Personal Research Database

Full Text: 1989\Soi Sci Soc Ame J53, 373.pdf

Abstract: Solute transport models often use batch-generated adsorption isotherms to partition solute between the aqueous and adsorbed phases, but the relationship at equilibrium between aqueous and adsorbed solute concentrations may be different in closed (batch) and open (flow) systems. Adsorption isotherms were generated for orthophosphate/goethite, silicate/goethite, orthophosphate/soil clay and orthophosphate/arsenated-goethite systems using batch and flow (miscible displacement) techniques. The contact times were 168 and 96 h in the batch and flow experiments, respectively. The shapes of the isotherms generated by the two methods were very similar in all cases, although the flow-generated isotherms were displaced slightly upward relative to the batch isotherms. Simple Langmuir plots of both batch and flow data were nonlinear for all systems, while in all systems containing phosphate, flow-generated distribution coefficients were greater than the corresponding batch-generated values, particularly at low surface coverage. In addition, adsorption maxima and values of the two-surface Langmuir parameter b1 were consistently greater in the flow systems. The results indicate that provided transport processes do not keep the flow system far from chemical equilibrium, batch-generated anion adsorption isotherms are likely to underestimate the extent of adsorption in the corresponding flow system, particularly at relatively low aqueous phase sorbate concentrations. This appears to be due, in part, to the removal of competitive antecedent species in the flow system effluent. It is suggested that flow systems are thermodynamically equivalent to batch systems having very wide solid/solution ratios.

Keywords: Adsorption, Flow of Water-Chemical Reactions, Clay Minerals-Solutions, Phosphates, Silicates, Anion Adsorption Isotherms

Notes: highly cited

? Jardine, P.M., Weber, N.L. and McCarthy, J.F. (1989), Mechanisms of dissolved organic-carbon adsorption on soil. Soil Science Society of America Journal, 53 (5), 1378-1385.

Full Text: 1989\Soi Sci Soc Ame J53, 1378.pdf

Abstract: The subsurface transport of inorganic and organic contaminants may be strongly related to the movement of dissolved organic carbon (DOC) through a soil profile. A variety of soil chemical and hydrologic factors control the mobility of the DOC, which may enhance or impede the transport of the associated contaminants. In this study, the sources of DOC adsorption on two proposed waste-site soils are defined, and the chemical mechanisms operative during the adsorption process are specified. Adsorption isotherms for the two soils determined at constant pH, ionic strength (I), and temperature indicated that DOC adsorption increased with increasing soil profile depth. Different adsorption capacities were exhibited by the two soils, however, which was related to their contrasting indigenous organic matter contents and mineralogies. The adsorption of DOC by the soils was not a function of solution I (I = 0.001 to 0.1 mol L−1 using NaCl); however, DOC adsorption was dependent on solution pH, with maximum adsorption occurring at ≃4.5. Competitive ion-exchange studies using Na2SO4 as an ionic-strength adjuster suggested that a portion of the DOC was electrostatically bound to the soil via anion exchange. By using thermodynamic principles, the predominant mechanism of DOC retention by the soil was found to be physical adsorption driven by favorable entropy changes. This is supported by preferential adsorption of the hydrophobic organic solutes to the soil relative to the hydrophilic organic solutes.

? Barry, D.A. (1990), Estimating Michaelis-Menten or Langmuir isotherm constants by weighted nonlinear least squares - Comment. Soil Science Society of America Journal, 54 (3), 941-942.

Full Text: 1990\Soi Sci Soc Ame J54, 941.pdf

Keywords: Langmuir.

? Persoff, P. (1990), Comments on estimating Michaelis-Menten or Langmuir isotherm constants by weighted nonlinear least squares - Reply. Soil Science Society of America Journal, 54 (3), 942.

Full Text: 1990\Soi Sci Soc Ame J54, 942.pdf

Keywords: Langmuir

Notes: highly cited

? Jaynes, W.F. and Boyd, S.A. (1991), Clay mineral type and organic compound sorption by hexadecyltrimethlyammonium exchanged clays. Soil Science Society of America Journal, 55 (1), 43-48.

