Solubility soil fulvic acids

In an average upper-crustal granodiorite, it is mainly feldspars that weather to form clay minerals (eqns. 4.13 4.14). Since feldspars are framework silicates, the formation of clay minerals (sheet silicates) must involve an intermediate step. This step is not at all well understood although it has been proposed that fulvic acids, from the decay of organic matter in soil, may react with aluminium to form a soluble aluminium-fulvic acid complex, with aluminium in six-fold coordination. This gibbsitic unit may then have Si04 tetrahedra adsorbed on to it to form clay mineral structures. 

Schnitzer and Barton (1963) separated a soil fulvic acid into a methanol-insoluble and -soluble fraction. The methanol-soluble fraction had less carbon than the original substance. Steelink et al. (1983) treated Aldrich and Fluka humic acids by exhaustively extracting them with methanol. The methtmol-soluble fraction revealed methyl ester functions, as detected by... 

In this work a novel five-step leaching scheme for HM has been developed addressing exchangeable, acid soluble (carbonate), easily reducible (bound to Mn oxides), easily oxidizable (bound to humic and fulvic acids), and moderately reducible (bound to amorphous Ee oxides) fractions extractable by 0.05 M Ca(N03), 0.43 M CH3COOH, 0.1 M NH,OH-HCl (non-acidified), 0.1 M K/,03 (pH 11), and 0.1 M (NH4),C,04 (pH 3), respectively. The sequence of extractants was chosen according to recent studies on the selectivity of leachants toward dissolved phases of soils. 

Humic substances in sediments and soils have commonly been, defined as heteropolycondensates of decomposing plant and animal detritus 46. For lack of a better structural definition, these macromolecular substances have been divided into three categories fulvic acids and humic acid and humin. Fulvic acids and humic acids are soluble in dilute alkaline solutions, whereas humin is insoluble. 

Many researchers have attempted to unravel the mystery of the structure of humus. One approach has been to isolate fractions by extracting humus using various extraction procedures. These procedures result in the isolation of three or more fractions humic acid, fulvic acid, and humin. Humic material is isolated from soil by treating it with alkali. The insoluble material remaining after this treatment is called humin. The alkali solution is acidified to a pH of 1.0 and the precipitate is called humic acid, while the soluble... 

Fulvic acid fraction Fraction of soil organic matter that is soluble in both alkali and acid... 

Organic matter extracted from earth materials usually is fractionated on the basis of solubility characteristics. The fractions commonly obtained include humic acid (soluble in alkaline solution, insoluble in acidic solution), fulvic acid (soluble in aqueous media at any pH), hymatomelamic acid (alcohol-soluble part of humic acid), and humin (insoluble in alkaline solutions). This operational fractionation is based in part on the classical definition by Aiken et al. (1985). It should be noticed, however, that this fractionation of soil organic matter does not lead to a pure compound each named fraction consists of a very complicated, heterogeneous mixture of organic substances. Hayes and Malcom (2001) emphasize that biomolecules, which are not part of humic substances, also may precipitate at a pH of 1 or 2 with the humic acids. Furthermore, the more polar compounds may precipitate with fulvic acids. 

The Suwannee River was sampled at its origin at the outlet of the Okefenokee Swamp. This fulvic acid, therefore, is likely to be less degraded than a sample from the Calcasieu River that was taken near its mouth on the estuary during a warm, low-flow period in early summer. Metal-ion solubility controls and sorption on mineral surfaces in upland soils also might fractionate the fulvic acid in the Calcasieu River. In contrast, the Suwannee River mineral-soil solubility controls are less significant. 

NOM is common in sediments, soils, and near ambient (<50 °C) water. The materials result from the partial decomposition of organisms. They contain a wide variety of organic compounds, including carboxylic acids, carbohydrates, phenols, amino acids, and humic substances (Drever, 1997, 107-119 Wang and Mulligan, 2006, 202). Humic substances are especially important in interacting with arsenic. They result from the partial microbial decomposition of aquatic and terrestrial plants. The major components of humic substances are humin, humic acids, and fulvic acids. By definition, humin is insoluble in water. While fulvic acids are water-soluble under all pH conditions, humic acids are only soluble in water at pH >2 (Drever, 1997, 113-114). 

Fulvic acids A group of naturally occurring organic compounds of biological origin that are common in the A horizons of soils and other natural environments. While humic acids are only soluble in water at pH > 2, fulvic acids are water-soluble under all pH conditions (Drever, 1997), 113-114 (compare humic acid and humin). 

Comparison of pyrolysis mass spectra for aqueous soil extract, fulvic acid, and water-soluble humic acid... 

Fig. 5.2. Pyrolysis mass spectra (A) Hawaiian soil extract (B) fulvic acid from Typic Chromoxerert (C) water-soluble humic acid from Typic Chromoxerert. (Taken from ref. 356.)...

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