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 surface charge (SC) of synthetic goethite and hematite was quantified in the presence of different electrolytes (NaCl, CaCl 2, Na 2 SO 4 and CaSO 4 ) by combining the streaming potential with polyelectrolyte titration.
Abstract: Soil solution chemistry, especially pH and the presence of multivalent ions, affects the surface charge (SC) of Fe oxides and accordingly colloidal stability and sorption properties. The SC of synthetic goethite and hematite was quantified in the presence of different electrolytes (NaCl, CaCl 2 , Na 2 SO 4 and CaSO 4 ) by combining the streaming potential with polyelectrolyte titration. The point of zero charge (PZC) for goethite was observed at pH 8.2 and the stability field around the PZC, where colloids are flocculated, is more extended (61 pH unit) than that of hematite with a PZC at pH 7.1 (60.5 pH unit). The SC decreases with increasing SO 4 concentration, indicating adsorption of SO 4 on the oxide, whereas the presence of Ca increases the SC. At pH 4, the addition of 0.1 mmol l –1 Na 2 SO 4 induced a decrease in SC from 1.5 to 0.380 μmol c m –2 for goethite and from 0.85 to 0.42 μmol c m –2 for hematite. In a suspension with 0.1 mmol l –1 Na 2 SO 4 , the number of colloids is already reduced, and both oxides flocculate rapidly and completely at >0.5 mmol l –1 Na 2 SO 4 . While the addition of SO 4 did not affect charge titrations with the cationic polyelectrolyte, the anionic polyelectrolyte formed complexes with Ca, resulting in an overestimation of positive SC. The electrolyte CaSO 4 is most efficient at keeping goethite and hematite in the pH range 4–10 in the flocculated state. Besides pH, the presence of multivalent ions should also be considered when predicting colloid mediated transport and adsorption properties of anionic substances by Fe oxides in soil systems.
37 citations
Cites background from "The crystallo-chemistry of oxide-hu..."
...At acidic pH, Ca had only a slight effect on the adsorption of weak organic acids, whereas at intermediate and high pH, the adsorption of, e.g. humic acid (Varadachari et al., 2000), fulvic acid (Weng et al., 2005) and forest floor organic matter (Mikutta et al., 2007) was significantly increased....
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TL;DR: In this article, the authors investigated the interaction between dissolvable biochar and soil components, for instance the soil minerals, and its effect on the stability of dissolvable biochar was measured by chemical oxidation and biodegradation.
31 citations
TL;DR: In this paper, the interaction between sepiolite and humic acid (HA) and its influence on the mechanism of the formation of organo-clay-humic acid complexes were examined by characterizing the structure of sepiolites through UV/Vis spectroscopy, field emission scanning electron microscopy (SEM+FEG), specific surface area, pore size and volume, and Fourier transform infrared spectroscope (FTIR).
21 citations
Cites background from "The crystallo-chemistry of oxide-hu..."
...In goethite and hematite, both cation bridging and surface coordination are involved in bonding (Varadachari et al., 1991; Varadachari et al., 1995; Varadachari et al., 1997; Varadachari et al., 2000)....
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...cation bridging and surface coordination are involved in bonding (Varadachari et al., 1991; Varadachari et al., 1995; Varadachari et al., 1997; Varadachari et al., 2000)....
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TL;DR: In this article, the amount of Ca2+, Mg2+, Fe3+/2+ and Al3+, as well as humic acid (HA) extracted from 5 soils (Entisol, Alfisol, Vertisol, two Mollisols, and two others) were extracted with 0.1 n citrate, EDTA, and oxalate at pH 7.0-10.0.
