Notes Comprehe­nsive Guide to Fluid Rock Interact­ions - Essentia­l Study Script 1.193 Words / ~18 pages Author Mario B. in Nov. 2010

Overview: Die 'Mitschr­ift (Lernskr­ipt)' zu "Fluid rock interact­ions" ist ein umfassen­des Lehrmitt­el für Studiere­nde und Fachleut­e der Geowisse­nschafte­n. Sie deckt grundleg­ende Konzepte wie Lösungsc­hemie, Redoxrea­ktionen und Bodenbil­dung ab. Das Skript erklärt die Stabilit­ät von Feststof­fen bei niedrige­n Temperat­uren, die Mechanis­men von Auflösun­g und Fällung sowie den Elementf­luss an der Erdoberf­läche. Es behandel­t auch komplexe Themen wie organisc­he Komplexi­erung und Ionenaus­tausch in Böden. Dieses Lernskri­pt ist ein wertvoll­es Werkzeug für das Verständni­s von Prozesse­n, die für Umweltwi­ssenscha­ften und Ingenieu­rwesen relevant sind.

Fluid rock interactions SCRIPT

 

1.      Intoduction

2.      Solution chemistry and physicochemical parameters

3.      Stability of solids at low temperature

4.      Redox reactions

5.      Co precipation and solid solution

6.      Evaporates

 

Solution Chemistry

 

Interstital and soil solution?

 

Fluid rock interaction at low temperatures?

 

Ionenradius und Ladung?

The composition of rain water and fog?

H+, NH4+, Cl-, SO42-, NO3- sind die Hauptkomponenten,

bei Regen sind die Milliäquivalente/ L viel niedriger. Kommt durch größere Anhaftungsmöglichkeit beim Nebel.

 

Chemische Zusammensetzung von Boden und Flußwasser?

A= Boden, B= Flußwasser

 

Charge balance of CO2 dissolved in water at fixed pressure?

 die Kationen müssen die Anionen ausgleichen,

 

Was passiert wenn man eine starke Säure und eine starke Base dazugibt- NaCl, NaOH?

 

Dissolved inorganic carbon?

 

Iteration steps of general procedure?

 

Concentration and Activity?

 

Korrelation Ionenstärke/ Aktivitätskoeffizient?

Je höher die Ionenstärke desto niedriger die Aktivität

 

Was ist eine aquatische Komplex Formation?

·        Schneller Prozess

·        Metal cation + ligands+ hydrogen ion form complex

·        Stability constant K

·        Je jöher K desto stabiler

 

Stability of solids

 

General reaction?

Rate als kontrollierender Schritt?

·        Dissolution: If controlling step is reaction at the surface, including diffusion through a solid layer, the concentration in the solution will be uniform.

·        Aqueous Dissolution: If controlling step is aqueous diffusion, the concentration in solution close to the solid will be the value for equilibrium with the solid.

·        If both are controlling then it’s a gradual.

 

Precipitation von Gips?

·        Es muss mehr Ca+ als SO4 2- vorhanden sein,

·        je höher der Ca/SO4 ratio, desto mehr fällt aus

 

Calcite dissolution at equilibrium?

Je höher pH desto geringer der Partialdruck von CO2, exponentielles Verhältnis, Je höher der Partialdruck von CO2, desto mehr Ca2+ kann gelöst werden. Sprich bei niedrigem pH Wert kann auch mehr Ca2+ gelöst werden.

 

Solubility of amorphous silica?

Je höher die Temperatur desto mehr SiO2 kann gelöst werden, je geringer der pH Wert desto mehr kann gelöst werden,

 

 

 

 

 

 Concentrations of dissolved silica?

 

Aluminium oxides/ hydroxides?

 

Wie sieht die Struktur von Gibbsite aus?

Network of Al-hydroxide-octahedrons

 

Löslichkeit von Aluminium?

Aluminium verhält sich amphoter

 

Löslichkeit von Aluminium in Böden?

 

 

 

Solubility of Al(OH)2 in the presence of Oxalate

 

Silikatverwitterung

Mit atmosphärischem CO2 Buffer

 

Global silica input into the sea water- production of biomass

à Senkung von C02

 

Silikatverwitterungsreaktionen?

 

Liberation of polysilicic and monosilicic acids?

 

 

K20 Al2O3 SiO2 H2O System

 

Stability of the system?

 

Two stage Feldspar Dissolution?

 

 

Redox reactions

 

pe Value

Oxidation of Pyrite in acidic soils

 

 

 

 

 

 

 

Formation of Iron Oxide from Fe2+ and Fe3+

 

Corrosion in drinking water pipes

 

Co- precipitation and solid solution

 

Calcit Typ and aragonite typ?

Distribution coefficient of calcite?

 

Isomorpher Ersatz von Ca2+ durch Sr2+?

Sr ist in Aragonit viel größer als in Kalzit

 

Br as Proxy for Evaporation of Sea Water

 

Substitution of Al in Goethite?

Isomorphic substitution of Al3+ by Fe3+

 

Solid solution Lippmann Approach?

 

 

 

 

 

 

 

Evaporites

 

Abhnahme von H2O durch Verdunstung und Abnahme des Salzgehaltes durch Kristallisation,

 

Mg2+ as Indicator of Salinity and Water Activity

Solubility of Calcium Sulfate Minerals

Binary system Na2SO4- H20

Incongruent Dissolution of Carnallite?

Quarternary System?

