Reducing As availability in calcareous soils using nanoscale zero valent iron.

Abstract

Different methods, including the use of nanoscale zero-valent iron (NZVI), have been used to treat arsenic (As)-contaminated environments, with much less data on the use of NZVI in arsenic-calcareous-polluted soils. Accordingly, two different experiments were conducted to investigate the effects of NZVI on the removal of As from three different calcareous-polluted soils. In the first experiment, the effects of soil type (differing in the rate of clay particles and organic carbon including S1 (8.0 and 0.05%), S2 (20 and 0.2%), and S3 (20.5 and 0.8%)) and NZVI concentration (0, 50, and 100g kg-1 of dry soil) on the removal of As extractable with distilled water were evaluated using a factorial design with three replicates. In the second experiment, the NZVI concentrations were reduced to 0, 2.5, 5.0, and 25gkg-1, and the NZVI contact time (0.5, 48, 96, 192, 384, and 768h) was also tested. The analysis of variance in both experiments indicated the significant effects (P<0.01) of the experimental treatments on the removal of As. The concentrations of available As in S3 (42.7mgkg-1), S2 (20.22mgkg-1), and S1 (24.22mgkg-1) after using the 50gkg-1 NZVI treatment decreased to 0, 0, and 0.05mgkg-1, respectively, which was not significantly different from the 100gkg-1 NZVI treatment. In the second experiment, using the 25gkg-1 NZVI treatment, the concentration of available As significantly decreased in S1 from 16.48 to 0.1767mgkg-1, in S2 from 13.34 to 0.31mgkg-1, and in S3 from 33.67 to 0.84mgkg-1. In the three soils, with increasing NZVI concentration and contact time, the concentration of available As in the solution phase significantly decreased (P=0.01). S3, due to a higher rate of organic matter, was less responsive to the NZVI treatments than the other soils. The effectiveness of the nanoremediation method, tested in this research work, on the stabilization of As in calcareous soils, is verified.