Adsorption and mass transfer studies of methylene blue onto comminuted seedpods from Luehea divaricata and Inga laurina

In this work, comminuted seedpods of the forest species Luehea divaricata (LDPR) and Inga laurina (ILPR) were used as alternative and environmental-friendly adsorbents for the methylene blue (MB) removal from aqueous solutions. Batch adsorption experiments were carried out at the native pH of the solution (pH = 8.7), with curves of removal and adsorption capacity crossed at 0.75 g L-1, having 125 mg g(-1) for LDPR and 115 mg g(-1) for ILPR. The kinetic models of pseudo-first-order (PFO) and HSDM-Crank were the most adequate to represent MB dye concentration decay data for both biosorbents. The equilibrium curves were better adjusted by the Langmuir model for both adsorbents, with maximum adsorption capacity increased from 279 to 325 mg g(-1) for LDPR, and 199 to 233 mg g(-1) for ILPR, as a function of an increase in temperature from 298 to 328 K. The thermodynamic parameters showed that both systems are spontaneous with a dominance of physisorption. Mass transfer analysis indicates that the external mass transfer is the limiting step, with Bi < 0.5. Surface diffusion increased with the adsorption capacity, presenting linear and exponential behavior for the ILPR and PLPR adsorbents, respectively. Both materials proved to be efficient in treating a simulated effluent with similar industrial wastewater characteristics, reaching superior values at 70% of color removal.

Automated summary

Comminuted seedpods of LDPR and ILPR were used as alternative adsorbents for MB removal, with PFO and HSDM-Crank as the most suitable kinetic models and the Langmuir model as the best fit for equilibrium curves. The thermodynamic parameters indicated spontaneous adsorption dominated by physisorption, with external mass transfer as the limiting step and surface diffusion increasing with adsorption capacity. The materials showed efficiency in treating simulated effluent with superior color removal values exceeding 70%.