Biochar soil amendment for
environmental and agronomic benefits:
Selection Criteria
Sophie Minori Uchimiya, K. Thomas Klasson,
Isabel Lima
USDA-ARS Southern Regional Research Center
New Orleans, LA 70124
Unit ed States Department of Agriculture • Agricultural Research Service
Overview of the sustainable biochar concept
Woolf et al. Nature Communications (2010)
bioenergy
soil fertilization
C sequestration
remediation
Caution
Metals, PAHs, other VM components, air pollution, available biomass, soil type…
 localized, site-specific, case-by-case biochar utilization for specific purpose
photosynthesis
Acknowledgement: National Institute
for Agro-Environmental Sciences
Tsukuba, Japan
Why add biochar?
Charred plant
fragments found in
the grassland, forest,
and field soils, e.g.,
black chernozem
soils
Charred C globally
-Up to 35% of total
organic C in US
agricultural soils
(Skjemstad et al., 2002)
-Intentional slash-andchar: oxosol-turnedanthrosol Terra Preta
(Lehmann et al., 2003)
Andosol (kuroboku) Volcanic ash+field burning to keep glassland (forest management).
Rich in old C (1400 years 14C) as Fe, Al complexes, 3-33% charred carbon
Source: Sindo et al. Org. Geochem., 2004; Nishimura et al. Soil Sci. Plant Nutr., 2008.
Heavy metal stabilization mechanism
(1) electrostatic interactions between metal cations and –charged biochar surface >PZC
(2) ionic exchange between ionizable protons on biochar surface and metal cations
(3) delocalized  electrons of aromatic biochar structure coordinate d-electron especially
for softer Lewis acids (Pb<Cu<Cd)
(4) specific binding of metal ions by surface ligands (carboxyl, hydroxyl, phenol, P- and
basic N-containing) abundant in VM component of biochar (Polo et al., ES&T, 2002)
(5) ash (e.g., Al2O3)
(6) particulate formation induced by pH, phosphate (e.g., pyromorphite)…
1. Model systems (add Pb, Cu, Ni, Cd to agricultural soils)
• systematically compare different (1) metal contaminants, (2) soil, (3) biochar properties.
Norfolk loamy sand: acidic, eroded, low TOC, low CEC Typic Kandiudult.
San Joaquin soil: alkaline, 40-60% clay (montmorillonite) cemented Abruptic Durixeralfs.
 biochar necessary for Norfolk but not San Joaquin.
• Cu sorption-desorption isotherms for binding reversibility.
• Effects of NOM and carbonized vs. noncarbonized fractions (Cu mobilized by carboxyl)
 Degree of stabilization: Pb > Cu > Cd > Ni (common for soil, mineral, chars)
2. Contaminated (shooting range) soils of known pH, CEC, TOC
Effects of pyrolysis T on biochar property and heavy metal retention ability
 BET surface area
 fixed C
 ash content
 pH
Cu
200
180
160
140
120
CH350≈700BL<PS800
<CH500≈CH650<<CH800
100
80
60
40
20
0
240
220
l
0
0
0
0
0
L
35 H50 H65 H80 S80 00B soi
H
P
7
C
C
C
C
[Pb] (M)
160
Cd
CH350 << 700BL < PS800
< CH500 ≈ CH650 ≈ CH800
l
0
0
0
0
0
L
35 H50 H65 H80 S80 00B soi
H
P
7
C
C
C
C
l
0
0
0
0
0
L
35 H50 H65 H80 S80 00B soi
H
P
7
C
C
C
C
10.0
Pb
200
180
Ni
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
