Use of low-cost natural waste from the furniture industry for the removal of methylene blue by adsorption: isotherms, kinetics and thermodynamics

Residues from the wood industry have great potential to be used as adsorbents in the textile wastewater treatment. In this sense, this work aimed to evaluate the feasibility of removing methylene blue (MB) dye from aqueous solutions using Pinus elliottii sawdust. Initially, this material was subjected to a sequential solvent extraction to improve its adsorption capacity. After drying, it was characterized by several analytical techniques, including morphological and spectroscopic analyses. The influence of the experimental parameters on the adsorption process, such as contact time (2–240 min), pH (3.0–10.0), stirring intensity (90–210 rpm), adsorbent dosage (1.0–5.0 g L −1 ) and initial MB concentration (60–140 mg L −1 ), as well as the equilibrium, kinetics and thermodynamics were also evaluated. In general, the characterization analyses evidenced the presence of several types of oxygenated functional groups in the adsorbent chemical structure and a favorable morphology for dye removal. Regarding the adsorption process, the preliminary tests showed that all experimental parameters evaluated, in some way, interfere in the MB removal. The data set suggests that equilibrium was best described by the Freundlich model, although Fisher’s test ( F ) have shown that the Langmuir model could also be applied to describe the experimental results. Thermodynamics parameters, by other hand, revealed that MB dye adsorption onto the treated Pinus elliottii sawdust was spontaneous and endothermic, occurring mainly by physisorption. Concerning the removal rate, it was verified that the pseudo-second-order model better explains the kinetic data and that, according to the F test, there is a significant difference between the tested kinetic models. Finally, the data set indicated that the treated Pinus elliottii sawdust can remove about 97% of MB, and that the adsorbent used here has many of the characteristics required to be employed in the removal of cationic dyes from textile wastewater. Graphic abstract