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.

POE chain length selectivity in the clouding of a Triton surfactant.

The POE chain length distribution between the coacervate and aqueous phases of a clouded Triton X-114 solution was studied. The average chain length of the surfactant in the aqueous layer was determined by HPLC and compared to the distribution in the original (unclouded) solution. Both the clouding temperature and the equilibration time were found to govern the chain length selectivity. A slight excess of longer POE chains were encountered in the aqueous layer, thus enriching the coacervate layer with shorter, less soluble chains. Chain length selection appeared to occur when the surfactant particles were dispersed in the clouded suspension, rather than after the establishment of the aqueous and coacervate layers.

The physico-chemical properties and biostimulative activities of humic substances regenerated from lignite.

The positive effect of humic acids on the growth of plant roots is well known, however, the mechanisms and role of their physical structure in these processes have not been fully explained yet. In this work, South-Moravian lignite was oxidized by means of nitric acid and hydrogen peroxide to produce a set of regenerated humic acids. The elemental composition, solid state stability and solution characteristics were determined and correlated in vitro with their biological activity. A modified hydroponic method was applied to determine the effects of their potassium salts on Zea mays seedlings roots with respect to the plant weight, root length, root division, and starch and protein content. The relations between the determined parameters were evaluated through Principal Component Analysis and Pearson's correlation coefficients. The results indicated that the most important factor determining the biological activity of South-Moravian lignite potassium humates is related to the nature of self-assemblies, while the chemical composition had no direct connection with the root growth of Zea mays seedlings. It was demonstrated a controlled processing that provided humic substances with different chemical and physicochemical properties and variable biological activity.

Humic acids as reducing agents: the involvement of quinoid moieties in arsenate reduction.

PURPOSE: Dissolved humic acids abiotically reduced inorganic arsenic to varying degrees, depending on solution pH, ionic strength, and type of humate used. The functionalities of dissolved organic matter responsible for these redox reactions remained in question, but quinoid moieties undoubtedly played an important role. It is not fully understood whether the quinoids are solely responsible for arsenate reduction, and what the kinetics of the relevant processes are. METHODS: Electron spin resonance (ESR) spectroscopy was used to monitor the radical content of the humates, both as bulk material and as size fractions. Information on the redox status of the humates was obtained from fluorescence excitation-emission matrices and correlated with the observed spin count. Size data were obtained from fractionation and UV-Vis spectrometry. Arsenic speciation was carried out by ion chromatography. RESULTS: ESR spectroscopy showed a free radical content of 3.4 x 1,017-20 x 1,017 spins/g for bulk and fractionated aqueous humic acids. The number of electrons corresponding to these counts could not account for the entire charge transferred to arsenate during abiotic reduction. The rate constants of the reactions were found to be independent of the humic concentration. Leonardite humic acid separated on a XAD-8 resin yielded fractions that on the short time frame (0-5 h) had rate constants of 0.035 h(-1) for the hydrophobic fraction compared to 0.0052 h(-1) for the hydrophilic fraction. The rate constants for the hydrophobic and hydrophilic fractions over the longer time frame (100-200 h) were similar-7.3 x 10(-4) and 7.2 x 10(-4) h(-1), respectively. Fluorescence excitation-emission matrices of humates involved in arsenate reduction exhibited shifts typical of quinoid components undergoing redox transformations. These gradual shifts took place during the first 24 h of reduction process, after which the spectra no longer changed. The reduction of arsenate, however, continued after this period, indicating that species other than quinoids were involved. This was consistent with the fact that the rate constants for the later processes were smaller. CONCLUSIONS: The existence of different redox pools within the humate was confirmed, with the quinoid-centered redox entities showing the fastest kinetics. The results pertained to all size and polarity fractions.

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.

(31)P NMR peak width in humate-phosphate complexes.

The mobility of inorganic phosphate (P) attached to solid humic acid (HA) and fulvic acid (FA) via a metal "anchor" was investigated by (31)P NMR spectroscopy. The peak width of the (31)P resonance was monitored as an indicator of the degree of attachment of the element to the humic matrix. The concept was demonstrated by contrasting peak widths of thoroughly dry M-HA-P complexes with those that had been allowed to absorb different amounts of moisture. It was shown that the presence of moisture, which enhances the mobility of P, results in a significant reduction of chemical shift peak width. The work was extended to comparisons between dry systems with and without metal anchors; systems with anchors consisting of different metals; systems comprising different humates and fulvates; and systems with different size fractions of a humate. It was shown that both the type of humate/fulvate, and the metal anchor used lead to different degrees of mobility within the humic matrix. It was also found that the effect of metal addition on (31)P peak width is greater with fulvates and smaller HA fractions than with the larger HA components.

Preparation of ultrafine chalcopyrite nanoparticles via the photochemical decomposition of molecular single-source precursors.

The synthesis and characterization of ultrafine CuInS2 nanoparticles are described. Ultraviolet irradiation was used to decompose a molecular single source precursor, yielding organic soluble approximately 2 nm sized nanoparticles with a narrow size distribution. UV-vis absorption, 1H and 31P{1H} NMR, and fluorescence spectroscopies and mass spectrometry were used to characterize decomposition of the precursors and nanoparticle formation. The nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy energy dispersive X-ray spectroscopy, powder X-ray diffraction (XRD), electron diffraction, inductively coupled plasma analysis, UV-vis absorption spectroscopy, and fluorescence spectroscopy. They have a wurzite-type crystal structure with a copper-rich composition. The hypsochromic shift in their emission band due to quantum confinement effects is consistent with the size of the nanocrystals indicated in the HRTEM and XRD analyses.

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.

Conductometric characterization of dissolved humic materials.

Conductometric replacement titrations of humic and fulvic acids dissolved in a slight excess of hydroxide were carried out with standard acid. The slope of the titration curve corresponding to the protonation of humate/fulvate was related to the electrophoretic mobility of the polyanions or aggregates, and hence to their dimensions. Promising qualitative agreement was found between sizes of a number of these species and their conductance slopes. Both the separation of humic fractions and size reduction by photolysis and sonication led to the anticipated decrease in slope. The slight reduction in slope observed during the course of the titration was tentatively ascribed to contraction of the expanded (drained) humic aggregates.