Simultaneous and long-term effective immobilization of lead, cadmium and arsenic in multi-contaminated soil by ferrihydrite-supported animal-derived biochar

Abstract

The multi-contaminants of cationic Pb/Cd and anionic As in soils is difficult to simultaneously immobilize by common chemical amendments. Here, a novel ferrihydrite-supported animal-derived biochar (FAB) was prepared and added to pristine Pb/Cd/As-contaminated soil for incubation of 150 days. The amendment using FAB elevated soil pH and reduced soil electric conductivity and the release of soil dissolved organic carbon. After the addition of 3 %w/w FAB (FAB3 %), the bioavailability of Pb, Cd, and As decreased to 9.2, 57.5, and 7.6 mg/kg, respectively, which were 96 %, 47 %, and 36 % lower than that of the control soil (CK). The exchangeable Pb and Cd and specifically sorbed As were transformed into residual Pb, carbonate- and Fe-Mn oxide-bound Cd, and well-crystallized Fe-Al oxide-bound As, respectively. The diversity of soil bacterial community increased after FAB treatment. Dynamic leaching and first-order attenuation simulation experiments showed that FAB3 % can decrease the leachable heavy metal(loid)s to negligible concentration in real soil within 3–7 years, whereas that in CK soil was around 12 years. X-Ray adsorption near edge structure analysis showed that FAB immobilized heavy metal(loid)s in soil by forming pyromorphite coprecipitate with Pb(II), ion exchange between Cd(II) and Ca(II) in the hydroxyapatite component, and complexation between the ferrihydrite component and As(V).