title: Effect of coexisting Al(III) ions on Pb(II) sorption on biochars: Role of pH buffer and competition.
abstract: Biochar is being widely considered as a promising amendment agent for immobilizing heavy metals in contaminated acidic soils, where plenty of soluble Al(III) ions exist. In view of uncertain significance of the effects of coexisting Al(III) on Pb(II) sorption by biochars, this study used kenaf core biochar (KB550; high carbon, low ash) and sewage sludge biochar (SB550; low carbon, high ash) pyrolyzed at 550 °C to elucidate the influence of coexisting Al(III) species and biochars' mineral components on Pb(II) immobilization conducted in aqueous solution with initial pHs of 3.0-4.5. Results showed that Al(III) reduced Pb(II) sorption on KB550 primarily via pH buffering against biochar alkalinity, thus inhibiting lead carbonate formation. In contrast, the reduction on SB550 mainly resulted from direct competition for sorption sites, especially on Fe-rich phengite 2M1 and metakaolinite. Because of Pb-P precipitation and Pb-K interlayer exchange, the residual Pb(II) adsorption capacity resistant to coexisting Al(III) was 3-5 times higher on SB550 than on KB550. The Pb-K interlayer exchange was enhanced by lower pH and coexisting Al(III), while Pb-P precipitation was the dominant Pb(II) sorption mechanism on SB550 resistant to Al(III) buffering and competition at higher pH. Application of these two biochars as amendments confirmed that the mineral-rich SB550 was more suitable for Pb(II) immobilization in acidic soils with high levels of extractable Al(III).
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, China.
authors.forename: Yuxi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, China. Electronic address: zhangwh5@mail.sysu.edu.cn.
authors.forename: Weihua
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Division Soil and Water Management, University of Leuven, 3001 Heverlee, Belgium.
authors.forename: Hao
authors.initials: H
authors.lastname: Qiu
authors.affiliation: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Daniel C W
authors.initials: DCW
authors.lastname: Tsang
authors.affiliation: Université de Lorraine, INRA, Laboratoire Sols et Environnement, BP 172, 2 Avenue de la forêt de Haye, F-54505 Vandoeuvre-lès-Nancy Cédex, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Morel
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, China. Electronic address: eesqrl@mail.sysu.edu.cn.
authors.forename: Rongliang
authors.initials: R
authors.lastname: Qiu
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D002021:Buffers; D002254:Carbonates / Q000032:analysis* / Q000737:chemistry; D002606:Charcoal / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007854:Lead / Q000032:analysis* / Q000737:chemistry; D008962:Models, Theoretical; D012722:Sewage / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry
chemical_list: D002021:Buffers; D002254:Carbonates; D007477:Ions; D012722:Sewage; D012987:Soil; D012989:Soil Pollutants; C540010:biochar; D002606:Charcoal; D007854:Lead; C043262:lead carbonate; D000535:Aluminum
keywords: Aluminum ions; Biochar; Competitive sorption; Lead ion; Soil remediation