One-pot synthesis of nZVI-embedded biochar for remediation of two mining arsenic-contaminated soils: Arsenic immobilization associated with iron transformation.

Waste biomass derived biochar has been proven as an effective and friendly amendment for remediation of heavy metals-contaminated soil. However, biochar is less effective for soil arsenic (As) immobilization in most cases. To improve the ability of biochar for As immobilization, in this study, the composite of biochar embedded with nano zero valent iron (nZVI/BC) was prepared through simple one-step pyrolysis of biomass sawdust and Fe2O3 mixture and then applied for amendment of two mining As-contaminated soils. Pristine sawdust biochar (BC) and nZVI alone or in combination were included for comparison. Results show that the prepared nZVI/BC contained about 40% Fe which was mainly present as Fe°. All treatments except BC reduced As concentration in (NH4)2SO4 extraction and gastrointestinal solution. Particularly, nZVI/BC reduced the labile As in (NH4)2SO4 extraction in two soils by over 93% and bioaccessible As in gastrointestinal solution decreased by over 85%. Fe° on the surface of nZVI/BC was oxidized into amorphous FeOOH which adsorbed or co-precipitated with As. Meanwhile, Ca-Fe-As-O and Al-Fe-As-O co-precipitated at the interface between nZVI/BC and two soils enriched with Ca and Al, respectively. Results indicated that the simply-prepared nZVI/BC was a promising material for remediation of As-contaminated soils.