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 2Fe HCO /2O 2 + 2H 2 0 >>>> Fe 2 O 3 + 4H 2 CO 3

Chemical Weathering I. Introduction II. Process of Decomposition A. Overview: B. Oxidation and Reduction an element loses electrons to an Oxygen ion 2Fe HCO /2O 2 + 2H 2 0 >>>> Fe 2 O 3 + 4H 2 CO 3 Ferrous bicarbonate ferric carbonic acid 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: CO 2 + H 2 O = H 2 CO 3 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: CO 2 + H 2 O = H 2 CO 3 Carbon dioxide water carbonic acid CaCO 3 + H 2 CO 3 = Ca + + HCO 3 - 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 KAlSi 3 O 8 + 2H + + 9H 2 O >>>> H 4 Al 2 Si 2 O 9 + 4H 4 SiO 4 + 2K + orthoclasekaolinite 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 cations other 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, Mg 2+, Na + ) > K + > Fe 2+ > Si 4+ > 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, Mg 2+, Na + ) > K + > Fe 2+ > Si 4+ > Ti 4+ > Fe 3+ > Al 3 * All related to the ionic potential valence (z) / ionic radius

very mobile = less than 3 very 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 Weathering IV. 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 Weathering IV. Degree and Rate of Decomposition A. Mineral Stability B. Secondary Minerals C. Estimates based on chemical analysis