ARS | Publication request: Heavy metal and phenol adsorption properties of biochars from pyrolyzed switchgrass and woody biomass in correlation with surface structures

Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2013
Publication Date: February 25, 2013
Citation: Han, Y., Boateng, A.A., Qi, P.X., Lima, I.M., Jainmin, C. 2013. Heavy metal and phenol adsorption properties of biochars from pyrolyzed switchgrass and woody biomass in correlation with surface properties. Environmental Management. 118:196-204.

Interpretive Summary: Biochar can adsorb heavy metal ions and toxic organic compounds from aqueous solution and soil. The adsorption properties of biochar depend on the porous structure and surface chemical properties which are, in turn, a function of the feedstock and pyrolysis conditions. We carried out both fast (high heat rate) and slow (low heat rate) pyrolysis experiments as well as steam activation to investigate how the structures and surface functional groups of biochar and activated carbon affect the heavy metal and phenol adsorption properties. The heavy metals used were zinc and copper. We determined that lower acidity with pH 4.8 was more favorable for heavy metal immobilization than in soil conditions where pH is neutral (pH 7). We demonstrated that phenol adsorption capability is directly proportional to the micropore surface area as well as the combined level of the accessible acid groups present. These findings are helpful in selecting biochars and activated carbons that may be suitable for application in soils to remove heavy metals and for treatment of industrial waste water contaminated with phenolic compounds.

Technical Abstract: In this work, three types of biomass, switchgrass (SG), hardwood (HW) and softwood (SW) were either fast pyrolyzed (FP) in a fluidized-bed reactor at 500 degree C or slow pyrolyzed at 500 degree C (for 1hr) and at 700 degree C (for 0.5hr) with the biochar produced at 500 degree C further steam activated. The surface structures were studied in detail, and surface acidic functional groups were determined quantitatively by the Boehm Titration method. The adsorption properties of heavy metals, Zn2+ and Cu2+ onto the biochars and activated carbons were investigated by analyzing the adsorption isotherms, correlated with the surface properties, and further evidenced by SEM. The adsorption behavior of phenol onto biochars and activated carbons, analyzed by ATR-FTIR and GC, demonstrated that phenol adsorption capability is directly proportional to the micropore surface area as well as the combined level of the accessible carboxylic and lactonic groups. The relative adsorption capacity with respect to the biomass precursor follows the order: SW > HW > SG.