1 research outputs found
Ferrate(VI)-Prompted Removal of Metals in Aqueous Media: Mechanistic Delineation of Enhanced Efficiency via Metal Entrenchment in Magnetic Oxides
The removal efficiency of heavy metal
ions (cadmium(II), Cd(II);
cobalt(II), Co(II); nickel(II), Ni(II); copper(II), Cu(II)) by potassium
ferrate(VI) (K<sub>2</sub>FeO<sub>4</sub>, Fe(VI)) was studied as
a function of added amount of Fe(VI) (or Fe) and varying pH. At pH
= 6.6, the effective removal of Co(II), Ni(II), and Cu(II) from water
was observed at a low Fe-to-heavy metal ion ratio (Fe/M(II) = 2:1)
while a removal efficiency of 70% was seen for Cd(II) ions at a high
Fe/Cd(II) weight ratio of 15:1. The role of ionic radius and metal
valence state was explored by conducting similar removal experiments
using Al(III) ions. The unique combination of X-ray diffraction (XRD),
X-ray photoelectron spectroscopy (XPS), in-field Mössbauer
spectroscopy, and magnetization measurements enabled the delineation
of several distinct mechanisms for the Fe(VI)-prompted removal of
metal ions. Under a Fe/M weight ratio of 5:1, Co(II), Ni(II), and
Cu(II) were removed by the formation of MFe<sub>2</sub>O<sub>4</sub> spinel phase and partially through their structural incorporation
into octahedral positions of γ-Fe<sub>2</sub>O<sub>3</sub> (maghemite)
nanoparticles. In comparison, smaller sized Al(III) ions got incorporated
easily into the tetrahedral positions of γ-Fe<sub>2</sub>O<sub>3</sub> nanoparticles. In contrast, Cd(II) ions either did not form
the spinel ferrite structure or were not incorporated into the lattic
of iron(III) oxide phase due to the distinct electronic structure
and ionic radius. Environmentally friendly removal of heavy metal
ions at a much smaller dosage of Fe than those of commonly applied
iron-containing coagulants and the formation of ferrimagnetic species
preventing metal ions leaching back into the environment and allowing
their magnetic separation are highlighted