Oxidation of humic acids

There are a few reports on the combined application of ultrasound and ultraviolet light (UV) for the destruction of chemical pollutants. A study of the oxidation of humic acid and trihalomethane precursors with ozone revealed that the most effective destruction of the organic carbon compounds was achieved when both uv and ultrasound were used in combination with ozonation [35]. In other cases e. g. the removal of 1,1,1-tri-chloroethane from aqueous solutions, the combined application of ultrasound and UV proved to be more efficient than the use of either technique individually [36]. 

R.A. Sierka and G.L. Amy, Catalytic effects of ultraviolet light and/or ultrasound on the ozone oxidation of humic acid and tri-halomethane precursors, Ozone Sci. e[ Eng., 1985, 6, 275-290. 

Khan, S. U. and Schnitzer, M. (1972). Permanganate oxidation of humic acids, fulvic acids, and humins extracted from Ah horizons of a black chernozem, a black solod, and black solonetz soil. Can. J. Soil Sci. 52, 43-51. 

Zhang X, Dua A J, Lee P, Sun D D and Leckie J O (2008a), Ti02 nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water , J Membrane Sci, 313,44-51. 

Yigit, Z., Inan, H. (2009). A study of photocatalytic oxidation of humic acid on anatase and mixed-phase anatase-rutile Ti02 nanoparticles, Water Air Soil Pollution Focus, Vol.9,... 

Various aquatic plants, such as reed manna grass Glyceria maxima), rice-plant, Arundodonax and Anisogrammaanomala, have been used for PMFCs. Water-soluble root exudates of these plants, including carbohydrates, carboxylic acids and amino acids serve as the most important electron donors for electricity production. In addition, soil (if present) can also act as an electron source via chemical or anaerobic respiration processes, such as chemical oxidation of humic acids, iron(ll), and sulphur compounds, and microbial oxidation of sulphur and ammonia by specific microbes. 

The chemiluminescence observed during the oxidation of humic acids is possibly related to pyrogallol or gallic acid oxidation. Humic acids are important soil constituents and the study of their chemiluminescence might be a tool in soil research. The problem here is the still very poorly defined chemical structure of humic acids. 

Lignite, generally leonardite, and lignite derivatives are appHed in water-based muds as thinners and filtration control agents. Leonardite is an oxidized lignite having a high content of humic acids, which may be described as carboxylated phenoHc polymers (59,60). Litde is known about the chemical stmcture. 

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] ... 

Coal with a mean particle size of less than 3 mm is slurried with water and then oxidized with oxygen or mixtures of oxygen and air at temperatures ranging from 100° to 300° C, at partial oxygen pressures ranging from 0.1 to 10 MPa and reaction periods ranging from 5 to 600 minutes [425]. In the absence of catalysts, such as alkaline bases, the main products of oxidation are humic acids. 

The effect of solution chemistry on the speciation of the organic contaminant 1-naphtol (1-hydroxynaphthalene) and its complexatiom with humic acid is reported by Karthikeyan and Chorover (2000). The complexation of 1-naphtol with humic acid (HA) was studied during seven days of contact, as a function of pH (4 to 11), ionic strength (0.001 and 0.1 M LiCl), and dissolved concentration (DO of 0 and 8 mg L ) using fluorescence, UV absorbance, and equilibrium dialysis techniques. In a LiCl solution, even in the absence of HA, oxidative transformation of 1-naphtol mediated by was observed. In addition, the presence of humic acid in solution, in the absence of DO, was found to promote 1-naphtol oxidation. These reactions are affected by the solution chemistry (pH, ionic strength, and cation composition). 

The low carbon content of humic acids isolated from rotted straw and chernozem may be caused not only by oxidizing processes but also by the... 

Prevailing uncertainties are perhaps most clearly illustrated by the properties of humic acids obtained from a nominally single source—e.g., oxidized coal. Such humic acids will resemble each other in color and typically have equivalent weights around 250. However, depending upon factors which are... 

In these circumstances—and in view of increasing industrial interest in coal-based humic acids as chemical source materials (4)—we thought it pertinent to reinvestigate the mechanism of humic acid formation and, as a first step, to direct particular attention to the development of acidity and alkali solubility during progressive uncatalyzed oxidation of a subbituminous coal (Table 1) with dry oxygen. The choice of this particular system is, prima facie, arbitrary since conversion of coal into humic acids can, in principle, be accomplished by several methods. (Among those commonly used are reactions... 

Measurements of alkali solubles in these coal samples—conventionally accepted as indices of humic acid concentrations—were initially performed by using Kreulen s method (7). However, even when the most stringent precautions were taken to exclude air, this method yielded markedly time-dependent results (presumably owing to oxidation of the coal by the relatively strong alkali solution), and a more satisfactory colorimetric technique (by J. F. Fryer) was therefore employed. This entailed extracting the coal sample with 0.1 N aqueous sodium hydroxide for 16-20 hours in an inert atmosphere and subsequent photoelectric scanning of the extract solutions. Actual humic acid concentrations were then obtained from specially constructed reference curves which related optical density (at an appropriate wavelength) to humic acid contents. The inherent error in this determination is estimated at less than 10%. 

In this scheme, Reaction 1 represents a direct (pre-ignition) combustion reaction which may or may not be accompanied by formation of carbon monoxide Reaction 2 describes the oxidation reaction (and its sequences) examined in the present study. B and C in Reaction 2 denote degradation products of humic acids (e.g. hymatomelanic, fulvic, and/or so-called water soluble coal acids), and ki,, etc. represent the corresponding rate constants. 

If it is also recalled that alkali soluble material (humic acid) builds up much more slowly than acidity (and always markedly dependent on T and [O]), and that the distinctly acidic parent coal is effectively insoluble in alkali, it becomes evident that acidity and alkali solubility are not necessarily covariant, and that accepted definitions of humic acid are, chemically speaking entirely arbitrary. Under the conditions of this study the oxidation appears to involve two simultaneous but seemingly unrelated reactions which result in the development of acidity and in molecular (skeletal) breakdown, respectively, and this suggests that alkali solubility is mainly a consequence of degradation which is only coincidentally connected with the formation of acidic functional groups. Figure 20 illustrates this concept qualitatively and leads to the inference that the wide spread in molecular weights of humic acids reported... 

Two minor points worthy of note are (a) formation of carbon dioxide and water at temperatures below ca. 300°C. appears, from the evidence of this study, to be caused mainly by Reaction 1—i.e., at such relatively low temperatures, Reaction 2 does not proceed significantly towards its ultimate conclusion (b) abstraction of humic acids by stripping of functional groups— i.e., by reactions characterized by fa, is likewise minimal at T < 300°C. (The fact that no observable decay of humic acids occurs during extended oxidation unless reaction temperatures approach 300°C. is, perhaps, a direct consequence of (a) and (b).)... 

In our experience at all temperatures oxidation would lead to the formation of humic acids of course, it is a question of time at lower temperatures. 

A kinetic model for the UV/H202 process based on UV/H202-induced OH radical oxidation of butylchloride in the presence of humic acid was developed (Liao and Gurol, 1995). 

Figure 14.21 illustrates the effect of humic acid or carbonate on the efficiency of the oxidation of TCB. The rate of TCB degradation decreased at both 1.6 and 10 mg/L humic acid. It appears that humic acid scavenges OH and other radicals responsible for the degradation of TCB. Furthermore, the presence of humic acid is likely to reduce the transmission of UV light, thereby decreasing the rate of ozone decomposition through OH radicals (Masten et al., 1996). 

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