Physical and Structural Properties -Specific Surface -Water Sorption/Reaction -X-ray Diffraction Chemical Properties -Bulk (NMR, elemental) -Recalcitrance -Surface -Hydrophilicity Beneficial Properties for Soil Amendments

1. Biochars Are Not Created Equal:
A Survey of their Physical, Structural, and Chemical
Properties and Implications for Soil Application
J.E. Amonette*, Y. Hu, N. Schlekewey, S. S.
Dai, Z. W. Shaff, C. K. Russell, S. D. Burton,
and B. W. Arey
jim.amonette@pnl.gov
Pacific Northwest National Laboratory,
Richland, WA 99352
National Society of Consulting Soil Scientists
Amelia Island, FL
04 March 2010
PNNL-SA-71408

2. Outline
Physical and Structural Properties
Specific Surface
Water Sorption/Reaction
X-ray Diffraction
Chemical Properties
Bulk (NMR, elemental)
Recalcitrance
Surface
Hydrophilicity
Beneficial Properties for Soil Amendments
Amonette 04Mar2010

3. Physical and Structural Properties
Pine Wood Char
Oak Wood Char
Corn Cob Char
Amonette 04Mar2010

4. Physical Properties
Slow
Slow
Fast
Fast
Gas
Gasifier
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5. X-ray Diffraction Analysis
Slow Pyrolysis and Hydrothermal Chars
Gasification and (steam present)
Fast Pyrolysis Chars Combustion Char (high mineral content)
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6. Transformations during pyrolysis
Amonette 04Mar2010
Keiluweit et al., 2010 EST online

7. Physical Structure and
Chemical Properties Depend
on Carbon Bonding Network
Radovic et al., 2001
13CCP-MAS NMR
Amonette et al., 2008
Amonette 04Mar2010

8. What if you don’t have a 13C-CP-
MAS-NMR, XRD, FIB-SEM or some
other super duper DPY-UTH-
ALPHABET-SOUP gizmo . . .???
What are the most cost-effective
analyses for routine classification?
Amonette 04Mar2010

9. Proximate Analysis
Provides quick sense of
stability and chemistry in
three parameters:
100 Hydrothermal
Volatile matter is mass Slow Pyrolysis
lost in heating charcoal 90 Fast Pyrolysis
to 950°C in covered Gasification
crucible for 6 minutes 80 Ash-Free Line
50% VM/FC
Ash content is mass of 70 100% VM/FC
residue after
combustion 60
Fixed C is remainder Fixed C, % 50
High ash content (KCl, 40
SiO2), seen in corn
30
stovers, wheatstraw,
switchgrass, and 20
manure chars (CaO) 10 Increasing
Pyrolytic chars tend to Ash
0 Content
have VM/FC ratios of 0 10 20 30 40 50 60
0.5 to 1.0 Volatile Matter, %
JE Amonette 29 August 2009
Higher fixed C contents
suggest greater C
stability
Amonette 04Mar2010

10. Ultimate Analysis
More expensive than proximate analysis
Measures
C, H, O, N, S elemental content
Moisture content
Mineral ash remaining after combustion
Used to help classify chars and determine the degree of
alteration from original biomass
Elemental ratios often plotted to aid classification (e.g.,
van Krevelen diagrams)
Amonette 04Mar2010

11. Sum to 100%
Ultimate Analysis Volatile Fixed
LOD C H N O S Ash Matter C
Sample % % % % % % % % %
HT Grass 2.29 53.83 5.24 2.17 18.40 0.57 22.88 48.92 28.20
HT Wood 4.81 66.20 5.46 2.98 18.62 0.27 7.24 48.20 44.56
WSU S 2.94 46.04 1.74 0.70 14.28 0.23 40.55 19.83 39.62
OKEB 4.03 70.35 3.92 0.42 23.28 0.02 2.88 37.36 55.73
PBEB 4.41 66.75 3.64 0.35 26.08 0.03 3.93 43.35 48.31
PCEB 2.90 72.34 4.42 0.17 21.94 0.02 1.19 41.37 54.54
PCN 2.44 71.25 4.60 0.17 23.51 0.02 0.99 44.63 51.94
CS1 2.33 54.92 2.59 0.90 15.60 0.08 29.51 21.47 46.69
CS2 2.20 36.54 2.20 0.97 17.78 0.09 48.35 22.60 26.85
PNNL-M (MP) 3.30 68.45 3.94 0.25 25.50 0.02 3.29 40.14 53.27
PNNL-P 2.99 72.09 3.88 0.18 23.30 0.02 2.54 36.44 58.03
PNNL-S (SG) 2.75 56.15 2.88 1.08 19.07 0.15 25.77 24.30 47.18
OAK 2.97 79.64 2.68 0.28 15.47 <0.01 3.70 22.75 70.58
WAL 5.50 45.53 0.86 0.49 17.68 1.00 45.11 20.32 29.07
HW 1.02 90.44 1.84 0.24 5.02 <0.01 3.07 8.10 87.81
WS 1.97 53.18 1.64 0.39 8.53 0.17 37.99 8.72 51.32
OK 4.45 53.38 2.34 0.81 14.21 0.09 32.46 17.50 45.59
CSB 2.54 53.41 1.01 0.39 7.08 0.06 41.07 7.64 48.75
Oak 3.62 78.11 2.81 0.31 15.64 0.02 3.74 27.60 68.66
Amonette 04Mar2010

