Kinetic and thermodynamic study of the adsorption of methylene blue on wood ashes [Etude cinétique et thermodynamique de l'adsorption de bleu de méthylène sur les cendres de bois]

The objective of this work is the study of the adsorption of methylene blue dye (mb) on raw wood ashes to highlight their potential as a low-cost adsorbent for the treatment of colored water. analysis of wood ashes shows that they are rich in mineral salts,mainly calcium,potassium,magnesium,silicon,phosphorus,aluminium and other low-level elements such as iron and manganese. adsorption tests showed that the equilibrium time is a function of the initial concentration of dye. the equilibrium is established after 10,20 and 30 minutes for mb solutions at 20,40 and 60 mg.l-1,respectively. the adsorption of methylene blue dye on the wood ashes is perfectly described by a pseudo-second-order kinetic model. the maximum adsorption capacity determined by the mathematical model of langmuir is about 50 mg.g-1. the thermodynamic parameters related to the studied sorbent/adsorbate system indicate that the adsorption process is spontaneous and exothermic.