Full Text: 1991\Soi Sci Soc Ame J55, 43.pdf

Abstract: In order to relate mineralogy to sorbent efficiency, organo-clays were prepared from reference vermiculite, illite, smectite, and kaolinite clay minerals using the organic cation hexadecyltrimethylammonium (HDTMA). Adsorption isotherms using C-14-HDTMA indicated stoichiometric adsorption of HDTMA up to the cation-exchange capacity (CEC). Organo-clays were prepared by adding HDTMA equivalent to the CEC and were evaluated as sorbents for nonionic organic compounds (NOCs) dissolved in water. X-ray diffraction analysis of the HDTMA clays revealed basal spacings of 28 angstrom for the vermiculite and 23, 20, and 18 angstrom for the high-charge, intermediate-charge, and low-charge smectites, respectively. The HDTMA vermiculite, illite, and smectites were all highly effective sorbents for NOCs, whereas Mg smectite was ineffective. The sorption isotherms of benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, t-butylbenzene, naphthalene, and biphenyl on the HDTMA clays indicated that sorption occurred by partition interactions with the HDTMA-derived organic phase. In general, both the greater HDTMA content and the larger basal spacings of high-charge HDTMA clays increased NOC sorption. Mineral-charge effects on the sorption of unsubstituted aromatic compounds (benzene, naphthalene, and biphenyl) were less evident than for alkyl-benzenes. Greater sorption of the alkylbenzenes by high-charge HDTMA clays can be attributed to the capability of the large basal spacings to accommodate larger solute molecules. The formation of organic cation exchanged soil clays derived from vermiculite, illite, or smectite may greatly improve the ability of soils to immobilize organic contaminants.

Keywords: Adsorption, Benzene, Cation Exchange, Isotherms, Layer Charge, Naphthalene, Reduction, Retention, Smectites, Sorption, Water

Notes: highly cited

? Qualls, R.G. and Haines, B.L. (1991), Geochemistry of dissolved organic nutrients in water percolating through a forest ecosystem. Soil Science Society of America Journal, 55 (4), 1112-1123.

Full Text: 1991\Soi Sci Soc Ame J55, 1112.pdf

Abstract: Dissolved organic matter (DOM) is a major vehicle for the translocation and loss of N and P from forest ecosystems. The chemical properties of DOM and its interactions with soil surfaces are crucial in determining the mobility of these organic nutrients. We fractionated DOM from throughfall, all soil horizons (Ultisols and Inceptisols), and stream water from an Appalachian mountain forest ecosystem into hydrophobic or hydrophilic acids, neutrals, and bases. We analyzed each fraction for dissolved organic C (DOC), N (DON), and P (DOP). Most of the DOC was in the acid fractions, with the humic fractions (hydrophobic acids and phenols) comprising 35 to 57% of the DOC in all samples except summer throughfall. Concentrations of all fractions declined with depth in the soil. As a percent of total DOC, the humics declined with depth, whereas the hydrophilic neutrals increased. Bases, which we expected to contain cationic amino groups, were < 2.5% of the DOC. Instead, most DON was in the humic, hydrophilic acid, and hydrophilic neutral fractions. Most DOP occurred in the hydrophilic acid, humic, and hydrophilic neutral fractions. The functional groups in which N and P occur had little influence on the behavior of most of the DOM as a whole since: (i) cationic DOM was such a minor component, and (ii) P was simply too rare to influence the anionic behavior of many molecules. Nevertheless, for those molecules in which P did occur, P may have influenced their behavior since a large percentage of the DOP was in the hydrophilic acid (i.e., anionic) fraction. The carboxylic and phenolic functional groups, or in some cases the neutrality, of the DOM molecules appeared to be much more important than N-containing groups in influencing the behavior of the N carried passively by the DOM.

Keywords: Humic Substances, Acid Treatment, Amino-Acids, River Water, Carbon, Adsorption, Chemistry, Retention, Solutes, Growth

? Aharoni, C., Sparks, D.L., Levinson, S. and Ravina, I. (1991), Kinetics of soil chemical reactions: Relationships between empirical equations and diffusion models. Soil Science Society of America Journal, 55 (5), 1307-1312.

Full Text: 1991\Soi Sci Soc Ame J55, 1307.pdf

Abstract: A variety of kinetic equations such as zero-order, first-order, second-order, Elovich, fractional-power, and parabolic-diffusion equations have been used to describe the kinetics of soil chemical processes. Often, several of these expressions seem to equally well describe the kinetics of a particular reaction. In this research, it is shown that the kinetics of phosphate sorption, release can be described by an expression that is approximated at beginning times by a fractional-power equation, at intermediate times by the Elovich equation, and at long times by an apparent first-order equation. Such kinetics, which can be characterized by a sigmoidal zeta(t) plot of the reciprocal of the rate against the time [(dq, dt)-1 vs. t], are consistent with theoretical homogeneous and heterogeneous models based on diffusion of the sorbate in the solid phase or at the solid, liquid interface. These models were applied to data from the published literature on sorption and release of phosphates by soils. For some soils, the experimental results were accounted for by assuming a constant diffusion coefficient. For other soils, it was assumed that diffusion processes with various diffusion coefficients take place simultaneously. Using these models, diffusion parameters can be estimated.

