Effect of Cadmium ion on Adsorption-Desorption Behavior of Simazine on Agricultural Soils
The effect of cadmium (Cd) on adsorptiondesorption behavior of Simazine [2-chloro-4, 6 bis (ethylamine)-1,3,5-triazine] which is anionic herbicide were investigated at three different temperature 10, 25 and 40 ±1˚C on six agricultural soil samples which has different texture. The first order rate law was most fitted with the best correlation factor, the Linear, Freundlich and Langmuir models also were applied to describe the adsorption-desorption affinities to the soil samples. Values of adsorption rate constant ka were in the range 0.836 – 1.818 h-1 while desorption rate constant kdes were in the range 0.779 – 1.376 h-1. The activation energy Ea * for adsorption processes followed the range 11.041- 17.684 KJmol-1. Values of equilibrium constant lnKo were in the range 0.048 – 0.278. The standard free energy change ΔGo values were in the range -0.126 to -0.655 KJmol-1. Values of the standard enthalpy change ΔHo followed the range -2.702 to – 4.850 KJmol-1. The value of standard entropy change ΔSo followed the range-7.557 to-14.965 Jmol-1k-1. The negative values revealed that the adsorption-desorption processes spontaneously, exothermic and physical in nature to some extent and chemical in others. The distribution coefficient Kd values for adsorption-desorption process varied between 2.369 – 2.611 mlg-1, 5.556- 22.85 mlg-1 respectively. Freundlich coefficient KF ranged between 0.180-0.506 mlg-1 for adsorption processes. The value Freundlich coefficient for desorption process KFdes ranged from 0.107 to0.498 mlg-1. Langmuir coefficient KL for adsorption process varied between 0.027 – 0.064 mlg-1. Langmuir coefficient KLdes values for desorption process from 0.014 to 0.067 mlg-1. All desorption isotherms exhibited hysteresis.
