Removal of fluoride from sodium hydroxide solutions

The removal of fluoride ions from sodium hydroxide solutions was studied. Sodium hydroxide solutions with fluoride ions arising from the regeneration of granular bone carbon were treated with different reagents to remove the fluoride ions by precipitation. Soda solutions with fluoride ions were treated with calcium chloride, calcium hydroxide, barium chloride, and the combination of calcium hydroxide- dibasic potassium phosphate and calcium chloride- dibasic potassium phosphate. The highest fluoride removal efficiency was reached with calcium chloride and dibasic potassium phosphate; 99.5% and 90.6% of fluoride ions were removed from a synthetic sodium hydroxide solutions and a solution arising from the regeneration of granular bone carbon, respectively. In the second stage, the treatments were carried out only with sodium hydroxide solution from regeneration, and the highest removal efficiency was 82% with calcium chloride- dibasic potassium phosphate; different parameters were considered in the precipitation process like reaction time, initial concentration of fluoride ions, temperature, molar ratio, and shaking speed. X-ray diffraction analysis of the sediments formed during the process was carried out, and fluorapatite and fluorite were verified. The precipitation of fluoride ions with calcium chloride- dibasic potassium phosphate is an effective method to remove fluoride ions from soda solutions.