Chemical Weathering

Chemical Weathering

Chemical Weathering 

I. Introduction  

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview:

Decomposition alters minerals into more stable minerals or substances at the earth’s surface.

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction

an element loses electrons to an Oxygen ion

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction

an element loses electrons to an Oxygen ion

2Fe2++ 4HCO3 -1 + 1/2O2 + 2H20 >>>> Fe2O3 + 4H2CO3

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction

an element loses electrons to an Oxygen ion

2Fe2++ 4HCO3 -1 + 1/2O2 + 2H20 >>>> Fe2O3 + 4H2CO3

Ferrous bicarbonate ferric carbonic acid Iron Iron

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution

The process of chemical weathering by which earth material passes into solution by removal of its atoms.

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution

The process of chemical weathering by which earth material passes into solution by removal of its atoms.

Most well-known:

CO2 + H2O = H2CO3

Carbon dioxide water carbonic acid

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution

The process of chemical weathering by which earth material passes into solution by removal of its atoms.

Most well-known:

CO2 + H2O = H2CO3

Carbon dioxide water carbonic acid

CaCO3 + H2CO3 = Ca+ + HCO3-

Limestone + carbonic acid = calcium ions + bicarbonate

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution

The process of chemical weathering by which earth material passes into solution by removal of its atoms.

Most well-known: Limestone + water + carbonic acid = calcium ions + CO2 + bicarbonate

pH controls solubility….

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis

Describes the reaction between minerals and hydrogen“converting primary minerals into secondary minerals”

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis

Describes the reaction between minerals and hydrogen“converting primary minerals into secondary minerals” 2 KAlSi3O8 + 2H+ + 9H2O >>>> H4Al2Si2O9 + 4H4SiO4 + 2K+

orthoclase kaolinite silica acid

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange

involves the substitution of ions in solution for those held by mineral grains.

 

Cation exchange capacity (CEC): the capability for absorbing cations

“High Base Saturation”…..the % of exchange sites occupied by cationsother than H+.”

In acid soils, H+ replaces the cations; but in basic soils, H+ replace by cations.

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview * Mobility of cations

(Ca+2, Mg2+, Na+) > K+ > Fe2+ > Si4+ > Ti 4+> Fe 3+> Al 3

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview * Mobility of cations

(Ca+2, Mg2+, Na+) > K+ > Fe2+ > Si4+ > Ti 4+> Fe 3+> Al 3

* All related to the ionic potentialvalence (z) / ionic radius

valence (z) / ionic radiusvery mobile = less than 3very immobile + greater than 9.5

 

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview B. Leaching“The separation, selective removal, or dissolving out of soluble constituents from a rock by the natural action of percolating water”

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview B. Leaching“The separation, selective removal, or dissolving out of soluble constituents from a rock by the natural action of percolating water”

The process is dependent on CLIMATE and SOIL PROPERTIES

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview B. Leaching C. pH

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview B. Leaching C. pH

* The mobility of ions is controlled by pH

pH controls solubility….

Chemical Weathering III. Mobility A. Overview B. Leaching C. pH D. Fixation/Retardation

Chemical Weathering 

 III. Mobility A. Overview B. Leaching C. pH D. Fixation/Retardation E. Chelation  

Chemical WeatheringIV. Degree and Rate of Decomposition A. Mineral Stability

Chemical Weathering 

I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction C. Solution D. Hydrolysis E. Ion Exchange III. Mobility A. Overview B. Leaching C. pH D. Fixation/Redardation E. Chelation IV. Degree and Rate of Decomposition A. Mineral Stability B. Secondary Minerals

Chemical WeatheringIV. Degree and Rate of Decomposition A. Mineral Stability B. Secondary Minerals C. Estimates based on chemical analysis