Premagnetization for Enhancing the Reactivity of Multiple Zerovalent Iron Samples toward Various Contaminants

Premagnetization was applied to enhance the removal of various oxidative contaminants (including amaranth (AR27), lead ion (Pb²⁺), cupric ion (Cu²⁺), selenite (Se⁴⁺), silver ion (Ag⁺), and chromate (Cr⁶⁺)) by zerovalent iron (ZVI) from different origins under well-controlled experimental conditions. The rate constants of contaminants by premagnetized ZVI (Mag-ZVI) samples were 1.2–12.2-fold greater than those by pristine ZVI (Pri-ZVI) samples. Generally, there was a linear correlation between the specific reaction rate constants (<i>k</i>_SA) of one particular contaminant removal by various Pri-ZVI or Mag-ZVI samples and those of the other contaminant, which could be successfully employed to predict the <i>k</i>_SA of one contaminant by one ZVI sample if <i>k</i>_SA of the other contaminant by this ZVI sample was available. The specific rate constant of Fe­(II) release at pH 4.0 was proposed in this study to stand for the intrinsic reactivity of a ZVI sample. All Mag-ZVI samples had higher intrinsic reactivity than their counterparts without premagnetization. There were strong correlations between the intrinsic reactivity of various Pri-ZVI/Mag-ZVI samples and the removal rate constants of a specific contaminant by these ZVI samples not only at pH 4.0 when the intrinsic reactivity was determined but also at other pH levels. This correlation could be employed to predict the removal rate constant of this contaminant by a ZVI sample that was not included in the original data set once the intrinsic reactivity of the ZVI sample was known

Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms

In this study, the effects of major anions (e.g., ClO₄^–, NO₃^–, Cl^–, and SO₄^2–) in water on the reactivity of zerovalent iron (ZVI) toward As­(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO₄^– and NO₃^– had negligible influence on As­(III) removal by ZVI, but Cl^– and SO₄^2– could improve As­(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As­(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As­(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO₄^2– > Cl^– > NO₃^– ≈ ClO₄^– (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO₃^–, HCO₃^–, and H₂PO₄^– on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO₄^2–. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe²⁺ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect