Personal Research Database

Full Text: 1984\Soi Sci Soc Ame J48, 39.pdf

Abstract: The kinetics of K exchange were investigated in Ca-saturated samples from the Ap horizon of an Evesboro soil from Delaware. Biphasic kinetics characterized the first-order plots for K adsorption and desorption at 283 and 298K with the two simultaneous reactions being attributed to exchange sites with varying reactivity for K and Ca ions. The rapid reaction was ascribed to exchange sites of the soil that are readily accessible to cation exchange reactions, whereas the slow reaction was attributed to exchange sites that are difficultly accessible to cation exchange reactions. Confirmation of the hiphasic kinetics was achieved through the use of cetyltrimethylammonium bromide (CTAB). Parabolic diffusion plots for K adsorption and desorption at 283 and 298 K indicated that an intraparticle diffusion process may be rate limiting for the difficultly accessible sites of the soil. The initial deviation from linearity of the parabolic plots for K desorption suggested that film diffusion may be rate limiting for desorption on readily accessible sites of the soil that form strong bonds with Ca ions. At 313 K the initial rapid kinetics of exchange was no longer present, and the exchange process was described by a single first-order reaction. The parabolic plots at 313 K suggested that this phenomenon could possibly be attributed to the finite rate at which the polymer structure of soil organic matter changes in response to the adsorption and desorption of the two reacting cations.

Jardine, P.M. and Sparks, D.L. (1984), Potassium-calcium exchange in a multireactive soil system: II. Thermodynamics. Soil Science Society of America Journal, 48 (1), 45-50.

Full Text: 1984\Soi Sci Soc Ame J48, 45.pdf

Abstract: Thermodynamics of K exchange were investigated in Ca-saturated samples from the Ap horizon of an Evesboro soil from Delaware. At 283 and 298 K the selectivity curves (lnkv vs. K) showed preference for K at low values of NK (mole fraction of K in solution) and for Ca at higher values. This selectivity reversal may be attributed to exchange sites of varying reactivity for K and Ca ions and supports the hypothesis of the multireactive nature of the soil. Although K was selectively bound at low NK, the soil exhibited an overall Ca preference as noted by the positive standard free energy values (G°). The standard enthalpy of exchange (H°) was negative, which indicated very strong binding of K ions with some sites of the soil. This may be associated with the presence of vermiculitic clay minerals that predominated in the <2-µm clay fraction. A thermodynamic investigation was also initiated on the various size fractions of the soil (i.e., sand, silt, and clay) and on soil that was treated with cetyltrimethylammonium bromide (CTAB) or NaOCl-DCB. These treatments explained the differences in ionic selectivity observed in the Evesboro soil.

Sparks, D.L. (1984), Ion activities: An historical and theoretical overview. Soil Science Society of America Journal, 48 (3), 514-518.

Full Text: 1984\Soi Sci Soc Ame J48, 514.pdf

Abstract: A knowledge of ion activities in soil-water systems is essential to a proper understanding of the physicochemical behavior of soils and to the environment of plant roots in the soil. However, with the notable exception of soil acidity, perhaps no other topic in soil chemistry has provoked such fierce arguments as the meaning of ionic activities as they apply to the soil solution. The purpose of this paper is to present an historical and theoretical overview of the use of ion activities in soil chemistry. Attempting to incorporate ionic species into a thermodynamic analysis of the soil solution is a convenient mathematical device, since an ionic species cannot be described in thermodynamic terms. Ionic species are strictly molecular or microscopic concepts. It is demonstrated in this paper that when ionic equilibria between aqueous solutions and solid phases are investigated, the division of the electrochemical potential into a term in electrical potential () and a term in chemical potential (µ) is entirely arbitrary. Additionally, the early 1950s arguments of Jenny, Marshall, Peech, Coleman, Overbeek, and Babcock dealing with junction potentials, suspension effects, and mobilities of ions is reviewed. The importance of soil solution activities in relation to nutrient uptake and plant growth is also presented.

? Harter, R.D. (1984), Curve-fit errors in Langmuir adsorption maxima. Soil Science Society of America Journal, 48 (4), 749-752.

