The use of red earth, lateritic soils and quarry dust as ...
The Biogeochemistry of Soils: Soils from Stars Composition of soils on earth is arguably unexpected...
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Transcript of The Biogeochemistry of Soils: Soils from Stars Composition of soils on earth is arguably unexpected...
The Biogeochemistry of Soils: Soils from Stars
•Composition of soils on earth is arguably unexpected
•Soils, and Earth, not reflective of chemistry of Universe
•Soils reflect chemical fractionation processes since beginning of universe:
–Big Bang
–Subsequent star formation/collapse
–Chemical differentiation during formation of solar system
–Chemical differentiation during formation of Earth
–Late cometary additions to Earth
Chemistry of Solar System
•Exponential decline in abundance w/ atomic number (number of protons)
•Sawtooth pattern
•Elements from Fe have passed through stars
•Solar system is dominantly H and He -6
-4
-2
0
2
4
6
0 20 40 60 80 100
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
Si
Cl
Ar
K
Ca
Sc
Ti
V
CrMn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Rb
Sr
Y
Zr
Nb
MoRu
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
In
Xe
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Re
OsIr
Pt
QuHgTl
Pb
Bi
Th
U
log (solar system mass fraction)
atomic number
Crust vs. Solar System
•Depleted in volatiles (as other inner planets)•Noble gases (group VIIIA)•H, C, N
•Core formation depleted crust in siderophile elements (group VIIIB..)
•Crust also reflects late stage cometary additions of light elements, etc. including water
-8
-6
-4
-2
0
2
4
6
0 20 40 60 80 100
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
AlSi
P
S
Cl
Ar
K
CaScTi
V
Cr
MnFe
Co
Ni
CuZn
Ga
Ge
As
Se
Br
Kr
RbSrY
ZrNb
Mo
RuRhPd
AgCd
In
SnSb
Te
I
Xe
Cs
BaLaCePrNd
SmEuGdTbDyHoErTmYbLu
HfTa
W
Re
Os
Ir
Pt
Au
Hg
TlPb
Bi
ThU
log (crust/solar system)
atomic number
period 2 period 3 period 4 period 5 period 6
lanthanides actinides
crust depleted
crust enriched
Soil vs. Crust
•Soil enriched in biochemically impt elements (C, N, S, Se)
•Soil depleted in alkali and alkine earths, Si, ….
•Date normalized to a relatively immobile element (Zr)
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 20 40 60 80 100
Li
Be
B
C
N
O
FNa
Mg
AlSi
P
S
Cl
KCaSc
TiVCrMn
Fe
Co
Ni
CuZnGa
Ge
As
Se
Br
Rb
Sr
YZr
Nb
MoAg
Cd
In
Sn
Sb
I
CsBa
La
CePrNd
SmEuGdTb
Dy
HoEr
TmYbLu
HfTa
WAu
Hg
Tl
PbBi
ThU
log(soil
Zr
/crust
Zr)
atomic number
soil enriched
soil depleted
Methods of (reasons for) Normalization to Index Element
100 kg @ t=0 80 kg @ t=X
1) Mineralogical composition of parent material and soil
Parent material Soil49 kg quartz (SiO) 49 kg quartz50 kg Ca silicate (CaSiO) 30 kg Ca silicate1 kg zircon (ZrSiO) 1 kg zircon
2) Molecular weights of elements and minerals
Molecular Wts (g/mole) Formula WtsSi=28.1 SiO=44.1O=16.0 CaSiO=84.2Ca=40.1 ZrSiO=135.3Zr=91.2
3) Sum of elemental mass in parent material and soils
Σ Siparen t material = (31.2)quartz+(16.7)C asilicate+(0.2)zircon= 48.1Σ Sisoil = (31.2)quartz+(10.0)C asilicate+(0.2)zircon= 41.4
Σ Caparen t material = (23.8)C asilicate
Σ Casoill = (14.3)C asilicate
Σ Zrparen t materia /l soil = (.7)zirl
Original land surface
20% weatheringloss
Parentmaterial
Soil
4) Concentrations in parent material and soil
Parent material Soil Enrich/Deplete
Si = .481 .518 enrichCa = .238 .179 depleteZr=.007 .009 enrich
5) Elemental ratios w/ and w/o normalization
No normalization Ratio Zr Normalization RatioCasoil/Caparent material .75 (Ca/Zr)soil/(Ca/Zr)pm .60Sisoil/Siparent material 1.08 (Si/Zr)soil/(Si/Zr)pm .86
Weathering Losses of Elements from Soils
•As might be expected, water enriched relative to crust via chemical reactions
•Relative concentration related to chemical nature of elements and their reactivity in water and type of bonds they form in crust
-1
0
1
2
3
4
5
6
0 20 40 60 80 100
LiBe
B
C
N
F
NaMg
Al
SiP
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
MnFeCoNi
CuZn
Ga
As
Se
Br
Rb
Sr
ZrNb
Mo
Ag
Cd
Sn
Sb
I
Cs
Ba
LaCe
Sm
EuTb Yb
Lu
Hf
Ta
W
AuHg
PbBi
Ra
Th
Ulog(water
Zr
/crust
Zr)
atomic number
Plant Composition and Soil Chemistry
Plants reflect water chemistry (with some selectivity) and photosynthesis/N fixation
-4
-2
0
2
4
6
0 20 40 60 80 100
H
Li
Be
B
CN
FNa
Mg
Al
Si
P
SCl
KCa
Sc
TiV
CrMn
Fe
Co
Ni
CuZn
Ga
As
Se
Br
Rb
Sr
YZr
MoAgCd
Sn
Sb
I
Cs
Ba
La
Ce
Sm
Eu
TbDy
YbLu
W
Au
Hg
TlPbBi
Th
U
log(plant
Zr
/crust
Zr)
atomic number
Soil Biogeochemistry Highlights
•Biological group
•Alkali/alkaline earths
•Halogens
•Rare earths
•Ti group
•Si, Al, Fe, P
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 20 40 60 80 100
Li
Na
K
RbCs
Be
MgCa
SrBa
F
Cl
BrI
CePrNd
SmEuGdTbDg
HoEm
TmYbLu
TiZr
Hf
C
N
S
SiPAl
Fe
ThU
log (soil
Zr
/crust
Zr)
atomic number
Soil Mineralogy: Primary Minerals
•Minerals are associations of elements
•Mineralogical composition a function of elemental behavior and abundances
–O 474,000 mg/kg–Si 277,000–Al 82,000–Fe 41,000–Ca 41,000–Na 23,000–Mg 23,000–K 21,000
•Relative abundance and behavior leads to reality that soils are dominated by aluminosilicates (O,Si, Al).
