Recycling of waste aluminum scraps to fabricate sulfidated zero-valent iron-aluminum particles for enhanced chromate removal

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium

“…Both the Cr­(VI) and Mg­(II) time-series data show a strong sensitivity to the initial pH (Figure C,D) and, therefore, to the temporal evolution of the pH as described by eq . For the lowest pH 0 (2 and 3), Cr­(VI) undergoes a steep initial drop that occurs on a time scale of around 10 min, which is consistent with the rapid conversion of Cr­(VI) to Cr­(III) at low pH by other reductants. ,− Batch experiments with higher pH 0 (4–7) gave slower initial Cr­(VI) removal kinetics and an overall shape that suggests a Langmuir–Hinshelwood progress curve with a linear decrease at a high contaminant concentration transitioning to exponential decay at a low concentration. The Langmuir–Hinshelwood kinetics are characteristic of surface-mediated processes .…”

“…A similar issue applies to ZVAl, so a recent study tried to overcome this by fabricating sulfidated zerovalent Fe− Al (S−Al 0 @Fe 0 ), which provided substantial enhancement of Cr(VI) removal compared to those of S−Fe 0 , Fe 0 −Al 0 , or Fe 0 only. 14 The strongest alternative reductant to ZVI is zerovalent magnesium (ZVMg), which has a much lower standard reduction potential (E SHE 0 = −2.37 V) than other relevant zerovalent metals, including ZVI (E SHE 0 = −0.44 V) and ZVZ (E SHE 0 = −0.76 V). This makes reduction of H 2 O/H + (to H 2 ) and most contaminants by ZVMg very favorable thermodynamically and introduces the possibility that some of these reactions may be mediated by hydrated electrons (e aq − ).…”

“…The latter study led to the realization that while the low reduction potential of pure Zn(0) should result in more reduction of water than ZVI and therefore less efficient treatment of contaminants, the oxides that form on ZVZ can be more strongly passivating than for ZVI, so the overall reactivity of ZVZ can be optimized for in situ remediation applications. A similar issue applies to ZVAl, so a recent study tried to overcome this by fabricating sulfidated zerovalent Fe–Al (S–Al 0 @Fe 0 ), which provided substantial enhancement of Cr­(VI) removal compared to those of S–Fe 0 , Fe 0 –Al 0 , or Fe 0 only …”