Thermodynamics of chromium sorption in soil groups of India

Abstract

A laboratory experiment was conducted to study the thermodynamics of chromium sorption in major soil types, viz Typic Ustorthent, Typic Haplustalf, Typic Eutrochrept, Vertic Ustopept, Sodic Haplustert, representing 5 agroecological zones of india. The thermodynamic parameters, viz thermodynamic equilibrium constant (KD),. standard free energy (G0), standard enthalpy (HD) and standard entropy (SD) were determined by using sorption data and concentrations of Cr (VI) in equilibrium solution at 2 different temperatures at 25 ± 2^oC and 45± 2^oC of soil suspension. Data of Cr sorption could be described satisfactorily by Freundlich and modified LangmUIr Isotherms. The Cr sorption was maximum In order of Typic Ustorthent > Typic Haplustalf > Typic Eutrochrept > Vertic Ustopept > Sodic Haplustert. The Typic Ustorthent sorbed Cr 1.5 and 2.0 times more than the sorption by Vertic Ustopept and Sodic Haplustert soils respectively. Such variations in Cr sorption maxima were correlated with the differences in pH, cation-exchange capacity (CEC) and organic matter content of the soils. The high values of Go for Cr indicated that the reaction is spontaneous. The value of H^o were found negative for Cr indicating that Cr sorption reaction was exothermic in all the soils.