Sorption and desorption behavior of lead in four different soils of India

Sorption and desorption mechanisms of lead (Pb) were determined in four different soils collected from different agro-climatic regions of India. The soils were classified as: Fine loamy mixed Typic Dystrudepts, fine sandy loam Typic Ustochrepts, fine loamy Typic Ustochrept, and fine sandy loam Udic Haplustalfs. Seven different Pb solutions [Pb(NO3)2 dissolved in 0.01M Ca(NO3)2] in a range of 400 to 2000μgL were applied to study the sorption amounts at 25(±2)C and 45(±2)C temperatures. With the increase in application rate and temperature, sorption amounts of Pb increased; however, percentages of sorption of applied Pb were decreased. Sorptions were positively and significantly (p ≤ 0.01) correlated with Langmuir adsorption isotherm. Thermodynamic parameters of sorption (i.e. K, G, H, and S) were also determined at two temperatures, 25(±2)C and 45(±2)C. Increase in K with the increase in temperature indicated positive effect of temperature on Pb sorption. High absolute values of G, and positive values of H, and S suggested that the sorption reaction was spontaneous and endothermic. Sorbed Pb were desorbed in Pb free 0.01 M Ca(NO3)2 solutions at 25(±2)C and 45(±2)C. Desorption amounts increased with increase in the Pb application rate, but not always with the increase in temperature.