Preparation and evaluation of low-cost adsorbent from pine wood powder (Pinus eldarica) for removal of cationic methylene blue dye from aqueous solution: Isotherm and kinetic studies.

Background and Objective: Human development and rapid population growth exert significant pressure on the quality and accessibility of water resources. Various types of pollutants discharged from different industries into water sources lead to water pollution. Dyes are among the most important water pollutants, originating from various industries such as food, tanning, pulp and paper, textile, and chemical industries. When dyes enter water systems, they render the water unfit for use and often make its treatment difficult; this is because the molecular structure of dyes is complex, and many dyes used in industry are synthetic, highly stable, and resistant to degradation. Various technologies have been reported for dye removal from aqueous environments, such as coagulation/flocculation, ion exchange, biological treatment, advanced oxidation processes, and adsorption. Among these methods, the adsorption process is recognized as one of the most effective techniques for wastewater treatment. In this research, the use of Pinus eldarica wood powder as an adsorbent for the removal of cationic dye from aqueous solution using a batch adsorption method was investigated.
Materials and Methods: The wood powder used as the adsorbent, with a mesh size of 60, was prepared from the waste of Pinus eldarica wood. To increase the adsorption capacity and activate the adsorption sites, the wood powder was subjected to alkaline chemical treatment with NaOH. The cationic dye Methylene Blue was used. The effects of three factors—adsorbent dosage, pH, and contact time—were investigated to obtain the maximum removal percentage (%R). FE-SEM, BET, XRD, and FTIR analyses were performed to study the physico-chemical properties of the NaOH-treated pine wood powder adsorbent.
Findings: Chemical modification of the wood powder was confirmed by FTIR spectroscopy. The BET surface area of the modified sample slightly increased compared to the unmodified sample, indicating the positive impact of the modification on the chemical adsorption tests. According to the XRD results, the crystallinity index of the pine wood powder increased after chemical treatment. The influence of the three factors (adsorbent dosage, pH, and contact time) on obtaining the maximum removal percentage (%R) of Methylene Blue was studied. The highest dye removal was observed at pH=6.5, an adsorbent dosage of 1.24 grams, and a contact time of 65 minutes. FE-SEM images showed that the surface morphology of the alkali-treated wood powder changed significantly after Methylene Blue adsorption, and the surface was covered by the dye via the adsorption process. To determine the reaction mechanism, pseudo-first-order and pseudo-second-order kinetic models were applied. The adsorption kinetic data were better fitted by the pseudo-second-order model, suggesting that the nature of the adsorption process is chemical. Analysis of the equilibrium data using Freundlich and Langmuir isotherms showed that the adsorption phenomenon followed both models. However, given the higher correlation coefficient from the Freundlich model equations, the Freundlich isotherm was a better model for the adsorption of Methylene Blue using the pine wood powder adsorbent. Furthermore, according to the results, the maximum adsorption capacity predicted by the Langmuir model increased with rising temperature.
Conclusion: In general, based on the results obtained using the cationic dye Methylene Blue, pine wood powder acted as an effective adsorbent for its adsorption. Also, the adsorbent dosage factor had a greater influence on the Methylene Blue removal percentage than the contact time.