcites were identified in the dolomite and magnesite reactors, suggesting that the Mg from the substrate minerals may have inhibited Mn carbonate formation. Biofilm community development and composition on all the substrates was also monitored over the 3-month period using denaturing gradient gel electrophoresis (DGGE). The DGGE profiles in all reactors showed no change with time and no difference between substrate types, suggesting that any microbiological effects are independent of mineral substrate. The identification of Mn carbonates in these systems has important implications for the design of Mn treatment systems in that the provision of a carbonate-rich substrate may not be necessary for successful Mn precipitation.

The Influence of Alloy Composition on Phase Transformations and Recrystallization in Twin-Roll Cast Al-Mn-Fe Alloys

Twin-roll casting (TRC) is an advantageous substitution for Direct-Chill (DC) casting in the manufacturing of rolled aluminium products. The results of a study of the phase transformations and their interaction with recrystallization occurring during the annealing of TRC Al-Mn based alloys are reported. Four alloys with different contents of Mn, Si and Fe were investigated. Precipitation was studied by resistometric measurements in the course of a heating at linear rate. The microstructural processes responsible for the observed changes in resistivity were identified by TEM examinations of quenched specimens. The changes in the microstructure and solute content during homogenisations at 450°C and 610°C were monitored by conductivity and hardness measurements and polarised light microscopy. It was elucidated that the temperature and kinetics of phase transformations are influenced not only by the content of Mn, but also by Si content. In alloys with low Si content, the decomposition of solid solution and the transformation of primary phases occur in much larger temperature range than in the alloys with high Si content. The precipitation of Mn and Si, concurrent to recrystallization, was observed to retard the latter, especially in alloys with high Mn and Si content.

Softening of an AA3103 Alloy Analysed Using Gallium Enhanced Microscopy

The softening behaviour during annealing was investigated in cold and hot rolled AA3103 alloys after different heat treatments. It was found that the evolution of boundary spacing determined using gallium enhanced microscopy gives a very good representation of the softening behaviour. The results show that cold rolled Al-Mn alloys soften by continuous growth of the subgrain structure, “continuous recrystallisation”, provided the pre-treatment of the ingots has been made to avoid too high a density of dispersoids and the cold rolling reduction has been very large. The very high strain creates a microstructure with a large fraction of high angle boundaries that are mostly parallel to the sheet surface. A recently developed subgrain growth model which takes the effect of solute drag into account, gives a good description of the softening kinetics. The solute drag is controlled by bulk diffusion of Mn. The simultaneous precipitation of Mn from the solid solution takes place by grain boundary diffusion of the Mn atoms mainly to pre-existing particles. The solute concentration decreases as the inverse of the boundary spacing, which is due to the grain growth mainly in the thickness (normal) direction.

Study of structures and magnetic properties of single crystalline HVPE–GaMnN films

We have grown single crystalline GaMnN films by a horizontal hydride vapor-phase epitaxy (HVPE) system. The structures and crystal quality were confirmed by XRD and Raman scattering measurements. The structure analysis indicated that we obtained uniform GaMnN solid-solution films; the Mn atoms were substituted for Ga sites and did not form Mn precipitates or clusters. The superconductor quantum interference device (SQUID) results show that the GaMnN films without the phase separation exhibit paramagnetic properties.

Preservation of As III and As V in surface and ground waters

The literature on preservation procedures for the stabilization of As redox species in waters is controversial. A paper by McCleskey et al. (Appl. Geocbem., 2004) states that any field collection procedure that filters out microorganisms, adds a reagent that prevents dissolved Fe and Mn oxidation and precipitation, and isolates the sample from solar radiation, will preserve the As III/V ratio. They state that reagents such as HC1, H2SO4 and EDTA will prevent Fe oxidation and precipitation but warn that high concentrations of EDTA (e.g. 12.5 mM) are necessary for samples high in dissolved Fe content. The USGS recommended preservation procedure is to make the surface or ground water 1.25 mM in EDTA and to use a medium of 12.5 M EDTA only for Fe-rich acid mine drainage. Earlier studies by the GSC (Hall et al., J. Anal. At. Spectrum, 1999) showed that HC1 (at 0.1%) did indeed effect an immediate change on the species distribution of As in several natural waters. Further work has shown that making up a calibration standard containing As III in an HC1 medium can also be problematic. For example, standards (0.5 or 5.0: g ~ L -1 ofAs III/V in 0.1 M HC1) are not stable when the solution is diluted with H20 and mixed by shaking: all the As III is converted to As V. However, if the solution is mixed by vortexing, whereupon less air is introduced to the solution, stability of the two As species is maintained. A GSC study using well waters from the West Bengal region showed that 1.25 mM EDTA did not prevent the oxidation of As III to As V and indeed, in some waters, total As showed a significant decrease in the EDTA medium compared to the HC1and HNO3 preserved counterparts. These waters do not contain high amounts of Fe (<10 mg 9 L1); rather they are highly alkaline with high concentrations of Ca (80-120 mg ~ Ll). The poor performance of EDTA is due to the instability of the Fe-EDTA complexes and preferential binding of EDTA by Ca, resulting in both oxidation of As III to As V and precipitation of Fe in some waters, removing arsenate (and arsenite) from solution also. Clearly, the higher concentration of EDTA (12.5 mM) is needed not only for Fe-rich waters, but also for Caand Mg-rich waters. This poster presents the data obtained to demonstrate this requirement for more concentrated EDTA in such waters and compares the EDTA and HC1 preservation approaches.

