Enriched fluoride sorption using alumina/chitosan composite.

Fluoride contamination in drinking water remains a global public health concern. Existing defluoridation methods often face limitations in efficiency or cost. Alumina has shown promise in fluoride removal but requires enhancement to meet practical needs. Chitosan, a biopolymer, is known for its adsorption properties and compatibility with various matrices. Combining alumina with chitosan may offer a dual mechanism for improved fluoride capture. Prior research has shown that alumina alone has a defluoridation capacity of 1566 mg F(-)/kg. However, this value is insufficient for large-scale applications. Chitosan alone has a much lower capacity of 52 mg F(-)/kg. This gap motivated the investigation of alumina-chitosan composites. The aim was to determine whether the composite could outperform either material alone. No prior work had resolved the optimal form or mechanism for such a composite. This study addresses that uncertainty by evaluating the composite's performance under various conditions.

The study aimed to improve the defluoridation capacity of alumina by combining it with chitosan. The researchers prepared an alumina/chitosan composite to assess its potential for enhanced fluoride removal. They tested the composite in different physical forms, such as beads, candles, and membranes. The goal was to determine the maximum defluoridation capacity of the composite. They also wanted to understand the factors influencing fluoride removal efficiency. The study focused on optimizing equilibrium parameters like contact time, pH, and temperature. The researchers sought to identify the best-fit isotherm model for the sorption process. They also aimed to analyze the surface characteristics of the composite using advanced techniques.

The researchers created an alumina/chitosan composite by embedding alumina particles into a chitosan matrix. They formed the composite into beads, candles, and membranes for testing. Batch experiments were conducted to evaluate fluoride removal efficiency. Variables such as contact time, pH, co-anions, and temperature were optimized. The equilibrium data were analyzed using Freundlich and Langmuir isotherm models. Thermodynamic parameters were calculated to assess the nature of the sorption process. Surface characterization was performed using FTIR, AFM, and SEM with EDAX analysis. These methods helped determine the composite's structural and chemical properties.

The alumina/chitosan composite achieved a maximum defluoridation capacity of 3809 mg F(-)/kg. This value is significantly higher than that of pure alumina (1566 mg F(-)/kg) and chitosan (52 mg F(-)/kg). The composite outperformed both individual components in fluoride removal. The study found that the composite's performance was optimal under specific pH and temperature conditions. The equilibrium data best fit the Langmuir isotherm model, indicating monolayer adsorption. Thermodynamic parameters suggested the process was spontaneous and endothermic. Surface analysis confirmed the presence of functional groups involved in fluoride binding. The composite's performance was validated using a field sample from a fluoride-affected village.

The study demonstrated that the alumina/chitosan composite has a high defluoridation capacity. The composite's performance exceeded that of alumina or chitosan alone. The Langmuir isotherm best described the sorption process, suggesting monolayer binding. The thermodynamic data indicated the process was spontaneous and endothermic. Surface characterization supported the proposed mechanism of fluoride sorption. The composite's effectiveness was confirmed using a field sample. The researchers propose that the composite could serve as a practical defluoridation material. This work provides a foundation for developing scalable defluoridation technologies.