Stabilization of Lead and Copper by Biochar Amendments In Arms Range Soils: Influence of Biochar Characteristics, Soil Property, and Equilibrium Conditions.

Soil amendment of char products (biochar) from thermochemical processing (slow/fast pyrolysis and gasification) of biomass for biofuel production has received considerable interests for contaminant sorption, soil fertilization, and carbon sequestration. Of potential sites for biochar application, heavy metal-contaminated shooting range, mining site, and industrially impacted urban soils represent a wide range of total organic carbon (TOC) content, cation exchange capacity (CEC), and pH. As an alternative to the excavation and disposal of contaminated soils at these sites, various removal (e.g., phytoremediation, bioleaching) and nonremoval (stabilization) strategies have been proposed. In this study, a series of agricultural waste-derived biochars and activated carbons were screened for their ability to stabilize heavy metals in small arms range soils collected across the U.S. that cover a wide range of pH, CEC, TOC, and total Pb (5,000-20,000 ƒÝg g-1) and Cu (200-3,000 ƒÝg g-1) contents. Biochars were first characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, surface charge, and by ATR-FTIR and 1H NMR. Biochar amended soils were exposed to a series of desorption conditions to address leaching by rainfall events, toxicity characteristics, and in vitro bioaccessibility. Equilibrium Pb, Cu, Sb, As, Ni, Zn, Al, Mg, Ca, Na, P, K, S, Fe concentrations were determined to understand the sorption-desorption behaviors of heavy metals and additional elements originating from biochar and soil. The complex data set was analyzed using a receptor model called positive matrix factorization to determine the chemical composition and distribution of the primary factors influencing the heavy metal stabilization phenomena in biochar amended soils. The results suggest the greatest extent of heavy metal stabilization in low CEC and TOC soils amended with biochars.