Successful adsorption of bright blue and methylene blue on modified pods of Caesalpinia echinata in discontinuous system

Pods of the forest species Caesalpinia echinata were used as an alternative adsorbent to remove bright blue (BB) and methylene blue (MB) dyes. The raw and acid-treated samples were characterized by techniques like SEM, XRD, and FTIR. The acid-treated pod sample was characterized by an amorphous structure containing several cavities, bumps, and functional groups. The Elovich model was the most satisfactory to describe the adsorption kinetic data. The isothermal studies were better described by the Langmuir model for BB dye, with a maximum capacity of 261 mg g^-1, and Tóth model for MB dye, giving a maximum capacity of 288 mg g^-1. The thermodynamic study indicated a spontaneous and favorable process and endothermic nature for both dyes. In the treatment of two simulated effluents containing a mixture of different compounds such as dyes and salts, to simulate real wastewaters, the adsorbent was highly efficient, presenting around 80% of color removal for both effluents. Therefore, the acid-treated pods of Caesalpinia echinata have great potential to be applied as an alternative adsorbents in treating colored effluents in discontinuous systems.