scholarly journals Silica Dissolution and Precipitation in Glaciated Volcanic Environments and Implications for Mars

2018 ◽  
Vol 45 (15) ◽  
pp. 7371-7381 ◽  
Author(s):  
A. M. Rutledge ◽  
B. H. N. Horgan ◽  
J. R. Havig ◽  
E. B. Rampe ◽  
N. A. Scudder ◽  
...  
Keyword(s):  
Silica Dissolution ◽  
Dissolution And Precipitation

The experimental determination of hydromagnesite precipitation rates at 22.5–75ºC

2014 ◽  
Vol 78 (6) ◽  
pp. 1405-1416 ◽  
Author(s):  
U.-N. Berninger ◽  
G. Jordan ◽  
J. Schott ◽  
E. H. Oelkers
Keyword(s):  
Low Temperature ◽  
Experimental Determination ◽  
Closed System ◽  
Equilibrium Constants ◽  
Magnesium Silicate ◽  
Silicate Mineral ◽  
Dissolution Rates ◽  
Dissolution And Precipitation

Natural hydromagnesite (Mg5(CO3)4(OH)2·4H2O) dissolution and precipitation experiments were performed in closed-system reactors as a function of temperature from 22.5 to 75ºC and at 8.6 < pH < 10.7. The equilibrium constants for the reaction Mg5(CO3)4(OH)2·4H2O + 6H+ = 5Mg2+ + 4HCO3– + 6H2O were determined by bracketing the final fluid compositions obtained from the dissolution and precipitation experiments. The resulting constants were found to be 1033.7±0.9, 1030.5±0.5 and 1026.5±0.5 at 22.5, 50 and 75ºC, respectively. Whereas dissolution rates were too fast to be determined from the experiments, precipitation rates were slower and quantified. The resulting BET surface areanormalized hydromagnesite precipitation rates increase by a factor of ~2 with pH decreasing from 10.7 to 8.6. Measured rates are approximately two orders of magnitude faster than corresponding forsterite dissolution rates, suggesting that the overall rates of the low-temperature carbonation of olivine are controlled by the relatively sluggish dissolution of the magnesium silicate mineral.

Hydrothermal Sintering under Mild Temperature Conditions: Preparation of Calcium-deficient Hydroxyapatite Compacts

2010 ◽  
Vol 65 (8) ◽  
pp. 1038-1044 ◽  
Author(s):  
Kazumichi Yanagisawa ◽  
Jae-Hyen Kim ◽  
Chisato Sakata ◽  
Ayumu Onda ◽  
Eri Sasabe ◽  
...  
Keyword(s):  
Reaction Time ◽  
Reaction Temperature ◽  
Hot Pressing ◽  
Reaction Parameter ◽  
High Bulk Density ◽  
Temperature And Pressure ◽  
Mild Temperature ◽  
Short Time ◽  
High Bulk ◽  
Dissolution And Precipitation

Calcium-deficient hydroxyapatite (CDHA) prepared by the coprecipitation method was solidified by the hydrothermal hot-pressing technique, and compacts of CDHA with high bulk density beyond 80% were obtained at 200 ℃. Each reaction parameter, viz. reaction temperature, pressure, and time, was systematically changed from the standard conditions to investigate its effects on density, Vickers hardness, and Ca/P ratio of the compacts obtained. The reaction temperature and pressure had a large effect on densification, but not the reaction time because the densification proceeds in a short time. The densification by hydrothermal hot-pressing involved dissolution and precipitation of the starting CDHA powder, so that the Ca/P ratio changed from 1.52 of the starting powders to 1.61 of the compact obtained by hydrothermal hot-pressing at 200 ℃ and 35 MPa for 24 h with the addition of 10 wt.-% water

Geochemistry of diagenetic non-silicate minerals: kinetic considerations

1985 ◽  
Vol 315 (1531) ◽  
pp. 39-56 ◽  
Keyword(s):  
Organic Matter ◽  
Ferric Iron ◽  
Local Equilibrium ◽  
Reducing Agent ◽  
Chemical Environment ◽  
Iron Sulphide ◽  
Burial Diagenesis ◽  
Vertical Zonation ◽  
Silicate Minerals ◽  
Dissolution And Precipitation

