The residual polyphenols in tea residue was utilized to produce zero-valent iron(ZVI),which was subsequently immobilized onto biochar(BC)derived from pyrolyzed tea residue,thus yielding a ZVI/BC composite for the remediation of Cr(Ⅵ)in aqueous systems and contaminated soils.The results demonstrated that polyphenols extracted from tea residue could effectively reduce Fe(Ⅱ)to ZVI,and the ZVI/BC composite exhibited excellent capability in removing Cr(Ⅵ).The adsorption of Cr(Ⅵ)onto ZVI/BC occurred through monolayer chemical adsorption,with ZVI serving as the primary reactive site,and the isothermal adsorption of ZVI/BC was in accordance with the Langmuir model.Optimal Cr(Ⅵ)adsorption performance was observed at an initial solution pH of 3.Compared with BC,ZVI/BC could promote the transformation of soil chromium from easily utilized forms(exchangeable and carbonate-bound forms)to less utilized forms(ferromanganese oxidized and organic forms)in soils.The removal of Cr(Ⅵ)from both soil and water by ZVI/BC predominantly involves reduction reactions,accompanied by surface complexation processes.
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