Fe-biochar for simultaneous stabilization of chromium and arsenic in soil:Rational design and long-term performance br

Excess chromium (Cr) and arsenic (As) coexist in soil such as chromated copper arsenate (CCA) contaminated sites,leading to high risks of pollution. Fe-biochar with adjustable redox activity offers the possibility of simultaneous sta-bilization of Cr and As. Here, a series of Fe-biochar with distinct Fe/C structure were rationally produced for the reme-diation of Cr and As contaminated soil (BCX-Fe, X represented the biomass/Fe ratio). Adsorption tests showed thatmaximal adsorption of BC5-Fe for Cr(VI) and As(III) reached 73.7 and 81.3 mg/g. A 90-day soil remediation experimentindicated that the introduction of 3% (w/w) Fe-biochar reduced the leaching state of Cr(VI) by 93.8-99.7% and As by75.2-95.6%. Under simulated groundwater erosion for 10 years and acid rain leaching for 7.5 years, the release levelsof Cr(VI) and As in the BC5-Fe remediated soil could meet the groundwater class IV standard in China (Cr(VI)<0.1mg/L, As<0.05 mg/L). Accelerated aging tests demonstrated that BC5-Fe had long-term Cr and As stabilization ability.The quenching experiment, EPR, and XPS suggested that the corrosion products of Fe dominated the adsorption andredox reactions, while the O groups acted as electron transfer stations and constituted redox microcirculation in the syn-chronous uptake of Cr/As. Based on these insights, we believe that our study will provide meaningful information aboutthe application potential of Fe-biochar for the heavy metal contaminated soil remediation