Abstract: Clay-humus complexes, isolated from 5 soils (Entisol, Alfisol, Vertisol, two Mollisols), were extracted with 0.1 n citrate, EDTA, and oxalate at pH 7.0-10.0; amounts of Ca2+, Mg2+, Fe3+/2+, Al3+, as well as humic acid (HA) in the extract were determined. HA extracted increased with pH and varied with nature of ligand; largest amounts were extracted by EDTA at high pH. In the Entisol clay-humus extract, Ca2+ is dominant. In Alfisol sample, Ca2+ and Mg2+ have little role in clay-HA bonding; apart from monovalent cations, bonding is mainly through Fe3+/2+ and Al3+, which are well correlated to HA extracted. The extract from Vertisol sample contains little Fe3+/2+ or Al3+ and major bonding is through Ca2+. In Mollisol I and II, Ca2+, Mg2+, Fe3+/2+, and Al3+ are all involved in bonding and are highly correlated to extracted HA. Difference in mineralogy determines the difference in bonding strength between Alfisol and Vertisol complexes. DTA indicates dual bonding modes. A major fraction of HA (in clay-humus complexes) shows thermal destabilisation due to multiple attachments on the clay surface; a small fraction is also thermally stabilised by ionic bonding with Ca2+/Mg2+ and absence of ring strain in the complex. Only the Alfisol HA does not show thermal stabilisation in the complex.
20 citations
TL;DR: In this paper, a chemical method based on batch desorption of adsorbed humus on clay humus complex by sodium hydroxide-sodium pyrophosphate solution was used to assess the stability of humus carbon using soils from two systems of continuous cropping such as rice-wheat and maizewheat.
Abstract: To assess soil quality with respect to carbon sequestration, one should know not only the amount of carbon present in soil but also the strength with which the carbon is held to the mineral surfaces. A chemical method based on batch desorption of adsorbed humus on clay humus complex by sodium hydroxide–sodium pyrophosphate solution was used to assess the stability of humus carbon using soils from two systems of continuous cropping such as rice-wheat and maize-wheat. Humus desorption data were found to be very closely fitted to a linear combination of three first-order equations indicating three different pools of carbon. Humus retention was found to be related to poorly crystalline smectites. Rice-wheat system showed greater contrasting difference in humus stability than maize-wheat system along the depth of the soil profile.
17 citations
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09 Oct 2011
TL;DR: Erratum to: Aminocarboxylic Acids to: Iminodiacetic Acid Derivatives to: Peptides to: Aliphatic Amines to: Protonation Values for other Ligands.
Abstract: Aminocarboxylic Acids.- Iminodiacetic Acid Derivatives.- Peptides.- Anilinecarboxylic Acids.- Pyrrolecarboxylic Acid.- Pyrazlinecarboxylic Acid.- Pyridinecarboxylic Acids.- Aliphatic Amines.- Azoles.- Azines.- Aminophosphonic Acids.- Carboxylic Acids.- Phosphorus Acids.- Phenols.- Carbonyl Ligands.- Alcohols.- Polyethers.- Thioethers.- Thiols.- Phosphines.- Hydroxamic Acids.- Oximes.- Amides.- Inorganic Ligands.- Protonation Values for other Ligands.- Ligands Considered But Not Included.- Erratum to: Aminocarboxylic Acids.- Erratum to: Iminodiacetic Acid Derivatives.- Erratum to: Peptides.- Erratum to: Aliphatic Amines.- Erratum to: Azoles.- Erratum to: Azines.- Erratum to: Carboxylic Acids.- Erratum to: Phosphorus Acids.- Erratum to: Phenols.- Erratum to: Carbonyl Ligands.- Erratum to: Alcohols.- Erratum to: Polyethers.- Erratum to: Thioethers.- Erratum to: Hydroxamic Acids.- Erratum to: Oximes.- Erratum to: Amides.- Erratum to: Inorganic Ligands.- Erratum to: Protonation Values for other Ligands.- Erratum to: Bibliography.
6,389 citations
TL;DR: In this article, the interaction of humic substances from Esthwaite Water with hydrous iron oxides (α-FeOOH, α-Fe2O3, amorphous Fe-gel) have been examined by measuring adsorption isotherms and by microelectrophoresis.
772 citations