(2018) Science of the Total Environment_Metal(loid) immobilization in soils with biochars pyrolyzed in N₂ and CO₂ environments

Igalavithana A.D., Yang X., Zahra H.R., Tack F.M.G., Tsang D.C.W., Kwon E.E., Ok Y.S.

(Elsevier B.V.) Science of the Total Environment ISSN: 489697 Vol.630 Issue. Article No. DOI: 10.1016/j.scitotenv.2018.02.185

Previous studies indicated that using CO₂ as a reaction agent in the pyrolysis of biomass led to an enhanced generation of syngas via direct reaction between volatile organic carbons (VOCs) evolved from the thermal degradation of biomass and CO². In addition, the physico-chemical properties of biochar in CO₂ were modified. In this current study, biochars generated from red pepper stalks in N₂ and CO₂ (RPS-N and RPS-C, respectively) were tested for their effects on the immobilization of Pb, Cd, Zn, and As in contaminated soils. Soils were incubated for one month with 2.5% of RPS, and two biochars (i.e., RPS-N and RPS-C) at 25 °C. After the incubation period soils were analyzed to determine the amendment effects on the behavior of metal(loid)s. The potential availability and mobility kinetics of metal(loid)s were assessed by single extraction of ammonium acetate and consecutive extraction of calcium chloride, respectively. Sequential extraction was used to further examine potential changes in geochemical fractions of metal(loid)s. The increased soil pH induced by application of the biochars reduced the potentially available Pb, Cd, and Zn, while RPS-C significantly reduced Pb due to the high surface area and aromaticity of RPS-C. However, RPS-C mobilized potentially available As compared to RPS-N due to the increased soil pH. Biochars reduced the mobility kinetics of Pb, Cd, and Zn, and RPS-N effectuated the greatest reduction of As mobility. The RPS-C increased the Fe and Mn oxides, hydroxide, and organically bound Pb, while both biochars and RPS-N increased residual Cd and Zn, and organically bound As, respectively. When considering the two biochars, RPS-C was highly effective for immobilization of Pb in soils, but it had no effect on Cd and Zn and a negative effect on As. In addition, RPS-C significantly increased the total exchangeable cations in soils. © 2018 Elsevier B.V.

This work was supported by the National Research Foundation of Korea ( NRF-2015R1A2A2A11001432 ).