Full Text: 1984\Soi Sci Soc Ame J48, 749.pdf

Abstract: Although the Langmuir equation does not always adequately estimate “adsorption” maxima, it remains useful for empirical description of data. The test of data fit to the equation has usually been by linearity of the “Langmuir plot,” viz. concentration/adsorption plotted as a function of concentration. This test, however, is inadequate because the plotting of concentration against itself reduces data variability and always provides a statistically significant correlation coefficient. A better test of fit is to ascertain whether the adsorption isotherm has the shape of the equation model. When isotherms do not have the correct shape and only low concentration data is used, the equation can provide estimates of the adsorption maximum that are in error by 50% or more.

? Polyzopoulos, N.A., Keramidas, V.Z. and Kiosse, H. (1985), Phosphate sorption by some alfisols of greece as described by commonly used isotherms. Soil Science Society of America Journal, 49 (1), 81-84.

Full Text: 1985\Soi Sci Soc Ame J49, 81.pdf

Abstract: The one- and two-surface Langmuir, the Freundlich, and the Temkin isotherms were fitted to P sorption data for 14 representative alfisols of Greece. Each was found to describe P sorption by these soils with comparable success, with the Freundlich and the two-surface Langmuir isotherms being slightly superior. The Freundlich equation is characterized by simplicity of form, based on more realistic assumptions, and now capable of rigorous derivation. It can therefore be used in preference to the others, since its parameters, as those of the Langmuir equation, allow comparisons among soils.

Keywords: Soils, Phosphorus – Adsorption, Thermoanalysis – Applications, Red Mediterranean Soils, Adsorption Isotherms, P Sorption Data

Havlin, J.L. and Westfall, D.G. (1985), Potassium release kinetics and plant response in calcareous soil. Soil Science Society of America Journal, 49 (2), 366-370.

Full Text: 1985\Soi Sci Soc Ame J49, 366.pdf

Abstract: Greenhouse and laboratory experiments were conducted to characterize the K supply and nonexchangeable K release kinetics in calcareous soils. Twelve soils were exhaustively cropped with alfalfa (Medicago sativa L.) in the greenhouse for 584 d (16 cuttings). Yield, K uptake, and changes in NH₄OAc exchangeable K were monitored. Calcium resin extractable K was determined in the laboratory (7000 h extraction) on the <0.25 mm fraction of each soil. Nonexchangeable K release was calculated from the greenhouse and laboratory data. Cumulative K release to Ca-resin was mathematically described by a power function equation and the empirical constants releated to alfalfa yield, K uptake, and exchangeable K levels. Results indicated that clay soils had a long-term supply of plant available K while light-textured soils did not. After 16 cuttings the exchangeable K levels in the clay, loam, and sand textured soils declined 44, 33 and 58%, respectively. Both independent methods of measuring nonexchangeable K release were highly correlated with each other (r = 0.91). Potassium release was also highly correlated to initial NH₄OAc-K and to cumulative or relative K uptake and yield. Intercept and slope constants of the power function kinetic equation were significantly correlated to alfalfa yield, K uptake, and initial exchangeable K. Results also indicated that the NH₄OAc-K soil test was an adequate measure of long-term K supply in these soils.

Havlin, J.L., Westfall, D.G. and Olsen, S.R. (1985), Mathematical models for potassium release kinetics in calcareous soils. Soil Science Society of America Journal, 49 (2), 371-376.

Full Text: 1985\Soi Sci Soc Ame J49, 371.pdf

Abstract: Potassium release from the coarse (20–50 µm), medium (5–20 µm) and fine silt (2–5 µm), and the coarse (2–0.2 µm) and medium-fine clay (<0.2 µm) fractions of six Great Plain soils was determined by successive extraction with Ca-saturated cation exchange resins. All soils contained primarily montmorillonite-mica minerals. Results indicated that 65 to 80% of the total K released in 7000 h of extraction time occurred in the clay (<2.0 µm) fraction. Four mathematical models (first-order rate, parabolic diffusion, power function, and Elovich) were used to describe cumulative K release. Comparisons of coefficients of determination (r2) and standard errors of the estimate (SE) indicated that the Elovich, power function, and parabolic diffusion equations adequately described cumulative K release, whereas the first-order rate equation did not. Rate constants for the three equations were highly correlated with mica content and relative alfalfa yield and K uptake. In the past, others have used complex equations containing three simultaneous first-order rate terms to describe K release, however, results reported herein show that simple one-term equations can be used.

? Ogwada, R.A. and Sparks, D.L. (1986), A critical-evaluation on the use of kinetics for determining thermodynamics of ion-exchange in soils. Soil Science Society of America Journal, 50 (2), 300-305.