Coprecipitation of Pu(IV) with Fe(III) and Cr(III) hydroxides from nitrate-acetate solutions under hydrothermal conditions simulating deep disposal of liquid radioactive wastes

Precipitation of Fe(III), Cr(III), Ni(II), and Mn(II) from nitrate-acetate solutions and coprecipitation of Pu(IV) with Fe(III) and Cr(III) were studied. The degree of precipitation of 80–95% is attained for Fe(III) at 95–200°C and pH>0.5–0.6, and for Cr(III), at T=95°C and pH≥4.0 or T=200°C and pH≥1.0. The phase composition of the precipitates formed by thermal hydrolysis of iron nitrate in model solutions was analyzed. Depending on pH and temperature, the solid phase contains various modifications of Fe2O3, FeOOH, and amorphous phases. Noticeable coprecipitation of plutonium from nitrate-acetate solutions is observed at pH≥4, and it is incorporated in the precipitate only at formation of FeOOH. No coprecipitation of Pu(IV) with Fe2O3 was found. Under the given experimental conditions, plutonium in aqueous solutions occurs in the oxidation state +4 forming monoacetate (or, probably, hydroxo acetate) complexes.

Manganese Oxidation by Bacterial Isolates from the Indian Ridge System

The abundance and activity of culturable manganese-oxidizing bacteria were assessed from near-bottom water samples of the tectonically active Carlsberg Ridge. Retrievable counts as colony forming units (CFU) on dilute nutrient agar medium (dilNA=2 gm l(-1) nutrient broth+2% agar) and on dilNA supplemented with 1, 2 and 3 mM MnCl(2).4H(2)O were in the order of 10(6) CFU l(-1). Retrievability of heterotrophs ranged from non-detectable levels (ND) to 2.82 x 10(6) CFU l(-1). The retrievable counts on Mn amended dilNA ranged from ND to 3.21 x 10(6), 1.47 x 10(6) and 1.45 x 10(6) CFU l(-1) on 1, 2 and 3 mM, respectively. About 87% of the Mn tolerant isolates (n=39) showed taxonomic affinities to Pseudomonas I and II sp. Two representative strains CR35 and CR48 (CR-Carlsberg Ridge) isolated on manganese-supplemented media were tested for their ability to tolerate a range of Mn amendments from 1 nM to 100 mM in terms of growth and respiration. CR35 represents 66% of the total CFU (3.04 x 10(6) CFU l(-1)), while CR48 represented only 6% of the total CFU (1.05 x 10(6) CFU l(-1)). The colonies of these two isolates were dark brown in color suggesting precipitation of Mn as oxide. Tests for the effect on growth and respiration were conducted in media simulating heterotrophic (amended with 0.01% glucose) and lithotrophic (unamended) conditions. Maximum stimulation in growth and respiration of CR35 occurred at 100 microM Mn both in unamended and amended media. At levels of Mn greater than 100 microM the counts decreased steadily. Total respiring cells of CR48 were stimulated to a maximum at 1 microM Mn in unamended medium and 1 nM in amended medium. Total cells counts for the same decreased beyond 100 microM Mn in unamended and 1 nM in amended medium. The isolates were tested for their ability to oxidize Mn amendments from 1 microM to 10 mM Mn. At the end of a 76-day incubation period, there was evidence of manganese oxide precipitation at high Mn concentrations (>or=1 mM) as a dark brown coloration on the sides of culture tubes. Highest Mn oxidation rates were observed at 10 mM Mn(II) concentration with CR35 oxidizing 27 and 25 microM Mn day(-1) in unamended and amended condition, respectively. CR48 oxidized Mn at the rate of 26 microM Mn day(-1) in unamended medium and 35 microM Mn day(-1) in amended medium. Scanning electron microscope (SEM) observations of both isolates revealed free-living cells in clustered matrices approximately 2 microm diameter. Energy dispersive spectrum of the cell matrix of CR35 cultured in 1 mM Mn detected 30% Mn, while the cell aggregates of CR48 harbored 7-10% Mn. The relatively high specific activity of these mixotrophic bacteria under relatively oligotrophic conditions suggests that they may be responsible for scavenging dissolved Mn from the Carlsberg Ridge waters and could potentially participate in oxidation.