Sorption and Desorption of Dyes (Congored and Neolangrey) in Soils of Tamil Nadu

Textile and dying industry effluents contain various types of chemical contaminants which contribute much to water and soil pollution. The fate and persistence of dyes depend on their sorption, transformation and transport (loss). In this study, we investigated the dye (Congored and Neolangrey) sorption behaviour on eight agricultural soils of Tamil Nadu as influenced by solution concentration, reaction time and removal of organic matter from the soils. The rate of sorption of Congored and Neolangrey by the given soils was rapid, which attained equilibrium in 150 min. Dye sorption kinetics in these soils was best described by the parabolic diffusion and the Elovich equations. The sorption of dyes on the original and the treated soils conformed to the Langmuir sorption isotherm. The sorption maximum (b values) ranged from 17.7 to 40.5 and 20.3 to 46.3 mg g⁻¹ for Congored and Neolangrey, respectively. The percentage of sorption varied from 34.2 to 67.6 for Congored and 40.9 to 76.0 for Neolangrey. The b values of the Langmuir sorption isotherm of soils after removal of organic matter were lower than those of the corresponding untreated soils. Significant positive correlation existed between Congored sorption and soil properties, viz. silt, organic carbon and pH, whereas, for Neolangrey sorption, silt alone correlated well. Multiple regression analysis predicted the combined influence of pH, sand and clay on the sorption of Congored and that of sand, silt, clay and pH on the sorption of Neolangrey. Desorption studies indicated that only less than 3.2 per cent of the dyes could be desorbed by distilled water for the range of concentrations tested. The desorption maximum values were less than 20 and 15 mg g⁻¹ for Congored and Neolangrey, respectively.