Study of dye desorption mechanism of bone char utilizing different regenerating agents

Abstract

The reactive blue BF-5G dye is used on the textile industry due to its bifunctional characteristic that enables a higher interaction between the dye and the fabric fibers. Nonetheless, the dyeing produces a high amount of wastewater and the removal of the dye with a regenerative adsorbent is an attractive cost-efficient process. Therefore, the aim of this work was to evaluate the desorption mechanism of the reactive blue BF-5G dye on bone char employing different regenerating agents at different pH conditions. Aqueous solutions with pH from 2 to 12 and alcoholic solutions of methyl, ethyl and isopropyl were used as regenerating agents in a batch system with constant temperature. The highest regeneration efficiency with water was at pH = 12 (~2.0%) which was low due to alkaline conditions. The increase of negative charges on the surface of the bone char at pH = 12, generated electrostatic repulsion between the adsorbent and the dye, followed by its desorption. In addition, with increasing concentration of sodium hydroxide, the desorption efficiency is reduced due to the fact that Na+ compensate the negative charge generated on the surface of the bone char. On the other hand, since dye desorption using organic regenerating agents is due to replacement of the dye molecules by an organic one, an increase in regeneration was observed. The highest regeneration efficiencies of ~21.0% and 19.5% were obtained using isopropyl and ethyl alcohols, respectively. These results indicate that the strong interactions between the dye and the bone char surface were not broken by the regenerating agents studied, thus achieving low dye desorption efficiency. Therefore, desorption efficiencies are related only to the regeneration of weaker interactions on bone char surfaces for these systems, in batch conditions.