Modeling Boron Adsorption on Kaolinite

Singh, Shivi P. N.; Mattigod, Shas V.

doi:10.1346/ccmn.1992.0400209

Cited by 33 publications

(15 citation statements)

References 32 publications

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“…Previous macroscopic models of metal ion uptake on kaolinite, however, have not explicitly included the AI-O-Si site as a binding site. In models in which two sites of specific adsorption are included, either non-bridging AI-OH and Si-OH sites (Riese, 1982;Zachara et al, 1988;Carroll-Webb and Walther, 1988;Carroll and Walther, 1990;Singh and Mattigod, 1992;Xie and Walther, 1992) or non-bridging and bridging AI-OH sites (Wieland and Stumm, 1992) are assumed. In addition, few models have considered explicitly bidentate bonding of the metal ion to the kaolinite surface as did .…”

Section: Discussionmentioning

confidence: 99%

“…Uptake is reduced by order-of-magnitude increases in the concentration of the 80 supporting electrolyte below pH ~ 7-8, but uptake is insensitive to change in electrolyte concentration above this pH range (Figure 2a) Cowan " 60 et al, 1992;O'Day, 1992;Zachara et al, 1994). Based o. on solution uptake experiments and potentiometric ti-_~ trations, uptake of cations, anions, and/or protons from o solution onto kaolinite as a function ofpH is generally O 40 modeled assuming two classes of sites: 1) ion exchange *~ or nonspecific adsorption sites that exchange background electrolyte cations with weakly bound, hydrat-20 ed adions ("outer-sphere" complexes) and 2) specific adsorption at amphoteric surface hydroxyl sites (e.g., AI-OH, St-OH) in which surface sites hydrolyze and adions bond directly to surface oxygens such that they are not easily displaced by electrolyte ions ("innersphere" complexes) (Farrah et al, 1980;Riese, 1982;Sposito, 1984;Zachara et al, i 1988;Carroll-Webb and Walther, 1988;Cowan et al, 1992;Singh and Mattigod, 1992;Wieland and Stumm, 1992;Xie and Walther, 1992;Zachara et al, 1994). In these previous macroscopic studies, however, different models of ion uptake have reproduced experimental ~" -5 data equally well and do not supply a unique solution.…”

Section: Sorption and Sorption Sites On Kaolinitementioning

confidence: 99%

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Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

O’Day

Parks

Brown

1994

Clays and clay miner.

127

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Abstract--X-ray absorption spectroscopy (XAS) was used to determine the local molecular environment of Co(II) surface complexes sorbed on three different kaolinites at ambient temperature and pressure in contact with an aqueous solution. Interatomic distances and types and numbers of backscattering atoms have been derived from analysis of the extended X-ray absorption fine structure (EXAFS). These data show that, at the lowest amounts of Co uptake on kaolinite (0.20--0.32 ~mol m-2), Co is surrounded by ~60 atoms at 2.04-2.08 A and a small number orAl or Si atoms (N = 0.6-1.5) at two distinct distances, 2.67-2.72 A and 3.38-3.43/~. These results indicate that Co bonds to the kaolinite surface as octahedrally coordinated, bidentate inner-sphere mononuclear complexes at low surface coverages, confirming indirect evidence from solution studies that a fraction of sorbed Co forms strongly bound complexes on kaolinite. In addition to inner-sphere complexes identified by EXAFS spectroscopy, solution studies provide evidence for the presence of weakly bound, outer-sphere Co complexes that cannot be detected directly by EXAFS. One orientation for inner-sphere complexes indicated by XAS is bidentate bonding of Co to oxygen atoms at two A1-O-Si edge sites or an A1-O-Si and AI-OH (inner hydroxyl) edge site, i.e., comersharing between Co octahedra and AI and Si potyhedra. At slightly higher surface sorption densities (0.51-0.57/~mol m-2), the presence of a small number of second-neighbor Co atoms (average Nco < 1) at 3.10-3.13/~ indicates the formation of oxy-or hydroxy-bridged, multinuclear surface complexes in addition to mononuclear complexes. At these surface coverages, Co-Co and Co-AI/Si distances derived from EXAFS are consistent with edge-sharing between Co and AI octahedra on either edges or (001) faces of the aluminol sheet in kaolinite. Multinuclear complexes form on kaolinite at low surface sorption densities equivalent to < 5% coverage by a monolayer of oxygen-ligated Co octahedra over the N2-BET surface area. These spectroscopic results have several implications for macroscopic modeling of metal ion uptake on kaolinite: 1) Primary binding sites on the kaolinite surface at low uptake are edge, non-bridging AI-OH inner hydroxyl sites and edge AI-O-Si bridging oxygen sites, not Si-OH sites typically assumed in sorption models; 2) specific adsorption of Co is via bidentate, inner-sphere complexation; and 3) at slightly higher uptake but still a small fraction of monolayer coverage, formation of Co multinuclear complexes, primarily edge-sharing with A1-OH octahedra, begins to dominate sorption.

