Metal(loid) immobilization in soils with biochars pyrolyzed in N2 and CO2 environments

Avanthi Deshani Igalavithana; Xiao Yang; Hilda Rizkia Zahra; Filip M G Tack; Daniel C W Tsang; Eilhann E Kwon; Yong Sik Ok

doi:10.1016/j.scitotenv.2018.02.185

Metal(loid) immobilization in soils with biochars pyrolyzed in N₂ and CO₂ environments

Sci Total Environ. 2018 Jul 15:630:1103-1114. doi: 10.1016/j.scitotenv.2018.02.185. Epub 2018 Mar 7.

Authors

Avanthi Deshani Igalavithana¹, Xiao Yang¹, Hilda Rizkia Zahra², Filip M G Tack², Daniel C W Tsang³, Eilhann E Kwon⁴, Yong Sik Ok⁵

Affiliations

¹ Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea; School of Natural Resources and Environmental Science, Kangwon National University, Chuncheon 24341, Republic of Korea.
² Department of Green Chemistry and Technology, Ghent University, B-9000 Gent, Belgium.
³ Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
⁴ Department of Environment and Energy, Sejong University, Seoul 05006, Republic of Korea.
⁵ Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea. Electronic address: yongsikok@korea.ac.kr.

PMID: 29554732
DOI: 10.1016/j.scitotenv.2018.02.185

Abstract

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.

Keywords: Black carbon; Charcoal; Pyrolysis; Surface functional groups; Toxic metals.