| Summary: | Granular metallic iron (gFe<sup>0</sup>) materials have been widely used for eliminating a wide range of pollutants from aqueous solutions over the past three decades. However, the intrinsic reactivity of gFe<sup>0</sup> is rarely evaluated and existing methods for such evaluations have not been standardized. The aim of the present study was to develop a simple spectrophotometric method to characterize the intrinsic reactivity of gFe<sup>0</sup> based on the extent of iron dissolution in an ascorbic acid (AA—0.002 M or 2 mM) solution. A modification of the ethylenediaminetetraacetic acid method (EDTA method) is suggested for this purpose. Being an excellent chelating agent for Fe<sup>II</sup> and a reducing agent for Fe<sup>III</sup>, AA sustains the oxidative dissolution of Fe<sup>0</sup> and the reductive dissolution of Fe<sup>III</sup> oxides from gFe<sup>0</sup> specimens. In other words, Fe<sup>0</sup> dissolution to Fe<sup>II</sup> ions is promoted while the further oxidation to Fe<sup>III</sup> ions is blocked. Thus, unlike the EDTA method that promotes Fe<sup>0</sup> oxidation to Fe<sup>III</sup> ions, the AA method promotes only the formation of Fe<sup>II</sup> species, despite the presence of dissolved O<sub>2</sub>. The AA test is more accurate than the EDTA test and is considerably less expensive. Eight selected gFe<sup>0</sup> specimens (ZVI1 through ZVI8) with established diversity in intrinsic reactivity were tested in parallel batch experiments (for 6 days) and three of these specimens (ZVI1, ZVI3, ZVI5) were further tested for iron leaching in column experiments (for 150 days). Results confirmed the better suitability (e.g., accuracy in assessing Fe<sup>0</sup> dissolution) of the AA test relative to the EDTA test as a powerful screening tool to select materials for various field applications. Thus, the AA test should be routinely used to characterize and rationalize the selection of gFe<sup>0</sup> in individual studies.
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