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Section: Discussionmentioning

confidence: 99%

Section: Sorption and Sorption Sites On Kaolinitementioning

confidence: 99%

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

O’Day

Parks

Brown

1994

Clays and clay miner.

127

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“…On the hydrous oxide at pH values >7 several mechanisms of sorption are expected to oper- ate. In addition to H bonding of boric acid molecules and van der Waals dispersion forces (Singh 1971), chemisorption of borate takes place (Singh and Mattigod 1992, Beyrouty et al 1984, Goldberg and Glauberg 1985. In this type of anion sorption on hydrous oxides ligand exchange takes place between borate and surface hydroxyls.…”

Section: Effect Of Ph On Boron Sorptionmentioning

confidence: 99%

Sorption of Boron by Hydrous Al-Oxide

Bussetti

Ferreiro

Helmy

1995

Clays and clay miner.

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Abstract--Boron sorption by hydrous Al-oxide was studied as a function of concentration, pH, temperature and in the presence of oxalate and phosphate. For comparison sorption of B was also measured with charcoal as adsorbent.At constant pH a Langmuir type equation was found to fit the results well at pH values below 7.2 where only boric acid molecules are present in solution. B sorption was dependent on pH with maximum sorption at pH 8.5. Oxalate and phosphate ligands form strong bonds to AI and were found to reduce B sorption. Sorption of boric acid molecules decreased with increasing temperature and the isosteric heat of reaction was 13.8 kJ mol -~. These results indicate that there are two mechanisms of sorption on hydrous Al-oxide, physical sorption of boric acid molecules and ligand exchange (chemisorption) of borate, and both mechanisms are favored onto the oxide.

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“…As discussed previously, the variations of logK ap = f(n) could be due to the contribution of the electrostatic effect (K col ), related to K ap [60,61] according to:…”

Section: Equilibrium Constantsmentioning

confidence: 99%

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

El-Yahyaoui¹,

Ellouzi²,

Zabadi

et al. 2017

Applied Sciences

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Abstract:The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH. The ion exchange method was adapted to establish the interaction mechanism. Stoichiometry exchange of H + /OH − was evaluated at a pH range of 3-10, and obtained values ranged between 0.0 and 1.0. The surface complexes formed between chromate and OCP were found to be > S(HCrO 4 ) and > S(CrO 4 ). The logarithmic stability constant logK 1-1 , and the logK 10 values of the complexes, were 6.0 in acidic medium and 0.1 in alkaline medium, respectively. At low pH and low surface coverage, the bidentate species > S(HCrO 4 ) 2 with logK 10.5 of about 2.9, was favored at a hydration time of less than 150 min. The contribution of an electrostatic effect to the chromium uptake by the OCP sorbent, was also evaluated. The results indicate that the adsorption of chromate on OCP is of an electrostatic nature at a pH ≤ 5.6, and of a chemical nature at a pH > 5.6.

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Modeling Boron Adsorption on Kaolinite

Cited by 33 publications

References 32 publications

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

Sorption of Boron by Hydrous Al-Oxide

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

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