Keywords: Desorption, Dissolution, Elovich Equation, Microporosity, Occlusion, Oxides, Phosphate Sorption, Release, Time

Stevenson, F.J. and Chen, Y. (1991), Stability-constants of copper(II) humate complexes determined by modified potentiometric titration. Soil Science Society of America Journal, 55 (6), 1586-1591.

Full Text: 1991\Soi Sci Soc Ame J55, 1586.pdf

Abstract: Humic substances form highly stable complexes with micronutrient cations. Little is known, however, regarding the nature of the complexes or of their stability constants. A ligand titration procedure using the Cu(II) ion-selective electrode was investigated as a means of determining stability constants of the Cu(II) complexes with humic and fulvic acids. The procedure was superior to conventional titration (metal ion as titrant) because constants for binding at the strongest sites are measured. Furthermore, under the titration conditions employed (pH of 4 and 5, low ionic strength, 0.01 M, low Cu(II) concentration, 10^-5 M), precipitation did not occur and thus did not adversely affect the binding measurements. A continuous-distribution model showed promise for modeling the binding data. The binding affinity of some humates for Cu(II) followed the order: soil humic acid (SHA) > peat humic acid (PHA) > lignite humic acid (LHA) > soil fulvic acid (SFA) fungal melanin. Intrinsic stability constants (log K (bnl)) at pH 4 and an ionic strength of .01 M for the five humate preparations were 8.3, 7.9, 7.4, 7.2, and 6.9, respectively, constants at pH 5 were 8.5, 8.4, 7.9, 7.6, and 7.6, respectively.

Keywords: Fulvic-Acid, Organic-Matter, Humic-Acid, Soil, Fractions

Stahl, R.S. and James, B.R. (1991), Zinc sorption by B horizon soils as a function of pH. Soil Science Society of America Journal, 55 (6), 1592-1597.

Full Text: 1991\Soi Sci Soc Ame J55, 1592.pdf

Abstract: Better information is needed to predict how soil acidity affects exchangeability of heavy metals in soils dominated by Fe and Mn oxides with pH-dependent charge. Our laboratory study sought to separate exchangeable and nonexchangeable Zn sorbed by four B horizon soil materials with varied mineralogy and sesquioxide contents. A Myersville silt loam (fine-loamy, mixed, mesic Ultic Hapludalf), a Jackland sandy loam (fine, mixed, mesic Aquic Hapludalf), a Christiana sandy loam (clayey, kaolinitic, mesic Typic Paleudult), and an Evesboro loamy sand (mesic, coated Typic Quartzipsamment) were compared for the exchangeability of Zn as a function of pH. Surface charge was measured across the pH range of 3.5 to 7.6, a 175 µmol ZnCl₂/kg soil treatment was applied, and sorbed Zn was exchanged with K. Cation-exchange capacity (CEC) was positively correlated with nonexchangeable but not with exchangeable Zn forms. All four soils retained nearly the same amount of Zn, even though CEC ranged from < 10 to > 80 mmol5/kg. An abrupt transition from exchangeable to nonexchangeable Zn occurred in the pH range 5.6 to 5.9 of the Myersville, Evesboro, and Christiana soils. Differences in oxide mineralogy and proton buffering intensity appeared more important than CEC as controls on the exchangeability of Zn in these soils. This result is germane to predicting retention of heavy metals in sewage-sludge-amended agricultural soils.

Keywords: Heavy-Metals, Adsorption, Solubility, Oxides, Mechanisms, Copper, Lead, Iron, Acid

Niemeyer, J., Chen, Y. and Bollag, J.M. (1992), Characterization of humic acids, composts, and peat by diffuse reflectance fourier-transform infrared-spectroscopy. Soil Science Society of America Journal, 56 (1), 135-140.