Full Text: 1986\Soi Sci Soc Ame J50, 300.pdf

Abstract: Thermodynamics of K-Ca exchange were compared using equilibrium and kinetic approaches in two Delaware soils. The classical Argersinger theory was employed for the equilibrium approach, while a kinetic approach was studied using miscible displacement, batch, and vigorously mixed batch techniques. These three techniques were used to determine how diffusion affects the comparison between thermodynamic parameters using kinetic and equilibrium approaches. Rate coefficients and energies of activation were profoundly affected by the type of kinetic technique employed and their magnitude was in the order: vigorously mixed batch > batch > miscible displacement. Energies of activation for adsorption (Eaa) in the two soils ranged from 7.42 kJ mol^–1 using the miscible displacement technique to 32.96 kJ mol^–1 with the vigorously mixed batch, while energies of activation for desorption (Ead) ranged from 11.87 to 42.1 kJ mol^–1 for the two methods, respectively. The magnitude of the Eaa and Ead values indicated pronounced diffusion effects in the miscible displacement and batch techniques, which were greatly reduced with the vigorously mixed batch method. Thermodynamic parameters (G°, H°, and S°) calculated using the equilibrium and kinetic approaches compared very well in trend, and gave the same inferences of ion behavior for the two soils studied. However, except for the vigorously mixed batch technique, the magnitude of the thermodynamic parameters for the two approaches compared poorly. For example, the G° values calculated using the equilibrium approach avg 4.67 kJ mol^–1 for the two soils, while they avg 4.92 kJ mol^–1 with the vigorously mixed batch, 2.12 kJ mol^–1 with the batch, and 2.12 kJ mol^–1 with the miscible displacement. The degree of comparison between the two approaches was directly related to the extent of diffusion controlled exchange. When the influence of diffusion was significantly reduced, as with the vigorously mixed batch technique, our data would indicate that a kinetic approach can be successfully used to gather thermodynamic information about a soil system.

Jardine, P.M. and Zelazny, L.W. (1986), Momomuclear and polynuclear aluminum speciation through differential kinetic reactions with ferron. Soil Science Society of America Journal, 50 (4), 895-900.

Full Text: 1986\Soi Sci Soc Ame J50, 895.pdf

Abstract: The kinetic reaction of ferron (8-hydroxy-7-iodo-5-quinoline-sulfonic acid) with partially neutralized Al solutions of varying basicity and age were investigated with the intent of separating mononuclear and polynuclear Al. Ferron solutions buffered with varying quantities of NaOAc, NH₂OH·HCl, and acetic acid suggested that reduction of ferron by NH₂OH·HCl may be essential before monotonically increasing absorbance vs. time functions occur for Al reactions with ferron. When ferron is buffered with appropriate quantities of NaOAc and NH₂OH·HCl it must be aged for 5 d at room temperature until reduction has slowed. This solution remains stable for 25 d and exhibits consistent kinetic reactions with Al during this time period. A large portion of ferron interactions with partially neutralized Al of varying basicity and age were described by a binary species first-order rate function, which provided the rates of monomer and small polymer reactions with ferron as well as the mole fraction of monomeric species present (fa). Modelfitted fa are based on the differential kinetic reactions of ferron with Al, thus arbitrary separation times for determining mononuclear and polynuclear Al are avoided. Rate parameters established for mononuclear Al solutions using a single species first-order equation compared well with those determined for mononuclear Al from partially neutralized solutions using the binary species model. Ferron reactions at longer times were related to the decomposition of large Al polymers, which were welldescribed by pseudo first-order kinetics.

? Ogwada, R.A. and Sparks, D.L. (1986), Kinetics of ion exchange on clay minerals and soil. I. Evaluation of methods. Soil Science Society of America Journal, 50 (5), 1158-1162.