3 binary systems

Sea water

 

Main types of marine Evaporites?

 

 

 

 

 

Mechanics and kinetics of dissolution and kinetics

 

Kinetics of geochemical processes?

1. Reactions are controlled by thermodynamics
2. Not all reactions that should occur, occur at a given time
3. Some are slow, some are inhibited by high activation energy barriers

 

 

What factors do drive the reaction rates?

1. Temperature
2. Pressure
3. pH
4. chemical composition
5. reactive surface area
6. mixing
7. physical transport
8. presence of catalysts

 

Element fluxes from the land to the sea?

Due chemical and physical denudation, more physical denudation,

 

Primary mechanisms of kinetics of dissolution?

Water+ gas+ primary mineral -> water+ gas + secondary minerals+ ions,

 

Which factors control the upper reaction?

1. Time
2. Amount of water
3. Temperature
4. Mineral structure
5. Chemical composition of water
6. Reactive surface area
7. Kinetics

Thatfore the climate is a major driver

 

pH effect?

General higher weathering rates at lower pH à apatite,

 

What types of minerals are in the upper crust?

87% are aluminosilicates

Si-O-Al

Si-O-Ca

Si-O-Na

 

 

 

Structure effect?

1. Complete destruction of mineral involves cleavage of metal-oxygen bond à amount of bonds, type of bond, type of metal
2. Partial destruction often only involves removal from the structure à inverse Bowen series

 

What bond energies hold the minerals together?

 

Chemical composition of the water?

1. Presence of reactive agents: free protons, free hydroxides, organic acids, inhibitors,
2. Presence of products: distance to chemical equilibrium

 

Presence of reactive agents?

Mineral structure is either destabilized due chemical attack or blocked due chemical protection because of adsorption of dissolved agents.

 

Net reaction?

Net rate= forward rate- backward rate à the more products the slower the net reaction

 

Gibbs free energy

1. Chemical potential of a compound
2. Chemical potential ∆G of a mixture of compounds
3. Chemical potential ∆G of a mixture of reactive compounds and distance from equilibria A

 

Rates / equilibrium relation?

The reaction rate is related to the degree of supersaturation or undersaturation

 

Factors for the reactive surface area?

1. Exposed area: physical or chemical protection possible,
2. Crystallographic directions: mineral dissolution rates are not equal on all surfaces,
3. Units for rates are normalized to weight, surface area, time,

 

Empirical rates?

 

What  are dangling oxygens?

Non bridging oxygens

 

 

 

What is the effect of diffusion as rate limiting step?

1. Transport control
2. Surface reaction control
3. Mixed transport and surface- reaction control

 

Formation of an activated complex as limiting step?

 

Equilibrium dissolution rate data?

 

Caveat?

1. Etch pit formation through weathering
2. Total surface area is not reactive surface area
3. Rates also depend on the crystallographic face

 

Nucleation and crystal growth as precipation reaction?

1. Homogenous nucleation: nuclei forms = f(Ω)
2. Heterogenous nucleation: precipitation onto existing foreign nuclei à surface precipitation

 

What happens during Crystal growth?

1. Adsorption onto nuclei
2. Surface nucleation: diffusion, dehydration, formation of 2d and 3d nuclei
3. Crystal growth

 

 

 

 

 

 

 

 

 

 

Rock weathering and soil Formation

 

Minerals in a soil profile?

1. Volume distribution of minerals changes with depth
2. Change of porosity and density
3. Emergence of secondary minerals
4. Development of secondary minerals
5. Development of secondary crusts
6. Change in texture and surface area
7. Incongruent dissolution

 

Jackson- Sherman weathering stages?

 

 

 

 

 

 

 

 

 

 

 

Soil forming processes?

1. Structure and texture development
2. Humus formation
3. Turbation and landscape erosion
4. Carbonatisation
5. Salt accumulation à salt cracking
6. Redox processes à permanent, intermittent
7. Weathering and mineral transformation à ice, clay formation, iron manganese oxy-hydroxide formation, ferralitisation desilification
8. Clay movement
9. Podzolisation
10. Lateritisation and bauxite formation

 

Incongruent dissolution?

The higher K (mol%) the higher the Al/Si mole ratio

 

Leached layer formation?

Leaching of labradorite(ca feldspar)

 

Organic Complexation and Ion Exchange on Soils

 

Organic acids, structure and occurrence?

 

 

 

 

Binding of Cu by organic acids?

 

Binding of organic acids to minerals?

1. Effect of pH
2. Hydrophobicity
3. Cation co- adsorption

 

Iron hydroxid formation?

 

Cation buffer in soils?

The higher the cation exchange capacity, the higher the organic matter content

 

Gaines Thomas equation?

 

 

Weathering at different scales and their possible applications

1. Soil profile: transfer of elements
2. Hillslope: element fluxes- element transfer, bufferzones
3. Catchment: forest productivity, acid rain
4. Landscape scale: erosion, pollutant export, land use management
5. Global models: climate change,

 

Different approaches to determine age of soil and weathering rates?

1. Soil profile analysis
2. Stream chemistry
3. Flowpath or catchment models- inverse modeling and mass balances, steady state models, kinetic models

 

Inverse modeling?

 

Water and element mass balance?

Runoff= precipitation- evapotranspiration- storage in the watershed

Net accumulation or depeletion= weathering+ deposition + anthropogenic input- chemical erosion- mechanical erosion – biomass uptake – storage in the watershed