12. Van Krevelen Diagram
van Kremelen Diagram
Shows degree of
alteration from biomass 0.18
towards pure C
0.16
Path leading to lignite 0.14 Biomass
and coal distinct from 0.12
pyrolytic chars
H:C Ratio
Lignite
Hydrothermal
0.10
More energy extracted Slow Pyrolysis
0.08 Fast Pyrolysis
during pyrolysis than Coal
0.06 Gasification
during “coalification”
0.04 Coal
Lignin
Minimal alteration for Cellulose
0.02
hydrothermal “chars”
0.00
0.00 0.20 0.40 0.60 0.80 1.00
O:C Ratio
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13. FC/VM Ratio
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H
T
0
2
4
6
8
10
12
G
ra
H ss
T
W
oo
d
W
S
U
S
O
KE
B
PB
Gasifier
Recalcitrance?
EB
PC
E
B
Hydrothermal
Fast Pyrolysis
Slow Pyrolysis
PC
N
C
S1
PN C
N S2
L-
M
(M
P)
PN
PN N
N L-
L- P
S
(S
G
)
O
AK
W
A
L
H
W
W
S
O
K
C
SB
O
ak

14. Modeled half-life (yr) of biochars prepared at different
temperatures from various feedstocks
Feedstock 250°C 400°C 525°C 650°C
Oak 840 1020 9590 96200
Pine -- 990 6790 17000
Cedar 730 23800 12800 20000000
Bubinga 1200 4300 -- 15600
Gamma 260 370 930 --
Grass
Sugar Cane 690 9310 2280 146600
Zimmerman, 2010 EST online
Amonette 04Mar2010

15. Estimated half-life in soils: effect of
temperature
Estimates of Half-life in Soils
(Slow Pyrolysis Biochars)
1400
Cheng et al. (2008)
1200
Kuzyakov et al. (2009)
1000
Time, years
800
600
400
200
0
5 10 15 20 25 30 35
Mean Annual Temp, C
Amonette 04Mar2010

16. Surface Chemistry
Slow
Fast
Gas
Slow Pyrolysis chars produced in presence of steam at 475°C tend to
be acidic (carboxylic acid groups activated)
Fast Pyrolysis chars produced in absence of steam at 500°C tend to
be slightly basic
Gasification chars produced in presence of steam at 700°C tend to be
very basic and make good liming agents
Amonette 04Mar2010

17. Surface Chemistry—Boehm titration results
1200
NaOH Analyte
Slow Pyrolysis (steam)
Na2CO3 Analyte
1000
NaHCO3 Analyte
Fast Pyrolysis (no steam)
HCl Analyte
800
Gasification (steam)
600
400
200
0
OKEB PBEB PCEB PCN OAK PNNL‐M PNNL‐P PNNL‐S HW OK (CSA) WS CSB
‐200
Amonette 04Mar2010

18. Inferred pH-Dependent Exchange Capacities
Oak Feedstock
1000
OKEB Slow Pyrolysis (steam), 475°C
800 OAK
Ion Sorption Capacity, meq/kg
OK (CSA)
Cations
600
400
Fast Pyrolysis, 500°C
200
Gasification (steam), 700°C
0
0 2 4 6 8 10 12 14
Anions
-200
-400
-600
pH
Amonette 04Mar2010

19. Hydrophilicity
75
Hydrothermal
70
Slow Pyrolysis
Fast Pyrolysis
65
-1
Gasifier
Surface Tension, mN m
Increasing Hydrophilicity
60
55
50
45
40
35
30
PN )
P
B
)
EB
B
P
SB
S
d
K
ak
W
S1
S2
AK
S
G
L
ss
L-
E
KE
oo
(M
O
W
A
(S
U
H
O
PC
PB
ra
C
C
C
N
W
O
W
S
O
M
G
S
W
L-
L-
N
N
PN
PN
Amonette 04Mar2010 “Molarity of ethanol drop” method

20. Speculations on the best biochar type for
soil application
Criteria
Near-neutral pH
High ion exchange capacities (CEC and AEC)
Moderate hydrophobicity to retain organics
High stability to oxidation
Low volatile content
Pre-treated with NH4+ to avoid induced N deficiency
Recommendation
Steam-activated
Carbonized (i.e., treated to higher temperature to remove
volatiles)
Slow pyrolysis probably better
If none of above, best to let biochar age weeks to months
(compost?) before adding to soil, unless being used to lime
Amonette 04Mar2010

21. Acknowledgments
Thanks to Stefan Czernik, Danny Day, Bob Hawkins, Hal
Collins, Manuel Garcia-Perez, Doug Elliott, Marcus
Antonietti, Emma Suddick, and Michael Antal for samples
of biochars analyzed here
Research supported by
USDOE Office of Fossil Energy through the National
Energy Technology Laboratory
USDOE Office of Biological and Environmental Research
(OBER) through the Carbon Sequestration in Terrestrial
Ecosystems (CSiTE) project.
Research was performed at the W.R. Wiley Environmental
Molecular Sciences Laboratory, a national scientific user
facility at the Pacific Northwest National Laboratory
(PNNL) sponsored by the USDOE-OBER.
PNNL is operated for the USDOE by Battelle Memorial
Institute under contract DE AC06 76RL01830.
Amonette 04Mar2010