Full Text: 1986\Soi Sci Soc Ame J50, 1158.pdf

Abstract: The effect of kinetic methodology on adsorption rate coefficients (ka) and energies of activation for adsorption (Eaa) were investigated using five different techniques. These techniques were: miscible displacement, batch, static, stirred, and vortex batch. Kinetics of K adsorption were studied on Ca-saturated kaolinite, a Chester soil (fine-loamy, mixed mesic Typic Hapludults) and vermiculite. The ka values were highest for kaolinite and lowest for vermiculite. The higher ka values observed for kaolinite would be expected since a relatively pure kaolin would exhibit only easily accessible planar surface sites for K exchange. The ka values for the Chester soil were a reflection of the intermediate properties of this soil between kaolinite and vermiculite. The type of kinetic technique greatly affected the time required for equilibrium to be attained in K adsorption. From greatest to least time, the order was: static > miscible displacement > batch > stirred > vortex batch. Both static and miscible displacement techniques yielded the lowest ka and Eaa values for all three colloids. This is primarily because these methods represent systems where the influence of diffusion on the rate of K adsorption is at its maximum. Only for kaolinite did the ka and Eaa values of both the stirred and batch techniques approximate, in magnitude, those of the vortex method. With the Chester soil and vermiculite, which contain appreciable interlayer sites, the stirred and batch techniques yielded ka and Eaa values much lower than those for the vortex batch method. These results indicate that in colloids where more significant intraparticle diffusion occurs, the batch or stirring technique as used in this study is not effective in eliminating the influence of diffusion.

? Ogwada, R.A. and Sparks, D.L. (1986), Kinetics of ion exchange on clay minerals and soil. II. Elucidation of rate-limiting steps. Soil Science Society of America Journal, 50 (5), 1162-1162.

Full Text: 1986\Soi Sci Soc Ame J50, 1162.pdf

Abstract: Kinetics of K⁺ adsorption were investigated on kaolinite, a Chester loam soil and vermiculite using static, stirred, and vortex batch techniques. The objective of this study was to elucidate the rate-limiting steps for K⁺ adsorption on the clay minerals and soil. We hypothesized that it is possible under laboratory conditions to set up a system in which the global rate is limited by mass transfer (under static conditions), in which only the intraparticle diffusion step is rate-limiting (stirred system), and a system in which the rates of film and intraparticle diffusion are both relatively rapid, presumably rendering the reaction step to be rate-controlling (vortex batch). We derived and assigned additive resistance relations to the three proposed experimental methods according to the above stated assumptions. Observed rate coefficients obtained from static, stirred and vortex batch systems were combined and used to calculate rate coefficients for film diffusion (kf), intraparticle diffusion (kI), and reaction kinetics (kr) in a static system. Film diffusion and intraparticle diffusion rate coefficients were approximately the same in vermiculite, indicating that both steps were rate-determining. In kaolinite and the Chester soil, film diffusion was the rate-limiting step. These conclusions were also verified using the parabolic diffusion equation. The kI values were on the avg 8.7 times as great as kf values in the kaolinite system, indicating that intraparticle diffusion was not important for kaolinite. Higher energies of activation for adsorption (Eaa) were observed for the reaction step than for intraparticle diffusion or film diffusion steps. These findings were expected since chemical reactions are more sensitive to temperature changes than diffusion processes.

? Schulthess, C.P. and Sparks, D.L. (1986), Back-titration technique for proton isotherm modeling of oxide surfaces. Soil Science Society of America Journal, 50 (6), 1406-1411.

Full Text: 1986\Soi Sci Soc Ame J50, 1406.pdf

Abstract: Batch potentiometric titration analyses were made on a -Al₂O₃ colloidal suspension and interpreted in terms of the electroneutrality principle. Three titration methods involving a singular reference curve were compared. The first reference used was theoretical, the latter two were representative supernatant curves: an electrolyte solution, and an aliquot of the zero point of titration (ZPT) supernatant. All three methods resulted in similar charge isotherms and a zero point of charge (ZPC) = 8.60. A fourth titration method was developed involving each supernatant of the batch titration sample to act as a unique reference. This latter method is a backtitration technique which accounts for all sources that also consume H⁺ ions, leaving the difference to be the adsorbed proton concentration only. The NaClO₄ electrolyte solution used is postulated to be adsorbed with competitive cation and anion exchange mechanisms with a point of zero salt effect (PZSE) = 7.50.

Carski, T.H. and Sparks, D.L. (1987), Differentiation of soil nitrogen fractions using a kinetic approach. Soil Science Society of America Journal, 51 (2), 314-317.

