Topic
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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TL;DR: Data indicate that aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples are smaller and less polydisperse than previously believed.
Abstract: The number- and weight-averaged molecular weights of a number of aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples were measured by high-pressure size exclusion chromatography (HPSEC). Molecular weights determined in this manner compared favorably with those values reported in the literature. Both recent literature values and our data indicate that these substances are smaller and less polydisperse than previously believed. Moreover, the molecular weights of the organic matter from three of the four natural water samples compared favorably to the fulvic acid samples extracted from similar environments
1,657 citations
TL;DR: In this article, it was shown that some microorganisms found in soils and sediments are able to use humic substances as an electron acceptor for the anaerobic oxidation of organic compounds and hydrogen.
Abstract: HUMIC substances are heterogeneous high-molecular-weight organic materials which are ubiquitous in terrestrial and aquatic environments. They are resistant to microbial degradation1 and thus are not generally considered to be dynamically involved in microbial metabolism, especially in anoxic habitats. However, we show here that some microorganisms found in soils and sediments are able to use humic substances as an electron acceptor for the anaerobic oxidation of organic compounds and hydrogen. This electron transport yields energy to support growth. Microbial humic reduction also enhances the capacity for microorganisms to reduce other, less accessible electron acceptors, such as insoluble Fe(III) oxides, because humic substances can shuttle electrons between the humic-reducing microorganisms and the Fe(III) oxide. The finding that microorganisms can donate electrons to humic acids has important implications for the mechanisms by which microorganisms oxidize both natural and contaminant organics in anaerobic soils and sediments, and suggests a biological source of electrons for humics-mediated reduction of contaminant metals and organics.
1,651 citations
TL;DR: In this paper, the role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated, and it is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion.
Abstract: The role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated. Results of fouling experiments with three humic acids demonstrate that membrane fouling increases with increasing electrolyte (NaC1) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed fouling layer. In addition to the aforementioned chemical effects, results show that NOM fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion; that is, NOM fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the fouling layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.
1,281 citations
TL;DR: In this article, it was shown that the ratio of optical densities or absorbances of dilute, aqueous humic and fulvic acid solutions at 465 and 665 nm is mainly governed by the particle size (or particle or molecular weight).
Abstract: The ratio of optical densities or absorbances of dilute, aqueous humic and fulvic acid solutions at 465 and 665 nm (E₄/E₆) is widely used by soil scientists for the characterization of these materials. While it has been suggested that the E₄/E₆ ratio is related to the degree of condensation of the aromatic carbon network, carbon content, and molecular weight of humic substances, little rigorous experimental evidence is available in the literature to confirm these hypotheses. The results of this investigation show that the E₄/E₆ ratio of humic and fulvic acid is: (i) mainly governed by the particle size (or particle or molecular weight); (ii) affected by pH; (iii) correlated with the free radical concentration, contents of O, C, CO₂H and total acidity in as far as these parameters are also functions of the particle size or particle or molecular weight; (iv) apparently not directly related to the relative concentration of condensed aromatic rings; (v) independent of humic acid and fulvic acid concentrations, at least in the 100–500 ppm range. Our data show, in agreement with M. M. Kononova (1966), that E₄/E₆ ratios for humic and fulvic acids should be determined between pH 7 and 8. This can best be done by dissolving the humic material in 0.05N NaHCO₃ solution at concentrations of 200–400 ppm.
1,037 citations
TL;DR: The Fe3O4/HA was able to remove over 99% of Hg(LL) and Pb(ll) and over 95% of Cu(II) and Cd( II) in natural and tap water at optimized pH.
Abstract: Humic acid (HA) coated Fe3O4 nanciparticles (Fe3O4/HA) were developed for the removal of toxic Hg(II), Pb(II), Cd(II), and Cu(II) from water. Fe3O4/HA were prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TOC and XPS analysis showed the as-prepared Fe3O4/ HA contains similar to 11% (w/w) of HA which are fractions abundant in O and N-based functional groups. TEM images and laser particle size analysis revealed the Fe3O4/HA (with similar to 10 nm Fe3O4 cores) aggregated in aqueous suspensions to form aggregates with an average hydrodynamic size of similar to 140 nm. With a saturation magnetization of 79.6 emu/g, the Fe3O4/HA can be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the heavy metals to Fe3O4/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities from 46.3 to 97.7 mg/g. The Fe3O4/HA was stable in tap water, natural waters, and acidic/ basic solutions ranging from 0.1 M HCl to 2 M NaOH with low leaching of Fe (<= 3.7%) and HA (<= 5.3%). The Fe3O4/HA was able to remove over 99% of Hg(II) and Pb(II) and over 95% of COO and Cd(II) in natural and tap water at optimized pH. Leaching back of the Fe3O4/HA sorbed heavy metals in water was found to be negligible.
1,016 citations