Kinetics and isotherm analysis of basic dyes adsorption onto almond shell (Prunus dulcis) as a low cost adsorbent

The feasibility of using an agricultural byproduct, almond shell (Prunus dulcis), as an adsorbent in removal of basic dyes, namely, methylene blue (MB), methyl violet (MV), and toluidine blue O (TB), were evaluated in a batch adsorption process. The adsorption characteristics of MB, MV, and TB onto almond shell (AS) were investigated with respect to the changes in initial pH of dye solutions, contact time, initial dye concentration, and temperature. The dye adsorption equilibria were rapidly attained after 30 min of contact time. The adsorption kinetics were analyzed using pseudofirst-order, pseudosecond-order, Elovich, and intraparticle diffusion models and the adsorption data were well described by the pseudosecond-order model. The equilibrium adsorption data were interpreted in terms of the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models. The monolayer adsorption capacity of AS was found to be 51.02 mg·g-1 for MB, 76.34 mg·g-1 for MV, and 72.99 mg·g-1 for TB by using the Langmuir model equation. The thermodynamic parameters proved that the present adsorption process was feasible, spontaneous and endothermic in nature in the temperature range of (5 to 40) °C.