The interaction between polymeric aluminium hydroxide, Alp, and fluoride has been investigated to optimize the conditions for removal of fluoride from waste waters of aluminium manufacturing plants using Alp. The results of these studies have shown that the nature of products formed between Alpand fluoride depends on the molar concentration ratio of fluoride to aluminium (rF), pH, and initial fluoride concentration. In the absence of interfering ions, fluoride can be effectively precipitated as Al13(OH)29F10with Alp, usingand 4 < pH ≤ 7. At rF > 1, Alpdissociates and fluoride is precipitated as cryolite, and the residual fluoride concentration is controlled by its high solubility.