Adsorption has been the most used method to remove fluoride from water, and in recent years researches have studied the use of new adsorbents for this purpose. Some of these new materials are biosorbents.

Chitin and chitosan are biosorbents that have showed an acceptable adsorption capacity for cations and recently, their anions (like fluoride) adsorption capacity has been demonstrated. Nevertheless, characteristics of chitin and chitosan as low mechanical resistance and high solubility in acid medium limit their application in real conditions found in water treatment. However, such disadvantages can be overcome by obtaining chitin and chitosan based biocomposites (mixtures of the biopolymer and synthetic polymers).

In this study, chitin-based biocomposites were physicochemically characterized and their fluoride removal capacity from water was evaluated. The ionic exchange capacity, solubility (pH 2-12), surface charge distribution, specific surface area and pore volume of the studied materials were determined. The morphology and chemical composition of both biosorbent and biocomposites were analized. Finally, equilibrium and kinetic studies of fluoride adsorption onto biocompoistes were carried out between pH 4 and 9 at 25°C.

Results showed an improvement in both mechanical properties and particle morphology of biocomposites with regard to the original biopolymer. This contributes to obtain good hydraulic flow and low pressure drop in packed column with biocomposites. Furthermore, the biosorbents were chemically and mechanically stabilized when these were mixed with a polymeric matrix, which caused that the biocomposites were less soluble and brittle than the biopolymer.

On the other hand, the fluoride adsorption results showed a higher adsorption capacity of biocomposites as the pH decreased. In adition, at optimum conditions, biocomposites had competitive adsorption capacities compared to a commercial activated alumina (DeseCamen®). The adsorption kinetic of biocomposites showed a rapid adsorption process, which indicates the possibility of a practicable operation in packed columns with these materials.

These findings encourage the use of chitin to remove anions from water, and when these are mixed with synthetic polymers, the resultant biocomposites offer a viable option to remove fluoride in packed columns.

Keywords: chitin, fluoride, adsorption, polymer, biocomposite