Structural Incorporation of Manganese into Goethite and Its Enhancement of Pb(II) Adsorption

Abstract

Natural goethite (α-FeOOH) commonly accommodates various metal elements by substituting for Fe, which greatly alters the surface reactivity of goethite. This study discloses the enhancement of Mn-substitution for the Pbadsorption capacity of goethite. The incorporated Mn in the synthesized goethite presents as Mn(III) and causes a slight decrease in the a and c of the unit cell parameters and an observable increase in the b direction due to the Jahn-Teller effect of the Mn(III)O octahedra. With the Mn content increasing, the particle size decreases gradually, and the surface clearly becomes roughened. The Pb adsorption capacity of goethite is observably enhanced by Mn substitution due to the modified surface complexes. And the increased surface-area-normalized adsorption capacity for Mn-substituted goethite indicated that the enhancement of Pb adsorption is not only attributed to the increase of surface area but also to the change of binding complexes. Extended X-ray absorption fine structure (EXAFS) analysis indicates that the binding structures of Pb on goethite presents as edge-sharing complexes with a regular R = 3.31 Å. In the case of Mn-goethite, Pb is also bound with the Mn surface site on the edge-sharing complex with a larger R = 3.47 Å. The mechanism for enhancing Pb adsorption on Mn-goethite can be interpreted as the preferred Pb binding on the Mn site of Mn-goethite surface. In a summary, the Mn-goethite has great potential for material development in environmental remediation.

Nanoanalytical Identification of Siderite Dissolution-Coupled Pb Removal Mechanisms from Oxic and Anoxic Aqueous Solutions

“…Shell-by-shell fits of the Pb L III -edge EXAFS region of the solids indicate a first shell Pb–O interatomic distance R of R Pb–O = 2.31 Å; this distance is indicative of Pb­(II) adsorbed to iron (oxyhydr)­oxides (Table ). Previous studies reported radial distances of R Pb–O ≤ 2.35 Å for a distorted trigonal pyramidal coordination of Pb with the surface oxygen of goethite. − A second single scattering path of R Pb–Fe = 3.31 Å falls within the reported range of R Pb–Fe distances of 2.91–3.49 Å, indicative of the bidentate mononuclear inner-sphere surface complexation with FeO 6 -octahedra in the iron (oxyhydr)­oxide surface . The coordination number of this pathway is similar (0.55) to values observed in previous EXAFS studies of Pb adsorbed on Fe­(III) oxyhydroxide surfaces and lies within the range of values expected for a bidentate mononuclear surface complex (≤1.0).…”

“…Shell-by-shell fitting of the Pb LIII-edge EXAFS spectra of the bulk solid reaction products indicated interatomic distances of RPb-O = 2.31 Å and RPb-Fe = 3.31 Å in the first and second coordination shell, respectively (Table 2). Both interatomic distances are in perfect agreement with distances reported for Pb-adsorbed to goethite 47 and characteristic for inner-sphere bidentate edge-sharing Pb(II)-adsorption to iron (oxyhydr)oxides [44][45][46][47] . This conclusion is supported by the XANES spectra of the bulk sample and area 2 (Figure 4).…”

“…This may be supported by the first shell Pb–O distance, which is slightly longer than for a trigonal sorption geometry ( R Pb–O ∼ 2.25–2.28 Å). , Contributions of these scatterings are particularly prominent in the locally resolved XANES mapping spectra and potentially result from dehydration and enclosure of Pb­(II) ions during advanced aggregation and growth of the iron oxyhydroxide surface precipitates on the reacted siderite grains. The absence of second-neighbor oxygens and the low coordination number suggest that Pb­(II) is adsorbed rather than incorporated. , Also, the absence of third shell scatterings excludes ternary absorption of carbonate; in contrast, the first-shell sensitive XANES spectrum suggests the Pb-carbonate coordination of cerussite.…”

Interfacial structures and acidity constants of goethite from first-principles Molecular Dynamics simulations

“…http://www.minsocam.org/ Axe, 2005;Hanna et al, 2014;Marsac et al, 2016;Yang et al, 2016;Yan and Jing, 2018). As common heavy metal contaminants in water and soils, Pb (II) and Cd(II) were selected as model cations in many experimental and modeling studies (Spadini et al, 1994;Venema et al, 1997;Randall et al, 1999;Ostergren et al, 2000;Elzinga et al, 2001;Boily et al, 2005;Granados-Correa et al, 2011;Leung and Criscenti, 2017;Liu et al, 2018). Using extended x-ray absorption fine structure (EXAFS) spectroscopy, it was found that Pb(II) and Cd(II) form predominantly edge-sharing and corner-sharing complexes on goethite, respectively (Randall et al, 1999;Ostergren et al, 2000).…”

Magnetic Mesoporous Calcium Carbonate-Based Nanocomposites for the Removal of Toxic Pb(II) and Cd(II) Ions from Water

“…Currently, large amounts of toxic contaminants have been discharged into surface and underground water, inevitably causing serious water pollution and threatening public health. − Heavy metal contamination has been considered as one of the most serious threats to organisms due to the nonbiodegradation and easily accumulation of heavy metals in organisms. − Among the heavy metals, Pb­(II) and Cd­(II) are pervasive contaminants in aqueous environments and always considered to be the most harmful for human health. − Thus, the effective removal of Pb­(II) and Cd­(II) from waste streams is urgently required.…”