title: Stabilization of cationic and anionic metal species in contaminated soils using sludge-derived biochar.
abstract: Currently, sludge pyrolysis has been considered as a promising technology to solve disposal problem of municipal sewage sludge, recover sludge heating value, sequester carbon and replenish nutrients in farmland soils. The resultant sludge-derived biochar (SDBC) is potentially an excellent stabilizing agent for metal species. This study applied the SDBC into four soils that had been contaminated in field with cationic Pb(II) and Cd(II)/Ni(II), and anionic Cr(VI) and As(III), respectively. The performance of metal stabilization under various operational and environmental conditions was evaluated with acid batch extraction and column leaching tests. Results indicated the SDBC could effectively stabilize these metals, which was favored by elevated temperature and longer aging. Periodic temperature decrease from 45 to 4 °C resulted in the release of immobilized Cr(VI) and As(III) but not Pb(II). However, a longer aging time offset such metal remobilization. This was possibly because more Pb was strongly bound and even formed stable precipitates, as shown by XRD and sequential extraction results. With increasing time, Cr(VI) was sorbed and partly reduced to Cr(III), while immobilized As(III) was co-oxidized to As(V) as indicated by XPS spectra. Column tests revealed that adding SDBC as a separate layer was unfavorable because the concentrated Cd(II) and Ni(II) in localized positions increased the peak levels of metal release under continuous acid leaching. In contrast, uniformly mixed SDBC could effectively delay the metal breakthrough and reduce their released amounts. Yet, a long-term monitoring may be required for evaluating the potential leaching risks and bioavailability/toxicity of these immobilized and transformed species in the SDBC-amended soils.
authors: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, PR China.
authors: Shen'en
authors: S
authors: Fang
authors: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors: Daniel C W
authors: DC
authors: Tsang
authors: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, PR China.
authors: Fengsha
authors: F
authors: Zhou
authors: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, PR China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, PR China. Electronic address: zhangwh5@mail.sysu.edu.cn.
authors: Weihua
authors: W
authors: Zhang
authors: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, PR China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, PR China.
authors: Rongliang
authors: R
authors: Qiu
mesh_terms: D000838:Anions; D002412:Cations; D002606:Charcoal / Q000737:chemistry*; D004787:Environmental Pollution; D052918:Environmental Restoration and Remediation / Q000379:methods*; D019216:Metals, Heavy / Q000032:analysis / Q000737:chemistry*; D012722:Sewage; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*
chemical_list: D000838:Anions; D002412:Cations; D019216:Metals, Heavy; D012722:Sewage; D012987:Soil; D012989:Soil Pollutants; C540010:biochar; D002606:Charcoal
keywords: Aging; Biochar; Metal immobilization; Sewage sludge; Soil remediation