Brown humic acid

Brown humic acid Not coagulated from alkali solution in the presence of electrolyte Braunhumin- saure... 

Crenlc acid (Berz Apocrenic acid elius) Brown humic acids Gray humic acids (Springer)... 

FIGURE 8. Distribution of humus forms in grassland and forest soils. FA = fulvic acid GHA = gray humic acid BHA = brown humic acid. Adapted from Stevenson (1982). 

Alfisols, Spodosols, and Ultisols) are characterized by a high content of fulvic acids that of peat and grassland soils (Mollisols) contains high amounts of humic acid. The humic acids of forest soils are mostly of the brown humic acid type those of grassland soils are of the gray humic acid type, as illustrated in Figure 8. 

FIGURE 7.22 Fourier transform infrared (FTIR) spectra of brown humic acid (BHA) obtained and purified from a commercial humic substance (HS) (Acros Organics) (a) BHA alone, (b) loaded with 80 mmol-kg" Co, (c) loaded with 1280 mmol-kg Co, (d) and (e) the same with NF , and (f) and (g) the same with Cu. (Reprinted with permission from Alvarez-Puebla, R.A. et al., 2004, Langmuir, 20, no. 9,3657-3664. Copyright 2004 American Chemical Society.)... 

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. 

The composition varies with the heat treatment and the end point according to x-ray diffraction studies it is a form of carbon that reconverts to weU-ordered graphite on heating to 1800°C. Before the use of x-rays, chemists used the Brodie reaction to differentiate between graphitic carbons and turbostratic carbons. Turbostratic carbons yield a brown solution of humic acids, whereas further oxidation of graphite oxide produces mellitic acid (benzenehexacarboxyhc acid) [517-60-2] ... 

Brown and Bellinger [123] have proposed an ultraviolet technique that is applicable to both polluted and unpolluted fresh and some estuarine waters. Humic acid and other organics are removed on an ion exchange resin. Bromide interference in seawater samples can be minimised by suitable dilution of the sample but this raises the lower limit of detection such that only on relatively rich (0.5 mg/1 NO3N) estuarine and inshore waters could the method be used. Chloride at concentrations in excess of 10 000 mg/1 do not interfere. 

Quinone is very sensitive to alkalis, even to carbonate and ammonia, and is converted by them into a brown acid possibly identical with the natural humic acid of brown coal (lignite) (Eller). The mechanism of this reaction remains obscure. 

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. 

We are greatly indebted to J. F. Fryer for the many analyses and humic acid determinations which were required for this study, and we would also like to than R. A. S. Brown for some helpful discussions and his assistance in compiling the experimental results. 

Humic acids - [COAL] (Vol 6) -in brown coals [LIGNITE AND BROWN COAL] (Vol 15)... 

Ulmic acid (brown) and Humic acid (black), the components soluble in alkali... 

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