Adsorption of two azo reactive dyes by tannery sludge activated carbon: effect of temperature and pH

Adsorption of azo reactive dyes by tannery sludge activated carbon was investigated using CI Reactive Red 31 (RR-31) and CI Reactive Red 2 (RR-2) by batch operation. The Langmuir constants (Q(o) and b) and the Freundlich constant (K-f) increased with increasing temperature. This behavior implied an endothermic process for the reactive dyes. The enthalpy value of adsorption OH) for RR-31 and RR-2 was 8.51 kJ/mol and -1.616 kJ/mol, respectively, indicating that the adsorption of the less charged dyes (RR-2) was mainly physical process, but that of the more charged dyes (RR- 31) was chemical in nature. The optimum system pH of 7.0 +/- 0.3 was maintained even when the solution pH was varied from 2 to 11.