Increasing Ph

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Eric H Oelkers - One of the best experts on this subject based on the ideXlab platform.

  • does variscite control PhosPhate availability in acidic natural waters an experimental study of variscite dissolution rates
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Teresa Roncalherrero, Eric H Oelkers
    Abstract:

    Abstract The dissolution rates of natural, well crystallized variscite (AlPO4·2H2O) were determined from the evolution of aqueous Al and P concentrations in closed and open-system mixed-flow reactors at 25 °C and Ph from 1.5 to 9.0. Measured dissolution rates decrease with Increasing Ph, from 6 × 10−16 mol/cm2/s at Ph 1.5 to 5 × 10−17 mol/cm2/s at Ph 5.89, and then increase with Increasing Ph to 4 × 10−16 mol/cm2/s at Ph 9.0. Geochemical modeling calculations, performed using measured dissolution rates, indicate that it would take no more than a few weeks or months to equilibrate a mildly acidic, Al and P-free solution with variscite. Hence, variscite can buffer aqueous PhosPhate concentrations in mildly acidic near surface environments. This conclusion is confirmed by consideration of the compositions of natural waters.

  • variscite dissolution rates in aqueous solution does variscite control the availability of PhosPhate in acidic natural waters
    Mineralogical Magazine, 2008
    Co-Authors: Teresa Roncalherrero, Eric H Oelkers
    Abstract:

    The dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 Ph. Measured dissolution rates decrease with Increasing Ph from 5.05 × 10−16 mol/cm2/s at Ph = 1.51 to 4.92 × 10−17 mol/cm2/s at Ph = 5.89 and then increase with Increasing Ph to 1.64 × 10−17 mol/cm2/s at Ph = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous PhosPhate concentrations in a significant number of near surface environments.

Teresa Roncalherrero - One of the best experts on this subject based on the ideXlab platform.

  • does variscite control PhosPhate availability in acidic natural waters an experimental study of variscite dissolution rates
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Teresa Roncalherrero, Eric H Oelkers
    Abstract:

    Abstract The dissolution rates of natural, well crystallized variscite (AlPO4·2H2O) were determined from the evolution of aqueous Al and P concentrations in closed and open-system mixed-flow reactors at 25 °C and Ph from 1.5 to 9.0. Measured dissolution rates decrease with Increasing Ph, from 6 × 10−16 mol/cm2/s at Ph 1.5 to 5 × 10−17 mol/cm2/s at Ph 5.89, and then increase with Increasing Ph to 4 × 10−16 mol/cm2/s at Ph 9.0. Geochemical modeling calculations, performed using measured dissolution rates, indicate that it would take no more than a few weeks or months to equilibrate a mildly acidic, Al and P-free solution with variscite. Hence, variscite can buffer aqueous PhosPhate concentrations in mildly acidic near surface environments. This conclusion is confirmed by consideration of the compositions of natural waters.

  • variscite dissolution rates in aqueous solution does variscite control the availability of PhosPhate in acidic natural waters
    Mineralogical Magazine, 2008
    Co-Authors: Teresa Roncalherrero, Eric H Oelkers
    Abstract:

    The dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 Ph. Measured dissolution rates decrease with Increasing Ph from 5.05 × 10−16 mol/cm2/s at Ph = 1.51 to 4.92 × 10−17 mol/cm2/s at Ph = 5.89 and then increase with Increasing Ph to 1.64 × 10−17 mol/cm2/s at Ph = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous PhosPhate concentrations in a significant number of near surface environments.

Julianne M. Gibbs - One of the best experts on this subject based on the ideXlab platform.

Mokhtar Rashwan - One of the best experts on this subject based on the ideXlab platform.

  • structure of the silica divalent electrolyte interface molecular insight into charge inversion with Increasing Ph
    Journal of Physical Chemistry C, 2020
    Co-Authors: Mokhtar Rashwan, Benjamin Rehl, Adrien Sthoer, Md. Shafiul Azam, Hongbo Zeng, Qingxia Liu, Eric Tyrode, Akemi M. Darlington, Julianne M. Gibbs
    Abstract:

    The molecular origin of overcharging at mineral oxide surfaces remains a cause of contention within the geochemistry, Physics, and colloidal chemistry communities owing to competing “chemical” vers...

  • Structure of the Silica/Divalent Electrolyte Interface: Molecular Insight into Charge Inversion with Increasing Ph
    The Journal of Physical Chemistry C, 2020
    Co-Authors: Mokhtar Rashwan, Benjamin Rehl, Adrien Sthoer, Hongbo Zeng, Qingxia Liu, Eric Tyrode, Akemi M. Darlington, Shafiul Azam, Julianne M. Gibbs
    Abstract:

    The molecular origin of overcharging at mineral oxide surfaces remains a cause of contention within the geochemistry, Physics, and colloidal chemistry communities owing to competing “chemical” vers...

