An Adsorbent Diatomite/Aluminum Hydroxide for Fluorine Removal and its Properties

The paper describes a new sorbent diatomite/aluminum hydroxide (AI-D), obtained by modifying the natural mineral – diatomite,, with aluminum ions and it usage in the removal of fluoride ions from model solutions. The phase composition, texture, and adsorption-structural characteristics of the modified diatomite were studied. As a result of diatomite modification with aluminum, Al trihydrate is formed on its surface and in the volume of large pores, which is accompanied by an increase in the specific surface and a decrease in macropores, thus leading to an increase in the adsorption capacity of AI-D with respect to fluorine ions. The sorption isotherms F were obtained and it was shown that of the five models used, the two-step Langmuir model best describes the experimental equilibrium data on fluorine adsorption on AI-D (R² = 0.9836). The mechanism of fluorine adsorption on AI-D involves the electrostatic interaction of fluoride ions with positive aluminum-containing active centers on the surface of diatomite, followed by the formation of aluminum-fluoride complexes. The removal of fluorine takes place also due to the ion exchange of the hydroxi groups of the sorbent surface to fluoride ions. Under optimal conditions of the sorption process, the extraction of fluorine from water is 85% at an initial concentration of 10 mgF/l.