700BL≈PS800
<CH350≈CH500≈CH650<CH800
140
120
100
80
60
40
1.0
9.5
9.0
0.9
pH
pHpzc
8.5
0.8
8.0
0.7
7.5
0.6
7.0
0.5
0.4
0.3
CH350<700BL<PS800
<CH500≈CH650<CH800
6.5
6.0
5.5
5.0
4.5
0.2
4.0
20
0.1
0
0.0
l
0
0
0
0
0
L
35 H50 H65 H80 S80 00B soi
H
P
7
C
C
C
C
total
pH
Concentration (M)
220
broiler litter
biochar
Surface functional groups
Norfolk soil 10 wt% amendment, 300 M each metal added together
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
[Cu]+[Ni]+[Cd]+[Pb] (mM)
240
√ volatile matter
√ O/C, N/C
√ pHpzc
phosphoric acid
activated carbon
3.5
l
0
0
0
0
0
L
35 H50 H65 H80 S80 00B soi
H
P
7
C
C
C
C
3.0
t0
t48
char
l
0
0
0
0
0
L
35 50 65
80 80 0B soi
CH CH CH CH PS 70
Biochar characteristics (O/C) translate into heavy metal sorption ability in soil
steam activated carbons (flax shive, cotton gin)
phosphoric acid activated carbons (pecan shell)
Heavy metal retention ability  O/C
cottonseed hull chars
200
Cu
Concentration (M)
180
steam activated
carbons
160
140
phosphoric acid
activated carbons
120
100
80
60
cottonseedhull
chars
40
20
0
0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
Ni
0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
Cd
0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
1.0
Pb
200
180
160
140
120
100
80
60
40
20
0
[Cu]+[Ni]+[Cd]+[Pb] (mM)
220
[Pb] (M)
360
340
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
0.9
flax shive steam (O/C = 0.04)
0.8
0.7
chemical oxidation
to increase O/C
0.6
0.5
30% HNO3
0.4
O/C
(O/C = 0.18)
0.3
0.2
various oxidants available
(H2O2, KMnO4, ozone, air)
0.1
0.0
0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
O/C
Cu+Ni+Cd+Pb
0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
O/C
Uchimiya et al., J. Hazard. Mater. 2011, 190, 432–441.
Comparison of 5 Manure *work conducted in collaboration
Varieties (350, 700 oC)
with ARS Florence, SC
“best” Pb, Cu, Ni, Cd stabilizer: 700oC poultry, turkey, feedlot
(b) Pb (soil-only = 212 ± 4 M)
2.4
8.1
pH
7.8
2.2
Pb
2.0
7.5
1.8
[Pb] (M)
7.2
6.6
poultry
swine
1.0
0.8
0.6
5.7
turkey
5.4
dairy
0.4
0.2
(a) pH (after 48h equilibration)
0.0
14
Cu
12
6
4
5
PL 0
70
TL 0
35
TL 0
70
FL 0
35
FL 0
7
M 00
D
35
M 0
D
7
SW 00
35
SW 0
70
0
so
il
PL
3
[Cd] (M)
8
(c) Cu (soil-only = 226 ± 14 M)
2
0
PL
35
PL 0
70
TL 0
35
TL 0
70
FL 0
35
FL 0
7
M 00
D
35
M 0
D
7
SW 00
35
SW 0
70
0
[Cu] (M)
10
160
140
120
100
80
60
40
20
0
280
260
240
(e) Ni
Ni
220
200
180
160
140
300 M each
metal at t0
120
100
80
60
40
20
0
50
16
poor stabilizers contained
very high320
(swine)
(d) Cd or low
300
Cd
280 P
(dairy) ash,
260
240properties help
 biochar
220
200
predict function
in soil
180
PL
3
PL
3
5
PL 0
70
TL 0
35
TL 0
70
FL 0
35
FL 0
7
M 00
D
35
M 0
D
7
SW 00
35
SW 0
70
0
so
il
5.1
feedlot
1.2
PL
35
PL 0
70
TL 0
35
TL 0
70
FL 0
35
FL 0
7
M 00
D
35
M 0
D
7
SW 00
35
SW 0
70
0
so
il
6.0
1.4
[Ni] (M)
6.3
1.6
PL
70
TL 0
35
TL 0
70
FL 0
35
FL 0
7
M 00
D
35
M 0
D
7
SW 00
35
SW 0
70
0
so
il
pH
6.9
Uchimiya et al., J. Environ. Qual., 2012, 41, 1138-1149.
