Removal of orange 16 reactive dye from aqueous solutions by waste sunflower seed shells

Abstract

In this work, the use of an agro-industrial waste, i.e., sunflower seed shells, was investigated as a sorbent for the removal of Orange 16 reactive dye from aqueous environments. Batch experiments were performed as a function of pH, sorbent dose, dye concentration, temperature and contact time. The percent dye removal increased with increasing sorbent dose and temperature of the aqueous solution, and decreased with increasing dye concentration; the required contact time was five hours. The Freundlich, Langmuir, Dubinin-Radushkevich and Tempkin adsorption isotherms were used to describe the equilibrium sorption data and to determine the corresponding isotherm constants. The thermodynamic parameters ?G, ?H and ?S were also determined. These parameters indicated that the sorption of reactive dye onto sunflower seed shells was a spontaneous, endothermic and entropy-driven process. The kinetic data were evaluated by pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models. The results of the kinetic study indicated that the sorption of Orange 16 reactive dye onto sunflower seed shells is a complex process and both chemical surface sorption and intraparticle diffusion contribute to the rate-limiting step. Therefore, the sunflower seed shell showed itself to be a promising cheap sorbent for the decolourization of aqueous coloured solutions or effluents.