  • Structure of the Silica/Divalent Electrolyte Interface: Molecular Insight into Charge Inversion with Increasing Ph
    2020
    Co-Authors: Mokhtar Rashwan, Benjamin Rehl, Adrien Sthoer, Akemi Darlington, Md. Shafiul Azam, Hongbo Zeng, Qingxia Liu, Eric Tyrode, Julianne Gibbs
    Abstract:

    The molecular origin of overcharging at mineral oxide surfaces remains a cause of contention within the geochemistry, Physics, and colloidal chemistry communities owing to competing “chemical” vs “Physical” interpretations. Here, we combine vibrational sum frequency spectroscopy and streaming potential measurements to obtain molecular and macroscopic insights into the Ph-dependent interactions of calcium ions with a fused silica surface. In 100 mM CaCl<sub>2</sub> electrolyte, we observe evidence of charge neutralization at Ph~10.5, as deducted from a minimum in the interfacial water signal. Concurrently, adsorption of calcium hydroxide cations is inferred from the appearance of a spectral feature at ~3610 cm<sup>-1</sup>. However, the interfacial water signal increases at higher Ph, while adsorbed calcium hydroxide appears to remain constant, indicating that overcharging results from hydrated Ca<sup>2+</sup> ions present within the Stern layer. These findings suggest that both specific adsorption of hydrolyzed ions and ion-ion correlations of hydrated ions govern silica overcharging with Increasing Ph.

Mathieu Pédrot - One of the best experts on this subject based on the ideXlab platform.

  • Increasing Ph drives organic matter solubilization from wetland soils under reducing conditions
    Geoderma, 2009
    Co-Authors: Malagorzata Grybos, Mélanie Davranche, Gérard Gruau, Patrice Petitjean, Mathieu Pédrot
    Abstract:

    In wetlands, large quantities of dissolved organic matter (DOM) are solubilized under reducing conditions. Controlled incubations of a wetland soil were performed under oxic and anoxic conditions to investigate the extent to which the following processes account for this Phenomenon: i) production of organic metabolites by microbes during soil reduction; ii) release of organic matter (OM) from Mn- and Fe-oxyhydroxides that undergo reductive dissolution; and iii) desorption of OM from soil minerals due to Ph changes. Anaerobic incubation releases 2.5% of the total soil organic carbon (OC) as dissolved organic carbon (DOC), and is accompanied by a Ph rise from 5.5 to 7.4 and by the soil Mn- and Fe-reduction. The three processes above all take place. However, anaerobic incubation at a constant Ph of 5.5 (preventing OM desorption) releases only 0.5% of the total soil OC, while aerobic incubation at Ph 7.4 (preventing Mn- and Fe-reduction) releases 1.7% of the total soil OC. By contrast, aerobic incubation at Ph 5.5 (preventing both Mn- and Fe-reduction and Ph rise) does not solubilize any DOC. The DOC released is markedly aromatic, indicating little contribution from microbial metabolites, but, rather, the presence of microbes leading to OM mineralization. The Ph rise is the key factor controlling OM solubilization under reducing conditions. This rise of Ph accounts for >60% of the total released DOC, which is not due to reductive dissolution as such.

  • Increasing Ph drives organic matter solubilization from wetland soils under reducing conditions
    Geoderma, 2009
    Co-Authors: Malagorzata Grybos, Mélanie Davranche, Gérard Gruau, Patrice Petitjean, Mathieu Pédrot
    Abstract:

    International audienceIn wetlands, large quantities of dissolved organic matter (DOM) are solubilized under reducing conditions. Controlled incubations of a wetland soil were performed under oxic and anoxic conditions to investigate the extent to which the following processes account for this Phenomenon: i) production of organic metabolites by microbes during soil reduction; ii) release of organic matter (OM) from Mn- and Fe-oxyhydroxides that undergo reductive dissolution; and iii) desorption of OM from soil minerals due to Ph changes. Anaerobic incubation releases 2.5% of the total soil organic carbon (OC) as dissolved organic carbon (DOC), and is accompanied by a Ph rise from 5.5 to 7.4 and by the soil Mn- and Fe-reduction. The three processes above all take place. However, anaerobic incubation at a constant Ph of 5.5 (preventing OM desorption) releases only 0.5% of the total soil OC, while aerobic incubation at Ph 7.4 (preventing Mn- and Fe-reduction) releases 1.7% of the total soil OC. By contrast, aerobic incubation at Ph 5.5 (preventing both Mn- and Fe-reduction and Ph rise) does not solubilize any DOC. The DOC released is markedly aromatic, indicating little contribution from microbial metabolites, but, rather, the presence of microbes leading to OM mineralization. The Ph rise is the key factor controlling OM solubilization under reducing conditions. This rise of Ph accounts for >60% of the total released DOC, which is not due to reductive dissolution as such

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