Use of soil amendments to immobilize antimony and lead in moderately contaminated shooting range soils

Shooting ranges are a source of environmental concern around the world as they are a source of toxic antimony (Sb) and lead (Pb). In-situ chemical stabilization is a strategy to reduce metal(loid) leaching and bioavailability. However it is difficult to find the right treatment due to the fact that Pb is a cation and Sb an anion, under oxidised conditions and they often show the opposite mobility in soil, on the application of amendments. A batch experiment was set up with two soils (slightly acidic and alkaline), two red mud based amendments (ViroSoil™ 1 and 2) alone and in combination with two reducing agents (zero valent iron and iron sulphate), to assess the effect of the treatments on metal(loid) leaching and compare it to unamended soil and soil amended with goethite, a known Sb adsorbent. Iron sulphate was effective at reducing Sb leaching due to the reduction of Sb^V to Sb^III which bound more strongly to iron (hyr)oxides in soil. However it had an adverse effect on the leaching of Pb due to its acidifying effect and reductive dissolution of manganese (hyd)roxides. Combining ViroSoil™ amendments with FeSO₄ still reduced Sb leaching but also Pb leaching and proved a suitable treatment.