Isolation, characterization and valorization of lignin from Pinus elliottii sawdust as a low-cost biosorbent for zinc removal

One of the main problems faced by the galvanic industry is the wastewater generated during the electrodeposition of metals. Prior to its discharge into the environment, the wastewater must be properly treated. Therefore, an increasing number of studies involving adsorption processes have been performed on the removal of metallic ions from wastewater using biosorbent materials due to their low cost and uncomplicated operation conditions. Within this context, the main objective of this study was to extract the lignin present in Pinus elliottii sawdust for its subsequent application in the removal of Zn(II) from aqueous solutions. After the extraction of lignin by the Klason method, the obtained material was characterized using several analytical tools. The effects of experimental parameters on the adsorption process, such as lignin dosage and the initial pH of the medium, were also evaluated. In general, the physical–chemical characterization showed that P. elliottii lignin is mainly composed of oxygenated functional groups, consists of particles of different sizes and shapes, and has high thermal stability. Concerning the adsorption studies, the experimental results revealed that the kinetics were better described using a pseudo-first-order model. At equilibrium, on the other hand, the Langmuir isotherm had the highest determination coefficient and the lowest mean square error, with a maximum adsorption capacity (q_max) of 16.55 mg g⁻¹. In addition, the mathematical models were equally evaluated using Fisher’s F test, which demonstrated that they can also describe the behavior of the experimental data. Finally, the set of all results showed that although the lignin in this work had a low q_max value compared to other adsorbents of the same nature, it can still be used for the removal of Zn(II) from aqueous solutions.