The crystallo-chemistry of oxide-humus complexes
TL;DR: Theoretical analysis of crystal surface structures revealed the following as mentioned in this paper : Residual charge carried by O or OH on surfaces of goethite, hematite, and gibbsite also contain octahedral sites in which one O/OH position is vacant.
Abstract: Complexation of humic substances with goethite, hematite, gibbsite, and boehmite has been explained from a viewpoint of crystal structure of the minerals. Theoretical analysis of crystal surface structures revealed the following. (i) Residual charge carried by O or OH on surfaces of gibbsite is –1/2; on boehmite it is –3/2 or –1/2; on goethite it is –4/3, –2/3, or –1/3; and on hematite it is –3/2, –1, or –1/2. Cations adsorbed to neutralise these charges can form bridging links with humic acid; higher charges form stronger links. (ii) Surfaces of goethite, hematite, and gibbsite also contain octahedral sites in which one O/OH position is vacant. These may provide centres for the formation of strong coordination bonds. (iii) Such vacant octahedral positions are absent in boehmite. It follows that in gibbsite, cation bridging links would be weak and vacant octahedral sites would be the dominant bonding sites; in goethite and hematite, both cation bridging and surface coordination sites would be present; in boehmite, cation bridging would be the only strong bonding mode. Derivations from crystallochemical analysis are supported by experimental observations. Infrared studies also show strong OH involvement in boehmite complexation in contrast to the weakness of OH involvement in gibbsite complexes.
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TL;DR: In this paper, the authors studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as 'ligand exchange', 'Ca2+ bridging', and 'van der Waals forces'.
371 citations
TL;DR: STXM-NEXAFS spectroscopy was used to investigate C associations with Ca, Fe, Al, and Si species in soil clay fractions from an upland pasture hillslope and showed similar correlation with Fe to Al and Si, implying a similar association of Fe oxides and aluminosilicates with organic matter in organo-mineral associations.
Abstract: There is a growing acceptance that associations with soil minerals may be the most important overarching stabilization mechanism for soil organic matter. However, direct investigation of organo-mineral associations has been hampered by a lack of methods that can simultaneously characterize organic matter (OM) and soil minerals. In this study, STXM-NEXAFS spectroscopy at the C 1s, Ca 2p, Fe 2p, Al 1s, and Si 1s edges was used to investigate C associations with Ca, Fe, Al, and Si species in soil clay fractions from an upland pasture hillslope. Bulk techniques including C and N NEXAFS, Fe K-edge EXAFS spectroscopy, and XRD were applied to provide additional information. Results demonstrated that C was associated with Ca, Fe, Al, and Si with no separate phase in soil clay particles. In soil clay particles, the pervasive C forms were aromatic C, carboxyl C, and polysaccharides with the relative abundance of carboxyl C and polysaccharides varying spatially at the submicrometer scale. Only limited regions in the...
114 citations
TL;DR: The ability to stabilize water-in-oil (W/O) emulsions for six studied asphaltene subfractions is dependent on their solubility rather than on their concentration, polarity, molecular weight, or other parameters.
Abstract: The ability to stabilize water-in-oil (W/O) emulsions for six studied asphaltene subfractions is dependent on their solubility rather than on their concentration, polarity, molecular weight, or other parameters. Paraffinic froth treatment technology recently introduced in the oil sand industry yields a clean bitumen product (<0.1 wt % water and <0.1 wt % solids) at a solvent-to-bitumen ratio above a critical value, which corresponds to the onset of asphaltene precipitation. Six subfractions of Athabasca bitumen asphaltenes were obtained by precipitation with a gradually increasing heptane-to-bitumen (H/B) ratio, from 1.25 to 40. The properties of the asphaltene subfractions obtained were investigated by elemental analysis, Fourier transform infrared (FTIR) and ultraviolet-visible (UV−vis) spectroscopy, and vapor pressure osmometry (VPO). There were no significant differences in the molecular masses of the six asphaltene subfractions. However, the aromaticity and the metalloporphyrin (vanadyl) content in t...
88 citations
TL;DR: The sorption of DOC (derived from mature wheat straw) was more strongly affected by SAR than by EC, andDOC sorption in salt-affected soil is more strongly controlled by CEC and Fe/Al concentration than by clay concentration per se except in sodic soils where DOC sorption is low due to the high sodium saturation of the exchange complex.
74 citations
Cites background from "The crystallo-chemistry of oxide-hu..."
...This also highlights the importance of divalent cations such as Ca for DOC sorption (Baldock and Skjemstad, 2000; Mikutta et al., 2007; Varadachari et al., 2000)....
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...This also highlights the importance of divalent cations such as Ca2+ for DOC sorption (Baldock and Skjemstad, 2000; Mikutta et al., 2007; Varadachari et al., 2000)....
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TL;DR: It is proposed that proton displacement due to the interaction between humic substances and the oxide, along with the formation of ternary complexes with the Pb(II) cation bridging the oxide and the Humic substances (Type A complexes), cause the deviation from additivity.
41 citations
Cites background from "The crystallo-chemistry of oxide-hu..."
...Also, it is possible that in the presence of Pb(II) HA adsorption to goethite would increase, as observed by Varadachari et al. (1997, 2000) for other systems....
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...There are several studies on that interaction; particularly for humic substances–iron oxides showing the formation of complexes (Varadachari et al., 2000; Saito et al., 2004; Fu and Quan, 2005)....
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01 May 1976
TL;DR: In this paper, the authors greatly indebted to Professor Dr. W.A. Flaig, Director of the Institute for Biochemistry, Braunschweig, Germany, Ir. E.C. Rietz and Dr. P. Krohmer, Uberlingen, Germany for critical reading the manuscript.
Abstract: The authors are greatly indebted to Professor Dr. W. Flaig, Director of the Institute for Biochemistry, Braunschweig, Germany, Ir. W.C. van Mierlo, Director of the Laboratory for Soil Mechanics, Delft, The Netherlands, the late Professor Dr. F .A. van Baren, Institute for Soil Science, Utrecht, The Netherlands, Dr. F.W.G. Pijls, Director of the Institute of Soil Survey, Wageningen, The Netherlands, and Professor Ir. E.C.W.A. Geuze, Rensselaar Polytechnical Institute, Troy, Mich., U.S.A., for their great encouragement in the enterprise of this second Atlas on clay minerals and their admixtures, and to Dipl. Phys. E. Rietz, Braunschweig, Germany, and Dr. P. Krohmer, Uberlingen, Germany, for critical reading the manuscript.
723 citations
TL;DR: The specific adsorption of anions depends on the pK values of the anion acids and the adsorbed anions confer a negative charge on the surface displacing the zero point of charge to lower pH values.
Abstract: The specific adsorption of anions depends on the pK values of the anion acids The adsorbed anions confer a negative charge on the surface displacing the zero point of charge to lower pH values
435 citations
TL;DR: Adsorption isotherms for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite were obtained with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced as discussed by the authors.
Abstract: Adsorption isotherms were obtained for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite. The results were interpreted with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced. The mechanism of adsorption involved ligand exchange with the surface hydroxyl groups and hydrogen bonding. The hydroxyl groups displaced included singly coordinated species on the (100) face of goethite and on the edge faces of gibbsite. The doubly coordinated hydroxyl groups on the (001) face of gibbsite were not replaced, and this face adsorbed only un-ionized fulvic acid probably by a hydrogen bonding mechanism. Imogolite adsorbed most fulvic acid because of its high porosity. Only isolated places on its surface reacted with fulvic acid to form carboxylate groups.
302 citations
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26 Oct 2015
133 citations