scholarly journals Review of: Dissolution and precipitation of fractures in soluble rock

2016 ◽  
Author(s):  
Anonymous
Keyword(s):  
Soluble Rock ◽  
Dissolution And Precipitation

scholarly journals Dissolution and precipitation of fractures in soluble rock

2016 ◽  
Author(s):  
Georg Kaufmann ◽  
Franci Gabrovšek ◽  
Douchko Romanov
Keyword(s):  
Preferential Flow ◽  
Selective Dissolution ◽  
Secondary Porosity ◽  
Flow Paths ◽  
Rock Types ◽  
Preferential Flow Paths ◽  
Soluble Rock ◽  
Flow Through ◽  
Preferential Pathways ◽  
Dissolution And Precipitation

Abstract. Soluble rocks such as limestone, anhydrite, and gypsum are characterised by their large secondary permeability, which results from the interaction of water circulating through the rock and dissolving the soluble fracture walls. This highly selective dissolution process enlarges the fractures to voids and eventually cavities, which then carry the majority of flow through an aquifer along preferential flow paths. We employ a numerical model describing the evolution of secondary porosity in a soluble rock to study the evolution of isolated fractures in different rock types. Our main focus is three-fold: The identification of shallow versus deep flow paths and their evolution for different rock types; the effect of precipitation of the dissolved material in the fracture; and finally the complication of fracture enlargement in fractures composed of several different soluble materials. Our results show that the evolution of fractures composed of limestone and gypsum is comparable, but the evolution time scale is drastically different. For anhydrite, owing to its difference in the kinetical rate law describing the removal of soluble rock, when compared to limestone and anhydrite, the evolution is even faster. Precipitation of the dissolved rock due to changes in the hydrochemical conditions can clog fractures fairly fast, thus changing the pattern of preferential pathways in the soluble aquifer, especially with depth. Finally, limestone fracture coated with gypsum, as frequently observed in caves, will result in a substantial increase in fracture enlargement with time, thus giving these fractures a hydraulic advantage over pure limestone fractures in their competition for capturing flow.

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.

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