Use of solid wastes of the soda ash plant as an adsorbent for the removal of anionic dyes: Equilibrium and kinetic studies

Solid wastes (SW) from the distiller waste (DW), which is the by-product of the ammonia-soda process (the Solvay method) for the production of soda ash, has been used as an alternative adsorbent for removing the anionic dyes from aqueous medium. The effects of pH, initial dye concentration and temperature were investigated on kinetics and equilibrium of the adsorption. The results indicated that adsorption was strongly pH dependent. The typical dependence of dye uptake on temperature and the kinetics of adsorption indicated the process to be chemisorption. The results showed that as the pH increased, extent of dye uptake increased and Ca(OH)(2) particles precipitated at higher pHs were mainly responsible for the removal of anionic Procion Crimson H-EXL (Reactive Red 231) dye. The necessary time to reach the equilibrium was found to be less than 2 min. Dye uptake process followed the pseudo-second-order rate expression. The Freundlich isotherm best fitted for the adsorption of the dye on SW. Various thermodynamic parameters, such as Delta G degrees, Delta H degrees and Delta S degrees were calculated. The thermodynamics of PC/SW system indicated spontaneous and exothermic nature of the process. (C) 2007 Elsevier B.V. All rights reserved.