Development of iron-containing adsorbents for fluoride ion removal

Ingestion of too much fluoride ions through drinking water can seriously harm human health. Adsorption is one of the most effective approaches that have been proposed for removing fluoride ions from the aquatic environment. Analysis of modern publications shows that the search for new effective sorbents obtained by resource-saving technologies is an urgent scientific and practical problem. It is proposed to use sediments from groundwater deironing stations as sorbents. These sludges are formed in significant quantities and create significant environmental problems. Therefore, the object of the study is samples of agglomerated iron-containing adsorbents. Two samples of sorbents with different iron contents were studied. The influence of various parameters on the efficiency of fluoride ion adsorption was analyzed: contact time, initial fluoride concentration and adsorbent dose, pH value of the initial solution, and the presence of competing ions. The experimental data fit well with the pseudo-second-order kinetic model (coefficient of determination R2 = 0.8581 for sample A03 and R2 = 0.9947 for A06). The best correlation of the experimental data with the Langmuir model is the coefficient of determination R2 = 0.965 for A03 and for A06 R2 = 0.970. It was found that the maximum efficiency was achieved at pH 4. With an increase in the initial fluoride concentration, the sorption capacity increases, and the removal efficiency first increases and then decreases. For the sorbent A03, the optimal dose is 5 g/dm3, and for A06 – 6 g/dm3. The study of the influence of foreign ions on the sorption of fluoride ions on the sorbent showed that all the studied ions to some extent worsen the defluoridation efficiency. The use of the proposed sorbent will allow solving the following environmental issues: replenishing the list of cheap Ukrainian sorbents for fluoride removal and utilization of sludge from iron removal stations.