Immobilization of Antimony(III) in Oxic Soil Using Combined Application of Hydroxyapatite and Ferrihydrite

The combined application of hydroxyapatite and ferrihydrite can simultaneously immobilize lead and antimony(V) in oxic soil. However, this has not been demonstrated for antimony(III). In this study, antimony(III) sorption experiments in solution and dissolution experiments in oxic soil were conducted using the combined application of hydroxyapatite and ferrihydrite to elucidate the contribution of the materials to antimony(III) sorption and to evaluate the amount of antimony dissolved from the antimony(III)-sorbed materials by the change in redox state in oxic soil. All the antimony(III) in 50 mg l−1 solution at pH 5 was sorbed on the combined materials without oxidation. The contribution of ferrihydrite and hydroxyapatite on antimony(III) sorption was 92.6 and 7.4 %, respectively. The antimony(III) sorbed on the combined materials was not oxidized within 7 days of incubation period in oxic soil. However, after 90 days of incubation period, all the antimony(III) was oxidized to antimony(V). The percentage of antimony dissolution from the simulative-immobilized soil with the antimony(III)-sorbed combined material was constant at less than 1 % during incubation periods. Therefore, no enhancement in the antimony soil mobility in the soil with the combined application was observed, although antimony(III) was oxidized. These results suggest that the combined application of hydroxyapatite and ferrihydrite could immobilize antimony(III) without re-dissolving antimony through oxidation. Thus, the combined application would be applicable to lead- and antimony-contaminated soil.