The kinetics of mixed Ni-Al hydroxide formation on clay and aluminum oxide minerals: a time-resolved XAFS study

Scheidegger, André M.; Strawn, Daniel G.; Lamble, G. M.; Sparks, Donald L.

doi:10.1016/s0016-7037(98)00136-7

Cited by 207 publications

(210 citation statements)

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“…Clustering of Co and A1 atoms is also consistent with the strain broadening found by Rietveld refnement of the powder XRD pattern. Differences between the a cell parameter from XRD and the cation-cation distance from EXAFS data were also reported for takovite (Scheidegger et al, 1998), the Ni-A1 analog of hydrotalcite, but not for pyroaurite, the Mg-Fe(III) analog (Vucelic et al, 1997). Cation clustering and the associated discrepancy between XRD lattice parameters and EXAFS interatomic distances may be a consequence of strain arising from significant differences in ionic radius between the two cations occupying the hydroxide layers of hydrotalcite-like phases, as for Co(II), r = 0.735 and AI(III), r = 0.530 *); and Ni(II), r = 0.700 ,~, and Al(III); but not Mg(]I), r = 0.720 A, and Fe(IIl), r = 0.645 A (Shannon and Prewitt, 1969).…”

Section: Structurementioning

confidence: 76%

Ambient-Temperature Synthesis, Evolution, and Characterization of Cobalt-Aluminum Hydrotalcite-Like Solids

Thompson

1999

Clays and clay miner.

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Abstract--Double hydroxide solids precipitated homogeneously from three laboratory-synthesized aqueous solutions that simulated mildly contaminated surface or groundwater. Over a limited pH range, precipitates formed rapidly from dissolved ions, and more slowly by incorporating ions dissolving from other solids, including highly soluble aluminous solids. The precipitates were characterized by size and shape via transmission electron microscopy (TEM), by composition via inductively coupled plasma-mass spectrometry (ICP-MS) of mother solutions and analytical electron microscopy (AEM) of precipitates, and by structure via powder X-ray diffraction (XRD), TEM, and extended X-ray absorption fine structure (EXAFS) spectroscopy. They were identified as nanocrystalline cobalt hydrotalcite (CoHT) of the form [Co(II)1 xAl(III)x(OH)~]x+(A " ~/n).mH20, with x = 0.17-0.25, A = CO32 , NO3-, or H3SiO 4 , n = anion charge and m undetermined. Complete solid solution may exist at the macroscopic level for the range of stoichiometries reported, but clustering of Co atoms within hydroxide layers indicates a degree of immiscibility at the molecular scale. Composition evolved toward the Co-rich endmember with time for at least one precipitate. The small layer charge in the x = 0.17 precipitate caused anionic interlayers to be incomplete, producing interstratification of hydrotalcite and brucite-like layers. Solubility products estimated from solution measurements for the observed final CoHT stoichiometries suggest that CoHT is less soluble than the inactive forms of Co(OH)2 and COCO3 near neutral pH. Low solubility and rapid formation suggest that CoHT solids may be important sinks for Co in contact with near neutral pH waters. Because hydrotalcite can incorporate a range of transition metals, precipitation of hydrotalcite may be similarly effective for removing other trace metals from natural waters.

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Section: Structurementioning

confidence: 76%

Ambient-Temperature Synthesis, Evolution, and Characterization of Cobalt-Aluminum Hydrotalcite-Like Solids

Thompson

1999

Clays and clay miner.

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“…Another Cd 2þ ion was located on the Cd octahedron layers which connect the next layer though NO 3 À counter cation and OH À group. The distance between the absorbed Cd and the Cd in the octaheron layer was observed in 0.390 nm in the EXAFS of Cd 5 (OH) 8 …”

mentioning

confidence: 98%

“…Recent studies using EXAFS (extend X-ray absorption fine structure) have shown that heavy metals are sorbed on clay and oxide surfaces accompanied by the formation of multinuclear or polynuclear surface complexes (i.e., surface precipitate) much more frequently than previously expected based on the thermodynamical models. [5][6][7][8][9] These microscopic studies have promoted our understanding of the real sorption mechanism. EXAFS analyses of Cd species on the montmorillonite, however, have never been reported in spite of its importance for soil pollution mainly because the K-edge EXAFS requires X-rays with higher energy than 23 keV.…”