The early stages of burial diagenesis involve the reactions of various oxidizing agents with organic matter, which is the only reducing agent buried with the sediment. In a system in which a local equilibrium is established, thermodynamic principles indicate that, inter alia , manganese, iron and sulphate should each be consumed successively to give rise to a clearly characterized vertical zonation. However, ferric iron may not react fast enough and the relative rates of reduction of Fe III and sulphate not only control the formation of iron sulphide and associated carbonate but also may lead to extreme chemical and isotopic dis-equilibrium. This produces kinetically controlled ‘micro -environments’. On a larger scale, sulphide will diffuse upward to a zone in which its oxidation leads to a reduction of pH. The various dramatic changes in chemical environment across such an interface cause both dissolution and precipitation reactions. These explain common geological observations: the occurrence of flint nodules (and their restriction to chalk hosts) and the association of phosphate with glauconite.

Design of supersaturable formulation of telmisartan with pH modifier: in vitro study on dissolution and precipitation

2017 ◽  
Vol 47 (2) ◽  
pp. 163-171 ◽  
Author(s):  
Shinji Yamashita ◽  
Arima Fukunishi ◽  
Haruki Higashino ◽  
Makoto Kataoka ◽  
Koichi Wada
Keyword(s):  
In Vitro Study ◽  
Vitro Study ◽  
Ph Modifier ◽  
Dissolution And Precipitation

scholarly journals Time-Space Characterization of Wellbore-Cement Alteration by CO2-Rich Brine

Geosciences ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 490
Author(s):  
Maria Garcia-Rios ◽  
Philippe Gouze
Keyword(s):  
Numerical Models ◽  
Reaction Rates ◽  
Diffusion Reaction ◽  
Cement Matrix ◽  
Relative Distribution ◽  
Reaction Fronts ◽  
Time Space ◽  
Mass Transfers ◽  
Dissolution And Precipitation ◽  
Diffusion Properties

The risk of CO2 leakage from damaged wellbore is identified as a critical issue for the feasibility and environmental acceptance of CO2 underground storage. For instance, Portland cement can be altered if flow of CO2-rich water occurs in hydraulic discontinuities such as cement-tubing or cement-caprock interfaces. In this case, the raw cement matrix is altered by diffusion of the solutes. This fact leads to the formation of distinctive alteration fronts indicating the dissolution of portlandite, the formation of a carbonate-rich layer and the decalcification of the calcium silicate hydrate, controlled by the interplay between the reaction kinetics, the diffusion-controlled renewing of the reactants and products, and the changes in the diffusion properties caused by the changes in porosity induced by the dissolution and precipitation mechanisms. In principle, these mass transfers can be easily simulated using diffusion-reaction numerical models. However, the large uncertainties of the parameters characterizing the reaction rates (mainly the kinetic and thermodynamic coefficients and the evolving reactive surface area) and of the porosity-dependent diffusion properties prevent making reliable predictions required for risk assessment. In this paper, we present the results of a set of experiments consisting in the alteration of a holed disk of class-G cement in contact with a CO2-rich brine at reservoir conditions (P = 12 MPa and T = 60 °C) for various durations. This new experimental protocol allows producing time-resolved data for both the spatially distributed mass transfers inside the cement body and the total mass transfers inferred from the boundary conditions mass balance. The experimental results are used to study the effect of the fluid salinity and the pCO2 on the overall reaction efficiency. Experiments at high salinity triggers more portlandite dissolution, thinner carbonate layers, and larger alteration areas than those at low salinity. These features are accompanied with different spatial distribution of the alteration layers resulting from a complex interplay between salinity-controlled dissolution and precipitation mechanisms. Conversely, the effect of the pCO2 is more intuitive: Increasing pCO2 results in increasing the overall alteration rate without modifying the relative distribution of the reaction fronts.

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