Vol. 12, Issue 4 (2023)

Author(s):
Dr. SN Suman, Dr. SK Thakur, Dr. Vipin Kumar, Dr. Mukesh Kumar and Dr. AP Rakesh

Abstract:
Laboratory investigations were carried out to study thermodynamic parameters (DG°, DH°, DS°) of cadmium sorption in calcareous soils. Ten soils varying in clay, organic carbon and CaCO₃ content were used for sorption study. Each soil was treated with sewage sludge @ 25 and 50 g kg^-1 and incubated for 30 days at 25 + 2 °C giving four wetting and drying cycles. These untreated and treated soils were used for Cd sorption. The Cd sorption was determined by equilibrating 2 g of soils with 20 ml of CdCl₂ solution containing 5 to 750 m mol Cd²⁺ L^-1 at 20 + 2 and 40 + 2 °C. The ionic strength of the solution was kept constant with background electrolyte, KNO₃ containing ambient concentration of 0.01 mol L^-1. The sorption was calculated by depletion of Cd concentration in equilibrium solution. The Cd sorption data were fitted into different equations and the thermodynamic parameters were calculated on the basis of sorption data. The thermodynamic parameters indicated that retention of Cd by soils was governed by spontaneous reaction as the value of ∆G° was negative for both untreated and treated soils. The spontaneity of the reaction of Cd²⁺ with soils increased with rise in temperature. The value of DH° are positive and negative indicating both exothermic and endothermic reactions are operating in retention of Cd by soils. The value of DS° decreased progressively with enrichment of soils with sludge at different levels. This may be due to decrease in randomness of the system as Cd²⁺ present in the solution phase shifted to adsorption phase.