Biochar soil amendment for environmental and agronomic benefits: Selection Criteria

1. 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

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

3. 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-and-char: oxosol-turned-anthrosol 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.

4. 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 formationinduced 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

5. Effects of pyrolysis T on biochar property and heavy metal retention ability phosphoric acid activated carbon  BET surface area  fixed C  ash content  pH √ volatile matter √ O/C, N/C √ pHpzc broiler litter biochar Surface functional groups Norfolk soil 10 wt% amendment, 300 mM each metal added together Cu Cd Ni CH350≈700BL<PS800 <CH500≈CH650<<CH800 CH350 << 700BL < PS800 < CH500 ≈ CH650 ≈ CH800 pHpzc Pb total pH 700BL≈PS800 <CH350≈CH500≈CH650<CH800 CH350<700BL<PS800 <CH500≈CH650<CH800

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

7. Comparison of 5 Manure Varieties (350, 700 oC) *work conducted in collaboration with ARS Florence, SC “best” Pb, Cu, Ni, Cd stabilizer: 700oC poultry, turkey, feedlot Pb pH poultry feedlot swine turkey dairy poor stabilizers contained very high (swine) or low (dairy) ash, P  biochar properties help predict function in soil Cu Cd Ni 300 mM each metal at t0 Uchimiya et al., J. Environ. Qual., 2012,41, 1138-1149.

8. 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.

9. portable x-ray fluorescence for in situ screening of soil metal concentrations Images provided by Dr. Bannon (US Army) close up

10. 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)

11. Biochar oxidation to increase surface functional groups (O/C) while maintaining stability (H/C)  O/C  polarity  H/C  aromaticity  O/C without changing H/C by chemical oxidation (30% HNO3) of flax shive (steam activated) Uchimiya et al. J. Agr. Food Chem. 2011,59, 2501–2510.

12. Conc. nitric/sulfuric acid oxidation: carboxyl, hydroxyl, carbonyl O/Ctotal acidityfixed 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-oxidized0.31 2.7 N/A ×5-10 O/C Method source Cho et al. (Langmuir 2010)  carboxyl the most for MWCNTs 5g char/400mL acid 6 hr at 70 oC 3:1 = sulfuric:nitric (both conc.) highly exothermic

13. O/C = 0.04 Equilibration#1 (no buffer, 1wk) *some biochars (CH350 for MD2) increased Pb and Cu. O/C = 0.39 Oxidation enhanced Pb, Cu retention Broiler litter (BL) biochars: No clear temperature effects on Pb or Cu

14. Equilibration#1 (no buffer, 1wk) pH change vs. Pb, Cu retention as a function of biochar amendment rate pHPbCu flax-oxidized    flax ≈  ≈ BL650    BL350    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?

15. Broiler litter (BL) biochars BL350 more effective for Pb Oxidation enhanced Pb, Cu retention 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)

16. 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? Total (microwave digestion) elemental composition does not predict the release behaviors Which biochar to use? 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)