Simplified Fluoride Distillation Method

Water

“…Shoup (224) reported that interferences commonly found in public water supplies could be precipitated or reduced in quantity below the level of interference with cadmium and mercury nitrates in a boric acid-sodium hydroxide buffer at pH 8.0. Bellack (26) presented a direct distillation method in which the distillate obtained from a sulfuric acid mixture has the same volume as the original water sample with full fluoride recovery. A steam-distillation method was described by Zenin (268) in which fluoride is recovered as fluosilicic acid.…”

Sulfate carryover in direct distillation of fluoride. Comments

“…As observed by Bellack (2), sulfate is diluted to concentrations within acceptable limits in the entire 300-ml distillate.…”

“…As shown by Bellack (2), carryover of sulfate occurs only during the final stages of the distillation, beginning after distillation of 150-175 ml. Although the concentration of sulfate in the final 25 ml of distillate exceeds 250 mgA•, dilution reduces the concentration in the total 300 ml of distillate to well below 50 mgA.…”