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Humic acid

About: Humic acid is a research topic. Over the lifetime, 13030 publications have been published within this topic receiving 330804 citations. The topic is also known as: humic acids & humin acids.


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Journal ArticleDOI
TL;DR: In this article, a non-ideal competitive adsorption (NICA) model was used to predict the competitive effect of Ca on Cd and Cu binding at various pHs.
Abstract: A Donnan-type model for nonspecific binding of electrolyte ions has been combined with the non-ideal competitive adsorption (NICA) model for specific binding to produce a model for ion binding to humic substances. The model considers site heterogeneity, non-ideality, multicomponent competition, and electrostatic interactions. The NICA-Donnan model was fitted to data for H, Ca, Cd, Cu, and Pb binding by a purified peat humic acid. The model fits were good and covered a wide range of pH and free metal concentrations. The parameters from these single metal data sets were then used to predict the competitive effect of Ca on Cd and Cu binding at various pHs. These predictions agreed well with the experimental data although there were some small but systematic differences. The new NICA-Donnan model also predicted reasonably well the increase in Cd and Cu binding on changing from a 0.1 M KNO3 background electrolyte to 0.01 M KNO3. A shortcoming of the model is that in some cases it significantly underestimated t...

540 citations

Journal ArticleDOI
TL;DR: In this article, the nature of organic carbon in the < 2, 2-20, 20-53, 53-200, and 200-2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS).
Abstract: The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 µm fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.

531 citations

Journal ArticleDOI
TL;DR: In this article, an operationally defined carboxyl content of humic substances extracted from rivers, streams, lakes, wetlands, and groundwaters throughout the United States and Canada is reported.

530 citations

Journal ArticleDOI
TL;DR: In this article, competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents, including a mineral soil, a peat soil, soil humic acid particles, a glassy polymer, and a mesoporous silica gel.
Abstract: This is part of a larger study that addresses the question of whether site-specific sorption of organic compounds takes place in soil organic matter (SOM). Competitive sorption is one indication that such interactions may take place. Competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents. The co-solutes included several s-triazine analogs, a substituted benzene analog (5-chloro-1,3-dimethoxybenzene), and a dissimilar compound, trichloroethene (TCE). The sorbents included a mineral soil (3% OM), a peat soil (93% OM), soil humic acid particles (99% OM), rubbery polymers (polyethylene, cellulose, chitin), a glassy polymer [poly(2,6-diphenyl-p-phenylene oxide)], and a mesoporous silica gel. The rubbery polymers afforded linear single-solute isotherms and no competition, both consistent with ideal (Henry's law) partition sorption. The other sorbents, including the glassy polymer, gave nonlinear single-solute isotherms and significant compet...

528 citations

Journal ArticleDOI
TL;DR: In this article, a strong correlation was observed between the pyrene binding coefficient, Kdoc, and the molecular weights, molar absorptivities at 280 nm, and aromaticity of the aquatic humic substances.
Abstract: The binding of pyrene to a number of humic substances isolated from various aquatic sources and a commercial humic acid was measured using the solubility enhancement method. The humic materials used in this study were characterized by various spectroscopic and liquid chroma tography methods. A strong correlation was observed between the pyrene binding coefficient, Kdoc, and the molecular weights, molar absorptivities at 280 nm, and aromaticity of the aquatic humic substances. Binding of pyrene to the commercial humic acid, however, was significantly stronger and did not obey the relationships observed between Kdoc and the chemical properties of the aquatic humic substrates. These results suggest that the molecular weight and the aromatic content of the humic substrates exert influences on the binding of nonpolar and planar aromatic molecules and that the physicochemical properties of both humic materials and organic solutes are important in controlling the speciation of nonpolar organic contaminants in na...

519 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
2023391
2022950
2021414
2020531
2019710