A strong acid cation exchange resin Amberlite IR-120 H+ and its hybrids with Mn(OH)2, Cu(OH)2 and Fe(OH)3 are used for the removal of chromium (III) from spent tannery bath. The experimental data give good fits with the Langmuir sorption model. The thermodynamic parameters entropy (ΔS°), enthalpy (ΔH°) and free energy (ΔG°) changes are computed, which reveal that the chromium removal from tannery wastes by ion exchangers is an endothermic, physical sorption and entropically driven process. The rate of sorption is found to increase with the increase of resin dosage, stirring speed and temperature. Different kinetic models such as film diffusion, particle diffusion and Lagergren pseudo first order are used to evaluate the mechanism of the process. It is found that the hybrid ion exchange resins have better removal capacity as compared to the parent ion exchanger. The increase in the removal capacity is found to be in the order of the corresponding PZC values of the hybrid ion exchangers. Further, it is suggested that the higher exchange capacity is the result of Donnan effect and specific adsorption of chromium by the oxides / hydroxides present inside the matrix of the organic cation exchanger.
Tauqeer Ahmad, Syed Mustafa, Abdul Naeem, Farooq Anwar, Tahir Mehmood and Khizar Hussain Shah
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