Enhanced fluoride removal using montmorillonite clay modified with CoFe₂O₄ and metal-organic frameworks

The use of modified clays can play an effective role as an effective adsorbent in removing fluoride (Flu) ions from water and aqueous solutions. In the present research, montmorillonite clay (MMt) was modified using CoFe₂O₄ magnetic particles and Al-Fe fumarate metal-organic framework (Al-Fe Fum) and was utilized as an efficient adsorbent for removing Flu from aqueous solution. The properties of MMt and MMt/CoFe₂O₄/Al-Fe Fum samples were investigated using different techniques. The results showed that with the modification of MMt using CoFe₂O₄ magnetic particles and the metal-organic framework of Al-Fe Fum, the BET surface has increased notably from 13.217 to 365.80 m²/g. To investigate the effect of independent variables and their interaction on the efficiency of the Flu adsorption, response surface method-central compound design (RSM-CCD) was served. Based on the results of ANOVA, the F-value and p-value parameters for the desired model were determined to be 783.09 and < 0.0001, respectively, which confirms the success and high ability of the model. The number of R², adjusted R², and Predicted R² for adsorption of Flu ion was determined to be 0.998, 0.997, and 0.995, respectively, which shows that the proposed regression model can describe the process of adsorption and interaction between variables well. Compared to other kinetic models, the pseudo 2nd order kinetic model has a greater ability to describe the Flu adsorption behavior. The R² parameter value determined that the Freundlich isotherm model has a suitable ability to investigate the isotherm behavior and confirms the effect of heterogeneous surfaces in the process. Generally, the outcomes signified that the MMt and MMt/CoFe₂O₄/Al-Fe Fum samples can be reused several times in the process of Flu adsorption, while the efficiency is more than 90%.