摘要:

Sorption is one of the most important chemical processes in soil. It affects the fate and mobility of nutrients and contaminants in soils and waters greatly. This per critically reviews the mechanisms of sorption/desorption phenomena at the mineral/water interface. A brief discussion of macroscopic, equilibrium approaches for describing sorption processes is provided. However, emphasis will be placed on the importance of understanding the rates of sorption/desorption processes and coupling the kinetic investigations with in-situ atomic/molecular resolution surface techniques. The use of X-ray absorption fine structure (XAFS) spectroscopy and scanning force microscopy (SFM) will be emphasized.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

A Swedish soils database containing soil-water retention data, particle-size fractions, dry bulk density, and organic matter content, was analyzed in order to find a relatively simple predictor of the soil-water retention curve (SWRC). As a SWRC model we chose a three-parameter function selected from nine van Genuchten-type retention models that were fitted to the measured retention data by nonlinear parameter optimization. Cumulative particle-size (CP) data were described by a logistic distribution model. Additionally, the mean and standard deviation of the CP distribution were estimated directly from the measured particle-size data. Regression equations were subsequently used to estimate the parameters in the selected SWRC model from available soil properties, particle-size data, and CP distribution parameters. Four alternative pedotransfer models were formulated to estimate the SWRC curve from the basic soil properties. These models predicted the SWRC curves from either the original soil data or from the CP distribution parameters. A mean estimation error of less than 2.5% was used to indicate a good estimation. The highest ratio (67%) of good estimations and the lowest ratio (12%) of poor estimations were obtained when both the original soil properties and the CP model parameters were used. Our study shows that the resulting simple SWRC model gives a good description and a usable prediction of the retention properties of Swedish soils for a wide range of soil textures.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The biodegradation of styrene in waterlogged soils and aquifer solids was initially rapid, but the rate then declined. Significant amounts of styrene persisted under waterlogged conditions. Trace amounts of phenylethanol, phenylacetic acid, phenylacetaldehyde, and benzoic acid appeared in soils but not in aquifer solids. Styrene oxide was not detected. Addition of nitrate did not stimulate styrene degradation in aquifer solids and Lima loam. Because many waste sites are anoxic, the persistence of styrene under waterlogged conditions may be of environmental importance.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Iron released from pyrite during oxidation in slightly acid to alkaline conditions is known to produce one or more forms of iron oxide. There is, however, no solid understanding of how, and to what degree, these iron oxides affect pyrite oxidation. This was investigated by leaching pyrite in a chromatographic column with a 1-cm i.d. and a flow rate of 0.43 mL min-1at room temperature with a solution containing hydrogen peroxide (H2O2) buffered with acetate. When the leaching solution reached pyrite surfaces, H2O2oxidized a small portion of pyrite and released Fe3+. The latter hydrolyzed to form an amorphous ferric oxyhydroxide that precipitated as a passive coating on the pyritic surfaces. The rate of pyrite oxidation was shown to be suppressed greatly by these coatings. This suppressive effect was attributed first to the coating's ability to serve as a sink for Fe3+, thus making it no longer available to oxidize pyrite, and second to the coating's ability to act as a barrier to the upcoming H2O2, thereby physically protecting the pyritic surfaces. It was also shown that the above leaching solution acted as a coating agent when buffered at pH 4.0 to 6.0. Values higher than pH 6 were not investigated.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The bonding structures of arsenite (As(III)) and arsenate (As(V)) on goethite (α-FeOOH) were studied by Transmission-Fourier Transform Infrared (T-FTIR) and Attenuated Total Reflectance-FTIR (ATR-FTIR) spectroscopy. ATR-FTIR spectra of deuterated goethite showed three bands of OD stretch, corresponding to singly, doubly, and triply coordinated OH hydroxyls on the goethite surface. Both FTIR modes provided similar structural information for arsenic adsorption. Most arsenate and arsenite oxyanions replaced two singly coordinated surface OH groups (A-type) to form binuclear bridging complexes Fe-O-AsO(OH)-O-Fe and Fe-O-As(OH)-O-Fe. However, their effects on doubly (C-type) and triply (B-type) coordinated surface OH groups are different. As(III) mainly reacted with C-type OH groups, whereas As(V) reacted with B-type OH groups. These reactions may be attributed to hydrogen-bonding and/or chemical bonding. Finally, we applied a sequential extraction method to evaluate the fractions with different bonding strengths. Relatively strong chemical extraction was necessary to remove 75 to 80% of adsorbed arsenite or arsenate from goethite. The strong retention of As(III) and As(V) is most likely caused by the formation of binuclear complexes with goethite.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Phosphorus (P) adsorption and desorption characteristics of Minnesota Basalt Lunar Simulant (MBLS) and Lunar Glass Simulant (LGS) were evaluated. Results of P interactions with lunar simulants indicated that mineral and glass components adsorbed between 50 and 70% of the applied P and that between 85 and 100% of the applied P was desorbed. The Extended Freundlich equation best described the adsorption data (r2= 0.92), whereas the Raven/Hossner equation best described the desorption data (r2= 0.97). Kinetic desorption results indicated that MBLS and LGS released most of their P within 15 h. The expanded Elovich equation fit the data best at shorter times while t/QDTequation had a better fit at longer times. These results indicate that P does not strongly adsorb to the two simulants and that any P that was adsorbed was readily desorbed in the presence of anion exchange resin. This work suggests that multiple small applications of P (10-20 mg P kg-1) should be added to the simulants to ensure adequate solution P for plant uptake and efficient use of P fertilizer.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID