Adsorption Characteristics of New Coccine Dye on to Sludge Ash

Abstract

The adsorption characteristics of an anionic azo dye (New Coccine) on to sewage sludge ash were studied. Results showed that the ash could remove the dye effectively from aqueous solution. The adsorption rate was fast and could be expressed by the modified Freundlich equation. It was found that pH is the most important parameter affecting the adsorption characteristics. The experimental data were correlated well to the non-linear multilayer adsorption isotherm. The ash adsorption capacities for the dye were in the range 3.25–5.70 mol/g and were affected by the pH, ionic strength and temperature. Decreasing pH, ionic strength and temperature increased the adsorption density. The effect of electrical double-layer thickness on the adsorption was discussed. Thermodynamic parameters indicated that the adsorption was an exothermic process. Values of the first-layer adsorption energy, ΔG10, ranged from −6.86 to −7.45 kcal/mol, suggesting that the adsorption could be considered as a physical process simultaneously enhanced by the electrostatic effect. The multilayer adsorption energy, ΔG20, ranged from −4.33 to −4.51 kcal/mol, suggesting that the adsorption was of the typical physical type. On the basis of the monolayer dye adsorption capacity, the specific surface area of the ash was calculated as 3.84–6.73 m2/g.