Structure of Silicates
•Silica tetrahedron
–Net charge
–Role of Al
•Covalent bonds (Si-O, Al-O) vs. ionic bonds (cations-O)
–Bond type based on electronegativity differences and tendency to attract electrons
•Big differences lead to ionic bonds
•Similar electronegativities lead to covalent bonds
•Linage of tetrahedra dictate classes of silicates and their chemical behavior
– Nesosilicates
–Inosilicates
–Phyllosilicates
–Tectosilicates
Electronegativities of the Elements
•Electonegativities dictated by position on table: elements with outer shells almost filled highly electonegative, those just starting new shell not. •Si-O form mainly covalent bond
The Silica Tetrahedron
•1 Si, 4 O = -4 net charge
•Tetrahedra can be linked by sharing O, thereby reducing net negative charge.
•Class of silicate is determined by number of shared O, and need for cations to neutralize net negative charge
Nesosilicates: Singe Tetrahedra Linked with Cations
Foresterite
•Single tetra linked with Mg+2
•Other minerals in group have all Fe+2
•Highly susceptable to chemical weathering via ejection of cations by acid (H+)
•Products then form secondary silicates and oxides
Inosilicates: Chains
Diopside:
•Single chains
Tremolite:
•Double chains
Phyllosilicates: Sheets
Muscovite
•‘dioctahedral w/ Al+3
Phlogopite
•‘trioctahedral’ w/ Mg+2
•K+ strongly adsorbed in cavities
Tectosilicates: Framework
Anorthite (Ca)
•50% Al for Si substition
Albite (Na)
•25% Al substition
Quartz
•No substition/O charge
Primary Silicate Summary
SilicateClassifiication
TetrahedronArrangement
Examples Chemical Formula ofSpeicific Minerals
(+)chargeper 100Oxygen
MeltingTemperature(C)
Nesosilicates independenttetrahedra
olivine series (foresterite)Mg2SiO4 100 1890 (1)
(fayalite)Fe2SiO4 100 1205 (1)Inosilicates single chains pyroxene
group(augite)Ca(Mg,Fe,Al)(Al,Si)2O6
66 (2) ~1200 (1)
double chains amphibolegroup
(hornblende)NaCa2(Mg,Fe,Al)5(Si,Al)8
O22(OH)2
55(1)
Phyllosilicates sheets mica group (biotite)(Mg,Fe)3(AlSi3O10)(OH)2
80 ~1100 (1)
(muscovite)KAl2(AlSi3O10)(OH)2
80 ~980(3)
Tectosilicates framework plagioclasegroup
(anorthite) CaAl2Si2O8 100 1550 (1)
(albite) NaAlSi3O8 50 1100 (1)feldspar group (orthoclase) KalSi3O8 50 1150 (1)silica group (quartz) SiO2 0 867 (1)
(1) Data from W.A. Deer, R.A. Howie, and J. Zussman, An Introductionto the Rock Forming Minerals,Longman Group, Ltd., London (1966)(2) Value for endmember with no Al substitution for Si. Value will decrease in proportion to added Al.(3) From ranges reported in: D.S. Fanning, V.A. Keramidas, and M.A. El-Desoky, Micas. Chap. 12 in:J.B. Dixon and S.B. Weed (eds), Minerals in Soil Environments, 2nd Ed., Soil Science Society of America,Madison, WI (1989).
Mineralogical Composition of Igneous Rocks
Stability of Primary Minerals in Soils
•Increasing Si/O ratio increases stability
–More covalent bonds
–Fewer ionic bonds
–Less susceptable to acids
•Decreasing Si/Al ratio reduces stability
–Al creates charge imbalance and need for cations
•Presence of Fe+2 reduces stability
–Fe+2 oxidizes to +3
–Size and charge altered and Fe is expelled