THE COMPARISON OF THE VALUES OF THE SELECTIVITY COEFFICIENT OF HANG DONG

Abstract

The selectivity coefficient (K _{adsorbed/added cation}) of Hang Dong soil series was conducted in 2 systems. The first system is the one pair cationic system which the soils were saturated with one type of cation. In the other system which was named the multicationic system, the soils were left naturally. In both system, the cation was added to the soils in different fraction of cation exchange capacity then incubated for one month. The equilibrium solution in soils was determined and calculated for the selectivity coefficient according to 6 equations. These equations are Equilibrium constant, Mass action, Modified Gapon, Langmiur, Vanselow, and Statistical. The results show that the values of selectivity coefficient obtained from the one pair cationic system differ from those obtained from multicationic system. However the values from the latter are less fluctuated and therefore are more reliable. Recommended equations of each cationic pair for practical work are as followed: Vanselow or Statistical equation were appropriate for K_ca/K and K_Mg/K while the Mass action equation was suitable for K_ca/Na K_Mg/Na K_na/K and K_Mg/Ca Finally, the magnitude of replacing power of cation in Hang Dong soil series are Mg²⁺> Ca²⁺> K⁺> Na⁺.