Stabilization of As and Sb in contaminated acidic shooting range soil with apatite mine tailings: Challenge of co-contamination

Differences in the behavior of shot-derived metal Pb and the metalloids Sb and As render the remediation of metal(loid)-contaminated shooting range soils challenging. Treatment methods that generally reduce Pb solubility may simultaneously increase Sb and As solubility due, for example, to pH changes and ion competition. We investigated the potential of tailings from phosphate mining, previously shown to immobilize Pb, to stabilize acidic shooting range soil without incurring the risk of enhanced Sb(V) and As(V) solubility. In a 2.5-year field trial, the soil of a former shooting range, surface-treated with tailings consisting of phlogopite, the carbonate minerals calcite and dolomite, and residues of apatite, displayed no evidence of increased Sb or As solubility. Results from a parallel laboratory-scale pot experiment, carried out with test soils collected from the field site, supported the findings. Under acidic conditions, dissolution of the carbonate fraction of the tailings, and the subsequent decrease in soil acidity, contributed to the release of Sb and As from organic associations and/or Al and Fe (hydr)oxide surfaces. We concluded that the numerous Ca 2+ ions liberated upon the dissolution of carbonates reacted with the anionic species of Sb(V) and As(V) to form sparingly soluble Ca-antimonates and Ca-arsenates. Moreover, the solubility of intrinsic and apatite-derived P in the test soils, initially hypothesized to compete for adsorption sites with Sb and As and thereby increase their solubility, also decreased after tailings treatment. In conclusion, Pb-contaminated shooting range soil was successfully stabilized with the tailings without increasing Sb or As solubility. • A metal(loid)-contaminated shooting range was stabilized with phosphate mine tailings. • Multicomponent tailings immobilized Pb without increasing Sb or As solubility. • Carbonate-derived Ca 2+ ions contributed to Sb and As precipitation. • The challenge of co-contamination can be dealt with by applying multicomponent tailings.