Biochar Amendment for Reducing Leachability of Nitro Explosives and Metals from Contaminated Soils and Mine Tailings

The mobility and bioavailability of nitro explosives (2,4-dinitrotoluene [DNT], 2,4,6-trinitrotoluene [TNT], and hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX]) in biochar-amended soils and toxic metals (As, Cd, Cu, Pb, and Zn) in biochar-amended mine tailings were investigated via various types of leaching procedures in laboratory-scale batch experiments. The results from the toxicity characteristic leaching procedure (TCLP) and hydroxypropyl-b-cyclodextrin (HPCD) extraction showed that approximately 55 to 95% of the explosives were released from the contaminated soils and would thus be considered as mobile. With the addition of biochar, the extracted concentrations of explosives were reduced to less than 10% of the initial concentrations after 10 d. According to the results from a Korean waste leaching method, the TCLP method, and diethylenetriaminepentaacetic acid (DTPA) extraction, adding biochar to mine tailings reduced the extractability and bioavailability of metals. The chemical forms of the metals, types of extractants, pH, and curing period strongly affected the extractability of metals from mine tailings. The results suggest that biochar is a promising immobilizer of explosives and metals in contaminated soils and mine tailings under limited conditions.