Full Text: 1992\Soi Sci Soc Ame J56, 135.pdf

Abstract: Transmission infrared (IR) spectroscopy, either dispersive or Fourier transformed (FTIR), has been used extensively in studies on humic substances. A variety of bands characteristic of molecular structures and functional groups have been identified for these substances. The development of an attachment mounted onto FTIR spectrophotometers has allowed the determination of diffuse reflectance Fourier-transformed infrared (DRIFT) spectra. The purpose of this work was to study the applicability of DRIFT to soil organic-matter research and to compare the use of this instrumentation to dispersive and Fourier-transformed transmission IR spectroscopy. The DRIFT spectra were determined for humic acids, peat samples, and composts. In addition, the possibility of using DRIFT spectra to quantitatively measure sample concentration and measuring the relative concentration of functional groups was assessed. Sample preparation for DRIFT is much simpler than for transmission IR spectroscopy, interferences due to water adsorption are reduced, and resolution is improved. The spectra obtained using DRIFT had a higher degree of resolution as compared with dispersive and Fourier-transform transmission IR spectroscopy. Bands indicative of aliphatic C-H, carboxyl and corboxylate functional groups, aromatic C = C, and C-O stretch of polysaccharides were prominent and very well resolved. The DRIFT spectra obtained can also be used to fingerprint organic matter acquired from various sources. Spectra obtained at various concentrations of humic acid indicated that DRIFT cannot be used to estimate concentrations of organic matter in a given mixture. Relative concentrations of functional groups, however, were found to be fairly constant regardless of sample concentration. Therefore, changes in the relative concentration of functional groups can be measured during the humification process. It is expected that the application of DRIFT to organic-matter research will prove especially useful for characterizing bulky heterogeneous samples such as peat and composts.

Keywords: Spectra

Notes: highly cited

? Qualls, R.G. and Haines, B.L. (1992), Biodegradability of dissolved organic matter in forest throughfall, soil solution, and stream water. Soil Science Society of America Journal, 56 (2), 578-586.

Full Text: 1992\Soi Sci Soc Ame J56, 578.pdf

Abstract: High concentrations of dissolved organic matter (DOM) were leached into rainwater passing through the canopy and forest floor of an oak (Quercus spp.)-hickory (Carya spp.) forest in the southern Appalachian Mountains. More than 95% of this dissolved organic C (DOC) and N (DON) was removed as water percolated through the soil profile and left the ecosystem in stream water. Our objective was to examine the importance of decomposition in the removal of DOC and DON. Samples of DOM from throughfall, forest floow water, soil water from A and B soil horizons, and stream water were all adjusted to a common initial DOC concentration, inoculated with soil and stream microbes, and incubated in solution for 134 d. In general, only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation. The relative order of average decomposition of DOC from the various strata was, from fastest to slowest: throughfall, Oi horizon (forest floor), Oa horizon (forest floor), B horizon, stream, AB horizon, isolated fulvic acid, and upper A horizon. In short, biodegradability of DOM in the ecosystem profile declined vertically from throughfall to the A horizon and then increased with depth. The DON generally did not decay faster than the DOC - results consistent with the idea that hydrolysis of organic N is linked to mineralization of DOC rather than occurring selectively in response to the biochemical need for N. Throughfall DOM could be decomposed during its passage through the upper soil, but decomposition seems too slow to be responsible for the bulk of removal of DON and DOC that occurs in the mineral soil. Adsorption, rather than biodegradation, is more likely responsible for maintaining low DOC substrate concentrations in the mineral soil and preventing its loss into stream water.

Keywords: Leaf Leachate, Carbon, Decomposition, Mechanisms, Kinetics, Leaves, River

? Fendorf, S.E., Sparks, D.L., Franz, J.A. and Camaioni, D.M. (1993), Electron-paramagnetic resonance stopped-flow kinetic-study of manganese(II) sorption desorption on birnessite. Soil Science Society of America Journal, 57 (1), 57-62.

Full Text: 1993\Soi Sci Soc Ame J57, 57.pdf

Abstract: Many important reactions involving colloidal suspensions are rapid. Here, we introduce the application of a technique capable of rapidly measuring a reactant species (within 20 ms after the reaction initiation) in situ: an electron paramagnetic resonance spectroscopically monitored stopped-flow method (EPR-SF). The utility of this technique is demonstrated by investigating the sorption of Mn²⁺ on delta-MnO₂. The sorption reaction was complete in <1 s, with >80% of the Mn²⁺ being sorbed within 200 ms. A first-order rate dependence on Mn²⁺ was observed. Measurement of the initial reaction rate allowed the forward (sorption) rate constant to be determined (k(f) = 3.7410^-3 s^-1), and the reverse (desorption) rate constant was determined using an integrated reversible first-order rate expression (k(r) = 3.0810^-4 s^-1). Using these rate constants, the predicted time dependence of Mn²⁺ sorption was in good agreement with the measured sorption rate. The results indicate that chemical kinetics are being measured that allow determination of precise reaction rates and mechanisms.

