Antimony (Sb) contaminated shooting range soil: Sb mobility and immobilization by soil amendments

Antimony (Sb) in lead bullets poses a major environmental risk in shooting range soils. Here we studied the effect of iron (Fe)-based amendments on the mobility of Sb in contaminated soil from shooting ranges in Norway. Untreated soil showed high Sb concentrations in water extracts from batch tests (0.22-1.59 mg L(-1)) and soil leachate from column tests (0.3-0.7 mg L(-1)), occurring exclusively as Sb(V). Sorption of Sb to different iron-based sorbents was well described by the Freundlich equation (Fe2(SO4)3, log KF = 6.35, n = 1.51; CFH-12 (Fe oxyhydroxide), log KF = 4.16-4.32, n = 0.75-0.76); Fe(0) grit, log KF = 3.26, n = 0.47). These sorbents mixed with soil (0.5 and 2% w/w), showed significant sorption of Sb in batch tests (46-92%). However, for Fe2(SO4)3 and CFH-12 liming was also necessary to prevent mobilization of lead, copper, and zinc. Column tests showed significant retention of Sb (89-98%) in soil amended with CFH-12 (2%) mixed with limestone (1%) compared to unamended soil. The sorption capacity of soils amended with Fe(0) (2%) increased steadily up to 72% over the duration period of the column test (64 days), most likely due to the gradual oxidation of Fe(0) to Fe oxyhydroxides. Based on the experimental results, CFH-12 and oxidized Fe(0) are effective amendments for the stabilization of Sb in shooting range soils.