U n i t e d S t a t e s D e p a r t m e n t o f A g r i c u l t u r e • A g r i c u l t u r a l R e s e a r c h S e r v i c e

Biochar soil amendment for environmental and agronomic benefits: Selection Criteria

Sophie Minori Uchimiya, K. Thomas Klasson, Isabel Lima

USDA-ARS Southern Regional Research CenterNew Orleans, LA 70124

CautionMetals, PAHs, other VM components, air pollution, available biomass, soil type… localized, site-specific, case-by-case biochar utilization for specific purpose

Overview of the sustainable biochar concept Woolf et al. Nature Communications (2010)

photosynthesis

bioenergy

soil fertilizationC sequestrationremediation

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.

Charred C globally-Up to 35% of total organic C in US agricultural soils (Skjemstad et al., 2002)-Intentional slash-and-char: oxosol-turned-anthrosol Terra Preta (Lehmann et al., 2003)

Why add biochar?

Charred plant fragments found in the grassland, forest, and field soils, e.g., black chernozem soils

Acknowledgement: National Institute for Agro-Environmental Sciences Tsukuba, Japan

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

Co

nce

ntr

atio

n ( M

)

0

20

40

60

80

100

120

140

160

180

200

220

240

CH350CH500

CH650CH800

PS800700BL

soil 020406080

100120140160180200220240260280300320

CH350CH500

CH650CH800

PS800700BL

soil0

20406080

100120140160180200220240260280300320

CH350CH500

CH650CH800

PS800700BL

soil

[Pb

] (

M)

0

20

40

60

80

100

120

140

160

180

200

220

240

CH350CH500

CH650CH800

PS800700BL

soil

[Cu

]+[N

i]+

[Cd

]+[P

b]

(mM

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

CH350CH500

CH650CH800

PS800700BL

soil

pH

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

CH350CH500

CH650CH800

PS800700BL

soil

t0

t48

char

Effects of pyrolysis T on biochar property and heavy metal retention ability

Cu

Pb

CdNi

total pHpHpzc

CH350≈700BL<PS800<CH500≈CH650<<CH800

700BL≈PS800 <CH350≈CH500≈CH650<CH800

CH350<700BL<PS800 <CH500≈CH650<CH800

CH350 << 700BL < PS800 < CH500 ≈ CH650 ≈ CH800

Norfolk soil 10 wt% amendment, 300 M each metal added together

BET surface area fixed C ash content pH

√ volatile matter√ O/C, N/C√ pHpzc

Surface functional groups

phosphoric acidactivated carbon

broiler litterbiochar

0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30

Co

nce

ntr

atio

n ( M

)

0

20

40

60

80

100

120

140

160

180

200 Cu

0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.300

20406080

100120140160180200220240260280300320

O/C0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30

020406080

100120140160180200220240260280300320340360

0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30

[Pb

] (

M)

0

20

40

60

80

100

120

140

160

180

200

220

0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30

[Cu

]+[N

i]+

[Cd

]+[P

b]

(mM

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

cottonseedhull chars

steam activated carbons

phosphoric acidactivated carbons

Ni Cd

Pb Cu+Ni+Cd+Pb

O/CO/C

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)

cottonseed hull chars

Heavy metal retention ability O/C

Uchimiya et al., J. Hazard. Mater. 2011, 190, 432–441.

flax shive steam (O/C = 0.04)

30% HNO3 (O/C = 0.18)

chemical oxidation to increase O/C

various oxidants available (H2O2, KMnO4, ozone, air)

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

[Cu

] (

M)

0

2

4

6

8

10

12

14

16

020406080

100120140160180200220240260280300320

(e) Ni(d) Cd

(b) Pb (soil-only = 212 ± 4 M)

PL350

PL700

TL350

TL700

FL350

FL700

MD35

0

MD70

0

SW35

0

SW70

0[N

i] ( M

)

[Pb

] (

M)

PL350

PL700

TL350

TL700

FL350

FL700

MD35

0

MD70

0

SW35

0

SW70

0so

il

PL350

PL700

TL350

TL700

FL350

FL700

MD35

0

MD70

0

SW35

0

SW70

0so

il

PL350

PL700

TL350

TL700

FL350

FL700

MD35

0

MD70

0

SW35

0

SW70

0

(c) Cu (soil-only = 226 ± 14 M)

soil

PL350

PL700

TL350

TL700

FL350

FL700

MD35

0

MD70

0

SW35

0

SW70

0so

il5.1

5.4

5.7

6.0

6.3

6.6

6.9

7.2

7.5

7.8

8.1

(a) pH (after 48h equilibration)

pH

[Cd

] (

M)

Uchimiya et al., J. Environ. Qual., 2012, 41, 1138-1149.