Full Text: 1987\Soi Sci Soc Ame J51, 314.pdf

Abstract: The chemically induced release of NH₄-N from four Delaware soils was monitored over time. The extractants used were 0.02 M KMnO₄-0.5 M H₂SO₄ at 297 K and 0.01 M CaCl₂ at 368 K. Data were analyzed using first-order kinetics. The kinetic approach presented does allow direct differentiation of two NH₄⁺ releasing reactions. Two simultaneous first-order reactions were needed to describe three of the soils, while a single equation described the remaining soil. The equations were considered to represent the release of NH₄⁺ from an inorganic and an organic source. Using this approach, estimates of these pools were made and compared with estimates based on traditional batch techniques. Extraction with acid-KMnO₄ yielded kinetic estimates of the inorganic and organic pools, which exceeded the batch estimates of these pools. Kinetic estimates based on extraction with CaCl₂ were similar to batch estimates of inorganic N, but much less than either acid-KMnO₄ or batch estimates of organic N. Neither extractant gives direct evidence for the existence of a chemically active organic pool, however, there is indirect evidence for such a pool.

Notes: highly cited

Boyd, S.A., Mortland, M.M. and Chiou, C.T. (1988), Sorption characteristics of organic compounds on hexadecyltrimethylammonium-smectite. Soil Science Society of America Journal, 52 (3), 652-657.

Full Text: 1988\Soi Sci Soc Ame J52, 652.pdf

Abstract: When hexadedyltrimethylammonium (HDTMA) ion is exchanged for metal cations like calcium in smectite, the sorptive properties of the clay are greatly modified. The resultant HDTMA-smectite complex behaves as a dual sorbent, in the sorption of organic compounds, in which the mineral fraction functions as a solid adsorbent and the organic (HDTMA) phase as a partition medium. Capacities of mineral adsorption and partition uptake by HDTMA in the HDTMA-smectites are illustrated by sorption of benzene, trichloroethene (TCE), and water as vapors on the dry sample and by sorption of benzene and TCE from water. The exchanged HDTMA in clay is found to be a much more powerful partition medium than ordinary soil organic matter in the uptake of benzene and TCE. Based on this finding, HDTMA-smectite appears to be an effective sorbent for removing organic contaminants from water. It is suggested that such sorptive organo-clay complexes could be used to enhance the containment capabilities of clay landfill liners and bentonite slurry walls.

Persoff, P. and Thomas, J.F. (1988), Estimating Michaelis-Menten or Langmuir isotherm constants by weighted nonlinear least-squares. Soil Science Society of America Journal, 52 (3), 886-889.

Full Text: 1988\Soi Sci Soc Ame J52, 886.pdf

Abstract: We derive a nonlinear least squares fitting method for determining either Michaelis-Menten equation or Langmuir adsorption isotherm constants from experimental data. Data points can be weighted unequally if their relative precisions are known. Comparison of this method with the commonly used linearization methods, using simulated data sets containing normally distributed random errors, showed that this method yields more accurate and precise estimates of the constants than any of the linearizations. A short BASIC program to facilitate computation is presented.

Puls, R.W. and Bohn, H.L. (1988), Sorption of cadmium, nickel, and zinc by kaolinite and montmorillonite suspensions. Soil Science Society of America Journal, 52 (5), 1289-1292.

Full Text: 1988\Soi Sci Soc Ame J52, 1289.pdf

Abstract: Sorption is the predominant process governing metal ion movement in soils and includes the following physical and chemical mechanisms: adsorption, precipitation and absorption. This research attempts to use the hard-soft-acid-base principle to explain sorption selectivity of the metal cations Cd, Ni and Zn by kaolinite and montmorillonite clays. The hard-soft character of the clay surfaces, which is due to their surface functional groups, may be inferred by cation sorption selectivity experiments where pH and complex ion formation are controlled and monitored. Calcium saturated clays were suspended in Ca(ClO₄)₂, CaCl₂ or CaSO₄ and spikes of the above metals as divalent cations were added and their reactivity assessed within the framework of the HSAB Principle. For kaolinite in Ca(ClO₄)₂, metal sorption followed the sequence Cd > Zn > Ni. For montmorillonite in Ca(ClO₄)₂, metal sorption followed the sequence Cd Zn > Ni. In CaCl₂ and CaSO₄, the selectivity was different due to the presence of Cl^– and SO₂^–4 which competed with the mineral surfaces for the divalent metal cations.

? Miller, D.M., Sumner, M.E. and Miller, W.P. (1989), Comparison of batch- and flow-generated anion adsorption isotherms. Soil Science Society of America Journal,