Biochar for Shooting
Range Remediation
Typical Firing Range
Highest Pb Concentrations
Collaboration with Dr. Desmond Bannon (Aberdeen Proving Ground)
Bannon et al. Environ. Sci. Technol. 2009, 43, 9071-9076.
Uchimiya et al. J. Agr. Food Chem., 2012, 60, 1798–1809.
Uchimiya et al. J. Agr. Food Chem., 2012, 60, 5035−5044.
portable x-ray fluorescence for in situ
screening of soil metal concentrations
Images provided by Dr. Bannon (US Army)
close up
Biochar for Pb, Cu Stabilization
in Arms Range Soils
Heavy metal-contaminated shooting range, mine, and industrially impacted soils
• >3,000 DoD ranges: chemical stabilization (e.g., phosphate rock for Pb) as an alternative to costly soil
excavation and disposal (Cao et al., Environ. Pollut. 2010).
• Mixed results for biochar:  Cd, Zn, PAHs;  As, Cu (Beesley et al., Environ. Pollut. 2010).
How do biochars retain heavy metals in Pb, Cu contaminated arms range soils?
Surface ligand complexation: biochar with and without oxidation (conc. HNO3/H2SO4,70 oC, 6h)  same
stability (H/C, fixed C), higher O/C and carboxyl content.
Stable phosphorus phases: manure biochars (350, 650 oC).
pH: equilibration in acetate buffer (5 mg L-1 Pb TCLP regulatory limit).
Soil property, equilibration condition,
and additional elements (Sb, P, K…)
Biochar-induced changes in soil property:
pH, CEC, TOC, DOC, inorganic elements
Impact of extraction fluid/cycle on equilibrium
soluble concentrations of heavy metals and additional
elements of biochar/soil origin: Sb, Zn, Al, P, K, Na, Ca
 “best” biochar depends on purpose,
remediation vs. agricultural use,
risk of oxoanions (As, Sb)…
heavy metal contaminated
training range soils
(Bannon et al., ES&T 2010)
Biochar oxidation to
increase surface functional
groups (O/C) while
maintaining stability (H/C)
cottonseed hulls
pyrolysis temperature (oC)
grass (Keiluweit)
wood (Keilweit)
pine needle (Chen)
25 100 200 250 300 350 400 500 600 650 700 800
broiler litter
2.0
 H/C
 aromaticity 1.8
 O/C
 polarity
1.6
1.4
base
treatment
1.0
s te a m
0.8
0.6
0.4
de
ion
activ
a ti o n
H/C
1.2
at
dr
y
h
steam
 O/C without changing H/C by
chemical oxidation (30% HNO3)
of flax shive (steam activated)
0.2
0.0
0.00 0.06 0.12 0.18 0.24 0.30 0.36 0.42 0.48 0.54 0.60 0.66 0.72
Uchimiya et al. J. Agr. Food Chem. 2011, 59, 2501–2510.
O/C
C=O
carboxyl C=C
C=O
C-O
flax
flax-conc.nitric/sulfuric
flax-30%nitric
Conc. nitric/sulfuric acid oxidation:
carboxyl, hydroxyl, carbonyl
O/C total acidity fixed C
wt%
mequiv g-1
wt%
flax
0.04
0
89
flax-oxidized
0.39
3.3
N/A
CH800
0.06
0
77
2.7
N/A
×5-10 O/C
CH800-oxidized 0.31
1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800
C=O
CH800
carboxyl C=C
C-O
CH800-conc.nitric/sulfuric
C=O
CH800-30%nitric
Method source
Cho et al. (Langmuir 2010)
 carboxyl the most for MWCNTs
5g char/400mL acid
6 hr at 70 oC
1800 1700 1600 1500 1400 1300 1200 1100 1000 900
-1
Wavenumber (cm )
3:1 = sulfuric:nitric
(both conc.)
