Adsorption of Eriochrome Black T on polyaniline from aqueous and methanolic solutions

The adsorption bf Eriochrome Black T (EBT) has been studied on acidic and b asic forms of polyaniline from aqueous and methanolic solutions. The adsorp tion has been studied as a function of adsorbate concentration (2-40x10(-4) M), adsorbent particle size (30 - 140 mesh) and temperature (293.15-313.15 K). The data have been fitted to Langmuir isotherm and its parameters have been obtained. Langmuir parameter b has large magnitude and increases with temperature suggesting that the adsorption is endothermic and entropy domi nated. Kinetic studies have been performed to calculate rate constants for adsorption processes. The first order kinetics in the initial stages confir ms that the rate controlling step is the diffusion of the dye molecules thr ough a stagnant layer formed around the adsorbent particles. This mechanism is overtaken at later stages by the rearrangement of the dye molecules on the surface of the adsorbent and finally by intraparticle diffusion. The en ergetics of the adsorption process have been obtained.