Nonequilibrium models for predicting forms of precipitated manganese oxides

Hem, John David; Lind, Carol J.

doi:10.1016/0016-7037(83)90219-3

Cited by 164 publications

(84 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The intermediates can exist for extended periods of time, especially in the neutral pH region. Nonequilibrium models for predicting forms of precipitated Mn-oxides had been proposed before (Hem and Lind, 1983). In the course of our experiments, we have found that transformations of metastable Mn-hydroxides may regulate the noble metal behavior in natural hydrothermal systems.…”

Section: Discussionsupporting

confidence: 51%

“…The Mn-oxides are very sensitive to any variation of oxidizing conditions of their environments. Well-known Mn(II) oxidation at low temperatures breaks equilibrium in the systems that in its turn causes an essential change of solubility of coexisting metals (Hem and Lind, 1983). In the present study, the X-ray analysis of resultant Mn1 phase composition has revealed that, at 300°C and 200°C, MnO was oxidized to (Murray et al, 1985).…”

Section: Mn-oxide Buffer Systemmentioning

confidence: 52%

See 1 more Smart Citation

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

et al. 2000

View full text Add to dashboard Cite

: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log mAu–mNaCl–T frame fixed linear dependence between log mAu and T at any studied iso‐pleth (mNaCl) in the form of log mAu = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log mAu) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied fO2/fS2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower fO2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H2O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H2O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 mHCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log mPt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)2 and Mn2(OH)3Cl). These phases are metastable and transfer to Mn3O4 with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn3O4, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn2O3–MnO2 buffer. So at 400C, dissolved Au (log mAu) increases from –4. 40 in water to –1. 00 in 0. 1 mHCl, and ones of Pt (log mPt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.

show abstract

Section: Discussionsupporting

confidence: 51%

Section: Mn-oxide Buffer Systemmentioning

confidence: 52%

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

et al. 2000

View full text Add to dashboard Cite

show abstract

“…Since the decrease in pH upon darkening is generally much slower than the change in oxygen concentration (unpubl. data), the still relatively high pH may have resulted in the precipitation of ferrous and manganous carbonates (Hem and Lind 1983). Additionally, a high pH favors the adsorption of Fe II and Mn II to manganese-oxides.…”

Section: Discussionmentioning

confidence: 98%

Photosynthesis and the dynamics of oxygen consumption in a microbial mat as calculated from transient oxygen microprofiles

Epping

Khalili

Thar

1999

Limnology & Oceanography

View full text Add to dashboard Cite

A new method is presented to determine the rates of oxygen consumption, net oxygen metabolism (defined as photosynthesis minus oxygen consumption), and gross photosynthesis at high vertical resolution in benthic phototrophic communities. The rates of oxygen consumption and of net oxygen metabolism as a function of depth and time are calculated from the dynamics in oxygen concentration, as measured with oxygen microsensors during light-dark cycles, by numerically solving the general non-steady state diffusion-reaction equation. The results, as obtained for a temperate intertidal microbial mat, strongly suggest that the vertical distribution and the dynamics in oxygen consumption are controlled by the supply of both oxygen and oxidizable substrates from different sources. The depth distribution of gross photosynthesis, as obtained by the cycling procedure, showed reasonable agreement with the photosynthesis profile, as measured with the conventional light-dark shift method prior to the light-dark cycling experiment, thus supporting the applicability of the method.

show abstract

“…These observations are consistent with our conclusion that Ca 2+ is preferentially incorporated as an interlayer cation in the hyporheic zone layered Mn oxides. Hem and Lind (1983) and Hem (1996, 1993) proposed an abiotic Mn(II) oxidation model in which sorbed Mn(II) is oxidized to form hausmannite (Mn 3 O 4 ), which subsequently disproportionates to yield Mn(IV) oxides and Mn 2+ . This model is thermodynamically plausible at Pinal Creek because hausmannite, which is less stable than the MnOOH minerals discussed in Section 4.3, can disproportionate into Mn(IV) oxides under the observed aqueous chemical concentrations (Best et al, 1999).…”

Section: Comparison To Previous Studies At Pinal Creekmentioning

confidence: 99%

Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ

Bargar

Fuller

Marcus

et al. 2009

Geochimica et Cosmochimica Acta

110

106

View full text Add to dashboard Cite

The microbial catalysis of Mn(II) oxidation is believed to be a dominant source of abundant sorption-and redox-active Mn oxides in marine, freshwater, and subsurface aquatic environments. In spite of their importance, environmental oxides of known biogenic origin have generally not been characterized in detail from a structural perspective. Hyporheic zone Mn oxide grain coatings at Pinal Creek, Arizona, a metals-contaminated stream, have been identified as being dominantly microbial in origin and are well studied from bulk chemistry and contaminant hydrology perspectives. This site thus presents an excellent opportunity to study the structures of terrestrial microbial Mn oxides in detail. XRD and EXAFS measurements performed in this study indicate that the hydrated Pinal Creek Mn oxide grain coatings are layer-type Mn oxides with dominantly hexagonal or pseudo-hexagonal layer symmetry. XRD and TEM measurements suggest the oxides to be nanoparticulate plates with average dimensions on the order of 11 nm thick Â 35 nm diameter, but with individual particles exhibiting thickness as small as a single layer and sheets as wide as 500 nm. The hydrated oxides exhibit a 10-Å basal-plane spacing and turbostratic disorder. EXAFS analyses suggest the oxides contain layer Mn(IV) site vacancy defects, and layer Mn(III) is inferred to be present, as deduced from Jahn-Teller distortion of the local structure. The physical geometry and structural details of the coatings suggest formation within microbial biofilms. The biogenic Mn oxides are stable with respect to transformation into thermodynamically more stable phases over a time scale of at least 5 months. The nanoparticulate layered structural motif, also observed in pure culture laboratory studies, appears to be characteristic of biogenic Mn oxides and may explain the common occurrence of this mineral habit in soils and sediments.

show abstract

Nonequilibrium models for predicting forms of precipitated manganese oxides

Cited by 164 publications

References 7 publications

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Photosynthesis and the dynamics of oxygen consumption in a microbial mat as calculated from transient oxygen microprofiles

Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ

Contact Info

Product

Resources

About