800
highly exothermic
20
O/C = 0.04 flax
18
-1
[Pb] (mg L )
14
3.0
12
2.5
10
2.0
8
Equilibration#1 (no buffer, 1wk)
*some biochars (CH350 for MD2)
increased Pb and Cu.
BL650
1.5
6
4
MD1 soil-only
2
O/C = 0.39
1.0
flax-oxidized
0.5
0
BL350
0.0
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
2.0
0.5
-1
MD2 soil-only
3.5
16
[Cu] (mg L )
4.0
Oxidation enhanced
Pb, Cu retention
0.4
flax
0.3
MD1 soil-only
MD2 soil-only
1.8
1.6
Broiler litter (BL) biochars:
No clear temperature effects
on Pb or Cu
1.4
1.2
1.0
BL350
0.8
0.2
0.6
0.1
flax-oxidized
0.0
BL650
0.4
0.2
0.0
0
2
4
6
8
10 12 14 16 18 20
biochar amendment rate (wt%)
0
2
4
6
8
10 12 14 16 18 20
biochar amendment rate (wt%)
MD1 soil-only
6
flax
10.0
BL650
9.5
pH
5
9.0
4
8.5
flax-oxidized
3
8.0
7.5
2
BL350
7.0
1
6.5
Equilibration#1 (no buffer, 1wk)
0
MD2 soil-only
6.0
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
biochar amendment rate (wt%)
biochar amendment rate (wt%)
pH change vs. Pb, Cu retention as a function of biochar amendment rate
pH
Pb
Cu



≈

≈
BL650



BL350



flax-oxidized
flax
Uchimiya et al. (J. Agr. Food Chem. 2012)
√ pH is not the sole factor  use buffer (pH 4.9 acetate) to further investigate.
Are biochars still effective for Pb, Cu retention under acidic pH?
210
240
MD1 soil-only
210
[Pb] (mg L-1)
180
flax
150
BL650
150
Broiler litter (BL) biochars
BL350 more effective for Pb
120
90
90
60
60
flax-oxidized
0
0
2
4
6
8
10 12 14 16 18 20
MD1 soil-only
12
[Cu] (mg L )
180
120
30
-1
MD2 soil-only
(c) flax (Cu)
Oxidation enhanced
Pb, Cu retention
10
8
flax
6
30
BL350
0
16
0
2
4
6
8
10 12 14 16 18 20
14
12
10
BL650
BL350
8
6Equilibration#2 (pH4.9 acetate)
>10-fold Pb, Cu without biochar
4compared to Eq#1 for both soils
4
2
flax-oxidized
0
0
2
4
6
8
10 12 14 16 18 20
biochar amendment rate (wt%)
2All biochars effective for Pb, Cu despite acidic pH
0√ Oxygen-containing surface functional groups
√0Complex
and12
solid
with
2 4 formation
6 8 10
14phase
16 formation
18 20
phosphate
(especially
Pb)
biochar
amendment
rate (wt%)
Element leaching summary
Ash content: Greater acid dissolution of Ca, P, Mg for manure biochar (>35 wt% ash)
than plant biochar (10 wt% ash)
Alkali metals (Na, K): nearly100% dissolution at initial equilibration period
Alkaline earth metals (Ca, Mg): stabilized as carbonate and phosphate phases at high pH;
significant acid dissolution
Phosphorus: amendment rate-dependent release behaviors
with and without buffer for manure biochars (up to 6wt% P)
Oxoanion (SbV(OH)6–)
Plant biochars rich in COO–  desorption by repulsive interactions
Manure biochars rich in PO43–  no desorption
Sb stabilized by Al2O3, MgO, and other ash components?
Which biochar to use?
Total (microwave digestion) elemental composition does not predict the release behaviors
Biochar selection for Pb stabilization
low Sb, As risk, excess P undesirable (e.g., disused shooting range)  COO– rich biochars
oxoanion is a risk, P desirable as plant nutrient  manure biochars
Uchimiya et al. (J. Agr. Food Chem. 2012)