poultry

turkey

feedlot

dairy

swine

Comparison of 5 Manure Varieties (350, 700 oC)

*work conducted in collaborationwith ARS Florence, SC

“best” Pb, Cu, Ni, Cd stabilizer: 700oC poultry, turkey, feedlot

pH Pb

Cu NiCd

poor stabilizers contained very high (swine) or low (dairy) ash, P biochar properties help predict function in soil

300 M eachmetal at t0

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.

close up

portable x-ray fluorescence for in situ screening of soil metal concentrations

Images provided by Dr. Bannon (US Army)

heavy metal contaminated training range soils (Bannon et al., ES&T 2010)

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)…

O/C0.00 0.06 0.12 0.18 0.24 0.30 0.36 0.42 0.48 0.54 0.60 0.66 0.72

H/C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

cottonseed hulls

grass (Keiluweit)

wood (Keilweit)

pine needle (Chen)

broiler litter

dehydration

base treatment

stea

m a

ctiv

atio

n

steam

pyrolysis temperature (oC)

100 200 300 350 400 600 650500250 700 80025

Biochar oxidation to increase surface functional groups (O/C) while maintaining stability (H/C)

Uchimiya et al. J. Agr. Food Chem. 2011, 59, 2501–2510.

H/C aromaticity

O/C polarity

O/C without changing H/C bychemical oxidation (30% HNO3) of flax shive (steam activated)

800900100011001200130014001500160017001800

C=OC=C C-Ocarboxyl

C=O flax-conc.nitric/sulfuricflax-30%nitric

flax

Wavenumber (cm-1)800900100011001200130014001500160017001800

C=OC=C C-Ocarboxyl

C=O CH800-conc.nitric/sulfuricCH800-30%nitric

CH800

3:1 = sulfuric:nitric(both conc.)highly exothermic

5g char/400mL acid 6 hr at 70 oC

Method sourceCho et al. (Langmuir 2010) carboxyl the most for MWCNTs

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

CH800-oxidized 0.31 2.7 N/A

Conc. nitric/sulfuric acid oxidation:

carboxyl, hydroxyl, carbonyl

×5-10 O/C

0 2 4 6 8 10 12 14 16 18 200.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 2 4 6 8 10 12 14 16 18 20

[Cu

] (m

g L

-1)

0.0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10 12 14 16 18 20

[Pb

] (m

g L

-1)

0

2

4

6

8

10

12

14

16

18

20flax

biochar amendment rate (wt%)

MD1 soil-onlyflax-oxidized

flax-oxidized

flax

MD1 soil-only

MD2 soil-only

BL650

BL350

biochar amendment rate (wt%)

MD2 soil-only

BL350

BL650

Equilibration#1 (no buffer, 1wk) *some biochars (CH350 for MD2) increased Pb and Cu.

Broiler litter (BL) biochars:No clear temperature effects on Pb or Cu

Oxidation enhanced Pb, Cu retention

O/C = 0.04

O/C = 0.39

0 2 4 6 8 10 12 14 16 18 20

pH

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14 16 18 206.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

biochar amendment rate (wt%) biochar amendment rate (wt%)

MD2 soil-only

MD1 soil-only flax

flax-oxidized

BL350

BL650

√ 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?

Equilibration#1 (no buffer, 1wk)

pH change vs. Pb, Cu retention as a function of biochar amendment rate

pH Pb Cu

flax-oxidized

flax ≈ ≈

BL650

BL350 Uchimiya et al. (J. Agr. Food Chem. 2012)

0 2 4 6 8 10 12 14 16 18 200

30

60

90

120

150

180

210

240

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16 18 20

[Cu

] (m

g L

-1)

0

2

4

6

8

10

12

0 2 4 6 8 10 12 14 16 18 20

[Pb

] (m

g L

-1)

0

30

60

90

120

150

180

210 MD1 soil-only

(c) flax (Cu)

biochar amendment rate (wt%)

flax

flax-oxidized

MD1 soil-only

flax-oxidized

flax

MD2 soil-only

BL650

BL350

biochar amendment rate (wt%)

BL650

BL350

Equilibration#2 (pH4.9 acetate) >10-fold Pb, Cu without biochar compared to Eq#1 for both soils

All biochars effective for Pb, Cu despite acidic pH√ Oxygen-containing surface functional groups√ Complex formation and solid phase formation with phosphate (especially Pb)

Oxidation enhanced Pb, Cu retention

Broiler litter (BL) biocharsBL350 more effective for Pb

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 interactionsManure biochars rich in PO4

3– no desorptionSb stabilized by Al2O3, MgO, and other ash components?

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

Which biochar to use?

Uchimiya et al. (J. Agr. Food Chem. 2012)