Characterizing the Suitability of Granular Fe0 for the Water Treatment Industry

Abstract

There is a burgeoning interest in reliably characterizing the intrinsic reactivity of metallic iron materials (Fe0) or zero-valent iron materials (ZVI) used in the water treatment industry. The present work is a contribution to a science-based selection of Fe0 for water treatment. A total of eight (8) granular ZVI materials (ZVI1 to ZVI8) were tested. Fe0 dissolution in ethylenediaminetetraacetic acid (EDTA test) and 1,10-Phenanthroline (Phen test) is characterized in parallel experiments for up to 250 h (10 days). 50 mL of each solution and 0.1 g of each Fe0 material are equilibrated in quiescent batch experiments using 2 mM EDTA or Phen. Results indicated a far higher extent of iron dissolution in EDTA than in Phen under the experimental conditions. The tested materials could be grouped into three reactivity classes: (i) low (ZVI4, ZVI6, ZVI7, and ZVI8), (ii) moderate (ZVI1 and ZVI5) and (iii) high (ZVI2 and ZVI3). The order of reactivity was the same for both tests: ZVI2 ≅ ZVI3 > ZVI1 ≅ ZVI5 > ZVI4 ≅ ZVI6 ≅ ZVI7 ≅ ZVI8. Phen results revealed for the first time the time-dependent variation of the kinetics of iron corrosion (corrosion rate) in short-term batch experiments. Overall, the results demonstrated the superiority of the Phen test for evaluating the initial stage of Fe0 dissolution. Long-term column experiments are recommended to deepen the acquired knowledge.

A Novel and Facile Method to Characterize the Suitability of Metallic Iron for Water Treatment

“…Reardon [42] presented H 2 evolution at neutral pH values as a tool to characterize the reactivity of iron. Probably due to the large Fe 0 amount needed to quantitatively produce H 2 and the long duration of the experiments, this method has not been considered [21]. Noubactep [68] presented H 2 evolution in HCl (initial pH = 2) as a more rapid mean for the same purpose.…”

“…Noubactep et al [45] presented the EDTA method which was independently introduced two years later by Pierce et al [50]. The EDTA method has been continuously used and revisited by Noubactep and collaborators as summarized in [21,52]. Kim et al [47] introduced a method to measure the 'reductive power' of Fe 0 .…”

“…An ascorbate buffer was used to reduce Fe 3 -EDTA before adding Phen for Fe 2 complexation before Fe determination. Samples from the Phen experiments were treated in the same way as the same calibration curve was used [21].…”

“…For the Phen test, only three values are positive but all low (0.055, 0.312, and 1.100 mg), while the 6 negative numbers are very low, (< 0.6 mg). The negative 'b' values from the Phen test were due to the very slow kinetics for iron dissolution from less reactive samples (Figure 3b) while negative value from EDTA test was attributed to dissolved O2 and atmospheric corrosion products [20,21,52]. The most important parameters from these tests are the k values.…”

“…In a purely analytical perspective, it is recalled that samples from the Phen test, despite already depicting the orange coloration of Fe-Phen complexes, should be treated in the same way like the calibration standards. In this study ascorbic acid was used because of parallel experiments with EDTA [21]. In routine Phen tests, all other reducing agents (e.g., hydroxylamine) can be used, but the authors recommend ascorbic acid for its less toxicity and even its better affordability [59].…”