Study On Influence Factors And Fractal Characteristics Of Dye Compounds Absorbed Onto Granular Activated Charcoal

In this paper the adsorption properties of six dye compounds onto granular activated charcoal were studied. The results showed that the influences of pH, ion strength , temperature, shake strength and the amount of granular activated charcoal were important for adsorption, the amount absorbed increased with increase of temperature, and actually the solid concentration effect was oberseved in adsorption process. The adsorption of the six dye compounds exhibited Freundlich adsorption behavior. The Langmuir fractal adsorption equation was used to model the adsorption isotherm data between granular activated charcoal and six kinds of dye compounds, and the relative coefficients exceed 90%. Based on that modeling results the calculated surface fractal dimension Ds of granular activated charcoal is 2.5902.The adsorption dynamic processes of six dye compounds onto granular activated charcoal were studied in this paper. Results showed that the adsorption behaviors of these compounds followed experiential non-linear kinetic equations, and higher adsorption rate was observed at higher temperature generally. The calculated apparent activated energy (Ed) values were within the range of 0. 20^l. 75 kJ.mol^-1, demonstrating the adsorption processes were relatively fast. The adsorption dynamic process was divided into a fast adsorption step and a slow one. The residual dye concentration in solution varied with adsorption time according to the following relation: c_out ∝t^-α, showing that the adsorption dynamic process was a fractal-like one, and the surface fractal dimension Ds could be determined through the equation: α =1/(1-1/n).To elucidate the adsorption kinetics of complex molecules onto fractal surfaces, the relations of reaction exponent h with both fractal spectrum dimension d_s and surface fractal dimension Ds were developed. Further analysis indicated that the adsorption kinetic processes have fractal-like characteristics. The stepwise rate coefficient (k) has a power-law relation with reaction time (t), and the corresponding spectral dimensions d_s are less than two. It was also noted that increasing the initial concentrations of dye compounds led to increases of d_s values, but decreases of the h and k₀ values.