Keywords: Solid-Solution Interface, Aqueous Suspensions, Spin-Resonance, Adsorption, Ion, (Hydr)Oxides, Spectroscopy, Chemistry, Oxidation, Exchange

? Jardine, P.M., Jacobs, G.K. and Wilson, G.V. (1993), Unsaturated transport processes in undisturbed heterogeneous porous media: I. Inorganic contaminants. Soil Science Society of America Journal, 57 (4), 945-953.

Full Text: 1993\Soi Sci Soc Ame J57, 945.pdf

Abstract: Prolonged disposal of organic and inorganic waste in shallow land burial sites throughout the USA has prompted detailed investigations of subsurface contaminant transport processes. The fate and transport of contaminant leakage from pits, trenches, and cribs into the vadose zone via storm events is not well understood. The objective of this study was to investigate the thermodynamic and kinetic processes controlling the transport of inorganic contaminants in unsaturated, heterogeneous subsurface media. Large undisturbed columns were isolated from a proposed waste site consisting of fractured saprolite (weathered interbedded shale and limestone), and steady-state nonreactive and reactive solute transport experiments were performed at a variety of pressure heads. Observed breakthrough curves (BTC) for binary and ternary mixtures in the Co-Sr-Ca system were delayed relative to nonreactive Br BTC, indicating that the former tracers were adsorbed by the solid phase. Transport of the binary mixtures Co-Ca and Sr-Ca was predicted reasonably well with the equilibrium convective-dispersive (CD) equation using independent measurements of all model parameters. However, application of the nonequilibrium or kinetic CD model to the observed Sr and Co binary data resulted in an improved description of contaminant transport. Cation-exchange equilibria relationships on homogenized subsurface material, using both shake batch and miscible displacement methods, adequately described the thermodynamic processes that were prevalent during contaminant transport. These results suggest that preferential transport of reactive contaminants is negligible for the unsaturated conditions used in this study, and that the structured saprolite within the subsurface media is a chemically active constituent during reactive solute transport. Although the transport of contaminants in the ternary Co-Sr-Ca system tem exhibited many of the same features as the binary transport studies, an attempt to simulate the transport of contaminants in the ternary system as independent species was less than adequate.

Keywords: Controlling Subsurface Transport, 2 Contrasting Watersheds, Solute Transport, Storm Events, Forested Watersheds, Upper Subcatchment, Soil, Macroporosity, Adsorption, Columns

Hinz, C. and Selim, H.M. (1994), Transport of zinc and cadmium in soils: Experimental evidence and modeling approaches. Soil Science Society of America Journal, 58 (5), 1316-1327.

Full Text: 1994\Soi Sci Soc Ame J58, 1316.pdf

Abstract: This study was conducted to assess the suitability of several isotherm equations in describing single solute and binary ion exchange of Zn and Cd in two soils (Windsor and Olivier). Isotherms were determined using batch methods for equilibration times of 1 and 14 d. Ion exchange batch experiments (based on NH₄OAc extraction) were carried out at different heavy metal/Ca ratios. Several isotherm equations were capable of describing 1- and 14-d sorption isotherms. However, the general Langmuir-Freundlich was most suitable for describing single solute (Zn and Cd) isotherms, whereas the Rothmund-Kornfeld ion exchange equation well described binary data sets (Zn-Ca and Cd-Ca). Miscible displacement experiments were carried out to study Zn and Cd transport in uniformly packed soil columns (10 cm in length) for different how velocities. For Windsor soil, the general isotherm equation predicted Zn transport results adequately but not Cd results. Moreover, under conditions of variable ionic strength, the use of constant selectivity (equal affinity) for ion exchange provided consistently superior predictions of Zn and Cd transport than the Rothmund-Kornfeld (variable affinity) approach. Attempts to predict Cd and Zn transport in Olivier soil, using several isotherms and ion exchange approaches, were not successful. Local equilibrium appeared dominant for Windsor soil, whereas nonequilibrium sorption behavior may be rate limiting for Zn and Cd transport in Olivier soil.

Keywords: Ion-Exchange, Adsorption-Isotherms, Retention, Equation, Cations, Columns, Batch

? Schmidhalter, U., Kahr, G., Evequoz, M., Studer, C. and Oertli, J.J. (1994), Adsorption of thiamin (Vitamin-B-1) on soils and clays. Soil Science Society of America Journal,