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confidence: 99%

EXAFS Studies about the Sorption of Cadmium Ions on Montmorillonite

Takamatsu¹,

Asakura²,

Chun³

et al. 2006

Chemistry Letters

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We investigated local structures around cadmium (Cd) sorbed on montmorillonite at various pH values by EXAFS (extend X-ray absorption fine structure). We found two sorption types, an outer-sphere complex and a surface precipitate. The outer-sphere complex was mainly formed at a lower pH which had an identical structure to aqueous Cd 2þ , while the surface precipitate was found at high pH which had a one-layerCadmium (Cd) is a toxic heavy metal that results in significant pollution of many soil and groundwater systems. Furtherworse, Cd is known to bioaccumulate. Since the mobility and bioavailability of Cd in polluted systems are strongly related to its sorption structures, it is important to understand the sorption structures on clay minerals which are main soil components. Montmorillonite is a dioctahedral smectite mineral that is prevalent in soil environments and has a high surface area and cationexchange capacity (CEC). Over past several decades, macroscopic investigation on the sorption mechanisms of metals on montmorillonite presented many thermodynamic models such as ''surface complexation models'' to describe metal sorption reactions at the solid-water interface.1 The models explained the pH-dependent sorption properties on the montmorillonite. 2-4Outer-sphere complex is mainly formed on permanent charge sites on the interlayer of montmorillonite at low pH values while inner-sphere complex formation occurs at high pH values, where the metals are fixed to deprotonated surface hydroxides on the edge of montmorillonite. However, we have to determine the molecular structures of the sorbed species directly in order to reveal the real sorption mechanism. Recent studies using EXAFS (extend X-ray absorption fine structure) have shown that heavy metals are sorbed on clay and oxide surfaces accompanied by the formation of multinuclear or polynuclear surface complexes (i.e., surface precipitate) much more frequently than previously expected based on the thermodynamical models. 5-9 These microscopic studies have promoted our understanding of the real sorption mechanism. EXAFS analyses of Cd species on the montmorillonite, however, have never been reported in spite of its importance for soil pollution mainly because the K-edge EXAFS requires X-rays with higher energy than 23 keV. We carried out K-edge Cd EXAFS measurements for Cd sorbed on montmorillonite in a vertical Wiggler beam line in SPring-8 and Photon Factory beam line, which provide a high energy X-ray. EXAFS provides only averaged local structure information for all coexisting metal species having the same absorption edge. We varied the pH values in order to change the sorption species continuously and applied a regression analysis to quantitatively evaluate the composition of each sorption structure.Cd was sorbed on Na-montmorillonite (Kunipia-F, Kunimine Industries Co.) using a batch technique at several different pH values. Cd(NO 3 ) 2 (0.002 mol L À1 ) and NaNO 3 (0.004 mol L À1 ) solutions were applied and the reaction time was 24 h (295 AE 1 K). The p...

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“…In principle, for LDH systems for which there are few data or data of uncertain quality, EXAFS (extended X-ray absorption fine structure) could be used as a method to determine a value for that avoids the need to synthesize a series of phases with variable x: d(M-O) and d(M-M) (which is equal to the a parameter) can be determined using EXAFS, which can then be used in equation (13) Scheidegger et al (1998) and Vespa et al (2006); and data for Mg-based systems in Bellotto et al (1996). The data in these articles all result in values of > 90 , which indicates that the octahedra are squashed, but unfortunately the precision of the data as reported is not sufficiently high to be useful in calculations of the a parameter.…”

mentioning

confidence: 99%

Zn- and Co-based layered double hydroxides: prediction of theaparameter from the fraction of trivalent cations andvice versa

Richardson

2013

Acta Crystallogr Sect B

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A recently proposed method to calculate the a parameter of the unit cell of layered double hydroxides from the fraction of trivalent cations is extended to Zn-and Co-based phases. It is shown to be useful as a sanity test for extant and future structure determinations and computer-simulation studies.Layered double hydroxide (LDH) phases are derived from layered single hydroxides [i.e. -M(OH) 2 phases] by the substitution of a fraction (x) of the divalent cations by trivalent cations. Synthetic preparations are studied widely because of their use in a wide range of applications (Cavani et al., 1991) and there are many natural LDH phases (Mills et al., 2012). The author has recently derived equations that enable calculation of x from the a parameter of the unit cell of LDH phases and vice versa, whichever is known with most confidence (Richardson, 2013). The version for phases that have just one type of trivalent cation is given in equation (1).In equation (1) Table 1 of Shannon (1976) and r(OH À ) was shown to have a value of 1.365 Å (Richardson, 2013).The first part of the right-hand side of equation (1) was shown to be equal to the a parameter of an M(OH) 2 -type phase, a M OH ð Þ 2, and so the a parameter for the layered double hydroxide (LDH), a LDH , can be expressed as in equation (2), which is essentially a statement of Vegard's Law, i.e. that in a solid solution series there is a linear relation between the lattice constant and composition (Vegard, 1921;West, 1984;Denton & Ashcroft, 1991).The M(OH) 2 -type phase was shown to be an form of divalent metal hydroxide (Feitknecht, 1938) rather than the -M(OH) 2 polymorph [it is not a M(OH) 2 polymorph because it has the composition M(OH) 2 ÁmH 2 O]. Values for the bond angle were determined for Ni-and Mg-based LDH phases by fitting equation (1) to extensive sets of a-x data compiled from the literature, which produced values of 97.83 and 97.41 for Ni-and Mg-based phases respectively. These values were shown to be independent of the type of trivalent cation and of the type of interlayer anion; i.e. the extent to which the metaloxygen octahedra are squashed is determined solely by the type of divalent cation. The determination of the values for means that equation (1) can be used as a sanity test for the results of extant and future computer-simulation studies and crystal structure determinations for Ni-and Mg-based preparations where x has any value (including x = 0) and that have seemingly any type of trivalent cation.

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The kinetics of mixed Ni-Al hydroxide formation on clay and aluminum oxide minerals: a time-resolved XAFS study

Cited by 207 publications

References 50 publications

Ambient-Temperature Synthesis, Evolution, and Characterization of Cobalt-Aluminum Hydrotalcite-Like Solids

Ambient-Temperature Synthesis, Evolution, and Characterization of Cobalt-Aluminum Hydrotalcite-Like Solids

EXAFS Studies about the Sorption of Cadmium Ions on Montmorillonite

Zn- and Co-based layered double hydroxides: prediction of theaparameter from the fraction of trivalent cations andvice versa

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