Remediation of soil contaminated with arsenic, zinc, and nickel by pilot‐scale soil washing

Abstract

AbstractThe use of soil washing has successfully demonstrated bench‐scale and field applications for the remediation of oxyanions and cationic heavy metals. However, it is not easy to simultaneously remove both oxyanions and cations using one wash solution in the same extraction. Also contaminated soils from metal mining areas present other difficulties to remove contaminants because of their strong binding properties. Correspondingly, the efficiency of soil washing can be inhibited by the limited extraction of contaminants. The objective of this study was to find the optimal process conditions for the enhanced washing of recalcitrant contaminants. This study focused on the effectiveness of engineering‐scale washing of field soil using three types of inorganic acids (HCl, H2SO4, and H3PO4). In this study, soil contaminated with arsenic, nickel, and zinc was obtained from a closed iron/serpentine mining area. The H2SO4 and H3PO4 wash solutions, including the competitive oxyanion, enhanced the removal of arsenic. The acid attack on arsenic binding in the Fe/Mn oxide and organic/sulfides fractions may be a possible removal mechanism in addition to anionic competitive desorption. The low efficiency of soil washing results from the strong binding associated with minerals and the enrichment of contaminants in the highly reactive fine particles. For this soil used, the physical separation of particles could enhance the overall effectiveness of soil washing. Therefore, for the soils contaminated with recalcitrant contaminants in metal mining areas, the physical separation of fine particles can be significant in addition to the chemical extraction. © 2005 American Institute of Chemical Engineers Environ Prog, 2005