Binary K-Ca exchange on a clay separated from a soil with dominate illite (mica) mineralogy: 2- Determination of selectivity Coefficients and thermodynamic parameters and effects on them of K-depletion

Document Type : Research Paper

Authors

1 University College of Agriculture and Natural Resources, University of Tehran

2 Associate Professor, Faculty of Agricultural Engineering and Technology, University of Tehran

Abstract

Selectivity coefficients and thermodynamic parameters of K-Ca exchange in a clay separated from a soil with dominant illite (mica) mineralogy were studied at two different ionic strengths (0.3 and 0.002 M). The clay was depleted for periods of 0, 6, 25 and 150 hours. The values of the Kerr (KKer), the Vanselow (KV), the Gapon (KG), the Gaines-Thomas (KGT) and the Davies (KD) selectivity coefficients were increased with K saturation. In the range of EK≤0.7, KV was smaller than 1, suggested that the exchangers preferred K+ over Ca2+ in this range, however at high EK values, Ca2+ was preferentially selected. Rothmund-Kornfeld model was fitted well to exchange data. β in this equation was smaller than 0.66, demonstrating heterogeneity of exchange sites in the clays. The value of β decreased with K-depletion. Furthermore, β decreased with reduction in ionic strength from 0.3 to 0.002 M, indicating an increase in surface sites heterogeneity. Regular solution (RS) model was also well fitted to the data. Thermodynamic equilibrium constants (Kex) were smaller than 1 and the standard free energy of the exchange reactions (ΔG°ex) were positive in all clays. The values of Kex in different K-depleted clays were not significantly different, indicating that the depletion-collapse cycle of these illitic clays did not change their selectivity for K+ or Ca2+. The decrease in the ionic strength led to the increase in Kex and decrease in ΔG°ex, an indication of reduced tendency of clay for K+ relative to Ca2+. With increasing EK, Kex remained relatively constant. ƒK increased with ECa and ƒCa decreased. Comparison of ƒK and ƒCa calculated by the thermodynamic method and the regular solution model indicated that the values of ƒK in RS model were greater than of thermodynamic method.

Keywords

Main Subjects

References

Agbenin, J. O. and Yakubu, S. (2006). Potassium–calcium and potassium–magnesium exchange equilibria in an acid savanna soil from northern Nigeria. Geoderma, 136, 542–554.
Appel, C., Rhue, D., Ma, L. and Reve, B. (2002). Heat of K/Ca and K/Pb exchange in two tropical soils as measured by flow calorimetry. Soil Science, 167, 773–781.
Bernas, B. (1968). A new method for decomposition and comprehensive analysis of silicates by atomic f. Analytical Chemistry, 40, 1682-1687.
Buckley, D.E. and Cranston, R.E. (1971). Atomic absorption analysis of 18 elements from a single decomposition of aluminosilicate. Chemical Geology, 7, 273-284.
Carson, D. C. and Dixon, J. B. (1972). Potassium selectivity in certain montmorillonite soil clays. Soil Science Society American Proceedings, 36, 838-843.
Chung, J. B., Zasoski, R.G. and Burau, R.G. (1994). Aluminum–potassium and aluminum–calcium exchange equilibria in bulk and rhizosphere. Soil Science Society of American Journal, 58, 1376–1382.
Deist, J. and Talibudeen, O. (1967). Thermodynamics of K-Ca exchange in soils. Journal of Soil Science, 18, 138-148.
Essington, M. E. (2004) Soil and water chemistry: an integrative approach. CRC Press, Boca Raton. FL. USA.
Feigenbaum, S., Bar-Tal, A., Portnoy, R. and Sparks, D. (1991). Binary and Ternary Exchange of Potassium on Calcareous Montmorillonitic. Soil Science Society of American Journal. 55:49-56.
Goulding, K. W. T. (1983). Thermodynamics of potassium exchange in soils and clay minerals. Advances in Agronomy, 36, 215–264.
Goulding, K. W. T. 1981. Potassium retention and release in Rothamsted and Saxmundhum soils. Journal of Science Food and Agriculture, 32, 667-670.
Goulding, K. W. T. and Talibudeen, O. (1979). Potassium reserves in a sandy clay soil from the Saxmundhum experiment: Kinetics and equilibrium thermodynamics. Journal of Soil Science, 30, 291-302.
Goulding, K. W. T. and Talibudeen, O. (1980). Heterogeneity of cation exchange sites for K–Ca exchange in aluminosilicates. Journal of Colloid and Interface Science, 78, 15–24.
Hutcheon, A. T. (1966). Thermodynamics of cation exchange on clay: Ca-K montmorillonite. Journal of Soil Science, 17, 339-355.
Jardine, P. M. and Sparks, D.L. (1984). Potassium-calcium exchange in a multireactive soil system. II. Thermodynamics. Soil Science Society of American Journal, 48, 45–50.
Jensen, H. E. (1973). Potassium-calcium exchange equilibria on a montmorillonite and kaolinite clay. I. A test of argersinger thermodynamic approach. Agrochemia, 17, 181-190.
Jensen, H.E., K.L., Babcock. 1973. Cation exchange equilibria on a Yolo loam soil. Hilgradia, 41, 475–487.
Laird, D. A. and Shang, C. (1997). Relationship between cation exchange selectivity and crystalline swelling in expanding 2:1 phyllosilicates. Clays and Clay Minerals, 45(5), 681-689.
Lanyon, L. E. and Heald, W. R. (1982) Magnesium, calcium, strontium, and barium. In A. L. Page et al. (Ed.), Methods of soil analysis. (Part 2). (pp. 247-261). Soil Science Society of America, Madison, WI.
Loeppert, R.H. and Suarez, D.L. (1996) Carbonate and gypsum. In D. L. Sparks (Ed.), Methods of soil analysis, (pp. 437-474). Soil Science Society of America, Madison, WI.
Moujahid, Y. and Bouabid, R. (2014). Potassium-Calcium exchange in clays of selected Moroccan vertisols. Journal of Materials and Environmental Science, 5 (5), 1541-1550.
Ogwada, R. A. and Sparks, D. L. (1986). Use of mole or equivalent fractions in determining thermodynamic parameters for potassium exchange in soils. Soil Science, 141 (4), 268-273.
Shainberg, I ., Alperovitch, N. I. and Keren, R. (1987). Charge density and Na-K-Ca exchange on smectites. Clays and Clay Minerals, 35(I), 68-73.
Smith, S. A. (2000). Potassium dynamics and exchange equilibria in loess-derived soils. Ph.D. dissertation, The University of Tennessee, Knoxville.
Smith, S. J. and Scott, A. D. (1966). Extractable potassium in Grundite illite: 1. Method of extraction. Soil Science, 102, 115-122.
Sposito, G. (2008) The Chemistry of Soils (2nd ed.). Oxford University Press. New York.
Talibudeen, O. (1971). The fertility status of soil potassium related to K-Ca exchange isotherms. Proceedings of the International Symposium on Soil Fertility Evaluation, New Dehli, India, I, pp. 98-103.
Talibudeen, O. (1972). Exchange of potassium in soils in relation to other cations. Potassium in the Soil. Proceedings of the 9th Colloquium of the International Potash Institute, Landshut, Germany. pp. 97-112.
Udo, E. J. (1978). Thermodynamics of potassium-calcium and magnesium-calcium exchange reactions on a kaolinitic soil clay. Soil Science Society of American Journal, 42, 556-560.
Iranian Journal of Soil and Water Research
Volume 48, Issue 3
October 2017
Pages 599-612

Files

Share

How to cite

Statistics