几种土壤K-Ca交换特征及热力学函数的研究

Studies on Some Properties and Thermodynamic Functions of K-Ca Exchanges in Several Soils

应用平衡方法对黄褐土、塿土、黑垆土的K-G交换特征及热力学函数进行了初步研究,结果表明:黄褐土对K^+的亲和力相对较小;塿土、黑垆土对K^+的相对亲和力较强,且其交换等温线分别在X_k^l等于0.46和0.41处出现拐点,说明其粘粒表面存在着两种对K^+结合能不同的吸附位。3种土壤对K^+的选择性为:塿土≥黑垆土>黄褐土,选择系数变化的总趋势是随固相吸附K^+的摩尔分数增加而减小,随温度的升高而下降。3种土壤K-Ca交换的热力学函数△G°、△H°和 △S°均为负值,表明3种土壤对K^+均有一定的亲和力,交换反应为放热过程。从△G°、△H°和△S°的绝对值大小来看,3种土壤对K^+的偏好和结合的稳定程度为:塿土>黑垆土>黄褐土,这与其对K~±的选择性结论一致。

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 soil>Yellow 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 soil>Yellow cinnamon soil. It is in agreement with the selectivity of three soils for K^+.