Humic acids minerals

Onken, B.M. and Traina, S.J. The sorption of p3U ene and anthracene to humic acid-mineral complexes effect of fractional organic carbon content. J. Environ. Qual, 26(1) 126-132,1997. 

Righetto, L. et al.. Competitive actinide interactions in colloidal humic acid-mineral oxide systems. Environ. Sci. Technol., 25, 1913, 1991. 

Humic acids are alkaH-extractable materials and total humic acid content is a term that refers to the humic acid content of coal that has had its carboxylate cations removed with sodium pyrophosphate. Values for some typical AustraHan brown coals range from 24—92% (13). Treatment of lignitic coals with mineral acid to release the alkaH and alkaline cations may dissolve up to 20% of the coal. The naturally moist coals are slightly acidic and have a pH of 3.5—6.5. 

C-labeled 2,4-dichlorophenol bound to synthetic or natural humic acids or polymerized by HjOj and peroxidase was mineralized to CO2 only to a limited extent (<10%), and the greater part remained bound to the polymers (Dec et al. 1990). 

Figure 7. U(VI) sorption onto muscovite (7a, Schmeide et al. 2000) and hematite (7b, Lenhart and Honeyman 1999) in the absence (U) and in the presence of humic acid (U+HA). 7a [U02 ] = 1 pmol/L, [HA] = 5 mg/L, muscovite content of about 1.2g/L. Complexation of U with HA in solution and onto mineral surface may influence U sorption. For instance, U sorption onto muscovite is enhanced in presence of HA at low pH. 7b [U] = 1 jamol/L, [HA] = 10 mg/L. Hematite content in solution = 0.9 and 9g/L. Uptake of U increases with increasing hematite content. In presence of hematite, an increase of U sorption onto hematite is observed at low pH, especially at low hematite content.

Schmeide K, Pompe S, Buhner M, Heise KH, Bernhard G, Nitsche H (2000) Uranium (VI) sorption onto phyllite and selected minerals in the presence of humic acid. Radiochim Acta 88 723-728 Schwarcz HP, Latham AG (1989) Dirty calcites 1. Uranium series dating of contaminated calcite using leachate alone. Chem Geol 80 35-43... 

Chromium has a similar electron configuration to Cu, because both have an outer electronic orbit of 4s. Since Cr3+, the most stable form, has a similar ionic radius (0.64 A0) to Mg (0.65 A0), it is possible that Cr3+ could readily substitute for Mg in silicates. Chromium has a lower electronegativity (1.6) than Cu2+ (2.0) and Ni (1.8). It is assumed that when substitution in an ionic crystal is possible, the element having a lower electronegativity will be preferred because of its ability to form a more ionic bond (McBride, 1981). Since chromium has an ionic radius similar to trivalent Fe (0.65°A), it can also substitute for Fe3+ in iron oxides. This may explain the observations (Han and Banin, 1997, 1999 Han et al., 2001a, c) that the native Cr in arid soils is mostly and strongly bound in the clay mineral structure and iron oxides compared to other heavy metals studied. On the other hand, humic acids have a high affinity with Cr (III) similar to Cu (Adriano, 1986). The chromium in most soils probably occurs as Cr (III) (Adriano, 1986). The chromium (III) in soils, especially when bound to... 

Singer A, Huang PM (1990) Effect of humic acid on the crystallization of aluminum hydroxides. Clays Clay Miner 38 47-52... 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Fig. 2. Relationship between log Koc of phenanthrene and the fraction of aromatic carbon in the humic acids extracted from soil horizons as determined by 13C NMR. O, organic horizons A, surface mineral horizons 1-3, subhorizons. Modified from Xing (2001).

Katagi T (1991) Photodegradation of the pyrethroid insecticide esfenvalerate on soil, clay minerals, and humic acid surfaces. J Agric Food Chem 39 1351-1356... 

Shand CA, Cheshire MV, Bedrock CN, Chapman PJ, Fraser AR, Chudek JA. Solid-phase P-13 NMR spectra of peat and mineral soils, humic acids and soil solution components influence of iron and manganese. Plant Soil 1999 214 153-163. 

The effect of mineral and organic soil constituents on the mineralisation of LAS, AE, stearyl trimethylammonium chloride (STAC) and sodium stearate (main soap component) in soils was studied by Knaebel and co-workers [38]. The four 14C-labelled compounds were aseptically adsorbed to montmorillonite, kaolinite, illite, sand and humic acids and subsequently mixed with soil yielding surfactant concentrations of about 50 jig kg-1. The CO2 formation in the serum bottle respirometers was monitored over a period of 2 months indicating that the mineralisation extent was highest for LAS (49-75%). Somewhat lower amounts of produced CO2 were reported for AE and the stearate ranging from 34-58% and 29-47%, respectively. The mineralisation extent of the cationic surfactant did not exceed 21% (kaolinite) and achieved only 7% in the montmorillonite-modified soil. Associating the mineral type with the mineralisation kinetics showed that sand... 

The dissociation of water coordinated to exchangeable cations of clays results in Brtfnsted acidity. At low moisture content, the Brrfnsted sites may produce extreme acidities at the clay surface-As a result, acid-catalyzed reactions, such as hydrolysis, addition, elimination, and hydrogen exchange, are promoted. Base-catalyzed reactions are inhibited and neutral reactions are not influenced. Metal oxides and primary minerals can promote the oxidative polymerization of some substituted phenols to humic acid-like products, probably through OH radicals formed from the reaction between dissolved oxygen and Fe + sites in silicates. In general, clay minerals promote many of the reactions that also occur in homogenous acid or oxidant solutions. However, rates and selectivity may be different and difficult to predict under environmental conditions. This problem merits further study. 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

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