THERMODYNAMICS OF REACTIVE DYE ADSORPTION FROM AQUEOUS SOLUTION ON THE ASHES FROM CITY HEATING STATION

This paper describes the adsorption thermodynamics of textile reactive dyes from aqueous solution on the waste ashes formed by burning brown coal at a city heating station. The values of thermodynamic parameters are the actual indicators for practical application in the adsorption process. Based on characteristic diagrams the thermodynamic parameters, enthalpy and entropy of adsorption are determined, and based on those data the Gibbs's free energy changes were determined. In all cases, there is a negative sign of the thermodynamic parameters. Entropy change (-2 to -3 J/K.mol) increases with increasing initial concentration of the adsorbate and decreases with increasing amount of adsorbent, suggesting a decrease in disordered system at the interface of solid - solution during the adsorption of dye on the ashes. Free energy (-1.7 to 5 kJ/mol) decreases with the concentration of adsorbate discontinuously but continuously with increasing temperature, which is associated with spontaneous nature of the process. Small negative values of enthalpy change (-2 to -6 kJ/mol), point to the physical nature and the energy stability of the reactive dyes adsorption by ashes.