chemical properties of secondary phyllosilicates
DESCRIPTION
Chemical Properties of Secondary Phyllosilicates. Isomorphous substitution ‘replacement’ of an ion by another of similar size, but differing charge Creates net negative charge on mineral structure Cation Exchange Capacity - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/1.jpg)
Chemical Properties of Secondary Phyllosilicates
Isomorphous substitution•‘replacement’ of an ion by another of similar size, but differing charge
•Creates net negative charge on mineral structure
Cation Exchange Capacity•Measure of ability of soil to retain positively charged ions (meq/100 g)
•Measured on basis of cations retained per 100 g soil
Base Saturation•Fraction of total CEC that is counter balanced by ‘base cations’ (Ca, Mg, Na, K)
•Remaining charge neutralization by H, Al is refered to as ‘exchangable acidity”
![Page 2: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/2.jpg)
Estimating soil clay mineralogy from CEC
CEC/100 g soil x 1/clay% x 100 = CEC/100g clay
(meq/100g soil)(100gsoil/g clay)(100)
Organic matter correction
CEC/100gsoil x C% x CEC/g C = corrected CEC (insert into equation above)
(meq/100gsoil)(gC/100gsoil)(meq/gC)
![Page 3: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/3.jpg)
Example from Brazil
![Page 4: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/4.jpg)
Correction of A horizon
CEC= 6.7 meq/100 g soil
C = 2.76% (x2 = OM)
Clay = 34.7%
CEC/100g clay =19.3
Mineralogy=kaolinite and geothite (~5 meq/100g clay)
6.7 - (2.76x2)(1 meq/g SOM) = 1.94meq/100 soil (corr)
(1.94)(100/34.7)(100)= 5.6 meq/100 clay
![Page 5: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/5.jpg)
Method of calculating amounts (mass) from concentrations
•Data sheets give horizon concentrations of various componds in a given horizon (clay%, C%, CEC/100 g, etc)
•Common to ask what is mass per unit area (m-2) per horizon or entire soil profile.
•To do calculation, need horizon thickness, concentration, gravel content and bulk denisty.
![Page 6: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/6.jpg)
Calculation of mass of compounds in soils
•Most concentration data given on < 2mm fraction (“fine earth”). Therefore:
Mass/horizon = (horizon vol - rock vol)(BD)(conc/100)
Volume= cm3
BD= g/cm3
Mass/soil= all horizons
ABtBC
![Page 7: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/7.jpg)
Rock volume adjustment
1. Volume adjustment
- useful only if gravel given in volume values
- subtract directly from horizon volume
- most gravel given in weight percentages….
2. Weight adjustment [mass = (vol)(BD)(FE)(conc/100), where FE=
€
100 −%rock
BD%rock
2.65−
100 −%rock
BD
=%vol of horizon occupied by non-rock
= (vol fines/100g soil)/(vol total soil/100g soil)
![Page 8: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/8.jpg)
Clay Dispersion and Flocculation: mechanisms and soil impacts
•Clay formation can occur througout soil, though clay is usually concentrated below surface
–Implies some sort of transport
•The suspension of clays in downward moving water is related to their electrical properties and the chemistry of the surrounding waters
![Page 9: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/9.jpg)
Role of Clay Mineral Type
Mobility Requires:
1. CEC
2. expandability
![Page 10: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/10.jpg)
Concentration vs. Composition
![Page 11: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/11.jpg)
Basics of Clay Mobility
ESP= ratio of Na/Ca+Mg on claysRatios > 15 produce undesirable features (from irrigation)
SAR~ ratio of Na/Ca+Mg in soln.SAR easier to measure than ESP
The combination of SAR and solute conc of soil water (or irrigation) determines clay mobility
![Page 12: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/12.jpg)
Effect of Na in soils
Leads to:
•Rapid downward transport•Development of Btn horizons•Columnar structure
![Page 13: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/13.jpg)
Sodic Soils of San Joaquin Valley
Btn horizon formation in < 10,000 yrs due to:
1. High pH (9-10) which rapidly dissolves silicates and increase Si solubilty
2. High Na, in combination with dilute rain, disperse clays near surface
3. High salt content rapidly increase soln. Conc. With depth, flocculating clay
![Page 14: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/14.jpg)
Topographic Transect of east SJ Valley
![Page 15: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/15.jpg)
The toposequence
•Granitic alluvium•~10,000 yrs
•Depth to H2O table primary variable
–Causes increase in salt/Na content–Increases weathering–Increases clay dispersion
![Page 16: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/16.jpg)
Fresno soil: highest water table and Btn
A
E
Btnk1
Btnk2
Bqnkm
Bqnk1
Bqnk2
BC
![Page 17: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/17.jpg)
Hesperia: moderate depth and no Bt but high CaCO3
A
Bk1
Bk2
etc
![Page 18: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/18.jpg)
Hanford: no Bt or salts
A
Bw
C
![Page 19: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/19.jpg)
Basin-rim landscape
![Page 20: Chemical Properties of Secondary Phyllosilicates](https://reader035.vdocuments.site/reader035/viewer/2022062808/5681528c550346895dc0af89/html5/thumbnails/20.jpg)