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《Journal of Northwest Sci-Tech University of Agriculture and Forestry》 1990-S1
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Studies on Some Properties and Thermodynamic Functions of K-Ca Exchanges in Several Soils

Chen Sigen Zhang Yinpin Bai Jingling Sun Yianluo (Soil Agro-chemistry Department)  
Some properties and thermodynamic functions of K-Ca exchanges in several soils were studied by using the equilibrum method. The results showed that Yellow cinnamon soil for affinity of K+ was relatively small, while Lou soil and Black lu soil for affinity of K+ was greater. Turning points occured when X11 of isotherms of K-Ca exchanges was equal to 0.46 and 0.41 in Lou soil and Black Lu soil respectively. This indicated that there were two absorption sites with different energy for K+ on soil surface. Thus, the selectivity of three kinds of soils for K+ was as follows: Lou soil≥Black Lu soilYellow cinnamon soil. In the general tendency, the potassium selectivity coefficients of the soils was reduced with an increase in mole fraction of K+ on the soil phase and decreased with an increase in the system temperature. Because all of the thermodynamic parameters for K-Ca exchanges of soils are negative, thus, indicating that certain affinity for K+. and that the exchange reaction is an exothermic proces. Ass viewed from for K-Ca exchanges, the sequence of the preference for K+ and the stability of K+ adsorbeb by the soils were as follows; Lou soil≥Black Lu soilYellow cinnamon soil. It is in agreement with the selectivity of three soils for K~+.
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