Thermodynamic parameters of zinc sorption in some calcareous soils

Sorption is one of the most chemical important process, in which determine micronutrients availability in soil. Sorption isotherms provide useful information about sorption capacity of soils. Sorption data can be used to determined sorption thermodynamic parameters. To evaluate the sorption of zinc (Zn) onto some soils, an experiment was conducted with ten calcareous soils of Hamadan province in the west of Iran. Half g soil samples were equilibrated at 25±1 and 45±1°C with 25 ml of 0.01M CaCl 2 containing 0 to 30 mg L -1 Zn as ZnSO 4. Suspensions were centrifuged, filtered and concentration of Zn in the clear extract solution was determined using atomic absorption spectrophotometer. Amount of Zn sorbed by the soil was calculated from difference between initial and final concentration of Zn in the equilibrium solution. Sorption of Zn was evaluated using adsorption isotherms. The thermodynamic parameters viz. K � , �G � , �H � andS � were determined using sorption data and concentration of Zn in equilibrium solution at two different temperatures.The results showed that Zn Sorption was described by linear, Feeundlich, Temkin and D-R models. The values of K o increased with rise in temperature from 25 to 45 °C in all the soils. The AG o values at 25 °C and 45 °C were negative and ranged from -7.00 to -16.64 and -13.24 to -41.93 kJ mol -1 , respectively. The values of AH o and AS o were positive and ranged from 357.47 to 74.02 kJ mol -1 and 1255.97 to 281.79 J mol -1 K -1 , respectively. Evaluation of thermodynamic parameters provide an insight into mechanism of Zn sorption in the soils. The values of AG o were found negative indicating Zn sorption was spontaneous and the values of AH o were positive indicating Zn sorption was endothermic. Thermodynamic parameters revealed Zn sorption increased as the value of K o , AG o , AH o and AS o increased with temperature. Also the results showed that calcareous soils can sorb high amounts of Zn and that thermodynamic parameters are useful in describing Zn sorption. we suggest that such research be done in contaminated soils. Also we suggest that effect of thermodynamic sorption parameters on Zn uptake by plant be done using the pot experiment. (Journal of American Science 2010;6(7):298-304). (ISSN: 1545-1003).