Ray von Wandruszka

Micro-Organization in Dissolved Humic Acids

The proposed pseudomicellar character of five dissolved humic acids has been investigated by monitoring the fluorescence behavior of a pyrene probe added to the solutions. Fluorescence quenching by bromide in the presence of these humic acids was found to be consistent with a hydrophobic microenvironment. The presence of metal ions, with either quenching or nonquenching counterions, increased the pyrene fluorescence of several of the humic acids. The results indicate that cations have the property of increasing intramolecular micellization in these humic acids, thereby minimizing quenching interactions. The proposed mechanism involves enhanced shielding of the probe rather than its expulsion into the aqueous bulk as has been suggested previously

Adsorbents for the removal of arsenic, cadmium, and lead from contaminated waters.

The removal of cadmium, arsenic, and lead from drinking and irrigation water is a recurring challenge, especially in developing countries. Cost considerations can make it expedient to use local materials, produced in agricultural or industrial operations, as adsorbents for these toxins. Performance of these materials may not always be optimal, but their immediate availability often makes them attractive choices. This review presents a compilation of adsorption techniques, many of which are based on the use of low-value products.

Phosphorus retention in calcareous soils and the effect of organic matter on its mobility

A survey of the interactions between phosphorus (P) species and the components of calcareous soils shows that both surface reactions and precipitation take place, especially in the presence of calcite and limestone. The principal products of these reactions are dicalcium phosphate and octacalcium phosphate, which may interconvert after formation. The role of calcium carbonate in P retention by calcareous soils is, however, significant only at relatively high P concentrations – non-carbonate clays play a more important part at lower concentrations. In the presence of iron oxide particles, occlusion of P frequently occurs in these bodies, especially with forms of the element that are pedogenic in origin. Progressive mineralization and immobilization, often biological in nature, are generally observed when P is added as a fertilizer. Manure serves both as a source of subsurface P and an effective mobilizing agent. Blockage of P sorption sites by organic acids, as well as complexation of exchangeable Al and Fe in the soil, are potential causes of this mobilization. Swine and chicken manure are especially rich P sources, largely due the practice of adding the element to the feed of nonruminants. Humic materials, both native and added, appear to increase recovery of Olsen P. In the presence of metal cations, strong complexes between inorganic P and humates are formed. The influence of humic soil amendments on P mobility warrants further investigation.

The micellar model of humic acid : Evidence from pyrene fluorescence measurements

A series of studies has shown that the fluorescence intensity of pyrene dissolved in certain humic acid (HA) solutions increased significantly when salts were added, even those of highly quenching anions. The phenomenon was found to depend on the cation of the salt, generally varying with its charge

Humic acids: Their detergent qualities and potential uses in pollution remediation

Humic acids are amphiphilic species whose behavior in aqueous solution suggests that they form pseudomicelles–aggregates akin to the micelles familiar from synthetic surfactant chemistry. It is thought that humic pseudomicelles can be formed by both intramolecular coiling and intermolecular association, depending on the molecular weight, structural characteristics, and polydispersity of the humic acid in question. The process does not feature a critical micelle concentration. Experimental evidence indicates that metal ions enhance the detergent character of dissolved humic acid by facilitating the coiling and folding of the polymer chains. A recently conceived alternative model suggests that humic acids consist of relatively small subunits that associate through weak molecular interactions. This view appears to run counter to certain experimental observations, but deserves careful attention. The strong association between metal ions and solid humic acid makes it possible to use an inexpensive commercial grade for the decontamination of polluted water. A continuous elution process through a column packed with humic acid allows for the removal of both heavy metals and organic xenobiotics from aqueous solution.Humic acids are amphiphilic species whose behavior in aqueous solution suggests that they form pseudomicelles–aggregates akin to the micelles familiar from synthetic surfactant chemistry. It is thought that humic pseudomicelles can be formed by both intramolecular coiling and intermolecular association, depending on the molecular weight, structural characteristics, and polydispersity of the humic acid in question. The process does not feature a critical micelle concentration. Experimental evidence indicates that metal ions enhance the detergent character of dissolved humic acid by facilitating the coiling and folding of the polymer chains. A recently conceived alternative model suggests that humic acids consist of relatively small subunits that associate through weak molecular interactions. This view appears to run counter to certain experimental observations, but deserves careful attention. The strong association between metal ions and solid humic acid makes it possible to use an inexpensive commercial grade for the decontamination of polluted water. A continuous elution process through a column packed with humic acid allows for the removal of both heavy metals and organic xenobiotics from aqueous solution.

The effect of molecular size on humic acid associations

Aqueous solutions of two humic acids were subjected to UV photolysis, resulting in chain scission of the solute. The molecular fragments were found to have diminished detergent properties, indicated by a reduced tendency to associate with small hydrophobic species. This is ascribed to the inability of smaller and stiffer humic acid segments to form structured pseudomicellar domains that can sequester nonpolar species. It was noted that photolysis is more likely to involve covalent bond breakage than dissociation of hydrogen bonded conglomerates. An association index, based on fluorescence anisotropy, provided a quantitative measure of humic acid associations.

The Sequestration of Hydrophobic Micropollutants by Dissolved Humic Acids

A potential mechanism for the interactions of dissolved humic acids with nonpolar micropollutants was assessed by monitoring the fluorescence of pyrene added to aqueous humic acid solutions. The results support the concept of the cation-assisted formation of intramolecular domains in humic acids and

Luminescence of Micellar Solutions

Abstract Luminescence spectroscopy provides a unique set of tools for the study of micellar systems. Variations in emission and excitation spectra of fluorescent probes may be used to assess the onset of micellization, while fluorescence lifetime, anisotropy, sensitization, and quenching measurements have made it possible to determine important micellar characteristics. Thus, critical micelle concentrations; micellar aggregation numbers; shapes, sizes, and structures of micelles; and micellar microviscosities have been determined. Work has been carried out with both normal and reverse micelles, and the influence of various solution-borne species on these aggregates has been evaluated through fluorescence and phosphorescence measurements. For the analytical chemist, it is of considerable practical importance that many luminescent compounds exhibit enhanced or changed emission characteristics in solutions of detergent micelles. Intensity enhancements in excess of two orders of magnitude may be encountered i...

Decontamination of oil-polluted soil by cloud point extraction

An extraction procedure based on cloud point phase separation of nonionic surfactants was used to remove oil contamination from soils. The detergent employed was Triton X-114, and its clouding behavior was monitored by means of a fluorescence probe. Changes in the I (1)I (3) ratio of pyrene indicated gradual dehydration of the detergent micelles upon heating. The rate of phase separation, and the volume and water content of the micellar phase were determined. In the practical clean-up, 85-98% of the oil present in the soil was found to enter the micellar phase of the separated washing liquid. A 15-min washing time with 3-5% detergent was found to be sufficient for this degree of contaminant removal from soil containing 0.009-0.017% oil, using a liquid:solid ratio of 5:2. The extraction efficiency decreased with increasing carbon content of the soil. The process holds promise for large-scale treatment of oil-polluted soils.

Binding of inorganic phosphate to dissolved metal humates

A cobalt-wire electrode was used to determine the concentration of free phosphate (P) in solutions containing a series of metal humates (MHA). The results were used in Scatchard plots to determine the stability constants of the dissolved MHA-P complexes formed. The constants were found to be high, with logK values in the range 4.8-6.0. Solutions containing MHA-P complexes were found to be relatively inert to the addition of phosphate-precipitating cations, indicating that MHA has a solubilizing effect on P and may enhance its mobility in the environment.